Coldest July on Record for Illinois, Illinois State Water Survey

ISWS Press Release

For Immediate Release August 3, 2009
Coldest July on Record for Illinois
Jim Angel - (217) 333-0729,
Lisa Sheppard - (217) 244-7270,

CHAMPAIGN, Ill. – Based on preliminary data for Illinois, the statewide average temperature for July was 70.4 degrees, 5.3 degrees below normal. This ranks as the coldest July in the statewide records and a degree colder than the previous record set in 1924 (71.5 degrees), according to State Climatologist Jim Angel of the Illinois State Water Survey (

Furthermore, while southern Illinois has reported a few days with temperatures in the 90s so far in July, much of the rest of the state has seen none. The normal range of days in the 90s is typically between 5 in northern Illinois to 15 in southern Illinois.

One clear impact has been a lowered energy demand for cooling homes and businesses during July; cooling degree days (CDD) were down 48 percent from normal during this time. Meanwhile, modified growing degree days (a measure of corn development) were down 17 percent from normal, suggesting less favorable growing conditions.

Statewide precipitation for July was 4.9 inches, 1.1 inches above normal. Precipitation since January 1 stands at 29.0 inches, 5.6 inches above normal.

Historically, a cool July is most often followed by a cool August. The specific odds on August temperatures after a cool July are 45 percent cooler than normal, 34 percent near normal, and 21 percent above normal. The National Oceanic and Atmospheric Administration Climate Prediction Center indicates that cooler than normal temperatures are likely to prevail for August across Illinois, and for the northern two-thirds of Illinois for the August-October period.

The Illinois State Water Survey at the University of Illinois at Urbana-Champaign under the Institute of Natural Resource Sustainability is the primary agency in Illinois concerned with water and atmospheric resources.

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