Winter 2015-16 Temperature Outlook Update: Considerably Warm North, Chilly South

If you live in the north-central portion of the country and thought that the early-season blast of snow and cold from Winter Storm Bella was a sign of things to come, not so fast.

There are signs that December could be significantly warmer than average from the northern Rockies to the northern Plains, Upper Midwest and northern Great Lakes.

To the south, near to slightly below average temperatures are forecast across parts of the Southwest, southern Plains and western Gulf Coast for the beginning of winter. Cooler-than average conditions may later spread further east and northeast into January and February, reaching the eastern third of the country in the process.

The strong El Niño event currently underway is a big player in the winter forecast. Stronger El Niño winters tend to favor cooler conditions across the South with warmer than average temperatures in the North.

With this El Niño the strongest in 18 years and nearing its peak and considerable agreement from computer model guidance, there is increasing confidence in such a temperature pattern.

(MORE: Strongest El Niño in 18 Years Expected to Peak This Winter)

“The recent brief cold spell across the central/eastern U.S. was just that, brief. A textbook El Niño pattern will become established as we head into December, with a powerful Aleutian low and strong Canadian ridging, “ said Dr. Todd Crawford, WSI chief meteorologist, a division of The Weather Company.

Among the medium-range computer forecast ensemble members there is “unusually strong agreement out to 360 hours, depicting a robust pattern that closely matches the response also found in the last two “Super” El Niño events of 1982 and 1997.”

(MORE: The Impact of El Niño on Snowfall)

Winter Outlook Summary

After a brief taste of winter earlier in November, warmer-than-average temperatures have returned to end November and this warmer trend will likely last through December.

A classic El Niño pattern will become established in December with a strong southward dip in the jet stream, or trough, expected near the Aleutian Islands in Alaska which will lead to a strong upper-level ridge of high pressure over Canada.

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This will allow temperatures to be much warmer than you would normally expect in December across the northern tier of states. The area that is expected to see temperatures the most above average will be from the northern Plains into the Upper Midwest and Great Lakes region.

Temperatures will be chillier than an average December from southern and central Arizona through the majority of Texas and into Louisiana and southern Mississippi.

Colder than average temperatures are usually found in the South during an El Niño winter. This is due to a more active sub-tropical jet stream which can bring more rain and clouds than an average winter to the South, which helps keep temperatures colder.

A Shift In the New Year?

There are still indications that colder-than-average temperatures may develop in the East beginning in January and even more so in February. The risk of upper-level atmospheric blocking in the North Atlantic increases in January and February which can force colder temperatures into the Eastern U.S. for prolonged periods.

There was unusually strong blocking this past July, which may lead to blocking during this winter and blocking can trump El Niño conditions. However, according to the WSI outlook, "the only winters that have had big North Atlantic blocking since 1970 were within two years of a solar minimum" and the next solar minimum isn't expected for approximately five years.

Another element that can help determine the risks for atmospheric blocking are whether there will be a significant stratospheric warming (SSW) event. However, these SSW events, which increase the odds of colder conditions in parts of the mid-latitudes in the Northern Hemisphere due to the breakdown of the polar vortex, are very difficult to predict.

(MORE: 5 Things to Expect This Winter)

Crawford points out that "the unusually strong Siberian high in November does increase the chances of having a sudden stratospheric warming event during the winter, but other indicators still suggest otherwise." This strong Siberian high is driven from above-average snow cover in Siberia in October.

One of these contrary indicators is the current value of the solar flux, which currently corresponds to cooler stratospheric temperatures this winter, which would reduce the odds of a SSW event that would drive blocking.

However, another factor to consider is that the European computer forecast model shows a very strong signal for upper-level ridging to develop from western North America north to the pole during late winter, which indicates the chance for colder temperatures to dive into portions of the East late this winter.

Chillier than average conditions may expand across the southern tier for the second half of the winter, stretching from the Southwest through the Southeast. As mentioned above this is what is expected in a textbook El Niño winter. Temperatures that are much colder than average will be focused across most of Texas and Louisiana in January and will expand through the Deep South and the Southeast in February.

It is important to remember that these forecasts are for the overall month and season. These expected temperatures will be accompanied by periods of both colder and warmer temperatures.

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