textproduct: Central Illinois

KEY MESSAGES

- A Slight Risk of severe thunderstorms exists this afternoon/evening north of a line from Beardstown to Lincoln to Gibson City. Hail (15%), wind (15%), and tornado (2%) threats will exist in this area, with lower probabilities further south.

DISCUSSION

Issued at 215 AM CDT Fri Aug 21 2026

Weak high pressure over IL this morning will give way to a weak cold front tonight along with an upper level wave. With CAPEs of 2000-3000 J/kg and shear around 30-35 kts, severe storms will be possible late this afternoon and this evening. Expect some discrete cells developing in northern IL/eastern IA early in the afternoon, drifting south-southeast through central IL during the late afternoon and evening hours. The SPC has central IL in a Slight Risk for today (level 2 out of 5) north of a line from Beardstown to Lincoln to Gibson City. Hail (15%), wind (15%), and tornado (2%) threats will exist in the Slight Risk area. Further south a Marginal Risk exists...north of a line from Effingham to Danville, with mainly low end hail/wind (5%) threats for this evening in this area.

Late tonight, storms will likely wind down by midnight or shortly thereafter, with winds shifting to the northwest after the cold front moves through the area. Expect sunny skies, light northwest winds, and temperatures rebounding into the low 80s during the afternoon. A few of the models have an isolated storm or two developing in central IL on Saturday afternoon. However, the probability is at 10% or less, so did not include it in the forecast. Leaving out thunder for Saturday matches SPC's guidance as well.

Northwesterly flow aloft will continue through the weekend and into next week. An upper level trough moving southeast across the Great Lakes region by mid week could bring a few showers or storms to the area. But generally expect a drier pattern along with temps near to slightly below normal for the remainder of the period.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 558 AM CDT Fri Aug 21 2026

Expect light winds today along with mostly clear skies. We should see some cumulus around 4 kft this afternoon and we still have a 30-50% chance for thunderstorms today. However, the timing has shifted back somewhat. The last few runs of the CAMs have pushed TS activity back to the evening or even the overnight hours for the central IL terminals. Will shift back the timing a bit.

ILX WATCHES/WARNINGS/ADVISORIES

None.