Illinois State Water Survey - University of Illinois at Urbana-Champaign
INRS State Scientific Surveys
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.
| 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.