What Are The Models Saying This Winter? - CMC1 Model

This is a continuation of this series of posts, where we are analyzing long range climate model projections for the beginning of the winter of 2014-2015. This post will feature the CMC1 model.

The temperature forecast from the CMC1 model, valid for December 2014, shows a very chilly winter for many in this country. This model suggests we will see an abundance of warm air overspreading Alaska and the west coast of North America. This is likely the result of high pressure, which then forces mid-level troughing to the east. This mid-level troughing, which will be discussed more later in this post, results in below normal temperature anomalies over the Central and East US, extending as far north as upper Canada. If you follow the weather closely, you may recognize this pattern as a positive Pacific-North American (PNA) index pattern. Like last winter, the Pacific pattern looks to have a grip on the downstream weather here in the US, resulting in a cold start to the winter.

The precipitation forecast from the CMC1 model shows a pattern almost identical to a traditional El Nino winter precipitation pattern. We first see anomalously wet conditions along the West Coast, a telltale El Nino signal due to the subtropical jet stream's natural enhancement due to the aforementioned El Nino. This enhanced subtropical jet stream then leads to more storm systems hitting the West Coast, and then more precipitation. We then see significantly below normal precipitation across the Central US, hitting the Ohio Valley the hardest. Once again, this is an El Nino signature. The El Nino is evident yet again in the CMC1 model's forecast for a very wet start to winter on the East Coast. This all strikes me as odd, since the temperature forecast does not reflect an El Nino temperature pattern, but given how this past winter went, you really have to expect the unexpected.

Lastly, we see the forecast of z200 anomalies for December 2014 from the CMC1 model. We're going to focus on the contour lines over the northern Hemisphere. In this forecast, we see the contour lines arching northward over the west coast of North America, signifying ridging/high pressure in that area. We discussed the likely presence of high pressure along the west coast earlier in the temperature forecast, and now we are seeing that theory come to fruition. We then see the contour lines plummet south over the Central US, which is how we got that cold December forecast at the top of this post. Oddly enough, we then see ridging in the Southeast US, which would typically divert storm systems north through the Ohio Valley. However, the precipitation forecast for the Ohio Valley is very dry, as shown above. This is likely the long range model up to its antics, which means confidence is similarly low.

Additional models will be discussed in coming days.

Andrew

Active Severe Weather Potential Looming for Mid-June

I am still monitoring the potential for a period of active weather in mid-June.

The image above shows a long range forecast of outgoing longwave radiation (OLR) anomalies over the equatorial region of the globe, valid on June 14th. In both of these images, the yellows represent positive OLR, or suppressed tropical convection, while the blues denote negative OLR, or enhanced tropical convection. We can see a strong active Madden-Julian Oscillation (MJO) signal on the bottom panel, with deep blues indicating abnormal convection occurring over southern India into the waters east of the subcontinent. The placement of this enhanced convection tells me we are looking at a Phase 2 MJO, as the OLR composite shows below.

OLR anomalies for each MJO phase

Now, outside of the fact that Phase 2 MJO events have been known to increase the risk of violent tornado outbreaks in the spring months, the mid-level pattern during a June Phase 2 MJO event also signals the potential for severe weather.

The image above, produced by Americanwx, shows 500mb height anomalies over the northern hemisphere when the Madden-Julian Oscillation is in Phase 2 during the month of June. In this image, warm colors indicate high pressure/calm and warm weather, while cool colors denote stormy and cooler weather. During a typical MJO Phase 2 event in June, we tend to see ridging set up from the Bering Sea to the Great Lakes, enhanced slightly by weak troughing in the West. Because of this weak West US troughing, warmth and moisture are pumped north into the Central and East US from the Gulf of Mexico. This action then feeds into the increased potential for severe weather. Based on this composite, I do feel this time period may be defined by some active severe weather.

More evidence for an active severe weather period in mid-June arises when we take a look at the long range CFS severe weather forecast. The dates on the right display the date the forecast was made on, and the dates on the bottom legend indicate when this forecast is valid for. Warmer colors indicate the higher potential for severe weather. For instance, if I want to know the severe weather potential for May 30th on a forecast made on May 5th, I go up the legend on the left to find May 5th, then scroll on the corresponding horizontal line to find the May 30th box. In this case, we have been seeing the majority of recent forecasts highlighting the June 10-25 period as the one to watch out for, as the varying-colored boxes show on the upper-right corner of this image. Sometimes, there is safety in numbers in the weather world. In this case, with the relative consistency of these forecasts for the mid-June timeframe, I feel comfortable raising the concern of a potential active period for the aforementioned timeframe.

Andrew

Positive QBO Beginning to Weaken; May Signal Cold Upcoming Winter

It does look like the positive phase of the Quasi-Biennial Oscillation is ending as we progress into summer, a move that may herald a cooler than normal upcoming winter. The Quasi-Biennial Oscillation (QBO) is an oscillation measured by the direction and intensity of winds in the middle of the stratosphere, usually around the 30 millibar level. When the QBO is in its positive phase, winds are called 'westerly', as they flow from west to east at an anomalously high speed. The positive QBO typically strengthens the polar vortex, thus resulting in a warmer than normal winter for lower latitudes. The negative QBO is when winds at the 30mb level are 'easterly', or going from east to west. Since this is the opposite direction as typical low pressure circulation in the Northern Hemisphere, the polar vortex is weakened, and cold weather tends to permeate the lower latitudes more frequently in the winter. Going by this, it would be plausible to associate this weakening +QBO with what could be a destabilized polar vortex next winter. This may mean additional opportunities for the polar vortex and associated cold weather air masses to penetrate deep into the United States, as they did last winter.

I discussed how my analogs for the upcoming winter showed upper latitude blocking, a feature that would be enhanced with the presence of a neutral, or more likely weak negative QBO phase. At this point, it is too early to tell whether we will be in a definitively negative QBO or a neutral QBO next winter, but the general concept of the weakening +QBO is clear, and this could be another element to a chilly winter ahead.

Andrew

What Are The Models Saying This Winter? - NASA Model

This is a series of posts that I have made in previous years, in which I display a specific long range model and its prediction for the upcoming winter. Based on its success in past years, I have decided to kick off the multi-month series early, to give you an early heads up on the upcoming winter.

Today's model will be the NASA model.

The above image shows the NASA model's forecast of 200mb wind speed anomalies across the world, with 200mb pressure contour lines superimposed. We want to mainly pay attention to the contour lines for today's analysis, since it seems to be the easiest for many to decipher over the anomalies. If we look at North America, we see the contour lines arching up across the West Coast, likely indicative of the presence of high pressure/ridging. This ridging over the western portion of North America then leads to a depression in the contour lines, where cold air would funnel southward into the central and eastern portions of the continent. This cold air would be helped along south by that troughing/depression in the contour lines. In other words, going solely by this image from this single model, we would be looking at a very similar set-up as last winter, with warmth over the West and cold over the East.

If we look at the North American temperature forecast for December 2014, the same timeframe as the image above, we see a similar story to my analog package which I posted about earlier this week. We see cold weather present across the South US, with warmth prevailing over Canada and the North US. This temperature forecast looks very similar to a textbook El Nino event, which is expected to form this summer and result, possibly, in a temperature pattern similar to the one above for this winter.

Lastly, the temperature forecast from the NASA model, valid December 2014, confirms the idea of a textbook El Nino pattern. We can recognize this El Nino pattern by viewing the below-normal precipitation across the Great Lakes and Ohio Valley, with a very wet precipitation pattern swallowing the Southeast and East Coast. These two features are common during an El Nino winter, and may very well appear this winter. On the West Coast, in accordance with the ongoing drought, we see well-below-normal precipitation values extending from California to Washington. All in all, even though this is a long range forecast, this solution is indeed a plausible one from this model.

To summarize, the NASA model is predicting the following conditions to begin the winter of 2014-2015:
• Cool South US
• Warm North US
• Wet & Stormy East Coast, Dry West Coast
• Very similar to a typical El Nino pattern

Andrew

Potential Severe Weather Outbreak Projected for Mid-June

I'm seeing an increased probability for a severe weather event, potentially an outbreak, for the middle of June.

The image above shows a long range forecast of outgoing longwave radiation (OLR) anomalies over the equatorial region of the globe. In both of these images, the yellows represent positive OLR, or suppressed tropical convection, while the blues denote negative OLR, or enhanced tropical convection. We can see a strong active Madden-Julian Oscillation (MJO) signal on the bottom panel, with deep blues indicating abnormal convection occurring over southern India into the waters east of the subcontinent.

If we take a look at MJO composites for each phase, with blues once again defining enhanced convection and oranges signifying suppressed convection, it would seem that storms just east of India fit in best with a Phase 2 or 3 MJO event, seen on the left panels of this graphic above. Considering there has been a link observed between the MJO being in Phase 2 and violent tornado outbreaks occurring consequentially, there is reason to monitor this period for potential severe weather.

The image above shows projected 500mb height anomalies over the northern hemisphere. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. In the image above, if we look towards the Bering Sea, we can see a very strong ridge of high pressure, seen by the splotch of red around the Aleutian Islands. This image is valid for May 13-14, and if we extrapolate it out 2-3 weeks using the Bering Sea Rule, we can expect high pressure and warm weather to appear in the East US. This extrapolated timeframe looks to fall around the time when this potential severe weather outbreak may strike, and the presence of strong high pressure migrating across the Eastern and Central US may amplify the potential for active weather.

Another device we can use to predict potentially active weather is this grid chart. The dates on the right display the date the forecast was made on, and the dates on the bottom legend indicate when this forecast is valid for. Warmer colors indicate the higher potential for severe weather. For instance, if I want to know the severe weather potential for May 20th on a forecast made on May 5th, I go up the legend on the left to find May 5th, then scroll on the corresponding horizontal line to find the May 20th box. In this case, we have been seeing elevated supercell composite values around the June 15-20 period for some time now, as the red box indicates. This is a long range forecast, but as you can see with severe weather events further to the left on the image, we can get a feel for severe weather potential a long way out, with more accurate forecasts usually coming a few days to a week prior to the event.

This potential event will be updated in coming days as more information becomes available.

Andrew