Illinois State Water Survey
Institute of Natural Resource Sustainability
University of Illinois at Urbana-Champaign

Illinois State Climatologist Office

Jim Angel, state climatologist

Statewide Records and Normals for Illinois

Jim Angel, state climatologist

Here are normal monthly and seasonal temperatures and precipitation as well as selected records for the state of Illinois. The normals are based on the 1971-2000 averaging period. A majority of the official climate data comes from a large network of volunteer observers known as the cooperative observer network with official training and equipment from the National Weather Service. For normals and extremes for individual stations, please refer to historical summaries of Illinois stations

Monthly and Seasonal Normals

Month/Season Temperature (F) Precipitation (in)
January 24.6 1.97
February 30.1 1.99
March 40.7 3.22
April 51.7 3.83
May 62.4 4.31
June 71.6 4.12
July 75.4 3.94
August 73.2 3.69
September 65.8 3.24
October 54.2 2.87
November 41.5 3.34
December 29.8 2.73
     
Winter 28.1 6.68
Spring 51.6 11.36
Summer 73.4 11.75
Fall 53.8 9.45
Annual 51.7 39.23

Selected Records

The following records were collected from the available digital archives of the official climate records. It is possible that some earlier paper records of observations may beat the records presented here. However, they are harder to obtain and process.

The highest temperature reported in Illinois was 117°F in East St. Louis on July 14, 1954.

The lowest temperature reported in Illinois was -36°F in Congerville on January 5, 1999.

The most rainfall from a single event was 16.94 inches in Aurora during a 24-hour period spanning July 17-18, 1996.

The most precipitation in a year was a virtual tie between New Burnside in 1950 (74.58 inches) and Carbondale in 1945 (74.50 inches).

The most snow from a single event appears to be Astoria on February 27-28, 1900 with 37.8 inches.

The most snow for a single winter was 105.1 inches at Antioch during the winter of 1978-1979.