Two Wild Cards Impact The 2020 Winter Weather Outlook

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La Niña plays a major role in this year’s winter weather outlook with cooler than normal water temperatures in the tropical Pacific Ocean already developing.  The intensity of that cooler water will peak sometime toward the end of 2020 before the water gradually warms through the late winter.  This will ensure that the atmosphere will continue to respond to La Niña conditions through the entire winter.  But, two wild cards could be major factors in how the winter forecast evolves.

One significant wild card is the Polar Vortex.  Last winter, it remained strong and anchored across the North Pole.  This kept most of the cold air bottled up and the result was a warmer than anticipated winter season.  Some of the models suggest that could happen again this winter.  However, if the Polar Vortex is disturbed, there are opportunities for brief colder stretches. Although this creates uncertainty, confidence in the forecast is high because the La Niña is forecast to be strong enough to be the main influence of the pattern.  

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The other wild card will be the month of November. It is a good indicator of how December and January might play out during typical La Niña winters.  If we see persistent cold reaching the Central and Eastern U.S. during November, chances are there will be repeat bursts in December or January.  However, if we get past November and there are no signs of cold through December, the chances are greatly reduced it will come later in the winter, especially in the Eastern and Southern US.  This is key because when the cold does come in La Niña winters, it can be intense for a brief period, even if most of the remainder of the winter turns out to be warm.  

Taking the aforementioned wild cards into account, here is the winter weather outlook for the United States.

Eastern U.S.

In the East, there will be some early cool risks that develop in November and December.  This is likely to impact the Northeast more than the Southeast and will come in short bursts.  Warmer periods are also possible, bringing the temperatures closer to normal early in the winter.  

While there will be opportunities for early season snow with the colder temperatures across northern areas, the winter is expected to start dry.  The outlook is then for warming to build in January and February across most of the East.  This is especially true across the Southeast where a few periods of spring-like weather will be possible. However, signs are pointing towards a cooler end to the winter in March, with the pattern gradually turn wetter later in the winter.  For northern areas, that will mean more snow opportunities, while across the South, this this typically leads to elevated severe weather risks.  

North Central U.S.

The North Central states should see a slower start to winter.  Generally, temperatures should be near-to-above normal with below normal precipitation continuing through November and likely December.  This will unfortunately add to drought concerns across portions of the region. The late winter period will likely feature a turn toward colder weather conditions, especially across the Northern Plains.  Colder air will build up across western Canada and some of this air is expected to occasionally come down into the North Central states.  This effort will be resisted by warmer air across the east and south, so we may have wetter conditions across the Midwest later in the winter. It will also mean higher risks for snow and mixed precipitation.

Southwest and South Central U.S.

The Southwest and South Central states are likely to experience above normal temperatures through most of winter. There will be cooler risks later in the year across California and Nevada, along with portions of the South Central states.  These cooler periods could be intense across the portions of the South Central states. The main story will be expanding drought conditions across the Desert Southwest through Texas.  Most storm systems should be located across the northern states with few opportunities for meaningful precipitation in these areas, which means the wildfire season in California and the Desert Southwest would extend into the early winter. 

Northwest U.S. 

The Northwest states should see a more active winter season. After a mild start to the season, especially in November, below normal temperatures will gradually take hold as the winter progresses, especially across the northern Rockies.   Above-normal rain and mountain snow is likely across the Pacific Northwest through the northern Rockies.  A few systems could feature significant precipitation, which is good news for extinguishing existing fires in these areas.  However, rain falling over burned areas could produce enhanced risks of flooding and mudslides.  These cooler and wetter conditions should linger into the early spring season.

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