The preliminary statewide average August temperature was 74.5 degrees, 0.9 degrees above 1991-2020 average, 1.1 degrees above the 20th century average, 0.8 degrees above the most recent 30-year average, and the 41st warmest August on record going back to 1895.
The preliminary statewide average total August precipitation was 5.69 inches, 2.13 inches above the 1991-2020 average, 2.19 inches above the 20th century average, 2.17 inches above the most recent 30-year average, and the fifth wettest August on record statewide.
Data are provisional and may change slightly over time.
Swing, Swing…
The final month of summer brought both summer and fall weather to Illinois, as is often the case. Daily average temperatures and temperature departures from normal in Champaign-Urbana show the roller coaster of August weather. The month began with temperatures that were a couple degrees cooler than normal, followed by a prolonged stretch of very warm and very humid weather. A cold front brought in much cooler weather in the third week of August, followed by a rapid warm up to transition into September (Figure 1).
Warm and cold periods combined, average temperatures ranged from the low 70s in northern Illinois to the high 70s in southern Illinois, within 1 degree of average in most of northern and central Illinois, and between 2 and 4 degrees above average in southern Illinois (Figure 2).
Most parts of the state pushed into the mid to upper 90s in the middle of the month, including during the State Fair — of course. Some of the more impressive high temperatures that week included 100 degrees in Alton and 98 in Cairo. Extreme humidity accompanied the heat, making for several hours of dew point temperatures well into the 80s. Springfield set new all-time dew point temperature records with multiple hours of 84-degree dew points on Aug. 16. A wonderful cooldown followed the intense heat. Many places saw nighttime temperatures dip into the low 50s and a few in the high 40s, including 49 degrees in Elgin.
The warmest point in the state last month was Olmstead at 79.0 degrees, and the coolest point was Stockton at 69.5 degrees. Overall, the preliminary statewide average August temperature was 74.5 degrees, 0.9 degrees above 1991-2020 average, 1.1 degrees above the 20th century average, 0.8 degrees above the most recent 30-year average, and the 41st warmest August on record going back to 1895.
Frequent Severe Weather and an Exceptionally Wet August
August rainfall can be intense but is more often isolated in nature, meaning most folks don’t have flooding issues. Last month was an exception in more ways than one, as most of central and north-central Illinois experienced an exceptionally wet final month of summer.
Total precipitation ranged from just under 2 inches in southeast Illinois to over 12 inches in central Illinois. Much of the Interstate 74 corridor from the Quad Cities to Danville had 4 to 8 inches above average precipitation in August, while parts of south-central Illinois were 1 to 3 inches drier than normal (Figure 3).
Multiple rounds of thunderstorms ran around a large ridge in the southern Great Plains and moved from northwest to southeast across central Illinois between August 13 and August 15, producing widespread 3-to-6-inch rainfall totals and isolated pockets of 8 to 12 inches. Excess rain caused flooding in central Illinois rivers, reaching moderate flood stage on the Vermilion River near Danville, the Sangamon River at Monticello, and the Mackinaw River near Congerville.
Last month was a top 10 wettest August on record in much of central and north-central Illinois and was the wettest August on record in Danville (Table 1).
| Location | August Total Rainfall (inches) | Ranking | Wettest Since |
| Danville | 13.98 inches | Wettest | |
| Champaign-Urbana | 9.45 inches | 4th wettest | 1993 |
| Bloomington-Normal | 9.41 inches | 4th wettest | 1977 |
| Galesburg | 9.89 inches | 4th wettest | 1980 |
In contrast, precipitation was a bit harder to come by in south-central Illinois, especially along and just south of the Interstate 70 corridor. However, wetter conditions in that area in previous months mostly kept drought at bay.
Overall, the preliminary statewide average total August precipitation was 5.69 inches, 2.13 inches above the 1991-2020 average, 2.19 inches above the 20th century average, 2.17 inches above the most recent 30-year average, and the fifth wettest August on record statewide.
Another Month of Frequent Severe Weather
Illinois had already set a new annual tornado record by July 1 this year, along with a new state hail record and more severe thunderstorm warnings than in any previous year on record. But that didn’t stop August from bringing an unusually active set of severe weather.
Among the most notable severe weather events last month were tornado outbreaks in the Chicagoland area on Aug. 9 and Aug.11, the latter of which was brought to us by a derecho. Extremely strong storms also brought straight-line winds and significant damage in Bloomington-Normal on Aug. 13, temporarily halting student move in at Illinois State University, and significant damage in Springfield on Aug. 16.
As of the last week of August, Illinois officially had 210 tornadoes in 2026, which is 68 more than in any previous entire year and more than twice as many tornadoes as Texas, Oklahoma, Kansas, Nebraska, South Dakota, North Dakota, and Minnesota combined (Figure 4).
A Wild Summer Ride Comes to an End
The preliminary statewide average summer temperature was 74.8 degrees, 1.0 degree above the 1991-2020 average, 1.3 degrees above the 20th century average, 0.9 degrees above the most recent 30-year average and tied for the 31st warmest summer on record going back to 1895.
Summer started with a mild June that was 1 to 2 degrees cooler than normal in northern and central Illinois. The heat turned on in July and pushed temperatures to 2 to 4 degrees above average in the hottest time of the year. August’s mildly warmer than normal conditions wrapped up the season, ending as a somewhat, but not extremely, warm summer (Figure 5).
The preliminary statewide-average total summer precipitation was 16.39 inches, 4.12 inches above the 1991-2020 average, 5.17 inches above the 20th century average, 3.99 inches above the most recent 30-year average, and the eighth wettest summer on record statewide. It was the wettest summer in Illinois since 2015.
As is often the case for summer, different parts of the state experience different summers. June was very wet in central and north-central Illinois, while being very dry in southern Illinois. July was extremely dry for most everyone except Chicago and far southern Illinois, and August was exceptionally wet in central Illinois while being slightly to somewhat drier than average for others (Figure 6).
This summer was a top five wettest on record for many places around the state, exemplifying how active our weather was this season (Table 2).
| Location | Summer Total Rainfall (inches) | Ranking | Wettest Since |
| Danville | 26.38 inches | Wettest | |
| Aurora | 24.29 inches | 2nd wettest | 1996 |
| Galesburg | 21.09 inches | 3rd wettest | 1993 |
| Charleston | 19.45 inches | 5th wettest | 2018 |
Outlooks
September brings in what is undoubtedly the best season in Illinois. Additionally, fall and winter often get a bit more influence from El Niño as that pattern continues to strengthen. The corresponding September outlooks look that way, with best chances of a warmer start to the fall season and slighter better chances of drier conditions in southern Illinois (Figure 7).
