CHAMPAIGN, Ill. — Although the southern half of Illinois was wetter than the northern half in August, the statewide average rainfall for the month was 2.01 inches, or 1.58 inches below the 30-year normal as drought continues, according to Illinois State Climatologist Trent Ford at the University of Illinois’ Illinois State Water Survey.
August precipitation totals ranged from less than a quarter of an inch in northwest Illinois to over 8 inches in southwest Illinois. In general, the northern half of the state experienced 1 to 4 inches below average and is considered abnormally dry in the Aug. 25 edition of the U.S. Drought Monitor. There are also pockets of moderate drought in western and northeast Illinois.
Meanwhile, most of southern Illinois experienced a 1 to 3 inches above average rainfall.
Climatological summer — June through August — precipitation patterns also showed contrasting conditions in northern and southern Illinois. The northern half of the state finished summer with between 1 and 4 inches below average precipitation, while southern Illinois was 1 to 6 inches wetter than average over the summer.
Temperatures
The statewide August temperature of 72.7 degrees is nearly 1 degree below normal. Average temperatures were in the mid- to high 70s across the state, very close to the long-term average in northern Illinois, and between 1 and 4 degrees below average in southern Illinois.
Following the warmer-than-average months of June and July, August began much cooler than average. The below-average temperatures persisted through the third week of the month. Temperatures were between 1 and 4 degrees below average through the first three weeks of August.
During the fourth week of August, most stations observed daily high temperatures in the 90s, including five consecutive 90-plus-degree days in Rockford. This was the longest such streak in Rockford in August since 2011. The station at Chicago’s O’Hare International Airport observed 10 days with a high temperature at or above 90 degrees last month.
Although the fourth week of August was unusually warm in northern Illinois, temperatures were closer to average in southern Illinois.