tag:blogger.com,1999:blog-14481802281407499672024-03-15T20:09:16.949-05:00The Weather CentreThe mission of The Weather Centre is to provide a place where someone of any level of weather knowledge can read posts and be able to understand what is going on. Some weather blogs prefer to be extremely technical, and others will post good information once a week. I aim to compromise with daily, easy to read posts that still delivers to both the average person and the technical weather enthusiast.Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.comBlogger4848125tag:blogger.com,1999:blog-1448180228140749967.post-91826713732411589812021-12-10T15:00:00.000-06:002021-12-10T15:00:10.713-06:00December - January Outlook: Colder Pattern Expected in North; Mild in East, South; Frigid Canada<p>As I discussed on this blog's <a href="https://www.facebook.com/TheWeatherCentre/">Facebook page</a> yesterday, this is my outlook for the end of December through the month of January. We'll be using four primary components in this outlook: the stratosphere, the Pacific Decadal Oscillation, the La Nina, and the Madden-Julian Oscillation. I'll describe each component below, closing this article with my forecast.</p><p><br /></p><p><span style="font-size: large;"><i><u>I. Stratosphere</u></i></span></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEgpUkekJdCy5Rv5v2kxDFStQEwFv3lLR7DGOgWJ_xixLXWkynsCOSY_XTa2QS4e3nbNwVFMD9iviwpXLuFBZ_gV5K_8K5fNjSiCiQojJ8JXwxyO8Iw9Bd6GVejFImCqxKVLn5Arz67lH9q8Wu2G3_wt08O10LMN-5692j7lO9QNr4jLtKmb21gndS4jMw=s1000" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="1000" data-original-width="1000" height="400" src="https://blogger.googleusercontent.com/img/a/AVvXsEgpUkekJdCy5Rv5v2kxDFStQEwFv3lLR7DGOgWJ_xixLXWkynsCOSY_XTa2QS4e3nbNwVFMD9iviwpXLuFBZ_gV5K_8K5fNjSiCiQojJ8JXwxyO8Iw9Bd6GVejFImCqxKVLn5Arz67lH9q8Wu2G3_wt08O10LMN-5692j7lO9QNr4jLtKmb21gndS4jMw=w400-h400" width="400" /></a></div><br />As things stand at this writing, the stratospheric polar vortex (SPV) is a bit battered & bruised, but overall in good shape. Attached on the right is a look at the 70-millibar pattern over the Northern Hemisphere, exemplifying something we saw develop in the last couple days: a split in the SPV at the 50-millibar level and lower. Indeed, the two distinct closed-off height contours in this image reflect a split vortex at the lower levels, while at the upper-stratosphere (10-millibar level), where it really matters for sudden stratospheric warming (SSW) purposes, the vortex remains intact.<p></p><p>You may ask, what's the difference if the vortex splits at lower levels or upper levels? If were to see the SPV split up into two pieces throughout the entire stratosphere - not only the 70-millibar level but up through the 10-millibar level as well - it would signify that the stratospheric polar vortex is really in trouble, and greatly increase the probabilities of Arctic air being unleashed to lower latitudes of the Northern Hemisphere. Because the vortex is still intact at that key 10-millibar level, I would consider this something worth briefly discussing, but not something that will have a massive influence on the outlook.</p><p><br /></p><p>In fact, the only influence I'm drawing from the stratosphere is quite a warm influence; model guidance over the next two weeks suggests the stratospheric polar vortex will remain around normal or above-normal strength for this time of year, which should help to lock that frigid Arctic air up in Canada. This is confirmed in the latest Arctic Oscillation (AO) forecast from the long-range ECMWF model, shown below, with the average of these 51 ensemble members having the AO stay almost entirely positive during the period, and may even be substantially positive for January:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEiWCByQcQ15CAB6rTI5j9M0wE_WKzLxiOW8mVy3PKHciE4k9fCQ56rnWa1zhZLZ8nY_mOOSuRGo_ChHDsxgCUfh11Fa9hM2YkZDfu-WaKTU1nr6Y0-WJoAFFCyNZNcRKnwqkktsvmngPtMFhvcatyeMlUbfk7uLMwrq6Ze39_6NaCSWOV4_y4tDO7BpIg=s984" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="808" data-original-width="984" height="526" src="https://blogger.googleusercontent.com/img/a/AVvXsEiWCByQcQ15CAB6rTI5j9M0wE_WKzLxiOW8mVy3PKHciE4k9fCQ56rnWa1zhZLZ8nY_mOOSuRGo_ChHDsxgCUfh11Fa9hM2YkZDfu-WaKTU1nr6Y0-WJoAFFCyNZNcRKnwqkktsvmngPtMFhvcatyeMlUbfk7uLMwrq6Ze39_6NaCSWOV4_y4tDO7BpIg=w640-h526" width="640" /></a></div><p>For the month of January, then, the stratosphere adds warm risks across most of North America.</p><p><br /></p><p><i><u><span style="font-size: large;">II. Pacific Decadal Oscillation</span></u></i></p><p>Another key component to my January outlook is an index called the Pacific Decadal Oscillation. This is a longer-term oscillation, on the order of months and years compared to regimes like the Arctic Oscillation and North Atlantic Oscillation (AO and NAO, respectively) which work on the order of days to weeks. Below I've attached a look at the PDO not using sea surface temperature anomalies, as is normally the case, but judging how the atmosphere is determining the PDO's phase:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEh26tCpaybJZC_4MdjgAHAg0T8ENfmIVlN0IvE8kC4f8WzW4mBFeDt2MKqvQ5T1lCT6R5rmpyMjm_6Da7QsEN3NSnytuYMljCkelwaK_434_lrdt6GlQbubeXbEJ3q73lVWfFiKo1oOhUY7mlLfZ_ubK-OURZiWU35RSjgc1jPC8UGZbU9LQJZgARHUug=s1262" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="400" data-original-width="1262" height="202" src="https://blogger.googleusercontent.com/img/a/AVvXsEh26tCpaybJZC_4MdjgAHAg0T8ENfmIVlN0IvE8kC4f8WzW4mBFeDt2MKqvQ5T1lCT6R5rmpyMjm_6Da7QsEN3NSnytuYMljCkelwaK_434_lrdt6GlQbubeXbEJ3q73lVWfFiKo1oOhUY7mlLfZ_ubK-OURZiWU35RSjgc1jPC8UGZbU9LQJZgARHUug=w640-h202" width="640" /></a></div><br /><p>The above image shows an index of the Pacific Decadal Oscillation using atmospheric measurements, as opposed to the alignment of sea surface temperature anomalies. This matters because, while one can see how certain water temperature anomalies line up, what really matters is if the atmosphere "picks up" on that signal and responds accordingly. After all, if water temperatures say our PDO should be negative but the atmosphere doesn't act like it's in a negative phase, is it *truly* negative?</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEjS_7LNg8xcynwdslG9fLLPYmCqQFccKCKMBexPzeCXQJlMev0PV_VkXeActXROwCa8BmX68MSYyALm27O5AZqZ5yvyR-rJE2AuTa8DvZTZagWuqEfnFMdsnP2TEEWl5p5TVVb4jI1e4HAmVccLucDRiUtScFawjXvq0LHyBgWXmb7AY68v_noG-F0anA=s565" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="437" data-original-width="565" height="310" src="https://blogger.googleusercontent.com/img/a/AVvXsEjS_7LNg8xcynwdslG9fLLPYmCqQFccKCKMBexPzeCXQJlMev0PV_VkXeActXROwCa8BmX68MSYyALm27O5AZqZ5yvyR-rJE2AuTa8DvZTZagWuqEfnFMdsnP2TEEWl5p5TVVb4jI1e4HAmVccLucDRiUtScFawjXvq0LHyBgWXmb7AY68v_noG-F0anA=w400-h310" width="400" /></a></div><br />In any event, the above image shows the Pacific Decadal Oscillation in its most negative state since the late 2000s, and at its second-most-negative reading since the late-1970s. This matters because, as the image on the left shows, the PDO materially impacts the Northern Hemisphere during boreal winter. For some more context, the image on the left shows the correlation between the mid-level pattern and the PDO index. If values are negative, it means a positive-PDO results in stormy/cold weather, or a negative-PDO results in warm/calm weather during the Dec-Feb period. Similarly, if correlation values are positive, it means a positive-PDO results in warm/calm weather over that area, while a negative-PDO results in cold/stormy weather over that area.<p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEjh0C9qzwtxNASbKQie4--SSeJSIyqFd7cV3DvXPoSmxxJ4zB8yZqQoCvASB0ke7GrWUVARMKRJUBSE49nMO-JbE5SJxZ94A_CbYqYzGFwFSL2IN3ndP7eYYQJKkA_TnKFodM-s6NwcR1LjMiGDTYLPLoUnPvKSi4dD8CjTuo_v1yp2SdBktheeQ4R6og=s443" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="418" data-original-width="443" height="378" src="https://blogger.googleusercontent.com/img/a/AVvXsEjh0C9qzwtxNASbKQie4--SSeJSIyqFd7cV3DvXPoSmxxJ4zB8yZqQoCvASB0ke7GrWUVARMKRJUBSE49nMO-JbE5SJxZ94A_CbYqYzGFwFSL2IN3ndP7eYYQJKkA_TnKFodM-s6NwcR1LjMiGDTYLPLoUnPvKSi4dD8CjTuo_v1yp2SdBktheeQ4R6og=w400-h378" width="400" /></a></div><p><br /></p>We can confirm this by looking at the correlation between the PDO index and surface temperatures during the winter months, as in the image directly on the left. Indeed, given that we're in a negative-PDO, the positive correlation values in the West suggest this negative-PDO results in colder weather, while negative correlation values in the East U.S. imply a warmer pattern from a negative-PDO.<p></p><p>Given how strong the PDO is currently seen in the atmosphere, and how strongly negative it is, my outlook anticipates persistent colder and stormier weather across the West U.S., equivalent to a negative-PNA index (resulting in milder risks across the East U.S.).</p><p><br /></p><p><br /></p><p><i><u><span style="font-size: large;"><br /></span></u></i></p><p><i><u><span style="font-size: large;">III. La Nina</span></u></i></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEiEygG3_Uyl6oi6rKxfpixCRqWOW_J-43PLlpedULkouBkn7YWOLz5Yp-jwP3h8BqFEv7JMhqDJtyFWSecRNcNkI2Zw2kwuvaFbLVxy74FUk0oVUeAHnJEYIjZeYJnfDFcoux33jraqh_B_m0t5-WzhWefTx5hvkh8X45zxdzO_ZNUPWeOrWVNukSvQeA=s1200" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="800" data-original-width="1200" height="266" src="https://blogger.googleusercontent.com/img/a/AVvXsEiEygG3_Uyl6oi6rKxfpixCRqWOW_J-43PLlpedULkouBkn7YWOLz5Yp-jwP3h8BqFEv7JMhqDJtyFWSecRNcNkI2Zw2kwuvaFbLVxy74FUk0oVUeAHnJEYIjZeYJnfDFcoux33jraqh_B_m0t5-WzhWefTx5hvkh8X45zxdzO_ZNUPWeOrWVNukSvQeA=w400-h266" width="400" /></a></div><br />We remain steadfastly in a La Nina environment, with water temperatures in the Equatorial Pacific comfortably colder than normal and the Southern Oscillation Index (SOI; a shorter-term indicator to identify whether we are in a La Nina or El Nino) staying in the positive-teens, indicative of a La Nina reflecting in the atmosphere as well (instead of just showing up in ocean water temperatures).<p></p><p>The probability-based forecast of the ENSO phenomenon from the Climate Prediction Center and Columbia University is shown on the right, and portrays very high confidence in the ongoing La Nina persisting through meteorological winter into meteorological spring. We see that the La Nina (negative-ENSO state) correlates positively to below-normal temps during Dec-Feb across the Northern U.S. as below...</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEh8ayOwgUfe41w8RxY8zfH7NEksMZl-b3U7MDRY7ww8UCQtikFzOBzVdYETahU0nFW7824KMA9300Ty9uHjDCEJwdmxLzbkl-SRNUIzpLtc3yWOVA28ssOde39JQI0x3K2HQtSA7lSGFhjcdPQp_Vf4LIaJt5AOPbf3TcRC1HDFTU0cbfO8qm7iVx7CZA=s443" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="418" data-original-width="443" height="378" src="https://blogger.googleusercontent.com/img/a/AVvXsEh8ayOwgUfe41w8RxY8zfH7NEksMZl-b3U7MDRY7ww8UCQtikFzOBzVdYETahU0nFW7824KMA9300Ty9uHjDCEJwdmxLzbkl-SRNUIzpLtc3yWOVA28ssOde39JQI0x3K2HQtSA7lSGFhjcdPQp_Vf4LIaJt5AOPbf3TcRC1HDFTU0cbfO8qm7iVx7CZA=w400-h378" width="400" /></a></div><p><br /></p><p>... while the La Nina tends to provoke above-normal temperature anomalies in the South U.S. as the Pacific jet stream is shunted northwards to deliver storm systems to the Pacific Northwest, rather than the Desert Southwest. Combining the negative-PDO with the La Nina, and accounting for constructive influence between the La Nina and negative-PDO as discussed in Rao et al. 2019, <u>below-normal temperatures seem quite likely across the West U.S. and especially into western Canada for January 2022</u>.</p><p><br /></p><p><i><u><span style="font-size: large;">IV. Madden-Julian Oscillation (MJO)</span></u></i></p><p>Perhaps the most important part of this outlook, the Madden-Julian Oscillation (MJO) looks to come back to life over the coming weeks, prompting a shift in the global weather pattern.</p><p>Before diving into this component of the outlook, let's review what the MJO is and why it matters. In a nutshell, the MJO is based on the positioning and intensity of enhanced thunderstorm activity across the world, along the Equator. The location of this enhanced thunderstorm activity along different parts of the Equatorial prompts different global weather regimes; indeed, the MJO is often seen as the most important sub-seasonal oscillation currently known.</p><p>The MJO is said to be in one of eight phases at any given time, depending on where enhanced thunderstorm activity along the Equator is located. If there is minimal thunderstorm activity, then the MJO is simply too weak to have a material impact on the global weather pattern. This is all summed up well in the phase-space diagram below:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEg4cMrxomDbFENJeLeTgPYKptIhD_gOCytDflekcqDwQLkHOaHwmLV97_YRC9bo-dOXsAsnjbD3k6aGvzIfqdoJrWzWtIJqZ8n2wIxb797fo64oN3Wl88sKIlnj94DQIA6yYhSmWusPE15YxfdaUh_tgRZUn8QW3algsM3bXtUmXZIq3aQ2DMa_G-Jg6g=s547" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="547" data-original-width="547" height="640" src="https://blogger.googleusercontent.com/img/a/AVvXsEg4cMrxomDbFENJeLeTgPYKptIhD_gOCytDflekcqDwQLkHOaHwmLV97_YRC9bo-dOXsAsnjbD3k6aGvzIfqdoJrWzWtIJqZ8n2wIxb797fo64oN3Wl88sKIlnj94DQIA6yYhSmWusPE15YxfdaUh_tgRZUn8QW3algsM3bXtUmXZIq3aQ2DMa_G-Jg6g=w640-h640" width="640" /></a></div><br /><p>This chart might look intimidating at first blush, but we can break it down to make it easier to understand. As I discussed, the MJO can be broken into eight different phases, depending on where thunderstorm activity is most focused along the Equator. Each of those eight phases is labeled in this phase-space diagram, and the rough location of where that enhanced thunderstorm activity is during any given phase is written on the axes of the chart. You'll also notice number ticks on both axes - that tells us the intensity of the MJO at any given time. For instance, if the jagged line goes further away from that middle circle and towards larger-magnitude numbers on the x- and y-axis (whether positive or negative), it means the MJO is becoming stronger, and the global weather pattern should increasingly reflect the 'typical' pattern that develops when the MJO is in that given phase.</p><p>Examining the chart further, we find a black jagged line which then turns into a multi-colored thick line, surrounded by a whole spaghetti mess of thin yellow lines. That solid black line shows the progression of the MJO over the last five weeks or so - we see that the MJO began November in that middle circle, meaning the MJO was too weak to be placed in a specific phase / too weak to influence the global weather pattern on a material level. The MJO then spent almost all of November in a weak Phase 4-5 state, bouncing in and out of that middle circle. Since December 1st, however, the MJO has woken up and surged into Phase 6, where we now find ourselves.</p><p>The red, blue and purple lines represent the average, bias-corrected forecasted state of the MJO from the latest long-range ECMWF model; here, it's the forecast from December 8th through January 9th. To that extent, each thin yellow line is one of the 51 ECMWF long-range ensembles. </p><p>And now that we're through with all of that, we can finally get into the forecast part!</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEi4f-6-DQJVyAh__6LbqJVgzEIN8FzCzIk_9Rpw6Zg37UhxBw47koLAng7MBvm1jYfrg72U_FObLD0aaG9ctQGEjBLKAu2iq2pMQ19DWPuxbKajacHFx1GgjNLRLz60Mu1FHlwgLn9SnRMgSJqLNnjJyvc8vHW4_P7f2Gb6W9PafE1hotl4Cys5eDkA3A=s965" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="965" data-original-width="689" height="400" src="https://blogger.googleusercontent.com/img/a/AVvXsEi4f-6-DQJVyAh__6LbqJVgzEIN8FzCzIk_9Rpw6Zg37UhxBw47koLAng7MBvm1jYfrg72U_FObLD0aaG9ctQGEjBLKAu2iq2pMQ19DWPuxbKajacHFx1GgjNLRLz60Mu1FHlwgLn9SnRMgSJqLNnjJyvc8vHW4_P7f2Gb6W9PafE1hotl4Cys5eDkA3A=w285-h400" width="285" /></a></div><br />The ECMWF has been consistent in taking the MJO through Phase 6 until December 18th or so, remaining in a rather strong state through the entire timeframe. Referring to typical temperature anomalies in each MJO phase on the right, we see that a Phase 6 event in meteorological winter corresponds to much warmer than normal temperatures in the eastern half of the country, while the West U.S. experiences below-normal temperatures and generally stormier weather.<p></p><div>This does look to verify, with temperatures set to soar across the eastern half of the country in the coming days (not shown).</div><div><br /></div><div>By December 20th, the MJO is projected to push into Phase 7, still at a rather strong level, and the index remains in Phase 7 through the first several days of the new year (albeit at a weaker magnitude). Phase 7 still encourages warmer weather in the East U.S., but we now also see colder weather pushing south and east from western Canada into the northern U.S. Rockies and north-central U.S. <u>Put together, it seems likely that the remainder of December will be warm across the eastern half of the country, though with a shot of cold air between December 25 - 31</u> as the MJO's trip into Phase 7 inspires increased chances for cold Canadian air to develop in western Canada and eventually push into the U.S. for a brief period. A return to warmth is expected thereafter.</div><div><br /></div><div><br /></div><div><span style="font-size: large;"><i><u>January 2022 Outlook</u></i></span></div><div><br /></div><div>With our four components examined above and the end-December outlook written in the previous sentence, we can get to work on what really matters: the January 2022 outlook.</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEhkXCw7w_NqEiXoSj7I-K9TGA1LqO3YEUIRTVmXN6DJbCD2P-GYxPcbr-kRtMyVme3iUJYGnxNmb81rMc1mg4vrCF4dW6eypnAPsmn09hiQIJkdpzn-MiND2Jx1tpoJawifMqMY_dn6u_TG8bMCRhrop784B3ay3JYAaK6A9xSOBZvlDgisu9fMnlJkog=s2048" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1244" data-original-width="2048" height="388" src="https://blogger.googleusercontent.com/img/a/AVvXsEhkXCw7w_NqEiXoSj7I-K9TGA1LqO3YEUIRTVmXN6DJbCD2P-GYxPcbr-kRtMyVme3iUJYGnxNmb81rMc1mg4vrCF4dW6eypnAPsmn09hiQIJkdpzn-MiND2Jx1tpoJawifMqMY_dn6u_TG8bMCRhrop784B3ay3JYAaK6A9xSOBZvlDgisu9fMnlJkog=w640-h388" width="640" /></a></div><div><br /></div><div>I am expecting the month of January to feature below-normal temperatures across the West U.S., extending into the Rockies and especially in western Canada. It seems likely that temperatures will be much colder than normal in western Canada, a consequence of the typical January La Nina pattern, negative-PDO and MJO in Phase 7 - all of which encourage colder weather in western North America. </div><div><br /></div><div>Temperatures should go through quite a bit of back-and-forth in the Plains, a consequence of creeping cold from Canada bumping up against formidable warmth in the East. A strong polar vortex should allow warm weather to win out over colder weather on average, and I expect most of the Central to be on the warmer side of normal.</div><div><br /></div><div>The East U.S. is likely to lean firmly warmer than normal, with these warm signals showing up in the MJO, La Nina, negative-PDO and strong polar vortices at the tropospheric and stratospheric levels. Confidence in the East Coast being warmer than normal is higher than normal. Indeed, confidence in this forecast is higher than normal, and it's been some time since I've made an outlook with forecast confidence at this high of a level.</div><div><br /></div><div>Andrew</div>Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com6tag:blogger.com,1999:blog-1448180228140749967.post-16208191044968399652021-12-09T10:21:00.000-06:002021-12-09T10:21:56.390-06:00Long-Range ECMWF ENS Control Member Shows Frigid January; Will it Verify?<p> The latest long-range ensembles from the European forecasting agency came in the other day, and while on the whole they produced a generally milder outlook, we did see a surprise forecast from the 'control' member of these ensembles - a remarkably frigid January.</p><p>Before we get into the good stuff, let's review what that means.</p><p>The ECMWF agency is known for their namesake weather model, but they also provide a critical forecasting tool with their ensemble system. In an <b><u>ensemble forecast</u></b>, an initial forecast model is taken, tweaked ever so slightly, and then re-ran. That's one ensemble 'member'. Then, they take that initial data again, tweak it ever so slightly in a different way, and re-run it again. That's another ensemble member, and it continues. <u>The ECMWF's ensemble system has 51 different members - they are all different versions of the ECMWF weather model, but each one has slightly different starting conditions in order to produce a different forecast</u>. </p><p>You might ask why one would do that, since it sounds a lot like all we're doing is intentionally changing the initial conditions and letting it run free. That doesn't sound very productive, does it? <u>In reality, the value comes from how similar all of these 51 members are at each point in time</u>. For example, if all 51 ensemble members showed a winter storm in the Midwest ten days from today, that would be a big boost to forecast confidence. Why? Because if all 51 members have that storm happening, it means no matter what the weather conditions are right now (i.e. even if they're tweaked in all kinds of ways), we still end up with a winter storm on the horizon. As a result, ensemble forecasting is a potent part of any forecaster's toolbox.</p><p>But each ensemble set - whether it's the ECMWF ensembles, the American (GFS) ensembles, or any other set - has one member that is different from the rest. This member's initial conditions are the best possible data we have, and all the other members are those slightly-tweaked versions of this one. We call this special ensemble member the <u>control</u>. Indeed, the control member is the raw forecast taken strictly using initial data. Nothing is tweaked, nothing is altered, just the raw initial conditions. Every other ensemble member takes that control member data, tweaks it a bit, and re-runs it, like I described above. </p><p>One may argue that this makes the control member more attention-worthy, since it only uses the best initial conditions data we have and isn't artificially tweaked. Whether that argument has merit is something I have yet to verify on my own.</p><p><br /></p><p>In any event, now that we understand why an ensemble's 'control' member is worth monitoring, let's get down to the good stuff: the reason why this post was made.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi3DI9sWELf9O_5Af29I0e7f67DHjhdMBIUIu-kNn9mvPZ2SvisZmeYQ_pQeqcUEf5Xlz7bCv4VXxDuIWlzkWn1Lfb4Drik2s0YzH_fGK3FoffDg-7GzoOxNcEmxvaeBp9MlbZYfkK6mgD6/s984/ecmwf+control+dec25jan1+t+anom.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="808" data-original-width="984" height="526" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi3DI9sWELf9O_5Af29I0e7f67DHjhdMBIUIu-kNn9mvPZ2SvisZmeYQ_pQeqcUEf5Xlz7bCv4VXxDuIWlzkWn1Lfb4Drik2s0YzH_fGK3FoffDg-7GzoOxNcEmxvaeBp9MlbZYfkK6mgD6/w640-h526/ecmwf+control+dec25jan1+t+anom.png" width="640" /></a></div><br /><p>Attached above from WeatherBell (all images on this post are from WeatherBell) is a look at the seven-day average temperature anomaly from the ECMWF ensemble control member over the December 25th - January 1st timeframe. We see that the control member anticipates a deep and formidable reservoir of below-normal temperatures in western Canada, which begins bleeding south and east into the United States as December turns to January. Indeed, seven-day average anomalies of more than 25 degrees Fahrenheit below normal are nothing to shake a stick at!</p><p>The outlook continues into mid-January below:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgTo3Os6PzmtR0Q7DpGaB6Mb2bwtNp2w_PvsChRwa9c1dWWx8zBjDXv0E4TZvG-n8HBNkz03zcDhjt_xy9Kgn9gHNtZe-29cNrLSNVftCHb2oTHsdlfAfnZjb6WOw6vNUfZrJ9Jxnxc-RF8/s984/ecmwf+control+mid+jan+t+anom.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="808" data-original-width="984" height="526" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgTo3Os6PzmtR0Q7DpGaB6Mb2bwtNp2w_PvsChRwa9c1dWWx8zBjDXv0E4TZvG-n8HBNkz03zcDhjt_xy9Kgn9gHNtZe-29cNrLSNVftCHb2oTHsdlfAfnZjb6WOw6vNUfZrJ9Jxnxc-RF8/w640-h526/ecmwf+control+mid+jan+t+anom.png" width="640" /></a></div><br /><p>From January 11th - 18th, temperatures are shown by the ECMWF ensemble control member to be much colder than normal across almost all of the country, particularly east of the Front Range and especially in the Ohio Valley. With seven-day average temperatures seen at almost 20 degrees F below normal in parts of Ohio, Indiana and Kentucky, it's clear that the ECMWF Control member expects the Arctic gates to burst open in the first month of the new year.</p><p>Teleconnections accordingly show a breakdown in the tropospheric polar vortex as judged by a collapse in the Arctic Oscillation in the blue line (control member's forecast)...</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgNFQ5l7LZ4z5IXesca5bd386_COCznv1V5qauHb6IlXILJ8pQHVMPV8GNj0pZq0CJbL8SUXVP4O9UGuE7unVUJg4k6ReraYpAPX_sGO3VNTTRHTLtExYNhdniFAGOUNQo1RuredF0C9mCt/s984/EPS+AO.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="808" data-original-width="984" height="526" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgNFQ5l7LZ4z5IXesca5bd386_COCznv1V5qauHb6IlXILJ8pQHVMPV8GNj0pZq0CJbL8SUXVP4O9UGuE7unVUJg4k6ReraYpAPX_sGO3VNTTRHTLtExYNhdniFAGOUNQo1RuredF0C9mCt/w640-h526/EPS+AO.png" width="640" /></a></div><br /><p>... and a similar plunge in the North Atlantic Oscillation (NAO) from the control member allows that frigid Canadian cold to plow eastwards...</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbDX3srpabg2l-WhMFzxZAiFCFqx1TDRMy5NLCPBt8MXF2yOYmhuBTSYheAprjzxXbdzEKLNZif7FTtbsJmI90MEnn0c-9xvYjIzZSrclGKeZSr20OZ9AScgt4rwsnuFyn9YDN-Hg3MUKL/s984/EPS+NAO.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="808" data-original-width="984" height="526" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbDX3srpabg2l-WhMFzxZAiFCFqx1TDRMy5NLCPBt8MXF2yOYmhuBTSYheAprjzxXbdzEKLNZif7FTtbsJmI90MEnn0c-9xvYjIzZSrclGKeZSr20OZ9AScgt4rwsnuFyn9YDN-Hg3MUKL/w640-h526/EPS+NAO.png" width="640" /></a></div><br /><p>Now, that's all good and fun to look at, but this post wasn't written to get all the cold weather fans out there hyped up. Indeed, as the above two teleconnection charts show, the control member is an extreme outlier in the late-December and early-January period, and the average of all ensemble members just barely turns the NAO negative at the end of this month. The mean doesn't even turn negative at all for the Arctic Oscillation!</p><p>My takeaway is this: we're seeing some noteworthy cold signals for the end of December and start of January from the ECMWF control and the CFS ensemble system (a different analysis of that coming later today), but we can't rely on models that far out. To me, it's just not smart forecasting to use them for anything aside from large grains of salt, if that makes sense. Instead, I'm focusing on a changing global weather regime as the Madden-Julian Oscillation changes into colder phases for the end of December and through January. That, I feel, is where the real intrigue lies for Arctic outbreak risks as we enter the new year.</p><p>Stay tuned for that aforementioned post later today.</p><p>To Summarize:</p><p></p><ul style="text-align: left;"><li>The ECMWF ensemble's 'control' member - often seen as the most accurate member of the ensemble group - is expecting much-below-normal temperatures from the end of December through much of January in the U.S.</li><li>At this stage, while it's intriguing, I would not take this signal as anything more than a large grain of salt</li><li>There is more value in monitoring the changing global pattern as the new year kicks off, and a post discussing that will be published a little later today.</li></ul><p></p><p>Andrew</p>Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-59189999073331548162021-12-06T16:34:00.002-06:002021-12-06T16:34:28.862-06:00December 10-12 Potentially Significant Winter Storm<p> There is increasing potential for accumulating snow across the north-central and Upper Midwest in the coming days, as a strong low-pressure system moves northeast through the Central Plains and Great Lakes. Note that there are two disturbances in this timeframe - one affecting the Midwest, and another affecting the East Coast. <u>This post covers the first region.</u></p><p>Because of relatively large variance between model guidance, I will first examine the GFS model, followed by the ECMWF model. A summary of my own thoughts will conclude.</p><p><br /></p><p><span style="font-size: medium;"><b><i><u>GFS Model Analysis</u></i></b></span></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgXpExNxaWEJuZ-WkN6L-4MJqj_NdPKgvsLDJOOhMubrLqoJG34gQUemHGnza9wpgOj9WUPmbnqQ-HAUJba5WS4KdJ459Dm79wo0C-1L6R9zIfsNBJd28mx3Vt4v_ARmW2N3p-OFlT6fNqs/s1024/GFS+Energy+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+102.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgXpExNxaWEJuZ-WkN6L-4MJqj_NdPKgvsLDJOOhMubrLqoJG34gQUemHGnza9wpgOj9WUPmbnqQ-HAUJba5WS4KdJ459Dm79wo0C-1L6R9zIfsNBJd28mx3Vt4v_ARmW2N3p-OFlT6fNqs/w640-h480/GFS+Energy+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+102.png" width="640" /></a></div><div><br /></div>Attached above is a look at 3-hour accumulated precipitation (by type) and sea level pressure contours, per weathermodels.com and per the 12z GFS, valid at 12pm Central Time on December 10th. The GFS anticipates a strong surface low (989 millibars) to eject from the Rockies into the Kansas / Nebraska area around this time, tossing out a band of snow well ahead of the low stretching into South Dakota, Minnesota and northern Wisconsin. Snowfall intensifies in SD as the low approaches and allows for the deformation zone to form.<br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhEUP1y1d2gsE1rQ5zrpNgwUkXFKzsWsH6NeVWxj5AZFpytV5pgEcFVV88922ytbVhxF96lGSWySehJDwfOGYgiwSJMHqSQwSF2jwpxDn5RSaMxJ8PuucaLeJM982FedGQ4mM5qLjtXQvXZ/s1024/GFS+Energy+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+114.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhEUP1y1d2gsE1rQ5zrpNgwUkXFKzsWsH6NeVWxj5AZFpytV5pgEcFVV88922ytbVhxF96lGSWySehJDwfOGYgiwSJMHqSQwSF2jwpxDn5RSaMxJ8PuucaLeJM982FedGQ4mM5qLjtXQvXZ/w640-h480/GFS+Energy+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+114.png" width="640" /></a></div><br /><p>Moving ahead to 12:01 am on December 11th, we find the storm to be a quick-moving one, with the surface low now in the Dubuque, Iowa vicinity and developing into a mature cyclone (evidenced by ongoing rain and thunderstorm activity in the South and a continued band of moderate snows north and northwest of the low). Accumulating snow looks to overspread Minnesota and northern Wisconsin at this point in time.</p><p>The primary issue for those hoping for snow appears to be an aggressive warm front associated with the storm system. Indeed, a warm antecedent air mass (a.k.a. relatively warm weather in the Central U.S. in advance of this storm system exiting the Rockies in the first place) will allow the warm front to keep precipitation type as liquid well north and east of the surface low, stretching past Michigan and into south-central Canada!</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhsoTEjisTNyBnQe2gBBJtEMvamWd2sGpWiUCyUtopk8uIEV2IDomqEqmzl_Cz07cZQcO-RI_rzU4xfWvt-XFMC2FUCkjhNgra8IfgoPIThS-z7JMbAsoUJ0ad0RTD012bKsJ8Ipqis3JZC/s984/gfs-deterministic-conus-snow_72hr-9234800.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="808" data-original-width="984" height="526" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhsoTEjisTNyBnQe2gBBJtEMvamWd2sGpWiUCyUtopk8uIEV2IDomqEqmzl_Cz07cZQcO-RI_rzU4xfWvt-XFMC2FUCkjhNgra8IfgoPIThS-z7JMbAsoUJ0ad0RTD012bKsJ8Ipqis3JZC/w640-h526/gfs-deterministic-conus-snow_72hr-9234800.png" width="640" /></a></div><br /><p>Taking a look at projected accumulated snowfall for this event (remember, NOT including the East Coast disturbance around this same time) shows a relatively impressive snowstorm for parts of the Upper Midwest and Plains. Assuming a 10-to-1 snow-to-liquid conversion (meaning 10" of snow can be melted down to 1" of water), a swath of South Dakota is at risk for snows exceeding 6", while portions of Minnesota and especially northern Wisconsin could see a run at more than 12" of snow as the disturbance associated with this storm system matures and intensifies. Indeed, taking the GFS verbatim, some locations in northern Wisconsin may have a shot at 18" of snow!</p><p>It's also possible these totals are a little under what they may actually turn out to be, as surface temperatures look to be firmly in the mid- to lower-20s during this event, turning that 10-to-1 snow ratio more into a 15-to-1 ratio.</p><p><br /></p><p>Now that we've gotten a look at what the GFS model wants, let's peek at the ECMWF's interpretation.</p><p><b><i><u><span style="font-size: medium;">ECMWF Model Analysis</span></u></i></b></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhLxSlMMmFGW9WSIilCACNE4fV8sdbAnOERzWzykLYtri4d1pYF5CVPq55eQOu9xAUGRiydwODYnptS9QDmtCN6gl93uMeEavcj5iTYvBg61m6ZPqNNsOO_5BW_nlNOSCf5fj3WH3wP4D9M/s1024/9-km+ECMWF+USA+Cities+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+102.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhLxSlMMmFGW9WSIilCACNE4fV8sdbAnOERzWzykLYtri4d1pYF5CVPq55eQOu9xAUGRiydwODYnptS9QDmtCN6gl93uMeEavcj5iTYvBg61m6ZPqNNsOO_5BW_nlNOSCf5fj3WH3wP4D9M/w640-h480/9-km+ECMWF+USA+Cities+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+102.png" width="640" /></a></div><br /><p>We'll be examining the same points in time here as we did in the GFS analysis: for instance, this first graph shows forecasted precipitation type and sea level pressure contours at noon on December 10th. The ECMWF places this surface low somewhat to the south of the GFS, resulting in a southward shift of the moderate snow band. Indeed, rather than South Dakota receiving the moderate snows from this system as in the GFS, we find much of Nebraska (but not Omaha!) under the gun for accumulating snow. The overall precipitation presentation in the eastern Rockies also looks more robust in the ECMWF, implying that the system may put down more snow than what the GFS showed us.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhBC1mnZ2lUjn8RZhGrGa-VY_LBVI_IczY5gkQgdd3W6Z5yfYUEt5py3Gn_oHbOEVAOzg8QlC1d77Ijhxq4eoLZ8drviV-g0i1zMLY2ONZiqVFhU4PiLjo94gunlhEtCerA496OJuw4vdgx/s1024/9-km+ECMWF+USA+Cities+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+114.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhBC1mnZ2lUjn8RZhGrGa-VY_LBVI_IczY5gkQgdd3W6Z5yfYUEt5py3Gn_oHbOEVAOzg8QlC1d77Ijhxq4eoLZ8drviV-g0i1zMLY2ONZiqVFhU4PiLjo94gunlhEtCerA496OJuw4vdgx/w640-h480/9-km+ECMWF+USA+Cities+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+114.png" width="640" /></a></div><br /><p>Moving ahead to 12:01am on December 11th, we find the ECMWF placing the surface low pretty close to where the GFS showed it, but the big difference is the marked increase in moisture available immediately north and west of the surface low. While the GFS has snowfall coming to an end not too long after the surface low passes a given line of longitude, the ECMWF allows moderate to heavy snowfall to continue in Nebraska even as the surface low is near Dubuque!</p><p>The result is a much snowier storm system:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgCYE97rnHFG-PWcOA_n4ggREnvsRq1EPsmRowJA722veZDlthVu_MT_OLotxh4XqJ4IlUcRnyqWk8WC-OiZyIIemv0beqQsQicbUlrit-FBLEKcXLALLP-frdlnqNpkqqdWQ2bJtLf-oTo/s984/ecmwf-deterministic-conus-snow_72hr-9256400.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="808" data-original-width="984" height="526" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgCYE97rnHFG-PWcOA_n4ggREnvsRq1EPsmRowJA722veZDlthVu_MT_OLotxh4XqJ4IlUcRnyqWk8WC-OiZyIIemv0beqQsQicbUlrit-FBLEKcXLALLP-frdlnqNpkqqdWQ2bJtLf-oTo/w640-h526/ecmwf-deterministic-conus-snow_72hr-9256400.png" width="640" /></a></div><br /><p>As depicted above, via WeatherBell, the 12z ECMWF delivers over 12" of snow to the northern tier of Nebraska, even laying down several inches of snow on the back end of the storm system in parts of eastern Nebraska. A sharp gradient near the surface low likely results in a modest icing threat in the Omaha metro area, while continued snow accumulations exceeding 15" track north and east through northwest Iowa, southern Minnesota and northern Wisconsin.</p><p><br /></p><p><b><i><u><span style="font-size: medium;">My Thoughts</span></u></i></b></p><p>A look at how each model handles the mid-level pattern gives some insight as to why these two forecasts are markedly different. </p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgcmk88RZpgGKmjAxsvwSQekg6-1ffSyhMx3OceqP6oasMFsyZ3Ojd_K74k1UAgymEvbJo4uCoUDyf1Y7QMuMO6p7GkKmkU4Zrieeopf_3x8zlkhzEoXF0LGCmqwiOdW6jkZeVZU1CyhkpQ/s1024/9-km+ECMWF+Global+Pressure+500+hPa+Rel+Vorticity+500+hPa+Rel+Vorticity+78.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgcmk88RZpgGKmjAxsvwSQekg6-1ffSyhMx3OceqP6oasMFsyZ3Ojd_K74k1UAgymEvbJo4uCoUDyf1Y7QMuMO6p7GkKmkU4Zrieeopf_3x8zlkhzEoXF0LGCmqwiOdW6jkZeVZU1CyhkpQ/w400-h300/9-km+ECMWF+Global+Pressure+500+hPa+Rel+Vorticity+500+hPa+Rel+Vorticity+78.png" width="400" /></a></div><br />The first thing that is complicating this outlook is the fact that we're dealing with two separate pieces of energy in making this winter storm happen. I've highlighted these two pieces of energy in a 500-millibar relative vorticity image on the right, valid at noon on December 9th. That might all sound a bit complicated, but in a nutshell, the more colors you see, the more likely it is that there is a 'piece' of energy present that can develop into a storm system.<p></p><p>Both models agree that these two pieces of energy will make landfall on the West Coast in the Pacific Northwest and in California, respectively. It's how they mingle and interact when they meet up in the Rockies that is throwing models for a loop. </p><p>The GFS model wants to hold the core of this energy back in the Rockies a little longer than the ECMWF, making the system positively-tilted at the mid-levels (a development that keeps the storm system relatively immature, and making it tougher to get those heavier snow totals). In contrast, the ECMWF allows a core of this energy to track north and east with the surface low and tilt negatively as it does so, amplifying the surface low and resulting in a more enthusiastic snowfall outlook across the Central.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgxsJP18LaxAE-_Z7VF9zKWuls-0w2WTHqWKoaV2T5PViNYRF86mvRCpsJl4JjhrIGVaNhqSLcEMY3D0BTJwml-qapMhWp62GrCpthrFijRx3aewJqu91yx9D73tEmpmpKbq66AbQnQE6EX/s1200/eps_ao_2021120612.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="600" data-original-width="1200" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgxsJP18LaxAE-_Z7VF9zKWuls-0w2WTHqWKoaV2T5PViNYRF86mvRCpsJl4JjhrIGVaNhqSLcEMY3D0BTJwml-qapMhWp62GrCpthrFijRx3aewJqu91yx9D73tEmpmpKbq66AbQnQE6EX/w640-h320/eps_ao_2021120612.png" width="640" /></a></div><br />The current strongly-positive state of the Arctic Oscillation (shown above) helps mold the broader weather pattern by making it less likely that we get these big storm systems with big snow totals, and does lead some credibility to the weaker, more progressive GFS model. At the same time, the Pacific-North American index (PNA) is poised to be strongly-negative at this point in time, which helps fire up a ridge of high pressure in the East U.S. and gives any storm systems in the Central a "ramp" in the mid-levels on which these pieces of energy can tilt negatively and mature into powerful storms.<p></p><p><u>Putting all these pieces together, I am in favor of the GFS' solution right now, but I do think it's pretty realistic we could see a southward adjustment like the ECMWF shows</u>, in which case we would also see a stronger storm system and higher snow totals. The overwhelming negative state of the PNA drives that conclusion, with multiple GFS ensembles joining a majority of ECMWF ensembles in playing that southern shift out and making for a stronger storm.</p><p><br /></p><p>To Summarize:</p><p></p><ul style="text-align: left;"><li>A potentially significant winter storm is expected in the December 10th - 12th timeframe across the Central U.S.</li><li>At this time, South Dakota, northwest Iowa, southern Minnesota and northern Wisconsin may see snowfall totals of 4-12", with those higher amounts much more likely in NW Iowa / S MN and especially northern WI</li><li>Given regional teleconnections, it seems quite plausible that future forecasts shift this snow axis a bit south and increase snowfall totals, as the ECMWF model projects</li><li>It is too early to tell for sure, but there may be a minimal icing threat along the freezing-temperature line. Material ice accretion is not expected from this storm.</li></ul><div>Andrew</div><p></p>Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com5tag:blogger.com,1999:blog-1448180228140749967.post-55570288316934318282021-12-01T12:39:00.003-06:002021-12-01T12:39:59.734-06:00Long Range Outlook: Colder Pattern Developing Dec. 20 - Jan. 10; Polar Vortex Under Duress<p> Good afternoon, everyone, and happy first day of meteorological winter!</p><p>The other day I wrote how the outlook appeared to be favoring above-normal temperatures for the month of December into early January, as the stratospheric polar vortex (SPV) is currently stronger than normal and model forecasts for that period had been aggressive with keeping the vortex strong. Since then, however, we have seen a shift in model guidance that bring the SPV under attack to a stronger degree, and a broader shift in the global weather regime may favor a round of sharply colder Canadian air in the December 20-30 timeframe.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEisKVDT_D7M90mi5sH0ZR6Cv3g_BG1Qw139OQ4AUB2qEAKR8KH8I0y9aZ8Ob3d_OlwDkbsq4kyjaFmx3GQehRgnIIMLwjMHDPyLUWfIeyMUJ1FZb_VjA9s8XQ4Y__YeURcTFIyR-ANzN2_S/s1000/GEFS+Dec09+Strat.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1000" data-original-width="1000" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEisKVDT_D7M90mi5sH0ZR6Cv3g_BG1Qw139OQ4AUB2qEAKR8KH8I0y9aZ8Ob3d_OlwDkbsq4kyjaFmx3GQehRgnIIMLwjMHDPyLUWfIeyMUJ1FZb_VjA9s8XQ4Y__YeURcTFIyR-ANzN2_S/w640-h640/GEFS+Dec09+Strat.png" title="weathermodels.com" width="640" /></a></div><br /><p>Previous forecast model runs anticipated the development of a single, weak ridge of high pressure way up in the stratosphere that would appear to be a nuisance towards, but not disrupt, the stratospheric polar vortex. Consequentially, all stratospheric signals seemed to be aiming in a warmer direction for U.S. weather for the balance of December and into January.</p><p>Latest model guidance has changed its tune. The GFS ensembles are shown above, with the 10-millibar forecast of geopotential height anomalies shown in color and pressure contours juxtaposed on top. We see that the GFS ensembles are showing a vortex splitting event to occur around December 7-9, with two distinct ridges of high pressure (one in Eurasia and another in the Pacific) pinching the SPV across the North Pole so that one lobe of the vortex breaks off and settles over Greenland, while the second lobe drifts into Siberia. </p><p>This isn't the most impressive vortex splitting event you'll ever see, but it's enough to disrupt the flow of the stratospheric vortex and, in turn, open the door for a round of Arctic air about two to three weeks later. This puts us roughly in the December 20th - January 5th timeframe, and this will be the period to watch for a potential round of much colder than normal air in North America.</p><p>So we know that the stratospheric polar vortex will come under pressure over the next week or two, perhaps splitting in the process. Supposing a cold air event may become more likely two to three weeks later, how will the overall pattern look around then? We start with an analysis of tropical convection.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjYXGWV-zzWbtuShdP_-V1t_u5xpjdrs6HJJjhVb86WQ62ga5t_KSRDnjh2ebB65NRhG5iwdf3uYwbqeWkCMn0Bqouo0cN9TKyTo6wPzNhb35HnFycAbLHemmN4ZNwp98ELJD2-LzhP5R1j/s1280/eps_chi200_anomaly_hov_equatorial_2021112900_MEAN.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1024" data-original-width="1280" height="512" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjYXGWV-zzWbtuShdP_-V1t_u5xpjdrs6HJJjhVb86WQ62ga5t_KSRDnjh2ebB65NRhG5iwdf3uYwbqeWkCMn0Bqouo0cN9TKyTo6wPzNhb35HnFycAbLHemmN4ZNwp98ELJD2-LzhP5R1j/w640-h512/eps_chi200_anomaly_hov_equatorial_2021112900_MEAN.png" width="640" /></a></div><p>The chart above (from weathermodels.com) is complex at first blush, but can be easily broken down. This shows forecasted thunderstorm activity along the Equator (in a band between the 15 North and 15 South lines of latitude) from the long-range ECMWF model across all lines of longitude, from today through January 15th (y-axis scale). The variable being measured here is upper-level velocity potential anomalies, which is a fancy parameter for judging how conducive the atmosphere will be for thunderstorm activity. </p><p>Here, yellows and oranges represent above-normal velocity potential anomalies, which suppress thunderstorm activity. On the flip side, greens and blues indicate lower VP anomalies, which then enhance thunderstorm activity.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9w591mKseljlGYF0wkajgQjHEI9emN5uX_fj4oZX73P_Za_Rac6fPo53Y0A9Y_PszJXbHkW_y77f-nAHrJsPvzLlWoPoYPQ5QG31FOdE3aQAQMqBkxs8yRRp116Sdc5IbdEju47aX2cZQ/s585/Screen+Shot+2021-12-01+at+12.04.17+PM.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="585" data-original-width="416" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9w591mKseljlGYF0wkajgQjHEI9emN5uX_fj4oZX73P_Za_Rac6fPo53Y0A9Y_PszJXbHkW_y77f-nAHrJsPvzLlWoPoYPQ5QG31FOdE3aQAQMqBkxs8yRRp116Sdc5IbdEju47aX2cZQ/w285-h400/Screen+Shot+2021-12-01+at+12.04.17+PM.png" width="285" /></a></div><br />We can then ascertain what phase the Madden-Julian Oscillation (MJO) is in by seeing when those greens and blues pop up across different parts of the world. For example, over the next few days, we see blues and greens across the islands northwest of Australia and southeast of India, which correspond to MJO phases 3, 4 and 5. This feature has recently helped to enhance above-normal temperatures in the United States, as Phases 3-5 encourages warmer weather across the continent. How do we know this? The composite image on the right (from the Climate Prediction Center) shows temperature anomalies during the Nov-Dec-Jan period for each of the eight MJO phases.<p></p><p>By the same token, when enhanced Equatorial thunderstorm activity develops northeast of Australia in the open Equatorial Pacific, the MJO tends to be in Phases 7-8, which correlate colder for most of the country. The whole process starts over again with enhanced thunderstorms in the Equatorial Atlantic and over Africa, which is MJO Phase 1 territory.</p><p><br /></p><p>Returning to the ECMWF forecast image above, after our MJO Phase 4 influence dies down by December 10th, we are expecting to see a robust resurgence in tropical convection in the Equatorial Atlantic, which I've highlighted in the graphic. While not explicitly shown, thunderstorm activity around those waters and into Africa correlates to a more-or-less MJO Phase 8 or 1 type of pattern, and will tend to lean cooler for most of the United States as a result. This enhanced thunderstorm activity in the Atlantic kicks off by December 10th and may stick around through early January, with ebbs and flows in the intensity of this thunderstorm activity.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhlbthvoNwbT2dz2D1e0oQ_7xXj4wazaqKcD0qxe4nlAGPznK4_h7Km9ZeX5wbYo9Rhthe_2OHaiYU-kiG1lvzc_YaZdD1aPEXkSQbvziPQ7oujUiWLE6kmEK9E6Vrf3nHK3OBkyCi1eZ1G/s547/LR+ECMWF+MJO.gif" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="547" data-original-width="547" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhlbthvoNwbT2dz2D1e0oQ_7xXj4wazaqKcD0qxe4nlAGPznK4_h7Km9ZeX5wbYo9Rhthe_2OHaiYU-kiG1lvzc_YaZdD1aPEXkSQbvziPQ7oujUiWLE6kmEK9E6Vrf3nHK3OBkyCi1eZ1G/w400-h400/LR+ECMWF+MJO.gif" width="400" /></a></div><br /><p>Rather than rely on subjective interpretations of the MJO to decide where the oscillation is heading, we can also make use of an objective MJO phase-space analysis, shown above for the same long-range ECMWF model we were just subjectively analyzing. In this objective analysis above (from the CPC), the MJO is seen meandering (and strengthening) in Phase 7 from December 17th through the end of the forecast period, December 30th. This is a little earlier in the phase progression from the Phases 8 and 1 I had been expecting, but no matter - the general theme of a global pattern shift in favor of colder weather for the last ten days of December and into early January remains intact.</p><p><br /></p><p>The stratosphere will be coming under some duress in the next several days, which may raise the risk of a cold air event in the U.S. for the end of December and into early January, while the MJO is shifting into pro-cold phases for the last ten days of December and perhaps onwards. Now that we see what kind of environment may be setting up, let's see if model guidance is latching on to any cold weather threats.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-6G-QWLB7400UQsetkhJsazLA8CinoVQXSqcb9HFPrQEyo8i8C2SvhcfUdfHtYep7mGUhLH947ptQAc4-HeBfc3la-wE3k6Fox47dgBy_HmeRIJzu6YDkQFZLNF_IA5XojCehWK1y4vu-/s1024/cfs+dec16-26.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-6G-QWLB7400UQsetkhJsazLA8CinoVQXSqcb9HFPrQEyo8i8C2SvhcfUdfHtYep7mGUhLH947ptQAc4-HeBfc3la-wE3k6Fox47dgBy_HmeRIJzu6YDkQFZLNF_IA5XojCehWK1y4vu-/w400-h300/cfs+dec16-26.png" width="400" /></a></div><br /><p>Beginning with the American CFS model, we take a look at 10-day temperature anomalies across North America from December 16th through the 26th. The pattern looks generally warm for the U.S., but the real thing I'm watching is that reservoir of colder-than-normal air building in western Canada, and similarly anomalous above-normal temperatures in the Arctic Circle. This suggests a shift in Arctic air to the south, displaced into western Canada and further east into Greenland. While not a necessity for cold air events, a reservoir of cold Canadian air in the western part of the country is traditionally a good sign.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgDMwEYDZ9bsx2uVTd-oCCDSqL3TDLWIBAkqZEF7CIDRE5ohQscnGUi9pkO64h7XbhCSGL-7yQj8BlqJEuQdTwbUKBexzUdtqqbeqaUXEHgkPtQ_yDfnsdAUepFYkOqEJ9S7trNOPs5W4J3/s1024/cfs+dec21-31.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgDMwEYDZ9bsx2uVTd-oCCDSqL3TDLWIBAkqZEF7CIDRE5ohQscnGUi9pkO64h7XbhCSGL-7yQj8BlqJEuQdTwbUKBexzUdtqqbeqaUXEHgkPtQ_yDfnsdAUepFYkOqEJ9S7trNOPs5W4J3/w400-h300/cfs+dec21-31.png" width="400" /></a></div><p>Moving ahead to the December 21st - 31st timeframe, we see what that cold Canadian air reservoir does: it spills south and east. With continued warm air displacement into the Arctic Circle, below-normal temperatures have free rein to grind south and east into the United States and deeper into Canada. Above-normal temperatures are still anticipated to linger in the South and along the Eastern Seaboard, but this may be something that happens earlier in this period followed by colder weather later towards the end of the year.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEitFemilsZS84Vr6Ewh0rL2R1R93MB32471P5l62Pgn1APuCq60C4GnWZPPHCn6kpK5TjyMKPSmrm1TyaiDYWrqvlnemMWDKS3X0yW0hrr75pztTbn4-cDeyi1f7KZcWCJGU8qmiO8yV2AR/s1024/cfs+dec31+0+jan10.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEitFemilsZS84Vr6Ewh0rL2R1R93MB32471P5l62Pgn1APuCq60C4GnWZPPHCn6kpK5TjyMKPSmrm1TyaiDYWrqvlnemMWDKS3X0yW0hrr75pztTbn4-cDeyi1f7KZcWCJGU8qmiO8yV2AR/w400-h300/cfs+dec31+0+jan10.png" width="400" /></a></div>Our last analysis of the CFS model comes for the December 31st - January 10th timeframe. It appears as though the CFS takes that MJO Phase 7 temperature composite to heart and continues to displace cold Arctic air southwards into Canada and the northern U.S., with much colder than normal temperatures seen across the continent. <div>Even with this colder pattern, above-normal temperatures are still evident across the South, symptomatic of a jet stream that refuses to dip too far south (perhaps a consequence of implied storminess over Greenland; a +NAO regime for you weather enthusiasts).<br /><div><p><br /></p><p>All in all, I see the CFS model as pretty conducive for a cold air event in this December 20th - January 10th timeframe, particularly with such a formidable reservoir of Arctic air in western (and eventually all of) Canada. As our last bit, let's turn our attention to the long-range ECMWF model and see what it says.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRF_OTwrhrYLpLbnPJKZY5v8OZkIe-y-p45R-olEnKwPmOjl_GHSlasbZNZvUcjQgKysgQR6EKqPY01Uwy65Gkht0CaX8BbEwtscp0SATrwZ1zKsFaR8SnOdyf_XvQDv1Hq-VpEElGKjQH/s1024/ECMWF+dec18-25.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRF_OTwrhrYLpLbnPJKZY5v8OZkIe-y-p45R-olEnKwPmOjl_GHSlasbZNZvUcjQgKysgQR6EKqPY01Uwy65Gkht0CaX8BbEwtscp0SATrwZ1zKsFaR8SnOdyf_XvQDv1Hq-VpEElGKjQH/w640-h480/ECMWF+dec18-25.png" width="640" /></a></div><p>Unsurprisingly, the long-range ECMWF is less keen to bring about a much colder weather regime to North America, but it does take the intriguing step of developing and intensifying that reservoir of cold air in western Canada. With anomalies seen deeper here than what the CFS shows, it does open the door for the risk of a more intense cold air event if we took this forecast verbatim. Of course, that would be too easy, and the ECMWF instead brings cold weather to the far north-central U.S. but maintains warmth in the South and East for the balance of the year and into early January.</p><p><br /></p><p>To Summarize:</p><p></p><ul style="text-align: left;"><li>The stratospheric outlook has changed since earlier this week, and it now appears more likely that the stratospheric polar vortex will be disrupted to some degree in the December 5-10 period</li><li>Combined with changes in the global weather pattern (via the MJO) to a state more conducive for below-normal temperatures in the U.S., the chances of a colder last several days of December & colder opening days of January are rising</li><li>Model guidance contains differences, but with both main models showing a formidable reservoir of frigid air accumulating in western Canada by December 25th, I am feeling optimistic that future forecasts for the northern third of the country (and potentially further south) will continue to trend colder</li><li>More on this to come</li></ul><p></p><p>Andrew</p></div></div>Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com1tag:blogger.com,1999:blog-1448180228140749967.post-45478572373590854242021-11-30T14:19:00.002-06:002021-11-30T14:19:37.736-06:00December 4-6 Potential Winter Storm<p>A disturbance is forecasted to track eastwards from the Pacific Northwest & Southwestern Canada across the northern Plains, bringing accumulating snow to the region before intensifying as an additional piece of energy interacts with this original system around and east of the Great Lakes.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj6qDt44MyuRTReOlcAAT5Y3ZIugyqB0b3CEharTDzGgJGZNCBGDL3eiX17PcdXhzCYgoBcMk0GBtnfAYMaFS1CNO_JL8n3QCaUuwWxVJadshCNQaXA4cyYwH4qPOqm3P2fuoqSXR79Wbgi/s1024/9-km+ECMWF+USA+Cities+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+102.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj6qDt44MyuRTReOlcAAT5Y3ZIugyqB0b3CEharTDzGgJGZNCBGDL3eiX17PcdXhzCYgoBcMk0GBtnfAYMaFS1CNO_JL8n3QCaUuwWxVJadshCNQaXA4cyYwH4qPOqm3P2fuoqSXR79Wbgi/w640-h480/9-km+ECMWF+USA+Cities+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+102.png" width="640" /></a></div><br /><p>This event begins during the day and evening on December 4th, with an upper-level disturbance riding east-southeast along a band of tight upper-level confluence and spawning a surface low-pressure system in the Dakotas. The above image shows forecasted precipitation types and sea-level pressure contours as of 12pm Central Time, December 1st. While the bulk of the precipitation is seen in the Rockies, the eastward progression of this system begins at this time as an arm of light snow pushes eastwards into the Dakotas.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgh9ijXpfFiJfgoyDydtqLL4WkuhGP3IyRI6cA7oFB4ivXVQ9mvbAJlsxf0Yv5ZK5ZwJh4m5CYjBE9n7ceapg2FCVp929rd7K7yDgBqfIU39fQASDGn7dDk4KFn-pxwWrz6ghKr52fdOHb1/s1024/9-km+ECMWF+USA+Cities+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+120.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgh9ijXpfFiJfgoyDydtqLL4WkuhGP3IyRI6cA7oFB4ivXVQ9mvbAJlsxf0Yv5ZK5ZwJh4m5CYjBE9n7ceapg2FCVp929rd7K7yDgBqfIU39fQASDGn7dDk4KFn-pxwWrz6ghKr52fdOHb1/w640-h480/9-km+ECMWF+USA+Cities+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+120.png" width="640" /></a></div><br /><p>By 6am Central Time on December 5th, the surface low has pushed east in accordance with the eastward progression of this upper-level system. Some moisture fetch from the South U.S., evidenced by weak rainfall in MO/AR/TX, adds to the system and helps gently boost snowfall totals in Minnesota and Wisconsin. Accumulations are expected to be in the 2-4" range across the Dakotas, northern Minnesota and northern Wisconsin over this December 4-5 period.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiX3YuK5AhSTV2REKqSBts95i9JPgwlog-XNHDL6n01HYhJltsClxA6v4vpj5BDN8ci8q5JQG_xW75Y6vX8CSgSuLCfxkc6hThHicdmK5F4eVQxJM7AgwNIMs7KAaXTBsR_h6pi2hjPamKs/s1024/9-km+ECMWF+USA+Cities+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+144.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiX3YuK5AhSTV2REKqSBts95i9JPgwlog-XNHDL6n01HYhJltsClxA6v4vpj5BDN8ci8q5JQG_xW75Y6vX8CSgSuLCfxkc6hThHicdmK5F4eVQxJM7AgwNIMs7KAaXTBsR_h6pi2hjPamKs/w640-h480/9-km+ECMWF+USA+Cities+Precip+Type+%2526+MSLP+Precip+Type+%2526+MSLP+144.png" width="640" /></a></div><br /><p>Things become much more interesting overnight December 5th into the morning of December 6th, as our surface low pushes eastwards and the upper-level piece of energy finally gets an opportunity to strengthen after being squeezed by a progressive and prohibitive jet stream back in the West and Central. As shown above, the latest European model run sees moderate to heavy snow in southeast Canada and into extreme northern parts of New England, turning into a mixed precipitation event as a surge of warm Southern air brings rain to most of the region.</p><p>The GFS model is a little better with snowfall chances in New England (1-3" in western and central New York), but in general we should see the best shot for over 4" of snow in southern Canada. The latest ECMWF snow accumulation chart for this event is shown below, and there is some question as to how strong this system could actually get. I don't think the ultra-aggressive totals shown by the ECMWF will come to fruition, but it seems plausible that some areas along or just north of the U.S. / Canada border in New England could hit 6".</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg_dgBqncMFWzXC3af_AD1SImLSRTR3AlocE5zsLHy058s7kFgtbiF4B0V54clRIpxv9UA946zAB_TwHMA3YeJlY-2xT15F31CkVkgkW8_ReV3manEvtPSS7AhNVNPMX53ORAfnBe6LycXS/s984/ecmwf-deterministic-conus-snow_72hr-8835200.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="808" data-original-width="984" height="526" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg_dgBqncMFWzXC3af_AD1SImLSRTR3AlocE5zsLHy058s7kFgtbiF4B0V54clRIpxv9UA946zAB_TwHMA3YeJlY-2xT15F31CkVkgkW8_ReV3manEvtPSS7AhNVNPMX53ORAfnBe6LycXS/w640-h526/ecmwf-deterministic-conus-snow_72hr-8835200.png" width="640" /></a></div><br /><p>To Summarize:</p><p></p><ul style="text-align: left;"><li>A winter weather event is expected to impact the northern Plains, Great Lakes and New England in the December 4-6 timeframe</li><li>Snow accumulations of 1-3" appear possible in the Dakotas, northern MN and northern WI during the December 4-5 window</li><li>Some heavier accumulations nearing 6" may be possible in extreme southeast Canada, but questions remain as to how notably this storm system will intensify as it nears the Atlantic</li></ul><div>Andrew</div><p></p>Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com7tag:blogger.com,1999:blog-1448180228140749967.post-8135450322564966502021-11-29T19:19:00.002-06:002021-11-29T19:19:13.365-06:00Stratospheric Polar Vortex Showing Long-Range Rumblings<p> Good evening, everyone!</p><p>As has been the case in previous attempts to re-start this blog, my stay here will be brief - I am blessed enough to be transitioning to a new job that will continue to allow me to forecast the weather, but for about the next month or so, the proprietary covers are off, if you will, allowing me to get back to where we first started!</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg-9a2HB2tXCGTF9xbYlRQoXXFEbGBtnpjnLjJ0DxSRa2qJ7WyMuSv7dTlR6cHg7_ALf3FDft8TYYA9mPgvllSYbTiBB9Y8DRe-4KsKdqe3OMv7ARFfrXXp3PmVBEYCv0pwhNy94VXl_TDK/s1000/9-km+ECMWF+Stratosphere+10+hPa+Geopotential+Height+Anomaly+10+hPa+Geopotential+Height+Anomaly+0.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img alt="weathermodels.com" border="0" data-original-height="1000" data-original-width="1000" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg-9a2HB2tXCGTF9xbYlRQoXXFEbGBtnpjnLjJ0DxSRa2qJ7WyMuSv7dTlR6cHg7_ALf3FDft8TYYA9mPgvllSYbTiBB9Y8DRe-4KsKdqe3OMv7ARFfrXXp3PmVBEYCv0pwhNy94VXl_TDK/w400-h400/9-km+ECMWF+Stratosphere+10+hPa+Geopotential+Height+Anomaly+10+hPa+Geopotential+Height+Anomaly+0.png" width="400" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><p>Attached above is a look at the current state of the 10-millibar part of the atmosphere, corresponding to the upper levels of the stratosphere and - more importantly - the slice of the atmosphere most relevant to tracking the stratospheric polar vortex. Here, blues and greens represent below-normal geopotential height anomalies (in this case, indicating the polar vortex is stronger than normal) while oranges and reds represent above-normal geopotential height anomalies (here, meaning the polar vortex is weaker than normal).</p><p>As the graphic shows, the stratospheric polar vortex is currently pretty well consolidated, with broad below-normal anomalies across the Arctic Circle and minimal (if any) attempts at bringing warmer air towards the North Pole. This is a primary driver behind my expectations for a warmer than normal December across most of the United States, perhaps save for the Pacific Northwest in line with traditional La Nina climatology. But things begin to change as we move towards the middle of December:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg-QkmPjhtDSBXRwZGqSfOVBG6SkUf__WAshedP4uN2OAOuDLGWZGE_jIk-I1XRd5QczuOVXZrp7EhXkIAwdOho5c7UnwVZMkBCWyZjjwYY9OF-8kqVypW-S3qAex7XvYprm8FrPgfMKp67/s1000/9-km+ECMWF+Stratosphere+10+hPa+Geopotential+Height+Anomaly+10+hPa+Geopotential+Height+Anomaly+240.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img alt="weathermodels.com" border="0" data-original-height="1000" data-original-width="1000" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg-QkmPjhtDSBXRwZGqSfOVBG6SkUf__WAshedP4uN2OAOuDLGWZGE_jIk-I1XRd5QczuOVXZrp7EhXkIAwdOho5c7UnwVZMkBCWyZjjwYY9OF-8kqVypW-S3qAex7XvYprm8FrPgfMKp67/w400-h400/9-km+ECMWF+Stratosphere+10+hPa+Geopotential+Height+Anomaly+10+hPa+Geopotential+Height+Anomaly+240.png" width="400" /></a></div><br /><p>The 10-day forecast from the latest ECMWF model shows a notable change by December 9th, as a broad ridge begins forcing its way poleward from western and central Canada. A secondary, weaker ridge is also evident in Eurasia, making for what looks on paper like a wave-2 vortex-splitting attempt but in reality ends up shoving the vortex into Siberia and not really splitting at all.</p><p>Temperatures also jump considerably over North America at this level of the stratosphere during this same time as this ridge formation...</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhdW8CW6ij9TOVf5dkGcXGaU5Jc6XPjkoe8fJXRmKa1vDLzqaCV3bnPX5LQAGL6qnna8vmTUmIzNK-Tk6qgEmm6RMXfEWKETHK8jjRFNSDypkXgz9tZQayjRjuncl_UXZF6q_bnctsm916R/s1000/9-km+ECMWF+Stratosphere+10+hPa+Temperature+Anomaly+10+hPa+Temperature+Anomaly+240.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img alt="weathermodels.com" border="0" data-original-height="1000" data-original-width="1000" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhdW8CW6ij9TOVf5dkGcXGaU5Jc6XPjkoe8fJXRmKa1vDLzqaCV3bnPX5LQAGL6qnna8vmTUmIzNK-Tk6qgEmm6RMXfEWKETHK8jjRFNSDypkXgz9tZQayjRjuncl_UXZF6q_bnctsm916R/w400-h400/9-km+ECMWF+Stratosphere+10+hPa+Temperature+Anomaly+10+hPa+Temperature+Anomaly+240.png" width="400" /></a></div><p><br /></p><p>All of this is good and well, and we do see some support from the GFS ensembles (not shown), but it doesn't look very promising to me. For one, this warming event appears to originate in North America; my preferred origination point for a polar vortex disruption is in the Bering Sea, as this area (in my experience) has tended to bring about the more powerful polar vortex disrupting events. Second, if this really is a vortex-split attempt instead of a vortex-displacement attempt (a la the weak secondary ridge in Eurasia), and if we take this forecast verbatim, there's no way we see this transpire. </p><p>Think of it this way: a vortex-disrupting SSW involves a single, massive ridge that brings blowtorch-level warmth into the Arctic Circle. A vortex-splitting SSW involves two somewhat-strong ridges that pinch the polar vortex somewhere around the North Pole, cutting the vortex into pieces. Here, we see a single moderately strong ridge. That doesn't inspire confidence to me, and as a result I think this is a flash in the pan: a good sign for future SSW opportunities, but not enough to result in the risk of a severe Arctic outbreak at the turn of the new year.</p><p><br /></p><p>To Summarize:</p><p></p><ul style="text-align: left;"><li>The stratospheric polar vortex is currently stronger than normal, raising the risk of above-normal temperatures across the U.S. through December.</li><li>There are some indications of a warming event around the middle of the month, but from what I see, this doesn't appear likely at this time to significantly disrupt the polar vortex</li><li>Consequentially, the chances of an SSW by mid-December appear low</li></ul><div>Andrew</div><p></p>Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-80524125417984698922019-08-17T12:00:00.000-05:002019-08-17T12:00:01.388-05:00Preliminary 2019-2020 Winter Forecast<div dir="ltr" style="text-align: left;" trbidi="on">
<div class="separator" style="clear: both; text-align: justify;">
<span style="text-align: left;">Hello everyone, and welcome to my Preliminary 2019-2020 Winter Forecast. Within the Word document I composed it in, this publication consumed almost 55 pages and about 50 figures, clocking in at almost 20,000 words. I believe it is the most detailed / most well-researched article I have written on this blog, and I'm very pleased to have you read it.</span></div>
<div class="separator" style="clear: both; text-align: justify;">
<span style="text-align: left;"><br /></span></div>
<div class="separator" style="clear: both; text-align: justify;">
<span style="text-align: left;">Certain constraints to my publication mean some of the data below are marginally out of date by approximately two to three weeks, as the forecast was prepared in late July. Where I am able to, I have made efforts to update the information, but on the whole the forecast is not affected.</span></div>
<div class="separator" style="clear: both; text-align: justify;">
<span style="text-align: left;"><br /></span></div>
<div class="separator" style="clear: both; text-align: justify;">
<span style="text-align: left;">For those wishing to skip the 'meat' of this forecast, feel free to scroll to the end for the forecast graphic.</span></div>
<div class="separator" style="clear: both; text-align: justify;">
<span style="text-align: left;"><br /></span></div>
<div class="separator" style="clear: both; text-align: justify;">
<span style="text-align: left;">Please enjoy the outlook.</span></div>
<div class="separator" style="clear: both; text-align: justify;">
<span style="text-align: left;"><br /></span></div>
<div class="separator" style="clear: both; text-align: justify;">
<span style="text-align: left;"><br /></span></div>
<div class="separator" style="clear: both; text-align: justify;">
<b style="text-align: left;"><u><span style="font-size: 18.0pt; line-height: 107%;"><br /></span></u></b></div>
<div class="separator" style="clear: both; text-align: justify;">
<b style="text-align: left;"><u><span style="font-size: 18.0pt; line-height: 107%;">1. Sea Surface Temperatures</span></u></b></div>
<div class="MsoNormal" style="text-indent: .25in;">
<i><span style="font-size: 14.0pt; line-height: 107%;">a. </span></i><b><i><span style="font-size: 16.0pt; line-height: 107%;">El Nino – Southern Oscillation (ENSO)</span></i></b><i><span style="font-size: 14.0pt; line-height: 107%;"><o:p></o:p></span></i></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Seasonal forecasting is almost always based off of the state of the El Nino – Southern Oscillation, or ENSO for short. This forecast is no different. We must first understand the concept of ENSO, however, and why we care about it.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The ENSO phenomenon, in a nutshell, is a primary driver of
seasonal (and, through other shorter-term oscillations, weekly or even daily)
weather patterns by way of sea surface temperature (SST) anomalies in the
waters across the Equatorial Pacific. When these sea surface temperatures are
above normal by a magnitude of at least 0.5 degrees Celsius, we call it an 'El
Nino' event. When these anomalies are below-normal by at least 0.5 degrees
Celsius, we call it a 'La Nina' event. If anomalies are positioned within the
-0.5 / +0.5 degree range, the environment is called ‘ENSO-neutral’. While we
monitor the entire Equatorial Pacific to analyze the ENSO phenomenon, there are
four primary "zones" through which to observe, a graphic of which is
shown here. They are:<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoListParagraphCxSpFirst" style="mso-list: l0 level1 lfo1; text-indent: -.25in;">
<!--[if !supportLists]--><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;"><span style="mso-list: Ignore;">·<span style="font: 7.0pt "Times New Roman";"> • </span></span></span>Nino
1+2. This is a small slice of the Pacific located between the Equator and the
10º South latitude line, extending from the far western tip of Peru to the 90º
West longitude line.<o:p></o:p></div>
<div class="MsoListParagraphCxSpMiddle">
<br /></div>
<div class="MsoListParagraphCxSpMiddle" style="mso-list: l0 level1 lfo1; text-indent: -.25in;">
<!--[if !supportLists]--><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;"><span style="mso-list: Ignore;">·<span style="font: 7.0pt "Times New Roman";"> • </span></span></span><!--[endif]-->Nino 3. This is a larger slice of the Equatorial
Pacific which spans from 5º North to 5º South latitude lines, and from 90º West
to 150º West longitude lines.<o:p></o:p></div>
<div class="MsoListParagraphCxSpMiddle">
<br /></div>
<div class="MsoListParagraphCxSpMiddle" style="mso-list: l0 level1 lfo1; text-indent: -.25in;">
<!--[if !supportLists]--><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;"><span style="mso-list: Ignore;">·<span style="font: 7.0pt "Times New Roman";"> • </span></span></span><!--[endif]-->Nino 4. This is also a larger slice, and also
extends between 5ºN and 5ºS on the latitude markers. For Nino 4, however, the
space is spread by longitude from 150º West to about 160º East, crossing the
dateline in the process.<o:p></o:p></div>
<div class="MsoListParagraphCxSpMiddle">
<br />
<o:p></o:p></div>
<div class="MsoListParagraphCxSpLast" style="mso-list: l0 level1 lfo1; text-indent: -.25in;">
<!--[if !supportLists]--><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;"><span style="mso-list: Ignore;">·<span style="font: 7.0pt "Times New Roman";"> • </span></span></span><!--[endif]-->Nino 3.4. This is the critical area to watch,
and is typically viewed as the primary space with which to assess the state of
the ENSO phenomenon. Spatially, it extends from 5ºN-5ºS latitudinally, and 120º
West to 165º West longitudinally.<o:p></o:p></div>
<div class="MsoListParagraphCxSpLast" style="mso-list: l0 level1 lfo1; text-indent: -.25in;">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiB7aUzsX7A7-6VcQ_-WT6zbafWQxEnIVSBkBg3dgN-LX_j-m0Qd0Ps5iOp3UyHUbcYLqcIStTDXEafdilIXDMrQLWUtgShPGSzJJB5BFcsa0S1WGbtb_a4a8BH-feA2Y4QB0S5aE8_y3M2/s1600/ninoareas_c.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="251" data-original-width="572" height="280" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiB7aUzsX7A7-6VcQ_-WT6zbafWQxEnIVSBkBg3dgN-LX_j-m0Qd0Ps5iOp3UyHUbcYLqcIStTDXEafdilIXDMrQLWUtgShPGSzJJB5BFcsa0S1WGbtb_a4a8BH-feA2Y4QB0S5aE8_y3M2/s640/ninoareas_c.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 1: The four ENSO monitoring regions (CPC)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Why do we break this space up into four different pieces
rather than just average out the sea surface temperature anomalies and call it
a day? A number of scientists with far more knowledge and research than I have
come to determine that there can be more than one type of El Nino - where
typically El Nino events bring warmer than normal waters to the eastern
Pacific, an "El Nino Modoki" event brings warm waters to the western
Pacific, and cooler waters to the eastern Pacific. This is not a trivial
difference, but for our purposes here, we won't dive into that topic. Indeed,
the probability of an El Nino Modoki event is quite low at this time, and looks
to remain quite low through the winter months. For now, the key is
understanding there are four different regions in which we monitor the ENSO
phenomenon, with the Nino 3.4 region broadly being of most importance. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgzyF4z9BPfThjbRn2TKhj_3zlhv-ew6atENKafzfei3rDDfL3S7ZxRrSyfuPui2XG_-QQud0vDl_b4PH0R8ezqKGbcCy8QZdiZG4fKUrK0h4iASegE-fLN6PSSOUj1jfdqxQUdMrga43-o/s1600/Picture1.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="550" data-original-width="479" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgzyF4z9BPfThjbRn2TKhj_3zlhv-ew6atENKafzfei3rDDfL3S7ZxRrSyfuPui2XG_-QQud0vDl_b4PH0R8ezqKGbcCy8QZdiZG4fKUrK0h4iASegE-fLN6PSSOUj1jfdqxQUdMrga43-o/s320/Picture1.png" width="278" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 2: SST anomalies by ENSO region (CPC)</td></tr>
</tbody></table>
<div class="MsoNormal">
The Climate Prediction
Center, the United States government agency most directly involved with
seasonal forecasting, declared an ‘El Nino Advisory’ earlier this year to
signal that an El Nino was ongoing. The Advisory remains in place as of this
writing, and as such we remain in an El Nino state.<o:p></o:p></div>
<div class="MsoNormal">
Let’s now view SST anomalies by each region described above.<span style="mso-no-proof: yes;"> </span><o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In the <u>Nino 1+2 region</u> (bottom panel), sea surface
temperature anomalies (SSTAs) have turned decidedly below-normal within the
last month or so. This comes after a period from October 2018 through mid-March
of this year, where anomalies were firmly in positive territory. From the end
of March to early June, however, the trend shifted to mixed anomalies hovering
around zero, and has now moved to comfortably negative anomalies. This is not a
good sign for the sustainability of the ongoing El Nino, and stands as a
caution flag for the other three regions that the El Nino is on a rather-shaky
foundation.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The picture given by the <u>Nino 3 region</u> isn’t any more
reassuring, with SSTAs falling into weakly-positive territory as of the most
recent data reading. Indeed, the latest value sets a fresh 10-month low for sea
surface temperature anomalies in that region, indicating that at the very least
the ongoing El Nino has very much come off the boil. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Moving to the key <u>Nino 3.4
region</u>, some cooling has also been observed, but SSTAs are still firmly in
positive territory and are only marginally below the +0.5 degree C threshold
that typically defines an El Nino. After peaking above +1.0 degrees C at the
end of 2018, anomalies in the Nino 3.4 region have gradually tapered off, and
with an eroding subsurface warm pool (to be discussed later), this trend is
expected to continue, placing the future of the El Nino in doubt.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
]In the aggregate, the <u>Nino
4 region</u> has seen little change since November 2018, with latest anomalies
only a bit below +1.0 degrees C. Still, the erosion of warm waters below the
surface means some weakening is also possible here in coming months. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgspnaGxQv9Xd5OkJwGlU_EA6pGi3oU_TDYUpLro5gc2pf_8Dnj1_ZfIQqP8pOpnYKcSZ0zumnsWzrRFzPIWi6L2YOdYVBZOQpxD44Fz8MPoseBwQKsR49H0rb7SJGNGeKgGjt3D7jg9K3w/s1600/Screen+Shot+2019-08-10+at+9.47.19+PM.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="227" data-original-width="323" height="280" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgspnaGxQv9Xd5OkJwGlU_EA6pGi3oU_TDYUpLro5gc2pf_8Dnj1_ZfIQqP8pOpnYKcSZ0zumnsWzrRFzPIWi6L2YOdYVBZOQpxD44Fz8MPoseBwQKsR49H0rb7SJGNGeKgGjt3D7jg9K3w/s400/Screen+Shot+2019-08-10+at+9.47.19+PM.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 3: Observed SSTAs (CPC)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Putting all the pieces
together into one yields a graphic like the one above, showing weekly
SST anomalies over the Equatorial Pacific. As of July 17<sup>th</sup>, the
picture was a very muddy one as far as surface anomalies go, with broad
slightly-above-normal SSTs evident in the western ENSO monitoring regions, but
some below-normal sea surface temperatures now appearing from the eastern
portion of Nino region 3.4 all the way to the coast of Ecuador. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
This is a troubling development for the state of the El
Nino. Indeed, it seems as if the previously-stable El Nino has given way to a
disintegrating El Nino, or perhaps even an El Nino that is about to fade out
altogether. There’s still quite a bit more to discuss in this publication, but
even just a cursory analysis of the state of the El Nino prompts quite a bit of
alarm.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The concern over the stability of the El Nino is not
assuaged when looking at water temperature anomalies below the surface, from
the top of the water all the way down to 450 meters below. The top panel of the
graphic below shows such anomalies, with raw temperatures displayed on
the bottom panel. Looking at the anomaly panel shows why the El Nino seems to
have been dissipating. To understand why, we need to learn a little bit about <b>Equatorial
Kelvin Waves</b>.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJNw3smYKHHnx92Akx6xqnFSf398EuefrWhfPx0RiuRKj_mM8DOTxdvvZI0bm9gHaVIiBQn-j9ykMGo_ZQ59eIJ9sfZR26g8_0ezMjLb3M1zL_m_LfIIkKsZKN9wCo1GfYN_CFGyWs0Pgj/s1600/Picture3.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="785" data-original-width="606" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJNw3smYKHHnx92Akx6xqnFSf398EuefrWhfPx0RiuRKj_mM8DOTxdvvZI0bm9gHaVIiBQn-j9ykMGo_ZQ59eIJ9sfZR26g8_0ezMjLb3M1zL_m_LfIIkKsZKN9wCo1GfYN_CFGyWs0Pgj/s640/Picture3.png" width="492" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 4: Water temperatures in terms of anomalies (top panel) and in raw values (bottom panel); (CPC)</td></tr>
</tbody></table>
<div class="MsoNormal">
While the phrase ‘Equatorial
Kelvin Waves’ seems rather daunting, it can be explained pretty simply for our
purposes. From time to time, these ‘waves’ form in the far western Equatorial
Pacific as surface winds, which usually blow from east to west over these
waters, literally pile up water in the western Equatorial Pacific. Granted,
this accumulation of water is not on a significant scale, but it is detectable
on a scale of centimeters. Periodically, these surface winds weaken, which
allow that piled-up warm water out in the western Equatorial Pacific to flow
back to the east as the ocean tries to even itself out. This ‘wave’ of
warmer-than-normal waters making its way eastward is an Equatorial Kelvin Wave,
and in particular the movement of warm waters eastward is a <b>downwelling EKW</b>.
<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In sum, from time to time a ‘wave’ of warmer than normal
waters pushes east across the Equatorial Pacific. To be sure, this is not a literal
wave like a tsunami, but a slow-moving, expansive wave in its own right.
Suppose this scenario were to happen. It leads to that body of warmer than
normal waters in the central and eastern Equatorial Pacific now, since it was
transported from out west. If that sounds like an El Nino, you’re right:
downwelling Equatorial Kelvin Waves are identified as both triggers and
enhancements to El Nino events, since they transport a body of warmer than
normal waters into the ENSO monitoring regions. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
On the flip side, however, the
ocean is now out of balance in another respect: suddenly in the central and
eastern Pacific, there’s a body of warm water. Again, the ocean tries to get
itself into balance, and a body of cooler than normal waters now flows from
west to east along the Equatorial Pacific. This is called an <b>upwelling EKW,</b>
and commonly transpires in the wake of a downwelling wave. Additionally, just
as a downwelling EKW can provoke or intensify an El Nino, an upwelling EKW can
provoke or intensify a La Nina.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
We have now ascertained that there are two types of
Equatorial Kelvin Waves: a ‘downwelling’ wave, which transports warmer than normal
waters from the west Pacific to the east; and an ‘upwelling’ wave, which
transports cooler than normal waters from the west to the east. This may be one
of those topics that is difficult to understand in words but is easier to grasp
with visualizations, which are available to show these processes in the chart
on the right.<o:p></o:p></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgGRbXhNwEfw-eFU8w9vCw-HrKnVBpaiPWTMrKK6vEj2O9xKVKWBz_Aic2SPf9g_hocd9GEhGf10_83yIPVRsZwIsfwTOcvTJRrYl-LlS_IZNzoGXetm4hNPH_sGxU5MRS1X5wItDJQtfrG/s1600/Picture4.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="743" data-original-width="574" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgGRbXhNwEfw-eFU8w9vCw-HrKnVBpaiPWTMrKK6vEj2O9xKVKWBz_Aic2SPf9g_hocd9GEhGf10_83yIPVRsZwIsfwTOcvTJRrYl-LlS_IZNzoGXetm4hNPH_sGxU5MRS1X5wItDJQtfrG/s640/Picture4.png" width="494" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 5: Anomalous depth of the 20 degrees Celsius temperature line between 2 degrees N and 2 degrees S latitude (CPC)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The chart above shows the anomalous depth of the 20
degree Celsius line along the Equatorial Pacific between 2 degrees N and 2
degrees S latitude. Longitude markers are shown on the x-axis, and time is on
the y-axis. Warm colors on the chart indicate that the 20 degree Celsius level
is deeper down in the waters than normal, usually because the waters are
warming (i.e. in an El Nino and/or downwelling EKW). Similarly, cooler colors
indicate that the 20 degree C mark is closer to the surface than normal,
brought about by a cooling of the subsurface (and surface) water temperatures
(i.e. by way of La Nina and/or upwelling EKW). This graphic enables us to
visualize the downwelling and upwelling Equatorial Kelvin Waves, which I have marked
in light-blue and red, respectively. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3uQy6jHpRXyyExDhC3szdIsSM1XPQTLFx0Bdly43MjyIGocJiCN2PTPV7ideLC0NbdDLnRVXpeONFJBfNKci6Bi-7VAkmj94qSb21YCDgW4KIrLQSVziiU_skmRKjCj_ePIPHpTFRsi8q/s1600/Picture5.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="644" data-original-width="497" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3uQy6jHpRXyyExDhC3szdIsSM1XPQTLFx0Bdly43MjyIGocJiCN2PTPV7ideLC0NbdDLnRVXpeONFJBfNKci6Bi-7VAkmj94qSb21YCDgW4KIrLQSVziiU_skmRKjCj_ePIPHpTFRsi8q/s640/Picture5.png" width="491" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 6: Sea level anomalies (CPC)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
For example, the development of a downwelling Equatorial
Kelvin Wave was seen in fall 2018, highlighted with the solid cyan line, with
the 20 degree Celsius temperature line moving further down below the surface as
waters warmed with the EKW’s passage. One could argue a weak upwelling EKW then
followed between October and December 2018, but then another downwelling EKW
pushed through beginning in November 2018 and trailing off in January 2019. <o:p></o:p></div>
<div class="MsoNormal">
It was here that the El Nino first ran into trouble.
Beginning in late November, as the red line shows, a more-formidable upwelling
Kelvin Wave traversed the Equatorial Pacific, briefly wiping out the positive
water temperature anomalies that the previous two downwelling waves had
delivered. A strong downwelling EKW came in response, however, right at the end
of 2018 and only moved out of the picture in early April 2018.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The El Nino has never
recovered from that point on, as another upwelling Equatorial Kelvin Wave
sliced through the Pacific during the spring months of this year. Alarmingly, a
downwelling EKW never really followed, with only marginal positive anomalies
showing up in early June. Now, beginning in late June, another upwelling wave
is on the move, putting to rest any positive anomalies and further endangering
the already-fragile El Nino. It remains to be seen if another downwelling wave
is on its way – the 20 degree C depth has recently begun to hint at such a
development between the longitude lines of 170 E and 150 W – but unless a
strong downwelling wave does develop and moves quickly, the floundering El
Nino’s outlook into the fall and winter months is bleak. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
I made mention of the literal ‘piling up’ of warm waters in
the western Equatorial Pacific that signified the initial stages of a
downwelling Kelvin Wave, and the Climate Prediction Center allows us to see
this in action. On the right, sea level anomalies are shown for the most recent
data available. To confirm the presence of a downwelling EKW, we would want to
see positive sea level anomalies juxtaposed over the longitudes where the 20
degrees C depth is further below the surface than normal. Looking at the
marginally-positive sea level anomalies between 170 W and about 150 E, and
seeing the (very) marginally-deeper-than-normal 20 degree C line in the chart
from the previous page over the same longitudes, <b><span style="color: red;">it
does appear that a downwelling Equatorial Kelvin Wave is building</span></b>. <b><span style="color: red;">This is significant</span></b>, because it may represent a
lifeline for the struggling El Nino, especially if this downwelling EKW is a
strong one. Time will tell just how this situation evolves – <u>I believe that
if this downwelling EKW is not strong enough, or doesn’t even fully materialize
because it’s still only now beginning to build, the El Nino will not survive
into the winter</u>.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Now,
the El Nino – Southern Oscillation mechanism is not only evident in ocean
temperatures. Since it affects weather patterns worldwide, it should not be a
surprise that scientists have found the atmosphere to act in particular ways
when an El Nino is present, and in particular ways when a La Nina is present. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiafl-xCWwrQWgh54J1ZXCaU-KrGZGBReLkAOVt_1IFeu_0iGBdf9wquoUuAVISPQNnsDZ3M0y3el7KkSo_T2UKQCrOQ-L330VKwt1P5NDNnomGRGHCS2VZ7_HWrIP82awevyK-RAZ4odZf/s1600/walkercircubc.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="861" data-original-width="462" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiafl-xCWwrQWgh54J1ZXCaU-KrGZGBReLkAOVt_1IFeu_0iGBdf9wquoUuAVISPQNnsDZ3M0y3el7KkSo_T2UKQCrOQ-L330VKwt1P5NDNnomGRGHCS2VZ7_HWrIP82awevyK-RAZ4odZf/s640/walkercircubc.png" width="342" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 7: The Walker Circulation during an El Nino (bottom), La Nina (top) and Neutral-ENSO conditions (middle); University of British Columbia</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Above, an image from the
University of British Columbia in Canada shows the typical atmospheric set-up
during a La Nina on the top graphic, a neutral-ENSO situation in the middle
graphic, and in an El Nino event on the bottom graphic. However, it may seem
strange that these views of the atmosphere only cover a longitude-by-height
view over the Equatorial Pacific, instead of a look at how the global
atmosphere reacts to different states of the ENSO phenomenon. Why is that?<o:p></o:p></div>
<div class="MsoNormal">
This graphic has an important purpose. As I just mentioned,
the atmosphere is also a channel by which the ENSO phenomenon shows what state
it is in. A primary method of determining the ENSO state is by viewing the <b>Walker
Circulation</b>, a pattern over the Equatorial Pacific. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In general, when a La Nina is present, the Walker
Circulation will see surface winds moving east-to-west across the entire extent
of the Equatorial Pacific, pushing the air up on itself roughly over Darwin,
Australia. This motion of air being pushed together is called <b>convergence</b>,
and when it occurs at the surface the air has nowhere to go but up, thus
creating convection. Thus, the air travels east-to-west across the ocean and is
transported to the top of the troposphere by way of convection. When the warm
surface air parcel cools at those high altitudes to the point that the air
parcel is the same temperature as the air around it, the air parcel stops
rising: remember, an air parcel will only rise on its own if it is warmer than
the environment around it. However, the air still has to go somewhere: the
convective process continues, and there are more air parcels still moving up
via convection. Since this original air parcel can no longer rise, and can’t
sink back down right where it is, it must spread out. The motion of air
spreading out from a point is called <b>divergence</b>. We see this in the La
Nina graphic as the green arrow now switching directions and pulling the air
parcel from west-to-east, back towards South America and the eastern reaches of
the Equatorial Pacific. Briefly, recall at the start how our air parcel was
being transported from the east Pacific to the west at the surface. That air
has to come from somewhere: it can’t just appear out of nothing! It’s
convenient, then, that the air traveling west-to-east high up in the atmosphere
starts to slow down when it reaches the eastern Equatorial Pacific, and
actually begins to descend back to the surface. This air descending over the
eastern Equatorial Pacific (called <b>subsidence</b>) makes for sunny skies and
calm weather – after all, convection (rising air) can’t physically occur in an
area of subsidence (sinking air). This then completes the Walker Circulation.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
You might be thinking ‘<i>Okay,
that’s great and all, but why does it matter to finding out if the atmosphere
is in an El Nino or La Nina state?</i>’ I can assure you this leads to a
revelation – wasting time is only a negative for everyone involved! Take a look
at the Neutral-ENSO and La Nina graphics of the Walker Circulation. You’ll
notice that while the premise of a circulation remains intact for the other two
ENSO states, the location of the convection and subsidence, and even the
direction of winds both at the surface and aloft, changes as the ENSO state
changes. In a Neutral-ENSO scenario, for example, the circulation remains
intact as in a La Nina, but now the area of surface convergence has moved
offshore of Australia, somewhere between Darwin and Tahiti. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Perhaps the largest change is in an El Nino Walker
Circulation. Initially things are the same as a La Nina, with surface winds
going from east-to-west from the eastern Equatorial Pacific. However, rather
than surface convergence occurring over Darwin, it now occurs over Tahiti.
That’s a pretty big change – what happened? Let’s go back to the concept of
divergence. Remember how I said that air high up in the troposphere,
transported there from the surface by convection, had to spread out because it
could no longer rise and had no room to immediately sink? It spreads out in <u>all
directions</u>, not just to the east like the La Nina panel might lead you to
believe. So, the air from the convection over Tahiti spreads out both to the
east and the west. When it spreads out west, it then sinks somewhere over
Darwin, and then starts traveling along the surface again – but this time, from
west-to-east. Now we’ve got surface winds in the eastern Pacific going to the
west, and surface winds in the western Pacific going to the east. That makes a
lot of air pile up all in one place. You can probably guess what happens then –
a lot of convection right over Tahiti, where the surface winds collide and
create surface convergence. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiX72JPbnmWIykEJNUQF-_G0VIg3AVWKccXUVyLERhviQE94HVahIoTT7XJUZq7_MYbzn_wOepSCM5uz-nXV17_dohLxHWg91VRXlTWBVK0SZw57VUsY8LL_hcQdv7F-9ZxuK-EKsankIWR/s1600/715721windsfc.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="527" data-original-width="681" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiX72JPbnmWIykEJNUQF-_G0VIg3AVWKccXUVyLERhviQE94HVahIoTT7XJUZq7_MYbzn_wOepSCM5uz-nXV17_dohLxHWg91VRXlTWBVK0SZw57VUsY8LL_hcQdv7F-9ZxuK-EKsankIWR/s640/715721windsfc.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 8: Surface vector winds averaged from July 15th through July 21st over the Tropical Pacific (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Now that we’ve identified how the
Walker Circulation should appear in each of the three stages of the ENSO
phenomenon, let’s take a look at recent atmospheric conditions to see if the
atmosphere is acting as if the ENSO phenomenon is in a different state than an
El Nino, or if it is affirming the El Nino. We will use 200-millibar winds to
judge wind direction high up in the troposphere, surface winds to judge the
surface winds, and <b>outgoing longwave radiation (OLR)</b> to examine the
presence of convection. I will explain the concept of OLR when we come upon it.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
We begin with a seven-day average of surface winds, as shown
in Figure 8 above. The purpose of using a seven-day average as opposed
to a monthly average is to make sure any sudden change in wind pattern that may
have occurred in only a few days out of the month won’t be glossed over, just
to give an example. Analyzing Figure 8 shows a pretty remarkable testimonial to
the presence of a La Nina, instead of an El Nino. Indeed, surface wind vectors
are seen pointing from the east to the west along almost the entirety of the
Equatorial Pacific, with the vector arrows converging around the 160 degree E
line of longitude. While this isn’t the same as convergence over the same
longitude as Darwin, Australia, it is remarkably close, and the firmly-westward
winds at the surface imply the presence of a La Nina… at least at the surface.
Figure 9 looks at vector winds at the 200 millibar level, about the level of
the atmosphere where the jet stream resides here in the U.S..<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg6sFdw-XCaJ2gSnRy68DaFUQH4RjmXjRbma_L8fE1Z1y5KRcBGM9W4UrIUPDl1EXK4dwiNRNPV_xNsXtrwhtsDS_u0BU6GF33Js36NyfFtD1UjkfGH3RL3N1lOlfHxqUnS24Yfi74B-cDS/s1600/Pictur7e1.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="521" data-original-width="672" height="496" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg6sFdw-XCaJ2gSnRy68DaFUQH4RjmXjRbma_L8fE1Z1y5KRcBGM9W4UrIUPDl1EXK4dwiNRNPV_xNsXtrwhtsDS_u0BU6GF33Js36NyfFtD1UjkfGH3RL3N1lOlfHxqUnS24Yfi74B-cDS/s640/Pictur7e1.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 9: 200 millibar wind vectors averaged from July 15th through July 21st (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The
interpretation of 200-millibar winds is more mixed than the surface. Whereas
surface winds showed a rather-convincing portrayal of La Nina conditions, upper-level
winds actually seem more aligned with an El Nino, particularly given the
westward winds along the Equatorial Pacific from about 160 degrees West
longitude into Papua New Guinea. This is a feature most commonly seen in El
Nino events, typically produced by convection over Tahiti creating divergence
aloft. However, we do not see a corresponding band of eastward upper-level
winds to the east of that 160 E line of longitude, which would have really
cemented the case for El Nino conditions. Instead, there are a couple of areas
of circulation along the Equator, which does not help our interpretation of how
ENSO is affecting the atmosphere.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmelorywk5tac2aamKuJW0ziUHJCJ4eLqcmDag1Ghtl6LFZG6gH6X2eWi6e8ddHm9e04F6RThsKPXq-SSvB8QiJOmOLuEgAITEAn5gi1C-1pOxNem_6VA7z6hEH3_FzHdau3CKd2MYtnW0/s1600/OLRgraph.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="449" data-original-width="579" height="492" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmelorywk5tac2aamKuJW0ziUHJCJ4eLqcmDag1Ghtl6LFZG6gH6X2eWi6e8ddHm9e04F6RThsKPXq-SSvB8QiJOmOLuEgAITEAn5gi1C-1pOxNem_6VA7z6hEH3_FzHdau3CKd2MYtnW0/s640/OLRgraph.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 10: Outgoing Longwave Radiation anomalies from July 15th through the 21st (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
To try and find
more-concrete evidence, Figure 10 takes a look at <b>outgoing longwave
radiation (OLR)</b>. While the actual definition and mechanics behind it are
slightly more complex, for our purposes we can simplify OLR to know that
negative values indicate the presence of enhanced convection, while positive
values indicate the presence of suppressed convection. Please note the (admittedly)
strange color scale, where negative (positive) OLR values are shaded in warm
(cool) colors.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Figure 10 seems to be the tiebreaker between surface winds
(which favored a La Nina) and upper-level winds (which seem to lean in favor of
El Nino conditions), in favor of an El Nino. The July 15<sup>th</sup> – July 21<sup>st</sup>
OLR averages show enhanced convection broadly in the vicinity of Tahiti, with subsidence
north of Darwin near Papua New Guinea as well as just northwest of Ecuador. The
fact that these areas of rising and sinking motion are not along the same line
of latitude makes the idea that this seems to portray El Nino conditions a
little more fragile, but we will press ahead with it anyway. With convection
over/near Tahiti and suppressed convection in the general area of Darwin and
Peru/Ecuador, <b><u>the atmosphere seems reflective of a weak El Nino</u></b>,
which goes along with what sea surface temperatures indicate. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Up
to this point, through sea surface temperature anomalies, subsurface water
temperature anomalies and a look at the atmosphere, we have determined there is
a weak El Nino in place. However, the official source for what state the ENSO
phenomenon is in is the National Oceanic & Atmospheric Administration
(NOAA). As of July 11<sup>th</sup>, NOAA’s <u>Climate Prediction Center (CPC)
branch determined that an El Nino Advisory was warranted</u>, indicating that
an El Nino is currently ongoing. But, given how fragile the El Nino is looking,
what does the forecast hold?<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEif8mXrdpwz_v_G0WT2sMtPbuv6UHvGFvyJtjgxZp213qauBeWCJYSo4DA_jDKMkxJT0IUev6puc33AHUFULNaI0pC6W2fIb4zYmhOv4jONdvAaJSJA8pBi9Zq0PK51qwhq2CPvhvH8JERU/s1600/multimodel.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="545" data-original-width="706" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEif8mXrdpwz_v_G0WT2sMtPbuv6UHvGFvyJtjgxZp213qauBeWCJYSo4DA_jDKMkxJT0IUev6puc33AHUFULNaI0pC6W2fIb4zYmhOv4jONdvAaJSJA8pBi9Zq0PK51qwhq2CPvhvH8JERU/s640/multimodel.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 11: Multi-model ensemble forecast of SSTAs in the Nino 3.4 region through January 2020 (CPC).</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Shown above is a combination of climate models’
forecasts for the sea surface temperature anomaly in Nino region 3.4 from July
2019 through January 2020. As a brief reminder, El Nino’s are technically in
place when the anomaly is at or above +0.5 degrees C, while La Nina’s exhibit
anomalies at or below -0.5 degrees C. Neutral-ENSO conditions are defined when anomalies
are within that +/- 0.5 degree range. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Within the graphic as shown in Figure 11, these models agree
on the Nino 3.4 region continuing to cool down, albeit to varying degrees,
through the fall months. By September, all models included have the Nino 3.4
region in Neutral-ENSO territory, with one model even predicting a slight La
Nina in that month. The trend then shifts back upward heading into the late
fall months, but a recovery in the El Nino currently seems unlikely, with the average
of these models still staying in neutral-ENSO territory. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
This solution is anticipated by the NOAA as well, with their
most recent El Nino Advisory cautioning that a decline to neutral-ENSO
conditions was expected in coming months, and was likely to persist into the
fall and winter months. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
If we should expect to be in an ENSO-neutral situation this
winter, what can we expect? Figures 12 and 13 below provide some context.<o:p></o:p></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEglaXcnfZEs-2UBughweXXfImjwPIe6jXEEVDl09GYIc36A2tIj4MsTxoH88O8JejZr41fE3d-qp5qNiNXkr4_elnAQIw6G9n6XWEmJRAcUQJ7jU1kZiZe0CLf6jvAVvWK12X08Oj2Ly9v9/s1600/fig12.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="683" data-original-width="745" height="366" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEglaXcnfZEs-2UBughweXXfImjwPIe6jXEEVDl09GYIc36A2tIj4MsTxoH88O8JejZr41fE3d-qp5qNiNXkr4_elnAQIw6G9n6XWEmJRAcUQJ7jU1kZiZe0CLf6jvAVvWK12X08Oj2Ly9v9/s400/fig12.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 12: DJF Temperature Anomalies in Neutral-ENSO situations (ESRL)</td></tr>
</tbody></table>
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiK2Y_mbtr9urR2FDmBTdnem-Dg-xsInpcGgsAkE_dHDEsMTvex5sQKZWo40U1lA5Yd5r-6kniyLEMu-eTO6CeDfH_f-Pmjz0waHJqdAAUUNJ-FphcOOHE6VHy6gjioai_iriw6O6BcCI1c/s1600/fig13.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="682" data-original-width="745" height="365" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiK2Y_mbtr9urR2FDmBTdnem-Dg-xsInpcGgsAkE_dHDEsMTvex5sQKZWo40U1lA5Yd5r-6kniyLEMu-eTO6CeDfH_f-Pmjz0waHJqdAAUUNJ-FphcOOHE6VHy6gjioai_iriw6O6BcCI1c/s400/fig13.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 13: DJF Precipitation Anomalies in Neutral-ENSO situations (ESRL)</td></tr>
</tbody></table>
<div>
</div>
<div class="MsoNormal" style="page-break-after: avoid;">
Figure 12 above shows
temperature anomalies in the December-January-February period when the ENSO
phenomenon was in its neutral state. I identified neutral-ENSO winters by using
the Climate Prediction Center’s Oceanic Nino Index (ONI), and included almost
all neutral-ENSO winters since 1950. Figure 12 shows a pretty one-sided view,
with exclusively below-normal temperature anomalies evident in neutral-ENSO
winters, maximized in the northern Plains and upper Midwest, with near-average
temperatures in the Southwest and far Southeast. It seems as though a
neutral-ENSO winter entails cold air in Canada being rather prone to ejecting south to lower
latitudes in the United States, and could be something to watch closely.<o:p></o:p></div>
<div class="MsoNormal" style="page-break-after: avoid;">
<br /></div>
<div class="MsoNormal" style="page-break-after: avoid;">
Figure 13 analyzes
precipitation anomalies over the same three-month window, using the same years
as in Figure 12. Here, the pattern is oriented in a pretty interesting middle
ground between what one typically sees in a La Nina vs an El Nino. Whereas a La
Nina brings wetter than normal conditions to the Midwest and Ohio Valley
regions, and an El Nino brings dry weather to those same areas with wet weather
along the East Coast, Neutral-ENSO winters seem to strike a compromise, placing
modest below-normal precipitation anomalies in portions of the Midwest and
Plains while keeping wetter anomalies in the eastern portions of the Ohio
Valley towards the Gulf Coast. <b><span style="color: red;">From all this, it
seems like a Neutral-ENSO winter may very well bring about colder than normal
conditions for much of the country, while a snowier than normal winter could be
in store for the Appalachia / Ohio Valley region</span></b>. <o:p></o:p></div>
<div class="MsoNormal" style="page-break-after: avoid;">
<br /></div>
<div class="MsoNormal" style="page-break-after: avoid;">
What does the broader
atmospheric pattern look like in neutral-ENSO conditions? I’m glad you asked!<o:p></o:p></div>
<div class="MsoNormal" style="page-break-after: avoid;">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg7IItoAR4BBQuo8GcR0s0DYys8p-7i0VxwTzbyySHL_BXvJQjN7_bHc6hThHcYP0cLLfW2gBHOwP0E1tHxewaq5bOFGGbKgnadoPGo-b-M3e7gkbQAV-8P91I2kcj-TXdqCfbEkfG7jfQP/s1600/fig14.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="660" data-original-width="851" height="496" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg7IItoAR4BBQuo8GcR0s0DYys8p-7i0VxwTzbyySHL_BXvJQjN7_bHc6hThHcYP0cLLfW2gBHOwP0E1tHxewaq5bOFGGbKgnadoPGo-b-M3e7gkbQAV-8P91I2kcj-TXdqCfbEkfG7jfQP/s640/fig14.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 14: DJF 500-millibar geopotential height anomalies in Neutral ENSO situations (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal" style="page-break-after: avoid;">
Figure 14, above, shows
500-millibar geopotential height anomalies over the Northern Hemisphere in the
same years as outlined in Figures 12 and 13, as well as over the same
three-month window. Recall that negative values / cool shadings in this graphic
represent negative anomalies (therefore colder and stormier weather), while
positive values / warm shadings represent positive anomalies (therefore warmer
and calmer weather). Per the figure, neutral-ENSO winters have historically
featured high pressure ridges in the Bering Sea, as well as one positioned
squarely over Greenland. A ridge positioned over the Bering Sea is identified
as the negative phase of the<b> West Pacific Oscillation (WPO),</b> which
results in cooler than normal weather over the eastern two-thirds of the United
States. Similarly, a ridge over Greenland signals the negative phase of the <b>North
Atlantic Oscillation (NAO),</b> which tends to buckle the jet stream south and
provide colder weather for the Central and (especially) East U.S. That jet stream
buckling also gives credibility to the above-normal precipitation anomalies in
Appalachia / the Ohio Valley, as the -NAO is what tends to be the key factor to
ignite big storms in the Eastern U.S., including Nor’easters. </div>
<div class="MsoNormal" style="page-break-after: avoid;">
<br /></div>
<div class="MsoNormal" style="page-break-after: avoid;">
What is seen
preventing those Nor’easters and pushing the above-normal precipitation track further inland as opposed to right
along the East Coast is the modest ridge just offshore the Southeast, which
acts as a diverting mechanism for storms traversing the Southern Plains,
forcing them northeast into the Ohio Valley instead of due east towards Georgia
and Alabama. Also of note in this graphic is how the -WPO ridge and -NAO ridge
are strong enough to force the tropospheric polar vortex to lower latitudes. We
will discuss this more later on, but it is critical to know that there are
essentially two ‘versions’ of the polar vortex: the stratospheric polar vortex,
and the tropospheric polar vortex. Of course, when placed on a 3D scale they
are one in the same, but given that we look at slices of the atmosphere rather
than 3D graphics, it is better for us to think of two polar vortices as opposed
to one. Again, this will be elaborated on later in the Stratosphere section. <o:p></o:p></div>
<div class="MsoNormal" style="page-break-after: avoid;">
<br /></div>
<div class="MsoNormal" style="page-break-after: avoid;">
In Figure 14, it seems as
though a Neutral-ENSO state will encourage the tropospheric polar vortex to
split up and be forced to lower latitudes as a result of the two aforementioned
ridges. Figure 15, below, illustrates what happens to the stratospheric
polar vortex, at about the 50-millibar level. At the stratospheric level, it
appears as though an ENSO-neutral situation provokes strong ridging over the
Arctic Circle, forcing the polar vortex to lower latitudes at a weakened
strength. As a consequence, it becomes far easier for below-normal temperature
anomalies to flow to lower latitudes over the course of the winter. It also
becomes far easier to achieve a sudden stratospheric warming (SSW), which will be
discussed in detail in the Stratosphere section. For now, however,
understanding that a neutral-ENSO state appears to materially disrupt both the
tropospheric and stratospheric polar vortices is a key takeaway.<o:p></o:p></div>
<div class="MsoNormal" style="page-break-after: avoid;">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiEhDsA-eB3mrVUFvjU4t1Tgzx7h5DLQ94PK1nNRXclZl6B19x5Cgchoyoyc2ngJD0f_iV_tPVbkN8XmO3xRYTCP0NHAXuVXFhQ2I562imwAWp1PMhHmplS1asRWkY7jDOIoPAoUJ6f4nEl/s1600/fig15.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="637" data-original-width="821" height="496" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiEhDsA-eB3mrVUFvjU4t1Tgzx7h5DLQ94PK1nNRXclZl6B19x5Cgchoyoyc2ngJD0f_iV_tPVbkN8XmO3xRYTCP0NHAXuVXFhQ2I562imwAWp1PMhHmplS1asRWkY7jDOIoPAoUJ6f4nEl/s640/fig15.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 15: DJF 50-millibar geopotential height anomalies in Neutral-ENSO situations (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
In summary, we are currently in a weak El Nino environment,
as per both sea surface temperatures and signals from the atmospheric pattern.
However, forecast models anticipate the El Nino will weaken into the fall, and
neutral-ENSO conditions appear probable for this winter season. In the event of
a neutral-ENSO winter, it appears cooler than normal temperatures are more
likely than warmer temperatures, with the coldest anomalies most likely to be
maximized in the upper Midwest and northern Plains. Enhanced snowfall could hit
the Ohio Valley and Appalachia regions. In addition, a neutral-ENSO winter may
set up a pattern very favorable for intense cold across wide swaths of the
country (mainly in the eastern two-thirds) as disruptions to the tropospheric
and stratospheric polar vortices are seen as more likely.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><i><span style="font-size: 14.0pt; line-height: 107%;">b. </span></i><b><i><span style="font-size: 16.0pt; line-height: 107%;">Pacific Decadal Oscillation (PDO)</span></i></b><i><o:p></o:p></i></div>
<div class="MsoNormal">
<b><i><span style="font-size: 16.0pt; line-height: 107%;"><br /></span></i></b></div>
<div class="MsoNormal">
There are a number of ocean-based oscillations that are
highly relevant to seasonal forecasting, and one could argue that the Pacific
Decadal Oscillation (PDO) is the second-most-important for North America, after
ENSO. As a result, before we dive in to see what the PDO is doing, we need to
understand what the PDO actually is.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj-0gteKd0CKR0wkujldGPKWqmBxM_KHmH_yb0OiNqoskHnbsc7mm6ouqFkY3k8hzO_JjPnqKMSUW5pfu_wIjB1uW03Z-L_hf3lzsCFTUPlYJZfGFHfLTzb96nF5STKchqkO4wcL1ZIX3XC/s1600/fig16.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="381" data-original-width="911" height="266" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj-0gteKd0CKR0wkujldGPKWqmBxM_KHmH_yb0OiNqoskHnbsc7mm6ouqFkY3k8hzO_JjPnqKMSUW5pfu_wIjB1uW03Z-L_hf3lzsCFTUPlYJZfGFHfLTzb96nF5STKchqkO4wcL1ZIX3XC/s640/fig16.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 16: Screenshot from the University of Washington's PDO page showing SST anomalies (shaded) and surface winds (arrows) in a positive PDO (left panel) and negative PDO (right panel) (UW)</td></tr>
</tbody></table>
<div class="MsoNormal">
Figure 16, displayed on the right,
provides a look at the Pacific Ocean during the positive phase of the PDO (left
panel) and the negative phase of the PDO (right panel). Note that, unlike ENSO,
there is no neutral phase. In a positive PDO, sea surface temperatures along
the coast in the Gulf of Alaska down to the coast of California are above
normal, with positive SSTAs extending into the Equatorial Pacific. In contrast,
below-normal SSTAs exist from the well-offshore reaches of the Gulf of Alaska
westward to Japan. Aside from sea surface temperatures, surface winds in a
positive PDO are generally eastward from Japan into the Gulf of Alaska, with
northward vectors along the coastline of North America.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
You might draw out that those warmer than normal anomalies
in the Equatorial Pacific during a -PDO kind of look like an El Nino. That’s
not a mistake: according to the Earth System Research Laboratory (ESRL), the
PDO and Nino 3.4 region’s SST anomalies have a correlation of 0.42. <o:p></o:p></div>
<div class="MsoNormal">
In a negative PDO, the script is flipped, with below-normal
SST anomalies seen along the western coast of North America into the Equatorial
Pacific, and warmer than normal waters deep in the Gulf of Alaska out towards
Japan. With regards to surface winds, westward flow is seen from the Gulf of Alaska
towards East Asia, while surface winds are southbound just offshore western
Canada and western U.S. We’ll begin with recent SST anomalies in Figure 17.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiChvDnHdv6D8f3NOkwoLA7TprKFUzWGfv6x6WzU5DdKtf6WK-8VYsLZebIG_Yiu-V7JBWZVJnt2Z-UFArN9LT3fjjuXrh99emfHCTdN01FsPYrylnDZ1CiJXKLUWbHecbWQ7n5BUH3Pcdz/s1600/fig17.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="483" data-original-width="886" height="348" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiChvDnHdv6D8f3NOkwoLA7TprKFUzWGfv6x6WzU5DdKtf6WK-8VYsLZebIG_Yiu-V7JBWZVJnt2Z-UFArN9LT3fjjuXrh99emfHCTdN01FsPYrylnDZ1CiJXKLUWbHecbWQ7n5BUH3Pcdz/s640/fig17.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 17: Recent SST Anomalies over the entire globe. This section will focus on the Northern Pacific. (NOAA)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
As shown above, while there are a few areas of
significant anomalies across the northern Pacific, there isn’t really any
textbook pattern that quickly tells us what phase the PDO is in. On one hand,
below-normal SSTAs west of Baja California that try and curve southwestward near
the -130 degree line of longitude would typically signal a -PDO. However, such
below-normal anomalies don’t extend into the waters just west of Canada and
into the shoreside Gulf of Alaska region. On the other hand, well below normal
sea surface temperature anomalies northeast of Japan are typical of a +PDO, but
they don’t extend far enough east to really indicate to me that it’s a “real”
positive PDO. Instead, it just seems like a really messy amalgamation of SST
anomalies.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Although this is messy, that doesn’t mean these anomalies
aren’t worth looking at in their own right – quite to the contrary, in fact. In
the Regions of Interest section of this Sea Surface Temperatures portion, we will
go over the northeast Pacific and Gulf of Alaska and investigate why the
placement of certain anomalies can prove quite pivotal to how the winter turns
out, even without accounting for the state of the Pacific Decadal Oscillation.
That will come later on, however – for now, the focus is on deciphering what
the PDO is up to.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
We did note that surface winds over the north-central
Pacific and along the western coast of North America can be reliable in
determining the PDO phase. To try and get a sense for it, Figure 18 shows surface
vector wind anomalies from June 1<sup>st</sup> through July 21<sup>st</sup> in
the northern Pacific. You will notice this is a wider timeframe than the images
we viewed as part of the ENSO section. This is deliberate: unlike over the
Equatorial Pacific, the northern Pacific regularly experiences significant low
pressure systems that trek across and around the Aleutian Islands, easily distorting
a 7-day view of surface winds if a storm system happens to be moving through at
that particular time. To try and assuage these distortive effects, the
timeframe is expanded to just under two months. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEikhJXyaGNnLcYvwnvJH1iPZfNbT3EODlK8FmIhxxgIKZWudksPZY1t4G9W2XLEjIj0wq58Deh2yUlbBWiEZe_RWnlLULwntiKhlOAC-7nbXHWulNKGZ7YRdaqSDq9N0of7Xp_GUYmW78Q-/s1600/fig18.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="547" data-original-width="707" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEikhJXyaGNnLcYvwnvJH1iPZfNbT3EODlK8FmIhxxgIKZWudksPZY1t4G9W2XLEjIj0wq58Deh2yUlbBWiEZe_RWnlLULwntiKhlOAC-7nbXHWulNKGZ7YRdaqSDq9N0of7Xp_GUYmW78Q-/s640/fig18.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 18: Surface wind vector anomalies over the north Pacific from June 21st through July 21st (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Viewing Figure 18 above, we
are able to finally see something that’s more concrete in pointing towards a
specific PDO phase. With surface winds anomalously pushing to the west from the
Gulf of Alaska almost all the way to Japan (though admittedly not nearly as
strong when they get west of the Aleutian Islands), and winds forcing their way
from north to south just offshore the western coast of North America, <b><u>surface
winds seem representative of a negative PDO</u></b>. To be sure, we can’t yet
confirm a negative PDO, given the conflicting SST anomalies above, but it
appears the atmosphere is leaning in the direction of a -PDO state.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
One could argue the SSTs can make the case for a -PDO
stronger when viewing the negative SSTAs west of Baja California and positive
SSTAs in a horseshoe-style pattern in the Gulf of Alaska, but that pool of deep
negative anomalies east of Japan is too significant for me to be comfortable
calling this a -PDO event.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjSS7dVS8BLg2UYRi82kwSMw2KsZ9AoIlxzafsHgmXU2aXqXW9ju75meGx9n0J3PfARn3n83so3TjdbmbN9YcQxOzy22FkKjY2XZsOrt1SXgtHHTzXzwCZHlCYPk6Fo4eqVMUahV5lYy2Hk/s1600/fig19.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="367" data-original-width="629" height="372" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjSS7dVS8BLg2UYRi82kwSMw2KsZ9AoIlxzafsHgmXU2aXqXW9ju75meGx9n0J3PfARn3n83so3TjdbmbN9YcQxOzy22FkKjY2XZsOrt1SXgtHHTzXzwCZHlCYPk6Fo4eqVMUahV5lYy2Hk/s640/fig19.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 19: Pacific Decadal Oscillation since late 2009 (NOAA/NCDC)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The deciphering process can be made
somewhat easier by the presence of the Pacific Decadal Oscillation index,
calculated at NOAA. A nearly-decade-long view of the PDO index is shown in
Figure 19 on the right. After undergoing a prolonged and strong negative spell
from early 2010 through early 2014, the PDO then turned positive for the
following two years. Since about late 2016, however, the PDO index has been
mixed, with a tendency to lean negative in the last year or so. On a
month-by-month level, the PDO was seen modestly positive in April and May of
this year, after having been negative since February 2018, and clocked in at
-0.00 in June. That’s not a typo, and tells us what we’ve already ascertained: SST
anomalies aren’t clear enough to determine which phase the oscillation is in,
and what strength that would be (note that the PDO index is based solely off of
SSTs and not surface winds). <o:p></o:p></div>
<div class="MsoNormal">
The last item to look at and try to determine the PDO phase
is the tendency of sea surface temperature anomalies over the last year, as
seen in Figure 20.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjhyphenhyphenMo6JqY5TVpRZlcgGx3UiS-YswCyitEBK4EoGMn_v5eek_x-yyVH-phTd9nEal66VN34la75sbRVMIoJbUzcgrChHyRWz-RDewtSfxofMxoljbYmQ07SLCbHnvhvMgpvuD5QrQ0FKbQA/s1600/fig20.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="543" data-original-width="492" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjhyphenhyphenMo6JqY5TVpRZlcgGx3UiS-YswCyitEBK4EoGMn_v5eek_x-yyVH-phTd9nEal66VN34la75sbRVMIoJbUzcgrChHyRWz-RDewtSfxofMxoljbYmQ07SLCbHnvhvMgpvuD5QrQ0FKbQA/s640/fig20.png" width="578" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 20: June 2019 SST anomalies (top) and change from June 2018 (bottom), (CPC)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Figure
20 is a two-panel graphic, showing sea surface temperature anomalies from June
2019 on top and the change in SST anomalies from June 2018 to June 2019 on the
bottom. Since we have more-recent SST anomaly data available in Figure 17, we
will only pay attention to the bottom panel. When glancing over the SST anomaly
change from a year earlier, it’s quickly apparent that the trend has been
towards a negative PDO. That does not mean things have transitioned into a
-PDO; as we found out earlier, SST anomalies are too messy to really determine
a firm phase for right now. Instead, the trend has been for SST anomalies to go
away from a comfortably-positive PDO state into at least a non-existent state,
as evidenced by the -0.00 figure in the PDO index. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In other words, while we don’t appear to be in a negative
PDO with certainty, the trend in sea surface temperatures has certainly been in
that direction, and surface winds appear to be of the same opinion. Further,
this isn’t just a year-long trend: it has continued in the short-term, with
SSTs cooling further west of Baja California, cooling south of the Aleutian
Islands, and warming in the rest of the Gulf of Alaska, all symptoms of a
negative PDO event if the trends continue. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Given that the PDO technically is not strong enough to have
a specific phase (via the PDO index), and given how all these negative PDO
signals are only drawn from trends rather than actual observed data (i.e.
prominent negative SSTAs as opposed to anomalies that are only trending from
warm to average), I will go forward in this PDO section and explain what each
PDO phase could result in, while not favoring any specific phase for this
winter. Instead, I will go over what each phase entails, and in the coming
weeks and months I will continue reviewing data to eventually make a
determination as to what the PDO is doing. The goal of this format is so that
when this winter’s PDO phase is eventually determined, you will have already
learned beforehand what each PDO phase is capable of, and thus there should be
far less confusion as to how that phase will affect the country.<o:p></o:p></div>
<div class="MsoNormal">
I am hard-pressed to imagine that this winter’s PDO phase is
not determined by the time my 2019-2020 Official Winter Forecast is prepared in
October, and the intention is to effectively use the PDO
in the forecast then instead of laying out the different possibilities, as I
will have to do here.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The graphics below depict the correlations between the PDO
and temperature (Figure 21) as well as between the PDO and precipitation
(Figure 22) during the December-January-February window. Positive readings in
these images indicate that the PDO is positively correlated with either
temperature anomalies or precipitation anomalies in that given area, depending
on the figure being viewed, while negative readings imply negative
correlations.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEisww2iNad4Tzoy29bAlsh5rlcJTx3voOLPUD_cxQc2jcBoC6X1zd37MDa1d4KS8b9zPI911sfEwRBCI-nhVvjAw29WulYxEF3GcUnXs7jPslRbUYAQU4JhEauyF9MPngWtUIPxjly61xEg/s1600/fig21.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="479" data-original-width="505" height="378" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEisww2iNad4Tzoy29bAlsh5rlcJTx3voOLPUD_cxQc2jcBoC6X1zd37MDa1d4KS8b9zPI911sfEwRBCI-nhVvjAw29WulYxEF3GcUnXs7jPslRbUYAQU4JhEauyF9MPngWtUIPxjly61xEg/s400/fig21.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 21: DJF Correlation between PDO and Temperature (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
Figure 21 above depicts the correlation
between the PDO index and temperatures in the DJF period, as described. One of
the most noticeable features is the high positive correlation observed along
the western coast of the United States, exceeding 0.50. This suggests a pretty
reliable signal that a positive PDO event will provoke warmer than normal
temperatures in the West during the winter months, while a negative PDO event
will entice cooler than normal temperatures. An opposite picture is seen in the
eastern half of the country, with negative correlation values deeper than -0.4
seen along the Gulf Coast. In other words, if the PDO is positive this winter,
cooler than normal temperatures seem more plausible in the Southeast, and
vice-versa. In the Plains and Midwest up into the Northeast, though,
correlation values are situated around 0.00, suggesting that no matter how the
PDO turns out this winter, it will be difficult to ascertain temperature
anomalies based solely on this oscillation.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi14W80WDqECIxkf_b5MZOeb75Gacff5cZinYI3gAakdqFBHvy29SMF4ZKXD1eG0yfrnyhH5J5YLO5z1hU_aVXvAKw8YOC87K0R2Oyt2JOt5daN8SPUoRS8KFW-uPKsR-nnS8QiH0zafTKB/s1600/fig22.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="496" data-original-width="523" height="378" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi14W80WDqECIxkf_b5MZOeb75Gacff5cZinYI3gAakdqFBHvy29SMF4ZKXD1eG0yfrnyhH5J5YLO5z1hU_aVXvAKw8YOC87K0R2Oyt2JOt5daN8SPUoRS8KFW-uPKsR-nnS8QiH0zafTKB/s400/fig22.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 22: DJF Correlation between the PDO and precipitation (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Turning to precipitation, Figure 22
provides a look at the correlation between the PDO index and precipitation
anomalies, once again during the DJF time period. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In general, precipitation anomalies are most likely to be
negatively correlated to the PDO, with correlation values deeper than -0.5 in
portions of Kentucky and southern Indiana. As such, if a negative PDO were to
evolve for this winter, a snowier than normal cold season could be in store for
the Ohio Valley into the Midwest. In contrast, notable positive correlation
values are evident in the Southeast, as well as in parts of the southern
Plains. For those regions, a positive PDO could present an opportunity for
above-normal precipitation this winter.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In summary, the recently-positive PDO has weakened to a
level too weak to accurately discern at this time. While the PDO phase should
be identifiable in time for the 2019-2020 Official Winter Forecast, it seems
most prudent for now to lay out the different impacts each phase of the PDO can
have, and then determine the phase itself in the next outlook. This is in the
best interest of maintaining the forecast’s integrity and not putting the cart
before the horse, so to say.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b><i><span style="font-size: 16.0pt; line-height: 107%;"><span style="mso-tab-count: 1;"> </span></span></i></b><i><span style="font-size: 16.0pt; line-height: 107%;">c<b>. Atlantic Multi-Decadal
Oscillation (AMO)<o:p></o:p></b></span></i></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Rounding out the top three seasonal
ocean-based oscillations most relevant to North American weather is the
Atlantic Multi-Decadal Oscillation, or AMO. As the name implies, this is a very
long-range oscillation, and changes phases on a scale of decades (note the
plural), as opposed to years in the case of the PDO, or even months in the case
of ENSO. Note that this change in phases refers to a change in the overarching
state – it is not uncommon for the AMO to turn negative for a short period even
though it may be in the middle of a multi-decade positive state, for example.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjOqcourtx40f6I7JtL1eXTaKiUVyKQbP7zohKUA4vG-yEvkwyblyST5zFj9arypuD9yLnfebih7ByNzfbQRcIOzkwSgNa6W7-So5Er1-3A88ejyp0esCLJebHetB1htkyMvBkyW9_TwdMt/s1600/fig23.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="457" data-original-width="609" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjOqcourtx40f6I7JtL1eXTaKiUVyKQbP7zohKUA4vG-yEvkwyblyST5zFj9arypuD9yLnfebih7ByNzfbQRcIOzkwSgNa6W7-So5Er1-3A88ejyp0esCLJebHetB1htkyMvBkyW9_TwdMt/s640/fig23.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 23: Long-term view of the AMO (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
To visualize the extremely-long-term nature of the AMO,
Figure 23 shows a 71-year history of the oscillation. Similar to the PDO, the
AMO has only two phases: positive and negative. Readings of 0.00 imply the AMO
simply does not have a discernable phase; there is no ‘neutral’ phase. <o:p></o:p></div>
<div class="MsoNormal">
From the beginning of the dataset in 1948 to roughly 1962,
the AMO was in its positive phase, with the heavy majority of data points in
that span above zero. From about 1962 to about 1995, the AMO was in a
comfortably-negative phase, which then reversed into a positive phase that runs
from 1995 to present-day. While there were plenty of situations where the AMO
briefly spiked into positive territory during its negative phase or dipped into
negative territory amidst its positive phase, it is crucial to know what the
‘real’, overarching state of the AMO is. For example, even though the index recently
dipped into negative territory, the index remains firmly entrenched in a
positive phase over the longer-term. As a result, even though the index
recently was negative, <b>we will assume a positive AMO for the coming winter</b>,
given that is the ongoing overarching state. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Before moving on to what a positive AMO means during the
winter months, I want to briefly address why I believe it is prudent to assume
a +AMO, even though recent data is hinting at some weakening in the overall
+AMO regime. Figure 24, below, shows a short-term view of the same dataset as
in Figure 23, from 2010 to present day. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjNtqsuIfI1V0kfei0tnfse4Aim81qgMEfahPUPV5ITjY6qTrp5mNuOhbTDwuJb71_Hus4ofAd7ujI58gIwaf78RaEXp4uMiTLjbUbYZrWnynr6FRhSMipDUFSa-qxdYRd7t4sd1SJCvwIC/s1600/fig24.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="358" data-original-width="794" height="288" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjNtqsuIfI1V0kfei0tnfse4Aim81qgMEfahPUPV5ITjY6qTrp5mNuOhbTDwuJb71_Hus4ofAd7ujI58gIwaf78RaEXp4uMiTLjbUbYZrWnynr6FRhSMipDUFSa-qxdYRd7t4sd1SJCvwIC/s640/fig24.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 24: Short-term view of the AMO, since 2010. Please note that the chart title is incorrect, this is the Atlantic Multi-decadal Oscillation, not Atlantic "Meriodional" Oscillation. (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Figure
24 provides a very good look at what I mean when talking about these
aberrations of brief negative values during a positive AMO regime or
vice-versa. Indeed, since 2010, the AMO turned negative five separate times,
though the overwhelming tendency to stay in positive territory shows how the
“overarching” and “real” state of the AMO is positive. As the name implies, this
is a multi-decadal oscillation, meaning any change in the index should be able
to be seen well in advance (i.e. by a year, perhaps more).<span style="mso-spacerun: yes;"> </span><o:p></o:p></div>
<div class="MsoNormal">
<span style="mso-spacerun: yes;"><br /></span></div>
<div class="MsoNormal">
Following the most recent departure into negative territory,
at the tail end of 2018, the AMO has been seen moving back firmly into positive
territory, now flirting with the highest values in more than a year. This adds
credibility to the idea that this coming winter should see a positive AMO. Unfortunately,
that credibility is undermined by the incorrect naming of this chart, and the
fact that “meridional” is misspelled. Nevertheless, the chart data itself is
correct upon examination.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
But
there’s an issue here – we haven’t gone over how the positive AMO is identified,
we have only established that it’s positive. I try to make forecasting a
learning experience in addition to a reading experience, and if this
publication doesn’t explain how to identify the phase of the AMO, that’s a
problem. Refer back to Figure 17 for a moment, showing sea surface temperature
anomalies around the globe. More specifically, refer to Figure 25 below,
where I have zoomed in on the north Atlantic. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgPn_i3mP4UFM332emLubnvld2xp6Uj5J8XbhTb3Tooed78bHN8dB7TM1lQwT82vhI1fsRSk8q9ZP9tH0Pk91Nx56Qm3OgrC1wRdAvhr95elzofWqi1DzPEEqrR0vSKGJ84ehED5djPG4hx/s1600/fig25.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="292" data-original-width="477" height="195" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgPn_i3mP4UFM332emLubnvld2xp6Uj5J8XbhTb3Tooed78bHN8dB7TM1lQwT82vhI1fsRSk8q9ZP9tH0Pk91Nx56Qm3OgrC1wRdAvhr95elzofWqi1DzPEEqrR0vSKGJ84ehED5djPG4hx/s320/fig25.png" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"></td><td class="tr-caption" style="text-align: left;"><span style="font-size: 12.800000190734863px;">Figure 25: Zoomed screenshot from Figure 17, SSTAs over the North Atlantic (NOAA)</span></td></tr>
</tbody></table>
<div class="MsoNormal">
The Atlantic Multidecadal Oscillation comes from the
Atlantic, as the name implies, but more specifically we look to the north
Atlantic to determine the behavior of the AMO. In a positive AMO, sea surface
temperatures are warmer than normal in and around Greenland. Given that we are
in a positive AMO state, it is thus no surprise to see widespread and
noteworthy positive SSTAs across those waters. If this were a negative AMO
environment, one would expect to see below-normal water temperatures around
Greenland.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Thus far, this section has illustrated how to determine the
AMO phase, discussed what phase of the AMO we are currently in, and pointed out
why it’s rather easy to forecast the AMO for a number of months in advance,
especially if the oscillation is firmly entrenched in either its positive or
negative phase. Now that it’s evident we are in a +AMO regime and will remain
in such a regime into the winter, we can see what a positive AMO usually brings
for North America in the winter season. For this, I will be using correlation
graphics for temperature and precipitation, like what was done in the PDO
section. First, though, we need to get a sense for positive AMO winters in
general via correlation graphics. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjxY7aEPXRV0zUF5x0EYfOtJE0Dj_useu6oG5fkRW8a9ZjV90b_vdDXCaVfYEIfp70yaXKHqjEfu55A1G-tEpOA0Jd4ee7c1g5zVHu-Ry4_sjGEJMyyA3C_nczcwAtWoioyl6_4pmDVfctD/s1600/fig26.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="467" data-original-width="493" height="378" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjxY7aEPXRV0zUF5x0EYfOtJE0Dj_useu6oG5fkRW8a9ZjV90b_vdDXCaVfYEIfp70yaXKHqjEfu55A1G-tEpOA0Jd4ee7c1g5zVHu-Ry4_sjGEJMyyA3C_nczcwAtWoioyl6_4pmDVfctD/s400/fig26.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 26: DJF Temperature correlation with the AMO (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Figure 26, shown above, depicts the
correlation between surface temperatures and the Atlantic Multidecadal
Oscillation (AMO) during the December-January-February window. This graphic
indicates that while the majority of the country doesn’t see a significant
correlation between the AMO and temperatures during the winter months, there
are a few areas worth mentioning.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Of note is the maximization of positive
correlation values in the state of Maine, where the positive correlation
magnitude exceeds +0.40. This implies that in a positive (negative) AMO winter,
temperatures in the far Northeast will be warmer (colder) than normal. This
positive correlation drops off immediately after exiting Maine, but is a
still-notable +0.30 to +0.399 in portions of New England. A modest positive
correlation between the AMO and temperatures is evident in the Ohio Valley,
Midwest, Great Lakes and Southern Plains regions, while the remainder of the
country generally sees a minimal correlation between the AMO and temperatures.
Given that we expect a +AMO this winter, the chances for a warmer than normal
winter in New England and perhaps into the Midwest/Great Lakes/Plains appear
higher.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi1VFXNYLP7jKioE5j97nZ_o214W7lmM2Eg1N_2z2X9HW8_03vrmkVsTqKThSgzgiGsgBHCJOZoM3xt1XW1dWdVEEvankF-LZ-U3so0WD8z169hGY-G8Cd1C4Y3PSrlYH-2-emL18Q31hWo/s1600/fig27.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="433" data-original-width="457" height="378" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi1VFXNYLP7jKioE5j97nZ_o214W7lmM2Eg1N_2z2X9HW8_03vrmkVsTqKThSgzgiGsgBHCJOZoM3xt1XW1dWdVEEvankF-LZ-U3so0WD8z169hGY-G8Cd1C4Y3PSrlYH-2-emL18Q31hWo/s400/fig27.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 27: DJF Precipitation correlation with the AMO (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Just above, Figure 27 depicts the correlation between
precipitation and the AMO, again during the three winter months. Again, while
the majority of correlation values are rather insignificant, there are a few
areas to make note of. Primarily of interest here is the positive correlation maximized
in the western U.S., especially in northern California. With a +AMO state
expected, this would seem to increase the chances of a wetter than normal
winter in the West. That in itself would seem to imply a more active than
normal storm track for the winter, perhaps a reason why we also see a positive
correlation in the Ohio Valley region. This opens the door to the possibility
of an active winter storm season, with the primary storm tracks running
northeast through the Plains (delivering above-normal precipitation to the
Nebraska/South Dakota/Iowa region) and another bowling through the Ohio Valley
(bringing wetter than normal anomalies to that region). That possibility would
be far higher if the AMO were the only seasonal oscillation with a material
effect on North America and if those correlations were stronger, but neither of
those is the case. Therefore, the +AMO seems to merely encourage warmer
temperatures in the Central and Northeast U.S., but perhaps with wetter than
normal conditions in the central Plains and Ohio Valley. Whether this
transpires, with numerous other oscillations also in the picture, remains to be
seen.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
On a final note, it is worth mentioning that the Earth
System Research Laboratory (ESRL) has found there is a negative correlation
between the PDO and AMO across all months of the year, on the order of -0.28.
While this isn’t a significant correlation, it could be of use here as we know
the AMO phase but not the PDO phase for the coming winter. If the AMO is
presumed in this forecast to be positive for the winter season, this negative
correlation would imply that the PDO ought to lean negative, bolstering the
case for a negative PDO that was broadly made in the PDO section but not
formally proposed as the likely PDO state for the coming winter. On a
month-by-month basis, the AMO-PDO correlation for December, January and
February is -0.27, -0.25 and -0.32, respectively, good for a three-month
average of -0.28 on the dot. In other words, while this adds to the case for a
negative PDO this winter, we still have yet to find concrete evidence
supporting a formal forecast of a certain PDO phase. That will likely come in
the Official winter forecast in late September.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In summary, the Atlantic Multidecadal Oscillation has moved
back into positive territory after briefly going negative last winter,
continuing the overarching state of a positive AMO environment. The AMO is
expected to remain positive for the 2019-2020 winter, with well-above-normal
sea surface temperature anomalies evident around Greenland. As a consequence, given
positive correlations with temperature across swaths of the Central and Eastern
U.S., the possibility of a warmer than normal winter appears to be on the rise.
However, the possibility of stormier than normal weather in the Southwest, and
snowier than normal conditions in the central Plains and Ohio Valley, also
appears to be on the increase should the +AMO persist as expected.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><i><span style="font-size: 16.0pt; line-height: 107%;">d. <b>Regions of Interest</b></span><o:p></o:p></i></div>
<div class="MsoNormal">
In addition to the three primary oscillations discussed above,
there are five areas I monitor that I believe also affect the winter pattern to
a non-trivial degree. Figure 28 below, showing weekly SST anomalies across the globe
for the period ended July 20<sup>th</sup>, will serve as the reference graphic
for the first three of five regions. These regions, in order of presentation,
are: East Asia / West Pacific; Bering Sea / North Pacific; Gulf of Alaska /
Northeast Pacific; the northern Atlantic; and the Great Lakes.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjEm5K97zKUo8OypLeCPJd9-aPJKi-6ZzZJIFvW7yxhFHuv1Tfdh7MB9XV-Pfjauqy4nDZxN9P9DJ-fKT4m61I0a0VFZEKx-Vb05bO0OxlD8Ki1ZQAaXW72RBgxtyIHXaTfbmRQUecdAidY/s1600/fig28.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="585" data-original-width="917" height="408" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjEm5K97zKUo8OypLeCPJd9-aPJKi-6ZzZJIFvW7yxhFHuv1Tfdh7MB9XV-Pfjauqy4nDZxN9P9DJ-fKT4m61I0a0VFZEKx-Vb05bO0OxlD8Ki1ZQAaXW72RBgxtyIHXaTfbmRQUecdAidY/s640/fig28.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 28: SST anomalies for the week ended July 20th (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><i><span style="font-size: 12.0pt; line-height: 107%;">i.<b> </b></span></i><b><i><span style="font-size: 14.0pt; line-height: 107%;">East Asia / West Pacific</span><o:p></o:p></i></b></div>
<div class="MsoNormal">
The East Asian / West Pacific region is of high interest to forecasters
like myself who enjoy making use of rather-unconventional tools that have, so
far, proven to be accurate. One of these tools is the concept that anomalous
weather events over the United States can be predicted with pretty high
accuracy by viewing those same anomalies over the region of Japan about 6-10
days prior to that event’s occurrence in the United States. While this is not a
widely-used forecasting method due to its relative lack of research and
relative lack of prominence, I believe it to be important enough to include a
brief discussion over the sea surface temperature anomalies in that region.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Looking over Figure 28 and examining the Western Pacific,
the picture is rather mixed. While there are pockets of below-normal SSTAs in
the waters surrounding southern Japan, as well as due east of the country,
there is also a swath of above-normal anomalies just northeast of Japan, with essentially-neutral
anomalies in between. Ideally, the predominant presence of above-normal or
below-normal sea surface temperature anomalies would allow us to determine how
the weather will play out for that area over the coming winter. However, anomalies
as weak and spatially-minimized as these don’t afford us that opportunity. At
best, an argument could be made that below-normal sea surface temperature
anomalies south of Japan favor a stormier-than-normal winter ahead for East
Asia, and thereby favor a stormier-than-normal winter in the United States as
well. However, that’s a bit of a stretch in my eyes. Instead, it seems most
appropriate to acknowledge that there is not yet a clear signal for SST
anomalies around Japan, precluding us from determining how the winter there
(and by extension, in the U.S.) will play out. Similar to the PDO, I expect the
picture to become clearer for the Official winter forecast in a couple of
months.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><i><span style="font-size: 14.0pt; line-height: 107%;">ii<b>. Bering Sea / North Pacifc</b></span><b><o:p></o:p></b></i></div>
<div class="MsoNormal">
Another area of interest to this forecast is the waters in
and around the Bering Sea, extending into the north-central Pacific in general.
This holds special importance in my opinion given how critical the Bering Sea
is for the stratosphere during the winter, thus making it a critical factor in
the North American winter pattern as well. To understand why this is such an
important piece, we need to jump ahead a bit and glean some content from the
Stratosphere section of this outlook. <o:p></o:p></div>
<div class="MsoNormal">
Undoubtedly, if you have any interest in the broad weather
pattern during the winter months, you’ve heard of the infamous “polar vortex”
at some point or another. The idea that the polar vortex brings severe cold to
lower latitudes is correct, but its description has been mangled in the media.
Contrary to what some articles will imply, the polar vortex does not “return”
or “happen again” – it is a permanent feature in the Arctic Circle during the
winter months, and is present every winter. Additionally, the polar vortex is
not an “event” – what happens in those cases is that some sort of disturbance
in the upper latitudes forces a piece of the tropospheric polar vortex to break
off from the main vortex. That smaller piece is then shunted down to lower
latitudes, which can (and does) move over northern portions of the United
States, bringing intense cold with it. So, if you hear someone talking about
“the polar vortex happening again this winter”, make sure you remind yourself
that the polar vortex happens *every* winter (indeed, without it, there
wouldn’t be a winter as we know it) and what the person should really be asking
is if something will happen to make a piece of the polar vortex split off and
move to lower latitudes. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Now that I’ve gotten that off my chest, we need to turn to the
question of ‘what causes these splits in the polar vortex?’. You might also be
wondering how the polar vortex can be present every single winter, even though
it only seems to “happen” once every several years in the United States. Both
of these are good questions. We’ll use the answer to the second question to
also answer the first question. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In the winter, there is a large vortex spanning the entirety
of the atmosphere relevant to weather forecasting, from the surface to the
upper reaches of the stratosphere. This is the polar vortex, but it acts
differently at different levels of the atmosphere. The polar vortex we’re most
familiar with is what I refer to as the <b>tropospheric polar vortex</b>. In
reality, the atmosphere is three-dimensional, so this is one big vortex, but
for our purposes it’s necessary to separate them into two. The ‘other’ one is
the <b>stratospheric polar vortex</b>. When the news talks about the polar
vortex moving south into our neck of the woods, what they’re really talking
about is a piece of the tropospheric polar vortex becoming detached from the
main vortex and managing to be moved to lower latitudes over North America. In
practice, it can be shunted to any lower latitude, including over Europe, Asia,
Siberia, or the oceans. This movement of the polar vortex to lower latitudes
happens quite often, but since there’s so much space on this planet and North
America is only so large, the stars align only every once in a while for that
piece of the tropospheric polar vortex to impact the U.S. What you won’t hear
on the news, though, is how that split / disruption in the tropospheric polar
vortex happened in the first place. Almost exclusively, especially in the event
of a major disruption to the tropospheric polar vortex, this process begins in
the stratospheric polar vortex. Usually, that involves a sudden and intense
event of warm air rushing into the stratosphere and ravaging the stratospheric
polar vortex, which eventually feeds down to the tropospheric polar vortex
(usually with a ~2 week lag). Now, we have to identify where those sudden warm
air bursts (called Sudden Stratospheric Warmings, or SSWs) come from, and
that’s where the Bering Sea comes into play.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
For reasons I’m not entirely familiar with, the Bering Sea
is an incredibly fertile area for these sudden stratospheric warming events to
happen. A ‘typical’ SSW event involves a ridge of high pressure and warm air
blossoming over the Bering Sea and then flooding into the Arctic Circle. While
this blossoming into the Arctic Circle is not a given – indeed, sometimes the
warm air simply dissipates over the Bering Sea and no SSW occurs – it seems to
be most likely when that warm air forms over the Bering Sea. I will discuss all
of this in the Stratosphere section, so no worries if it seems tough to
understand. The key takeaway here is that the Bering Sea is a key area for high
pressure to form in the stratosphere, which can then lead to severe cold
weather events in North America.<o:p></o:p></div>
<div class="MsoNormal">
Let’s take a look back at Figure 28 and focus our attention
on the Bering Sea. The Bering Sea should draw your attention even if it weren’t
the focus of this section: the waters in that area have the highest positive
SST anomalies in the Northern Hemisphere, and actually in the world per this
chart! This is a significant anomaly, and provides a good look at what the
coming winter could entail if these strong positive anomalies persist. <b><span style="color: red;">The presence of strong positive SST anomalies in the Bering
Sea indicate a materially-increased chance of sudden stratospheric warmings
this winter, which therefore increase the risk of severe outbreaks of cold air
into the United States</span></b>. This is not a given, of course, but the
chance of lobes of the polar vortex protruding into the United States this
winter is increased by a non-trivial amount with the presence of such strong
positive SSTAs in the Bering Sea. <o:p></o:p></div>
<div class="MsoNormal">
I will touch on this topic again in the next iteration of
this winter forecast, given its importance, and these anomalies will need to be
watched to see if they do persist into the fall.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><i><span style="font-size: 14.0pt; line-height: 107%;">iii. <b>Gulf of Alaska / Northeast
Pacific</b></span><o:p></o:p></i></div>
<div class="MsoNormal">
The majority of concerns around the Gulf of Alaska were
taken care of in the Pacific Decadal Oscillation section, so this section
should be brief. It is necessary to view sea surface temperature anomalies in
the Gulf of Alaska in their own right, outside of the PDO, however, warranting
a separate section here. Figure 28 shows a swath of well-above-normal SST
anomalies in the Gulf of Alaska and northeast Pacific as a whole, an
interesting development should it persist into the winter. In general,
above-normal water temperatures encourage the development of high pressure
systems, while below-normal water temperatures encourage the development of low
pressure systems. There’s a bit of ‘the chicken or the egg’ issue as far as if
low pressure systems cause negative SSTAs or vice-versa, but what is clear is
that negative SST anomalies are more commonly seen in areas with stormier-than-normal
activity, while positive SST anomalies are more commonly seen in areas with predominantly-calm
weather. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Going along with this, the wide swath of above-normal water
temperatures in the Gulf of Alaska seems to favor the development of high pressure
systems more often than low pressure systems in that region. To tie it in to
the Bering Sea, it seems as though ridges of high pressure could form over the
Gulf of Alaska and extend into the Bering Sea, perhaps to the extent that it
becomes a blocking ridge and even encourages cross-polar flow to bring
significant cold air to North America. All of that contains a lot of
contingencies, of course, and situations like <b>cross-polar flow</b> (where a
ridge of high pressure pushes so far north that it moves into the Arctic Circle
and actually allows air to flow directly from Siberia to North America, instead
of being transferred across the Pacific and warming up in the process) can only
be forecasted a matter of days in advance. Regardless, the positioning of warmer-than-normal
water temperatures across the northeast Pacific and the Bering Sea indicates to
me that this is a possibility if those anomalies sustain into the winter
season.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Even if this doesn’t materialize, and we keep our attention
only on the Gulf of Alaska, the strong positive SSTAs are supportive of a high
pressure system over that area. Hawk-eyed weather enthusiasts will recognize
the placement of high pressure in the Gulf of Alaska as signaling the negative
phase of the <b>East Pacific Oscillation (EPO)</b>, which is an atmospheric
pattern that favors an influx of colder than normal air to the eastern half of
North America when it is negative. Consequentially, should those positive
anomalies persist in the Gulf of Alaska (which is subject to what the PDO does,
of course), a negative EPO becomes materially more likely, and <b><span style="color: red;">this increases the chances of a colder than normal winter for
the eastern half of the U.S., while also increasing the chances of a warmer
than normal winter in Alaska and the western third of North America</span></b>.
<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><i><span style="font-size: 14.0pt; line-height: 107%;">iv. <b>Northern Atlantic</b></span><o:p></o:p></i></div>
<div class="MsoNormal">
As mentioned at the start of this section, Figure 28 would
be used for the first three areas of interest. For these last two areas of
interest, we will make use of Figure 29, showing a zoomed-in view of SST
anomalies that will better serve our analysis for the remainder of this
section.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjz5g1SaA0l193esa4pVJpII7d-XDLHlpfDu2HMsPF6NxOMk_xSbX94nxdez7Oa_HbbdqTlrWBxh-_Dq9dQFaWGRSpnSDdcRr_TMLOqCwr31iNlMhnJVvFWTQdaE8VG_hZgKQ-SVZjskVfW/s1600/fig29.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="456" data-original-width="696" height="261" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjz5g1SaA0l193esa4pVJpII7d-XDLHlpfDu2HMsPF6NxOMk_xSbX94nxdez7Oa_HbbdqTlrWBxh-_Dq9dQFaWGRSpnSDdcRr_TMLOqCwr31iNlMhnJVvFWTQdaE8VG_hZgKQ-SVZjskVfW/s400/fig29.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 29: SST Anomalies focused on the Atlantic Ocean and Great Lakes (IRI/Columbia Univ)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Turning
our attention to the northern Atlantic, it is necessary to define exactly where
we are looking. While the waters near Greenland certainly have some substantial
positive SST anomalies, that area is covered by the Atlantic Multidecadal
Oscillation, and was already discussed in that section. For this piece, our
attention will be given to the waters just east of the East Coast.<o:p></o:p></div>
<div class="MsoNormal">
In Figure 29, the waters offshore of the Eastern Seaboard
are seen as markedly above-normal, particularly maximized offshore of the
Mid-Atlantic. The presence of these stout positive sea surface temperature
anomalies will alarm winter-weather fans in the East U.S. and excite
winter-weather fans in the Central U.S., but for the Northeast it’s more of a
‘glass half full’ situation. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Consider the storm track of the notorious ‘Nor’easter’
system, which is known for dropping feet of snow in locations along the Eastern
Seaboard when these systems crawl up the coastline and rapidly intensify thanks
to the temperature gradient that the storm usually rides along. Warmer than
normal water temperatures offshore the Eastern Seaboard can only intensify that
temperature gradient, especially if any Nor’easter is able to pull cold
Canadian air down south as it grinds northeast along the shoreline. An
increased temperature gradient opens the door for further strengthening,
potentially making any Nor’easters that occur even stronger than they would
have been without the swath of above-normal water temperatures. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
It’s also a cause for concern for those who enjoy
Nor’easters, however. As discussed in the prior section for the Gulf of Alaska,
warmer than normal SSTs tend to be associated with high pressure systems. Thus,
the risk is that Nor’easters could be discouraged from occurring if these warm
waters offshore the East provoke high pressure systems and direct any storm
systems in the Plains northeast through the Ohio Valley and Midwest, instead of
south into the Southeast and eventually northeast into a full-fledged
Nor’easter. The absence of strong positive SSTAs near the Southeast U.S. tells
me this probability isn’t as high as it could be, but <b>this risk of high
pressure systems forming and keeping parts of the East warm throughout portions
of the winter is certainly there if waters east of Washington D.C. and Boston
remain warmer than average into the winter</b>.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><i><span style="font-size: 14.0pt; line-height: 107%;">v. <b>Great Lakes</b></span><o:p></o:p></i></div>
<div class="MsoNormal">
The last area of interest in the Sea Surface Temperatures
section is the Great Lakes. This is most pertinent for lake-effect snow
purposes, but may also dictate temperature trends to some degree for areas
immediately downwind of the Lakes. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Referring back to Figure 29, the crude temperature anomalies
shown for the Great Lakes show essentially all of the Lakes as being
above-normal in sea surface temperatures, an indication that enhanced
lake-effect snowfall is possible for areas downwind this winter. A potential
exception is Lake Superior, where anomalies are zero to even slightly negative,
but anomalies across all of these lakes could change substantially by the time
winter actually rolls around. For the time being, though, enhanced snowfall
does appear possible for lake-effect snow regions this winter. Temperatures may
also average warmer than normal for those areas, especially if the positive
anomalies increase.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><i><span style="font-size: 16.0pt; line-height: 107%;">e. <b>Summary</b></span><o:p></o:p></i></div>
<div class="MsoNormal">
When analyzing sea surface temperatures across the world, it
becomes immediately clear that there are many variables affecting the outlook,
with the possibility of numerous wrenches being thrown into the forecast and
making the outlook miss the mark. However, with the exception of the PDO, it
appears the majority of these key variables can be determined at this point. In
the Equatorial Pacific, it looks as if the El Nino will struggle to sustain
itself into the fall, and ENSO-Neutral conditions are expected for the coming
winter. The Pacific Decadal Oscillation is currently too weak to be in any
particular phase, and while it appears as though a negative PDO is favored over
a positive PDO, there is too much uncertainty to make a definitive statement on
that oscillation. The Atlantic Multidecadal Oscillation still appears to be in
its overarching positive phase, and as such a positive AMO is expected for this
winter. Also of note are well-above-normal water temperature anomalies in the
Bering Sea and Gulf of Alaska, both of which seem favorable for a colder than
normal winter in much of the country. Indeterminate SST anomalies near Japan
preclude any hints of how active the storm track will be for the winter season,
but this will become clearer in the Official winter forecast. <o:p></o:p></div>
<div class="MsoNormal">
<b><span style="color: red;">In the aggregate, ocean-based
oscillations appear to lean in favor of a cooler than normal winter for the
majority of the country. It is too early to pinpoint where the strongest
below-normal anomalies will land, but I do feel comfortable forecasting a
below-normal winter for temperatures at this point in time, based on what the
Sea Surface Temperatures section has shown.</span></b> <b>This may change as we
review more material – this is only one section of this outlook,
of course!<o:p></o:p></b></div>
<div class="MsoNormal">
<b><br /></b></div>
<div class="MsoNormal">
<b><br /></b></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><b><u><span style="font-size: 18.0pt; line-height: 107%;">2. Stratosphere</span><o:p></o:p></u></b></div>
<div class="MsoNormal">
Although the stratosphere does not have a number of
influential oscillations like the world’s oceans have, the stratosphere remains
an important feature to discuss in any winter outlook. The primary oscillation that
involves the stratosphere is the Quasi-Biennial Oscillation (QBO), and that is
where we will begin this section.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><i><span style="font-size: 16.0pt; line-height: 107%;">a. <b>Quasi-Biennial Oscillation
(QBO)</b></span><o:p></o:p></i></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The <b>Quasi-Biennial Oscillation</b>, or
QBO for short, is a rather intimidating name. However, like in the other
oscillations reviewed thus far, the concept will become more simple after some
explanation. At the start, however, it will likely be one of the most
difficult-to-understand parts of this outlook. Let’s dive right in.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3RGlhLTDV3l9QM2QMwMBlJMETFcTMa2DyWKAWNEjrtBd-p5TsEbkGQxQiHGXDtieid7BOhyphenhyphenG-pR7rDpkG-sGIVuyiXuRKldIuwwKeDaKgyR4rFkVeYWHNwzKx15eefqJGmsxv3ws1r-8m/s1600/fig30.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="576" data-original-width="745" height="492" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3RGlhLTDV3l9QM2QMwMBlJMETFcTMa2DyWKAWNEjrtBd-p5TsEbkGQxQiHGXDtieid7BOhyphenhyphenG-pR7rDpkG-sGIVuyiXuRKldIuwwKeDaKgyR4rFkVeYWHNwzKx15eefqJGmsxv3ws1r-8m/s640/fig30.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 30: Zonal winds on a latitude-height cross-section, as of July 25th (FU-Berlin)</td></tr>
</tbody></table>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<o:p> </o:p>Figure 30, above, comes from the Free
University of Berlin, affectionately annotated as FU-Berlin in reference to the
school, not as a slight to the country of Germany. The graphic is pretty
complicated at first blush, so let’s dissect it. The x-axis shows latitudes
from the Equator to the Arctic Circle, while the y-axis shows the atmosphere by
height, in millibars. For reference, the surface is roughly at the
1000-millibar level, the jet stream is at the 200-millibar level, and the
stratosphere begins at the 100-millibar level or so.</div>
<div class="MsoNormal">
<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The graphic itself shows mean zonal winds, in meters per
second. Zonal winds are winds that run west-to-east: when the graphic shows
positive zonal wind values, it means winds are going west-to-east, while
negative zonal wind values indicate winds are running east-to-west. One can
confirm this by viewing the large positive swath of zonal winds at the
200-millibar level, positioned around the 40 degree North line of latitude.
What might that be? That’s the Northern Hemisphere’s jet stream! The jet stream
runs west-to-east, of course, sits at the 200-millibar level of the atmosphere,
and generally meanders around the 40 degree N line of latitude. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
I have made some annotations on the graphic, most
importantly being the positive zonal winds (“westerlies”, from the west) at the
Equator from about the 20 millibar level to nearly the 100 millibar level. This
is the signal being given from the QBO, which is in its positive phase. When
the QBO is in its positive phase, these positive zonal winds / westerlies
are strengthened in the stratosphere, as is shown in the red circle. If this
were a negative QBO, instead of being positive, those zonal wind values would
be negative, indicating winds are going from the east to the west
(“easterlies”). We can confirm this by viewing Figure 31 below, which shows a
historical time series of zonal winds. Within Figure 31, positive zonal winds
are shaded in gray (remember, +QBO) while negative zonal winds (-QBO) are in
white. Indeed, in the figure, we see a wide swath of gray has propagated down
through the stratosphere as of late, signaling strengthened westerlies and
therefore a positive QBO.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhEskMijTCWw6vZwKgQN4SQy2Or22Fos9ICJMTAuEdQs3XCoBALGHjEm-PJExLiY_Y-3nRhBaE9QX_mlLk2VhCgL6Ii9mJkehmgMgor32my5XsaQ4suJPfhlm1yQ97mwA6mxGeW3Xi23bYN/s1600/fig31.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="851" data-original-width="594" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhEskMijTCWw6vZwKgQN4SQy2Or22Fos9ICJMTAuEdQs3XCoBALGHjEm-PJExLiY_Y-3nRhBaE9QX_mlLk2VhCgL6Ii9mJkehmgMgor32my5XsaQ4suJPfhlm1yQ97mwA6mxGeW3Xi23bYN/s640/fig31.png" width="444" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 31: Historical time series of zonal winds to depict QBO phase (FU-Berlin)</td></tr>
</tbody></table>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
You’ll notice in looking at Figure 31 that positive QBO
“waves” follow a pretty identical pattern. The positive zonal winds start out
at the top of the stratosphere, propagate downward rather steadily, and then linger
when they reach the area between about 50 millibars and 100 millibars. You’ll
also notice how the positive zonal winds seem to quickly be replaced by
negative zonal winds (the “easterlies”) at the 10 millibar – 30 millibar layer,
a quick change especially when compared to how long the westerlies linger at
the lower layers of the stratosphere. That rapid changeover is already
beginning to be seen, with the tight gradient between the 10 millibar and 20
millibar layers at the very end of Figure 31<b>. Our assumption for this
forecast is that the QBO will remain weakly positive into the winter</b>, after
having been firmly positive earlier this year into now. This will become key
when we create analogs for our winter forecast later on, but for now we just
need to note that the QBO will most likely be weakly positive for the 2019-2020
winter. The assumption that the QBO will keep its positive state into the
winter is based on the assumption that the downward propagation of westerlies
will be less sudden than that seen in mid-2017, and more akin to that seen in
2008-2009 or essentially any other year in Figure 31. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Now that we have established the QBO is expected to be
positive for this winter, we can view correlation graphics like we did for the
AMO and PDO to see what a positive QBO might mean as far as temperature,
precipitation, and the broader atmospheric flow goes.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiz3RILdhm6nPj7UTDi00H7nzwVYLzsdqfswVEtnRUvkJfg37Bhl3dhIEJOumaKxMHFuQmgn_13NSZHmqi8FT0UVkooTUPPnXpD8mB-NhCqAElDL9dhyp0de6k4Wi5YvTed___5kxT_krZ1/s1600/fig32.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="509" data-original-width="537" height="378" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiz3RILdhm6nPj7UTDi00H7nzwVYLzsdqfswVEtnRUvkJfg37Bhl3dhIEJOumaKxMHFuQmgn_13NSZHmqi8FT0UVkooTUPPnXpD8mB-NhCqAElDL9dhyp0de6k4Wi5YvTed___5kxT_krZ1/s400/fig32.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 32: DJF Temperature correlation with the QBO (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Figure 32, as shown above, depicts the
correlation between surface temperatures and the Quasi-Biennial Oscillation
phase over the December-January-February period. While viewing the chart, it
quickly becomes evident that the QBO does not impose as strong an effect on
conditions at the surface as oscillations like ENSO and the PDO do. Indeed, the
maximum absolute correlation value is situated in eastern New Mexico, at a
value of somewhere between +0.20 and +0.30. The majority of the country
exhibits a slight positive correlation of temperatures with the QBO, save for
slight negative correlations in southern Florida and the Pacific Northwest. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Taken at face value, this would seem to suggest that the
positive QBO will encourage a warmer than normal winter over much of the
country, but given how the QBO should only be weakly positive and the
correlation itself is only weakly positive<b>, I can’t see the QBO having a
particularly-significant effect on temperatures this winter</b> if it does
indeed hit the winter in a weakly-positive phase.<o:p></o:p></div>
<div class="MsoNormal">
<br />
<o:p></o:p></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi_UmMi0gyrZ5kLqXdNMSTSf5ZX1bwVo75dRATlZfPrcWaesEZXWDKf1rM6cgJyXZzhXX03KTJbt0E3moiY5UkVWeX7Q_LS5yy6O2NcVbej8CBbJQkbH5e3yKzhiYuX4oBZBiBAfnaqLAHp/s1600/fig33.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="517" data-original-width="544" height="380" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi_UmMi0gyrZ5kLqXdNMSTSf5ZX1bwVo75dRATlZfPrcWaesEZXWDKf1rM6cgJyXZzhXX03KTJbt0E3moiY5UkVWeX7Q_LS5yy6O2NcVbej8CBbJQkbH5e3yKzhiYuX4oBZBiBAfnaqLAHp/s400/fig33.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 33: DJF precipitation correlation with the QBO (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Figure 33, shown just above, shows the correlation between
precipitation and the QBO for the same DJF timeframe. While the correlations
between precipitation and the QBO are more diverse across the country, they are
only diverse in the sign of the correlation, and not the magnitude. Taking the
graphic as seen, a positive QBO would appear to most strongly encourage
above-normal precipitation near the Front Range of the Rockies, in the Upper
Midwest, and in western New York. In contrast, the positive QBO would also act
to incite below-normal precipitation along the Gulf Coast and into the southern
Plains. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Much like the temperature correlations, however, this would
only be the case if those correlations were stronger. Thus, given weak
correlations and the expectation of a weakly-positive QBO<b>, I don’t believe
the QBO will have a material effect on precipitation either</b>. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
That’s not to say we should completely disregard the QBO,
however: as I said earlier, wasting time is not something I go out of my way to
do. Since the QBO is based in the stratosphere, let’s see if there are any
impacts in the stratosphere from a positive QBO, with correlations exceeding
0.30. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhsl5Uc_2np3mz-qWydgY1jTuIR7sMIuUyoqYdWP-OWYPNL0KMQQt6NqxhB1DNUmKl_uPxIcgd1KDNT6asoM_9z_ZzOFpdVmbzxAkAPVq6USc3OEHGE13J5Gs4y9uhriiIL4b7UT9qIGsO3/s1600/fig34.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="501" data-original-width="647" height="308" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhsl5Uc_2np3mz-qWydgY1jTuIR7sMIuUyoqYdWP-OWYPNL0KMQQt6NqxhB1DNUmKl_uPxIcgd1KDNT6asoM_9z_ZzOFpdVmbzxAkAPVq6USc3OEHGE13J5Gs4y9uhriiIL4b7UT9qIGsO3/s400/fig34.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 34: DJF 50-millibar correlation with the QBO (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Figure
34 above portrays the correlation between the QBO and 50-millibar
geopotential height anomalies. Recall that the stratosphere is generally
defined as above the 100-millibar mark, so this places us at right about the
middle of the stratosphere.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
As hoped, the QBO does have correlation values exceeding
0.30 (in absolute terms), seen over the upper latitudes of the Northern
Hemisphere at somewhere between -0.30 and -0.40. This means that a positive QBO
should cause geopotential heights over the Arctic Circle to be deeper (a.k.a. a
stronger stratospheric polar vortex), while a negative QBO encourages
geopotential heights over the area to be higher (a weaker stratospheric polar
vortex). <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
A question you might be posing is ‘<i>How can some strong
winds at the Equator make the stratospheric polar vortex stronger? It’s thousands
of miles away from the Equator!</i>’ <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Consider a basic low-pressure system. At its core, a
low-pressure system is exactly what the name implies: an area of low pressure
relative to its surroundings. In the Northern Hemisphere, the <b>Coriolis Force</b>
means low pressure systems have air that rotates counter-clockwise (think of
humid air being pulled from the south ahead of the system and cool air being
pulled from the north on the back side of the system) <span style="mso-spacerun: yes;"> </span>and high pressure systems have air that
rotates clockwise. In the Southern Hemisphere, this is the opposite. Now,
imagine you’re up in space, thousands of miles away from Earth, and you’re
looking down on the Earth from right above the North Pole. From your view high
above the North Pole, the jet stream in the Northern Hemisphere rotates
counter-clockwise around the Earth. This is accurate, given the jet stream in
the Northern Hemisphere moves from west-to-east. <o:p></o:p></div>
<div class="MsoNormal">
So, you’re high above the Earth, looking down from your
position high above the North Pole, watching the Northern Hemisphere jet stream
flow around the Earth in a counter-clockwise fashion. Now, think about what
happens if the winds in the stratosphere over the Equator strengthen, as
happens in a positive QBO. Recognizing that the Earth’s atmosphere is a fluid
and not a 2-dimensional plane, think about what happens if you were to take a
garden hose and spray it horizontally underwater. What happens to the water
immediately surrounding the garden hose-propelled water? The water immediately
around the fast-moving water also speeds up to some degree. The same sort of
thing happens if you’re standing on a train station platform and an express
train goes by: the train is moving at 50 MPH, for example, and while the air
around you speeds up while the train goes by, it’s not going at 50 MPH. It
certainly sped up, though (and that’s probably a sign to stand further back
from the train tracks).<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
This can be easily related to a positive QBO event: when the
positive zonal winds in the stratosphere get faster due to a +QBO event, the
winds at lower levels of the atmosphere also speed up to some degree. In the Northern
Hemisphere, that means westerly winds in the upper-level of the atmosphere
strengthen, which acts to tighten up the stratospheric polar vortex (stronger
westerlies strengthen the wind fields of large vortices) and generally “locks
up” cold air in the upper latitudes of the Northern Hemisphere as a result of
stronger upper-level winds. This makes sense given that cold air outbreaks here
in the lower latitudes occur with a “wavy” jet stream, something that happens
less often as westerlies aloft get stronger.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Given this admittedly-rough description, it is no surprise
then that Figure 34 shows a negative correlation between geopotential heights
at the 50-millibar level and the QBO. A positive QBO leads to those increased
westerly winds, which strengthens the polar vortex and thereby decreases
geopotential height anomalies. In sum, <b>this positive QBO should act to
strengthen the stratospheric polar vortex (and by extension, to an extent, the
tropospheric polar vortex) marginally</b> relative to how strong it would be
without a +QBO. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
But let’s suppose
the QBO weakens faster than we expect, and we arrive in the winter season with
a QBO stuck at nearly zero. Not a problem – what’s happening right now is
already telling us what the coming winter will be like, with respect to the
QBO. Take a look at Figure 35 below. In Figure 35, we see another
correlation graphic at the 50-millibar level regarding geopotential heights,
but now with a twist. This is the correlation between December-January-February
50-millibar geopotential heights and the QBO index <i><u>during the preceding
July-August-September period</u></i>. In other words, we are seeing the
correlation that the July-August-September QBO has to December-January-February
50-millibar geopotential heights.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjyyq3rjA0-N6xIl2zI7toGXOr_9kaGLpZsBU1l7dZPCPGBopSu5OS9kXZTSsSygpOCCKqvrjRWPRsKUq88Vmw4ZDSw-lkVWZQGyTjTCDjD3HcYijzJ9uDOUoXP2fMHRdqXLFZXtZaQ28Oh/s1600/fig35.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="536" data-original-width="693" height="308" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjyyq3rjA0-N6xIl2zI7toGXOr_9kaGLpZsBU1l7dZPCPGBopSu5OS9kXZTSsSygpOCCKqvrjRWPRsKUq88Vmw4ZDSw-lkVWZQGyTjTCDjD3HcYijzJ9uDOUoXP2fMHRdqXLFZXtZaQ28Oh/s400/fig35.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">DJF 500mb Geopotential Height correlation with JAS QBO state (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Why should we care? Take a look at the chart: based on this
correlation, the 50-millibar geopotential heights over the upper latitudes of
the Northern Hemisphere are negatively correlated by a pretty strong margin –
stronger than in Figure 34, even – to the state of the QBO five months earlier,
in the July-August-September period. Since there is very high confidence in the
QBO remaining in its positive phase through September, <b><span style="color: red;">there seems to be a pretty strong argument that the
stratospheric polar vortex will err on the stronger side for the coming winter</span></b>.
<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The Quasi-Biennial Oscillation is currently in its positive
phase, and is expected to remain in its positive phase – albeit to a weaker
magnitude – moving into the winter. <b>This appears likely to strengthen the
stratospheric polar vortex, increasing the chances for a broadly warmer than
normal winter across the country.</b><o:p></o:p></div>
<div class="MsoNormal">
<b><br /></b></div>
<div class="MsoNormal">
<b><br /></b></div>
<div class="MsoNormal">
<b><br /></b></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><i><span style="font-size: 16.0pt; line-height: 107%;">b. <b>Recent Temperature Trends</b></span><o:p></o:p></i></div>
<div class="MsoNormal">
I want to briefly take a look at recent temperature trends
in two portions of the stratosphere. While there aren’t any groundbreaking
additions to the forecast by examining these trends, per se, I find it
beneficial to know the base from which stratospheric temperatures will be
starting from heading into the winter, as this could help indicate how strong
or weak the stratospheric polar vortex is when the winter kicks off. Figure 36
below starts off at the 70-millibar layer of the stratosphere,
near the lower end of that section of the atmosphere.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEirvCJl_i94vC8KQSGK5qqmlUOSYIuMgicpYsLi1lxH1rIIQQFTN73I8fxsAol6L0PuEZw-20DJQbbC0o3q79xS9nvCa6mKWEkpQpVG4ORSmQDYw4oySEGdWdJwuVkl9NvVcbgr57Z4VEed/s1600/fig36.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="595" data-original-width="893" height="426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEirvCJl_i94vC8KQSGK5qqmlUOSYIuMgicpYsLi1lxH1rIIQQFTN73I8fxsAol6L0PuEZw-20DJQbbC0o3q79xS9nvCa6mKWEkpQpVG4ORSmQDYw4oySEGdWdJwuVkl9NvVcbgr57Z4VEed/s640/fig36.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 36: Recent temperatures at the 70-millibar level, between the 65N and 90N latitude lines (CPC)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The graphic is
interesting in that it provides temperature data at the 70-millibar level going
all the way back to the start of 2018, allowing us to see how the previous
winter affected the stratosphere. For our purposes, however, we need to only
focus on temperatures during the spring and summer of 2019. Looking to those data,
it appears as though temperatures have recovered to right around the average
for this time of year after having meandered near record-lows within the last
few months. The same kind of situation unfolded last year, too, with
70-millibar temperatures generally hovering close to the average during the
summer months.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
When fall rolled around last year, stratospheric
temperatures at this level remained around average, only starting to move more
towards below-average values moving into November. This is generally the trend
for the stratosphere, where temperatures established during the summer relative
to the mean hold into the fall. Going by that premise, it doesn’t seem
immediately apparent that the stratosphere will be substantially colder than
normal to begin winter, which would be a boon to the strength of the polar
vortex. Indeed, barring any unexpected event that impacts temperatures,
recently-observed temperatures in the lower stratosphere don’t suggest a
particularly stronger or weaker polar vortex to begin the winter months.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Moving ahead, Figure 37 (below) depicts recent temperatures at the
1-millibar level of the atmosphere, right at the top of the stratosphere.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjczxOfULslUIPy0ewSNvuZHYViVPio9OfhLVDo_znP61hZLM-9zcCeXI_pH1xMQHRKeZWwW70oZkzu_yPZ5gKQkF0XEB6hzez9Pi_k8CkeZL0zuH1UjCf6H0gT_dHhOOUPvrcn7SrBSK1A/s1600/fig37.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="590" data-original-width="884" height="426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjczxOfULslUIPy0ewSNvuZHYViVPio9OfhLVDo_znP61hZLM-9zcCeXI_pH1xMQHRKeZWwW70oZkzu_yPZ5gKQkF0XEB6hzez9Pi_k8CkeZL0zuH1UjCf6H0gT_dHhOOUPvrcn7SrBSK1A/s640/fig37.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 37: Recent temperatures at the 1-millibar level, between the 65N and 90N lines of latitude (CPC)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
At the 1-millibar
level, it isn’t just the level of oxygen that’s remarkably low. As Figure 37
attests, temperatures at the top of the stratosphere are grinding out fresh
strings of record lows on numerous occasions since spring. The same sort of
thing transpired in the spring and summer of 2018, and sure enough,
temperatures at this level of the atmosphere clung tight to near- or
new-record-low temperatures well into the fall.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
As the graphic also shows, however, this did not condemn the
upper stratosphere to far-below-normal temperatures throughout the winter. In
fact, the outcome was quite the opposite, with temperatures spiking to
near-record-highs as a stratospheric warming event occurred.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The point of examining recent trends isn’t to try and
anticipate how the stratosphere will act during the winter – that’s dependent
on the number of stratospheric warming events during the season (a number that
can be zero). Instead, this is more relevant for the late fall and early winter
period, to try and establish what kind of shape the stratospheric polar vortex
will be in as winter begins. Once winter actually gets underway, of course, all
attention turns to any and all SSW possibilities.<o:p></o:p></div>
<div class="MsoNormal">
Based on what Figures 36 and 37 have shown, nothing truly
anomalous seems to be looming for the stratosphere as we move towards fall.
While temperatures are setting fresh record lows at the top of the
stratosphere, this would be far more noteworthy if it were occurring at the
lower levels of the stratosphere. This is because the top of the stratosphere
is naturally more volatile (one can visually compare the spread between record
highs and record lows in the winter to see this difference in volatility),
while lower levels of the stratosphere are generally more pertinent to the
stratospheric polar vortex as a whole. In other words, if you see a forecaster
proclaiming an imminent apocalypse because of a spike in temperatures at the
1-millibar layer, do what I do: ignore it, and wait to see if it shows up lower
down in the stratosphere. The stratosphere looks pretty normal heading into the
fall months.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="mso-tab-count: 1;"> </span><i style="mso-bidi-font-style: normal;"><span style="font-size: 16.0pt; line-height: 107%; mso-bidi-font-size: 11.0pt;">c. <b style="mso-bidi-font-weight: normal;">Relations to
Other Oscillations</b></span><o:p></o:p></i></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
While the
Quasi-Biennial Oscillation is the most-relevant (and perhaps only) oscillation
that directly involves the stratosphere, there are a number of other
oscillations that are not based in the stratosphere, but still exert
considerable influence on the behavior of the stratospheric polar vortex during
the winter months. The oscillations we will examine relative to the
stratosphere are the Atlantic Multidecadal Oscillation (AMO) as well as the
Arctic Oscillation (AO).<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhK09nGraow0breVi6ZH7e83ELPy0knldUuSlaYC5JQklZgo0Tt1i16wpI6Nkzage2HCRIFrF3rfnMkjZoqYSiktW3OIyZYUwckk4iqZ4zuT5DFiqDGjCkwnfK1i0PBSKIqhRnP2ORhdGGk/s1600/fig38.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="559" data-original-width="723" height="492" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhK09nGraow0breVi6ZH7e83ELPy0knldUuSlaYC5JQklZgo0Tt1i16wpI6Nkzage2HCRIFrF3rfnMkjZoqYSiktW3OIyZYUwckk4iqZ4zuT5DFiqDGjCkwnfK1i0PBSKIqhRnP2ORhdGGk/s640/fig38.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 38: DJF 50-millibar geopotential height correlation with DJF AMO (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Figure 38, attached above, shows the correlation
between geopotential heights at the 50-millibar level (~middle of the
stratosphere) during the December-January-February period and the AMO during
the same three-month period. The idea of this analysis is to see if the AMO,
despite being based out of ocean temperature anomalies, also affects conditions
in the stratosphere.<o:p></o:p></div>
<div class="MsoNormal">
The graphic yields an interesting result. Across the upper
latitudes of the Northern Hemisphere, positive correlation values are
widespread, maximized in northeast Canada at values exceeding +0.40. Compared
to some of the earlier correlation values we observed, this is a pretty
formidable correlation, indicates that the AMO does seem to wield some
influence on the stratosphere. Given that we expect a positive AMO this winter,
the implication here is that geopotential height anomalies should also lean
higher as a result, indicating a weaker stratospheric polar vortex. Given that
the QBO will most likely still be weakly-positive for the winter, this will not
be the favored outcome, but still indicates there is room for the stratospheric
polar vortex to weaken more than it may in a negative-AMO environment. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The next relationship I’d like to examine involves another
correlation, but also with a twist like we used in the QBO portion. In Figure
39, below, I have attached a correlation between 50-millibar
geopotential heights during the December-January-February period and the Arctic
Oscillation (AO) index from five months prior (July-August-September). It’s
worth briefly explaining what the Arctic Oscillation is before delving into the
correlation graphic.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The <b style="mso-bidi-font-weight: normal;">Arctic Oscillation (AO)</b> is an intraseasonal oscillation, in
contrast to pretty much all of the oscillations we have analyzed so far. As a
result, when using the AO, we look for changes in the index on a basis of <u>days,</u>
as opposed to a basis of months with the QBO or years with the PDO, or even
decades with the AMO.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The Arctic Oscillation is tracked by observing 1000-millibar
geopotential height anomalies over the far upper latitudes of the Northern
Hemisphere, above 20 degrees North to be specific. The AO has two phases: a
positive phase, and a negative phase. When the AO is said to be positive (+AO),
geopotential height anomalies over the upper latitudes are lower than normal.
This means the tropospheric polar vortex is stronger than normal, and this
stronger vortex “locks up” the colder air at the upper latitudes, keeping it
from flowing south. As a result, a positive AO is associated with above-normal
temperatures in the United States. When the AO is said to be negative (-AO),
geopotential height anomalies over the upper latitudes are higher than normal.
This means the tropospheric polar vortex is weaker, and enables colder air
masses to flow down to lower latitudes. As a result, a negative AO is commonly
associated with below-normal temperatures in the United States.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKZtLScFjHrE_hujnewfsCvQOCGnZqyZ1YG-VCXacgk-XD0jtoseVFGo7257oB21AhoaoMWr7uOdcTFezChOcUTa2KkETVNsQ98Ti3N7nmWJFvQeu_V8V-eHQGc8UwOVAY0CtZy3AnryE2/s1600/fig39.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="562" data-original-width="726" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKZtLScFjHrE_hujnewfsCvQOCGnZqyZ1YG-VCXacgk-XD0jtoseVFGo7257oB21AhoaoMWr7uOdcTFezChOcUTa2KkETVNsQ98Ti3N7nmWJFvQeu_V8V-eHQGc8UwOVAY0CtZy3AnryE2/s640/fig39.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 39: DJF 50-millibar geopotential height correlation with JAS Arctic Oscillation (AO leads by five months) (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<o:p></o:p><br />
<o:p></o:p></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
Figure
39 shows the correlation between 50-millibar geopotential heights during the
December-January-February period and the Arctic Oscillation during the
preceding July-August-September (JAS) period, meaning the AO index leads by
five months. The figure shows rather-strong negative correlations in the upper
latitudes of the Northern Hemisphere, indicating that a positive (negative)
Arctic Oscillation during the JAS period tends to bring about negative
(positive) geopotential heights in the stratosphere, resulting in a stronger
(weaker) stratospheric polar vortex.</div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhBEgxPtoO_DYYRdZstFaj9qfE_P728jTxXL7o36PZdiQNoM8jy-Wl9CgYvv7RWmnOOWkSs4gspE5cuePAhDHFfJHiLcJ2dKaAWL9XliMXumzjeCTNl4KU7qANtPLCZAsYqX1s46TcyGBe_/s1600/fig40.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="264" data-original-width="675" height="250" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhBEgxPtoO_DYYRdZstFaj9qfE_P728jTxXL7o36PZdiQNoM8jy-Wl9CgYvv7RWmnOOWkSs4gspE5cuePAhDHFfJHiLcJ2dKaAWL9XliMXumzjeCTNl4KU7qANtPLCZAsYqX1s46TcyGBe_/s640/fig40.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 40: Observed Arctic Oscillation (AO) since late March 2019 to July 26th, annotated by the author (CPC)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Now shown immediately above, Figure 40 shows observed Arctic
Oscillation index values since late March, giving us a glimpse at how the
oscillation has behaved as of late. I’ve highlighted in red the data since
July, as the correlation period in Figure 39 spans the July-August-September
period. During the month of July, the AO has been overwhelmingly negative, only
moving into a positive phase briefly around the middle of the month. This is
only just-under-one month of data, to be sure, but if this trend of a
negative-AO continues throughout the August and September periods, it would be
one of the stronger testaments in favor of a weaker stratospheric polar vortex
for the coming winter.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
This puts our Stratosphere section in a bit of an awkward
situation. On one hand, the Quasi-Biennial Oscillation is generally viewed as
the seasonal oscillation most directly affecting conditions in the
stratosphere, and it favors a stronger than normal polar vortex for the coming
winter, bringing about a tendency towards warmer than normal conditions across
most of the country. On the other hand, though, the QBO is expected to be only
weakly positive when the winter rolls around, dampening that correlation.
Additionally, relationships between the stratosphere and other oscillations in
the atmosphere suggest the polar vortex is actually expected to be weaker than
normal, based on how conditions so far in July have played out. Where do we go
from here?<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjB7l3q0NBod2GI7N5cUmDhy3m86aRjbKp9teJVm4s5busEtzNHqryE5_3-bHwuqfphB0uySusWBe1TgULjscLrNE9DekJwMVqI4YRONCnXrMAtuAL4KzvT-F25BXJcn9RJm3Usv-9remy2/s1600/fig41.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="543" data-original-width="703" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjB7l3q0NBod2GI7N5cUmDhy3m86aRjbKp9teJVm4s5busEtzNHqryE5_3-bHwuqfphB0uySusWBe1TgULjscLrNE9DekJwMVqI4YRONCnXrMAtuAL4KzvT-F25BXJcn9RJm3Usv-9remy2/s640/fig41.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 41: DJF 50-millibar geopotential height correlation to MJJ Multivariate ENSO Index (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<o:p></o:p></div>
<div class="MsoNormal">
There’s one more relationship I want to look at, depicted above in Figure 41. In the figure, a correlation is shown between
50-millibar geopotential heights in the December-January-February period and
the Multivariate ENSO Index (MEI) in the preceding May-June-July period,
meaning the MEI leads the DJF geopotential heights by seven months. To clarify,
the Multivariate ENSO Index (MEI) is an index established to determine the
state of the ENSO phenomenon by using more variables than just sea surface temperature
anomalies. As such, the MEI is one of the most comprehensive methods used to
determine the ENSO phase. As of the most recent data, the MEI was seen just
barely in Neutral-ENSO territory, at values of around +0.3 and +0.4. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In data provided by the ESRL – the agency that maintains the
MEI – values are provided in the format of a rolling two-month average. This
means that the most recent data point is for the May-June period combined,
rather than just the month of June. Since we don’t have July data yet, this is
to our benefit, because the May-June period covers the remaining two months of
the correlation period on the left. For the May-June period, the MEI was
clocked at +0.4, indicating conditions are just on the edge of a full-fledged
El Nino but aren’t quite established enough. Looking at the correlation graphic
on the left, we see that there is a positive correlation between MJJ MEI values
and DJF 50-millibar geopotential heights. In other words, a positive (negative)
MEI reading for the MJJ period correlates to positive (negative) geopotential
heights in the stratosphere, conducive for a weaker (stronger) polar vortex in
the following winter. These correlations are rather substantial, too: values
along the western portion of North America exceed +0.40, certainly one of the
stronger magnitudes of correlation we have seen over the course of this
publication. Given the +0.4 MEI value recorded for the May-June period, and the
likelihood that July will also contain conditions near or at El Nino status, I
expect the MJJ average for the Multivariate ENSO Index to be near or in El Nino
territory (at or above +0.5), thus <b style="mso-bidi-font-weight: normal;"><span style="color: red;">making it more likely that geopotential heights in the
stratosphere will be higher, weakening the stratospheric polar vortex and
boosting the chances of a cooler than normal winter.</span></b><o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
To summarize all of this, it looks as though we will see the
Quasi-Biennial Oscillation (QBO) stay in its positive phase into the winter,
albeit on a firm weakening trend. The positive QBO should encourage a stronger-than-normal
stratospheric polar vortex, which in turn looks to encourage a warmer than
normal winter for the majority of the country. However, correlations of the
stratospheric polar vortex strength to the Atlantic Multidecadal Oscillation,
the summertime state of the Arctic Oscillation and the late spring / early
summer state of the ENSO phenomenon all suggest that the stratospheric polar
vortex will actually turn out weaker for this winter, in opposition to what the
QBO seems to predict. Because these other oscillations have non-trivial
correlations to the strength of the wintertime stratospheric polar vortex, and
the QBO will likely be in a weak positive phase instead of at its maximum
amplitude, <b style="mso-bidi-font-weight: normal;"><span style="color: red;">I
believe it is more prudent to expect the stratospheric polar vortex to be
somewhere between average strength and weaker than normal for the coming
winter, given how the QBO will have an increasingly-weak influence as the
winter moves on. Consequentially, the stratosphere thus seems to favor a cooler
than normal winter for much of the United States</span></b>. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<!--[if !mso]>
<style>
v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style>
<![endif]--><!--[if gte mso 9]><xml>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]-->
<!--[if gte mso 9]><xml>
<w:WordDocument>
<w:View>Normal</w:View>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:DoNotPromoteQF/>
<w:LidThemeOther>EN-US</w:LidThemeOther>
<w:LidThemeAsian>X-NONE</w:LidThemeAsian>
<w:LidThemeComplexScript>X-NONE</w:LidThemeComplexScript>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:SnapToGridInCell/>
<w:WrapTextWithPunct/>
<w:UseAsianBreakRules/>
<w:DontGrowAutofit/>
<w:SplitPgBreakAndParaMark/>
<w:EnableOpenTypeKerning/>
<w:DontFlipMirrorIndents/>
<w:OverrideTableStyleHps/>
</w:Compatibility>
<m:mathPr>
<m:mathFont m:val="Cambria Math"/>
<m:brkBin m:val="before"/>
<m:brkBinSub m:val="--"/>
<m:smallFrac m:val="off"/>
<m:dispDef/>
<m:lMargin m:val="0"/>
<m:rMargin m:val="0"/>
<m:defJc m:val="centerGroup"/>
<m:wrapIndent m:val="1440"/>
<m:intLim m:val="subSup"/>
<m:naryLim m:val="undOvr"/>
</m:mathPr></w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" DefUnhideWhenUsed="false"
DefSemiHidden="false" DefQFormat="false" DefPriority="99"
LatentStyleCount="382">
<w:LsdException Locked="false" Priority="0" QFormat="true" Name="Normal"/>
<w:LsdException Locked="false" Priority="9" QFormat="true" Name="heading 1"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 2"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 3"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 4"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 5"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 6"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 7"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 8"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 9"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 9"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 1"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 2"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 3"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 4"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 5"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 6"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 7"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 8"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 9"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="footnote text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="header"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="footer"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index heading"/>
<w:LsdException Locked="false" Priority="35" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="caption"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="table of figures"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="envelope address"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="envelope return"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="footnote reference"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation reference"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="line number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="page number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="endnote reference"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="endnote text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="table of authorities"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="macro"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="toa heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 5"/>
<w:LsdException Locked="false" Priority="10" QFormat="true" Name="Title"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Closing"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Signature"/>
<w:LsdException Locked="false" Priority="1" SemiHidden="true"
UnhideWhenUsed="true" Name="Default Paragraph Font"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Message Header"/>
<w:LsdException Locked="false" Priority="11" QFormat="true" Name="Subtitle"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Salutation"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Date"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Block Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Hyperlink"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="FollowedHyperlink"/>
<w:LsdException Locked="false" Priority="22" QFormat="true" Name="Strong"/>
<w:LsdException Locked="false" Priority="20" QFormat="true" Name="Emphasis"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Document Map"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Plain Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="E-mail Signature"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Top of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Bottom of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal (Web)"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Acronym"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Address"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Cite"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Code"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Definition"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Keyboard"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Preformatted"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Sample"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Typewriter"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Variable"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal Table"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation subject"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="No List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Contemporary"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Elegant"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Professional"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Balloon Text"/>
<w:LsdException Locked="false" Priority="39" Name="Table Grid"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Theme"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 9"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Placeholder Text"/>
<w:LsdException Locked="false" Priority="1" QFormat="true" Name="No Spacing"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading"/>
<w:LsdException Locked="false" Priority="61" Name="Light List"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 1"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 1"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 1"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 1"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 1"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Revision"/>
<w:LsdException Locked="false" Priority="34" QFormat="true"
Name="List Paragraph"/>
<w:LsdException Locked="false" Priority="29" QFormat="true" Name="Quote"/>
<w:LsdException Locked="false" Priority="30" QFormat="true"
Name="Intense Quote"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 1"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 1"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 1"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 1"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 1"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 1"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 1"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 2"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 2"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 2"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 2"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 2"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 2"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 2"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 2"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 2"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 2"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 2"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 3"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 3"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 3"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 3"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 3"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 3"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 3"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 3"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 3"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 3"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 3"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 3"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 3"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 4"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 4"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 4"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 4"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 4"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 4"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 4"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 4"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 4"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 4"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 4"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 4"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 4"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 4"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 5"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 5"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 5"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 5"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 5"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 5"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 5"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 5"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 5"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 5"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 5"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 5"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 5"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 5"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 6"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 6"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 6"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 6"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 6"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 6"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 6"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 6"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 6"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 6"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 6"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 6"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 6"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 6"/>
<w:LsdException Locked="false" Priority="19" QFormat="true"
Name="Subtle Emphasis"/>
<w:LsdException Locked="false" Priority="21" QFormat="true"
Name="Intense Emphasis"/>
<w:LsdException Locked="false" Priority="31" QFormat="true"
Name="Subtle Reference"/>
<w:LsdException Locked="false" Priority="32" QFormat="true"
Name="Intense Reference"/>
<w:LsdException Locked="false" Priority="33" QFormat="true" Name="Book Title"/>
<w:LsdException Locked="false" Priority="37" SemiHidden="true"
UnhideWhenUsed="true" Name="Bibliography"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="TOC Heading"/>
<w:LsdException Locked="false" Priority="41" Name="Plain Table 1"/>
<w:LsdException Locked="false" Priority="42" Name="Plain Table 2"/>
<w:LsdException Locked="false" Priority="43" Name="Plain Table 3"/>
<w:LsdException Locked="false" Priority="44" Name="Plain Table 4"/>
<w:LsdException Locked="false" Priority="45" Name="Plain Table 5"/>
<w:LsdException Locked="false" Priority="40" Name="Grid Table Light"/>
<w:LsdException Locked="false" Priority="46" Name="Grid Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="Grid Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="Grid Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 6"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 6"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 6"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 6"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 6"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="46" Name="List Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="List Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="List Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 6"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 6"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 6"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 6"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 6"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Mention"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Smart Hyperlink"/>
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-priority:99;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:8.0pt;
mso-para-margin-left:0in;
line-height:107%;
mso-pagination:widow-orphan;
font-size:11.0pt;
font-family:Calibri;
mso-ascii-font-family:Calibri;
mso-ascii-theme-font:minor-latin;
mso-hansi-font-family:Calibri;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]--><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1128"/>
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1"/>
</o:shapelayout></xml><![endif]-->
<!--StartFragment-->
<span style="font-family: "calibri"; font-size: 11.0pt; line-height: 107%;"><br clear="all" style="mso-special-character: line-break; page-break-before: always;" />
</span>
<br />
<span style="font-family: "calibri"; font-size: 11.0pt; line-height: 107%;"><br /></span>
<br />
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b><u><span style="font-size: 18.0pt; line-height: 107%; mso-bidi-font-size: 11.0pt;">4. Seasonal Model Forecasts</span><o:p></o:p></u></b></div>
<div class="MsoNormal">
In my approach to seasonal forecasting, I like to think of
the process as one of constructing pillars, with the forecast itself standing
on those pillars. Most of the pillars rely on observed data, such as the
various oscillations above, and observed data do form the majority of my
forecast. However, I find seasonal forecast models to be of use as another
pillar – not for their accuracy, but as another piece to the puzzle. Just as it’s
possible to be too broad when creating a seasonal forecast (i.e. relying on
certain oscillations that actually have no relation to the winter pattern),
it’s equally possible to be too narrow, an example being excluding seasonal
forecast models. I will be the first to admit that I don’t particularly like
forecast models, due to their inaccuracies, but I’ll also be the first to admit
that they are worth looking at, at the very least. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
\We’ll look at a
handful of forecast models here. In order, and in side-by-side pairs, they will be: the CPC’s official
seasonal outlook; the CFS model forecast; the IRI multi-model outlook; the
ECMWF’s long-range modeling system; the Japan Meteorological Agency’s
long-range modeling system; the Beijing Climate Center’s long-range modeling
system; and the CPC’s NMME multi-model system. I will show all images first, in
the aforementioned order, and then explain each image and provide a broader
discussion afterwards.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwQDn3pXsCYPb9xFajBZZjPqF6uPb0YL9U4vO0OTrdqSynKWhPXzGBfeubGBYciG6amLBC0PXIpOvMpLnoNAzgtSrA-7jJIcxnNeAKTcP_ENlPyxsSwhftB_-f7URjIDLHyxpYRvTa355D/s1600/Screen+Shot+2019-08-11+at+8.22.54+PM.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="431" data-original-width="1227" height="224" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwQDn3pXsCYPb9xFajBZZjPqF6uPb0YL9U4vO0OTrdqSynKWhPXzGBfeubGBYciG6amLBC0PXIpOvMpLnoNAzgtSrA-7jJIcxnNeAKTcP_ENlPyxsSwhftB_-f7URjIDLHyxpYRvTa355D/s640/Screen+Shot+2019-08-11+at+8.22.54+PM.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Sub-images One (left) and Two (right)</td></tr>
</tbody></table>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh1aX5x5oLn1lGiSVX6vKTkbleWziZ-9GRDGtGx_dDuFKJHMsVe7miqE4N9r4PKkWrVAFq7m7orTddkjVFQCVEwBBgA6r7BYnMpcwI-i-ls5Iq8qkGAxhYYTBtLIjTdUiTW3qRMub_ofuW5/s1600/Screen+Shot+2019-08-11+at+8.23.07+PM.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="539" data-original-width="935" height="368" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh1aX5x5oLn1lGiSVX6vKTkbleWziZ-9GRDGtGx_dDuFKJHMsVe7miqE4N9r4PKkWrVAFq7m7orTddkjVFQCVEwBBgA6r7BYnMpcwI-i-ls5Iq8qkGAxhYYTBtLIjTdUiTW3qRMub_ofuW5/s640/Screen+Shot+2019-08-11+at+8.23.07+PM.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Sub-images Three (top-left), Four (top-right), Five (bottom-left) and Six (bottom-right)</td></tr>
</tbody></table>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiXB-h5N4GfGrU6ExorXLddYIKL9HyF7ujv5WrpSAip8BQVOS1iIoff8CPFa_zpRhdf4WwcwRLeF1_j_SBJnRcS5Fd1q0LWvFAW4OfMHM0x78nkkt9X5xukPdnaSY4AN28LkMrsluM37mKk/s1600/Screen+Shot+2019-08-11+at+8.23.20+PM.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="544" data-original-width="928" height="374" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiXB-h5N4GfGrU6ExorXLddYIKL9HyF7ujv5WrpSAip8BQVOS1iIoff8CPFa_zpRhdf4WwcwRLeF1_j_SBJnRcS5Fd1q0LWvFAW4OfMHM0x78nkkt9X5xukPdnaSY4AN28LkMrsluM37mKk/s640/Screen+Shot+2019-08-11+at+8.23.20+PM.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Sub-images Seven (top-left), Eight (top-right), Nine (bottom-left) and Ten (bottom-right)</td></tr>
</tbody></table>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiR3xf8Boxjgm8YWr1NnXKdDX_zhY-80BQMF-JMBRuR5Uw6e3fewT53gPPVRd345D0iJCOPOpjbFPueGJ-OWoBQpeEGBd-PYHvZIy7gUxfUmjGsPoqym0FANbT-fS-kIuZVD5MyTnbQbP99/s1600/Screen+Shot+2019-08-11+at+8.23.29+PM.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="523" data-original-width="922" height="362" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiR3xf8Boxjgm8YWr1NnXKdDX_zhY-80BQMF-JMBRuR5Uw6e3fewT53gPPVRd345D0iJCOPOpjbFPueGJ-OWoBQpeEGBd-PYHvZIy7gUxfUmjGsPoqym0FANbT-fS-kIuZVD5MyTnbQbP99/s640/Screen+Shot+2019-08-11+at+8.23.29+PM.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Sub-images Eleven (top-left), Twelve (top-right), Thirteen (bottom-left), and Fourteen (bottom-right)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<o:p></o:p></div>
<div class="MsoNormal">
Before discussing what these images show, I’d like to
identify each one and explain what they show. In sub-images One and Two, the official outlook from the Climate Prediction Center is shown for
the December-January-February window, with the probabilistic precipitation
forecast on the left and the temperature forecast on the right. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In the graphic showing sub-images Three through Six, the top two images (Three and Four) are from the NCEP’s CFS model
(essentially the American seasonal forecasting model), with precipitation
anomalies on the left and temperature anomalies on the right, both also valid
for the DJF period. The bottom two images that graphic (sub-images Five and Six) display probabilistic
forecasts from a multi-model composite created by the IRI establishment at
Columbia University, valid in the November-December-January window. The
left-hand image shows precipitation probabilities, while the right-hand image
depicts the temperature outlook.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Moving on to sub-images Seven through Ten, the seasonal forecasting model from
the European Centre for Medium-Range Weather Forecasts (ECMWF) is shown on the
top two images (Seven and Eight), with precipitation anomalies on the left and temperature
anomalies on the right, each valid for the NDJ timeframe. This is the seasonal
forecast model from the same agency that produces the operational ECMWF
forecast model, commonly favored during the winter season for reasons that are
sometimes far exaggerated and even outright wrong. The bottom two panels (sub-images Nine and Ten) show precipitation (left) and temperature (right) anomalies for the DJF
window from the Japan Agency for Marine-Earth Science and Technology’s (JAMSTEC)
model, a commonly-used model in seasonal forecasting. Precisely why it’s so
commonly used is still a mystery to me. In any event, the output from that
model comprises the bottom two images in the four-panel graphic of sub-images Seven through Ten.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Lastly, for sub-images Eleven through Fourteen, the top two graphics (Eleven and Twelve) show precipitation
(left) and temperature (right) forecasts during the DJF period from the Beijing
Climate Center. That’s right, this is the output from China’s seasonal
forecasting model. While I have no information about its accuracy, I find it
hard to believe that the computing power of one of the world’s top countries
for technology is insufficient to produce a forecast at least worth looking at.
To the ‘world’s top countries for technology’ extent, note that South Korea
also has a seasonal forecast model, but I have elected to not show it here
simply to focus in on the ‘key’ models. If we were to include all the forecast
models I have in my bookmarks folder on my laptop, we would still have to go
through the Korean model, the Brazilian model, and even the Russian model,
among others. Rounding out the last four-panel graphic, and comprising sub-images Thirteen and Fourteen, is another multi-model composite, this one
put together by the Climate Prediction Center under the ‘NMME’ moniker, with
precipitation and temperature graphics on the left and right, respectively,
valid for DJF.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
There are a number of points and clarifications I want to
make for this amalgamation of forecast models, and we’ll proceed in the same
order that they are posted above. Beginning with the Climate Prediction
Center’s outlook, I cannot stress enough how ambiguous the agency makes their
seasonal outlooks. To that extent, in prior seasonal forecasts, I’ve opted to
not show them at all, as historically they align temperature and precipitation
patterns almost exactly as what the ENSO phase would dictate. In other
scenarios, such as the one here, they’ll simply cover the majority of the
country with above-normal temperatures. To be sure, the scientists behind these
forecasts are undoubtedly far more intelligent and sharp-minded than myself,
but I still fail to see the usefulness behind leaning on the CPC’s outlook. If
anything, the precipitation outlook seems to just be a textbook El Nino set-up,
which (as we discussed) is rather unlikely heading into the winter. I
personally see minimal use in incorporating the CPC’s outlook here, aside from
merely showing it as that’s the product which will be shared to the public at
large.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Moving on to the CFS model’s outlook immediately below that
of the CPC, we find a forecast that seems to resemble a plausible pattern.
Examining the precipitation outlook alone, it seems the CFS model supports a
ridge of high pressure in the Southwest U.S. allowing the Pacific jet stream to
send storm systems into the Pacific Northwest from its namesake ocean. From there,
the storm systems would likely ride the jet stream south and eject into the
southern Plains, before being forced north by another area of high pressure in
the Southeast U.S. (I identify both of these ridges by observing the
well-below-normal precipitation anomalies). This results in a storm track
through the Ohio Valley and above-normal precipitation anomalies in the same
region. The temperature outlook graphic seems to confirm this assessment of the
implied atmospheric pattern, though it does seem willing to let that ridge in
the Southwest U.S. open up and flow eastward into the Central U.S. at times.
This is not too dissimilar from the typical pattern seen in a neutral-ENSO
year, like we saw in the ENSO section of this outlook, albeit with below-normal
precipitation anomalies maximized in the Southeast and the tract of
above-normal anomalies shifted marginally westward. The temperature pattern is
almost exactly opposite that of what neutral-ENSO winters typically bring, but
given how the CFS model is notorious for being too warm (or even outright hot)
in its forecasts, this is not too concerning in my book. All in all, the CFS
model seems to present a believable outlook for the coming winter.<o:p></o:p></div>
<div class="MsoNormal">
We now transition to the IRI multi-model composite, which
shows a forecast not too far off from that of the CFS. While there are material
differences in the forecast for the Southwest, the idea of enhanced
precipitation in or around the Ohio Valley area is intact, with below-normal
anomalies also evident in the Southeast. The temperature forecast also aligns
remarkably well with the CFS, with above-normal temperature anomalies in the
West extending eastward but to a lesser and lesser degree, particularly moving
into the Great Lakes region. Perhaps the CFS temperature forecast may be on to
something, rather than being too warm.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Moving on, we come across the ECMWF seasonal model
outlook. I want to emphasize that just because it’s from the ECMWF agency, it
is not necessarily as accurate as the short-range forecasting model of the same
name (a.k.a. the “European model”). However, given the success the ECMWF has
had with its short-range model, it seems prudent to at least go over what its
longer-range counterpart shows. What it shows is a solution structurally different
from the CFS and IRI, but in a couple key respects it remains similar. Perhaps
the largest difference is the lack of above-normal temperature anomalies in the
Southwest, a stark change from the CFS which held the highest positive
anomalies in that area. Still, the above-normal anomalies in the High Plains soften
with eastward progression as seen in the CFS & IRI, though they quickly
ramp up along the Eastern Seaboard thereafter. Perhaps the most similar feature
is in the precipitation outlook, where the ECMWF model has a swath of enhanced
precipitation just as the CFS and IRI outputs do. In this case, it is shifted
more to the southeast, but the presence of the above-normal precipitation
anomalies in that same orientation as the other two datasets suggests this may
be a credible piece to expect for the upcoming winter.<o:p></o:p></div>
<div class="MsoNormal">
I don’t find a particular reason to go over the JAMSTEC
model output, which closes out this four-panel graphic, as it’s essentially the same forecast as
the ECMWF model but with the anomalies on both ends of the scale exaggerated.
To that extent, the temperature forecast runs directly opposite of that from
the CFS model, but my main takeaway is that above-normal track of precipitation
showing up again in the East.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The Chinese long-range model, which comprises the top two
graphics of the last four-panel set, shows a forecast that is, in the aggregate, pretty similar
to the ECMWF and JAMSTEC models. We again see above-normal temperature
anomalies in the northeastern half of the country (if you were to slice the
country diagonally from Seattle to Miami) and a tendency towards more-seasonal
temperatures in the Southwest. On the precipitation front, hints of
above-normal precipitation are still present, but they have been shunted more
to the east and drier-than-normal shadings have appeared in the Central U.S.
That’s an interesting development, in my opnion, because it means the
precipitation outlook from the BCC’s model is now pretty similar to the typical
precipitation pattern brought about in a neutral-ENSO winter. The temperature
forecast may be diametrically opposite to the typical temperature pattern in a
neutral-ENSO winter, but the precipitation forecast is pretty spot on. Needless
to say, the massive discrepancy between the alignment of the temperature and
precipitation forecasts to their respective composites for neutral-ENSO winters
is rather disarming and implores me to not use the Chinese model in building
the forecast.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
As we come up on the final pair of model forecast images, depicting the NMME outlook, it quickly becomes apparent why the CPC’s
official forecast is so warm across the entire country. The NMME, an average of
a handful of climate models, shows surface temperature anomalies between 0.5
degrees and 1 degree (I assume in Celsius) covering quite literally almost the
entire country during the DJF period. I would like to be very clear in that I
do not fault the scientists who put in long hours and a significant amount of
intelligence to build the models that went into this averaged output, because
it truly is a fantastic resource to have. But at the same time, you don’t have
to be a meteorologist to think that it seems pretty much impossible for almost
the entire country to experience essentially-identical temperature anomalies
during the winter season, the time when the mid-latitude jet stream is at its
most amplified and cold air outbreaks are most able to plow southward from
Canada. I just don’t see how the NMME forecast is plausible, and will not be
using it as part of the forecast.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
What can we summarize all of these forecast models into? While
there’s quite a bit of variability in the temperature forecasts, one thing kept
sticking out again and again across the climate models: the presence of a tract
of above-normal precipitation somewhere in the Central U.S. or East U.S.,
oriented in a southwest-to-northeast fashion and indicative of where the
winter’s main storm track could be. That level of consistency is remarkable
given how we remain five months out from December, and climate models are
notorious for disagreement amongst themselves even a month or two in advance.
So, <b><span style="color: red;">while it’s
tough to draw any specific conclusions with regard to temperature, model
guidance deems it likely that the winter will be more active than normal with
regards to precipitation chances / storm systems</span></b>.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<div class="MsoNormal">
<br /></div>
<span style="font-family: "calibri"; font-size: 11.0pt; line-height: 107%;"><br clear="all" style="mso-special-character: line-break; page-break-before: always;" />
</span>
<br />
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b><u><span style="font-size: 18.0pt; line-height: 107%; mso-bidi-font-size: 11.0pt;">5. Analogs</span><o:p></o:p></u></b></div>
<div class="MsoNormal">
The creation of analog sets is one of my favorite parts of
the winter forecast process, because it’s about as close as you can get to
creating your own model for how the atmosphere should play out in advance without
having a supercomputer. For the uninitiated, the concept of analog forecasting
in a seasonal perspective is using the oscillations we have discussed so far
(ENSO, PDO, AMO…), seeing how they are currently situated and seeing how they
are expected to be during the winter, and then going back in time and plucking
out years that had those oscillations in similar states as they are expected to
be. In theory, this should give a more precise idea as to what should happen in
the future, as it uses multiple oscillations in finding similar years to create
a composite instead of just one oscillation (i.e. comparing +QBO to –QBO). In
practice, it’s more of an art than a science, but I believe it’s at least worth
going over.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Let’s surmise the key points of the last >40 pages (in the original Word document, at least) of
discussion and analysis in a short list.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoListParagraphCxSpFirst" style="mso-list: l0 level1 lfo1; text-indent: -.25in;">
<!--[if !supportLists]--><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;"> <i> ª </i></span></span><i>The El Nino currently in place is weakening, and
the ENSO phenomenon is expected to weaken from an El Nino to a neutral-ENSO
environment for the winter.<o:p></o:p></i></div>
<div class="MsoListParagraphCxSpMiddle" style="mso-list: l0 level1 lfo1; text-indent: -.25in;">
<!--[if !supportLists]--><i><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;"> • </span></span><!--[endif]-->The Pacific Decadal Oscillation is too weak to
be placed in a specific phase with confidence at this point, and it is
difficult to ascertain exactly where it will end up in the winter. Currently,
data seem to lean in favor of a negative PDO, but confidence is too low to make
this an expectation in the forecast.<o:p></o:p></i></div>
<div class="MsoListParagraphCxSpMiddle" style="mso-list: l0 level1 lfo1; text-indent: -.25in;">
<!--[if !supportLists]--><i><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;"> • </span></span><!--[endif]-->The Atlantic Multidecadal Oscillation is
expected to remain positive for the winter.<o:p></o:p></i></div>
<div class="MsoListParagraphCxSpLast" style="mso-list: l0 level1 lfo1; text-indent: -.25in;">
<!--[if !supportLists]--><i><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;"> • </span></span><!--[endif]-->The Quasi-Biennial Oscillation is expected to
remain positive, albeit in a weakening trend, for the winter.</i><o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in;">
<br /></div>
<div class="MsoNormal">
Since we don’t yet know how the PDO will play out, and it
would be more of a guessing game to assume a –PDO or +PDO in creating analogs,
I elected to leave the PDO out of my analog creation process, and instead
utilized the ENSO, AMO and QBO components only. The criteria for a winter
qualifying as an analog to the forecasted set-up are as follows:<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoListParagraphCxSpFirst" style="mso-list: l1 level1 lfo2; text-indent: -.25in;">
<!--[if !supportLists]--><b><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;">
</span></span><!--[endif]-->ENSO</b>: The sea surface temperature anomaly of the
Nino 3.4 region must have been between -0.5 and +0.5 for all three months of
the winter season.<o:p></o:p></div>
<div class="MsoListParagraphCxSpMiddle" style="mso-list: l1 level1 lfo2; text-indent: -.25in;">
<!--[if !supportLists]--><b><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;">
</span></span><!--[endif]-->AMO</b>: The AMO index must have been above 0.0 for
all three months of the winter season.<o:p></o:p></div>
<div class="MsoListParagraphCxSpLast" style="mso-list: l1 level1 lfo2; text-indent: -.25in;">
<!--[if !supportLists]--><b><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;">
</span></span><!--[endif]-->QBO</b>: The 30-millbar component of the QBO must
have been between 0.0 and +10.0 for all three months of the winter season, and
must have been in a declining state (i.e. not the beginning of a new +QBO
event).<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
When applying these criteria, I ended up with 15 analog
winters based on the ENSO dataset, 27 analog winters from the AMO dataset, and
10 analog winters from the QBO dataset. I then removed all analog winters that
did not show up in at least two of the three datasets. This gave a total of 11
analog winters. There were two winters that appeared in all three datasets, and
these were double-weighted in the analog creation process, as you will see in
the composite images below.<o:p></o:p></div>
<div class="MsoNormal">
Based on these criteria and the
subsequent filtering and weighting adjustments, I present my analog years for
the 2019-2020 winter below.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiHtJxYagmWkco7YpU6iFpEYa9U4j7QIy-8w5oYt7ljaAcqO8GfUkp_GFKgscNhWCv__2WEOtlq85fxLDoNeFxOI6IInnaVdG8oidkxD0Hw7QSsItwmjSFA_jg3CyGkeToZObYH1bPIGesm/s1600/fig43.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="768" height="362" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiHtJxYagmWkco7YpU6iFpEYa9U4j7QIy-8w5oYt7ljaAcqO8GfUkp_GFKgscNhWCv__2WEOtlq85fxLDoNeFxOI6IInnaVdG8oidkxD0Hw7QSsItwmjSFA_jg3CyGkeToZObYH1bPIGesm/s400/fig43.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 42: Analog-implied temperature outlook for the 2019-2020 winter (ESRL)</td></tr>
</tbody></table>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiYFucV8XPCnGA2wUkU2OyUhtG6ODWrr2F_mk3cUMogEFZ3FGJ7oFekBCMjAEPai7RePLtGqWKALYKeW_Jdzwp9zs9WtDPGKvri6E_HGxt4JOJwUUqIJvAHJuBiqkNrLh7u31VBjsuTHI9N/s1600/fig42.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="695" data-original-width="766" height="362" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiYFucV8XPCnGA2wUkU2OyUhtG6ODWrr2F_mk3cUMogEFZ3FGJ7oFekBCMjAEPai7RePLtGqWKALYKeW_Jdzwp9zs9WtDPGKvri6E_HGxt4JOJwUUqIJvAHJuBiqkNrLh7u31VBjsuTHI9N/s400/fig42.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 43: Analog-implied precipitation outlook for the 2019-2020 winter (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
I’ll discuss the four images relating to my analogs in order, beginning with the top graphic showing
temperature anomalies (Figure 42).<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
These analog years suggest that the coming winter will be a
colder than normal one for almost the entire country, maximized in the central
Plains as well as the southern Rockies. I am a bit skeptical of below-normal
temperatures covering the entire country, much like I was with above-normal
temperatures covering the entire country in the CPC and NMME forecasts, which
introduces some uncertainty to this analog set. <b><span style="color: red;">In any event, the primary takeaway here is that
years with a positive AMO, weakening positive QBO and neutral-ENSO environment
appear to favor below-normal temperatures for much of the country</span></b>.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Moving on to the bottom image above (Figure 43),
precipitation anomalies during the analog winters are shown. The output is
pretty neat: just like we saw in the heavy majority of seasonal forecast
models, as well as in the neutral-ENSO winter composite image, there is a tract
of above-normal precipitation across the South and extending up into the
Eastern U.S. The fact that it shows up in our analog composite as well really
adds quite a bit of credibility to the premise of a more active storm pattern
this winter, even though the exact location of this above-normal precipitation
swath may remain unclear. <b><span style="color: red;">For the time being, I do feel comfortable in expecting a
stormier than normal winter for the eastern two-thirds of the country, with the
exact location of this active pattern to be determined but leaning in favor of
the Appalachia / Ohio Valley area</span></b>.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEieAPEI5mA45B3_oUN_k0uICbB8eFLlp5eBia-Wm_u87EjtP0bHWJ-Y0EVeZ-PGW2VK69CwfeXy94-2FqwvXCr5DwwBu8UmFEZ7QI0m-vLXEbCLjBLB8pa5lcnuYrhaemDqj7GqsQ3FpTEj/s1600/fig44.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="586" data-original-width="756" height="310" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEieAPEI5mA45B3_oUN_k0uICbB8eFLlp5eBia-Wm_u87EjtP0bHWJ-Y0EVeZ-PGW2VK69CwfeXy94-2FqwvXCr5DwwBu8UmFEZ7QI0m-vLXEbCLjBLB8pa5lcnuYrhaemDqj7GqsQ3FpTEj/s400/fig44.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 44: Analog-implied 50-millibar geopotential height anomalies for the 2019-2020 winter (ESRL)</td></tr>
</tbody></table>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgMDl3QawWYa695Fp_Z3CgHvW6WY1kOH3uAq6Cgcvyg-26_I6pxGMro71oCulHy1J_fRQB_CcQmvZ5u32KSUFMqQmyzZz4JoMzLBsZCdpf6Scc8M1wAcnuDsgoB5E5YQ8O23KqpX07Pp3Qb/s1600/fig45.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="586" data-original-width="756" height="310" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgMDl3QawWYa695Fp_Z3CgHvW6WY1kOH3uAq6Cgcvyg-26_I6pxGMro71oCulHy1J_fRQB_CcQmvZ5u32KSUFMqQmyzZz4JoMzLBsZCdpf6Scc8M1wAcnuDsgoB5E5YQ8O23KqpX07Pp3Qb/s400/fig45.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 45: Analog-implied 500-millibar geopotential height anomalies for the 2019-2020 winter (ESRL)</td></tr>
</tbody></table>
<div class="MsoNormal">
In Figure 44 above (top of the two images), we move up to the stratosphere and
examine geopotential height anomalies at the 50-millibar level during the
analog winters. The output is dramatically different than what we had expected
based on what the QBO is showing, with widespread above-normal geopotential
height anomalies across the upper latitudes suggestive of a weaker-than-normal
stratospheric polar vortex, likely instigating the below-normal temperature
anomalies across much of the country at the surface. <b><span style="color: red;">It seems that even with a weakening positive
QBO, history suggests the stratospheric polar vortex will lean to the weaker
side, bolstering chances for a cooler than normal winter across the country
here at the surface</span></b>.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Lastly, Figure 45 shows 500-millibar geopotential height
anomalies for our analog winters. The implied atmospheric pattern for the
winter is wildly supportive of below-normal temperatures in the United States,
with a ridge over the Bering Sea (negative WPO) which extends into the Gulf of
Alaska (negative EPO) and a strong high pressure area over Greenland (negative
NAO) which extends into the Arctic Circle (negative AO). While the past is not
necessarily indicative of the future, the fact that our analog winters show an
atmospheric flow so favorable for below-normal temperatures hints at the same
sort of result for the coming winter.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
To summarize, we constructed analog winters based on the
ENSO, AMO and QBO oscillations, with appropriate criteria to capture where they
are expected to be during the coming winter. After filtering out those winters
which did not appear in at least two of the three databases, and weighting
those that showed up across all three databases heavier, <b><u><span style="color: red;">our analog set suggests this winter will be
a colder-than-normal one for much of the country, with a more
active-than-normal storm track laying down above-normal precipitation anomalies
somewhere in the Central and East U.S., likely in or around the Appalachia /
Ohio Valley nexus</span></u></b>.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<o:p><br /></o:p></div>
<span style="font-family: "calibri"; font-size: 11.0pt; line-height: 107%;"><br clear="all" style="mso-special-character: line-break; page-break-before: always;" />
</span>
<br />
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b><u><span style="font-size: 18.0pt; line-height: 107%; mso-bidi-font-size: 11.0pt;">6. Forecast</span><o:p></o:p></u></b></div>
<div class="MsoNormal">
With all of this data and analysis at our disposal, below is
my 2019-2020 Preliminary Winter Forecast graphic.<o:p></o:p></div>
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgcfRKY-vitTe4rqOH_K4IvZZXCWZiLtCg6yOynsfgYdHpTvP_LQGHDtpbLYoalw3h4unhnip9iL6LZheq3yFu0NcrH_Z1soDlDFF_eq_NGoSTkoVi2u0bhTJRM0hdA77kY6BIMqc04-dXW/s1600/forecastgraph.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="825" data-original-width="1320" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgcfRKY-vitTe4rqOH_K4IvZZXCWZiLtCg6yOynsfgYdHpTvP_LQGHDtpbLYoalw3h4unhnip9iL6LZheq3yFu0NcrH_Z1soDlDFF_eq_NGoSTkoVi2u0bhTJRM0hdA77kY6BIMqc04-dXW/s640/forecastgraph.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Figure 46: The Weather Centre's Preliminary 2019-2020 Winter Forecast graphic.</td></tr>
</tbody></table>
<div>
<br /></div>
<div class="MsoNormal">
I expect a majority of the country to lean towards cooler
weather for the coming winter, based on the analog set and by extension based
on some of the key seasonal teleconnections we have gone over. I did not
highlight temperature anomalies along the West Coast given a combination of
high uncertainty (absence of a definitive PDO state) and my suspicion that a
colder Central and East U.S. would primarily transpire with a ridge of high
pressure just offshore the west coast, leaving coastal areas average to
slightly above-normal. I highlighted an area of higher confidence in
below-normal temperatures over portions of the Plains into the Rockies,
primarily urged on by the analog set and neutral-ENSO temperature composite
graphic. I refrained from highlighting temperature anomalies in the Northeast
because I’m not totally convinced a ridge of high pressure would not form
immediately offshore if the central part of the country were to be
below-normal, but even without any highlighting I do think the Northeast has a
better chance at leaning colder than normal for this winter.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<span style="font-family: "calibri"; font-size: 11.0pt; line-height: 107%;">In precipitation, I have pretty high confidence
in a swath of above-normal precipitation somewhere in the Central or East U.S.,
in my opinion most likely within the green shaded area. At the same time, the
forecast graphic reflects hints of a drier than normal winter in portions of
the Central U.S., though this will likely be dependent on how that above-normal
swath plays out. I see a predominant upside risk to precipitation anomalies in
the Northeast and along the East Coast, particularly if the strong ridge over
Greenland plays out as shown in the analog composite images. I once again did
not point out any anomalies in the West due to high uncertainty, but think it
is more plausible to have an active winter in the Pacific Northwest while the
Southwest leans drier. Again, however, this is dependent on the eventual PDO
state.</span><!--EndFragment-->
<br />
<span style="font-family: "calibri"; font-size: 11.0pt; line-height: 107%;"><br /></span>
<span style="font-family: "calibri"; font-size: 11.0pt; line-height: 107%;">Thank you for reading my Preliminary 2019-2020 Winter Forecast. Please feel free to share the article, link to it, tweet it, etc. My favorite part of making these massive forecasts is having other people take a look and providing their thoughts!</span><br />
<span style="font-family: "calibri"; font-size: 11.0pt; line-height: 107%;"><br /></span>
<span style="font-family: "calibri"; line-height: 107%;"><span style="color: red;"><b>The Official 2019-2020 Winter Forecast will be released on October 12, 2019 at 12:00 PM Central Time.</b></span></span><br />
<span style="font-family: "calibri"; font-size: 11.0pt; line-height: 107%;"><br /></span>
<span style="font-family: "calibri"; font-size: 11.0pt; line-height: 107%;">Andrew</span></div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com11tag:blogger.com,1999:blog-1448180228140749967.post-48617731188021334542019-06-22T16:08:00.001-05:002019-06-22T16:08:26.906-05:00June 30 - July 4 Potential Storm System<div dir="ltr" style="text-align: left;" trbidi="on">
A potential storm system looks to impact the United States in the June 30th through July 4th timeframe.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj8Ghfty_zuKMwk1MPxbXX_ZfFVFAaM6ZqEtWb-I1ahl_OlquKavjoDzMEpfFRoXxD3r5TCUHgn-U2-87Pt4HwELiCOiV5XqmhPRSXngSkkPhtzrLf9qVCWER94wU76Cra2j9OtAwI4OAX2/s1600/gfs_mslp_pcpn_wpac_7.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="717" data-original-width="1024" height="448" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj8Ghfty_zuKMwk1MPxbXX_ZfFVFAaM6ZqEtWb-I1ahl_OlquKavjoDzMEpfFRoXxD3r5TCUHgn-U2-87Pt4HwELiCOiV5XqmhPRSXngSkkPhtzrLf9qVCWER94wU76Cra2j9OtAwI4OAX2/s640/gfs_mslp_pcpn_wpac_7.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">MSLP and precipitation forecast for 1 AM Central Time, June 24.<br />Source: Tropical Tidbits</td></tr>
</tbody></table>
Model guidance sees a storm system moving northeastward parallel to the coast of Japan on June 23rd and 24th, as depicted in the image above. Upper-level flow indicates this system will be the finale for broadly stormy weather seen over the East Asian region as of late, and it is plausible that this will be the case in the United States as well.<br />
<br />
Regular readers of this blog in the past will know that I frequently use a teleconnection whereby weather phenomena occurring over and near Japan correlate to similar phenomena in North America roughly 6-10 days later. I am employing this again here, and extrapolating the above model graphic gives us a potential storm system occurring in the United States in the June 30 - July 4 period.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgsCz3Zom5wqAoeObfir8QkLWG5UyXiJyxllnMJM2oQNztXJ1ELqUV9v1mWCjnLFutmBPMiPL4KvpEdU-2JYoDIoB0zMqmU4ENDi2InR6h686T8bsDgcBbwTtv-b5L2k84Lm9MLm3yWk1xK/s1600/gfs-ens_z500a_namer_39.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="638" data-original-width="1024" height="398" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgsCz3Zom5wqAoeObfir8QkLWG5UyXiJyxllnMJM2oQNztXJ1ELqUV9v1mWCjnLFutmBPMiPL4KvpEdU-2JYoDIoB0zMqmU4ENDi2InR6h686T8bsDgcBbwTtv-b5L2k84Lm9MLm3yWk1xK/s640/gfs-ens_z500a_namer_39.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 500-millibar geopotential height anomalies for 7PM Central Time, July 1st.<br />Source: Tropical Tidbits</td></tr>
</tbody></table>
Ensemble guidance suggests ridging will become a predominant theme over the western two-thirds of the country as an upper-level low nudges its way on over Greenland to promote +NAO conditions (which bring about more zonal upper-level flow over North America), and troughing in the Gulf of Alaska supports a modest ridge in western Canada. The consequence looks to be lower heights evolving over the waters just offshore of the Eastern Seaboard, and it seems plausible that any storm system that comes about during this timeframe will be encouraged to traverse the South (or the nation's midsection) on a rather-zonal path before being drawn northeast as it approaches the Mid-Atlantic, with the storm seeking the path of least resistance towards those lower geopotential heights. Coming days will provide for more accurate forecasts as the potential storm approaches, of course, but at this time it appears as though any potential storm system in the June 30 - July 4 period will most likely impact the South and East U.S., as opposed to a storm track that takes in northeast across the Plains like we saw last month into early June.<br />
<br />
<span style="font-size: large;"><i><u>To Summarize:</u></i></span><br />
<br />
- There is potential for a storm system to impact the United States in the June 30 - July 4 period.<br />
- Based on the projected atmospheric flow, any storm that does develop would be most inclined to move west-to-east across the South before perhaps trying to shift a bit northeast near the Eastern Seaboard.<br />
- As always, considerable uncertainty exists, especially with regards to the projected track of any storm system.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-28836038485673700762019-06-21T17:00:00.000-05:002019-06-21T17:00:08.938-05:00June ENSO Update: El Nino Increasingly In Danger for Fall and Winter<div dir="ltr" style="text-align: left;" trbidi="on">
It seems to me that the El Nino is in increasing danger for its survivability during the fall and winter months, with a variety of recent observations suggesting the El Nino has weakened and that near- to medium-term prospects are similarly downbeat. Click on any image to enlarge it.<br />
<br />
We first begin with a look at the latest sea surface temperature (SST) raw values and anomalies.<br />
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg9c-t2x6ISmjNZ88C0axYyB9ICVB-WQ14B2E7PPTCl2ucSqhR6FMqC-iR9IygoJ6d0pWL82iwMacyUnYhdZMCMrpKEDmy3_Ha-W7J9CPMBp2g3-ucoXcAwmZ9ct2KcHmcfFWxpRqTGXxq9/s1600/weekly+anoms+and+obs.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="828" data-original-width="641" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg9c-t2x6ISmjNZ88C0axYyB9ICVB-WQ14B2E7PPTCl2ucSqhR6FMqC-iR9IygoJ6d0pWL82iwMacyUnYhdZMCMrpKEDmy3_Ha-W7J9CPMBp2g3-ucoXcAwmZ9ct2KcHmcfFWxpRqTGXxq9/s640/weekly+anoms+and+obs.gif" width="494" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Observed sea surface temperatures (top panel) and SST anomalies (bottom panel) for the seven-day period centered on June 12th.<br />Source: CPC</td></tr>
</tbody></table>
<div>
<div>
The actual observed temperatures, as shown in the top panel, are arguably more pessimistic with regard to the current state of the El Nino than temperature anomalies reflect. Indeed, where the top panel seems to suggest a total erosion of warmer waters and a filling-in of cooler waters (which appears symptomatic of a La Nina), the anomalies in the bottom panel are more sanguine, reflecting aggregate-neutral anomalies from the western coast of Ecuador to about 130 degrees West longitude. To the west of that, a swath of above-normal SSTs reflect the presence of El Nino conditions in at least some part of the Equatorial Pacific. </div>
<div>
<br /></div>
<div>
In other words, while sea surface temperature anomalies (SSTAs) are rather mixed in the eastern Equatorial Pacific, it certainly looks more like an El Nino than a La Nina, a relief for fans of winter weather in the eastern United States. Of course, it’s never as simple as merely viewing one or two pieces of data. This situation gets far more intricate. In fact, there’s four different regions of the Equatorial Pacific that each make the situation rather intricate.</div>
</div>
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjuGTBaYM3Ijt5xlMHs9ApbDp2bfOZUQ3kNbVfn6wXLc_fMSAxCZ7DP3z0JytsIzQT0DhM1Lbq1W2pTGeB3TVKQQRKA1oZ9TOjZVGUr3vWlFyIQxc8_2zRuSBD17XP_yCGr38KGB3g-8HN_/s1600/four+nino+regions.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="251" data-original-width="572" height="280" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjuGTBaYM3Ijt5xlMHs9ApbDp2bfOZUQ3kNbVfn6wXLc_fMSAxCZ7DP3z0JytsIzQT0DhM1Lbq1W2pTGeB3TVKQQRKA1oZ9TOjZVGUr3vWlFyIQxc8_2zRuSBD17XP_yCGr38KGB3g-8HN_/s640/four+nino+regions.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The four regions used for monitoring the ENSO phenomenon.<br />Source: CPC</td></tr>
</tbody></table>
<div>
<div>
There are four different parts of the Equatorial Pacific that meteorologists monitor to determine the state of the El Nino-Southern Oscillation (ENSO), the phenomenon that defines an El Nino or La Nina. When these sea surface temperatures are above normal, we call it an 'El Nino' event. When these anomalies are below-normal, we call it a 'La Nina' event. While we monitor the entire Equatorial Pacific to analyze the ENSO phenomenon, these four primary "zones" are:</div>
<div>
<br /></div>
<div>
Nino 1+2. This is a small slice of the Pacific located between the Equator and the 10º South latitude line, extending from the far western tip of Peru to the 90º West longitude line.</div>
<div>
<br /></div>
<div>
Nino 3. This is a larger slice of the Equatorial Pacific which spans from 5º North to 5º South latitude lines, and from 90º West to 150º West longitude lines.</div>
<div>
<br /></div>
<div>
Nino 4. This is also a larger slice, and also extends between 5ºN and 5ºS on the latitude markers. For Nino 4, however, the space is spread by longitude from 150º West to about 160º East, crossing the dateline in the process.</div>
<div>
<br /></div>
<div>
Nino 3.4. This is the critical area to watch, and is typically viewed as the primary space with which to assess the state of the ENSO phenomenon. Spatially, it extends from 5ºN-5ºS latitudinally, and 120º West to 165º West longitudinally.</div>
<div>
<br /></div>
<div>
Why do we break this space up into four different pieces rather than just average out the sea surface temperature anomalies and call it a day? A number of scientists with far more knowledge and research than I have come to determine that there can be more than one type of El Nino - where typically El Nino's bring warmer than normal waters to the eastern Pacific, an "El Nino Modoki" event brings warm waters to the western Pacific, and cooler waters to the eastern Pacific. This is not a trivial difference, but for our purposes here, we won't dive into that topic. For now, the key is understanding there are four different regions in which we monitor the ENSO phenomenon, with the Nino 3.4 region broadly being of most importance.</div>
<div>
<br /></div>
<div>
Now that we have an understanding of the parts of the Equatorial Pacific that are most important when analyzing the state of the ENSO phenomenon, we can proceed on to other observational data as of late.</div>
</div>
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjzV_2uYRRGEP99Tmz7PW12uDBSiGPxbEinru9nCrsR2CcigOhwWUWvoyAvqZLPxmlfcG50-H0PUTb9mwu01rk2_oH9bvr9YIMS4iJMjolE8Tk8FI1gCucmy-HTmexfRex4GjtC9xklSYQA/s1600/four+nino+regions+anoms.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="352" data-original-width="306" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjzV_2uYRRGEP99Tmz7PW12uDBSiGPxbEinru9nCrsR2CcigOhwWUWvoyAvqZLPxmlfcG50-H0PUTb9mwu01rk2_oH9bvr9YIMS4iJMjolE8Tk8FI1gCucmy-HTmexfRex4GjtC9xklSYQA/s640/four+nino+regions+anoms.gif" width="556" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">SST Anomalies over the last year for the four ENSO monitoring regions.<br />Source: CPC</td></tr>
</tbody></table>
<div>
<div>
When breaking down observed SST anomalies over the four ENSO regions for the past year, as in the image above, it’s clear that this El Nino event is not clean-cut across the board. In Nino region 4, anomalies were recently seen about 1 degree C, a level that has been breached a number of times over the last year and a pretty strong signal of an El Nino event being in place – at least for that region. In Nino region 3.4, while positive SSTAs have been consistently seen over the past year, they aren’t at the same magnitude as in region 4, with a recent peak at the end of May only barely reaching 1.0 degree C above normal. Still, with this region consistently exhibiting anomalies above +0.5 degrees C, this region is also indicative of an El Nino, even if the signal is not as strong as in region 4.</div>
<div>
<br /></div>
<div>
Continuing eastward, region 3 is where this analysis begins to run into some troubles. While the recent history of region 3 anomalies has been positive and mostly above +0.5 degrees C, this same region saw anomalies turn negative as recently as early September 2018, with most-recent readings looking to dip below +0.5 degrees C to possibly a four-month low. Again, anomalies in this region have been pretty consistent in remaining above the +0.5 degree C level, which tells us an El Nino seems to be present. But the last year has shown anomalies that aren’t as stable as those seen in the last few months, which (at the very least) informs us that the current El Nino seems less established in eastern Eqautorial Pacific waters as compared to waters further west. Indeed, moving to Nino 1+2, this concept is confirmed. Anomalies are only now beginning to exit marginally-negative levels in this region, anomalies on a magnitude that set a ~10 month low earlier this month. Nino 1+2 seems to be more reflective of an ENSO-neutral set-up as opposed to the El Nino environment portrayed by the other three ENSO monitoring regions.</div>
<div>
<br /></div>
<div>
So far, we’ve established that there is indeed an El Nino present as per sea surface temperature anomalies. This is nothing new; the Climate Prediction Center has maintained an El Nino Advisory for some time now to reflect this. Let’s now turn to convective anomalies along the Equatorial Pacific and discuss something called the Walker Circulation.</div>
</div>
<div>
<br /></div>
<div>
<div>
If you’ve learned about the weather to some degree, you’ll know that a critical component to meteorology in the aggregate is the concept of heat transport. Whether it’s certain large-scale circulations like the Walker Circulation or Hadley Cell, or smaller-scale but still significant features like Rossby Waves or Kelvin Waves, the atmosphere has a plethora of ways by which it moves heat around the planet. Here, we’ll discuss the Walker Circulation.</div>
</div>
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj-e54Zh7Kc6c4nNUrxu91xzX22-42d3Qgxp-QgNuiP1W0ajLyErgTNzjjMyvK0VvlLFrTYak6xmpIggkMLKhrgn_ThVenmTxIBIQ_QGe_vBlgAd0SBVMfAgTcSrdKUCZl38ZL6rQBpLAnk/s1600/LaNina+walker+circulation.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="624" data-original-width="696" height="572" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj-e54Zh7Kc6c4nNUrxu91xzX22-42d3Qgxp-QgNuiP1W0ajLyErgTNzjjMyvK0VvlLFrTYak6xmpIggkMLKhrgn_ThVenmTxIBIQ_QGe_vBlgAd0SBVMfAgTcSrdKUCZl38ZL6rQBpLAnk/s640/LaNina+walker+circulation.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Typical Walker Circulation pattern in a La Nina.<br />Source: Wikipedia</td></tr>
</tbody></table>
<div>
<div>
The Walker Circulation, in a nutshell, is an atmospheric circulation along the Equatorial Pacific that is closely intertwined with the ENSO phenomenon. Indeed, the ENSO phenomenon itself is a consequence (and, to a degree, an instigator) of heat transport in the atmosphere and in the ocean. The Walker Circulation changes with regard to longitudinal position of rising and sinking air depending on the state of the ENSO phenomenon, but the constant is that it involves an area of rising air, movement aloft of this air either to the west or to the east, and subsequent sinking air back to the surface before it moves either west or east (opposite the direction the air moved when it was aloft) back to the starting point to create that ‘circulation’ feature. </div>
<div>
<br /></div>
<div>
The image above shows the Walker Circulation in a La Nina event as an example of how the circulation works. How can we tell this is a La Nina orientation of the Walker Circulation (aside from it being given by accessing the image)? Note the above-normal water temperatures in the far western Equatorial Pacific, just offshore Australia. This prompts convective activity, which sends warm air aloft. The air then travels to the east before cooling and then sinking over the waters just offshore of Peru. This sinking motion discourages thunderstorm development by suppressing air from rising. This air hits the surface of the water offshore Peru, and easterly surface winds transport that air back to where it started, just offshore of Australia. As a consequence of those easterly surface winds, water “piles up” offshore of Australia, a consequence of those surface winds pushing the water up against land. My favorite comparison to this phenomenon comes from the <a href="https://www.eoas.ubc.ca/courses/atsc113/sailing/met_concepts/09-met-winds/9c-walker-cell-enso/">University of British Columbia</a> where the author compares this “piling up” of water to someone in a bathtub blowing air towards the other end of the bathtub. In this scenario, the water is pushed to the other side of the bathtub and “piles up” there as well – albeit on a far smaller scale. To be sure, the actual piling up of water in the western Pacific from a La Nina Walker Circulation is also very small relative to the depth of the ocean, but it is still noticeable enough to address it. </div>
<div>
<br /></div>
<div>
Let’s use observational data now to see if we can identify how the Walker Circulation is acting, to try and ascertain if the atmosphere is joining sea surface temperatures in signaling the presence of an El Nino.</div>
</div>
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgsseFvbiBem9FR0xtzca7uRa6T7L8yMSFdrZT5yKfkZjVE7ZfzQ-9bEagD4tiTKJZ8WpMyFr4io0kSzpb6X5lc3DDB_Q9BB_DcdO-KMjGCh5w5KXyuSuNbS24-xH5K2FBiowkaGf-kovcp/s1600/olr+anomalies.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="216" data-original-width="483" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgsseFvbiBem9FR0xtzca7uRa6T7L8yMSFdrZT5yKfkZjVE7ZfzQ-9bEagD4tiTKJZ8WpMyFr4io0kSzpb6X5lc3DDB_Q9BB_DcdO-KMjGCh5w5KXyuSuNbS24-xH5K2FBiowkaGf-kovcp/s640/olr+anomalies.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">OLR Anomalies over the Tropical Pacific from May 23rd through June 17th.<br />Source: CPC</td></tr>
</tbody></table>
<div>
<div>
The image above is titled with a strange acronym – “OLR”. OLR stands for Outgoing Longwave Radiation, and while much smarter people with much more research can provide a much better interpretation of it, for the purposes of this post we only need to understand how it relates to convection. Negative values of OLR correspond to increased convective activity, while positive values of OLR correspond to suppressed convective activity. Therefore, rising air / thunderstorms in the above image are shown by cooler colors, while sinking air / suppressed convective activity is shown by warmer colors.</div>
<div>
<br /></div>
<div>
Taking a gander at the above image, enhanced convection is seen across a good chunk of the Equatorial Pacific, namely between the longitude lines of about 150 degrees East to 150 degrees West. In contrast, broadly neutral to slightly positive OLR anomalies are seen east of the aforementioned area, extending all the way to the western coasts of Peru and Ecuador. With regard to the Walker Circulation, it seems as though the area of rising air is located east of Papua New Guinea, with that air then transported to the east and allowed to sink over the waters west of Ecuador. The surface winds would then appear to transport that wind to the west, completing the circulation. </div>
<div>
<br /></div>
<div>
The only problem here is, this sort of circulation resembles the Walker Circulation in a La Nina, not an El Nino. In other words, if the Walker Circulation really is oriented like the paragraph above describes, water temperatures may support an El Nino but the atmosphere is more supportive of a La Nina.</div>
</div>
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-RThySS41eBlmhcVcM_pES4CrlPd1RKBujX0TOJCXvnb2d43abQUNln6PbPzzjjVzn5_PFNMFgoHYq1QhksyInwALKbN-Cl4ged9c5Ps-s5os9_WfipoOERcwp8BTZLGXpQXzg3_Tl7XD/s1600/compday.jFj0l9Opm8.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="542" data-original-width="700" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-RThySS41eBlmhcVcM_pES4CrlPd1RKBujX0TOJCXvnb2d43abQUNln6PbPzzjjVzn5_PFNMFgoHYq1QhksyInwALKbN-Cl4ged9c5Ps-s5os9_WfipoOERcwp8BTZLGXpQXzg3_Tl7XD/s640/compday.jFj0l9Opm8.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Observed 200-millibar vector winds from May 23rd through June 17th.<br />Source: ESRL</td></tr>
</tbody></table>
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiKZrnqbzXT-INVFZ0PoBew6H3q3xoFByq4tt5G8NVOsYSY5wEqqr7f2gGWnamK5pS1NN-1zwo_OcHQFxLdnGxXUWaGGuBtC9kweDMAzHtzY19aGEuxhNzgIAwGI4GHLctpWkeFcwjkDVYO/s1600/troppac+sfc+wind+walker.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="542" data-original-width="700" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiKZrnqbzXT-INVFZ0PoBew6H3q3xoFByq4tt5G8NVOsYSY5wEqqr7f2gGWnamK5pS1NN-1zwo_OcHQFxLdnGxXUWaGGuBtC9kweDMAzHtzY19aGEuxhNzgIAwGI4GHLctpWkeFcwjkDVYO/s640/troppac+sfc+wind+walker.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Observed surface wind vectors from May 23rd through June 17th.<br />Source: ESRL</td></tr>
</tbody></table>
<div>
<div>
We can identify what the Walker Circulation is doing by checking out some composites of atmospheric variables as of late. For the benefit of comparison, I will view these variables using the same timeframe presented in the OLR graphic of May 23rd to June 17th. </div>
<div>
<br /></div>
<div>
The top image above shows mean 200-millibar winds over the Tropical Pacific basin for this timeframe. In this graphic, we see the wind vector arrows looking like they’re ‘blossoming out’ away from a center point roughly located along the 180 degree line of longitude. This is called divergence, and represents air rising and then spreading out aloft. In severe weather, divergence aloft is crucial to sustaining thunderstorms, and the process is no different here. It is also no coincidence that the divergence aloft is juxtaposed with observed enhanced convection over roughly the same area – if there was convergence aloft and those arrows pointed in towards each other, convection would be suppressed. After the air rises east of Papua New Guinea, it has been transported to the east as shown in the graphic, before those vector arrows seem to converge at around the 120 or 130 degree West line of longitude along the Equator. This is that convergence phenomenon I just discussed, and represents air aloft that is coming together and now sinking.</div>
<div>
<br /></div>
<div>
After the air sinks back towards the surface, the second panel allows us to see how surface winds have been behaving over this ~month timeframe beginning in late May. After reaching the surface at around the 120 degree West line of longitude, surface winds have sent this air to the west and back to the starting point at about the 180 degree line of longitude, where the circulation starts over again.</div>
<div>
<br /></div>
<div>
In summary, over the last month the Walker Circulation has seen convection / rising air over about the 180 degree line of longitude, with the air then transported to the east aloft before converging and sinking at roughly the 120-130 West line of longitude. Once back at the surface, this air has been transported to the west back to its starting point, completing the circulation. Is this representative of an El Nino or La Nina? Let’s view the two Walker Circulation composites for each situation below.</div>
</div>
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi80d4rmbzCXU2HcpDgE84NZPAXo9QZMlT3w9veYmN8LSPwZoZvCHTguZfnpbLWpd9rof4FnIJlQHyR8Vaw-8yqlYRRSK67mGg8tGenfEGk-rOSoDkEIwQMkB8HJg68sN7Bf_HqTLYBSwnf/s1600/el+nino+walker+circ+UBC.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="300" data-original-width="600" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi80d4rmbzCXU2HcpDgE84NZPAXo9QZMlT3w9veYmN8LSPwZoZvCHTguZfnpbLWpd9rof4FnIJlQHyR8Vaw-8yqlYRRSK67mGg8tGenfEGk-rOSoDkEIwQMkB8HJg68sN7Bf_HqTLYBSwnf/s640/el+nino+walker+circ+UBC.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Typical Walker Circulation cells in an El Nino state, with shading indicating SST anomalies.<br />Source: UBC</td></tr>
</tbody></table>
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKYgw0aLz-PcxWmSsMZrxMwR7RU5BH0xMHDTFwYmoM0iQilbSfTeNiSB2-wXehj1W9onLKKT_4KN4INZ2ithlU8X4mn69xUM5RmP9a3LX2v2A61iDZip5iku-oA7gPBypeIKS_RW-OGvus/s1600/la+nina+walker+circ+UBC.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="300" data-original-width="600" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKYgw0aLz-PcxWmSsMZrxMwR7RU5BH0xMHDTFwYmoM0iQilbSfTeNiSB2-wXehj1W9onLKKT_4KN4INZ2ithlU8X4mn69xUM5RmP9a3LX2v2A61iDZip5iku-oA7gPBypeIKS_RW-OGvus/s640/la+nina+walker+circ+UBC.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Typical Walker Circulation cells in a La Nina state, with shading indicating SST anomalies.<br />Source: UBC</td></tr>
</tbody></table>
<div>
<div>
When comparing the above two Walker Circulation composites for the two ENSO states to what was described / observed above, the circulation observed over the last month doesn’t line up exactly with either image. Looking solely at the recent flow aloft and comparing it to the above two images, the recent Walker Circulation has certainly been more akin to that seen in a La Nina. As both the La Nina image above and the recently observed flow show, upper-level winds are shown to be moving eastward after the 180 degree longitude line, and move westward over the waters offshore of Peru and Ecuador. This same pattern is shown in the La Nina image above, while the opposite is shown in the El Nino composite. At the surface, winds also reflect a La Nina pattern to some degree, with westward winds both observed and shown in the La Nina composite west of the 130 degree West longitude line, but observed winds are still easterly from the 130 degree West line of longitude to the coast of Ecuador, opposite of what a La Nina would see for that area. Also posing trouble in our interpretation of the state of the Walker Circulation is that observed areas of enhanced and suppressed convection don’t really line up with either composite graphic precisely, and again only seem to “lean” more towards a La Nina than an El Nino Walker Circulation. </div>
<div>
<br /></div>
<div>
What do we then gather from all of this? Based on the behavior of the Walker Circulation, it seems that the atmosphere is more reflective of a La Nina than it is of an El Nino, in contrast to observed SST anomalies which promote a solid El Nino. This can be confirmed by viewing the Southern Oscillation Index (SOI), which has been seen at weakly-negative values (indicative of an El Nino) but also seen as “consistently near zero”, perhaps quantifying the somewhat-murky atmospheric features described above.</div>
</div>
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKuLM3ZCdyTySUcuy6JcxqnvJXx2Q9HF8v5q4wreyMI-5l9V0EJ63w6cO3CkAT9VL8yKgxFpc0wuBqz53LZZkaIJNRJ5HrJl4VETAJCdGThZPCLPmVfT4O5rZxhBHM3OItaGFo_-qJ_LkX/s1600/SOI.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="340" data-original-width="454" height="478" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKuLM3ZCdyTySUcuy6JcxqnvJXx2Q9HF8v5q4wreyMI-5l9V0EJ63w6cO3CkAT9VL8yKgxFpc0wuBqz53LZZkaIJNRJ5HrJl4VETAJCdGThZPCLPmVfT4O5rZxhBHM3OItaGFo_-qJ_LkX/s640/SOI.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Recent history of the Southern Oscillation Index (SOI).<br />Source: BOM</td></tr>
</tbody></table>
<div>
<div>
So, we’ve got oceanic temperatures which are in favor of an El Nino, and atmospheric patterns which are broadly more akin to a La Nina than an El Nino. To try and remedy this discrepancy, we now look to the behavior of water temperatures in the Pacific basin below the surface.</div>
</div>
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhRuHXqjDZo6DAUzyIpi7ppIFHVcB4WOyWOcYpSNGUtk-6MHiJPtKd0czuL1E9siYfggjtYycgVKaee3OlvZ0QnKB1H7Qoclf_kSXZFeAM1ZwCx9Bwi27K25cJt6j3DUqlljBeU74D6izHv/s1600/updated+upperoceanheatanom.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="677" data-original-width="536" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhRuHXqjDZo6DAUzyIpi7ppIFHVcB4WOyWOcYpSNGUtk-6MHiJPtKd0czuL1E9siYfggjtYycgVKaee3OlvZ0QnKB1H7Qoclf_kSXZFeAM1ZwCx9Bwi27K25cJt6j3DUqlljBeU74D6izHv/s640/updated+upperoceanheatanom.png" width="506" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Upper-ocean heat anomalies along the Equator.<br />Source: CPC</td></tr>
</tbody></table>
<div>
<div>
El Nino and La Nina events can be driven by Equatorial Kelvin Waves, and whether the wave moving eastward along the Equatorial Pacific is upwelling or downwelling. If that sentence made you raise an eyebrow, you're most likely not alone. I can assure you, though, it's actually pretty simple to understand. Let's break it down.</div>
<div>
<br /></div>
<div>
The phrase 'Equatorial Kelvin Wave' seems intimidating, so for our purposes here all we need to know is that, from time to time, these Equatorial Kelvin waves develop in the western part of the Equatorial Pacific and gradually move eastward along the Equator. When they move eastward along the Equator, they can be either 'downwelling' or 'upwelling' waves.</div>
<div>
Consider the explanation of a 'downwelling' Equatorial Kelvin wave as described by the NOAA:</div>
<div>
<br /></div>
<div>
<i>"Normally, winds blow from east to west across the tropical Pacific, which piles up warm water in the western Pacific. A weakening of these winds starts the surface layer of water cascading eastward..."</i></div>
<div>
<br /></div>
<div>
In other words, if this wind pattern that blows winds from east to west breaks down, that warmer than normal water begins pushing eastward along the Equatorial Pacific. This anomalously warm water works its way eastward gradually and tends to sustain itself in the process. As a consequence, downwelling Equatorial Kelvin waves tend to be associated with El Nino events. You can see my annotations of downwelling Kelvin waves as solid lines on the above image.</div>
</div>
<div>
<br /></div>
<div>
<div>
On the flip side, an 'upwelling' Equatorial Kelvin wave can be thought of as the ocean waters trying to get itself a little more in balance in the wake of this very warm downwelling wave. Thus, an upwelling wave again features a Kelvin wave slowly progressing eastward, but this time it cools down the upper-ocean waters to a degree that upwelling Kelvin waves are generally associated more with La Nina events. I’ve made an attempt to outline downwelling Kelvin Waves with gray lines, and upwelling Kelvin Waves with dark blue lines in the image above.</div>
<div>
<br /></div>
<div>
---</div>
<div>
<br /></div>
<div>
Over the last year, we have seen several instances where warmer than normal waters traverse the Equatorial Pacific, as shown by the streaks of warmer colors. I’ve annotated these as downwelling Kelvin Waves. We have also seen a couple instances where either the warmer than normal anomalies subside in an eastward-moving fashion, or the anomalies outright flip to below-normal levels. I have highlighted these as upwelling Kelvin Waves in the above graphic. There are a couple items in particular I want to discuss with regards to the graphic.</div>
<div>
<br /></div>
<div>
First is how the recent downwelling waves seem to have been weaker with each iteration since a strong one traversed the basin beginning in late September 2018. With the exception of the wave which eventually strengthened significantly in March, recent downwelling waves have proved underwhelming. This poses a risk to the sustainability of the El Nino, as weaker downwelling waves make the El Nino more vulnerable to a deterioration to neutral-ENSO conditions, or even marginal La Nina conditions, especially if a strong upwelling wave propagates through with the atmosphere already unconvinced over the presence of an El Nino.</div>
<div>
<br /></div>
<div>
Second is how the far western Pacific has become increasingly cooler over the last several months. Indeed, anomalies on the order of between -1 and -1.5 degrees C have most recently been spotted right at the 150 degree East line of longitude, which marks the coldest anomalies over that part of the basin in at least a full calendar year. If this is the start of another upwelling Kelvin Wave and these deeper negative anomalies sustain themselves, there is a risk that the El Nino takes a severe hit in SSTAs, perhaps threatening its sustainability into the fall and winter months.</div>
</div>
<div>
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUitDb-CKYspYP6PVYOd7Q_qTu8E1D_cVDNnWarSBpTIGXyG0M2y5XZwJYqCR20YLOh7CF3UhDKAmY9OMJMVIvoHgOd_F_68lHJps8BE3eFwSafZU5jRflaIuRyu_EYElotmCYdfx0XgaZ/s1600/nino34.ENSMEAN_plus.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="618" data-original-width="800" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUitDb-CKYspYP6PVYOd7Q_qTu8E1D_cVDNnWarSBpTIGXyG0M2y5XZwJYqCR20YLOh7CF3UhDKAmY9OMJMVIvoHgOd_F_68lHJps8BE3eFwSafZU5jRflaIuRyu_EYElotmCYdfx0XgaZ/s640/nino34.ENSMEAN_plus.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Model guidance for the Nino 3.4 region sea surface temperature anomalies.<br />Source: CPC</td></tr>
</tbody></table>
<div>
<div>
Seasonal model guidance is picking up on the increasingly-fragile El Nino. Where there is a good deal of spread between the individual model solutions in the above graphic, the general framework sees the Nino 3.4 region warming slightly this month into next before weakening through the fall, with a modest recovery back into weak-El Nino territory for the winter months. These models have a number of ensemble members of their own, which can all be tracked on a single image. As you might imagine, that image is very messy and does more harm than good in my opinion with regard to trying to explain what’s going on, hence why I’m not posting it here. However, I can tell you that the suite of ensembles and models show quite a spread in the forecast, implying substantial uncertainty over how the El Nino will evolve in the coming months. There is, of course, always uncertainty in these kinds of forecasts, but even for only a two-month forecast, the variation in ensemble forecasts for Nino 3.4 anomalies is from about -0.7 degrees C to about +1.75 degrees C. By December’s forecast, that variation blows out to a range of about -1.0 degrees C to more than +2.5 degrees C. The variation speaks to model uncertainty over how the El Nino will transpire over the next several months, including questions as to if it will be able to survive in what could be a hostile environment.</div>
</div>
<div>
<br /></div>
<div>
<br /></div>
<div>
<div>
<span style="font-size: large;"><b><i>To Summarize:</i></b></span></div>
<div>
-<span class="Apple-tab-span" style="white-space: pre;"> </span>Current oceanic conditions indicate the presence of an El Nino, with warmer than normal SSTs present across most of the ENSO monitoring regions.</div>
<div>
-<span class="Apple-tab-span" style="white-space: pre;"> </span>Atmospheric conditions are more ambiguous, appearing more in line with vaguely-La Nina conditions as opposed to El Nino conditions.</div>
<div>
-<span class="Apple-tab-span" style="white-space: pre;"> </span>Further weakening of the El Nino appears likely moving into late summer and fall, which could bring the survival of the El Nino into question. </div>
<div>
-<span class="Apple-tab-span" style="white-space: pre;"> </span>For the time being, it seems prudent to continue with the assumption of a weak El Nino moving into fall and early winter, but close monitoring is needed over the coming months as the El Nino is increasingly fragile.</div>
<div>
<br /></div>
<div>
<br /></div>
<div>
Andrew</div>
</div>
</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com1tag:blogger.com,1999:blog-1448180228140749967.post-4896092778137947592019-06-19T17:23:00.000-05:002019-06-19T17:23:10.579-05:00Ambiguous SSTAs, Wind Patterns Could Render PDO Ineffective for Fall<div dir="ltr" style="text-align: left;" trbidi="on">
<div class="" style="clear: both; text-align: center;">
<span style="text-align: left;">A combination of ambiguous sea surface temperature anomalies
(SSTAs) and wind patterns over the Pacific mean that the Pacific Decadal
Oscillation (PDO) could be rendered for a little while as too ambiguous to use
in seasonal forecasting as we move into the fall. Click on any image to enlarge it.</span></div>
<div class="MsoNormal">
<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhM2IWVUbBxqRQnQjjEMxY24O8gVXhCUP4NtfMYlzI_utWcNAcAU4V7uJseU2ZxETkikm_K5N8DGBQZd5D1_pbZaWfxzYD_BOZ7Qsq7dqJYJ0VvQLowHiH2qK9TtSlju2j9bli46suq1Y6m/s1600/Picture1.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="399" data-original-width="975" height="260" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhM2IWVUbBxqRQnQjjEMxY24O8gVXhCUP4NtfMYlzI_utWcNAcAU4V7uJseU2ZxETkikm_K5N8DGBQZd5D1_pbZaWfxzYD_BOZ7Qsq7dqJYJ0VvQLowHiH2qK9TtSlju2j9bli46suq1Y6m/s640/Picture1.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">
<!--[if gte mso 9]><xml>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]-->
<!--[if gte mso 9]><xml>
<w:WordDocument>
<w:View>Normal</w:View>
<w:Zoom>0</w:Zoom>
<w:TrackMoves/>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:DoNotPromoteQF/>
<w:LidThemeOther>EN-US</w:LidThemeOther>
<w:LidThemeAsian>X-NONE</w:LidThemeAsian>
<w:LidThemeComplexScript>X-NONE</w:LidThemeComplexScript>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:SnapToGridInCell/>
<w:WrapTextWithPunct/>
<w:UseAsianBreakRules/>
<w:DontGrowAutofit/>
<w:SplitPgBreakAndParaMark/>
<w:EnableOpenTypeKerning/>
<w:DontFlipMirrorIndents/>
<w:OverrideTableStyleHps/>
</w:Compatibility>
<m:mathPr>
<m:mathFont m:val="Cambria Math"/>
<m:brkBin m:val="before"/>
<m:brkBinSub m:val="--"/>
<m:smallFrac m:val="off"/>
<m:dispDef/>
<m:lMargin m:val="0"/>
<m:rMargin m:val="0"/>
<m:defJc m:val="centerGroup"/>
<m:wrapIndent m:val="1440"/>
<m:intLim m:val="subSup"/>
<m:naryLim m:val="undOvr"/>
</m:mathPr></w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" DefUnhideWhenUsed="false"
DefSemiHidden="false" DefQFormat="false" DefPriority="99"
LatentStyleCount="382">
<w:LsdException Locked="false" Priority="0" QFormat="true" Name="Normal"/>
<w:LsdException Locked="false" Priority="9" QFormat="true" Name="heading 1"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 2"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 3"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 4"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 5"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 6"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 7"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 8"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 9"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 9"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 1"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 2"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 3"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 4"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 5"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 6"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 7"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 8"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 9"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="footnote text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="header"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="footer"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index heading"/>
<w:LsdException Locked="false" Priority="35" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="caption"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="table of figures"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="envelope address"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="envelope return"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="footnote reference"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation reference"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="line number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="page number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="endnote reference"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="endnote text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="table of authorities"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="macro"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="toa heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 5"/>
<w:LsdException Locked="false" Priority="10" QFormat="true" Name="Title"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Closing"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Signature"/>
<w:LsdException Locked="false" Priority="1" SemiHidden="true"
UnhideWhenUsed="true" Name="Default Paragraph Font"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Message Header"/>
<w:LsdException Locked="false" Priority="11" QFormat="true" Name="Subtitle"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Salutation"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Date"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Block Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Hyperlink"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="FollowedHyperlink"/>
<w:LsdException Locked="false" Priority="22" QFormat="true" Name="Strong"/>
<w:LsdException Locked="false" Priority="20" QFormat="true" Name="Emphasis"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Document Map"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Plain Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="E-mail Signature"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Top of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Bottom of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal (Web)"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Acronym"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Address"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Cite"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Code"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Definition"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Keyboard"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Preformatted"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Sample"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Typewriter"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Variable"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal Table"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation subject"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="No List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Contemporary"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Elegant"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Professional"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Balloon Text"/>
<w:LsdException Locked="false" Priority="39" Name="Table Grid"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Theme"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 9"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Placeholder Text"/>
<w:LsdException Locked="false" Priority="1" QFormat="true" Name="No Spacing"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading"/>
<w:LsdException Locked="false" Priority="61" Name="Light List"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 1"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 1"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 1"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 1"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 1"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Revision"/>
<w:LsdException Locked="false" Priority="34" QFormat="true"
Name="List Paragraph"/>
<w:LsdException Locked="false" Priority="29" QFormat="true" Name="Quote"/>
<w:LsdException Locked="false" Priority="30" QFormat="true"
Name="Intense Quote"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 1"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 1"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 1"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 1"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 1"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 1"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 1"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 2"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 2"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 2"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 2"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 2"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 2"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 2"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 2"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 2"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 2"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 2"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 3"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 3"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 3"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 3"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 3"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 3"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 3"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 3"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 3"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 3"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 3"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 3"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 3"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 4"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 4"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 4"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 4"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 4"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 4"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 4"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 4"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 4"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 4"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 4"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 4"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 4"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 4"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 5"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 5"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 5"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 5"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 5"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 5"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 5"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 5"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 5"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 5"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 5"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 5"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 5"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 5"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 6"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 6"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 6"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 6"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 6"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 6"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 6"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 6"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 6"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 6"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 6"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 6"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 6"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 6"/>
<w:LsdException Locked="false" Priority="19" QFormat="true"
Name="Subtle Emphasis"/>
<w:LsdException Locked="false" Priority="21" QFormat="true"
Name="Intense Emphasis"/>
<w:LsdException Locked="false" Priority="31" QFormat="true"
Name="Subtle Reference"/>
<w:LsdException Locked="false" Priority="32" QFormat="true"
Name="Intense Reference"/>
<w:LsdException Locked="false" Priority="33" QFormat="true" Name="Book Title"/>
<w:LsdException Locked="false" Priority="37" SemiHidden="true"
UnhideWhenUsed="true" Name="Bibliography"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="TOC Heading"/>
<w:LsdException Locked="false" Priority="41" Name="Plain Table 1"/>
<w:LsdException Locked="false" Priority="42" Name="Plain Table 2"/>
<w:LsdException Locked="false" Priority="43" Name="Plain Table 3"/>
<w:LsdException Locked="false" Priority="44" Name="Plain Table 4"/>
<w:LsdException Locked="false" Priority="45" Name="Plain Table 5"/>
<w:LsdException Locked="false" Priority="40" Name="Grid Table Light"/>
<w:LsdException Locked="false" Priority="46" Name="Grid Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="Grid Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="Grid Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 6"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 6"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 6"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 6"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 6"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="46" Name="List Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="List Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="List Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 6"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 6"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 6"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 6"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 6"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Mention"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Smart Hyperlink"/>
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-priority:99;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:8.0pt;
mso-para-margin-left:0in;
line-height:107%;
mso-pagination:widow-orphan;
font-size:11.0pt;
font-family:Calibri;
mso-ascii-font-family:Calibri;
mso-ascii-theme-font:minor-latin;
mso-hansi-font-family:Calibri;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]-->
<!--StartFragment-->
<div class="MsoNormal">
Graphic showing SST anomalies (shaded) and surface wind
patterns (arrows) during the positive phase of the PDO (left image) and the
negative phase (right image).<o:p></o:p></div>
<div class="MsoNormal">
Source: University of Washington</div>
</td></tr>
</tbody></table>
<div class="MsoNormal">
The Pacific Decadal Oscillation comes in two phases: a
“warm” phase (positive phase) and a “cool” phase (negative phase). The state of
the PDO is identified primarily by the alignment of sea surface temperature
anomalies over the Pacific basin. When SSTAs are notably below normal east of
Japan into the waters south of Alaska, the PDO is said to be in the positive
phase. In contrast, when anomalies are above normal in those same areas, the
PDO is negative. This seems upside-down, so it’s helpful to also look at the
anomalies immediately offshore the western coast of North America. Indeed, in a
positive PDO those coastal waters exhibit positive SSTAs, while a negative PDO
typically brings colder waters.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Let’s see how the PDO looks currently.<o:p></o:p></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFOD23cQ17WgI9iJZwrVE0K6QGBVzbVOdCaArN7A3KD1-LE9mG6vGCVoG9fRR_kg23QPlp1nUjYVGevkfxNlundHqAIld5Xb4S2O-5ZbCaj56csGvo7R6TRzufYvgusUtXuSg74hLNfIvv/s1600/Picture2.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="532" data-original-width="975" height="348" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFOD23cQ17WgI9iJZwrVE0K6QGBVzbVOdCaArN7A3KD1-LE9mG6vGCVoG9fRR_kg23QPlp1nUjYVGevkfxNlundHqAIld5Xb4S2O-5ZbCaj56csGvo7R6TRzufYvgusUtXuSg74hLNfIvv/s640/Picture2.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><div class="MsoNormal" style="text-align: center;">
SST anomalies over the globe, as of June 17, 2019.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: center;">
Source: NOAA</div>
</td></tr>
</tbody></table>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
A look at the Pacific basin as of the last graphic of SST
anomalies doesn’t provide much of a clear-cut direction of where the PDO
currently stands. While there are cooler than normal sea surface temperatures
wrapping into the waters offshore of the western United States – typically
indicative of a negative PDO – there is a mass of colder than normal waters
south of the Aleutian Islands and extending west towards Japan – typically indicative
of a positive PDO. Additionally, there’s a swath of above-normal SST anomalies
extending from Hawaii into the Gulf of Alaska, which doesn’t fit comfortably
into either composite of the two PDO phases, making the picture quite muddy.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
However, also shown on that two-panel image above are
surface wind patterns exhibited during the different PDO phases. In a positive
PDO, surface winds over the north Pacific flow from west to east, while in a
negative PDO these surface winds flow from east to west. Let’s take a look at
recent surface wind patterns in the Pacific to try and decipher the PDO.</div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiKG1t2bfWNU3pP1fGCGVXJaZOZwyKP97FVEyBQTviGX4MMq3iiG5SpGHezupd32H-5FXzhrJE4infuZSc4326_jSPXJGF9u8CTezNUHi4tJOG-3DBM2rzsxt0-d_jx50cLxuCEA6kvTM7_/s1600/Picture3.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="755" data-original-width="975" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiKG1t2bfWNU3pP1fGCGVXJaZOZwyKP97FVEyBQTviGX4MMq3iiG5SpGHezupd32H-5FXzhrJE4infuZSc4326_jSPXJGF9u8CTezNUHi4tJOG-3DBM2rzsxt0-d_jx50cLxuCEA6kvTM7_/s640/Picture3.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><div class="MsoNormal" style="text-align: center;">
Surface winds over the Pacific basin, from April 1<sup>st</sup> through June 16<sup>th</sup>.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: center;">
Source: ESRL</div>
</td></tr>
</tbody></table>
<div class="MsoNormal">
Over the months of April, May, and the first half of June,
surface winds were seen flowing from west to east over the waters south of the
Aleutian Islands, a prominent mark of the PDO being in the positive phase.
Contrasting with this, however, is a channel of northerly winds just offshore
western North America, which the composite graphic at the top of this post
indicates is associated with a negative PDO. Much like the SSTA comparison,
surface wind patterns seem to be giving us conflicting signals that make it
difficult to draw out which phase the PDO is actually in.<o:p></o:p></div>
<div class="MsoNormal">
There’s one more method I want to look at to determine the
state of the PDO.</div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFH10UXWsZyHZuNxCv_C4dreOatkHZp126tKLvboJweBskO2IPaXTK2guX_Uw1gCg5NBU2UCC5gN_HpI3JsqegueROnTO6YIXzJarJUqt9pu2-1iutHjRTofUForNkljwxB5hhAF328YKr/s1600/Picture11.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="683" data-original-width="883" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFH10UXWsZyHZuNxCv_C4dreOatkHZp126tKLvboJweBskO2IPaXTK2guX_Uw1gCg5NBU2UCC5gN_HpI3JsqegueROnTO6YIXzJarJUqt9pu2-1iutHjRTofUForNkljwxB5hhAF328YKr/s640/Picture11.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><div class="MsoNormal" style="text-align: center;">
Seasonal correlation of 500-millibar geopotential heights with the PDO in the months of April through June.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: center;">
Source: ESRL</div>
</td></tr>
</tbody></table>
<div class="MsoNormal">
Shown above is an image that provides valuable insight on to
how the PDO affects the atmospheric pattern. It is a seasonal correlation
image, and although that sounds daunting, its interpretation is rather
straightforward. Suppose, for a moment, we assume there is a positive PDO in
place. The graphic above takes that information and asserts, based on history,
that the positive PDO will result generally in positive 500-millibar height
anomalies over the western swath of North America – in other words, a ridge.
Why? Because for all the warm colors in this graph, 500-millibar heights are
positively correlated to the PDO’s state. This means that in a negative PDO,
all areas under warmer colors would see lower 500-millibar heights. Similarly,
colder colors on this chart mean that if the PDO is in a positive (negative)
phase, 500-millibar heights will be lower (higher) in areas with colder-color
shading, indicative of troughs (ridges).<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Let’s see if we can use this image to determine where the
PDO is now.</div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjWE-AC8lP8Dr5A5ibZr0-DRUN1ixluvDyyxRLh4M2E7O7G9aHirDAovt4xbxjWZMaRcfpSItRuKJIWrEFxPu_CSbb5KbzqmqJoS32u8OFl8HRrXr4GHiDnqRKZJHLqprdTrBBAaSc2tTLI/s1600/Picture31.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="755" data-original-width="975" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjWE-AC8lP8Dr5A5ibZr0-DRUN1ixluvDyyxRLh4M2E7O7G9aHirDAovt4xbxjWZMaRcfpSItRuKJIWrEFxPu_CSbb5KbzqmqJoS32u8OFl8HRrXr4GHiDnqRKZJHLqprdTrBBAaSc2tTLI/s640/Picture31.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><div class="MsoNormal" style="text-align: center;">
500-millibar geopotential height anomalies from April 1<sup>st</sup> through mid-June. <o:p></o:p></div>
<div class="MsoNormal" style="text-align: center;">
Source: ESRL<span style="text-align: left;"> </span></div>
</td></tr>
</tbody></table>
<div class="MsoNormal">
Unfortunately, even this method doesn’t provide much more
clarity on the state of the PDO. During the April-through-mid-June time period,
we have seen below-normal geopotential heights (stormy weather) south of the
Aleutian Islands into Japan. Using the image immediately prior to the one
directly above, colder colors are draped over that same area, implying the PDO
state is opposite the 500-millibar height anomalies over the northern Pacific.
This would tell us that a positive PDO is present. However, moving into the
Gulf of Alaska, persistent ridging has taken place over this time period, in an
area that also has a negative correlation with the PDO. Therefore, that ridging
off the western coast of North America implies a negative PDO. These are the
same takeaways we found by analyzing SSTAs and surface wind patterns, and don’t
really improve our understanding of what phase the PDO is actually in.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
One could make an argument that it’s easier to just go by what
the NOAA’s PDO index itself actually says, which indicates we are in a
marginally-positive phase. In some situations, that’s certainly fine to do, but
as was shown extensively in this article, the atmosphere is not totally
reflective of a positive PDO state, meaning it would be misleading to just use
the index value. The ambiguity in the current state of the PDO makes me
question if it can be reliably used in seasonal forecasting for the fall
months, and possibly for the winter months if these conflicting signals
continue into late summer and early fall. Seasonal forecasters should take heed
of the ambiguity and weight longer-term teleconnections accordingly. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<!--[if !mso]>
<style>
v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style>
<![endif]--><!--[if gte mso 9]><xml>
<o:OfficeDocumentSettings>
<o:AllowPNG/>
</o:OfficeDocumentSettings>
</xml><![endif]-->
<!--[if gte mso 9]><xml>
<w:WordDocument>
<w:View>Normal</w:View>
<w:Zoom>0</w:Zoom>
<w:TrackMoves>false</w:TrackMoves>
<w:TrackFormatting/>
<w:PunctuationKerning/>
<w:ValidateAgainstSchemas/>
<w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid>
<w:IgnoreMixedContent>false</w:IgnoreMixedContent>
<w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText>
<w:DoNotPromoteQF/>
<w:LidThemeOther>EN-US</w:LidThemeOther>
<w:LidThemeAsian>X-NONE</w:LidThemeAsian>
<w:LidThemeComplexScript>X-NONE</w:LidThemeComplexScript>
<w:Compatibility>
<w:BreakWrappedTables/>
<w:SnapToGridInCell/>
<w:WrapTextWithPunct/>
<w:UseAsianBreakRules/>
<w:DontGrowAutofit/>
<w:SplitPgBreakAndParaMark/>
<w:EnableOpenTypeKerning/>
<w:DontFlipMirrorIndents/>
<w:OverrideTableStyleHps/>
</w:Compatibility>
<m:mathPr>
<m:mathFont m:val="Cambria Math"/>
<m:brkBin m:val="before"/>
<m:brkBinSub m:val="--"/>
<m:smallFrac m:val="off"/>
<m:dispDef/>
<m:lMargin m:val="0"/>
<m:rMargin m:val="0"/>
<m:defJc m:val="centerGroup"/>
<m:wrapIndent m:val="1440"/>
<m:intLim m:val="subSup"/>
<m:naryLim m:val="undOvr"/>
</m:mathPr></w:WordDocument>
</xml><![endif]--><!--[if gte mso 9]><xml>
<w:LatentStyles DefLockedState="false" DefUnhideWhenUsed="false"
DefSemiHidden="false" DefQFormat="false" DefPriority="99"
LatentStyleCount="382">
<w:LsdException Locked="false" Priority="0" QFormat="true" Name="Normal"/>
<w:LsdException Locked="false" Priority="9" QFormat="true" Name="heading 1"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 2"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 3"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 4"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 5"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 6"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 7"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 8"/>
<w:LsdException Locked="false" Priority="9" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="heading 9"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index 9"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 1"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 2"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 3"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 4"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 5"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 6"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 7"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 8"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" Name="toc 9"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="footnote text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="header"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="footer"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="index heading"/>
<w:LsdException Locked="false" Priority="35" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="caption"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="table of figures"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="envelope address"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="envelope return"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="footnote reference"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation reference"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="line number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="page number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="endnote reference"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="endnote text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="table of authorities"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="macro"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="toa heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 5"/>
<w:LsdException Locked="false" Priority="10" QFormat="true" Name="Title"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Closing"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Signature"/>
<w:LsdException Locked="false" Priority="1" SemiHidden="true"
UnhideWhenUsed="true" Name="Default Paragraph Font"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Message Header"/>
<w:LsdException Locked="false" Priority="11" QFormat="true" Name="Subtitle"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Salutation"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Date"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Block Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Hyperlink"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="FollowedHyperlink"/>
<w:LsdException Locked="false" Priority="22" QFormat="true" Name="Strong"/>
<w:LsdException Locked="false" Priority="20" QFormat="true" Name="Emphasis"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Document Map"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Plain Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="E-mail Signature"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Top of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Bottom of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal (Web)"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Acronym"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Address"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Cite"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Code"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Definition"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Keyboard"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Preformatted"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Sample"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Typewriter"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Variable"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal Table"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation subject"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="No List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Contemporary"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Elegant"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Professional"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Balloon Text"/>
<w:LsdException Locked="false" Priority="39" Name="Table Grid"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Theme"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Level 9"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Placeholder Text"/>
<w:LsdException Locked="false" Priority="1" QFormat="true" Name="No Spacing"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading"/>
<w:LsdException Locked="false" Priority="61" Name="Light List"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 1"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 1"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 1"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 1"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 1"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Revision"/>
<w:LsdException Locked="false" Priority="34" QFormat="true"
Name="List Paragraph"/>
<w:LsdException Locked="false" Priority="29" QFormat="true" Name="Quote"/>
<w:LsdException Locked="false" Priority="30" QFormat="true"
Name="Intense Quote"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 1"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 1"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 1"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 1"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 1"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 1"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 1"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 2"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 2"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 2"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 2"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 2"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 2"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 2"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 2"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 2"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 2"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 2"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 3"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 3"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 3"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 3"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 3"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 3"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 3"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 3"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 3"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 3"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 3"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 3"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 3"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 4"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 4"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 4"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 4"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 4"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 4"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 4"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 4"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 4"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 4"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 4"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 4"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 4"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 4"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 5"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 5"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 5"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 5"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 5"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 5"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 5"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 5"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 5"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 5"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 5"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 5"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 5"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 5"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 6"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 6"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 6"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 6"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 6"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 6"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 6"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 6"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 6"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 6"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 6"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 6"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 6"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 6"/>
<w:LsdException Locked="false" Priority="19" QFormat="true"
Name="Subtle Emphasis"/>
<w:LsdException Locked="false" Priority="21" QFormat="true"
Name="Intense Emphasis"/>
<w:LsdException Locked="false" Priority="31" QFormat="true"
Name="Subtle Reference"/>
<w:LsdException Locked="false" Priority="32" QFormat="true"
Name="Intense Reference"/>
<w:LsdException Locked="false" Priority="33" QFormat="true" Name="Book Title"/>
<w:LsdException Locked="false" Priority="37" SemiHidden="true"
UnhideWhenUsed="true" Name="Bibliography"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="TOC Heading"/>
<w:LsdException Locked="false" Priority="41" Name="Plain Table 1"/>
<w:LsdException Locked="false" Priority="42" Name="Plain Table 2"/>
<w:LsdException Locked="false" Priority="43" Name="Plain Table 3"/>
<w:LsdException Locked="false" Priority="44" Name="Plain Table 4"/>
<w:LsdException Locked="false" Priority="45" Name="Plain Table 5"/>
<w:LsdException Locked="false" Priority="40" Name="Grid Table Light"/>
<w:LsdException Locked="false" Priority="46" Name="Grid Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="Grid Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="Grid Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 6"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 6"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 6"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 6"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 6"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="46" Name="List Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="List Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="List Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 6"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 6"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 6"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 6"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 6"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Mention"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Smart Hyperlink"/>
</w:LatentStyles>
</xml><![endif]-->
<!--[if gte mso 10]>
<style>
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:"Table Normal";
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-priority:99;
mso-style-parent:"";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
mso-para-margin-top:0in;
mso-para-margin-right:0in;
mso-para-margin-bottom:8.0pt;
mso-para-margin-left:0in;
line-height:107%;
mso-pagination:widow-orphan;
font-size:11.0pt;
font-family:Calibri;
mso-ascii-font-family:Calibri;
mso-ascii-theme-font:minor-latin;
mso-hansi-font-family:Calibri;
mso-hansi-theme-font:minor-latin;}
</style>
<![endif]-->
<!--StartFragment-->
<!--EndFragment--><br />
<div class="MsoNormal">
Andrew<o:p></o:p></div>
</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-78077987817169156582019-06-13T14:22:00.000-05:002019-06-13T14:22:21.890-05:00June 21-25 Potentially Strong Storm System<div dir="ltr" style="text-align: left;" trbidi="on">
It appears a potentially strong storm system will move through the country in the June 21-25th time period.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgmZVeOp1NZNYCGpd4asSd014deVZkXX_qqYVRaTrZtpp4Lc2CFXBK217DNM9iJ8g5dDm6qwnsAWEaAkXae08HNk_-E1QiGWGzgrfdsqo_FehDinZpO9ST7XROLI8uhF1xDNK6X7-iwNibl/s1600/gfs_z500a_wpac_13.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="717" data-original-width="1024" height="448" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgmZVeOp1NZNYCGpd4asSd014deVZkXX_qqYVRaTrZtpp4Lc2CFXBK217DNM9iJ8g5dDm6qwnsAWEaAkXae08HNk_-E1QiGWGzgrfdsqo_FehDinZpO9ST7XROLI8uhF1xDNK6X7-iwNibl/s640/gfs_z500a_wpac_13.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 500-millibar geopotential height anomalies valid for 7pm June 15th.<br />
Source: Tropical Tidbits</td></tr>
</tbody></table>
By the evening of June 15th, model guidance sees a formidable trough sweeping across Japan, negatively-tilted (oriented from a northwest-to-southeast direction) with substantial negative height anomalies. In general, when an upper-level trough is oriented in that negative-tilt direction, it implies that the storm system it is associated with has reached its mature phase, and is broadly at or near its strongest point in the storm's life cycle.<br />
<br />
Regular readers of this blog in the past will know that I frequently use a teleconnection whereby weather phenomena occurring over and near Japan correlate to similar phenomena in North America roughly 6-10 days later. I am employing this again here, and extrapolating the above model graphic gives us a potential storm system occurring in the United States in the June 21-25 period.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhk5OBksnRUGycCJYQ57SWMLunrZPTF9dadmHKMU1fKwkMBnSvi9y7P7k2jXw0Em7u9Z50pj4UH7cJxF4GcqYFfZK5VU2uACp_8DN5MXORZQFXHkBViL5PRgPU8LTZDNc5itswha6hgwYAK/s1600/gfs_mslp_pcpn_wpac_12.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="717" data-original-width="1024" height="448" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhk5OBksnRUGycCJYQ57SWMLunrZPTF9dadmHKMU1fKwkMBnSvi9y7P7k2jXw0Em7u9Z50pj4UH7cJxF4GcqYFfZK5VU2uACp_8DN5MXORZQFXHkBViL5PRgPU8LTZDNc5itswha6hgwYAK/s640/gfs_mslp_pcpn_wpac_12.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted MSLP and 6-hour average precipitation rates valid for 7pm June 15th.<br />
Source: Tropical Tidbits</td></tr>
</tbody></table>
At the surface, we see why the 500-millibar geopotential height anomalies are so negative. Indeed, at the same time as the first image, a surface low with a minimum sea level pressure of 986 millibars is forecasted to be placed right over Japan. While it is not unusual for surface lows to plumb minimum pressure values firmly below 1000 millibars in the Pacific Ocean, particularly in the open waters near the Aleutian Islands, the substantial negative 500-millibar height anomalies at the top of this page and the substantial negative MSLP normalized anomalies below illustrate that even around Japan this storm system is somewhat strong.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-ObrtI_-pHDN5b0419gM16N6taTAgraZ6VctFi8faSZckHcBWItJAoHKF3so7CS0Nlmzkp8xgt1zSr5_YtQvzN-gIPn8eP2x9b8ugS7oXDKw7THQsUnGd5kx4fwpIFdJjOSW-FDcwKR9T/s1600/gfs_mslpaNorm_wpac_13.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="717" data-original-width="1024" height="448" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-ObrtI_-pHDN5b0419gM16N6taTAgraZ6VctFi8faSZckHcBWItJAoHKF3so7CS0Nlmzkp8xgt1zSr5_YtQvzN-gIPn8eP2x9b8ugS7oXDKw7THQsUnGd5kx4fwpIFdJjOSW-FDcwKR9T/s640/gfs_mslpaNorm_wpac_13.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted MSLP normalized anomalies valid for 7pm June 15th.<br />
Source: Tropical Tidbits</td></tr>
</tbody></table>
So, what can we expect for this June 21-25 timeframe?<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEic42anXiGvVz6BKxbIf_D1l0BaZOoHW-AqYx3-LDRKMO6z8lbV9yJK6kM0q3Ddj9al0o2l-pfT7YUy8bBb4khswELhsEoQFi9SqmcSGFtCFl_ZocjrGspNRfmVqhVC-4AGmnAKGfYa-tD9/s1600/gfs-ens_mslpa_us_49.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="1024" height="434" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEic42anXiGvVz6BKxbIf_D1l0BaZOoHW-AqYx3-LDRKMO6z8lbV9yJK6kM0q3Ddj9al0o2l-pfT7YUy8bBb4khswELhsEoQFi9SqmcSGFtCFl_ZocjrGspNRfmVqhVC-4AGmnAKGfYa-tD9/s640/gfs-ens_mslpa_us_49.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted MSLP anomalies via the GFS Ensembles valid for 1pm June 24th.<br />
Source: Tropical Tidbits</td></tr>
</tbody></table>
We can get a sense as to the general pattern shaping up, particularly since it's too far out to try and pick out individual model runs. Above, the forecasted MSLP anomalies from the GFS ensembles on the afternoon of June 24th are shown, and it provides a glimpse at what could be on the way.<br />
<br />
Naturally, given these images are the average of the model's ensembles, we aren't able to identify the exact strength or placement of the storm - as stated, we're aiming to identify the broad pattern. The ensembles see below-normal sea level pressure anomalies developing over the central U.S., maximized over the central and northern Plains. This would likely be the storm that would be correlated with the storm expected to impact Japan over the next few days, but it will still take some time for model guidance to reliably latch on to (or even lose) the storm system.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhs8v6-XkX8AME3y_7JvuTaCmb4oWaQyL50Uqv9LAgM7B_N5S6PqP1rEok8AJ_hOIqY_1mv0grCqqndtF7V78AiUBfOu-WClsy4HqyMPHw98RV7aoEzm0RfAKq0tIipmMN3imQOA8tvZQWh/s1600/gfs_T850a_ea_20.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="756" data-original-width="1024" height="472" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhs8v6-XkX8AME3y_7JvuTaCmb4oWaQyL50Uqv9LAgM7B_N5S6PqP1rEok8AJ_hOIqY_1mv0grCqqndtF7V78AiUBfOu-WClsy4HqyMPHw98RV7aoEzm0RfAKq0tIipmMN3imQOA8tvZQWh/s640/gfs_T850a_ea_20.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 850-millibar temperature anomalies valid for 1pm June 17th.<br />
Source: Tropical Tidbits</td></tr>
</tbody></table>
In the wake of the storm system, an airmass featuring substantially below-normal temperature anomalies looks to move in over Japan, which should then correlate with below-normal temperatures again invading the United States to round out the month of June.<br />
<br />
<span style="font-size: large;"><i><b>To Summarize:</b></i></span><br />
- A potentially strong storm system looks to impact the United States in the June 21-25 period.<br />
- Notably cooler than normal weather is expected to impact the country to end June, after the storm system moves through.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com1tag:blogger.com,1999:blog-1448180228140749967.post-55607918485843813442019-06-10T12:39:00.000-05:002019-06-10T12:39:57.945-05:00Does Siberian Snow Cover in October Really Predict North American Winters?<div dir="ltr" style="text-align: left;" trbidi="on">
Over the last several winters, an interesting phenomenon that has been discussed is that of Siberian snow cover trends over the month of October. The idea is that if snow cover is anomalously widespread over Siberia in October, the following winter in North America will lean towards being colder than normal. Similarly, if snow cover over Siberia is lackluster in October, temperatures across North America will tend to be warmer than normal during the following winter.<br />
<br />
This theory has been advanced by Dr. Judah Cohen of MIT, and I have been particularly fascinated by the concept. In an effort to see how reliable this method could be, in this post I present an admittedly-crude analysis of Eurasian snow cover in the month of October from 1967-2018 and view the subsequent winter seasons.<br />
<br />
I would like to make it explicitly clear that this is only meant to be a crude analysis of this phenomenon - I have a great deal of respect for Dr. Cohen, and there are doubtless other far more intelligent and far more able-minded scientists who can analyze this topic more closely and more accurately. This post is more of a preliminary and basic analysis on the topic. Feel free to read more about the concept as well: <a href="http://www.judahcohen.org/">link</a><br />
<br />
---<br />
<br />
Let's begin with an analysis of the data I will use in this analysis. I use data from <a href="https://climate.rutgers.edu/snowcover/index.php">Rutgers University's Global Snow Lab</a>, which provides content on the extent of snow cover across different swaths of the Northern Hemisphere, as well as the Northern Hemisphere in the aggregate. This data is almost completely continuous, save for October data in the year 1969. As such, we will work with 51 samples in this analysis. For this post, I am using snow cover data for the Eurasia region specifically, over the month of October only. I am using data on an anomaly basis: per the Rutgers GSL, the average snow cover in the month of October in Eurasia is approximately 9,497,000 square kilometers.<br />
<br />
<br />
<u><span style="font-size: large;">I. Winters Following Top Ten October Eurasia Snow Cover Anomalies</span></u><br />
<br />
First, I'll create a composite of winter-season temperature anomalies over North America for the winters following the ten years of highest positive snow cover anomalies in October over Eurasia. The composite is presented below. Click on any image to enlarge it.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhbqLnMwLapvhY4LPDhPiy9YqnjjrxnVrPVS_Mx1d0gHQ5MLb1BxNrxAj_-nafNjuSn_ImCXVzkbSfZA6m1PLQfxXDxO0G9xZupizGbNtsnJdCTBuXhhjKvQ8l0deithjqVBXorodNWmwLp/s1600/top10october.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="542" data-original-width="700" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhbqLnMwLapvhY4LPDhPiy9YqnjjrxnVrPVS_Mx1d0gHQ5MLb1BxNrxAj_-nafNjuSn_ImCXVzkbSfZA6m1PLQfxXDxO0G9xZupizGbNtsnJdCTBuXhhjKvQ8l0deithjqVBXorodNWmwLp/s640/top10october.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Surface temperature anomalies for the ten winters following the ten Octobers featuring the highest Eurasia snow cover anomalies.<br />
Source: ESRL</td></tr>
</tbody></table>
The ten years featuring the highest positive anomalies of snow cover in October over Eurasia, in order, are 1976, 2014, 2016, 2002, 1970, 2013, 2015, 1971, 1968 and 1972. I have graphed the composite surface temperature anomaly (in degrees Celsius) for the December-January-February period that followed each year in the above graphic. When putting these top ten years / top ten winters all together, the result is actually pretty in line with what this concept states, that stronger snow cover over Eurasia in the October preceding these winters should result in colder than normal winters for North America in the winters themselves.<br />
<br />
<br />
<u><span style="font-size: large;">II. Winters Following Bottom Ten October Eurasia Snow Cover Anomalies</span></u><br />
<br />
Next, let's look at the temperature composite for the bottom ten years - that is, the winters that followed the ten Octobers where the snow cover anomaly over Eurasia was the lowest. The image is shown below.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQ1FJv5ZwRqz-BbsQ-Er63aNHc5eshZM5IwnA3rhGyf1BSezASYpFPHO8p34qDWQBQC6iw8WDutOE7X6oez9cO5zoMbYkwHeN21cfVr_C-jDKC348i8WtrEyz_MTQ5Kt3uBZz7z3ptLn3T/s1600/GrdqG50xA5.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="542" data-original-width="700" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQ1FJv5ZwRqz-BbsQ-Er63aNHc5eshZM5IwnA3rhGyf1BSezASYpFPHO8p34qDWQBQC6iw8WDutOE7X6oez9cO5zoMbYkwHeN21cfVr_C-jDKC348i8WtrEyz_MTQ5Kt3uBZz7z3ptLn3T/s640/GrdqG50xA5.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Surface temperature anomalies for the bottom winters following the ten Octobers featuring the lowest Eurasia snow cover anomalies.<br />
Source: ESRL</td></tr>
</tbody></table>
The picture becomes less clear-cut when looking at the ten winters which followed the ten Octobers with the lowest Eurasian snow cover anomalies. While the below-normal temperature anomalies in North America have become less centralized from what we saw in the first temperature composite, we do not see predominantly above-normal temperatures over these ten winters. Indeed, the majority of the country is actually at neutral or slightly below-normal temperatures, with much of Canada entrenched in firmly below-normal temperature anomalies.<br />
<br />
However, I do see an area where this concept becomes useful.<br />
<br />
<br />
<u><span style="font-size: large;">III. 500-Millibar Geopotential Height Anomalies</span></u><br />
<br />
I want to take a look at those same top-ten and bottom-ten winters, except this time instead of viewing surface temperature anomalies over North America we'll go over 500-millibar geopotential height anomalies over the Northern Hemisphere.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhALulpbEr_WNbEiITh2yeXrDVvauLr92iCLQEvDyXUqa0vVUvoxgdOmEDcRm2oL_8pUsqbq9giAFcgvPLXqEx2WXWlhJUW83SSxQzChahqs6htl3f4_9iqx-2IOpGGEfj07a5VEm-ScMEf/s1600/top+ten+oct+500mbnh.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="542" data-original-width="700" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhALulpbEr_WNbEiITh2yeXrDVvauLr92iCLQEvDyXUqa0vVUvoxgdOmEDcRm2oL_8pUsqbq9giAFcgvPLXqEx2WXWlhJUW83SSxQzChahqs6htl3f4_9iqx-2IOpGGEfj07a5VEm-ScMEf/s640/top+ten+oct+500mbnh.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">500-millibar geopotential height anomalies for the ten winters following the ten Octobers featuring the highest Eurasia snow cover anomalies.<br />
Source: ESRL</td></tr>
</tbody></table>
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg-d5p9TIUhRnlwhY3BtlVXNahpNsDHhOUP97cgwhSGXeUve5arCS8TwdE2suSHCfSo9pgtAN6fuk8V3sk8cid5-BspKju6zxuf8cNQrOOK3YP_BeeqlabHAT1FESMOAeVCGx0Nb6LFUa8-/s1600/bottom+ten+oct+500mbnh.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="542" data-original-width="700" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg-d5p9TIUhRnlwhY3BtlVXNahpNsDHhOUP97cgwhSGXeUve5arCS8TwdE2suSHCfSo9pgtAN6fuk8V3sk8cid5-BspKju6zxuf8cNQrOOK3YP_BeeqlabHAT1FESMOAeVCGx0Nb6LFUa8-/s640/bottom+ten+oct+500mbnh.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">500-millibar geopotential height anomalies for the ten winters following the ten Octobers featuring the bottom Eurasia snow cover anomalies.<br />
Source: ESRL</td></tr>
</tbody></table>
Where the surface temperature anomalies were rather murky when trying to differentiate the winters following top-ten and bottom-ten Octobers in terms of snow cover anomalies over Eurasia, the picture becomes far more focused when expanding to 500-millibar geopotential height anomalies.<br />
<br />
The first image of the above two shows 500-millibar height anomalies for those ten winters following the ten Octobers with the highest positive snow cover anomalies over Eurasia. That composite shows that the winters featured a firmly-disrupted tropospheric polar vortex, with strong ridging evident from the north Pacific through the Bering Sea, across the Arctic Circle and into western Europe. This led to the tropospheric polar vortex being forced to lower latitudes, as shown by the deep negative anomalies in North America, far western Europe, and northern Eurasia. In contrast, the second image - showing 500-millibar height anomalies for those ten winters following the ten Octobers with the deepest below-normal snow cover anomalies over Eurasia - shows essentially the opposite. A stronger than normal tropospheric polar vortex is observed across the upper latitudes, with generalized and widespread ridging prevailing around the mid-latitude regions.<br />
<br />
This does seem to validate Dr. Cohen's theory, with more expansive snow cover over Siberia in October leading to a weaker stratospheric *and* tropospheric polar vortex in the Northern Hemisphere for the following winter.<br />
<br />
<br />
<i><span style="font-size: large;">To Summarize:</span></i><br />
- A crude analysis of Eurasian snow cover data seems to confirm Dr. Judah Cohen's theory that anomalously high (low) snow cover over Eurasia in October corresponds to an anomalously weak (strong) stratospheric and tropospheric polar vortex in the following winter, with broadly-attendant chances for colder (warmer) than normal temperatures for the winter.<br />
- While I was admittedly skeptical of this tool, the data in this preliminary analysis don't lie: this does seem to be a worthwhile tool for seasonal forecasting.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-50855824456794169862019-06-09T12:20:00.000-05:002019-06-09T12:20:06.279-05:00Long Range Outlook (Made June 9, 2019)<div dir="ltr" style="text-align: left;" trbidi="on">
This is a Long Range Outlook made for publication on June 9th. The forecast period will cover the remainder of June. Click on any image to enlarge it.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhRh2E1KqdI7etC_IGvFAMznWX8f0szDJ3lL3oW0M0HEaM1g_eNVmlfwb5Pd13jN1erVh4X3jQhaB1YlOTCAuSixIbgo47s3YhcG6xwGcDf-GKhollUD6JqZvkxHpM8qYD652Jp2fDabedM/s1600/gfs-ens_z500a_nhem_1.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1000" data-original-width="1024" height="624" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhRh2E1KqdI7etC_IGvFAMznWX8f0szDJ3lL3oW0M0HEaM1g_eNVmlfwb5Pd13jN1erVh4X3jQhaB1YlOTCAuSixIbgo47s3YhcG6xwGcDf-GKhollUD6JqZvkxHpM8qYD652Jp2fDabedM/s640/gfs-ens_z500a_nhem_1.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Observed 500-millibar geopotential height anomalies as of 1pm Central, June 8th.<br />
Source: Tropical Tidbits</td></tr>
</tbody></table>
A look around the Northern Hemisphere on the afternoon of June 8th shows a rather-busy pattern over North America, with an upper level low positioned over northwest Canada and a secondary trough dropping into the Pacific Northwest while still being influenced by the first system. A strong ridge maximized over the northern Great Lakes into southern Canada contrasts with a closed low positioned in the Southeast U.S., forming a Rex Block-looking pattern despite there not being any actual blocking event taking place. Indeed, even downstream of this pattern into Newfoundland, the flow is rather amplified with an upper level low grinding against a strong ridge that is firmly entrenched into Greenland. Upstream of the United States, weak ridging is evident in the northeast Pacific, helping to diffuse the Pacific jet stream in the process. A strong storm system is seen south of the Aleutian Islands, with additional disturbed weather skirting along the northern Pacific.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8_FN_ucflE-eokc8bn5CmPCKL_hgTS1Y8PFNy_tV4CMnzh5NQ42d-5YVS6rWVcCRLOsYQ2ymP7ObpygFhu2Y7KFaM0ueb2QEfsYKYrEiP_gbDuekX2BPfjk0L3pGNUBn78AhfX4TAmJI8/s1600/gfs-ens_z500a_nhem_16.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1000" data-original-width="1024" height="624" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8_FN_ucflE-eokc8bn5CmPCKL_hgTS1Y8PFNy_tV4CMnzh5NQ42d-5YVS6rWVcCRLOsYQ2ymP7ObpygFhu2Y7KFaM0ueb2QEfsYKYrEiP_gbDuekX2BPfjk0L3pGNUBn78AhfX4TAmJI8/s640/gfs-ens_z500a_nhem_16.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 500-millibar geopotential height anomalies valid 7am Central, June 12th.<br />
Source: Tropical Tidbits</td></tr>
</tbody></table>
Even within the five-day forecast window, the evolution of the flow over the Northern Hemisphere becomes rather complex rather quickly. The ridge and closed low mentioned in the eastern half of North America are seen drifting eastward, with model guidance suggesting the ridge will propagate northeastward into Greenland to maximize positive 500mb height anomalies. Additionally, the observed weak ridging in the northeast Pacific is expected to strengthen and entrench itself across the western coast of the continent, thereby setting up a pattern representative of the positive phase of the Pacific-North American (PNA) oscillation, seen by ridging along the West Coast, as well as the negative phase of the North Atlantic Oscillation (NAO), seen by ridging over Greenland.<br />
<br />
The result of these two features, as well as a messy picture for the West Pacific Oscillation and East Pacific Oscillation (EPO), is a likelihood of cooler than normal temperatures across the eastern two-thirds of the United States, as well as into Canada. The positive PNA and negative NAO will act to direct air from northern Canada down into the United States. Indeed, the five-day average 2-meters-above-the-surface temperature anomalies below, through the period ending June 14th, shows a substantial and widespread period of below-normal temperatures for the majority of the country.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEguiuCr5O3XHA9FML3X7-qbd2T5FT09LEtw3gby5tVUqXfSRGGEkvTRxgqgLf9k4zBVr5h7kqBl-8iL7O0R85sByvkum54BaO6_WzbEyGJ06Mr72dDH9eJeUm9juxPsR9zfpjuUytT6UAND/s1600/gfs-ens_T2maMean_us_2.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="1024" height="434" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEguiuCr5O3XHA9FML3X7-qbd2T5FT09LEtw3gby5tVUqXfSRGGEkvTRxgqgLf9k4zBVr5h7kqBl-8iL7O0R85sByvkum54BaO6_WzbEyGJ06Mr72dDH9eJeUm9juxPsR9zfpjuUytT6UAND/s640/gfs-ens_T2maMean_us_2.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 5-day average ~surface temperature anomalies, valid through the period ending 1pm June 14th.<br />
Source: Tropical Tidbits</td></tr>
</tbody></table>
Model guidance is showing strong confidence in the evolution of strong ridging over both western North America and Greenland as well:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEien1zX9LRS1b9kSqRnu_AHBdNa-n2JKo0Aa8RuaAmzsrTCY2vdpb-84WQLUBefakPGGq-zMb0mdYLeJagX_3doJBWdQQT9UBdxlkepIRRMiwu1VkgZcldYzoJxAPSDZztmmO5HlheejBwW/s1600/mmap_2019060800_96_nh.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="850" data-original-width="1100" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEien1zX9LRS1b9kSqRnu_AHBdNa-n2JKo0Aa8RuaAmzsrTCY2vdpb-84WQLUBefakPGGq-zMb0mdYLeJagX_3doJBWdQQT9UBdxlkepIRRMiwu1VkgZcldYzoJxAPSDZztmmO5HlheejBwW/s640/mmap_2019060800_96_nh.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">NCEP Relative Measure of Predictability for 500-millibar values at forecast hour 96 (June 11th 7pm).<br />
Source: NCEP</td></tr>
</tbody></table>
Given the high confidence in the projected pattern through the five-day forecast timeframe, it does appear that colder-than-normal temperatures are likely for the eastern two-thirds of the country through at least June 14th.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhMQq3Vpnv8_Wa5W-VzJ29McA1-D-7YzuIZHYxNdZK2eAgP3zVWI0rQsKnzcyztPBgaWkfOPqCnsYA8YGjdciQRy2a6LB9o9eYRdCdF6XndZ4wUmBtFG8dWoHahZaeaY0BQHJXkd7RsGoy-/s1600/ecmwf-ens_z500a_nhem_11.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1000" data-original-width="1024" height="624" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhMQq3Vpnv8_Wa5W-VzJ29McA1-D-7YzuIZHYxNdZK2eAgP3zVWI0rQsKnzcyztPBgaWkfOPqCnsYA8YGjdciQRy2a6LB9o9eYRdCdF6XndZ4wUmBtFG8dWoHahZaeaY0BQHJXkd7RsGoy-/s640/ecmwf-ens_z500a_nhem_11.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 500-millibar geopotential height anomalies valid 7am Central, June 18th.<br />
Source: Tropical Tidbits</td></tr>
</tbody></table>
Ensemble model guidance is in agreement that the strong ridge over Greenland (again, the negative-NAO pattern) will remain in place through at least the day 10 forecast period, as shown above by the ECMWF (European model) ensembles. Upstream of the contiguous United States, too, model guidance does not anticipate any significant changes in the aggregate pattern, with predictions of ridging continuing along the west coast of North America as an upper level low situates itself just south of Alaska.<br />
<br />
Let's now turn to teleconnections and oscillations to ascertain if model guidance is correct in depicting the forecast into the end of June.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjruZLsbxETLTEN7YKjrJztBIn5IhRucY4xTbfFAZKXNHDmNgq775nP12F51GMWH4Ro7IvzjKDemTZtRHk48CoLQtNVmh2cRxez95FZWKIjs_9evt-AXWC3OrQaAwmHlPYoFT6kI2JZJpes/s1600/4indices.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1024" data-original-width="1024" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjruZLsbxETLTEN7YKjrJztBIn5IhRucY4xTbfFAZKXNHDmNgq775nP12F51GMWH4Ro7IvzjKDemTZtRHk48CoLQtNVmh2cRxez95FZWKIjs_9evt-AXWC3OrQaAwmHlPYoFT6kI2JZJpes/s640/4indices.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="background-color: white; color: #3f3f3f; font-family: "trebuchet ms" , "trebuchet" , sans-serif; font-size: 10.800000190734863px; font-weight: bold;">Forecasted states of the Pacific-North American (PNA) index, top-left; North Atlantic Oscillation (NAO), top-right; Western Pacific Oscillation (WPO), bottom-left; and the Eastern Pacific Oscillation (EPO), bottom-right.</span><br />
<span style="background-color: white; color: #3f3f3f; font-family: "trebuchet ms" , "trebuchet" , sans-serif; font-size: 10.800000190734863px; font-weight: bold;">Source: Earth System Research Laboratory (ESRL)</span></td></tr>
</tbody></table>
Viewing model-forecasted teleconnections over the next two weeks or so, we find a broad pattern similar to what was described earlier, with the positive PNA and negative NAO expected to dominate the outlook for North American weather throughout the forecast period. Guidance does weaken the PNA significantly from a strong-positive state to a slight-negative state by June 20th. I personally don't see this as remarkably likely when compared to a forecast that has the PNA remaining positive (even if modestly so) through the period, and I'll discuss why shortly.<br />
<br />
As noted earlier, the WPO and EPO are not expected to be strong enough to materially disrupt the +PNA/-NAO combination, with the moderately-positive West Pacific Oscillation forecast actually a boon for helping to sustain the ridge along the western coast of North America, and thereby sustain the +PNA. Model guidance sees the EPO as hovering essentially around levels too weak to have a definitive impact on the weather pattern.<br />
<br />
I'd like to briefly discuss a second reason - in addition to the expected positive WPO - why I believe the ridge along the western coast of North America (the +PNA) will sustain longer than guidance indicates here.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhqredO2Dg2Yn0rAU9RhUzQ3iLjoJDKKcGwelgtcPi8O4tKFF9aFxzb63_U6QkRY2Ym09pLraRx_QZ4wiSEpoQjDK7DohBF4UP4pVHK5YW9dhpu5pNfcfOHe8nWAZy0Q4r382q7h1sF3MAv/s1600/ECMF_phase_51m_small.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="547" data-original-width="547" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhqredO2Dg2Yn0rAU9RhUzQ3iLjoJDKKcGwelgtcPi8O4tKFF9aFxzb63_U6QkRY2Ym09pLraRx_QZ4wiSEpoQjDK7DohBF4UP4pVHK5YW9dhpu5pNfcfOHe8nWAZy0Q4r382q7h1sF3MAv/s400/ECMF_phase_51m_small.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"></td><td class="tr-caption"><span style="font-size: 12.800000190734863px;">Madden-Julian Oscillation (MJO) phase space diagram forecast, from the ECMWF model.<br />Source: Climate Prediction Center and ensembles.</span></td><td class="tr-caption"><br /></td></tr>
</tbody></table>
For a refresher on the concept of the Madden-Julian Oscillation and how to dissect a phase-space diagram, feel free to read <a href="https://theweathercentre.blogspot.com/2019/05/special-long-range-outlook-early-to-mid.html">this post</a> from earlier. The European model and its ensembles anticipate the MJO staying in a low-grade Phase 3 state over the short-term, before shifting into Phase 4, strengthening somewhat, and then potentially weakening into the 'circle of death'. Given how model guidance in that linked post had expected us to be in the 'circle of death' at the time of this writing, rather than in Phase 3, we will only trust the forecast to take us from a low-grade Phase 3 to a low-grade Phase 4 through the end of June.<br />
<br />
We are able to see how the atmosphere typically acts when the MJO is in Phase 4 for the month of June below.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHqe9aoA1q8fGXAAKHOhDNpU2AgxTHF29z4mDNPDpUF91DCJFhvV7g7RNM3AT8zjHDKrjyJpIHLgAtNg_DgDRdKBoY2QWt1woJgdyEe5N_jY1BqJuK8IjMlHnBfG2EWMhqxcVdcs4gJkz6/s1600/JunePhase4all500mb.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="655" data-original-width="847" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHqe9aoA1q8fGXAAKHOhDNpU2AgxTHF29z4mDNPDpUF91DCJFhvV7g7RNM3AT8zjHDKrjyJpIHLgAtNg_DgDRdKBoY2QWt1woJgdyEe5N_jY1BqJuK8IjMlHnBfG2EWMhqxcVdcs4gJkz6/s640/JunePhase4all500mb.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">500-millibar geopotential height anomalies when the MJO is in Phase 4 during the month of June.<br />
Source: American Weather</td></tr>
</tbody></table>
When the MJO is in Phase 4 during the month of June, positive height anomalies tend to be favored over the Gulf of Alaska into parts of the Aleutian Islands, with another area of positive height anomalies over Greenland. Below-normal anomalies are then painted across a good swath of the eastern two-thirds of North America.<br />
<br />
If you're thinking that this Phase 4 composite above looks remarkably similar to the forecasted pattern beginning around June 11th, as discussed earlier in this post, you aren't the only one. It doesn't seem coincidental to me that model guidance maintains the +PNA/-NAO pattern through much of the remainder of June, particularly since the MJO moving into Phase 4 would support exactly this kind of pattern to continue.<br />
It is possible that guidance thinks the PNA will weaken and even reverse into a negative state by late June simply because the models are - correctly - trained to forecast the state of a teleconnection by comparing the forecasted pattern with a "textbook" pattern. For example, scientists have developed what the atmosphere should look like when the PNA is said to be positive, and thus models compare their forecast to that "ideal" pattern to determine what state the PNA will be in. However, the atmosphere is not binary like that - in other words, even though the PNA might be forecasted to be negative, the pattern itself may still resemble a positive PNA. Let's discuss this further.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgOffSBAijwn-e6LUpKrNGItRiCYNrqSlF4YRD8TlOU6UCmDdGV0h8n5Fe0mNbb11PSoPiQO9LRLm6iERa5r0TeGnChvKFnjVWHHR7mUCmRjUxqzcWQfUxMtcbix5sWgOBGtFIxx8ujD7TD/s1600/gfs-ens_z500a_namer_52.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="638" data-original-width="1024" height="398" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgOffSBAijwn-e6LUpKrNGItRiCYNrqSlF4YRD8TlOU6UCmDdGV0h8n5Fe0mNbb11PSoPiQO9LRLm6iERa5r0TeGnChvKFnjVWHHR7mUCmRjUxqzcWQfUxMtcbix5sWgOBGtFIxx8ujD7TD/s640/gfs-ens_z500a_namer_52.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 500-millibar geopotential height anomalies valid 7am Central, June 21st, with annotations.<br />
Source of image: Tropical Tidbits<br />
Source of annotations: Author</td></tr>
</tbody></table>
Shown above is the 500-millibar height anomaly forecast from the GFS Ensembles, valid the morning of June 21st. This is the purported date by which the PNA is forecasted to turn negative, as per the four-panel graphic examined earlier in this article. Looking at the broad forecasted pattern, however, shows the pitfalls that simply taking the index forecast & going with it can present.<br />
<br />
First, we recognize why guidance thinks the PNA will flip from strong-positive to a negative state: there is an expectation that troughing will develop along and off the coast of western North America, a part of which I have circled in red. To be sure, stormy activity in this region is indeed what a negative-PNA consists of, so the models are not at fault here. The issue we want to resolve is a lack of context that looking <u>only</u> at forecasts of the indexes results in.<br />
<br />
When broadening out beyond the trough along the western coast of the continent, the ridge that is expected to send the PNA into strong positive territory is seen, now having retrograded slightly into the Gulf of Alaska. The movement of the ridge to the west is indeed why troughing is seen developing along the western coast. But take a look at the way the ridge extends into Alaska to see what I mean by 'lack of context'. Instead of merely topping off around Anchorage, the positive anomalies extend well into Alaska, and join up with another ridge based in Canada, the combination of which then pushes into the Arctic Circle. That doesn't mean much for the trough along the west coast of the continent, but it's certainly something we need to note, and here's why.<br />
<br />
Take a look at Greenland again. The strong ridge is still forecasted to be positioned over Greenland, keeping the negative-NAO in place, as expected by the four-panel teleconnection graphic from above. Big deal, so what? So, the negative NAO pattern keeps colder than normal conditions in place over the Northeast U.S., Great Lakes and into the Mid-Atlantic. But with that strong ridge in Alaska and Canada, I find it more plausible that the lobe of colder weather will also affect the Midwest, parts of the Plains, and the Ohio Valley. Why? That ridge in western Canada will team up with the Greenland ridge to force the primary lobe of cold air to the south, as is already seen in the graphic above.<br />
<br />
But it's the fact that the Gulf of Alaska ridge extends its influence into the Canadian ridge that makes me think those regions will also be affected by cold air. The alignment of the Gulf of Alaska ridge suggests it shouldn't be difficult at all for that ridge to push northeastward into Canada, where the other ridge is based. If/when this happens, the trough along the western coast of North America will be suppressed, and perhaps even displaced to the south towards the Southwest U.S., which could then allow the ridge to build back into the southwest part of Canada or even into the Pacific Northwest again.<br />
<br />
All in all, that would allow a more positive-PNA-esque pattern to emerge (with respect to cold air hitting the mid-section of the country and not just the Northeast), even though by definition we should be in a neutral or even negative-PNA state, since that trough will still likely stick around, just a little farther south.<br />
<br />
Whether this scenario actually plays out is something only time will tell, of course, but I wanted to emphasize this because when looking at teleconnection forecasts, you need to also know the *context*. I have gotten burned plenty of times by only going off the teleconnection forecasts (for example, only seeing a -NAO or +PNA and basing the forecast off that) and not understanding the context for that forecast (for example, the +PNA might not be as sturdy as the teleconnection forecast shows because of a strong upper level low just to the west of North America, or something along those lines).<br />
<br />
---<br />
<br />
All told, this provides a good basis for my outlook for the remainder of June.<br />
<br />
- <i><u><span style="font-size: large;">Through the middle of June</span></u></i>, I expect colder than normal conditions to evolve for the eastern two-thirds of the country. This cooler weather will be widespread, with areas only west of the Front Range likely to see seasonal to above-normal temperatures. In terms of precipitation, any severe weather threats should stay confined to the southern portion of the country, with the jet stream and broader pattern alignment unfavorable for any severe weather outbreaks at this time.<br />
<br />
- <span style="font-size: large;"><u><i>From the middle of June to the end of June</i></u></span>, I expect a continuation of this cooler than normal pattern, though with a reprieve coming for the Plains and perhaps parts of the Midwest as a trough builds in to parts of western North America to return some parts of the central U.S. to more seasonal conditions. However, firmly cooler than normal conditions should persist for the eastern third of the country, especially in the Northeast. Any seasonal conditions will be pockmarked by cooler bouts of weather for those in the Midwest and Great Lakes into the Ohio Valley, though again the coldest conditions should stay further east. Storm chances should increase for the central part of the country with a return to more seasonal weather, but zonal flow aloft and the lack of a ridge in the Southeast should dissuade any significant severe threats from hitting the Central U.S., and likely from hitting the country in general.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-24626546297128080362019-06-05T12:55:00.000-05:002019-06-05T12:55:42.413-05:002019-2020 Winter Forecast Release Dates<div dir="ltr" style="text-align: left;" trbidi="on">
For the 2019-2020 winter, I will be publishing two outlooks: a Preliminary winter forecast, as well an Official winter forecast. There will not be a Final winter forecast.<br />
<br />
The <span style="color: red; font-size: large;"><u>Preliminary 2019-2020 Winter Forecast</u></span> will be published on <u><span style="color: red; font-size: large;">August 17, 2019 at 12:00 PM Central Time</span></u> (1:00 PM Eastern Time).<br />
<br />
The <span style="color: red; font-size: large;"><u>Official 2019-2020 Winter Forecast</u></span> will be published on <u><span style="color: red; font-size: large;">October 12, 2019 at 12:00 PM Central Time</span></u> (1:00 PM Eastern Time).<br />
<br />
Of course, these dates will be brought up over the course of the summer and early fall: this will not be the only time the release dates are published & talked about. Hope to see you there!<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4IwcIS94LCKmD4OPyDpG02tC6DRAlksljdXHmN5TPP3hyphenhyphenycKj-4K9ma8d1W5fMwiVJVJfjTLVEReKq9bNQpszbIptSlJ0e5AuCWPIbwbAiobyItscwlSUPPLC_e3rsJYhJb9uJdgNHGws/s1600/winter+forecast+dates.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="400" data-original-width="800" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4IwcIS94LCKmD4OPyDpG02tC6DRAlksljdXHmN5TPP3hyphenhyphenycKj-4K9ma8d1W5fMwiVJVJfjTLVEReKq9bNQpszbIptSlJ0e5AuCWPIbwbAiobyItscwlSUPPLC_e3rsJYhJb9uJdgNHGws/s640/winter+forecast+dates.png" width="640" /></a></div>
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com1tag:blogger.com,1999:blog-1448180228140749967.post-60594646931871274112019-06-05T11:51:00.000-05:002019-06-05T11:51:28.532-05:00Positive QBO Set to Strengthen Polar Vortex in Winter 2019-2020<div dir="ltr" style="text-align: left;" trbidi="on">
The emergence of a strong positive-QBO state in the stratosphere in recent months looks set to persist into the coming winter, with a likelihood of a stronger-than-normal stratospheric polar vortex as a consequence. This, of course, will feed into the broader winter outlook for the United States as a result. Click any image to enlarge it.<br />
<br />
---<br />
<br />
As a side note, thank you to all of those who sent well-wishes for my wisdom teeth surgery the other day! The surgery went very smoothly and the recovery has been remarkably painless, which lets me get back to writing these posts quicker!<br />
<br />
---<br />
<br />
Of course, before we dive into the juicy stuff, we need to first briefly review what the QBO phenomenon is.<br />
<br />
The Quasi-Biennial Oscillation, or QBO, in a nutshell measures the direction of winds in the stratosphere located over the equatorial regions. The QBO has two phases: a positive phase and a negative phase.<br />
In the positive phase of the QBO, stratospheric winds over the equator are westerly (from the west, to the east). This has the effect of strengthening these "westerlies" in the stratosphere in the upper latitudes of the Northern Hemisphere, in this case promoting a stronger polar vortex as the stronger westerlies strengthen the vortex.<br />
The negative phase of the QBO sees these stratospheric winds over the equator turn easterly (from the east, to the west), which has the effect of slowing down the westerly flow in the stratosphere of the upper-latitudes of the Northern Hemisphere. Consequentially, this weakens the stratospheric polar vortex, all else equal.<br />
<br />
Let's take a look at the recent history of the QBO to see what we're working with heading into the summer and fall months.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFX3QmRU_1pZwegjuQrBeeZDIVSRxdTqx07PbIfOJMdQbSHR3dE7XcF8IZGiDkBHWqMtc6cnFjrJNMCYMOTI24omT8ZmF_Snysp58gfb9RCUBxYFs1PQuhhDD6Oan8N52SUvkFkItGe7cd/s1600/Screen+Shot+2019-06-05+at+12.00.10+AM.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="283" data-original-width="605" height="298" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFX3QmRU_1pZwegjuQrBeeZDIVSRxdTqx07PbIfOJMdQbSHR3dE7XcF8IZGiDkBHWqMtc6cnFjrJNMCYMOTI24omT8ZmF_Snysp58gfb9RCUBxYFs1PQuhhDD6Oan8N52SUvkFkItGe7cd/s640/Screen+Shot+2019-06-05+at+12.00.10+AM.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Screenshot of recent wind values to illustrate the QBO. Positive (negative) QBO wind values are shown in gray (white) shaded areas.<br />
Source of screenshot: Free University of Berlin<br />
Source of annotations: Author</td></tr>
</tbody></table>
The QBO is readily seen in this time-series view of stratospheric wind values and directions over the Equator, with the positive phases of the oscillation laid out in gray shading and the negative phase shown in white shading.<br />
<br />
I've annotated this image to point out the recent emergence of westerlies over the Equator, displayed on the screenshot by the swath of gray shading and positive contour values. As of the latest observations, the westerlies had propagated down to about the 70-millibar level over the Equator, meaning this wave of westerly winds is well on its way and we are firmly entrenched in a positive QBO regime.<br />
<br />
Of course, this has notable implications for the coming winter. As this blog has discussed extensively in previous winters, the stratosphere can be used to glean extensive information about the broader forecast, whether on a scale of days or months. In this case, to identify what a positive QBO winter may entail (holding all else equal, of course), I've gone through the Climate Prediction Center's 30-millibar dataset of equatorial stratospheric wind speeds and direction and sorted each calendar month in a descending order. Then, for the three primary winter months (December, January and February), I pulled the years of the five strongest positive QBO values for each month. Given that the QBO is a prolonged oscillation (whereas something like the North Atlantic Oscillation changes in a matter of days), this method pulled out only eight distinct winters. I then created composite images of different atmospheric variables during the winter months for these eight years to give an idea of what a positive QBO environment generally entails.<br />
<br />
First, let's see what a 'typical' positive QBO brings in terms of the Northern Hemisphere's stratosphere.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9Apn_GIM8aKSc6Ix7ejpN8GHH8sLGe1waz2m2Imfp5ja_rK3VrRLfa0GcecYLNiS0Q1_Bk4nTe0gk9WnA3mKvDHpCUSBzBBqnJT2-qC-4b7fdL1OZeTDNK8oyCXeyUIMaWkHDJ12D_1Ep/s1600/posQBO50mbNH.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="542" data-original-width="700" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9Apn_GIM8aKSc6Ix7ejpN8GHH8sLGe1waz2m2Imfp5ja_rK3VrRLfa0GcecYLNiS0Q1_Bk4nTe0gk9WnA3mKvDHpCUSBzBBqnJT2-qC-4b7fdL1OZeTDNK8oyCXeyUIMaWkHDJ12D_1Ep/s640/posQBO50mbNH.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">50-millibar geopotential height anomalies over the Northern Hemisphere for the December-February periods of eight positive-QBO winters (with the year of the LAST month in the DJF period shown).<br />
Source: ESRL</td></tr>
</tbody></table>
As the above image shows, the aforementioned strategy produced the winters of 2016-2017, 2013-2014, 2015-2016, 2010-2011, 1990-1991, 1982-1983, 2008-2009 and 1992-1993, in no particular order. I first produced a graphic showing the geopotential height anomalies over the Northern Hemisphere for those winters at the 50-millibar level, right about at the mid-section of the stratosphere. This level was chosen to give a more-arbitrary view of the stratospheric polar vortex, as there can be issues preferring to look at the 100-millibar level as well as the 10-millibar level.<br />
<br />
Creating this composite image confirms the explanation given to what happens in a positive QBO environment: the stratospheric polar vortex in the Northern Hemisphere strengthens. Indeed, the strong negative anomalies centered over the Arctic Circle in this composite show the enhanced westerlies providing strength to the polar vortex, thereby keeping the cold air locked up in the Arctic. It's no wonder that those who enjoy winter weather are firmly in favor of the negative phase of the QBO!<br />
<br />
Next, I took these same years but changed the height level of the atmosphere from 50 millibars to 500 millibars.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQTb9-LFeMzvTfBNV7jNthX1qPdVM1LwFs2P3sNLHHQIpWO59zlE8x81jKaOZ6UA1nIRI2fJDzxkGG5PLXXjJ80dq9dAeIDzozjna-5ethdXDjjpsaRehrnqyoQ2MPanX2Lskj4Rm-X-lK/s1600/posQBO500mbNH.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="542" data-original-width="700" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQTb9-LFeMzvTfBNV7jNthX1qPdVM1LwFs2P3sNLHHQIpWO59zlE8x81jKaOZ6UA1nIRI2fJDzxkGG5PLXXjJ80dq9dAeIDzozjna-5ethdXDjjpsaRehrnqyoQ2MPanX2Lskj4Rm-X-lK/s640/posQBO500mbNH.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">500-millibar geopotential height anomalies over the Northern Hemisphere for the December-February periods of eight positive-QBO winters (with the year of the LAST month in the DJF period shown).<br />
Source: ESRL</td></tr>
</tbody></table>
The story isn't too different when moving down to the 500-millibar level, which is where meteorologists look to identify the features that more directly impact you and me. For example, warmer colors on this map illustrate ridges of high pressure, while cooler colors identify low pressure areas. Given the stronger polar vortex, it's therefore not a surprise to see a swath of below-normal height anomalies extending from Greenland into Canada, symptomatic of a relatively-stronger tropospheric polar vortex.<br />
<br />
I do want to briefly discuss another feature here, however, and that's the extreme positive height anomalies in the Bering Sea. A sharp-eyed weather enthusiast may recognize that swath of well-above-normal geopotential heights as an almost-textbook negative phase of the West Pacific Oscillation, or WPO. In contrast to the QBO, which records changes in terms of months, the WPO changes on a daily basis, making it more useful for daily & weekly forecasts as opposed to seasonal forecasts. Still, this is important, and especially-so for fans of winter weather.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj65FnZ4NQGvEixgkySDRu2DRVH6Vs0kFk5tY27uMVOKBc8m5Xbo1PNj3KvyROI9Y7h2ul9rL9Y67Ql7gnyTyT0jN2p-JeXXcnLVuHB6pW9Wbv1pZO7pSTpocmlf5l6IunJgzWdZ3OYWO1F/s1600/wpo.composite.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="792" data-original-width="612" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj65FnZ4NQGvEixgkySDRu2DRVH6Vs0kFk5tY27uMVOKBc8m5Xbo1PNj3KvyROI9Y7h2ul9rL9Y67Ql7gnyTyT0jN2p-JeXXcnLVuHB6pW9Wbv1pZO7pSTpocmlf5l6IunJgzWdZ3OYWO1F/s640/wpo.composite.gif" width="494" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Composite image of 500-millibar geopotential height anomalies (top panel) and surface temperature anomalies (bottom panel) in the positive phase of the West Pacific Oscillation.<br />
Source: ESRL</td></tr>
</tbody></table>
The composite image above shows what typically happens when the WPO is positive, so for our discussion of the *negative* phase, simply view the anomalies as opposite for a rough idea of what a negative WPO entails. All else equal, the negative phase of the West Pacific Oscillation involves a strong ridge over the Bering Sea, like what was shown in the positive-QBO composite image right above this. That strong ridge tends to try and force itself further north into the Arctic Circle, which then pushes the jet stream further north. As a consequence, downstream of that ridge, a trough over Canada is coerced into shifting south and even a little west, not dissimilar to what the positive-QBO composite image shows with negative anomalies in southwest Canada extending into the Pacific Northwest. This then can encourage a ridge to build in the eastern U.S., however, which prohibits the cold air from making it too far east.<br />
<br />
In other words, the positive phase of the QBO tends to create a strong ridge in the Bering Sea, holding all other variables equal, in a pattern that is then classified as the negative phase of the WPO. These two oscillations may be different in definition but their impact on the contiguous United States is similar: colder and stormier weather in the West U.S., the potential for a ridge in the eastern or southeastern U.S., and the threat for storm systems to ride the jet stream northeast across the Plains into the Midwest and Great Lakes.<br />
<br />
Let's see if that explanation holds up to the 'typical' surface temperature anomalies in a positive QBO event.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgpgXuG7aGeBxtgHAA9z3DFtwhdNrW_6lB0aX5T3LPt-QRpiMhqTQtmpPUn35d3cFkahlcsTIo0mISLRo5nV0SHzKsb_GOPJ8HftFa3bZtUniTuKqafv2xUXIFndVjXCf7nZOejbgyC8c6k/s1600/posQBOsurfacetempNA.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="542" data-original-width="700" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgpgXuG7aGeBxtgHAA9z3DFtwhdNrW_6lB0aX5T3LPt-QRpiMhqTQtmpPUn35d3cFkahlcsTIo0mISLRo5nV0SHzKsb_GOPJ8HftFa3bZtUniTuKqafv2xUXIFndVjXCf7nZOejbgyC8c6k/s640/posQBOsurfacetempNA.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Surface temperature anomalies over North America for the December-February periods of eight positive-QBO winters (with the year of the LAST month in the DJF period shown).<br />
Source: ESRL</td></tr>
</tbody></table>
The surface temperature anomalies in positive-QBO environments does seem to match up with what was described immediately prior. In these winters with a positive QBO, colder than normal temperatures are more predominant in the northern third of the country, maximized in the North Plains and northern Rockies into western Canada. Conversely, warmer-than-normal temperature anomalies tend to be more likely in the southern third of the country, with a particular preference for warmer temperatures along the East Coast as that ridge I mentioned seems to try and make an appearance.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhREDVnun0kgsdcDOOzK1yHqQBpDMvnlkxjiH72pNB1sMPQgpBUCpawooFX118-NUV5MPVGVls18axuuiYUQF8jcv3zvujyfUK6gCN5aMeChzURMBeYcut3noUlmExHch12H3GBenzy-MPv/s1600/C7uTGh77z6.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="542" data-original-width="700" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhREDVnun0kgsdcDOOzK1yHqQBpDMvnlkxjiH72pNB1sMPQgpBUCpawooFX118-NUV5MPVGVls18axuuiYUQF8jcv3zvujyfUK6gCN5aMeChzURMBeYcut3noUlmExHch12H3GBenzy-MPv/s640/C7uTGh77z6.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">250-millibar vector wind anomalies over North America for the December-February periods of eight positive-QBO winters (with the year of the LAST month in the DJF period shown).<br />
Source: ESRL</td></tr>
</tbody></table>
Just to push the point home a bit more, above is a composite image of vector wind anomalies over North America at the 250-millibar level (roughly the jet stream) for those eight positive-QBO winters. In other words, this gives an idea of how the jet stream is oriented during winters with a positive QBO, all else equal.<br />
<br />
In a positive QBO winter, we tend to see the strong ridge over the Bering Sea force the Pacific jet stream to the north, as previously discussed, before it buckles south as it crashes into North America. From there, things get a little tricky. It seems plausible that the jet stream oriented in this fashion wouldn't be sufficient enough to pull storm systems into the Southwest (not as an overarching theme, at least), but would be sufficient to likely come onshore somewhere in northern California or Oregon and then ride a rather-zonal path to the east before turning northeast somewhere over the Plains. This kind of storm track would keep the Northern Plains most pointedly under the gun for winter weather threats, but the hint of a subtropical jet stream along the Gulf Coast suggests this storm track would not necessarily be the only track. That's a positive thing for those in the East U.S. who are hoping for a snowy winter.<br />
<br />
<span style="font-size: large;"><b><i>To Summarize:</i></b></span><br />
- The Quasi-Biennial Oscillation (QBO) is currently in its positive phase, and is likely to remain this way into the coming winter.<br />
- Typically, a positive-QBO winter brings cooler than normal conditions to the northern third of the country and warmer conditions to the southern third and East Coast.<br />
- A positive QBO also seems prone to supporting a negative-WPO state.<br />
- Most importantly, however, a positive QBO supports a stronger stratospheric polar vortex, which restricts the flow of cold air to lower latitudes.<br />
- As such, a positive QBO this winter may temper the likelihood of colder than normal conditions for the United States as a whole.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com1tag:blogger.com,1999:blog-1448180228140749967.post-70999233536310179032019-05-28T13:04:00.000-05:002019-05-28T13:04:52.778-05:00ENSO Analysis and Outlook: Fall into Winter 2019<div dir="ltr" style="text-align: left;" trbidi="on">
This post will analyze the current state of the El Nino-Southern Oscillation (ENSO) phenomenon as well as forecasts for its nature through fall 2019 and into the early winter months of 2019. It is critical to note right off the bat that this is <u>*not*</u> an ENSO forecast for the winter of 2019-2020, but the forecast period we will be going over will tread into November and December. Click on any image to enlarge it.<br />
<br />
We will first define what the ENSO phenomenon is, and why we care about it.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgflBQSjnCGmGIXVvVJxo9MFQGZyQUuQlSVv1jKY6X6UENb31e96Q4HBdRy_WpRy2DPlYWiA1FByX3mgMj_NvFaUFeNcwvXSXkYYUsGeboUh0WrN7zmzXDLKyCTnicOPpainSY9HgIzWI1A/s1600/ninoareas_c.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="251" data-original-width="572" height="280" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgflBQSjnCGmGIXVvVJxo9MFQGZyQUuQlSVv1jKY6X6UENb31e96Q4HBdRy_WpRy2DPlYWiA1FByX3mgMj_NvFaUFeNcwvXSXkYYUsGeboUh0WrN7zmzXDLKyCTnicOPpainSY9HgIzWI1A/s640/ninoareas_c.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Graphical depiction of the four different ENSO monitoring areas.<br />
Source: Climate Prediction Center</td></tr>
</tbody></table>
The ENSO phenomenon, in a nutshell, is a primary driver of seasonal (and, through other shorter-term oscillations, weekly or even daily) weather patterns by way of sea surface temperature (SST) anomalies in the waters across the Equatorial Pacific. When these sea surface temperatures are above normal, we call it an 'El Nino' event. When these anomalies are below-normal, we call it a 'La Nina' event. While we monitor the entire Equatorial Pacific to analyze the ENSO phenomenon, there are four primary "zones" through which to observe. They are:<br />
<br />
<br />
<ul style="text-align: left;">
<li>Nino 1+2. This is a small slice of the Pacific located between the Equator and the 10º South latitude line, extending from the far western tip of Peru to the 90º West longitude line.</li>
<li>Nino 3. This is a larger slice of the Equatorial Pacific which spans from 5º North to 5º South latitude lines, and from 90º West to 150º West longitude lines.</li>
<li>Nino 4. This is also a larger slice, and also extends between 5ºN and 5ºS on the latitude markers. For Nino 4, however, the space is spread by longitude from 150º West to about 160º East, crossing the dateline in the process.</li>
<li>Nino 3.4. This is the critical area to watch, and is typically viewed as the primary space with which to assess the state of the ENSO phenomenon. Spatially, it extends from 5ºN-5ºS latitudinally, and 120º West to 165º West longitudinally. </li>
</ul>
<br />
Why do we break this space up into four different pieces rather than just average out the sea surface temperature anomalies and call it a day? A number of scientists with far more knowledge and research than I have come to determine that there can be more than one type of El Nino - where typically El Nino's bring warmer than normal waters to the eastern Pacific, an "El Nino Modoki" event brings warm waters to the western Pacific, and cooler waters to the eastern Pacific. This is not a trivial difference, but for our purposes here, we won't dive into that topic. For now, the key is understanding there are four different regions in which we monitor the ENSO phenomenon, with the Nino 3.4 region broadly being of most importance.<br />
<br />
Let's view sea surface temperature anomalies over the Pacific now, with a focus on those regions that were just outlined.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhkPoiN6Y4JCY5bzEBqYAiSyAq3t9M3qvzRiqJhs7j68-UTNIkdB_OYHbhh9YeV_GY5_ms1B9hSNLGCsAWiWXUEZak2qCtks6xzbwzcPyJZUCedzz0fN1AE9vtdGfEp5Tfw_wRgJes9FHiO/s1600/anomp.5.20.2019.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="580" data-original-width="930" height="398" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhkPoiN6Y4JCY5bzEBqYAiSyAq3t9M3qvzRiqJhs7j68-UTNIkdB_OYHbhh9YeV_GY5_ms1B9hSNLGCsAWiWXUEZak2qCtks6xzbwzcPyJZUCedzz0fN1AE9vtdGfEp5Tfw_wRgJes9FHiO/s640/anomp.5.20.2019.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Observed sea surface temperature anomalies on May 20th, centered over the Equatorial Pacific.<br />
Source: NOAA</td></tr>
</tbody></table>
As of May 20th, sea surface temperature anomalies along the Equatorial Pacific were, on the whole, above normal. A solid swath of above-normal anomalies extended across Oceania to about the 130º West longitude line. From there to about the 110º West longitude line, however, SST anomalies were seen closer to zero, with a very small area of slightly below-normal temperature anomalies. We'll get in to why that's there in a little bit. By the 100º West line of longitude, however, solidly above-normal sea surface temperature anomalies return to the western tip of Peru.<br />
<br />
Based on what was discussed earlier, this seems to point towards the presence of an El Nino event (the positive state of the ENSO phenomenon). To confirm or reject this, the Earth System Research Laboratory (ESRL) has composed a Multivariate ENSO Index (MEI) to quantify the state of the ENSO phenomenon, as shown below.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjaaeGBJV4PEYoNCuwrbKezzw1qITqG4cnIE4Bf7-yaaeiFoJt8pM0-I80sRqYG88UT9IfCTz6cQEORp66TTgYGZfIZsBzzt_DyF1TEp7amE83LChT8IDFxAw2NZ6Tx6u2KoxclGNKd0ssl/s1600/esrl+MEI.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="637" data-original-width="1150" height="354" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjaaeGBJV4PEYoNCuwrbKezzw1qITqG4cnIE4Bf7-yaaeiFoJt8pM0-I80sRqYG88UT9IfCTz6cQEORp66TTgYGZfIZsBzzt_DyF1TEp7amE83LChT8IDFxAw2NZ6Tx6u2KoxclGNKd0ssl/s640/esrl+MEI.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">MEI, showing positive (El Nino) and negative (La Nina) changes to the ENSO phenomenon.<br />
Source: ESRL</td></tr>
</tbody></table>
The MEI aims to determine if there is an El Nino in place (via positive index values), if there is a La Nina in place (via negative index values), or if there is a neutral-ENSO state (via index values equal to zero). You can identify a few extreme events on here, such as the strong El Nino in 1997 and the substantial La Nina event in 2010. Looking to the last several data points, it appears that there has been a general trend towards an El Nino event, but nothing particularly steady is in place.<br />
<br />
I say nothing steady is in place because, as a general rule of thumb, an El Nino (La Nina) is present if sea surface temperature anomalies are above-normal by at least +0.5 degrees Celsius (below-normal by at least -0.5 degrees Celsius). If SST anomalies are positive but just barely so, it's technically a neutral-ENSO state, but clearly there's a better shot at an El Nino forming down the line. The same logic applies to SST anomalies that are negative but just barely so, with respect to a La Nina.<br />
<br />
As of May 9th, the Climate Prediction Center continued its El Nino Advisory (<a href="https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.pdf">click here</a> for full briefing), which indicates that an El Nino event is ongoing. Indeed, the agency assigns a 70% probability of an El Nino continuing through the summer months, with a 55-60% chance of the El Nino persisting through the fall months. These probabilities may seem rather low given that the El Nino is actually occurring already, but as the rest of this post will show, it isn't that cut-and-dry with the ENSO phenomenon.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLgVAvD75cuusDaN9uGE3Li5Wz3Wnln9jne-xMAPuT2BzJcwVcWznIOj6AMAQRP8XtHz_8mRp7R6DG9DSbs-0M-xbWuS8BjI6i0VA08XujJMnbhlMO5ymiuncIWA8CZCwWJMRqeTrG96Il/s1600/nino+region+anoms.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="352" data-original-width="306" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLgVAvD75cuusDaN9uGE3Li5Wz3Wnln9jne-xMAPuT2BzJcwVcWznIOj6AMAQRP8XtHz_8mRp7R6DG9DSbs-0M-xbWuS8BjI6i0VA08XujJMnbhlMO5ymiuncIWA8CZCwWJMRqeTrG96Il/s400/nino+region+anoms.gif" width="347" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">SST anomalies for each of the ENSO regions.<br />
Source: CPC</td></tr>
</tbody></table>
Since we've already learned about the four different ENSO regions, it's time to apply that to observed data. Shown above are four panels of SST anomaly data over the past twelve months, with each panel corresponding to a different ENSO region. The top panel shows SST anomalies for the Nino 4 region; the second-from-top panel for the Nino 3.4 region; the second-from-bottom panel for the Nino 3 region; and the bottom panel for the Nino 1+2 region. In the aggregate, the data confirm that we are in an El Nino event, at least judging by sea surface temperature anomalies, with anomalies exceeding the +0.5º Celsius threshold in the Nino 4 and Nino 3.4 regions, with anomalies in the Nino 3 region right around that threshold. In contrast, the Nino 1+2 region has reversed to marginally-negative SST anomalies. This likely owes to the weak but broad area of slightly below-normal anomalies immediately southwest of the westernmost tip of Peru back on that observed SST anomaly graphic. Since it isn't a significant deviation, I don't see any major reason to raise concern over the difference in Nino 1+2 with the other three regions.<br />
<br />
We are also able to look at sea temperature anomalies with varying depth along the Equator in the Pacific, as shown below.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiGw8blE2AUCT5hy5r9X2blGtE5rMOeshtrgDBLF0tiKIlrRqdDONQjy-CaVGKnM88PNS7gG1pIGTto2iwrr5aWcovN0Gm-JvY8Md7AwahiSj4FRYOkEew92YeDfPzl1-KB4UlBbxrLxAbj/s1600/equatorial+temperature+depth.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="880" data-original-width="680" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiGw8blE2AUCT5hy5r9X2blGtE5rMOeshtrgDBLF0tiKIlrRqdDONQjy-CaVGKnM88PNS7gG1pIGTto2iwrr5aWcovN0Gm-JvY8Md7AwahiSj4FRYOkEew92YeDfPzl1-KB4UlBbxrLxAbj/s640/equatorial+temperature+depth.gif" width="494" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Equatorial temperature anomalies (top) and observed nominal temperatures (bottom) as of May 18th.<br />
Source: CPC</td></tr>
</tbody></table>
Viewing sea temperature anomalies along the Equator as a function of depth can prove massively beneficial to forecasting abilities, as it can enable the forecaster to identify an area of well-below-normal anomalies right below the surface that is eating away at above-normal SSTs on the surface. In this hypothetical, someone only viewing the surface map would think there's a solid El Nino in place, but the forecaster with the depth map as well can see that the El Nino is actually about to dissolve.<br />
<br />
Turning back to actual data, the depth chart above shows a broad expanse of above-normal water temperatures extending from 140º East to about 120º West longitudinally, with the positive anomalies reaching a depth of almost 150 meters in the western portion of this swath. However, when reaching the 120º-100º West longitude area, well-below-normal temperature anomalies appear, and seem to be threatening the warmer anomalies located at the surface. We can view an animation of this depth map to see how these two opposing bodies of water have been interacting lately.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ocean/anim/wkxzteq_anm.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="405" data-original-width="540" height="480" src="https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ocean/anim/wkxzteq_anm.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Sea temperature anomalies by depth, animated. Refresh the page if the animation stops looping.<br />
Source: CPC</td></tr>
</tbody></table>
Indeed, when viewing the animation we are able to grasp the rather-dire situation the ongoing El Nino seems to be in. After covering almost the entire Equatorial Pacific with well-above-normal temperature anomalies from the surface to almost 150 meters down in March, cooler than normal waters have gradually grown between 150 meters and 250 meters below the surface since then and have materially weakened the formerly-stout positive temperature anomalies below the surface. Even more concerningly for the El Nino, the negative temperature anomalies appear to be growing and deepening east of the 120º West line of longitude, suggesting that the positive SST anomalies in that vicinity may be at risk of dissolving in coming weeks.<br />
<br />
We have the ability to determine if this is likely to happen.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhO_RfyfVPkW_TNiQGVOnPVx3wxlqOZjlFqFiCW9X7G6N7XPSwwnBUzdX1YNXbpy8OJz1aSLAPgS4DLUPcZMGjUvColHX3tVC6ssDL7sYHPXESnL-wjMD_lY_R41T8FZUsdpWeqk3ZumxEL/s1600/tlon_heat.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="677" data-original-width="536" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhO_RfyfVPkW_TNiQGVOnPVx3wxlqOZjlFqFiCW9X7G6N7XPSwwnBUzdX1YNXbpy8OJz1aSLAPgS4DLUPcZMGjUvColHX3tVC6ssDL7sYHPXESnL-wjMD_lY_R41T8FZUsdpWeqk3ZumxEL/s640/tlon_heat.png" width="506" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Equatorial Pacific upper-ocean (through 300 meters) heat anomalies over the last year.<br />
Source of graphic: CPC<br />
Source of annotations: Author</td></tr>
</tbody></table>
El Nino and La Nina events can be driven by Equatorial Kelvin Waves, and whether the wave moving eastward along the Equatorial Pacific is upwelling or downwelling. If that sentence made you raise an eyebrow, you're most likely not alone. I can assure you, though it's actually pretty simple to understand. Let's break it down.<br />
<br />
The phrase 'Equatorial Kelvin Wave' seems intimidating, so for our purposes here all we need to know is that, from time to time, these Equatorial Kelvin waves develop in the western part of the Equatorial Pacific and gradually move eastward along the Equator. When they move eastward along the Equator, they can be either 'downwelling' or 'upwelling' waves.<br />
Consider the explanation of a 'downwelling' Equatorial Kelvin wave as described by the NOAA (read the full article <a href="https://www.climate.gov/news-features/blogs/enso/oceanic-kelvin-waves-next-polar-vortex">here</a>):<br />
<i><br /></i>
<i>"Normally, winds blow from east to west across the tropical Pacific, which piles up warm water in the western Pacific. A weakening of these winds starts the surface layer of water cascading eastward..."</i><br />
<br />
In other words, if this wind pattern that blows winds from east to west breaks down, that warmer than normal water begins pushing eastward along the Equatorial Pacific. This anomalously warm water works its way eastward gradually and tends to sustain itself in the process. As a consequence, downwelling Equatorial Kelvin waves tend to be associated with El Nino events. You can see my annotations of downwelling Kelvin waves as solid lines on the above image.<br />
On the flip side, an 'upwelling' Equatorial Kelvin wave can be thought of as the ocean waters trying to get itself a little more in balance in the wake of this very warm downwelling wave. Thus, an upwelling wave again features a Kelvin wave slowly progressing eastward, but this time it cools down the upper-ocean waters to a degree that upwelling Kelvin waves are generally associated more with La Nina events. In the above image, I've made an attempt to outline upwelling Kelvin waves by the dashed lines.<br />
<br />
Given that we've had three clear downwelling Equatorial Kelvin waves traversing the Equatorial Pacific over the last year, as outlined on the above image, it's not necessarily a shock that we are in an El Nino at this time. In addition, we are able to use the above image to see that the emergence of cooler than normal water temperatures in the eastern equatorial Pacific appear to be the result of an upwelling equatorial Kelvin wave, as shown by the dashed line at around 110º West longitude.<br />
<br />
I want to point out something that could endanger the El Nino by the time we reach late summer/early fall, however. Referring back to the above image, note how an area of cooler than normal water temperatures have developed between longitude lines 130º E and 160º E. I've circled this swath for two reasons: because it is a rather expansive area of cooler waters relative to previous below-normal anomalies in the other two more-apparent upwelling Kelvin wave episodes, and because it has brought about the strongest negative temperature anomalies in that portion of the equatorial Pacific in at least a year. The risk here is that this is the beginning of another upwelling equatorial Kelvin wave, which will move eastward with time and bring those below-normal temperature anomalies to the Nino regions. Should this occur (and it is not a certainty yet), it could endanger the El Nino, which is already in a more fragile position as a consequence of the existing sub-surface below-normal water temperature anomalies. We will have to monitor this in the coming weeks to see if it is indeed an upwelling Kelvin wave or merely an isolated area of cooler waters in the western equatorial Pacific.<br />
<br />
As discussed, however, even if this is not an upwelling Kelvin wave beginning to form, there has been a material change in the ENSO phenomenon as of late that necessitates discussion.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhw26s2srtMDOxw16LiN6JVgQl0PMLkH0EtPzHUCCMpym9c3gMz_coK43TKHxag7Qj1GzC0UF6EfQ0_VKv9YKQl77w-pcN8msqGchRkhMNRs7aPzb632Qhk9_YEYIlrnwiX1eqIZLA119S2/s1600/equatorial+upper+ocean+heat+anoms.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="304" data-original-width="607" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhw26s2srtMDOxw16LiN6JVgQl0PMLkH0EtPzHUCCMpym9c3gMz_coK43TKHxag7Qj1GzC0UF6EfQ0_VKv9YKQl77w-pcN8msqGchRkhMNRs7aPzb632Qhk9_YEYIlrnwiX1eqIZLA119S2/s640/equatorial+upper+ocean+heat+anoms.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Upper-ocean heat anomalies in degrees Celsius between 180º and 100º West longitude.<br />
Source: CPC</td></tr>
</tbody></table>
The Climate Prediction Center has allowed us to compile those same anomalies shown in the previous image into a single graphic. This chart shows upper-ocean heat anomalies (in degrees Celsius) between the longitude lines of 180º and 100º West, from the surface to 300 meters down, if I recall correctly. In the presence of an El Nino, these anomalies should be positive, while a La Nina should bring these anomalies into negative territory.<br />
<br />
During the month of May, we have seen a drastic shift in upper ocean heat anomalies, although in reality this shift began in mid-March. Indeed, after peaking at 1.5º C above-normal in the middle of March, those positive anomalies rapidly declined, to the point that they're now just barely in below-normal territory. The negative anomalies aren't strong enough to point to a La Nina, but the change from strongly positive values to marginally negative values is not a trivial one.<br />
<br />
What does it mean? It's a good view of the evaporating above-normal temperature anomalies below the surface of the equatorial Pacific that we discussed earlier. The negative anomalies are likely a bit overdone and not reflective of the true nature of the ENSO phenomenon, given that there is a small yet significant area of below-normal anomalies around the 120º West line of longitude that is most likely distorting this graphic to the downside. As such, while the degradation in positive anomalies is accurate and noteworthy, the recent move into negative territory doesn't seem to be precise in my eyes.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEizidGQ1SqTpBcqMZD8W5IErolPz5oFPRLsVStFwCN0DZcSLLDDvX_sMN5ZUaICmX5jLrDJzuZX4oOO1lWPSHZFmZbxtDimzAf9wNqLQxE0F7NpMMUsQ-KxMb-iHAHxO-rSL6aI_jldUyI_/s1600/alldepths.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="800" data-original-width="1600" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEizidGQ1SqTpBcqMZD8W5IErolPz5oFPRLsVStFwCN0DZcSLLDDvX_sMN5ZUaICmX5jLrDJzuZX4oOO1lWPSHZFmZbxtDimzAf9wNqLQxE0F7NpMMUsQ-KxMb-iHAHxO-rSL6aI_jldUyI_/s640/alldepths.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Temperature anomalies between 2º North and 2º South latitude at the subsurface depths of 55 meters (left), 105 meters (center) and 155 meters (right).<br />
Source: CPC</td></tr>
</tbody></table>
We are able to again see this material deterioration in the El Nino by looking at temperature anomalies along the Equatorial Pacific at three different depths: 55 meters, 105 meters and 155 meters below the surface. The 55-meter chart on the left shows the recent resurgence in below-normal temperature anomalies, erasing the above-normal anomalies that were in place as recently as late April. The 105-meter chart in the middle gives a better look at the underlying trend - indeed, steadfast positive temperature anomalies between 150º East and the dateline have deteriorated since late April, not to mention the elimination of well-above-normal anomalies centered around the 130º West line of longitude.<br />
Perhaps most alarmingly for the viability of the El Nino, the positive temperature anomalies at a depth of 155 meters (right) have completely disappeared and have instead been replaced by marginally below-normal anomalies ever since late March. The lack of a solid underwater base for the El Nino does not bode well for its survival into fall and winter, especially if that aforementioned swath of colder than normal waters around the space between longitude lines 130º E and 160º E does turn out to be another upwelling Kelvin wave. Only time will tell, but this will certainly be something to watch as we move into the fall months.<br />
<br />
We've analyzed a lot of observed data for the ENSO phenomenon, but scientists have put in a lot of hard work to create climate models that can anticipate the state of the phenomenon down the road. Let's take a look at these forecasts.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-ieQOFe7ROl8vxiw5ca18TH6T5288SMPtUc8Knshe_uwYnxi-2qfHmLIVHyr2AqMdObnvEjInSJqYfiG51-aMnWWBQcrIawXYvOtjUJ76IUr_RqzKf75oBz-me0ZYdihdYhy_Lw-qYn1c/s1600/iri+nino+34.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="800" data-original-width="1100" height="464" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-ieQOFe7ROl8vxiw5ca18TH6T5288SMPtUc8Knshe_uwYnxi-2qfHmLIVHyr2AqMdObnvEjInSJqYfiG51-aMnWWBQcrIawXYvOtjUJ76IUr_RqzKf75oBz-me0ZYdihdYhy_Lw-qYn1c/s640/iri+nino+34.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">IRI/CPC suite of forecasts for SST anomalies in the Nino 3.4 region.<br />
Source: IRI of Columbia University</td></tr>
</tbody></table>
There are two graphics of model guidance I want to go over. The first comes courtesy of Columbia University, and depicts a variety of weather models' forecast for sea surface temperature anomalies in the Nino 3.4 region from now until the January-February-March period of 2020. As stated at the start of this post, however we will only discuss forecasts going into November and December, as model guidance begins to diverge too much for my liking beyond that period.<br />
<br />
Model guidance is in pretty good agreement on keeping the El Nino around through at least the August-September-October (ASO) period, with one or two outliers both to the upside and downside of the consensus. Beyond that period, however, divergence increases, although a general theme through the November-December-January period is that positive SST anomalies appear probable, especially relative to the potential for negative anomalies. It is worth making mention, however, of a cluster of models that prefer taking the Nino 3.4 SST anomalies into a level below +0.5º Celsius but above zero, a neutral-ENSO scenario. For now, though, we will side with guidance that prefers a weak El Nino through the fall months.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjR9FbrypW1oomNISROxwWdFY_wDqosbLVqESA6rsvuSctokPCQcRb77Qe1m0gC3MhTp6C1s6WvENnAs_-5w_GfbZTpAJWzY4uHiq8cNQ1gfg4xmtE2UCun9-xdzZsGdV3EpCWXSWtqF1_6/s1600/nino34.NMME.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="450" data-original-width="563" height="510" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjR9FbrypW1oomNISROxwWdFY_wDqosbLVqESA6rsvuSctokPCQcRb77Qe1m0gC3MhTp6C1s6WvENnAs_-5w_GfbZTpAJWzY4uHiq8cNQ1gfg4xmtE2UCun9-xdzZsGdV3EpCWXSWtqF1_6/s640/nino34.NMME.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">NMME suite of forecasts for SST anomalies in Nino region 3.4.<br />
Source: CPC</td></tr>
</tbody></table>
The NMME suite incorporates many of the models used in the IRI/CPC suite, but is worth going over anyway because of its variance with the first contingent of models analyzed. While this group of models foresees the El Nino as likely to persist into August, it seems as though there is a higher chance of SST anomalies dipping into the 0.0º through +0.5º region, not high enough to merit an El Nino classification but again more likely to exhibit El Nino conditions as opposed to La Nina conditions. Beyond September, though guidance diverges too much to gather an accurate forecast.<br />
<br />
<b><i><span style="font-size: large;">To Summarize:</span></i></b><br />
- An El Nino is currently in place, with an El Nino Advisory declared by the Climate Prediction Center.<br />
- Recent sea temperature anomalies below the surface suggest the El Nino may be undergoing a material degradation, potentially posing a threat to the survival of the phenomenon through the fall and early winter.<br />
- Despite the apparent threats to the El Nino, model guidance sees the El Nino continuing into the fall months and perhaps into early winter. Beyond then, however, guidance diverges too much to ascertain what will transpire into the heart of winter 2019-2020.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-90918358375019028652019-05-26T20:27:00.007-05:002019-05-26T20:27:54.116-05:00June 1-6 Potential Warming Trend<div dir="ltr" style="text-align: left;" trbidi="on">
Model guidance is beginning to fixate on a broader trend away from cooler than normal temperatures in the central and east U.S. into a more seasonal, if not above-normal temperature pattern. Click on any image to enlarge it.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmeJtkl6TBNRHED27UlTYiSc7L7JubGm1RYZAwzybt7nsjLP-DOGW8x54HzRoDFdO01GuPYbCqPZIUnrxeQiunxLS6ol9qBpgXe5bsBzzY8Rj66zkwLmphOY8HYvbO8lTZ1OZ1eKXCO_MN/s1600/gfs-ens_z500a_namer_25.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="638" data-original-width="1024" height="248" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmeJtkl6TBNRHED27UlTYiSc7L7JubGm1RYZAwzybt7nsjLP-DOGW8x54HzRoDFdO01GuPYbCqPZIUnrxeQiunxLS6ol9qBpgXe5bsBzzY8Rj66zkwLmphOY8HYvbO8lTZ1OZ1eKXCO_MN/s400/gfs-ens_z500a_namer_25.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 500 millibar geopotential height anomalies per the GEFS, valid 1pm June 1st.<br />Source: Tropical Tidbits</td></tr>
</tbody></table>
By June 1st, the GFS ensembles (GEFS) anticipate somewhat of a pattern change, albeit only to a modest degree, from the troughs continually dropping into the West, bowling east through the Plains and then shifting northeast through the Great Lakes. The ensembles here anticipate a trough to again drop into the Southwest, but this time mild ridging is projected to build into the Pacific Northwest as an upper level low migrates eastward from the Bering Sea into the Gulf of Alaska. Note that the ridge in the Pacific Northwest and southwestern portion of Canada will be tempered as the Pacific jet stream carves its way through west-central Canada, as opposed to carrying the trough down into the Southwest U.S.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEilo5q5ZollerOLzp4Eg8CwYZDc_zKIMKtUzESzuuwwaUot65qiCc470mKN2A4QBm2jvYROXxi7_K44Bw2U0aJ14usiKrcYizViHh5VKAImxGLKGy7LKN2SAg_XoRP3DVHc5bwImkoqXlZy/s1600/rex_wx.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="384" data-original-width="500" height="306" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEilo5q5ZollerOLzp4Eg8CwYZDc_zKIMKtUzESzuuwwaUot65qiCc470mKN2A4QBm2jvYROXxi7_K44Bw2U0aJ14usiKrcYizViHh5VKAImxGLKGy7LKN2SAg_XoRP3DVHc5bwImkoqXlZy/s400/rex_wx.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Typical atmospheric pattern in a Rex Block pattern.<br />Source: National Weather Service</td></tr>
</tbody></table>
The result of this marginal shift in pattern is a Rex Block-like formation over the Western U.S. The image above shows a textbook Rex Block, where a ridge builds to force the jet stream northward, but an upper level low is positioned almost directly south of the ridge. The result downstream of the Rex Block is zonal flow, as shown by the almost-directly west-to-east isohypse alignment.<br />
<br />
We see almost that same pattern in the GEFS forecast at the top of this post, with a ridge building into parts of the Pacific Northwest and southwest Canada, a trough to the south of that ridge, and zonal flow across the rest of the country as a result. Further, also seen in the textbook Rex Block image, we still see that stubborn upper level low positioned in southern Canada, the same feature responsible for repeated shots of cooler than normal air for swaths of the northern U.S. as of late. For the record, continued ridging over the North Pole affirms these bouts of cooler than normal weather will remain possible for the northern U.S.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEizQ-stflQqHSSHACPv13ES9B_BcJwNoJoalW7YRTtyRAhPiz5Eijs0pRlLhHxONMVCnhrM6PrZ095TqHG66nd9CoPzLHQE0JFaRWeUl6E88ScVTFjGNWk0gNsvfck_ztnqw7ITkvKvq9c-/s1600/gfs-ens_T850a_namer_36.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="638" data-original-width="1024" height="247" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEizQ-stflQqHSSHACPv13ES9B_BcJwNoJoalW7YRTtyRAhPiz5Eijs0pRlLhHxONMVCnhrM6PrZ095TqHG66nd9CoPzLHQE0JFaRWeUl6E88ScVTFjGNWk0gNsvfck_ztnqw7ITkvKvq9c-/s400/gfs-ens_T850a_namer_36.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 850 millibar temperature anomalies as of 7am, June 4th.<br />Source: Tropical Tidbits</td></tr>
</tbody></table>
While the warming trend begins on June 1st as that zonal flow takes hold, the strongest above-normal temperature anomalies just a few thousand feet off the ground emerge on June 4th, with anomalies on a magnitude of 10 degrees Celsius above normal or higher forecasted by the GFS ensembles over parts of Oklahoma, Kansas, Nebraska and South Dakota. The entire Central U.S., parts of the Southeast and much of the Rockies look to be encompassed in these above-normal temperature anomalies before more seasonal weather begins to filter into the country's midsection.<br />
<br />
After June 6th, model guidance begins to become more uncertain as to the direction of the pattern, but early indications are warmer-than-normal temperatures may sustain themselves in the Western U.S., leading to cooler than normal conditions for the eastern third of the country. I discuss the broad pattern outlook in a special long range outlook post here from last week, but already it appears that my early-June forecast may miss the mark for failing to catch this nascent warming trend.<br />
<br />
<span style="font-size: large;"><b><i>To summarize:</i></b></span><br />
- A warming trend is forecasted for portions of the Central and East U.S. beginning June 1st and continuing through June 6th.<br />
- The warmest conditions look to be centered on the Plains, but temperatures gaining to at least seasonal levels appears likely from the Front Range in Colorado out into the Ohio Valley.<br />
- Forecasts diverge beyond June 6th, but warmer than normal conditions may persist in the West while cooler conditions take over in the East.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-70417588615689905312019-05-24T12:27:00.000-05:002019-05-24T12:27:57.391-05:00Special Long Range Outlook: Early to Mid June<div dir="ltr" style="text-align: left;" trbidi="on">
This is a follow-up on my previous long range outlook posted last weekend (<a href="https://theweathercentre.blogspot.com/2019/05/long-range-outlook-may-and-june-2019.html">click here to read</a>). In this post, I'll be using convective activity across the Equator as a basis for the forecast, and then consolidate that with the long range outlook previously published. Click on any image to enlarge it.<br />
<br />
<span style="color: red; font-size: large;">**If you do not wish to read this (admittedly technical) discussion, please scroll down until it says to stop.**</span><br />
<br />
Let's first review the concept of the Madden-Julian Oscillation (MJO), as this will prove critical to the rest of this article. The MJO is an oscillation that is based on the location of convective activity along the Equator. Depending on where this convection is, the MJO is said to be in one of eight phases.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEixU7tVPuU_lVNs77KmtDo4R5s5HAVDEXmLL1aGiZ6u8qhRHQvseQRUYuqoInJ2Q0IdVnkx945qDow3dA9M5e6WhtJzIJatUQBg4_YNlv2Sewjb7ItPic3ey0KxciS595s75QzNqL-OuSMj/s1600/MJO+OLR+composites.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="830" data-original-width="620" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEixU7tVPuU_lVNs77KmtDo4R5s5HAVDEXmLL1aGiZ6u8qhRHQvseQRUYuqoInJ2Q0IdVnkx945qDow3dA9M5e6WhtJzIJatUQBg4_YNlv2Sewjb7ItPic3ey0KxciS595s75QzNqL-OuSMj/s640/MJO+OLR+composites.png" width="476" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Portrayal of enhanced (suppressed) convection around the Equator, shown as green/blue (brown) colors, for each of the eight phases of the Madden Julian Oscillation.<br />
Source: NOAA</td></tr>
</tbody></table>
In a generalized sense, Phase 1 of the MJO typically sees enhanced convection along the Equator from South America into portions of Africa. In Phase 2, this enhanced convection shifts east into the Arabian Sea and marginally into the Bay of Bengal, with storms most focused directly south of the subcontinent of India. Drier than normal conditions are then normally seen north and east of Australian into Oceania. Phase 3 again sees an eastward shift of enhanced convection, now firmly into the Bay of Bengal and the broader majority of the Indian Ocean, more focused on the eastern half of that body of water. Additionally, we see further strengthening of that convection, maximized just southeast of India. Phase 4 sees the enhanced convection move into the Timor Sea and Arafura Sea. By Phase 5, the convective activity begins entering the far western Pacific Ocean, with calmer than normal conditions developing in portions of the Indian Ocean. Australia also experiences the enhanced convective activity in Phase 5, mainly over the northern section of the country. Phase 6 shifts the enhanced convection further east, and so on through Phase 7 and Phase 8.<br />
<br />
However, a number of scientists have put in long hours of hard work to focus in on how these areas of enhanced and depressed convection vary, if at all, in location and intensity depending on the time of year. The Bureau of Meteorology in Australia has created these composites over three-month windows - for our purposes, we will use the May-June-July window so as to be centered over June.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjxZJDR-W-TcF-w2-8o90kolfOuoEcJK6aHmqgsKCfyrfT7R-IQfhzaovKuVxoxDUabfFeh8QDAbwDV0qKxwwzC35q56md2MSSnNEqxHuKuyR6BABzZC8v89n1_OfvbFEdv-t3Sihcg0_9N/s1600/BOM+MJJ+OLR+Composite.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="807" data-original-width="800" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjxZJDR-W-TcF-w2-8o90kolfOuoEcJK6aHmqgsKCfyrfT7R-IQfhzaovKuVxoxDUabfFeh8QDAbwDV0qKxwwzC35q56md2MSSnNEqxHuKuyR6BABzZC8v89n1_OfvbFEdv-t3Sihcg0_9N/s400/BOM+MJJ+OLR+Composite.gif" width="396" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Portrayal of enhanced (suppressed) convection around the Equator, shown as cooler (warmer) colors, for each of the eight phases of the Madden Julian Oscillation during the May-June-July period.<br />
Source: Bureau of Meteorology</td></tr>
</tbody></table>
The location of areas of enhanced and suppressed convection are about the same as in the general composite graphic shown first. However, particularly in meteorology, more data and more accuracy is almost always a positive when making a forecast. As a consequence, I will refer to this image later on in this post, as opposed to the first image.<br />
<br />
It's reasonable to be skeptical as to why we should care about the location and intensity of convective activity along the Equator. I can imagine some of you are wondering how some showers and thunderstorms thousands of miles from you and your computer screen can possibly have any substantial impact on the weather pattern, much less be a driver of the pattern as a whole. This article will aim to show why we care about the MJO, and how we are able to use those showers and thunderstorms to make reasonable forecasts for the United States almost a month in advance.<br />
<br />
Now that we've reviewed what the MJO actually is and how we can determine which of the eight phases it is in, let's see which phase the MJO is currently in so we can begin building this outlook.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjA9NyK1jirkI0kdhaTsxSRrIjeGTejsznr6tr7K1gTizOwU3LGL6myVttzU2YBu7BijbROA4hHsqVSEdRQ5YwLmTXtGevtYXoPjOKON0nHB1DwtWJ0Tb38AvmfAABgG8cUOe0tKlYTvQIb/s1600/ECMF_MJO.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="547" data-original-width="547" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjA9NyK1jirkI0kdhaTsxSRrIjeGTejsznr6tr7K1gTizOwU3LGL6myVttzU2YBu7BijbROA4hHsqVSEdRQ5YwLmTXtGevtYXoPjOKON0nHB1DwtWJ0Tb38AvmfAABgG8cUOe0tKlYTvQIb/s400/ECMF_MJO.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Madden-Julian Oscillation (MJO) phase space diagram forecast, from the ECMWF model and ensembles.<br />
Source: Climate Prediction Center</td></tr>
</tbody></table>
The above graphic might appear intimidating, but in reality it's rather simple. The diagram itself is called a phase space diagram, and it uses two different mathematical models that analyze the concentration of clouds and the behavior of winds at different levels of the atmosphere to diagnose what phase the MJO is in, and how strong it is within that given phase. Those two different models are labeled RMM1 and RMM2, as shown by the 'x' and 'y' axes of the graph. In other words, they help create the graph to tell us what the MJO is doing.<br />
Reading the graph is relatively simple. The eight different phases are clearly marked, with locations typed out at different parts of the chart to indicate where enhanced convection is located when the MJO is in a given phase. You can confirm this by comparing the phase numbers and location names to the composite image(s) discussed earlier in this article. The graph also gives an idea of the strength of the MJO - the further it is from the circle in the center, the stronger the MJO is within any given phase. If the MJO is shown to be in that middle circle, it means the oscillation is too weak to definitively assign a phase to, and thus may not be a primary driver of the atmospheric pattern at that time. Luckily for us, model guidance has the MJO as being outside of that middle circle for the entire forecast period.<br />
<br />
Viewing this phase space diagram, we can see that the MJO was actually inside of that middle circle during the middle of April, just over a month ago. From there, however, the oscillation seemed to come to life and strengthened into Phase 2 by late April. From there, through May up to this point, enhanced convective activity propagated eastward from the Indian Ocean, bringing the MJO through phases 3 through 8, where it now sits. Indeed, the MJO has been positioned in phase 8 for about ten days now.<br />
<br />
This particular set of model guidance, from the European model (the ECMWF) and its ensembles, sees the MJO shifting into Phase 1 to wrap up May, and then transitioning back to Phase 2 in time for early June. Indeed, this guidance even sees convection moving eastward enough to set up in Phase 3 by about June 6th, though at that point discrepancies among ensemble members begin to materially degrade the quality of the forecast, not to mention those members have the MJO wobbling close to that circle in the center.<br />
Of course, there is more than just one model that tracks the MJO this way:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhCbk7zvyf38Jy90H_YYozdz063fhLVUllBKq3YwDn4IuDnC4HnGS0KSIZaG76Dhfy224x5lYWZFJUkKa8anuM6AL37FtnfptRQRV_AXe761guDh69PMK7Uz8MRj9ZfgQ5-FlIJ_IiGnIlb/s1600/CFSO_MJO.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="547" data-original-width="547" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhCbk7zvyf38Jy90H_YYozdz063fhLVUllBKq3YwDn4IuDnC4HnGS0KSIZaG76Dhfy224x5lYWZFJUkKa8anuM6AL37FtnfptRQRV_AXe761guDh69PMK7Uz8MRj9ZfgQ5-FlIJ_IiGnIlb/s400/CFSO_MJO.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Madden-Julian Oscillation (MJO) phase space diagram forecast, from the CFS model and ensembles.<br />
Source: Climate Prediction Center</td></tr>
</tbody></table>
This graph uses the same chart set-up and parameters as the one before, although this time instead of the ECMWF model and its ensembles, the CFS model and its ensembles are displayed. Even so, the CFS takes the MJO through almost an identical path as the ECMWF during the same time period, dragging the oscillation through Phases 1 and 2 to kick off June before trying to move towards Phase 3 by June 6th.<br />
<br />
This concept of the MJO moving into Phase 2 to begin June, after traversing Phase 1 to close out May, is more-or-less the consensus forecast across available models. As such, we will incorporate a Phase 2 MJO state into this outlook for the first five days of June or so. Now that we know what the MJO should do for the first several days of June, what does that translate to in terms of the weather pattern here in the United States?<br />
<br />
More hard work by scientists has allowed us to have answers to that question.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj2HtUD0X7CVM-QLArZZ3RE61f7_49SYnKPGeKGSHAiaMyGcJoDB1Lhyphenhyphen7cD-cVacYwJgX23TybP77D2hAR-qOHuFfao1yyPTy7QYdYny4qxnXiuj0NBHICMMyYG_HRpLGJLr1qGV-HZOreS/s1600/500mb+June+Phase+2+MJO.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="495" data-original-width="651" height="484" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj2HtUD0X7CVM-QLArZZ3RE61f7_49SYnKPGeKGSHAiaMyGcJoDB1Lhyphenhyphen7cD-cVacYwJgX23TybP77D2hAR-qOHuFfao1yyPTy7QYdYny4qxnXiuj0NBHICMMyYG_HRpLGJLr1qGV-HZOreS/s640/500mb+June+Phase+2+MJO.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">500 millibar geopotential height anomalies as observed during a Phase 2 MJO event in June.<br />
Source: Japan Meteorological Agency</td></tr>
</tbody></table>
The Japan Meteorological Agency (JMA) not only narrows down the typical 500 millibar geopotential height anomalies, 2m temperature, 200mb wind speed etc. patterns that occur by MJO phase, but also divides these into individual months. As a result, we are able to view the typical 500 millibar height anomalies seen when the MJO enters Phase 2 during the month of June. In the top image, cooler (warmer) colors represent below-normal (above-normal) height anomalies, which generally correspond to troughs and colder weather (ridges and warmer weather). We don't need to really worry about the bottom panel; it shows the outgoing long wave radiation (OLR) anomalies for a Phase 2 MJO event in June. It might sound complicated, but it's really the same thing as analyzed in the first two graphics of this post: in that bottom panel, cooler (warmer) colors represent areas of enhanced (suppressed) convection. We already know from earlier that a Phase 2 MJO event corresponds to enhanced convection in the Indian Ocean region, and this bottom panel is just reiterating that.<br />
<br />
Back to the top panel in this graphic, it appears that the MJO entering Phase 2 in the month of June tends to bring about stormier than normal activity in Russia and northeastern China, while maintaining a tendency towards ridging over Japan and southeast China. On the other side of the Pacific, a June Phase 2 MJO event encourages a ridge well offshore of the West Coast and southwest of the Gulf of Alaska, while stormier/cooler than normal activity is predominant in most of the Western U.S. Eagle-eyed readers will recognize the positioning of that stormier activity as corresponding to the negative phase of the Pacific-North American (PNA) index (you can read more about the PNA by <a href="http://theweathercentre.blogspot.com/2009/04/pacific-north-american-index-pna.html">clicking here</a>). As such, it's not surprising that the Central and Eastern U.S. then experiences a tendency for ridging and warmer weather during this state of the MJO for the month of June.<br />
In other words, when the MJO moves into Phase 2 during the month of June, the western U.S. tends to be stormier and cooler than normal, while the central and eastern U.S. will have a tendency in favor of ridging and generally warmer weather.<br />
<br />
But wait a second - that sounds pretty familiar to <a href="http://theweathercentre.blogspot.com/2019/05/long-range-outlook-may-and-june-2019.html">the forecast I published this past weekend</a>, with cooler weather in the West, warmer weather in the East and storms riding a ridge through the central part of the country, doesn't it? That's not by coincidence - if you've followed this blog over the years, you'll find that these articles have often made these kinds of confirming conclusions between teleconnections and oscillations, enabling these long-range outlooks to have at least a bit of justification behind them as opposed to throwing darts in the dark. Whether that justification ever ends up being accurate, though, is always a question mark!<br />
<br />
Indeed, long-range models see a pattern not dissimilar to that Phase 2 MJO composite evolving for the last bit of May and first bit of June:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi-_3Djnq_YXFTDFlr10oykAeQxuq4zYZIzo8ah1bRd1MrlZqvM-t7b207i4_-K-Ga4z6zwu4Z9PaG4GedNVY5IrtK8I80OOdocmGSrTFl6W5WHzmngDB76d3Uera0zO_X1LABTBER-OEJT/s1600/test8.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="819" data-original-width="1536" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi-_3Djnq_YXFTDFlr10oykAeQxuq4zYZIzo8ah1bRd1MrlZqvM-t7b207i4_-K-Ga4z6zwu4Z9PaG4GedNVY5IrtK8I80OOdocmGSrTFl6W5WHzmngDB76d3Uera0zO_X1LABTBER-OEJT/s640/test8.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 500 millibar geopotential height anomalies from the ECMWF model (left), GFS model (center) and CMC model (right), all valid for the period from May 31st to June 2nd.<br />
Source: Pennsylvania State University</td></tr>
</tbody></table>
Using these three models over the May 31 - June 2 forecast period, we can ascertain the general idea of troughing in the western U.S., signifying stormier weather, as well as a nascent ridge trying to form in the southern U.S. Note, however, that our forecast here seems to be scuttled by that large lobe of below-normal height anomalies and associated cooler weather in Canada. This seems to go right up against that MJO Phase 2 chart we were just looking at. What happened?<br />
<br />
We have to go back to something I briefly touched on at the beginning of this post to understand why model guidance isn't showing what we expected. When analyzing the structure of the MJO phase space chart, I went over the circle in the middle, where an MJO phase can't be determined definitely because the oscillation is too weak at that point in time. Consequentially, the MJO may not be a primary driver of the pattern at that time. What we must now remember is that the MJO may not be a primary driver of the pattern at this time, even if it is in a defined phase. The atmosphere doesn't abide by any single oscillation or teleconnection, it is all one big puzzle.<br />
<br />
In this case, models don't see North America getting a typical Phase 2 set-up because of Rossby waves sending much above-normal air into the Arctic Circle by way of those stout ridges over Eurasia and even potentially north of Japan. This forces the tropospheric polar vortex - already significantly weakened in the summer months, to be sure - to lower latitudes, as happens in the winter. Adding to that, we see a strong ridge positioned near Greenland (negative NAO pattern), which encourages cold weather in the upper latitudes to flow down to lower latitudes - in particular, the United States. These two factors (and likely more) combine to keep that swath of negative height anomalies locked out in Canada, bringing about that "unexpected" outcome. Additionally, during this forecast period, the MJO will be transitioning from Phase 1 to Phase 2, which makes it a little messy to use composite images. In any event, we now have three things to use in our forecast for early June:<br />
<br />
- Phase 2 of the MJO<br />
- Continuation of strong ridging over the Arctic Circle<br />
- The negative phase of the North Atlantic Oscillation (NAO)<br />
<br />
We'll make an actual forecast out of those factors at the end of this post. For now, let's move on to the mid-June outlook.<br />
<br />
I'll begin by using another scary-looking chart which, in reality, isn't too tough to read.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg5MrLGiGR_5KHTakGGzGZQXDfZQuWzDOllzyss87kA9_XypSIL76dAI-QsVgTWerOKKWg1xe6LxUowxclAv_njsw2t8iOx7mDPSPAJG3Cf2vaI-0N17ErOsNSaoK571wVwOWYszhyphenhyphen7daqT/s1600/olr.cfs.eqtr.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="907" data-original-width="809" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg5MrLGiGR_5KHTakGGzGZQXDfZQuWzDOllzyss87kA9_XypSIL76dAI-QsVgTWerOKKWg1xe6LxUowxclAv_njsw2t8iOx7mDPSPAJG3Cf2vaI-0N17ErOsNSaoK571wVwOWYszhyphenhyphen7daqT/s640/olr.cfs.eqtr.png" width="570" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Hovmoller of outgoing long wave radiation (OLR) between the latitudes of 5º North and 5º South, forecast period from May 22nd to June 19th, via the CFS model.<br />
Source: North Carolina State University / Carl Schreck</td></tr>
</tbody></table>
First and foremost, let's break down what this chart shows.<br />
<br />
For all areas above the solid black line positioned next to the May 22nd marker, all variables that will be described next are <u><span style="color: red;">observed</span></u>. For all areas below that solid black line, all variables are <span style="color: red;"><u>forecasted</u></span>.<br />
Next, we need to recognize that the solid colors here are merely showing the same thing we've looked at three times now: convective activity. As you might guess by now, green (brown) colors indicate the presence of enhanced (suppressed) convection.<br />
The third thing to note about this chart is that we will <u>not</u> be paying attention to any of those red, pink and blue ovals and shapes - they indicate different types of waves and are juxtaposed with different bursts and drops in convective activity, depending on what kind of wave it is, but for our purposes we will disregard all that so it doesn't get too confusing.<br />
The last thing to note about this chart so we can begin our forecast is that we <u>do</u> care about the black oval shapes. Remember back at the beginning of this post, when I explained that the MJO is an oscillation based on the location of enhanced convection along the Equator? Well, in this chart, those green areas show those same enhanced spots of convection at those same locations (see the longitude markers on the x axis) and also along the Equator (remember this chart shows convective activity between 5º North and 5º South latitude). The black ovals here are simply designed to highlight MJO waves (think of how the enhanced convection is a "wave" slowly moving east across the Indian and Pacific oceans).<br />
<br />
That's about all that's critical to understanding that very-messy chart: knowing that part of the chart shows observed conditions and part of it shows forecasted conditions, knowing that the shaded colors show enhanced or suppressed areas of convection just like we've already gone over in other graphics, knowing that we can disregard the colored ovals and shapes, and knowing that the black ovals merely point out to you where the MJO wave is.<br />
<br />
----<br />
<br />
So, why do we care about it anyway? Whereas the forecasts of the MJO made using the phase space graphics only go out to June 6th, the CFS Hovmoller (name of this chart type) above goes out into late June, meaning we can use it for our mid-June outlook.<br />
<br />
Let's start out at the June 5th marker on that chart. On June 5th, per this forecast, the MJO wave is forecasted to reach about the 85º East longitude region. If we refer back to the second graphic in this post, we can see that enhanced convection around 85ª - 90º East corresponds to the MJO being in Phase 2, nearing Phase 3. That lines up well with what the phase space forecasts anticipate by this time.<br />
<br />
Beyond that, however, we run into some trouble. The forecast here has that convection, and the MJO wave as a whole, dissipating by June 12th, with the enhanced convection anomalies vanishing even before that, around June 10th. That poses a dilemma for us, as it means this model sees the MJO entering that center circle if we were to view this using a phase space diagram.<br />
<br />
It seems like we're at the end of the road here. Of course, that's not the case.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg9tSSIrdMxgFZjp-8DW-TlLwCqF74ZlqfFJLVTnberHt3JPjL_7X7ye8cRd7yiOL_i29jBgu6DP4XIwYI5aJKP6ur4NyBsLYAxTnD32xkKM1ejx6YnkMtmN62bCqMTlT46ToxZFeqGDEaH/s1600/gfs-ens_chi200_global_27.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="527" data-original-width="1024" height="328" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg9tSSIrdMxgFZjp-8DW-TlLwCqF74ZlqfFJLVTnberHt3JPjL_7X7ye8cRd7yiOL_i29jBgu6DP4XIwYI5aJKP6ur4NyBsLYAxTnD32xkKM1ejx6YnkMtmN62bCqMTlT46ToxZFeqGDEaH/s640/gfs-ens_chi200_global_27.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 200mb Velocity Potential for 1pm June 5th, using the GFS Ensembles.<br />
Source: Tropical Tidbits</td></tr>
</tbody></table>
One way to identify the location of enhanced convection to track the MJO is by viewing anomalies in convective activity themselves, as we have done up to this point. Another way, however, is by viewing the upper air pattern to identify areas that are conducive for thunderstorm development. Recall that strong thunderstorms will build near the surface as air converges and rises, with the clouds of that storm then plateauing and spreading out high up in the sky when the air in those clouds becomes as cool as the environment, leading to the air high up in the sky to spread out and diverge. This is essentially what we're looking at here, only in this chart we're looking at those convergence/divergence motions only at the 200 millibar level (cruising altitude for most airplanes).<br />
Green shading and associated spreading-outwards arrows indicates divergence aloft. This is a plus for thunderstorm formation, as it encourages air lower down to converge and create thunderstorms. Orange shading and associated spreading-inwards arrows indicates convergence aloft, which piles air into the column and suppresses thunderstorm formation. As such, you can think of green shaded regions as being areas where thunderstorm development is encouraged, and brown shaded areas where it is discouraged.<br />
<br />
In this forecast for June 5th, ensemble guidance sees strong divergence aloft over Latin America and between the 120º West and 60º West longitude lines. Additionally, we see some divergence aloft over Africa. Remember that this time period is when the MJO wave is dying out and we expect it to enter that center circle in the phase space diagram, where the MJO is technically too weak to be sorted into a phase.<br />
Of course, the atmosphere could care less about what a bunch of humans say about phases - just because the MJO is seen as too weak to define doesn't mean the atmosphere will shut down convection, and certainly doesn't mean that convection in certain areas won't impact the U.S. until the MJO re-emerges into a given phase. So, since we see convection-favorable dynamics over Latin America and Africa at this timeframe, even though the MJO is technically now too weak to track, we are going to go into the mid-June forecast presuming that the pattern will reflect a Phase 1 MJO state, because the convection-favorable dynamics will encourage storms to form over Phase 1 locations. Again, the MJO will technically be too weak to track, but that definitely doesn't mean convection over the Phase 1 area won't produce Phase 1-like conditions.<br />
<br />
So, what happens in a Phase 1 MJO event in June?<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjOiOi1Bp-9fTuUB5V1KEC3HJs3RuoFVKmRW08E-3RCBOcJAKBIpO3SJaNxd9XLN294T3aOq8S_aTHYI6f8F_xxElYf_T_i6UYNpJgBiPg1-oGVpGn70PDdc5aRxXgldwAaqGRwS12NPP9x/s1600/z500_p1_06_1mon.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="495" data-original-width="651" height="303" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjOiOi1Bp-9fTuUB5V1KEC3HJs3RuoFVKmRW08E-3RCBOcJAKBIpO3SJaNxd9XLN294T3aOq8S_aTHYI6f8F_xxElYf_T_i6UYNpJgBiPg1-oGVpGn70PDdc5aRxXgldwAaqGRwS12NPP9x/s400/z500_p1_06_1mon.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">500 millibar geopotential height anomalies as observed during a Phase 1 MJO event in June.<br />
Source: Japan Meteorological Agency</td></tr>
</tbody></table>
A Phase 1 MJO state during June typically sees a strong upper level low positioned over the Bering Sea and Aleutian Islands of Alaska, with weak ridging from Hawaii towards the Pacific Northwest and a corresponding tendency for stormier weather in the West and South United States. Some ridging is seen in New England.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjtUT9STutIQ9jNl2j6yvhzqD496s0_C7fvoIewFven4JUSxWV06n6rkubVkyYHYZ79PJK7Y1e2xdV-NuY3PYCRYM2yXab6z504I3G-TW4QH97K3kz9NI7XIUkA7YgZao9VIhM4Lk6NB7dq/s1600/200mb+zonal+wind+June+Phase+1.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="495" data-original-width="651" height="303" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjtUT9STutIQ9jNl2j6yvhzqD496s0_C7fvoIewFven4JUSxWV06n6rkubVkyYHYZ79PJK7Y1e2xdV-NuY3PYCRYM2yXab6z504I3G-TW4QH97K3kz9NI7XIUkA7YgZao9VIhM4Lk6NB7dq/s400/200mb+zonal+wind+June+Phase+1.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">200 millibar zonal wind anomalies as observed during a Phase 1 MJO event in June.<br />
Source: Japan Meteorological Agency</td></tr>
</tbody></table>
What I find more interesting, however, is what typically happens to the jet stream during a Phase 1 MJO event in June. Looking at the north Pacific, we see quite a few contours with pink shading stretching from Japan all the way into the Gulf of Alaska. Those high positive contours and elongation from Japan to the Gulf of Alaska signal a strengthening and extension of the Pacific jet stream, a feature that acts to strengthen low pressure systems which drop into the Western U.S. on the back of this jet stream. I referenced the impact an extended Pacific jet can have when discussing the high severe weather threat earlier this week (<a href="https://theweathercentre.blogspot.com/2019/05/potentially-significant-severe-weather.html">click here</a>).<br />
<br />
Of course, we already saw earlier how the MJO is only one factor in a forecast, and that model guidance can (and often does) reflect this combination of teleconnections and oscillations in a way that is far from any one oscillation's "textbook" composite output (i.e. the composite for Phase 2 that we ran into trouble with earlier). Model guidance again is showing a different outcome by mid-June:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjuUgrwvRgcWH8CjEg_izli3NdKWKMGgtrJ_tf1j9JahKbcCyChikUBMej8Wqz_HH5mR-Ms1RtZNtKeBd-INEmf1mGTUHgTNypJSbjzRgAckOkCNqmE-F7fIKE0kCIzJzpB_ewwhqJo8_7O/s1600/f384.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="819" data-original-width="1024" height="318" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjuUgrwvRgcWH8CjEg_izli3NdKWKMGgtrJ_tf1j9JahKbcCyChikUBMej8Wqz_HH5mR-Ms1RtZNtKeBd-INEmf1mGTUHgTNypJSbjzRgAckOkCNqmE-F7fIKE0kCIzJzpB_ewwhqJo8_7O/s400/f384.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 500 millibar geopotential height anomalies (left) and "spaghetti" plot of all members (right) from the GFS Ensembles, valid 1pm on June 8th.<br />
Source: Pennsylvania State University</td></tr>
</tbody></table>
This is indeed a 384-hour model forecast, one of the big "no-no's" when it comes to making a forecast. While I agree that one should never base a forecast off of 16-day model guidance, I do believe that even these ultra-long-range model outputs can provide valuable hints about what the overall pattern will eventually be.<br />
<br />
The GFS ensembles expect the pattern over the Arctic Circle to not vary too much by June 8th, with strong ridging still forecasted over Eurasia into the Arctic Circle, as well as a stout ridge now moving into Canada. Still, we do see some hints of that Phase 1-esque pattern, with tightened isohypses south of the Bering Sea seeming to signal a stronger Pacific jet stream and a valley in isohypses over the Western U.S. reflecting troughs still positioned over that area.<br />
<br />
<span style="color: red; font-size: large;">**If you scrolled past the technical discussion, STOP HERE.**</span><br />
<br />
By now I've either put you through a lot of pain reading this, or you've gotten a satisfactory fill of technical forecasting for the day. You may also have decided to skip the technical discussion altogether. In any event, it's time to put these pieces together and make the forecast.<br />
<br />
<u><i><span style="font-size: large;"><b>For the first several days of June,</b></span></i></u> I expect a continuation of the current pattern. Strong ridging in the upper latitudes will keep the upper-level low over Canada in place and keep northern portions of the United States cooler than normal. Storm systems will continue to be deposited in the Western U.S., which will lead to a ridge to build in the East U.S. and allow those storm systems to ride northeast along the ridge, bringing repeated severe weather threats to the Central U.S. The presence of these troughs in the West will maintain predominantly cooler than normal and wetter than normal conditions. The pattern for the Southeast should remain relatively quiet, with this broad set-up not favorable for significant weather phenomena (i.e. big severe weather outbreaks).<br />
<br />
<b><i><u><span style="font-size: large;">From about June 8th through June 15th,</span></u></i></b> I expect marginal shifts in the pattern, but for the broad North American set-up to be relatively unchanged. Ridging is preliminarily expected to continue in the Arctic Circle, which will keep the Northern U.S. under the gun for cooler than normal conditions. An extension and strengthening of the Pacific jet stream, especially relative to the weakened and highly-meridional flow seen to end May, seems plausible in this timeframe, which will then have the potential to re-introduce higher-end severe weather threats. At this point, the ridge in the Southeast should become at least a little less stout, which may allow more severe weather threats in the eastern-third of the country and perhaps give a reprieve to the Central U.S. Broadly-seasonal temperatures may be expected outside of the North and parts of the West (cooler than normal), but this could change if that ridge projected over Canada for June 8th becomes dominant and establishes a well-above normal temperature pattern for the central part of the country.<br />
<br />
The longer-range forecast (i.e. beyond June 8th) will undoubtedly change, but hopefully this article gave you a look at how we can in fact use thunderstorms in the Equatorial Pacific to forecast the weather here many days in advance!<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com4tag:blogger.com,1999:blog-1448180228140749967.post-33259957494675059682019-05-22T16:33:00.002-05:002019-05-22T16:33:48.276-05:00May 28 - June 1 Potential Storm System & Cooler Weather<div dir="ltr" style="text-align: left;" trbidi="on">
<u>*Note: This post is using a forecasting technique that, while similar to the 6-10 day storm forecasting method I was using previously on this blog, is somewhat different and subject to more uncertainty. As such, treat this forecast with a higher level of caution.</u><br />
<br />
I am expecting a storm system and simultaneous influx of cooler than normal air into the contiguous United States to close out May and introduce June. Click on any image to enlarge it.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjXTTImDFBTJue9YncFtBxhe6mPYLvQS099_ZKHDGCYh7STrHWv1s8yvxLf2Bmh81ekC_rbowrLjd-ueufuA5xUsMMVUqIIkdF6DhjRB7cu7CYcw3x-Pq2QScmT9Vynx3_uJdwjaFR_YVs7/s1600/gfs-ens_z500a_ea_1.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="756" data-original-width="1024" height="295" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjXTTImDFBTJue9YncFtBxhe6mPYLvQS099_ZKHDGCYh7STrHWv1s8yvxLf2Bmh81ekC_rbowrLjd-ueufuA5xUsMMVUqIIkdF6DhjRB7cu7CYcw3x-Pq2QScmT9Vynx3_uJdwjaFR_YVs7/s400/gfs-ens_z500a_ea_1.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Observed 500 millibar geopotential height anomalies over Asia as of 7am central, Monday, May 20th.<br />Source: Tropical Tidbits.</td></tr>
</tbody></table>
As of this past Monday morning, an unusually-strong upper level low was observed over northeast China, with an individual disturbance rotating around the base of the low, seen here as entering western South Korea. This upper level low is situated between a pair of ridges, the stronger of which is placed east of Japan and near the Aleutian Islands of Alaska.<br />
<br />
In this somewhat-different forecasting method, I am using a swath of eastern Asia (namely parts of China, Mongolia and Russia into Japan) to anticipate weather patterns over different parts of the United States in about a 10-day timeframe. To allow for the aforementioned uncertainty, I have widened this to an 8-12 day band centered around May 30th, ten days after the observed graphic above. This is quite similar to the idea that weather in and around Japan correlates to a similar weather pattern in the United States 6-10 days later, but this venture tries to identify where these weather events may occur, instead of broadly anticipating a storm system, cold wave or heat wave over the broad country (which, to be sure, has proved very effective). This is merely an attempt to build on that, and of course has the potential to end in failure. For now, though, there's only one way to hold it (and myself) accountable: by placing a forecast out using it.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhdQy63dlxSnzPTROdvrwOH79C7smWzH7phM2mMZhnmIe5yiZYBxc4OEez0ctaHljPWLXpSG3DmuARbxRhzAUgsDPHEBICFqMR4zn7cFRYDWOBFJAVB3MS3UL2WxdnFqF_uhoTBUZOmiWHx/s1600/gfs_z500a_us_32.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="1024" height="271" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhdQy63dlxSnzPTROdvrwOH79C7smWzH7phM2mMZhnmIe5yiZYBxc4OEez0ctaHljPWLXpSG3DmuARbxRhzAUgsDPHEBICFqMR4zn7cFRYDWOBFJAVB3MS3UL2WxdnFqF_uhoTBUZOmiWHx/s400/gfs_z500a_us_32.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 500 millibar geopotential height anomalies over the United States as of 1am central, Thursday, May 30th.<br />Source: Tropical Tidbits.</td></tr>
</tbody></table>
By early May 30th, current model guidance sees a similar situation developing, with an unusually-strong upper level low placed over Canada with an individual disturbance rotating around the base of the low: here, it is seen crossing from the western Great Lakes into Canada. In this forecast, colder than normal air is again seen over the northern Plains, Midwest and Great Lakes to end May and just begin June. Also matching with the May 20th observed conditions over Asia, a pair of ridges are seen surrounding this upper level low.<br />
<br />
Indeed, model guidance sees below-normal temperatures a few thousand feet off the ground by the morning of May 30th over those same areas:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJFICExj-5OhLFje3fNdUR9p8SnwbrOiX5Dpqd2P02UfPhD4R4hglOoCeeHO4nIGJSgnvT4Da3mO21rSsVkKv7ltH_1SoPMQ8Yo2LIEPdUuTA9NCALAKUhenhmVWIFUgb6QeNa5qubXXU9/s1600/gfs_T850a_us_33.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="1024" height="271" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJFICExj-5OhLFje3fNdUR9p8SnwbrOiX5Dpqd2P02UfPhD4R4hglOoCeeHO4nIGJSgnvT4Da3mO21rSsVkKv7ltH_1SoPMQ8Yo2LIEPdUuTA9NCALAKUhenhmVWIFUgb6QeNa5qubXXU9/s400/gfs_T850a_us_33.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 850mb temperature anomalies over the United States as of 7am central, Thursday, May 30th.<br />Source: Tropical Tidbits.</td></tr>
</tbody></table>
<br />
As such, this forecast is as follows:<br />
<br />
- A storm system is expected to cross the central United States during the May 28th - May 30th period, with cooler than normal weather following over the northern portion of the country.<br />
- Ridging over the Eastern Seaboard should keep that area relatively warmer to end the current month.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-44117298698859863892019-05-21T12:37:00.001-05:002019-05-21T12:37:11.244-05:00Active Pattern to Continue Severe Weather Threats<div dir="ltr" style="text-align: left;" trbidi="on">
An active weather pattern is expected to continue threatening severe weather over the contiguous United States for the remainder of this workweek into the weekend and even next workweek, following up on my long-range forecast issued the other day (<a href="https://theweathercentre.blogspot.com/2019/05/long-range-outlook-may-and-june-2019.html">click here to read</a>). Click on any image to enlarge it.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjoHtfnazPZW6Fo3gH7dk_kmwefUOff1tg8HmU2Ut2v68eYEuQKyDbO6ODD_EFDT1dgAQ6rMFSxujgere1Lyu05NrW_MXcenk4FRICDdbXbdlcFkmew-v0cC8lUTMSynUcoGN3eU9Iu4oTa/s1600/jetstream_norhem_00.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="700" data-original-width="700" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjoHtfnazPZW6Fo3gH7dk_kmwefUOff1tg8HmU2Ut2v68eYEuQKyDbO6ODD_EFDT1dgAQ6rMFSxujgere1Lyu05NrW_MXcenk4FRICDdbXbdlcFkmew-v0cC8lUTMSynUcoGN3eU9Iu4oTa/s400/jetstream_norhem_00.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Latest analysis of the jet stream over the Northern Hemisphere.<br />Source: San Francisco State University</td></tr>
</tbody></table>
A look at the jet stream over the Northern Hemisphere spells out how the remainder of the week should bring continued threats for severe weather. The Pacific jet stream remains strong and extended west of the current trough that produced yesterday's severe weather, recording wind speeds in excess of 160 knots just off the West Coast. Maximizing that jet streak is the presence of another storm system making its way into the Pacific Northwest, which will be shunted south into the Southwest over the next day or two as a Rossby Wave blooms northward into the Gulf of Alaska. This particular storm system is expected to pose a threat for severe weather by the end of the workweek, something the Storm Prediction Center has already highlighted as shown below.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgsfJzNbcC37L5N07bICh2L_b98zwnXpDQrlUmYjOzkfVb4fMSFqtITWYn5y0IEZpzofQE2t5yOCTNugaWQn_XhalZqZeNVQVnGqtA3YhyXROzOtr2q1eKrWRWdOP-ly4-sVavgl_vpUB87/s1600/day3otlk_0730.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="555" data-original-width="815" height="216" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgsfJzNbcC37L5N07bICh2L_b98zwnXpDQrlUmYjOzkfVb4fMSFqtITWYn5y0IEZpzofQE2t5yOCTNugaWQn_XhalZqZeNVQVnGqtA3YhyXROzOtr2q1eKrWRWdOP-ly4-sVavgl_vpUB87/s320/day3otlk_0730.gif" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Severe weather outlook for Thursday, May 23rd.<br />Source: Storm Prediction Center</td></tr>
</tbody></table>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEisTXfhKw37TgP7chQo_WsJtKU2qHVKWvNoAjZatgadSHyp4MOxtC-KX1nIecbJ2VINjs3eI23ocLTlIVRbRql-aEstPp2zA40qTVJNvcyKqnWXIrqhXm5Y3nSqX3i2fZ3Eed6qowRrXEcp/s1600/day4prob.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="555" data-original-width="815" height="216" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEisTXfhKw37TgP7chQo_WsJtKU2qHVKWvNoAjZatgadSHyp4MOxtC-KX1nIecbJ2VINjs3eI23ocLTlIVRbRql-aEstPp2zA40qTVJNvcyKqnWXIrqhXm5Y3nSqX3i2fZ3Eed6qowRrXEcp/s320/day4prob.gif" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Long-range severe weather outlook for Friday, May 24th.<br />Source: Storm Prediction Center</td></tr>
</tbody></table>
As this storm system ejects into the Plains and Midwest to wrap up the workweek, a second trough is forecasted to make its way into the Southwest over the weekend.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgmLWLMgyw71VAMWpJ14zrwpYGcm-4qqBHYTBZNywxOTxMICCfvL50BegMiSc1HaTBCKqByFe14LyevUkLInv3qZfYMRFLc6JS-7oZmrJsoMpjHYkFPANYIFgMDN4iUV3SSPDcb9aD_AcjW/s1600/f144.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="819" data-original-width="1024" height="318" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgmLWLMgyw71VAMWpJ14zrwpYGcm-4qqBHYTBZNywxOTxMICCfvL50BegMiSc1HaTBCKqByFe14LyevUkLInv3qZfYMRFLc6JS-7oZmrJsoMpjHYkFPANYIFgMDN4iUV3SSPDcb9aD_AcjW/s400/f144.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">500 millibar geopotential height anomalies for Sunday evening, May 26th.<br />Source: Pennsylvania State University</td></tr>
</tbody></table>
Indeed, on Sunday night model guidance projects strong negative geopotential height anomalies to once again be present over the Southwest, indicative of the presence of a storm system in that region. The positioning of a ridge over the Central and Eastern U.S. should locate this storm system's severe weather threat again over the Plains and Midwest to kick off the next workweek (about a week from today), essentially placing the same cities and states under the gun that have seen severe weather threats for the past few days now.<br />
<br />
Just when it seems like it might quiet down, ensemble guidance then sees yet another storm system entering the Southwest by the end of May, which could pose yet another severe weather threat in these same areas for the beginning of June. However, model discrepancies become too large to have any material confidence in forecasts beyond the end of next workweek.<br />
<br />
<span style="font-size: large;"><b><i>To summarize:</i></b></span><br />
<br />
- An active weather pattern is expected to persist through this workweek and weekend into next workweek.<br />
- Multiple severe weather threats are expected to evolve over the Southern and Central Plains into the Midwest and Great Lakes regions, as a train of upper level lows ejects from the Southwest and are pushed north into those areas due to a high pressure stationed over the Southeast.<br />
- Severe weather threats are expected to continue through next workweek, but the potential for further threats may continue into the opening days of June.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-75853545287100258432019-05-19T13:27:00.000-05:002019-05-19T13:27:03.950-05:00Long Range Outlook: May and June 2019<div dir="ltr" style="text-align: left;" trbidi="on">
This post will discuss my thoughts on the outlook for the remainder of May and into June of this year. Click on any image to enlarge it.<br />
<br />
We begin with an analysis of the current atmospheric pattern across the Northern Hemisphere.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhd3Hw9stXs_LpG6XBQC5A-3fx-9pl_HpIlVVhvRCIal6S-et_4mCYQ3ENUlOxplOm5_ie5QXHdS8hz3B96xnXh18j3yC2q1OYKXsYMcqzd1SlYvqCq8TvH21a1a1kwvqxcDR7zeAak4jov/s1600/5+day+mean+500mb+pattern+OBS.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="570" data-original-width="480" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhd3Hw9stXs_LpG6XBQC5A-3fx-9pl_HpIlVVhvRCIal6S-et_4mCYQ3ENUlOxplOm5_ie5QXHdS8hz3B96xnXh18j3yC2q1OYKXsYMcqzd1SlYvqCq8TvH21a1a1kwvqxcDR7zeAak4jov/s400/5+day+mean+500mb+pattern+OBS.gif" width="336" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Five day (May 11 thru May 15) mean 500 millibar height anomalies.<br />Source: Japan Meteorological Agency (JMA)</td></tr>
</tbody></table>
The last several days have seen a rather volatile pattern positioned over the Arctic and similar upper latitudes. Most predominantly, there has been a trio of ridges pushing into the Arctic Circle, placed over Siberia, north-central Eurasia and far western Europe. The ridge placed over Eurasia has forced itself northward over the North Pole, disrupting the tropospheric polar vortex and splitting lobes of cold air to lower latitudes. Indeed, we have seen such an evolution take place, with strong negative geopotential height anomalies over the northern Atlantic Ocean, northeast Eurasia/Russia, and marginally in the Bering Sea and Canada.<br />
<br />
This is a similar process as what takes place when the tropospheric polar vortex is disrupted in the winter, with colder than normal air being forced down to lower latitudes as ridging forces the polar vortex to be displaced from its usual resting place over the North Pole. Consequentially, colder than normal temperatures have indeed been observed in the lower latitudes, including here in the United States.<br />
<br />
The movement of colder air into the United States has been driven more-so by a pattern resembling the positive phase of the Pacific-North American (PNA) oscillation, which is seen best by the presence of a ridge along the West Coast of the U.S., which encourages troughing and cooler air to shift southward from Canada into the central and eastern U.S. Additionally, a ridge near Greenland as of late has provided further impetus for the transport of colder air into the contiguous United States, a pattern which some of you may recognize as a set-up typical of the negative phase of the North Atlantic Oscillation (NAO). Again, both of these are patterns typically emphasized during the winter, but this provides a good example of how they can still function across seasons.<br />
<br />
In summary, we're entering this forecast period knowing the recent atmospheric regime is tilted in favor of colder temperatures for the United States. Let's begin with the outlook itself.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjSyrx-nzwOmDPXU86kHl95jHuiRnqROYO4FrdGP1KchUSYOTgJ0_Ut-gSe-gatSu38amotXUBtsUHdNwOuWN8rPKgzuQx5rZm1Yf19_CC0vKRglIhmv0K3NoPDrh8DBcqQFiazDZx_WfES/s1600/gfs+ecmwf+810day.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="819" data-original-width="1024" height="318" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjSyrx-nzwOmDPXU86kHl95jHuiRnqROYO4FrdGP1KchUSYOTgJ0_Ut-gSe-gatSu38amotXUBtsUHdNwOuWN8rPKgzuQx5rZm1Yf19_CC0vKRglIhmv0K3NoPDrh8DBcqQFiazDZx_WfES/s400/gfs+ecmwf+810day.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 500 millibar geopotential height anomalies from the ECMWF model (left) and GFS model (right) for the 8-10 day forecast period.<br />Source: Pennsylvania State University</td></tr>
</tbody></table>
My goal for this outlook is to begin with computer model guidance and then expand outwards to look at individual oscillations to try and discern if these computer models might be missing something in their forecast, or may be right on target. In accordance with that framework, we'll begin with the projected 500 millibar geopotential height anomalies in the 8-10 day forecast period from the ECMWF model (the "euro" model; left panel) and the GFS model (the "american" model; right panel). In general, warmer colors portray ridging (calmer and warmer weather), while colder colors portray troughs (stormier and cooler weather).<br />
<br />
Model guidance is in pretty good agreement over the evolution of the pattern over the United States into the end of the month, with both models suggesting a near-Rex Block formation along the western coast of North America. A Rex Block is traditionally exemplified by a ridge placed "on top" (to the north) of a trough. In this graphic, such a set-up would make it look like warmer colors would be positioned directly north of colder colors. While this sort of set-up isn't precisely laid out here, both models anticipate the development of zonal flow downstream of the Rockies, typically what happens downstream of a Rex Block.<br />
<br />
Such a zonal flow and ridging over the eastern two-thirds of the country is rather intriguing given what is forecasted in the upper latitudes, with both models forecasting a continued disruption of the tropospheric polar vortex as well as a continuation of high pressure near Greenland. As discussed earlier, both of these factors encourage colder than normal air to propagate to lower latitudes.<br />
<br />
So what's happening here?<br />
<br />
Let's take a closer look at the projected pattern over North America. I noted how it seemed like a vaguely Rex Block-esque pattern was forecasted to set up over the western coastline of the continent. But we missed a key item when looking at the positioning of the ridge and trough along the coastline: the trough is forecasted to sit in the Southwestern U.S. In other words, this prompts a pattern downstream more typical of the <b><u><i>negative</i></u></b> phase of the PNA oscillation, a flip from the recent positive PNA phase laid out at the start of this post. In a negative PNA regime, the trough in the West U.S. encourages the development of a ridge in the East U.S., which is indeed what we're seeing in the model guidance projections.<br />
This isn't too surprising when we consider that these factors that affect the PNA oscillation are <u>upstream</u> of the United States, where as the NAO and other factors more encouraging of cold air in this time period are either well north of the U.S. or are <u>downstream</u> of the country, limiting their impact.<br />
<br />
As outlined, let's now expand on this a bit and look at forecasts for four key atmospheric oscillations below.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHwSRCBIBhRrIEhR83CHiXx-agfvLSQqLCg4tC7a7aGz3pZpSa76Wzsi9QDy3w1UyplJXDl9t0Ns1uzWxpTon-7ujB7LrzM3ZWAui-GxMUwaIpM9owwaBz1ditXYM3_MOBeP08lQEbUotK/s1600/4indices.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1024" data-original-width="1024" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHwSRCBIBhRrIEhR83CHiXx-agfvLSQqLCg4tC7a7aGz3pZpSa76Wzsi9QDy3w1UyplJXDl9t0Ns1uzWxpTon-7ujB7LrzM3ZWAui-GxMUwaIpM9owwaBz1ditXYM3_MOBeP08lQEbUotK/s400/4indices.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted states of the Pacific-North American (PNA) index, top-left; North Atlantic Oscillation (NAO), top-right; Western Pacific Oscillation (WPO), bottom-left; and the Eastern Pacific Oscillation (EPO), bottom-right.<br />Source: Earth System Research Laboratory (ESRL)</td></tr>
</tbody></table>
The projected state of the PNA oscillation is shown in line with what we extracted before viewing this forecast, where a recent positive-PNA regime would flip to a negative-PNA situation in the 8-10 day period. This ESRL forecast builds on that by anticipating the PNA oscillation to remain in negative territory until the turn of the month. Be sure to note the strength of this negative-PNA regime, as we'll return to that later on.<br />
<br />
Moving to the NAO forecast, our earlier suspicions are again confirmed with the agency projecting this oscillation to remain in negative territory throughout the entire forecast period (indicating that ridging near Greenland will persist), albeit to a weakening degree by the end of the period.<br />
<br />
The WPO and EPO phenomena can be noteworthy and impactful when they're strongly oriented in one way or another, but they are both projected to flip states multiple times and remain at relatively-modest strengths during the forecast period. As such, we will focus more on the PNA and NAO for this outlook.<br />
<br />
We now have a pretty good idea of what is forecasted to evolve over the next ten days or so (feel free to scroll down to the end for a summary if it was a little tough to grasp), so let's now move into the two-week-plus forecast period.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4LIzvWueNtICs7-JuzaABJlX0B7gkS3YhhiUx6dnIcEhMlQs0LTglve0QgQRnIQdmKwph9fc_JulQsuNDh_b7rDvhKgcAnudZ4cseogc1MtCzAyLiff8qQR4qr2dURMcuxDn0m5k3hQp9/s1600/f384.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="819" data-original-width="1024" height="318" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4LIzvWueNtICs7-JuzaABJlX0B7gkS3YhhiUx6dnIcEhMlQs0LTglve0QgQRnIQdmKwph9fc_JulQsuNDh_b7rDvhKgcAnudZ4cseogc1MtCzAyLiff8qQR4qr2dURMcuxDn0m5k3hQp9/s400/f384.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted GFS ensemble 500 millibar geopotential height anomalies (left) and spaghetti plot (right) at the end of the forecast period (June 3rd).<br />Source: Pennsylvania State University</td></tr>
</tbody></table>
It is imperative to first recognize the degree to which this particular forecast graphic is imperiled as a consequence of its long time horizon. Rarely, if ever, do forecasts made sixteen days in advance actually come to fruition. Unfortunately, our computer models are simply not yet advanced enough and do not have enough real-time observational data to input to make such accurate forecasts. This is the caveat that sixteen days out is a very long time, and conclusions drawn from here are not to be fully invested in to.<br />
<br />
The GFS ensembles project the pattern 16 days out to be pretty similar to the pattern seen developing by the 8-10 day period. Indeed, the GFS ensembles anticipate ridging persisting over the Arctic Circle but a trough along the West Coast will sustain a negative-PNA pattern for the United States. In other words, such output indicates warmer conditions may be expected for the southern portions of the country, relatively seasonal weather for the country's midsection, and perhaps seasonal to cooler-than-normal conditions in the northern slice of the country. Cooler than normal and stormy weather would be anticipated for the western half of the country, with storm systems shuffling into the Southwest only to eject into the Plains and form the basis for severe weather threats in the Central U.S.<br />
<br />
--<br />
<br />
I'm a believer in the idea that the atmosphere takes all kinds of oscillations and phenomena into account when creating the weather for a given area - the United States does not exist in a vacuum where a negative-PNA state automatically produces warmer than normal weather for the entirety of the eastern U.S., for example, or where a positive-NAO state automatically produces zonal flow over the country. I also believe, however, that some phenomena can impact certain areas to greater degrees than other phenomena based on the location and intensity of these phenomena. For example, while the negative-PNA state may not automatically produce a 'textbook' negative-PNA outcome, its position as being upstream of the United States means the country's weather is more likely to be dictated by what the PNA does than what the NAO (way off in Greenland) does.<br />
These are not controversial beliefs by any means to any weather enthusiast, but it is worth stating because my outlook here will rely heavily on the latter belief. While my forecast for the first ~two weeks relies substantially on the evolution of a negative-PNA state, as discussed, I'll now shift the basis for my forecast to another indicator.<br />
<br />
--<br />
<br />
Consider the ESRL forecast for those four oscillations once again. Note how all of them seem to dwindle down to weak levels of whatever their respective states are forecasted to be. That makes for a tough forecast for the start of June, if four of the most impactful oscillations are expected to be too weak to make a significant impact. As such, I'll now briefly zoom out and review the broader atmospheric pattern currently in place across the globe: an El Nino.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhL20q1Xo-pJ1VcThQ7MtRaYSX0MMVMnVPux34FybzE_ezPV3MXKS9HW9T8FkDAdtVSSb8Sd8jMWF1N2liBpVyMjjA33SK8wXz-z2VJEXf2pSBMuJjhti2it6sHuQHjRo6AQ0YQSKCSRXpY/s1600/meiv2.timeseries.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="637" data-original-width="1150" height="353" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhL20q1Xo-pJ1VcThQ7MtRaYSX0MMVMnVPux34FybzE_ezPV3MXKS9HW9T8FkDAdtVSSb8Sd8jMWF1N2liBpVyMjjA33SK8wXz-z2VJEXf2pSBMuJjhti2it6sHuQHjRo6AQ0YQSKCSRXpY/s640/meiv2.timeseries.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Multivariate ENSO Index (MEI). Positive (negative) values indicate the presence of an El Nino (La Nina).<br />Source: Earth System Research Laboratory</td></tr>
</tbody></table>
Frequent visitors to this blog in past winters will readily recognize the importance of understanding the current state of the El Nino-Southern Oscillation (ENSO) phenomenon. The ENSO phenomenon is identified by observing sea surface temperature (SST) anomalies along the Equatorial Pacific. Cooler than normal water temperatures typically indicate the presence of a La Nina, while warmer than normal temperatures indicate the presence of an El Nino. Each of these states of the ENSO phenomenon broadly drive weather patterns around the globe, giving you an idea of just how material this is to any longer-term forecast.<br />
<br />
Using the MEI metric above, we see that positive values have recently increased, indicating the presence of warmer than normal water temperatures in the Equatorial Pacific and, potentially, an El Nino event. For the purposes of this post, the June outlook will operate under the assumption that an El Nino is in place. What does that mean for the forecast?<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiw4EYJSJLQQW4wDQTt642nNOqChQb1vO-Ud9BzXajaIXWVtNllyQQ_ocNEFnWTMdiTTpdhk9vS4HpZg-fbodZ9o64d64FOFpO3gD0A9mCmH_z40WPxeR6ZodrxLS_X5gabux9GEQ5xzJ2o/s1600/el+nino+temperature+anom.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="437" data-original-width="565" height="308" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiw4EYJSJLQQW4wDQTt642nNOqChQb1vO-Ud9BzXajaIXWVtNllyQQ_ocNEFnWTMdiTTpdhk9vS4HpZg-fbodZ9o64d64FOFpO3gD0A9mCmH_z40WPxeR6ZodrxLS_X5gabux9GEQ5xzJ2o/s400/el+nino+temperature+anom.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Surface temperature anomalies during summers where an El Nino was observed.<br />Source: Earth System Research Laboratory</td></tr>
</tbody></table>
The ESRL provides a neat tool whereby the user is able to analyze a variety of atmospheric variables that can be broadly expected given an El Nino or La Nina, given if it is occurring in the winter or summer. This provides a substantial advantage here, as we can glean what a "typical" El Nino in the summertime will give out in terms of temperature anomalies. The outcome is rather impressive, as it lines up well with what had already been established in the forecast through the end of May. Indeed, a "typical" summertime El Nino results in cooler than normal conditions in the northern U.S. as well as in the Rockies, with a small area of stronger cooler-than-normal anomalies in the Southwest. This fits well with the idea of a negative-PNA set-up, where troughs and cooler weather persist in the Southwest into the far northern U.S. as the jet stream then curves upward over the Plains due to ridging in the Southeast, a consequence of the aforementioned West U.S. troughing.<br />
<br />
As such, it may be prudent to begin the June forecast with a basic outline akin to a negative-PNA state, with cooler and stormier weather in the Western U.S. extending to the northern Plains, severe weather opportunities in the Central U.S., and broadly seasonal to warmer conditions in the Southeast. Now that we've zoomed out to examine the overarching pattern, it's time to return to individual oscillations. While the PNA, NAO, EPO and WPO all may be too weak by the start of June to dominate the broad pattern for the U.S., another oscillation looks to be strong enough at this point in time to shape the June outlook for the contiguous 48. This is the Madden-Julian Oscillation (MJO).<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjiE3k1IPdtuMhSNDk2umXAfgOVUfI6m68xwytzvW4DJgzdnhjBoQx-JvYHPpHohHWo7MLsUqJD3BFGmlGf1Plnu2lN6aasPvY4_KBss4KDI9rRR4trqXsV4HTAaXKiaQraihtkgmJBbyKn/s1600/gefs+ecmwf+MJO.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="464" data-original-width="1010" height="294" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjiE3k1IPdtuMhSNDk2umXAfgOVUfI6m68xwytzvW4DJgzdnhjBoQx-JvYHPpHohHWo7MLsUqJD3BFGmlGf1Plnu2lN6aasPvY4_KBss4KDI9rRR4trqXsV4HTAaXKiaQraihtkgmJBbyKn/s640/gefs+ecmwf+MJO.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted state of the Madden-Julian Oscillation (MJO) from mid-May through the end of May from the GFS ensembles (left panel) and the ECMWF ensembles (right panel).<br />Source: Climate Prediction Center</td></tr>
</tbody></table>
The Madden-Julian Oscillation (henceforth MJO) is categorized using a phase space diagram. In this case, that means that the MJO can take one of eight different phases. Why so many? The MJO phenomenon is identified by the placement of convective activity along the Equatorial Pacific, similar to the ENSO phenomenon. However, with the MJO, the zone of monitoring extends across the entire Equator, not just in the Equatorial Pacific. Each phase of this oscillation represents a different location for convection along the Equator, with Phase 8 and Phase 1 typically seeing convection placed over and around South America and/or Africa, and Phases 4 and 5 corresponding to convection north of Australia. Each of these eight phases has been found to produce different impacts on weather patterns around the globe, including here in the United States. We'll use that to our advantage a little later on.<br />
<br />
Both the GFS ensembles and ECMWF ensembles anticipate the MJO to move near or into Phase 2 by the beginning of June. The models differ as to the strength of the oscillation by this point in time, however, with the GFS expecting a notable Phase 2 state but the ECMWF bringing the oscillation weak enough to enter that circle in the middle of the graph, indicating that the MJO is too weak to be definitively placed into a certain phase. Model divergence like this beyond two weeks out is to be expected, but because both models have the MJO either approaching or being within the Phase 2 state, we will continue the June forecast under the assumption that the month will begin with the MJO in a Phase 2 state.<br />
<br />
As I noted earlier, each of the eight phases of the MJO affects global weather patterns in their own ways. The hard work of a number of scientists has enabled us to create composites for variables such as temperature, precipitation and upper-air flow for each phase of the MJO, so that we can have an idea of what kind of weather a certain phase of the MJO will bring for any given month. Let's view the surface temperature anomaly composite for a Phase 2 MJO state during the month of June.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFR1DnWzdfCuypTvMv6v2J795v5QLcs6je176Q2_FE5V847OkS6xRhLiYqbc1wcbdQ6m63DQYTzuoy3wVAJss_J3W8R9TNBBjzGqTQLoONBK4cgYHJCrcq_O4FwFeOXetXgWySQYG-kKUM/s1600/JunePhase2all2mT.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="655" data-original-width="847" height="308" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFR1DnWzdfCuypTvMv6v2J795v5QLcs6je176Q2_FE5V847OkS6xRhLiYqbc1wcbdQ6m63DQYTzuoy3wVAJss_J3W8R9TNBBjzGqTQLoONBK4cgYHJCrcq_O4FwFeOXetXgWySQYG-kKUM/s400/JunePhase2all2mT.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Surface temperature anomaly composite for a Phase 2 MJO state during the month of June.<br />Source: American Weather (americanwx.com)</td></tr>
</tbody></table>
Allow me to restate again the importance of recognizing that no one oscillation controls the weather pattern - indeed, the atmosphere can be thought of as a web of different phenomena, all of them impacted or imposing impacts someway, somehow by/on to others. As such, it's critical to remember that we are still trying to glean a general framework for the June forecast, rather than definitively identify what *will* happen. After all, if we knew what would definitively happen, I would be on a private island with an expensive yacht somewhere!<br />
<br />
As the composite image above shows, a Phase 2 MJO state occurring in June has historically resulted in warmer than normal temperatures over the southern and central Plains, extending northeast through the Great Lakes and Northeast regions. Slightly below-normal temperatures have been seen in the Pacific Northwest in such a situation.<br />
This brings about a pattern similar to the negative-PNA pattern that we have discussed rather extensively in this post, and seems to encourage the idea that the pattern forecasted to end May could continue into the opening portion of June.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhFEAJPVS04FeGZC89B5pswOTJQ3eJz_dXfCWX6c85MPefQj-oLFFU-aXYTCA9ZOVmyl87MwLU-qgpu5mx443fHphqiMFdiLK47XvJOe2MlduFlGSu8fq82oA2PUf8GHgSvs0V2_yffEShS/s1600/JunePhase2all500mb.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="655" data-original-width="847" height="308" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhFEAJPVS04FeGZC89B5pswOTJQ3eJz_dXfCWX6c85MPefQj-oLFFU-aXYTCA9ZOVmyl87MwLU-qgpu5mx443fHphqiMFdiLK47XvJOe2MlduFlGSu8fq82oA2PUf8GHgSvs0V2_yffEShS/s400/JunePhase2all500mb.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">500 millibar height anomaly composite for a Phase 2 MJO state during the month of June.<br />Source: American Weather (americanwx.com)</td></tr>
</tbody></table>
Indeed, when looking at the 500-millibar geopotential height anomalies for a June Phase 2 state of the MJO, a pattern similar to a negative-PNA set-up emerges, with slight hints of a trough in the Western US aligning with ridging in parts of the Eastern U.S. Note the upper level low in place near Greenland, though, which represents the positive phase of the North Atlantic Oscillation (NAO) and tends to encourage zonal flow & warmer conditions over the contiguous United States. It remains to be seen if this will transpire into June, as ESRL forecasts have the NAO maintaining a slightly-negative state into next month, which would then suppress ridging over the Eastern U.S. somewhat.<br />
<br />
Beyond this point, model guidance becomes too unreliable to rely on any combination of oscillations, and as such the remainder of June will expect a pattern broadly in line with a summertime El Nino, with recognition that individual oscillations could (and likely will) easily change such a pattern as next month draws closer and model guidance becomes more accurate as to the state of oscillations.<br />
<br />
<br />
<div style="text-align: center;">
<span style="font-size: large;"><u>Forecast Summary</u></span></div>
<br />
- <u>Western U.S.</u>: Expect warmer than normal weather to shift to stormier- and cooler-than-normal in coming days, with this regime change complete by seven days out. This stormy and cooler pattern should persist through the end of May. Tendency for stormy and cooler weather should continue into the opening days of June, with this same pattern encouraged by the El Nino for the entire month. Individual oscillations and other discrepancies may change this forecast for June, however.<br />
<br />
- <u>Central U.S.</u>: Expect a continued active weather pattern through the end of May, with ample severe weather opportunities as storm systems eject eastward from the Southwest and ride an upward-curving jet stream over the Plains. Temperatures will vary, with a tendency for cool weather in the north Plains and seasonal to warmer weather in the south Plains. Precipitation should be expected to be above normal.<br />
<br />
- <u>Eastern U.S.</u>: Expect warmer than normal conditions to evolve through the end of May and into June before a retrenchment to broadly seasonal conditions as the negative-PNA pattern breaks down. Precipitation anomalies are not seen dramatically going either way, though the Southeast U.S. may be monitored for somewhat below-normal precipitation. Broadly seasonal to somewhat warmer than normal conditions are possible for June in the aggregate.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com1tag:blogger.com,1999:blog-1448180228140749967.post-57424743321007019292019-05-18T14:29:00.002-05:002019-05-18T14:29:29.952-05:00Potentially Significant Severe Weather Event Monday<div dir="ltr" style="text-align: left;" trbidi="on">
A potentially significant severe weather event is being highlighted by the Storm Prediction Center (SPC) for Monday, with further threats emerging on Tuesday. Click on any image to enlarge. Check out the post on this weekend's severe threat <a href="https://theweathercentre.blogspot.com/2019/05/multi-day-severe-weather-outbreak.html">by clicking here</a>.<br />
<br />
<b><u><span style="font-size: large;">Monday, May 20th</span></u></b><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhmuID9as3MJb37Xmkj8mptvGAEE7IE4z28cGMlAUS9iV21ard37xrO-5tY1Qm88mXG-hj3c8i1U-WErlb4J36Mbl4eLTKRNcl_80_pNA5EBmJY8ns2DY6dpBqG3gwxTIQVRFsTrosZ0oWr/s1600/Screen+Shot+2019-05-18+at+1.46.41+PM.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="415" data-original-width="1217" height="218" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhmuID9as3MJb37Xmkj8mptvGAEE7IE4z28cGMlAUS9iV21ard37xrO-5tY1Qm88mXG-hj3c8i1U-WErlb4J36Mbl4eLTKRNcl_80_pNA5EBmJY8ns2DY6dpBqG3gwxTIQVRFsTrosZ0oWr/s640/Screen+Shot+2019-05-18+at+1.46.41+PM.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The Storm Prediction Center's categorical (left) and probabilistic (right) outlook for severe weather on Monday.<br />Source: Storm Prediction Center</td></tr>
</tbody></table>
The Storm Prediction Center has issued a Moderate Risk (level 4 out of 5) of severe weather for the western half of Oklahoma (not including the panhandle), north-central Texas into the Texas panhandle, and extreme south-central Kansas for Monday, with an Enhanced Risk (level 3 out of 5) surrounding that area through much of west Texas, the majority of Oklahoma and southern Kansas. On a probabilistic level, viewing the probability of severe weather within 25 miles of any given point, the SPC has placed a 45% chance of severe weather in the same areas first mentioned, thereby green-lighting the issuance of a Moderate Risk. Across both the Moderate and Enhanced risk areas, as well as a small part of the Slight risk region in western Texas and the Oklahoma panhandle, a hatched area is outlined, which delineates a 10% or greater probability of significant severe weather within 25 miles of any given point.<br />
<br />
The threat for Monday looks to be twofold over the course of the day, with the first threat appearing early in the morning.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhBiXHh93HlYekiT5dEn89LdYW50Y6PaR5uoxE82OWEkqHypChpqpyw7iYTkv_kwlyYVLddtS0OlEWf2Gvk7T2-03NmG7lfexTdK2OKzwxthl9J-xk1IxukXu6OtLH8ec6GNcQK77hwVhCa/s1600/NAM_221_2019051812_F45_WSPD_250_MB.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="972" height="285" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhBiXHh93HlYekiT5dEn89LdYW50Y6PaR5uoxE82OWEkqHypChpqpyw7iYTkv_kwlyYVLddtS0OlEWf2Gvk7T2-03NmG7lfexTdK2OKzwxthl9J-xk1IxukXu6OtLH8ec6GNcQK77hwVhCa/s400/NAM_221_2019051812_F45_WSPD_250_MB.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 250 millibar wind speeds and heights at 4am central Monday.<br />Source: TwisterData</td></tr>
</tbody></table>
By 4 am central time on Monday, weather models expect a strong upper-level low to move into the Southwest, heading up a robust extension of the Pacific jet stream that will include a jet streak exceeding 140 knots rounding the base of the low. It is this jet streak that may help fire off a substantial severe weather event later in the day. For the time being, though, notable divergence in the southern Plains should provide for an early-morning threat of strong to severe storms.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJqBbpjPvbeT8GqMfJvZvkMetxrO19xYUEOX7NQKrkLuILQKAJx6lXNa5hFdRF0K0-O-wzp1YUTI5V7aeFuOjQp4IJhoQ3-OMawrdX9kh2A21I-ZfOIK8KnxM_K3tASw7PrDlXtAtRkX2D/s1600/monday+dewpoint.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="972" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJqBbpjPvbeT8GqMfJvZvkMetxrO19xYUEOX7NQKrkLuILQKAJx6lXNa5hFdRF0K0-O-wzp1YUTI5V7aeFuOjQp4IJhoQ3-OMawrdX9kh2A21I-ZfOIK8KnxM_K3tASw7PrDlXtAtRkX2D/s400/monday+dewpoint.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 250 millibar wind speeds and heights at 7am central Monday.<br />Source: TwisterData</td></tr>
</tbody></table>
A little later in the morning, model guidance sees a reservoir of moisture readily available across the primary risk area, with dewpoints in excess of 60 degrees across Oklahoma and Texas. Further, a dryline is already evident in extreme western Texas and eastern New Mexico, which will provide the focus for thunderstorm development later on in the day.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLfXLEYedrSFLcmqq29xPy3TwpbGFqi6Vtchw-67_xjgh0k_iXdk6Na88_zjgbkbNOh__BmG37tka9o1iNjZvAy_eQvOpCdnULUQu1TCdKVHSpl_K745PKfCSclDYemNw3Z3IZOXWCQVg1/s1600/NAMNSTSGP_prec_radar_047.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="600" data-original-width="800" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLfXLEYedrSFLcmqq29xPy3TwpbGFqi6Vtchw-67_xjgh0k_iXdk6Na88_zjgbkbNOh__BmG37tka9o1iNjZvAy_eQvOpCdnULUQu1TCdKVHSpl_K745PKfCSclDYemNw3Z3IZOXWCQVg1/s400/NAMNSTSGP_prec_radar_047.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted radar reflectivity at 6am central Monday.<br />Source: College of DuPage</td></tr>
</tbody></table>
By the time the early morning commute on Monday is beginning, strong to severe thunderstorms are projected to be firing off the northern part of the dryline in the Texas and Oklahoma panhandles into southwest Kansas. Some scattered development is possible further south, but is not expected to be as widespread as areas further north by Amarillo. With limited instability and a material inversion expected to be in place at this point in time, thunderstorms are not expected to be significant, though with the upper air dynamics forecasted to be in place, severe weather cannot be ruled out.<br />
<br />
---<br />
<br />
By the afternoon hours, the potential for a significant severe weather event becomes more tangible.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgZKQtA-sBMHDfblSL_dYaUSpqwZow95S64celZEDek5aMFXyVWsUEUABKQNzfujvSUo9OTE0_lKhfIA3RClnOp4PB-3S-Fkr09xJhBJLEwyKjFTp9qVQe_D_RZYQHJV-7djFEfb0ZTovQN/s1600/monday+evening+300mb.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="972" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgZKQtA-sBMHDfblSL_dYaUSpqwZow95S64celZEDek5aMFXyVWsUEUABKQNzfujvSUo9OTE0_lKhfIA3RClnOp4PB-3S-Fkr09xJhBJLEwyKjFTp9qVQe_D_RZYQHJV-7djFEfb0ZTovQN/s400/monday+evening+300mb.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 250 millibar wind speeds and heights at 7pm central Monday.<br />Source: TwisterData</td></tr>
</tbody></table>
As briefly noted at the start of this post, the jet streak that had been rounding the base of the low in the morning is expected to curve around to the east side of the trough by the evening, seemingly in an effort to maximize the severe weather threat. Once again, upper-level divergence is forecasted to be present across Texas and Oklahoma, encouraging the development of thunderstorms in those areas.<br />
<br />
Further, note that the positioning of the trough has moved from looking as if it's tilting towards the bottom-left of the picture in the morning to now almost pointing straight down. This portrays a maturing and strengthening trough, an additional factor suggesting substantial severe weather is a possibility.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgU1GK6GSuHAcd5JDoS4nnfjRP2Y8qKINyiO3zJwYZrMXEUB3k_7P9-0UDWWA3NS80MBkcVjIqqRixpb9063cxrJE7N8POVJKecpnUjDfrrLiY8Z0K2UxHK35AQBq1lJDiy5D92AkX2cxFs/s1600/monday+evening+cape.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="972" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgU1GK6GSuHAcd5JDoS4nnfjRP2Y8qKINyiO3zJwYZrMXEUB3k_7P9-0UDWWA3NS80MBkcVjIqqRixpb9063cxrJE7N8POVJKecpnUjDfrrLiY8Z0K2UxHK35AQBq1lJDiy5D92AkX2cxFs/s400/monday+evening+cape.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted instability (CAPE) at 7pm central Monday.<br />Source: TwisterData</td></tr>
</tbody></table>
Also in the evening, instability is expected to have both moved northward to the Oklahoma/Kansas border and increased quite a bit throughout the day. Indeed, convective available potential energy (CAPE) on the order of 3,000 to 4,000+ joules per kilogram (j/kg) of CAPE is forecasted across western Texas and much of Oklahoma, even into western and southern Arkansas. For reference, a general rule of thumb holds that severe thunderstorms can function in only 2,000 j/kg of CAPE. The area will also be uncapped by the evening hours, removing any barriers to potentially explosive thunderstorm formation.<br />
<br />
This lack of a cap also presents a potential fly in the ointment for severe weather potential, however. Model guidance projects the cap to be eroded by 1pm, and instability building to more than 2,000 j/kg by that same time. This presents an opportunity for storms to fire earlier in the day, potentially corrupting a more substantial severe threat that could evolve in the evening hours. I find such a development possible, particularly if the early morning storms are able to lay down outflow boundaries that could then provide a lifting mechanism for those potential mid-day storms. Such an outcome must be monitored closely, as it could materially change the forecast.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjwcrYbLFjVOmAFWLh6o0bkcHyeQdRSZLeToNqpJmunyr-RUcK18kpygyrCjSucSgEc4Y10F3b4BSlxaIsH3t5sDoxyEv-Y4CHUrxJYWWSxTvMHG_LpF6sGb830uwvQos9VFzdeQ9sY1ud3/s1600/NAM_221_2019051812_F57_SHRM_500_MB.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="972" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjwcrYbLFjVOmAFWLh6o0bkcHyeQdRSZLeToNqpJmunyr-RUcK18kpygyrCjSucSgEc4Y10F3b4BSlxaIsH3t5sDoxyEv-Y4CHUrxJYWWSxTvMHG_LpF6sGb830uwvQos9VFzdeQ9sY1ud3/s400/NAM_221_2019051812_F57_SHRM_500_MB.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted surface-500 millibar wind shear at 4pm central Monday.<br />Source: TwisterData</td></tr>
</tbody></table>
If thunderstorms are still able to fire in the late afternoon and evening hours, the atmosphere appears primed for at least a decent severe weather event. Combined with abundant moisture, instability and a lifting mechanism by way of the dryline and any possible outflow boundaries from earlier storms, wind shear is expected to be sufficient for the development of rotating thunderstorms in western Texas, much of Oklahoma and especially in Kansas, which will be in close proximity to the surface low in eastern Colorado.<br />
<br />
More details will need to be ironed out in coming model runs today and tomorrow, but at this point in time it appears Monday evening will hold the potential for a significant severe weather outbreak in portions of Texas, Oklahoma and Kansas.<br />
<br />
<br />
<b><u><span style="font-size: large;">Tuesday, May 21st</span></u></b><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjxmDA3p1Nggat91-SplSchYLejvKvzpDQzFsiW6KPKphYhZhUjIzaWJf1BHbtw4e-VKywEtiLnair9mZS8Fmv4J-fizcEgvwLWNZqqiaxTC8yCsft1shTzFVGx4SS2GhgQyRbyr3zHIrA8/s1600/day4prob.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="555" data-original-width="815" height="271" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjxmDA3p1Nggat91-SplSchYLejvKvzpDQzFsiW6KPKphYhZhUjIzaWJf1BHbtw4e-VKywEtiLnair9mZS8Fmv4J-fizcEgvwLWNZqqiaxTC8yCsft1shTzFVGx4SS2GhgQyRbyr3zHIrA8/s400/day4prob.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted severe weather threat for Tuesday, May 21st.<br />Source: Storm Prediction Center</td></tr>
</tbody></table>
On Tuesday, the severe weather threat is expected to shift to the north and east, seemingly to a less-intense degree than Monday. The progression of the trough to the east will bring Missouri, much of Arkansas, southwest Illinois, extreme southeast Iowa and northeast Texas under the gun for potential severe weather. At this time, a significant severe weather event is not anticipated, but this may change depending on the evolution of Monday's severe weather episode.<br />
<br />
A potentially significant severe weather event is forecasted for Monday across portions of the southern Plains, with all modes of severe weather (including tornadoes, which could be strong) possible. The threat area will then shift eastward for Tuesday and likely decrease in intensity relative to the day before.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-28685275592326851172019-05-18T11:29:00.002-05:002019-05-18T11:29:30.704-05:00Multi-Day Severe Weather Outbreak Continues This Weekend<div dir="ltr" style="text-align: left;" trbidi="on">
A multi-day severe weather event that began at the end of this last workweek will continue through the weekend and into the start of next workweek. <u>This post will address the Saturday and Sunday threats, with a forthcoming post addressing the Monday and Tuesday threats</u>. Click on any image to enlarge it.<br />
<br />
<b><span style="font-size: large;"><u>Today: Saturday, May 18</u></span></b><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7XAAmxlV4DOv6Cle6mKA5rmr79oYfY4j7NSLM_Mzx5nSp7zuBJkS1nJuPutbJdjYRyPid15fvAxcIbTWUyW8nTpMLXpz1-y2NoJ5dZB42iIbyDwEq4mf1Tbd1PfOOTzUxJkviM-uy8gY1/s1600/day1otlk_1300.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="555" data-original-width="815" height="271" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7XAAmxlV4DOv6Cle6mKA5rmr79oYfY4j7NSLM_Mzx5nSp7zuBJkS1nJuPutbJdjYRyPid15fvAxcIbTWUyW8nTpMLXpz1-y2NoJ5dZB42iIbyDwEq4mf1Tbd1PfOOTzUxJkviM-uy8gY1/s400/day1otlk_1300.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Severe weather outlook for Saturday, May 18.<br />Source: Storm Prediction Center</td></tr>
</tbody></table>
For today (Saturday), the Storm Prediction Center has outlined a rather large area of severe weather risk, spread from the Gulf Coast across Texas and Louisiana up through the Plains and Midwest, tapering off in the Great Lakes and Upper Midwest regions. Out of five levels of severe weather risk, the SPC has assigned an Enhanced Risk (level 3/5) of severe weather to northeast Texas, northwest Louisiana, much of Arkansas and southeast Oklahoma. This means that thunderstorms (not necessarily severe) should be expected, and severe thunderstorms are relatively likely, with some potentially posing a threat for significant severe weather (i.e. very large hail, significant damaging winds, and even tornadoes).<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUAW_xOc01Yw2iug-ziML8iyCYa4l4RRZtupYIBxwlw1wfMzSJnHs82c5wBI05BqermSboD71Ol0_Xl3gKCjGi6_4NqRWCihPpD-0GakcotXZqlzk5LgY9N0nUlQ8t3TG8Rf-pw_T4UKeE/s1600/namussfc12wbg.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="562" data-original-width="750" height="298" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUAW_xOc01Yw2iug-ziML8iyCYa4l4RRZtupYIBxwlw1wfMzSJnHs82c5wBI05BqermSboD71Ol0_Xl3gKCjGi6_4NqRWCihPpD-0GakcotXZqlzk5LgY9N0nUlQ8t3TG8Rf-pw_T4UKeE/s400/namussfc12wbg.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Latest surface analysis as of 10:30am central time on May 18.<br />Source: Weather Prediction Center</td></tr>
</tbody></table>
A look at frontal positions and surface observations as of this typing reveals a low pressure system in southeastern South Dakota, with a strength of 998 millibars. As a general rule of thumb, low pressure systems below 1000 millibars are considered relatively strong, and this is no exception. A stationary front is seen draped across the Midwest, a boundary which has been the focus for thunderstorm development over the last couple of days already. To the south, another frontal boundary is identified through Nebraska, Kansas and Oklahoma, which is then attached to a second low pressure system in the Texas Panhandle.<br />
<br />
We can glean a few focal points for today's severe weather from this chart. First, the Weather Prediction Center (WPC) has identified an outflow boundary positioned in the northern half of Texas, west of Dallas. You may notice how this lines up well with the Enhanced risk of severe weather, and this is no mistake. It seems plausible that, with the movement of the dryline eastward, there will be more than enough forcing to ignite thunderstorms, particularly in the absence of a substantial cap. Indeed, this has proven to be the case, with strong to severe thunderstorms ongoing along that corridor in Texas.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJZUvtNBfo2hSExWGh5A0ZKoNIVYoRY9mzlrm4KcRzSFvdlGkhViKtx1Tw4pcgNSAFsVPaQYb15W9OBk04IHn80DP5eenQsL3XqrsqI6SmMt5cnmb_Idb57jwdko2E0LnccRH5tRm-_4Ut/s1600/COD-GOES-East-regional-southcentral.radar.20190518.153000.gif-over%253Dmap-bars%253D.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="900" data-original-width="1600" height="225" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJZUvtNBfo2hSExWGh5A0ZKoNIVYoRY9mzlrm4KcRzSFvdlGkhViKtx1Tw4pcgNSAFsVPaQYb15W9OBk04IHn80DP5eenQsL3XqrsqI6SmMt5cnmb_Idb57jwdko2E0LnccRH5tRm-_4Ut/s400/COD-GOES-East-regional-southcentral.radar.20190518.153000.gif-over%253Dmap-bars%253D.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Current (as of this posting) radar view.<br />Source: College of DuPage</td></tr>
</tbody></table>
The highest severe weather threat for today appears to rely on the continued eastward progression and consolidation of the aforementioned dryline. Model guidance has this dryline diffusing somewhat during the evening hours over central Texas, which may diminish some of the impetus for severe storms, but with the main event already ongoing this does not seem to be a significant concern.<br />
<br />
Additional severe weather is possible north of the Enhanced Risk area, although with a lower reservoir of instability and relatively weaker forcing for storms, the risk is understandably downgraded to Slight for areas in the Plains and Midwest. It should be cautioned that model guidance does have thunderstorms re-developing in northwest Oklahoma by the late afternoon hours, although SPC guidance suggests this will hinge on the development of the atmosphere in the wake of the ongoing storm complex. As such, residents in western Oklahoma and Kansas should keep updated throughout the day as the risk of severe weather may evolve differently than discussed here.<br />
<br />
<br />
<b><span style="font-size: large;"><u>Tomorrow: Sunday, May 19</u></span></b><br />
The threat of severe weather continues into Sunday.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjlRGtn4hwMDnpzH70ThyphenhyphencspmhLDt3dZWgmvqX3_gvqlh77VQXKu9WlTHfGs4iFlOvycPXgsSnTayMr_3zSevvaoWYb2lOsxgUYxkiImu5f54q_VzHxWCXQmUh6WuQcKNUMfgSdzHGQfU_1/s1600/day2otlk_0600.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="555" data-original-width="815" height="271" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjlRGtn4hwMDnpzH70ThyphenhyphencspmhLDt3dZWgmvqX3_gvqlh77VQXKu9WlTHfGs4iFlOvycPXgsSnTayMr_3zSevvaoWYb2lOsxgUYxkiImu5f54q_VzHxWCXQmUh6WuQcKNUMfgSdzHGQfU_1/s400/day2otlk_0600.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Severe weather outlook for Sunday, May 19.<br />Source: Storm Prediction Center</td></tr>
</tbody></table>
The highest level of severe weather highlighted by the Storm Prediction Center for Sunday is a Slight Risk, a level 2 out of 5 on the agency's risk scale. While this is lower than the Enhanced Risk, notable severe weather events have occurred in Slight Risk areas multiple times before. As such, this threat should not be completely brushed aside.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiiD4qI7fevla2zaIUQPcBztvnarsLQGnDuJffv6UgcfPHXrzHVsPQuIx2dWVo7aIvDNMis4QfJXGXVbxfjabnW3rqZ5dxUSGu61GO5cidEz37UZdtxslulidZqgqe1XvEo_B4kYfJxZKyu/s1600/NAM_221_2019051812_F30_PWATIN_SURFACE.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="972" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiiD4qI7fevla2zaIUQPcBztvnarsLQGnDuJffv6UgcfPHXrzHVsPQuIx2dWVo7aIvDNMis4QfJXGXVbxfjabnW3rqZ5dxUSGu61GO5cidEz37UZdtxslulidZqgqe1XvEo_B4kYfJxZKyu/s400/NAM_221_2019051812_F30_PWATIN_SURFACE.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted precipitable water values for 1pm central, Sunday.<br />Source: TwisterData</td></tr>
</tbody></table>
By Sunday afternoon, the system of frontal boundaries and primary low pressure system will move to the east and north, with the low pressure system ending up in the Wisconsin-Michigan vicinity by the afternoon hours. Precipitable water values in excess of 1.0" are expected across the Midwest and Ohio Valley, with a narrow corridor of 1.5"+ values expected ahead of the cold front. For reference, it can begin to feel 'muggy' when precipitable water values exceed 1.0", and it is generally noticeably humid when values exceed 1.5". This suggests not only a muggy day ahead on Sunday for some, but also a readily available area of moisture for thunderstorm development.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjbRjzMb99DbOp5gfbyVk8R4MIZOJ-H7eauZHJ5QP3LUyKqTLMtQMPojHPTsRuZ900XVrxxUo-TSChza7E7LWUAcY0tL8r7uTU1yjBAG-YfqhV68kJicL6McRpzTMUXmNYAFRC_LOmCmlFJ/s1600/NAM_221_2019051812_F30_CAPE_SURFACE.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="972" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjbRjzMb99DbOp5gfbyVk8R4MIZOJ-H7eauZHJ5QP3LUyKqTLMtQMPojHPTsRuZ900XVrxxUo-TSChza7E7LWUAcY0tL8r7uTU1yjBAG-YfqhV68kJicL6McRpzTMUXmNYAFRC_LOmCmlFJ/s400/NAM_221_2019051812_F30_CAPE_SURFACE.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted instability (CAPE) values for 1pm central, Sunday.<br />Source: TwisterData</td></tr>
</tbody></table>
At the same time as the above image, a wide swath of elevated instability is seen stretching from southeast Texas and Louisiana north into slivers of western Kentucky, southern Illinois and southeast Missouri. Instability as shown here, defined as Convective Available Potential Energy (CAPE), is generally conducive for severe thunderstorms when exceeding 2,000 joules per kilogram (j/kg).<br />
<br />
You may be wondering why there isn't a higher severe weather risk over southern Texas and Louisiana given the high instability forecasted, and that would be not only a very good question but a good way to consider how there are more factors than just instability required for severe thunderstorms to develop. Indeed, in my Severe & Unusual Weather course I took at the University of Oklahoma for my final semester, the teacher identified four necessary ingredients for strong thunderstorms: <b><u>Instability</u></b>, a <b><u>lifting mechanism</u></b>, <b><u>moisture</u></b>, and <b><u>wind shear.</u></b><br />
<br />
Looking over model guidance for southern Texas, we certainly have enough instability present, as the above graphic shows. The image above that one shows there will also be enough moisture, with precipitable water values exceeding 1.5". It's the wind shear and lifting mechanism features where the severe risk for southern Texas and Louisiana runs into problems.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhjtvdSiCkeNUFrvcpg51E_qCQP4dHU538dCyv5dqofa0hrFSTB0t3ZU6k8y_aKxqi59YZ75GGjZVXgggDMhYOONxBXb06HGin8d6Pf8W-E-AGXwBp-IRIMocCStjIdwiaEh9cvybHcUQWu/s1600/NAM_221_2019051812_F30_SHRM_500_MB.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="972" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhjtvdSiCkeNUFrvcpg51E_qCQP4dHU538dCyv5dqofa0hrFSTB0t3ZU6k8y_aKxqi59YZ75GGjZVXgggDMhYOONxBXb06HGin8d6Pf8W-E-AGXwBp-IRIMocCStjIdwiaEh9cvybHcUQWu/s400/NAM_221_2019051812_F30_SHRM_500_MB.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted surface-500 millibar wind shear ("bulk shear") values for 1pm central, Sunday.<br />Source: TwisterData</td></tr>
</tbody></table>
There are a number of ways to identify wind shear, and each one has its own merits. For example, there is value in examining wind shear at the lower levels of the troposphere, while there is also value in checking out wind shear across the majority of the troposphere. For this situation, we'll look at wind shear from the surface to the 500 millibar level. In the above graphic, we see a swath of 30+ knot wind shear stretching from Texas and Oklahoma into the Ohio Valley and Great Lakes regions.<br />
<br />
In my opinion, wind shear becomes abundant using the surface-500mb range when exceeding 50 knots, as this should be enough wind shear to separate the updraft from the downdraft and prevent any thunderstorms from popping up, sticking around for less than an hour, and then collapsing because there isn't enough wind shear for the updraft to be tilted away from the downdraft. We don't see this benchmark met in southeast Texas or Louisiana- indeed, values there struggle to exceed 30 knots.This suggests it will be difficult for thunderstorms to sustain themselves and become severe for a prolonged period of time. That's not to say they can't become severe at all, but we would want quite a bit more wind shear to believe that the environment near the Gulf Coast is conducive for severe weather on a larger scale.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKzJlJzUpMfu_1gG64v0uUSQU96jrG_iYCekUNgQaRa4H4zqswobQUXCTXsJtypWCv_mHMzPoiGPwfaK6t3q5yyK8UoaKdQSFz11HM-MRTo_MbyAlrxrc4o3utq9Ux74pf4ddThYB4WIHv/s1600/NAM_221_2019051812_F30_WSPD_500_MB.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="972" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKzJlJzUpMfu_1gG64v0uUSQU96jrG_iYCekUNgQaRa4H4zqswobQUXCTXsJtypWCv_mHMzPoiGPwfaK6t3q5yyK8UoaKdQSFz11HM-MRTo_MbyAlrxrc4o3utq9Ux74pf4ddThYB4WIHv/s400/NAM_221_2019051812_F30_WSPD_500_MB.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Forecasted 500 millibar wind speed & height values for 1pm central, Sunday.<br />Source: TwisterData</td></tr>
</tbody></table>
We also don't see a prominent mechanism to force the air at the surface higher and both initiate & sustain severe thunderstorms. The above image shows the 500 millibar geopotential height field, as well as wind speeds. This is the main level of the atmosphere meteorologists use to look for ridges and troughs, areas of relatively-calm and relatively-active weather, respectively. Ridges are identified by seeing the height contours (solid black lines) push northward- a great example of this is seen in the Southeast U.S. into the Atlantic Ocean. Troughs are identified by seeing height contours push southward, usually increasing wind speeds near the base of the trough as well. Great examples of troughs are seen here on the West Coast and Upper Midwest.<br />
<br />
As just mentioned, Sunday afternoon will see a trough pushing through the Upper Midwest, driving that low pressure system over the same area we discussed a little earlier. However, note the relative lack of any trough along the Gulf Coast. This absence of an explicit forcing mechanism in that area suggests it may be difficult to get storms to push up and sustain themselves, especially with a lack of wind shear. It is likely that having only two of those four 'main' ingredients for severe weather is reasoning behind the lack of a higher severe weather threat outlined in Texas and Louisiana. The presence of those four factors is also the reason why a higher risk *is* outlined further to the north. The absence of stronger instability and an environment with more moisture are likely driving forces as to why there isn't an Enhanced Risk of severe weather in the Ohio Valley and Midwest regions.<br />
<br />
<br />
Both today (Saturday) and tomorrow look to present opportunities for severe weather before this low pressure system moves out of the picture and another, potentially more intense severe weather event commences on Monday. A forthcoming post will address this new storm system.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com0tag:blogger.com,1999:blog-1448180228140749967.post-44420578440603494872018-01-18T17:07:00.001-06:002018-01-18T17:07:14.298-06:00January 23-27 Potential Winter Storm<div dir="ltr" style="text-align: left;" trbidi="on">
This is a brief update to the previous post concerning this possible winter storm, which <a href="http://theweathercentre.blogspot.com/2018/01/january-23-27-potentially-significant.html">you can find here</a>.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgaV1HzBztqtpWfTAz85ceXaL88NSvjzbAMC5huizCRWaxWmEuZQAg47DlQ0iUnfUdQDtBhbMIK5odu7GCKew7j8pJcvG-m0Q7RB8l5xiMC1j9NGD8HKrH0eNoWfpqSpVUGQeOl1DvUBDEc/s1600/gfs_mslp_pcpn_wpac_1.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="717" data-original-width="1024" height="448" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgaV1HzBztqtpWfTAz85ceXaL88NSvjzbAMC5huizCRWaxWmEuZQAg47DlQ0iUnfUdQDtBhbMIK5odu7GCKew7j8pJcvG-m0Q7RB8l5xiMC1j9NGD8HKrH0eNoWfpqSpVUGQeOl1DvUBDEc/s640/gfs_mslp_pcpn_wpac_1.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Tropical Tidbits</td></tr>
</tbody></table>
Shown above is a near-analysis of the meteorological environment over eastern Asia for the morning of January 17th. At this time, we saw a storm system skirting the eastern coast of Japan, intensifying somewhat as it did so. As I highlighted in my previous post, this will pose a threat for a winter storm in the January 23-27 period.<br />
<br />
I maintain that the Midwest/Ohio Valley regions continue to have a better chance of seeing wintry impacts as opposed to the East Coast, but long-range model guidance suggests the Plains may be able to get in to the mix, as shown below.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhs8Aqm_9Slds9WTNZCHTNJA3vrEkweLhwjbxEioF8TFb_RsjI7P1LiTn7chq6hDvB_wygTj5DgrXwFmic9fsUqdC6EaiZNQBn4WutxOrRB7T_8Cf0MPnxu2CD6Z1ZaT_YZuZEZTyzqb1wJ/s1600/gfs_mslp_pcpn_us_35.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="1024" height="434" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhs8Aqm_9Slds9WTNZCHTNJA3vrEkweLhwjbxEioF8TFb_RsjI7P1LiTn7chq6hDvB_wygTj5DgrXwFmic9fsUqdC6EaiZNQBn4WutxOrRB7T_8Cf0MPnxu2CD6Z1ZaT_YZuZEZTyzqb1wJ/s640/gfs_mslp_pcpn_us_35.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Tropical Tidbits</td></tr>
</tbody></table>
This 210-hour forecast from the GFS model has a sub-1000 millibar low pressure system moving north through the Plains, laying down accumulating snow in the northern Plains, with showers and thunderstorms likely occurring in portions of the Midwest down to the Gulf Coast. As is the caveat with any model forecast beyond 84 hours, this is bound to change, and likely will do so drastically. That's why long range model guidance is used more for identifying the *signal* of a storm, not yet the exact location of such a storm. As such, it is a good sign for those hoping for some stormy weather that the GFS is sniffing out such a possibility in this January 23-27 timeframe.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjJBJayJ0rk7XKAklRWWwps9xNQrIY08U5E6QzZLqFo4TQHoGUW6XLl5D6znWxTitA-yxJUUIkod4iEA1p65lSe6bXTZTtvP7DaaO00jHzQPl2zA72-eNF13vMdc__9e_efhSucZe2fySro/s1600/gem_mslp_pcpn_us_36.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="1024" height="434" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjJBJayJ0rk7XKAklRWWwps9xNQrIY08U5E6QzZLqFo4TQHoGUW6XLl5D6znWxTitA-yxJUUIkod4iEA1p65lSe6bXTZTtvP7DaaO00jHzQPl2zA72-eNF13vMdc__9e_efhSucZe2fySro/s640/gem_mslp_pcpn_us_36.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Tropical Tidbits</td></tr>
</tbody></table>
To exacerbate this point, above is the Canadian CMC's model interpretation of this storm. It predicts the storm will crawl near the Gulf Coast, impact the Southeast and eventually ride up the East Coast. That flies directly in the face of what I said earlier here, but I'm posting it to highlight how these model forecasts will drastically change in coming runs, as is typical. Again, the point is that the model is sniffing out a storm at all- the path will be refined in coming days.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiVOlQ-QthWB8cRs-4e2ieg0C_Rct1CccCd6WzxQc8roGxrXrwwLdiJhqTlcNZkOtvDTNOAYrcTNo_XMkht0WWGFKKNq-NIaWBZ93M44K1xznYotFCyiwNK3yrDnV-Ywr5prUJcLe_D4WD3/s1600/ecmwf_z500_mslp_us_11.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="696" data-original-width="1024" height="434" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiVOlQ-QthWB8cRs-4e2ieg0C_Rct1CccCd6WzxQc8roGxrXrwwLdiJhqTlcNZkOtvDTNOAYrcTNo_XMkht0WWGFKKNq-NIaWBZ93M44K1xznYotFCyiwNK3yrDnV-Ywr5prUJcLe_D4WD3/s640/ecmwf_z500_mslp_us_11.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Tropical Tidbits</td></tr>
</tbody></table>
Just to entertain all crowds, the ECMWF model above shows this storm cutting up through the Ohio Valley, though slightly outside of this timeframe. Details will be sorted out, but model guidance is latching on to the idea of a winter storm around the January 23-27 timeframe.<br />
<br />
<b><i><span style="font-size: large;">To Summarize:</span></i></b><br />
<br />
- Model guidance is sniffing out the potential for a winter storm in the January 23-27 period, as was highlighted in a previous post from January 10th.<br />
- Significant uncertainties exist with regard to the location of any wintry weather, and such impacts will not be known with any degree of accuracy for at least a few days.<br />
- For now, the Midwest/Ohio Valley/Plains regions look most likely to see impacts, but this comes from the synopsis of the atmosphere back on January 10th and these locations could very well not be affected by this system.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com3tag:blogger.com,1999:blog-1448180228140749967.post-53677975794752183292018-01-15T17:07:00.001-06:002018-01-15T17:07:42.133-06:00Stratospheric Warming Event Projected To End January<div dir="ltr" style="text-align: left;" trbidi="on">
Model guidance continues to indicate that the stratospheric polar vortex will come under further stress as we head toward the end of the month, with a wavenumber-1 event potentially unfolding in the stratosphere and opening the chance for February to be colder than normal.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhRpmQKp6Inud_83gTuPnBjxqmvd8-diCGdPYRSgQjjYPg0tCc_cR_xTZvXPGnG4vemacxeGnPhoZIb-DAKmfLxSY31li0im-KFAYjoj_YkpOZBZ7L1S-nqX8DC0QDpKYEwzc6_aTk0p1il/s1600/ecmwf70f240.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="612" data-original-width="792" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhRpmQKp6Inud_83gTuPnBjxqmvd8-diCGdPYRSgQjjYPg0tCc_cR_xTZvXPGnG4vemacxeGnPhoZIb-DAKmfLxSY31li0im-KFAYjoj_YkpOZBZ7L1S-nqX8DC0QDpKYEwzc6_aTk0p1il/s640/ecmwf70f240.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">FU-Berlin</td></tr>
</tbody></table>
Shown above is the 240-hour forecast of geopotential heights (contours) and temperatures (colored fill) from the ECMWF model, analyzing the 70-millibar slice of the stratosphere. This is around the middle or lower-middle part of the stratosphere, and as a rule of thumb stratospheric warming events tend to be stronger and more able to dislodge the polar vortex when the warming event is seen throughout multiple layers of the stratosphere. While I'm only showing the 70-milliber layer, model guidance has latched on to this warming potential throughout the stratosphere.<br />
<br />
In this image, we see the stratospheric polar vortex still pretty much in control, centered almost over the North Pole. The piece to analyze, however, is the swath of warmer air trying to push into the Arctic Circle, with the warmest temperatures located over the Bering Sea. The placement of these warmer anomalies is important, because when stratospheric warming events push into the Arctic Circle from the Bering Sea region, they tend to be more successful at disrupting the polar vortex. I'm sure there's some academic literature on exactly why this happens, but in the absence of reading such literature I take that as a rule of thumb.<br />
<br />
We can get a better look at the polar vortex through forecasted potential vorticity charts.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhGGCe_xeFfl_ptvCYg9aKmijqSpfCWGzPSQAraLVUaHj8iviTMKY37vx3VEEdhdvIvpEuOSj2RSiXHytm-4iIvnVo4IH4VNzeiI2m_Y_kiWujiRf4iaTGqfwtLE24OO19Q82SLzSwzQCIz/s1600/ecmwfpv550f240.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="612" data-original-width="792" height="494" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhGGCe_xeFfl_ptvCYg9aKmijqSpfCWGzPSQAraLVUaHj8iviTMKY37vx3VEEdhdvIvpEuOSj2RSiXHytm-4iIvnVo4IH4VNzeiI2m_Y_kiWujiRf4iaTGqfwtLE24OO19Q82SLzSwzQCIz/s640/ecmwfpv550f240.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">FU-Berlin</td></tr>
</tbody></table>
In a nutshell, these charts show the orientation of the polar vortex at different levels of the stratosphere. This map shows potential vorticity values at the 550 K level, which is somewhere around the 20-millibar level. Warmer colors depict areas of higher potential vorticity - in this case, the location of the polar vortex. Colder colors indicate where the polar vortex is not, in essence. At hour 240, we see the polar vortex in a rather elongated shape, dislodged from the Arctic Circle and positioned from Greenland across northern Eurasia. This shape of the polar vortex signals that it will be under duress at this point in time, as the polar vortex is 'typically' seen in a more circular shape. This elongated shape suggests pressure being applied from the Bering Sea area in the form of a ridge, which is confirmed by the deeper blue area stretching from the Gulf of Alaska to the Bering Sea. Similar to how higher levels of potential vorticity indicate the polar vortex, lower values (especially in this case) can be indicative of a ridge of high pressure.<br />
<br />
So far, we've gathered that model guidance projects the stratospheric polar vortex to come under substantial pressure in the next several days, likely continuing through the end of January. This pressure looks to be applied across much of the stratosphere, boosting the chances that any disruption in the polar vortex could then show up in the troposphere in the form of colder than normal weather. Let's sum it all up with a few graphs.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgZ4EfeiHrB-A40cizrep2iyoRA9dVql0zK6vgMlGtXFxbnTK0etIEF-2XMiDL5MxTmL0nPRRKA9mCD7nFBZ078CB-PG-w0vtjFAr8dJ-M3FvORvkyhs2jycU7nTIi2hW0XoUt_aXegW_RK/s1600/fluxes.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="792" data-original-width="612" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgZ4EfeiHrB-A40cizrep2iyoRA9dVql0zK6vgMlGtXFxbnTK0etIEF-2XMiDL5MxTmL0nPRRKA9mCD7nFBZ078CB-PG-w0vtjFAr8dJ-M3FvORvkyhs2jycU7nTIi2hW0XoUt_aXegW_RK/s640/fluxes.gif" width="494" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">FU-Berlin</td></tr>
</tbody></table>
The top panel shows observed zonal wind speeds at the 1-millibar level of the stratosphere - in other words, the strength of the far-upper stratospheric polar vortex. The 1-millibar level isn't as important as the 30-millibar or 50-millibar levels, as we discussed with the rule of thumb earlier in this post. However, it can still be valuable to look at, as a reversal in wind direction at the 1-millibar level could then filter down to lower levels. In this forecast image, the 1-millibar wind speed is forecast to continue declining slightly from a recent peak, before strengthening again and then once more weakening. This would take it back to roughly the same level we're at right now, if this forecast verified exactly as shown. Let's see if any signals can be identified in other panels.<br />
<br />
The second panel shows the 10-millibar zonal wind speed (blue line) and the 30-millibar zonal wind speed (red line), where both slices of the stratosphere look to see the strength of the polar vortex gradually decline as wind speeds slow down. While the deceleration here appears modest, there are signs that it will continue through the end of January. Both the geopotential flux and heat flux indicators in the third panel are set to significantly increase during the forecast period, which will lead to a slight deceleration across the 1-millibar, 10-millibar and 30-millibar areas. This will then revert back to near-zero, but at the end of the forecast period the ECMWF sees these fluxes strengthening again, leading to further wind speed deceleration in the aforementioned levels of the stratosphere. Perhaps most significantly, for this second acceleration in the two fluxes, you'll note how the EP-flux on the bottom panel is pointing straight up, when looking at it two-dimensionally. Stratospheric warming events are most probable when the geopotential and heat fluxes are high (which is forecasted) and the EP-flux arrows are pointed directly up (which is also forecasted for the end of the forecast period). As such, while the ongoing increase in fluxes may not do much damage to the polar vortex, the re-configuration of the EP-flux in time for the second projected warming event in about ten days could do far more damage, especially if it is a sustained warming event.<br />
<br />
As such, I expect a broadly seasonal to warmer-than-normal temperature pattern for the eastern 2/3 of the U.S. through the end of January, but the chances of colder-than-normal weather increasing, particularly after the first few days of February.<br />
<br />
<b><i><span style="font-size: large;">To Summarize:</span></i></b><br />
<br />
- Model guidance continues to indicate a potentially-disruptive warming event in the stratosphere towards the end of January.<br />
- As this warming event is expected to affect nearly all sections of the stratosphere, effects in the troposphere are likely in the first and second full weeks of February.<br />
- Colder than normal conditions are expected to increase in likelihood after the first few days of February.<br />
<br />
Andrew</div>
Andrewhttp://www.blogger.com/profile/09751979013231521196noreply@blogger.com1