We have generated maps of the new 1981-2010 normals for Illinois, including the new November snowfall normals and the number of days with “measurable” snowfall (0.1 inches or more). See the maps below (click to enlarge).
While we may sometimes see snow in late October, November is normally the start to the snowfall season for much of Illinois. However, the average amounts are small by the standard of later winter months, ranging from 1-2 inches in northern Illinois to less than an inch in central Illinois to zero in southeastern Illinois.
The number of days with measurable snowfall, or snowfall frequency, is uncannily like the snowfall totals. The snowfall frequency ranges from 1-2 days for November in northern Illinois, to less than a day in central Illinois, to zero in southeastern Illinois. When the frequency drops below one day it means snowfall does not occur every year. For example, an average frequency of 0.5 days means it happens only once every 2 years on average.