September 2019 was the fourth-warmest September on record since 1895, according to Illinois State Climatologist Trent Ford at the University of Illinois’ Illinois State Water Survey.
Precipitation in September varied widely across the state.
The preliminary average statewide September temperature was
71.3 degrees, which is 4.9 degrees above the long-term average. Monthly temperature departures ranged from 2 to 4 degrees warmer than normal in northeast Illinois to more than
6 degrees warmer than normal in southwest Illinois.
September average temperatures across the state ranged from
65 degrees in Jo Daviess County to
78 degrees in Lawrence County.
The lowest minimum temperature reported in Illinois was 45 degrees in Jo Daviess County on Sept. 5, and the highest maximum temperature was
97 degrees in both Alexander and Pope counties on Sept. 16.
More than 100 local daily climate records were broken in Illinois in September, most of which were high daily minimum temperature records.
These conditions were attributed to several very warm nights, including the night of Sept. 22, when the nighttime minimum temperature remained above 70 degrees as far north as Elizabeth in Jo Daviess County and Freeport in Stephenson County.
On the night of Sept. 10, the station in Rock Island reported a nighttime minimum temperature of 77 degrees, besting the previous daily record by 3 degrees.
Precipitation in Illinois varied tremendously from north to south across the state. The preliminary average statewide precipitation was 5.34 inches, which is 1.9 inches above the long-term September average. However, the data also show large differences in September precipitation totals across the state, with northern Illinois receiving much more than average precipitation, and southern Illinois receiving much less than average.
Areas of northern and north-central Illinois received in excess of 12 inches of rainfall in September, while areas of southeast Illinois received less than 0.25 inches over the same time period.
The latest U.S. Drought Monitor Sept. 24 map shows a pocket of moderate drought covering parts of Champaign, Ford, Iroquois, and Vermilion counties. Concurrently, below normal rainfall and above normal temperatures in the southern part of the state generated abnormally dry conditions in September.
Conditions in southern Illinois have shown some signs of a flash drought, which is a rapidly intensifying drought event, often provoked by an existing precipitation deficit combined with intense heat.
Reports from Illinois Farm Bureau CropWatchers regarding drought in east-central and southern Illinois are mixed. Some report the dryness and heat have helped late-planted crops reach maturity, while at the same time possibly sacrificing yield.
Short-term temperature forecasts call for a regression to cooler, more seasonal conditions in October. Longer-term Climate Forecast System forecasts from the National Centers for Environmental Protection show probabilities of a 32-degree freeze in Illinois remain below 30% into the third week of October.
Looking into October, the Climate Prediction Center’s 8-to-14-day outlook shows elevated probabilities of above-normal temperatures and elevated probabilities of above-normal precipitation across Illinois.
The CPC monthly outlook for October still shows elevated probabilities for below normal temperatures across the northern half of the state, with equal chances (above normal, normal, below normal precipitation) for all but the very northwest corner of Illinois.