Rainfall above normal over much of Illinois during warm September 

[OCT. 4, 2005]  CHAMPAIGN -- "September temperatures averaged 70.6 degrees F statewide -- 4.4 degrees above normal -- making this the seventh-warmest September since 1895 and the third-warmest September on record in northeastern Illinois," says Jim Angel, state climatologist with the Illinois State Water Survey, a division of the Illinois Department of Natural Resources. "This also is the fourth consecutive month of temperatures above normal and the seventh-warmest June-September on record. Temperatures ranged from 97 degrees at Belleville on Sept. 22 to 32 degrees at Mount Carroll on Sept. 29."

The September rainfall average of 3.91 inches was 0.73 inches above normal, but the rainfall total since March averaged 18.90 inches, which is 7.12 inches below normal and Illinois’ sixth driest March-September since 1895. While most of the state enjoyed the extra rainfall in September, rainfall north of Interstate 80 was only 2.79 inches, or 0.54 inches below normal. Nashville had the highest one-day precipitation total: 3.58 inches on Sept. 20. Lebanon had the highest monthly total: 10.11 inches.

Across the state, rainfall has remained below normal since March 1. For example, Chicago O’Hare Airport received only 12.8 inches, 11.9 inches below normal; Rockford, 16.1 inches, 10.5 inches below; Moline, 10.9 inches, 16.3 inches below normal; Peoria, 13.2 inches, 11.5 inches below normal; Quincy, 15.4 inches, 10.6 inches below normal; Springfield, 16.0 inches, 8.1 inches below normal; Champaign, 21.3 inches, 6.8 inches below normal; and Carbondale, 21.7 inches, 5.7 inches below normal.

"While good rains in August and September have alleviated drought conditions in portions of central and southern Illinois, the most severely affected area in northern Illinois remains stubbornly dry," Angel said. "Check the ISWS special drought website (http://www.sws.uiuc.edu/hilites/drought/)for regular updates."

Now that October has arrived, the first fall frost becomes a concern for gardeners. Based on 1971-2000 averages, it usually occurs between Oct. 7, in northern Illinois, and Oct. 21, in southern Illinois, with an average date of Oct. 14 in central Illinois.

For more information, see the map at http://www.sws.uiuc.edu/atmos/statecli/
Frost/avg_first_fall_frost_map.gif. An interesting feature of the map is the delay in the first frost date by about a week in the Chicago area, probably due to a combination of the warmer urban setting and the moderating influence of Lake Michigan.

Angel points out that the actual frost date varies quite a bit each year. "For planning purposes, one can expect the first frost within two weeks of those dates," he says.

[Illinois State Water Survey news release]