When does winter really start in Wisconsin?

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When does winter really start in Wisconsin?
wisconsin state outline barely visibl under snow cover

State outline barely visible under snowcover (click image to enlarge), this is Winter in Wisconsin. Photo: MODIS Image Gallery by Liam Gumley, SSEC (Space Science and Engineering Center, UW, Madison).

The beginning of astronomical winter doesn’t occur until the Winter Solstice, which is usually between December 20-22. On the winter solstice, the sun reaches is most southern point in the sky and our daytime hours reach an annual minimum as the nighttime hours reach an annual maximum.

This is the most recognizable definition of the beginning of winter, but it rarely coincides with an abrupt plunge into the season. In fact, anyone who has lived in the Upper Midwest or the interior of Canada knows that winter usually seems to arrive at least a month before late December.

In Madison, Wisconsin, we usually have had a measurable snow, a day with morning low temperatures in the single digits, and plenty of skating long before the winter solstice. In fact, the all-time record daily snowfall total occurred weeks before the solstice in 1990!

A more meaningful definition of the beginning of winter might be based on when, on average, precipitation has an equal chance of falling as rain or snow. For Madison, that day is November 15. Of course, since this is an average (calculated over many years) any individual year may completely ignore this pattern.

Statistics, after all, apply to groups, not individuals.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.