The Mostly Mundane Winter of 2021–2022

It’s April, and it’s time for winter to crawl back into hibernation. The Accumulated Winter Season Severity Index, or AWSSI, shows how it behaved.

The Accumulated Winter Season Severity Index (AWSSI) as of April 2, 2022. Each dot is a location where AWSSI is calculated daily throughout the winter. Colors of dots correspond to categories of winter severity, from mild (red) to extreme (purple). Map courtesy of the Midwestern Regional Climate Center.

The Accumulated Winter Season Severity Index, or AWSSI (pronounced like “Aussie”), tallies a “score” throughout the winter season based on temperatures, snowfall, and snowpack on the ground. As winter throws its cold and snowy stones, the score goes up. By the end of the season, that “score” gives a numerical value to the winter’s combined fury of snow and cold — or lack of fury. The points at each site fall into one of five categories: mild, moderate, average, severe, and extreme, based on how any given year compares to the history at each location. AWSSI winter starts when winter temperatures (that is, high temperatures at or below freezing) or measurable snow arrive, or on December 1, whichever is first. The winter ends for AWSSI totals on March 1, after the last snow, or after the last day below freezing, whichever comes last.

AWSSI chart for Missoula, MT, for 2021–2022 as of April 2, 2022. The winter has landed in the “Average” category, with a numerical AWSSI value of 702, and winter conditions have not added to the total since March 9.

Winter might not have ended yet in some places, but at this time of year, the points added to the overall winter score don’t typically change the category unless it was on the borderline already. What we see for…