2011 in Illinois – Wetter and Warmer than Normal

The year 2011 will go down as being wetter and warmer than normal for Illinois. It was also a year of extreme monthly temperatures and precipitation. For example, we had the 8th wettest June on record followed by the 6th driest August on record.


The statewide average precipitation for 2011 in Illinois was 45.62 inches; 5.43 inches above the 1981-2010 average of 40.20 inches. It was the 10th wettest year in Illinois. It was also the wettest April, 8th wettest June, and 6th wettest November on record. On the other hand, it was the 6th driest August and 21st driest October on record.
Our statewide records go back to 1895. Here are the monthly precipitation and departures in Illinois.

Table 1. Monthly and Annual Statewide Precipitation (inches)
Month/Season Precipitation (in) Precipitation Departure (in)
January 1.19 -0.93
February 3.17 1.06
March 2.67 -0.31
April 7.40 3.60
May 5.18 0.56
June 6.46 2.26
July 3.77 -0.28
August 1.92 -1.68
September 3.47 0.23
October 1.81 -1.45
November 5.13 1.66
December 3.45 0.71
Annual 45.62 5.43

Click to enlarge.


The statewide average temperature for 2011 in Illinois was 53.0 °F; 0.8 °F above the 1981-2010 average of 52.2 °F.  It was the 23rd warmest year on record. It was also the 4th warmest July, 7th warmest November, and 11th warmest December on record. On the other hand, it was the 17th coldest January and 10th coldest September on record.
Here are the monthly temperatures and departures for 2011.

Table 2. Monthly and Annual Statewide Temperature (°F)
Month/Season Temperature (°F) Temperature Departure (°F)
January 22.6 -3.7
February 30.0 -0.8
March 41.4 0.3
April 52.9 0.5
May 61.9 -0.6
June 72.8 1.0
July 79.9 4.6
August 74.8 1.3
September 63.4 -2.5
October 54.9 0.8
November 45.7 3.2
December 35.8 5.9
Annual 53.0 0.8

Click to enlarge.

The numbers for December are preliminary and will be updated when the final numbers become available. However, I do not expect them to change the overall results shown here.

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