Snow depth and daily temperature is what biologists use to compute the Winter Severity Index (WSI). Basically, the WSI tracks snowfall and temperature from December 1 through April 30 and provides a way of assessing the winter’s impact on wildlife. Any day in which the temperature drops to zero or under is scored as a 1. Additionally, any day in which there is 18 inches of snow on the ground also gets scored as a 1. So, if 12 days in January had 18 inches of snow cover and temperatures on 6 of those days dropped to zero or below, the score for January would be 18. A seasonal score of 50 or under = mild winter, 51-80 moderate, 81-100 severe, and over 100 very severe. Severe and very severe winters generally mean reduced deer numbers due to winter kill. Over the past few winters both Wisconsin and Minnesota have experienced severe winters in the northern parts of their states resulting in declining deer harvests in recent years.