The Winter Severity Index

Winter Weather

Harvest plans in northern Wisconsin very from year to year, in part depending on winter weather. Deer have both physiological and behavioral adaptations that allow them to endure Wisconsin winters-provided the deep snow and extremely cold temperatures do not persist too long. In very severe winters, losses of deer in northern Wisconsin can be dramatic (as much as 30% of the herd). Even in mild winters, some animals will die. In the south, winter weather rarely impacts deer survival. To keep tabs on winter weather conditions, the DNR maintains a Winter Serverity Index (WSI) at about 31 locations throughout northern Wisconsin.

The WSI was developed in the early 1970's. It is calculated by adding the number of days with 18 inches or more of snow on the ground to the number of days when minimum temperatures were 0 degrees Fahrenheit or below between December 1 and April 30. If you think of it as adding up points, a day when both conditions occurred would get two points. At the end of the winter all the points are added up, resulting in the WSI number for the whole winter. A winter with an index of less than 50 is considered mild, 50 to 79 is moderate, 80 to 99 is severe and over 100 is very severe.

The following is an update of the current WSI in northern Wisconsin and is posted based on the most recent data available.

WSI Update

Final

Questions for Wildlife Management