The Illinois statewide average temperature for January 1-15, 2010, was 21.5 degrees, 2.3 degrees below normal. The statewide average precipitation for the same period was 0.75 inches, 84 percent of normal. Precipitation includes both rainfall and the water content of any snowfall.
After a very active December in terms of snowfall, January has been relatively quiet so far. The only significant snowfall totals are in western Illinois and along Lake Michigan. However, the persistently cold weather means the snow has stuck around.
December 2010 in Illinois – Cold and Snowy
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.
Record December Snowfall: Champaign-Urbana
Champaign-Urbana set a record for their heaviest December snowfall total on record. The 20.4 inches of snow that has fallen so far in December surpassed the old record of 19.1 inches set in 1983.
The 5.0 inches of snow on Christmas Day clinched the December snowfall record. By the way, it was also the biggest snowfall on record for that date. It surpassed the old record of 3.8 inches that fell on December 25, 1944.
We have had measurable snow on the ground since December 4.
It has been persistently cold as well. The average temperature for December through the 27 is 21.3 degrees, the ninth coldest December on record. The forecast is for milder temperatures for the rest of the month so this December may slip a little in the rankings. Oddly, we only dropped below zero once, on December 9 with -1°F.
A complete listing of Champaign-Urbana observations are found here.
What happened to the rest of the 1983-84 winter? The snowfall total for January was only 5.6 inches. However, the heavy snow returned in February with 11.6 inches and 8.4 inches in March. Combined with the 0.2 inches that fell in November 1983, that winter season ended up with 44.9 inches.
Update on Cold Weather in Illinois
As of December 21, Illinois remains 10.2 degrees below normal for the month. At 20.9 degrees, this is now the 5th coldest December since statewide records began in 1895. It could still move up or down in the ranking, depending on how the rest of December behaves.
Statewide precipitation stands at 1.06 inches of precipitation (rainfall plus the water equivalent of any snow).
Snowfall totals for the month ranges from less than 2 inches in far southern Illinois to over 14 inches in northwest Illinois (see map below). Right now the two spots with the most snowfall in the state for December are a CoCoRaHS site near Marseilles with 18.5 inches and a CoCoRaHS site near Champaign with 18.3 inches of snow.
From my web page on current conditions in Illinois, here is the breakdown by region within the state as well as the statewide numbers at the bottom for December 1-21.
Illinois
12/01/2010 to 12/21/2010
Climate <------Temperature-----> <---------Precipitation--------->
Division Actual Normal Dev Actual Normal Dev Percent
-----------------------------------------------------------------------------
Northwest 15.2 26.3 -11.0 1.44 1.45 -0.01 99
Northeast 17.0 27.9 -10.9 1.30 1.63 -0.33 80
West 21.4 29.7 -8.3 0.56 1.63 -1.07 34
Central 18.9 29.7 -10.8 1.13 1.76 -0.63 64
East 17.6 30.1 -12.4 1.53 1.75 -0.23 87
West-southwest 23.8 32.5 -8.6 0.56 1.91 -1.35 29
East-southeast 23.3 33.6 -10.2 1.23 2.04 -0.80 61
Southwest 26.2 35.7 -9.5 0.79 2.31 -1.52 34
Southeast 26.4 36.4 -10.0 0.93 2.43 -1.50 38
State 20.9 31.1 -10.2 1.06 1.86 -0.79 57
Dev means Deviation From Normal, Percent means Percent of Normal
