Why Early November Will Be Colder Than Forecasted, and Other Long Range Hints

It is likely that the recent forecasts of a dissipating cold pattern in the 14-16 days range will end up incorrect, as the west Pacific continues to produce typhoons, one of which will end up in east Asia to confirm a continuing cold weather pattern through at least the first week of November.

In just 84 hours, on October 23, typhoon Francisco will begin to approach East Asia at just about the same time a closed low traverses eastern mainland Asia. It has been demonstrated that the weather pattern in East Asia can be (and often is) reciprocated in the East United States 6-10 days after the weather pattern in East Asia is observed. In the case of recurving typhoons, it is expected that a deep trough appears in the eastern half of the United States in the 6-10 days succeeding the typhoon's curving motion around East Asia.

Two days later, ensemble forecasts have the typhoon and closed low combining into a swath of negative height anomalies covering a decent portion of East Asia. This should lead to an enhanced period of colder weather in the Central and Eastern United States as a result. Ensemble forecasts then try to build ridging in East Asia after the troughing, but with that same ensemble set not catching on with the probable troughing pattern across the East US due to the typhoon scenario in East Asia, I am wary of trusting that solution.

The GFS model does show another big storm system hitting East Asia around the 140 hour forecast period, which could then prolong the cold pattern further, as far as ~November 4th, as the image above shows, but there's another piece of information that may have significant implications in the middle or near-end of November.

See that massive system around the Aleutian Islands? That storm system will be meandering north around the time period of this forecast image, which is roughly October 25th, and likely into the Bering Sea. This brings into effect something a knowledgable AccuWeather Forum moderator named the 'Bering Sea Rule'. The Bering Sea Rule involves a strong storm entering the Bering Sea, and a strong storm system affecting the East US 2.5 to 3 weeks later. With the large storm system projected to enter the Bering Sea in late October, it is possible/likely we see a storm system/cooler pattern forming in the Central and/or East US in time for the middle of November. You can find the full description of the Bering Sea Rule at this link.

What does seem apparent is the continuation of this cold weather pattern that as started in the last few days into early November, despite model projections of the cold weather pattern ending to kick off November. Beyond that, some colder weather may be provoked in the middle and early-ending periods of November.

Andrew

Intense Cold Snap Here to Stay

A cold snap which has just begun in the Plains and Midwest is here to stay, and will expand east in the process.

The atmospheric pattern has changed in the last couple of days, with ridging starting to build over the Gulf of Alaska and western coast of North America. This has started to lead to troughing/a colder weather pattern in the Central US, and this will intensify in the next several days, with the 10 day forecast above showing this pattern continue.

GFS ensemble temperature forecasts show this cold trend continuing and intensifying in the next several days, before the cold air mass slowly drifts east and weakens with time. I'm monitoring the GFS ensembles for moving the cold air out too quickly, as a recurving typhoon in the short and long range should keep at least a cool air mass across portions of the nation in the long-long range (i.e. 20-25 days).

This actually does have implications for the coming winter, and I will go in-depth with it when the Final 2013-2014 Winter Forecast is released next week, possibly on Thursday (one week from today).

Andrew

2013-2014 Winter Update: Midwest and Plains Deemed Frontrunners for Harsh Winter

This post is an update on the current outlook for the winter of 2013-2014, and will address why preliminary indications show that the Plains and Midwest may be frontrunners for a harsh winter this year.

Before we get into the discussion, I want to lay out the Lezak Recurring Cycle, which will be used in today's post. The Lezak Recurring Cycle, or LRC, is a tool developed by meteorologist Gary Lezak that, in essence, can enable forecasters to predict the overall weather pattern months in advance. The gist of the LRC involves a cycling weather pattern that develops in October and November of each year; no pattern is the same from year to year. Around mid November, the LRC begins to repeat, meaning we start to see a similar weather pattern in mid November that we saw in early October. This means that the cycling pattern has begun, and it will continue to cycle on a 40-60 day interval for the next ~10 months before it dissipates over the following summer. Now that we are in October, it is time to start looking for atmospheric phenomena that may factor into the LRC this year. Using the LRC, and long range model guidance, some early returns on who may get hit hard this winter are surfacing.

The first item to address is the October 4-6 winter storm, which delivered close to 5 feet of snow in a few isolated spots across western South Dakota. This storm system trekked northeast after strengthening over the Plains and dumping all of its snow. In the wake of this storm, a cold front meandered south through the southern Plains, Midwest and the Eastern US. Just on a very preliminary look at the winter storm, and the environment surrounding it, I would not be surprised to see this storm stay in the Plains and Midwest through the next couple of LRC cycles through this winter. To show why, take a look at the 500mb map for October 5th:

You can see the storm system in the Plains as a closed low, signified by the closed contour lines. There's a reason it went northeast rather than east- there was a ridge of high pressure in the Southeast. This ridge means it really can't just dive south or go due east unless the ridge moved, and in this case, it didn't. That said, considering the LRC should maintain a similar atmospheric pattern through its winter and spring cycles in the upcoming year, the storm system should go northeast again when it re-cycles in mid-November. I don't see this storm system being one that will become a big snow producer for the East, given the position of the ridge in the Southeast, but I would also be surprised to see extreme snowfall amounts like the ones seen in early October from this storm. Depending on how the jet stream changes from now until the next cycle in mid-November, the storm track may change slightly, but the overall pattern should remain similar enough to keep the storm track at least relatively on the same track as we saw in early October. With another storm system about to move into the Plains again, this region is looking at multiple snow and cold chances this winter, even though we're only ~25% into the LRC.

Let's take a look at what the models are predicting for the next week or two.

This image shows the European ensemble forecast (left) and the American ensemble forecast (right) for October 19, predicting 500mb height anomalies across the Northern Hemisphere. The grand idea here is that the weather pattern will be experiencing a drastic change in the medium-range. Both ensemble projections agree that a strong ridge will set up across Alaska and western Canada, and it may be strong enough to incite a cross-polar flow, which would enable cold air to be transported from Siberia to North America. Regardless of if this cross-polar flow does set up, significant negative height anomalies will form in the Central and East US as a result of this intense ridging in the western part of North America and ridging in Greenland (a +PNA signal and -NAO signal, respectively). A ridging pattern will be maintained to varying strengths in the Southeast US, which should keep the strongest cold weather in the Plains/Midwest and Great Lakes, hence why these regions are outlined for frontrunners for a harsh winter; the cold will be stronger when the LRC brings this cold pattern back in a couple of cycles for January. These negative height anomalies in the Central and East US will be enhanced by a recurving typhoon in the west Pacific named Wipha:

The American ensembles take this pattern further, maintaining it into the 2-week range:

The American ensembles continue to maintain ridging across western North America, aided by deepening negative height anomalies spreading south from the Bering Sea. Thanks to the continued ridging in western North America, persistent negative height anomalies are maintained in the Central and Eastern US. I'm a little skeptical of the negative height anomalies being shifted so far east, opposed to being in the Plains and Midwest, as ridging in the Southeast should still be present in this timeframe and the negative NAO pattern (ridging in Greenland; favorable for a chilly Northeast US) will have either weakened or dissipated by this time per the ensemble projections. On the other hand, a typhoon crashing into East Asia in the next 3 to 4 days (as shown below) should lead to a continued troughing Central/East US pattern beyond the next 10 days, enhancing the argument by the GFS ensembles.

Typhoon seen moving ashore in East Asia in 96 hours.

The weekly CFS model maintains a positive PNA pattern until the beginning of November, and if this verifies, the Midwest and Plains would continue to be frontrunners for a harsh winter this winter.

CFS PNA forecast through mid-November.

Andrew

Cold Pattern Evolving in Near Future May Repeat this Winter

A cold pattern that will be showing up in the near future could have a prolonged impact for this winter.

The image above shows 500 millibar height anomalies for October 19th, with the European ensemble projection on the left and the American ensemble projection on the right. Both ensemble sets are in agreement that a ridge of high pressure will develop over western Canada in cooperation with a developing trough over the waters in and around the Aleutian Islands. In response to the ridging in western North America, which we call a positive PNA (Pacific-North American index), a cold pattern will set up over the US, particularly for the Great Lakes, Midwest, Ohio Valley, and Northeast.

Both ensemble sets have the western North America ridge connecting with a weaker high pressure pattern over Greenland, which is described as a negative North Atlantic Oscillation (NAO). The negative NAO and positive PNA patterns are two major atmospheric patterns that help usher in cold air into the United States. While the ensemble systems have slight variations over the general Northern Hemisphere pattern, the concept that a colder weather regime will evolve over the Central and Eastern US is agreed upon by both ensemble systems. The temperature anomaly graphic below, which shows the American ensemble's temperature anomaly forecast for one day per panel, agrees with this colder regime:

But we aren't finished yet. The American ensemble insists that this cold weather pattern sticks around ... for quite a while.

This is the American ensemble 500 millibar height anomaly for October 25th. Does the pattern look familiar? It should, because it is nearly identical to the pattern being shown by both global ensemble sets at the top of the post for October 19th. A natural caveat for the long range forecast models is their notorious lack of accuracy. Taking that into account, it's possible we don't see this cold pattern stick around this long. At the same time, we have to examine all the possibilities, and one of them is that this pattern becomes more prolonged in nature. Looking at the temperature anomaly graph just above this 500mb anomaly chart, the ensembles are willing to maintain a cold air mass over the Central and Eastern US in the bottom row of panels. It is this bottom row of panels where the forecast period ends, and we cannot see projected conditions beyond October 26th (the far bottom right panel). The last 11 - that's right, ELEVEN - American ensemble runs consistently agree on this cold air mass being maintained in much of the country. Will it actually happen? It's too far out to tell, but model consistency does help the point of this colder pattern possibly becoming more prolonged in nature.

But the fun is not over yet. It is possible we could see this cold pattern return a few times throughout the winter through the Lezak Recurring Cycle.

The Lezak Recurring Cycle, or LRC, is a tool developed by meteorologist Gary Lezak that, in essence, can enable forecasters to predict the overall weather pattern months in advance. The gist of the LRC involves a cycling weather pattern that develops in October and November of each year; no pattern is the same from year to year. Around mid November, the LRC begins to repeat, meaning we start to see a similar weather pattern in mid November that we saw in early October. This means that the cycling pattern has begun, and it will continue to cycle on a 40-60 day interval for the next ~10 months before it dissipates over the following summer. Now that we are in October, it is time to start looking for atmospheric phenomena that may factor into the LRC this year. We already saw the big winter storm in the Plains, and time will tell if that becomes a part of this winter's LRC, and now we are looking at this possibly-prolonged cold weather pattern to see if it will factor into the LRC. Considering it should occur in mid to late October, chances would be good that we see this in this year's LRC. However, in meteorology, nothing is ever 100% guaranteed. Again, time will tell, but it's possible this cold fall pattern returns in November and January as a long(ish)-term frigid weather pattern.

Andrew

Long Range Lookout: Pattern Change in the Offing

It does appear we will see a shift in the atmospheric pattern in the next couple of weeks, as the hyperactive typhoon regime in the Pacific tapers off in response to a changing Madden-Julian Oscillation.

This graphic, provided by the NCEP, shows a composite of tropicalcyclones that have formed in the month of October by each phase of the MJO. The graphic indicates that typhoons tend to reach maximum occurrence in phases 5-7, and taper off as the MJO rounds out its later phases. We have been in Phases 5 and 6 for nearly a full month now, which explains why the last few weeks have had remarkable typhoon formation in the Pacific. Among those that formed in the last ~30 days were:

Typhoon Usagi (September 16- September 24)

Typhoon Pabuk (September 19- September 27)

Typhoon Wutip (September 25- October 1)

Tropical Storm Sepat (September 29 - October 2)

Typhoon Fitow (September 29 - Present Day)

Typhoon Danas (October 3 - Present Day)

These typhoons have come from the MJO being restricted to Phases 5 and 6 in the last month. However, the latest European forecast for the MJO shows gradual progression into Phases 7 and 8, phases which are shown by the NCEP graphic at the top of this page to include a tapering off of the hyperactive typhoon regime in the Pacific.

All of these typhoons have to go somewhere, and they go north into the Bering Sea and general northern Pacific. With these extratropical storms in the northern Pacific, they then propagate down into the West US and western Canada, where they dig deep into the Western US to provoke ridging of high pressure in the East US. As long as the typhoons continue to form in the western Pacific, there is little that should alter this pattern for at least the next several days. The MJO forecast above indicates the formation of typhoons will lessen after these next several days, but until then, the prospect for warmer weather in the East for as long as the next week appears very possible. The main point to get out of this typhoon discussion is that the warm weather will wind down as the typhoons wind down, and that should happen in the ~7-10 day period.

We're going to stay in the west Pacific and move our discussion into the East Asia region. The last couple of days have seen a massive ridge building up across East Asia that is just now beginning to weaken and pull east into the Pacific. Those who have followed this blog for a long time understand that there is a 6-10 day correlation between height anomalies in East Asia and height anomalies in the East US. Hence, this massive ridge in East Asia will translate to ridging in the East US in just over a week.

The ECMWF model (left) and GFS model (right) nail this correlation in showing a massive ridge across eastern Canada and the East US in the 8-10 day forecast period. This ridging in the East does something that the ridging in Asia couldn't do- it propagates north and into the upper latitudes. Both global models project that this strong high pressure in the East will exert tremendous influence on the pattern in and near the Arctic Circle in what could become an upper latitude blocking pattern. Long range GFS ensembles project a steadfast negative NAO developing due to ridging across Greenland, and a cool pattern then takes place over the Plains before gradually shifting east. It does appear the cool Plains/Midwest idea should end up verifying, and as long as the East US ridging stays on track to flow north into Greenland, the negative NAO should work out as well. Projected rising of the Pacific-North American index would certainly help cool Plains prospects in the long range in addition to the -NAO:

Summarization
The Eastern US will encounter warm weather for the next week to 10 days before the threat of any big heat moves out and seasonal-ish temperatures move in. The Plains will remain seasonal to slightly below normal as another storm system is projected to swipe the Central Plains and hit the Northern states. An overall cool down is anticipated beyond the 10 day forecast point. The West US will be inundated with cool weather for the next week and a half before rising temperatures make their return.

Andrew