textproduct: Central Illinois

KEY MESSAGES

- Typical summertime heat and humidity will return to central Illinois early next week. Heat index readings will peak at or above 100 degrees across all or parts of the area Sunday through Tuesday.

- Clusters of thunderstorms will track across the Midwest over the next several days. At this time, it appears the most likely time frame for storms in central Illinois will be late Saturday night into Sunday morning...then again Tuesday night into Wednesday.

DISCUSSION

Issued at 231 PM CDT Fri Aug 7 2026

A cold front currently extending from Minnesota to Nebraska will sag southeastward this evening, triggering scattered thunderstorms across Wisconsin and Iowa. A few of these cells could potentially spill into the N/NW KILX CWA in a weakening phase from late evening through the overnight hours. Have included low chance PoPs (20-30%) along/north of a Rushville to Bloomington line accordingly. The front will continue southeastward on Saturday, but will eventually become parallel with the upper flow and stall along the I-64 corridor. A weak bubble of high pressure behind the front will ensure a dry day for most of central Illinois, with just a slim chance (20%) for a stray shower/storm near the boundary along/south of I-70 during the afternoon.

As a nocturnal low-level jet streak strengthens across the Plains, a cluster of thunderstorms is expected to form along the trailing end of the boundary Saturday night, then track E/SE toward central Illinois overnight into Sunday morning. There is still wide variation among the 12z models with the FV-3/RRFS both focusing convection further north across Wisconsin...and the HRRR/ECMWF/ICON favoring a more southerly position over eastern Iowa/northern Missouri by 12z Sun. While the details are not yet fully settled, confidence is growing that a cluster of storms will impact at least parts of central Illinois. Have therefore focused highest PoPs (40-50%) along/north of the I-72 corridor late Saturday night into Sunday morning. Once any morning storms depart, the afternoon will be largely dry and decidedly more humid as dewpoints climb into the middle to upper 70s. With temperatures well into the 80s to near 90 degrees, heat index values will peak in the upper 90s to around 100 degrees by Sunday afternoon.

Even hotter conditions are expected on Monday/Tuesday as upper ridging shunts the bulk of the convection just north of the KILX CWA from northern Iowa across Wisconsin/northern Illinois. Will need to keep a close eye on the situation as mesoscale details become fine-tuned, but for now it appears both days will be mostly dry with highs in the 90s and heat index readings flirting with Heat Advisory criteria (105 degrees).

All model guidance agrees that a stronger short-wave trough will push a cold front southward into central Illinois Tuesday night through perhaps the end of next week. Nocturnal convection will likely blossom along the boundary Tuesday night into Wednesday morning, providing all of central and southeast Illinois with high PoPs (60-80%).

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Issued at 558 PM CDT Fri Aug 7 2026

VFR conditions expected through the forecast with cirrus tonight and diurnal cu on Saturday. A thunderstorm complex over eastern IA is expected to dissipate before reaching the central IL terminals this evening, leaving just high clouds in place. A weak front will cross the area Saturday morning, veering winds from southwest to west-northwest, all under 10 kt.

ILX WATCHES/WARNINGS/ADVISORIES

None.