CHAMPAIGN, Ill. — Mild temperatures in August this year in Illinois followed a heat wave in May, above-average temperatures in June and a cooler July, according to Illinois State Climatologist Trent Ford at the University of Illinois’ Illinois State Water Survey.
Rainfall in August varied across the state with near-normal precipitation for the month.
The only prolonged warm period in August was in the first week, when temperatures were 5 to 10 degrees above normal. High temperatures regularly reached into the 90s across the state, including 95 degrees at the Chicago Midway Airport.
A cold front that moved through the state around Aug. 9 brought much cooler, drier air into the region. Nighttime low temperatures in the second and third weeks of the month dipped into the 50s across Illinois.
August average temperatures ranged from the low 70s in northern Illinois to the high 70s in southern Illinois, within 1 degree of normal statewide. Overall, the preliminary statewide average August temperature was 73.8 degrees, 0.2 degrees above the 1991-2020 average.
The statewide climatological summer average temperature was 74.4 degrees, only 0.6 degrees above normal.
Total precipitation in August ranged from nearly 15 inches in parts of northwest and southeast Illinois to less than 1 inch in western Illinois.
The wettest point in the state in August was Freeport, with 14.55 inches of rain. In contrast, the driest point in the state last month was the Quincy Dam in Adams County, with only 0.41 inches of total rain.
Rainfall in late August relieved much of the drought in east-central Illinois, where June and July rainfall deficits had exceeded 7 inches.
The exception was the Interstate 74 corridor from Champaign to McLean counties. Moderate drought in western Illinois spans from Henderson to Adams counties.
The preliminary statewide average total August precipitation was 4.10 inches, 0.45 inches above the 1991-2020 average, and the statewide total average precipitation for the summer was 12.23 inches, 0.68 inches above normal.
The most recent September outlooks from the Climate Prediction Center lean toward warmer than normal conditions in Illinois. September precipitation outlooks are less confident, with equal chances of above and below normal precipitation.
Outlooks for the entire climatological fall, September to November, continue to lean toward warmer than normal conditions across most of the United States.
La Niña conditions are favored to return this season, and Climate Prediction Center outlooks for fall lean toward the drier than normal tendency during La Niña fall seasons.