December 2010 in Illinois turned out to be one of the coldest and snowiest on record. I updated the numbers on January 3 and the maps on January 5.
Temperature
The average statewide temperature was 24.0 degrees, 5.8 degrees below normal and the 12th coldest on record, based on preliminary data.
Snowfall
Snowfall was above-normal throughout the state in December and heaviest in a band from northwest Illinois into east-central Illinois (see maps below). Snowfall totals for December include 20.4 inches in Champaign-Urbana (snowiest December on record), 18.1 inches in Bloomington-Normal(second snowiest December on record), and 19.2 inches in Peoria (third snowiest December on record). Champaign-Urbana beat both Rockford (19.2 inches) and Chicago O’Hare Airport (16.2 inches) on snowfall totals. The largest snowfall total reported in the state was 30.0 inches near Galena by a CoCoRaHS observer. Streator reported 28.5 inches, the highest amount from a NWS cooperative observer.
Precipitation
Even though snowfall was above average in most locations, the average statewide precipitation was 1.8 inches, 0.9 inch below normal. Some of the snowfall did not have a high water content, especially if it fell when the temperatures were in the 20s. While the rule of thumb is that 10 inches of snow equals 1 inch of water, a 10 to 1 ratio, I have seen ratios ranging from 4 to 1 to 22 to 1 in Illinois.
