Winter Weather Outlook

When compared to 2020, the snow and ice season has gotten off to a slower start this year across the Plains, Midwest, and Northeast. This is due to above normal temperatures in place through October and into early November. However, this looks to make a quick change as we head into the next couple of weeks, with cooler temperatures settling in and opportunities for snow on the horizon.

© NOAA

Overall, winter (December-January-February) 2021-22 is looking somewhat similar to last year, but with some caveats. Last year, we discussed that La Nina was going to be one of the main pattern drivers, and it will be again this year. The difference lies in the strength of La Nina and the location of cooler Pacific Ocean waters.

Below normal sea surface temperatures in the Equatorial Pacific are basin-wide, which is more widespread than last year. Additionally, La Nina is expected to peak early in the winter and then gradually weaken through the end of the season, unlike last year where we saw it continue to strengthen.

Historically, when considering all La Nina years between 1951-2008, these conditions have led to snowier winters across the Pacific Northwest, Upper Midwest, and Northeast, with below normal snowfall in the Mid-Atlantic and Ohio Valley. However, when considering just weaker La Nina years, snowfall increased significantly across much of the Snow Belt.

Another factor to consider for Winter 2021-22 is the amount of Siberian snow cover already in place. This is significant because it allows for colder air to develop over Siberia, which is transported to North America during cross-polar flow. Cross-polar flow occurs when cold, continental air can travel directly across the North Pole from Siberia to North America. This occurs when the Polar Vortex begins to weaken. While these periods are typically short-lived, they can bring historically cold temperatures to the US and Canada.

The weakening La Nina during the second half of the winter season will present challenges to the forecast. Other factors will begin to have greater influence on the overarching pattern. The North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Pacific-North America Index (PNA), and Pacific Decadal Oscillation (PDO) are a few of these factors. While I won’t go into the specifics of these, it’s important to know they have direct influence on the upper-level flows of the atmosphere. When the NAO and AO are in negative phases, the US experiences colder temperatures and a more active pattern. In general, the second half of winter looks to feature this increased activity.

The greatest uncertainty for this winter will be the cold air supply. Analog data, seasonal model guidance, and the La Nina influence all point toward the potential of warmer-than-normal temperatures across central and eastern portions of the country. However, that’s not to say there won’t be cold periods. The timing of cold air arrival behind surface low-pressure systems will be key, as always, in determining snowfall potential.
 
The greatest confidence lies in the precipitation patterns. Above normal precipitation is expected across the Pacific Northwest and Great Lakes/Ohio Valley region. However, wet does not equal snow. Rather, it means increased precipitation. Additionally, drier-than-normal conditions are expected across Southern and Southwestern regions of the country. In these areas, drought is expected to persist and possibly develop further.

Frequent Snow Magazine contributors Joseph Cooper and Beth Carpenter are meteorologists and co-founders of Thermodynamic Solutions, a private meteorological consulting company based out of Indianapolis.