The Winter of 2019-2020 was one to forget across much of the United States if you’re a snow lover. A “Polar Vortex” that stayed close to the North Pole and intensified to near-record strength from January through March kept cold air locked up over Alaska and Canada, with milder than average conditions nearly running the table across the Continental United States. The question on everyone’s mind: Will we at least have a winter this year?
Setting the Scene: La Niña
Current sea surface temperature anomalies, courtesy of Tropical Tidbits.
A La Niña event has developed across the Tropical Pacific over the summer and is intensifying as we head through fall. The La Niña, outlined in the blue box on the above image, means waters are cooler than normal along the equator in the Pacific Ocean. This La Niña is expected to flirt with “moderate” strength this winter, meaning it will be strong enough to influence the pattern (it has already been influencing our pattern since June).
Typical wintertime La Nina pattern, courtesy of NOAA
What does this mean? It means there will be a ridge in the jet stream over the central Pacific, causing the jet stream to descend into western North America, bringing cold to that region. This means that in the Continental U.S., the coldest conditions are likely across the northwest quarter of the country, with mild conditions over the Southeast. Consider this as a starting point, however, El Niño and La Niña events come in different flavors. The strength and positioning of the La Niña, along with outside factors, still have a major say on what the exact pattern looks like through the winter.
Jet stream pattern in analog, or similar winters to what we may see this year; image provided by the NOAA/ESRL Physical Sciences Laboratory.
Factors that may have a say on the exact evolution of this winter include the La Niña leaning “east Pacific based”, very warm waters over the western Pacific, warm waters off the West Coast, and things such as stratospheric winds. The most recent years with similarities to this year that we evaluated as possible analogs for this winter include the winters of 2016-17 and 2017-18, 2010-11, 2008-09, 2007-08, and 2005-06. Astute observers with long memories may recall that 2017-18 and 2010-11 were fairly cold and snowy winters acorss a good portion of the eastern United States compared to the typical "mild" La Niña baseline, though it's too early to say with any confidence if that outcome can happen this year or not. We also evaluated a few winters farther back in time. The average pattern among our “analogs” is shown above and certainly bears resemblance to the typical La Niña pattern, but it does feature some potential for cold to occasionally work farther east or southeast at times and battle back against the southern and southeastern U.S. warmth. Out of our analog winters, many of them were "front loaded" with cold during the first half of winter, and then a pronounced warm-up over the eastern U.S. (with cold shifting to the Northwest and northern Rockies) during the middle or latter portions of winter.
Temperature and Precipitation Forecast:
Temperature and precipitation forecast for the winter in the Continental United States.
This boils down to a generally mild winter across the southern United States, a cold winter across the Northwest, and a lot of swings in between. Until confidence in the pattern increases either way, we do favor the winter to add up to "mild" for most of the East Coast and into the Ohio Valley, but with some swings and colder spells mixed in. We expect normal to above normal precipitaiton across much of the northern U.S. (in particular, the Northwest, northern Rockies, Great Lakes, Ohio Valley, and Northeast) and generally dry weather across the south.
Snowfall forecast for the winter in the Continental United States.
Given all of the above, here is our snowfall forecast for this winter. We will continue to evaluate patterns as we get closer to winter and adjust as needed. While the “base” La Niña pattern is evident (snowier conditions across the Pacific Northwest and northern Rockies, and generally less snow across the southern and eastern U.S.), keep in mind that this does not mean it won’t snow outside of the northern tier. Colder pushes of air farther south and east will be likely, especially during the first half of winter, but generally temporary. Interestingly, many areas can see considerably more snow than last winter and still see average or less than average snowfall; that’s how snowless last winter was in many areas. The clash of air masses will also likely lead to quite a few mixed precipitation events from the central Plains and mid-Mississippi Valley and on east across the Ohio Valley and into the Mid-Atlantic and southern New England, particularly in the Appalachians.
For more detail on the Winter Outlook, watch this video with meteorologist Mike Mihalik and chief meteorologist Jim Sullivan: