The true winter weather season normally begins in mid to late November and extends into late March. Periods of cold weather are still likely both before and after these dates but this four month plus period is the time when average temperatures are at or below freezing and most precipitation falls in the form of snow.
The average high temperature drops to the freezing mark on the 5th of December and stays at freezing or below until the 24th of February. The majority of days in mid winter have highs from the mid teens to the mid 30s although Arctic outbreaks may bring periods of frigid weather when high temperatures stay below zero for several days in a row. La Crosse averages 26 nights per winter when the temperature falls to zero or below with 11 such nights usually occurring in January.
There are several tracks which storm systems may take to produce snow in western Wisconsin. The heaviest snows usually develop when low pressure systems develop in the southern plains states and move northeastward into Missouri and Illinois. These storms often produce 6 to 10 inch snowfalls and may cause snows in excess of one foot such as those which occurred in January of 1996 and March of 1997.
More common are the lows which track southeastward from Alberta, Canada and the northern plains states toward the Upper Mississippi Valley. These lows typically produce lighter snows in the 1 to 4 inch range. Widespread blowing and drifting of snow may occur with these systems if the area of low pressure is strong.
The La Crosse area will experience freezing or mixed precipitation when cold high pressure is in place at the surface and a warm front approaches the region from the south. The warm air is forced to rise, causing precipitation to freeze as it falls into the cold air.
Winter is, on average, the cloudiest season of the year in La Crosse with lengthy periods when low clouds cover the sky. These clouds are typically stratus or stratocumulus which develop on the western side of storms which cross the upper midwest. Clear weather in the winter is most likely to occur when a fresh dry Arctic air mass moves south from Canada into the midwest.
The prevailing wind directions during most of the winter are either from the northwest or from the south. The average wind speeds in winter are between 8 and 9 mph which is, perhaps surprisingly, slightly less than the average wind speed in spring and fall.