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.

                        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
December snowfall in Illinois
Snowfall for Illinois for December 1-21, 2010.

Cold Start to December

After such nice weather in October and most of November, real winter weather arrived in Illinois for December. The statewide average temperature for the first 14 days of December was 22.0 degrees, 10.6 degrees below normal.
The statewide average precipitation is 0.83 inches, 0.5 inches below normal.
Snowfall has been widespread across the state in early December. Snowfall totals range from less than an inch in far southern Illinois to over 10 inches in northwestern Illinois. See map below for snowfall totals for December 1-14, 2010.

December 1-14, 2010 snowfall.
Snowfall for December 1-14, 2010, for Illinois.

Cool, Wet Start to May

The first half of May was both cool and wet. Preliminary data indicates that statewide temperatures were 1.4 °F below normal for the period May 1-17. Meanwhile, precipitation has been abundant. The statewide average precipitation was 4.15 inches, 1.79 inches above normal or 176 percent of normal. The heaviest rains have fallen in western and northern Illinois. The largest month-to-date total reported was 8.24 inches in Dallas City (along the Mississippi River between Quincy and Moline) by a CoCoRaHS observer.

Table 1. Precipitation totals by climate division in Illinois, along with the 1971-2000 normals, and percent of normal, for May 1-17, 2009.
Climate Region Precipitation (in) Normal (in) Departure (percent)
Northwest 4.64 2.25 206
Northeast 4.55 2.06 221
West 5.84 2.46 238
Central 4.17 2.32 179
East 3.17 2.21 143
South Southwest 4.26 2.43 175
South Southeast 3.67 2.46 149
Southwest 3.37 2.49 135
Southeast 3.51 2.66 132
State 4.15 2.36 176

Illinois was surrounded on three sides by very wet conditions in parts of Missouri, Iowa, Wisconsin, as well as Kentucky. The rains in Illinois have produced saturated soils in places and minor to moderate flooding along the Mississippi and Illinois Rivers and their tributaries.

May 1-16 precipitation
Precipitation totals for the Midwest for the period May 1-16, 2010 (click to enlarge).

May 1-16 percent of normal precipitation
Percent of normal precipitation across the Midwest for May 1-16, 2010 (click to enlarge).

Cold February Wraps Up a Cold Winter

CHAMPAIGN, Ill. – Based on preliminary data in Illinois, the statewide average temperature for February 2010 was 25.1 degrees, 5.1 degrees below normal. Snowfall for February was above normal. Amounts ranged from 6 inches in southern Illinois to over 18 inches in the Quad Cities and Chicago areas.
The cold February, along with colder-than-normal temperatures in December and January, made this the 19th coldest winter on record. The 3-month average temperature was 25.3 degrees, 2.9 degrees below average. Winters in the late 1970s were still much colder with a virtual tie between the winter of 1977-1978 at 19.6 degrees and the winter of 1978-1979 at 19.9 degrees.
Winter snowfall totals (December—February) ranged from about 45 inches in northeast Illinois to just under 15 inches in southern Illinois. This was 1 to 3 inches above normal for southern Illinois to over 10 inches above normal in northern and western Illinois. Wintertime precipitation, both rainfall and the water content of snow, measured 7.04 inches and was 0.35 inches above normal.
The latest National Weather Service outlook for March calls for an increased chance of below-normal temperatures in the southern two-thirds of Illinois. It also calls for an increased chance of drier-than-normal conditions for the month. See the Climate Prediction Center page.