textproduct: Central Illinois

KEY MESSAGES

- Summer heat and humidity return today and Wednesday. There is a 50-80% chance of heat indices greater than 95 degrees south of I-70 tomorrow afternoon.

- Rain and thunderstorms move in tomorrow into Thursday morning, bringing a damaging wind risk and heavy rainfall. QPF shows 1-3 inches of rainfall south of I-72, with the greatest amounts near and south of I-70.

DISCUSSION

Issued at 156 AM CDT Tue Sep 8 2026

Temperatures will warm back up into the 90s today and Wednesday as the upper ridging builds back eastward with 850 mb temperatures of 20-24C. Tomorrow, moisture transport will increase ahead of the cold front bringing soupy dewpoints in the 70s into the central part of the state. There is a 50-80% chance of heat indices greater than 95 degrees south of I-70 Wednesday afternoon, from the HREF. There could be some limitations with how hot it could get on Wednesday with the cloud cover from convective debris across the state and how fast the front may move through. For areas north of the IL River Valley, today could be the hottest day out of the two.

The cold front will move through tomorrow into tomorrow night as the ridge gets broken down by the upper low moving over Canada. It will clear out the sweltering mid to upper 90 temperatures, leaving highs in the low to mid 80s before building back to upper 80s to near 90 for the weekend. The LREF suggests that there is a 50-70% chance of high temperatures cooler than 80 degrees by next Tuesday. Could Autumn be near?

This front will also bring the next chance for substantial rain and strong-to-severe thunderstorms tomorrow into Thursday. The CAMs are showing a line of showers & convection along the front entering the northwest around 10z Wednesday. The initial area of convection may widely dry out during the day, leaving some scattered activity as the front pushed southeast through the state. This scattered activity could have strong to damaging winds and/or hail with them. Looks like by 00z Thursday, redevelopment will occur in the southeast in the evening as the LLJ kicks in, potentially training near and south of I-70. This redevelopment could continue into Thursday morning and may prove to be a flash flooding risk, rather than severe. However, this area can likely take quite a bit of rain before flooding becomes a major concern. The 6 hour FFG for the southeast is 3-5 inches. QPF shows 1-3 inches of rainfall south of I- 72, with the greatest amounts near and south of I-70, from 06z Wednesday to 00z Friday. PWATs in that area are forecast to be 2.0- 2.5 inches.

WPC has maintained a D2 marginal risk ERO south of I-72, with a slight risk area just off to the east, including southwestern IL. SPC has expanded the D2 marginal risk for severe weather north to a southern Knox County to Livingston County line and south. Damaging winds and hail are the most likely hazards with the area of storms.

Additional low-end chances exist for showers and thunderstorms through the weekend. Due to low predictability and model spread, broad-brushed 20-40% PoPs remain in place from Friday night through early next week.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 556 AM CDT Tue Sep 8 2026

VFR conditions are expected through the 12z TAF period today. Light and variable winds pick up out of the south this morning. Nearing the end of the period, PIA could start to see some rain move into the area, hence the PROB30 group from 10-12z tomorrow.

ILX WATCHES/WARNINGS/ADVISORIES

None.