Winter Seasonal Outlook by Kyle Elliott
3:00 p.m. Tuesday, November 2, 2021:
As seen below in my Twitter highlights, a second-year La Nina and "cool blob" in the northern Pacific will favor warmer-than-normal conditions and below-normal snowfall, in aggregate, across the eastern United States this winter. In addition, I expect a weak southern branch of the jet stream and an active northern (Pacific) branch to dominate. Because we typically get our "snowiest winters" and "blockbuster Nor'easters" when the southern branch of the jet stream is strong (during El Nino), I expect this year to feature just the opposite: a lack of big storms and generally weaker systems. So, the risk of a snowstorm >12" is minimal this winter season, but we'll likely see several smaller snowstorms (1-3, 3-6" events) that add up to a seasonal snowfall total of 15-25" for Lancaster County.
We'll likely receive our first measurable snowfall in December, but January has the greatest chance of being our coldest and snowiest month. I looked at six winters since 1980 ("analogs") with similar factors contributing to the outcome of the season and found that the majority featured well below-normal snowfall/above-normal temperatures in both December and February. However, near- to slightly below-normal temperatures and near- to slightly above-normal snowfall in January were a theme in all but one of these six winters. Thus, I foresee the greatest risk of a moderate snowfall (4-8, 6-10" event) and period of "sustained cold" occurring in January 2022, with "changeover" or "plain rain" events more common in both December and February. More times than not, the storm track will be to our north and west this winter, meaning that we'll be on the "warm side" of storm systems. While we can still get a period of snow and sleet on the front end of these systems, precipitation typically changes over to freezing rain or plain rain rather quickly.
Looking ahead to March, I have a great deal of uncertainty as to what the eventual outcome will be. Much will depend on the presence or lack of high-latitude blocking, which is very difficult to predict more than a few weeks in advance. If blocking were to develop late in Feburary and March, then we could be dealing with a "snowy surprise" like what occurred in March 2018. If blocking fails to develop, then March could turn out abnormally warm (more like March 2012). I may not be able to fine-tune these details until sometime in late January or Feburary... so stay tuned!
(1/4) Here we go... my first WINTER OUTLOOK as Director of the Millersville University Weather Information Center! Two primary winter-season influences will be our second-year La Nina and Northern Pacific "cool blob"... pic.twitter.com/oqXjXlwFLk— MU Weather Center (@MUweather) November 2, 2021
(2/4) High-latitude (NAO/AO) blocking will be a big "wild card" this winter.. more persistent blocking could lead to a colder and snowier winter in the East, while a lack of blocking could result in an even warmer and less snowy winter..— MU Weather Center (@MUweather) November 2, 2021
(3/4) Overall, this winter will feature alternating cold and mild spells, but with the # of above-average days outnumbering the # of below-average days. Aggregate temps. will be slightly above normal (+1-3°) but with snowfall a bit below normal (15 - 25"). Coldest month: January! pic.twitter.com/sWBQJPpTeR— MU Weather Center (@MUweather) November 2, 2021