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, 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.
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 this winter is pretty close to what we’re going to get.
With a shot of snow here and a burst of cold there, the winter left a seasonal tally that was nondescript, in most places. Winter severity covered the country in patchwork this winter, with areas of mild winter adjacent to areas of average to severe winter, and without large swaths of similar severity. (For comparison, the winter of 2014–2015 had a more typical pattern of regional similarity, with a mild winter in the western U.S. and an extreme one in the east.)
Snowfall evaded chunks of the central Great Plains, from South Dakota to Kansas, while it coated the southern neighbors in Oklahoma to Arkansas. While no parts of the country had a continuous swath of severe to extreme conditions, the greatest concentration of those categories were sprinkled across the northern contiguous U.S., from Oregon and Washington to northern Minnesota and Michigan’s upper peninsula, with another…