Cool, Wet Summer in Illinois, Illinois State Water Survey

ISWS Press Release

For Immediate Release September 2, 2009
Cool, Wet Summer in Illinois
Jim Angel - (217) 333-0729,
Lisa Sheppard - (217) 244-7270,

CHAMPAIGN, Ill. – Based on preliminary data for Illinois, this was the 11th coolest and 8th wettest summer since statewide records began in 1895. The average temperature for June–August was 71.4 degrees, 2.4 degrees below normal. The total precipitation for June–August was 15.2 inches, 3.6 inches above normal, according to State Climatologist Jim Angel of the Illinois State Water Survey (

The coolest summer on record was 1915 with an average of 69.3 degrees. In recent years, 1992 was ranked third with 70.2 degrees, and 2004 was ranked fourth with 70.4 degrees. The wettest summer on record was 1993 with 18.3 inches of rain.

The statewide average August temperature was 71.0 degrees, 2.6 degrees below normal and the 15th coolest August on record. The statewide August total precipitation was 5.0 inches, 1.4 inches above normal and the 17th wettest August on record.

The mild summer has lowered energy demand for cooling homes and businesses this summer; cooling degree days were down 26 percent from normal during June–August. On the downside, a wet spring delayed corn and soybean planting while a cool summer slowed their development.

"We were in a similar situation last year," says Angel. "The slow-developing crops benefited from unseasonably warm temperatures in late September and early October as well as a later-than-normal frost to finish the season in good shape. For now, National Weather Service forecasts suggest that September temperatures and precipitation should be near normal."

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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