textproduct: Central Illinois

KEY MESSAGES

- There is flash flooding ongoing across portions of central Illinois this morning, where thunderstorms track over areas that have already seen 4-6 inches of rain since Thursday. Areas north of a Havana to Bloomington line are most at risk.

- Storms have the potential to produce damaging winds today and tomorrow. SPC has a marginal (level 1 of 5) risk of severe weather for the weekend.

- The heat and humidity remain a concern for the weekend, with the hottest conditions in the southern half of the state.

DISCUSSION

Issued at 220 AM CDT Sat Aug 15 2026

Tonight, storms are moving across central IL. There is a low risk (but non-zero) for damaging winds within these storms, but the main concern is the flash flooding risk. WPC has areas near and north of I-72 in a moderate risk (level 3 of 4) for excessive rainfall for the overnight hours. The 00z sounding shows the environment having PWATs of 2.2-2.4 inches. Over the last few days, this area has gotten 3-6 inches of rain, with some locally higher amounts. The storms passing through tonight are expected to drop another 2-5 inches with the LPMM suggesting some localized pockets of up to 10 inches. Flash flood guidance seems a bit generous (too high). If the pockets of higher rain set up over where the ground is already extremely saturated, flash flooding is likely.

For the remainder of the day after this morning round of convection exits about 15-16z, there is a marginal risk for severe weather for additional activity that will move through. It will be very similar to what has happened over the last few days. The next round of MCS activity will move into central IL by late evening and will continue into the overnight hours. The main concern will be damaging winds and the heavy rain potential.

There is another marginal risk for severe weather again tomorrow for areas south of a Schuyler to McLean County line with a similar environment in place as previous days. The forecast will continue to evolve as we get newer runs of the models.

Temperatures remain hot and humid. The heat advisory for south of I- 70 is valid through Sunday. Heat indices of 100-110 degrees are forecast through Sunday, but how far north these heat indices get will depend solely on the convection location. Like yesterday for example, the convection lingered further south longer than forecast, so heat indices struggled to hit triple digits.

Next week may bring us a brief break in the active weather and the heat briefly. A high pressure area will set up over the Upper Mississippi Valley / Great Lakes region by Monday, behind a cold front that will move through central IL during the day. Temperatures starting Monday into much of the next week will be mainly in the upper 70s to 80s for highs and 60s to low 70s for lows.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 618 AM CDT Sat Aug 15 2026

Thunderstorms are moving across central Illinois and are expected to continue into mid morning before exiting east of the area. MVFR/VFR ceilings currently in place. Ceilings may bounce around if a stronger shower/storm moves through. Everyone should be VFR by early afternoon. Winds will become more southwesterly as the day goes on. Another round of convection is expected overnight, but timing and location are uncertain as of the 12z TAF period.

ILX WATCHES/WARNINGS/ADVISORIES

Flood Watch until 10 AM CDT this morning for ILZ027>031- 036>038-040-041-043>046-055-057. Heat Advisory until 8 PM CDT Sunday for ILZ066>068-071>073.