Illinois State Water Survey - University of Illinois at Urbana-Champaign

State Climatologist Office for Illinois

Statewide Records and Normals for Illinois

Dr. 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 1981-2010 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 for individual stations, please refer to the Illinois climate normals page.

Table 1. Monthly and Seasonal Normals
Month/Season Temperature (F) Precipitation (in)
January 26.3 2.12
February 30.8 2.11
March 41.1 2.98
April 52.4 3.80
May 62.5 4.62
June 71.8 4.20
July 75.3 4.05
August 73.5 3.60
September 65.9 3.24
October 54.1 3.26
November 42.5 3.47
December 29.9 2.74
Winter 29.0 6.97
Spring 52.0 11.40
Summer 73.5 11.85
Fall 54.2 9.97
Annual 52.2 40.20

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.

Illinois State Water Survey

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