textproduct: Central Illinois

KEY MESSAGES

- Seasonably warm and humid weather continues through at least Saturday with maximum afternoon heat indices around 100 degrees, give or take a few degrees.

- Shower and thunderstorm chances return late week with the best chances expected on Friday.

DISCUSSION

Issued at 133 PM CDT Wed Jul 15 2026

High pressure centered over the central US remains anchored in place atop of an upper low in the southern US (rex block), keeping temperatures seasonably warm. Dewpoints in the low to middle 70s have led to peak afternoon heat indices in the middle 90s to near 100 so far today, with similar conditions expected through at least Saturday. However, the return of scattered convection beginning tomorrow could alleviate the heat for some.

The upper ridge will begin to break down Thursday into Friday as several shortwave troughs work through the eastern Canadian provinces, just north of the Great Lakes Region. Bits of energy from the previously mentioned upper low will ooze northward in a weakened state as soon as tomorrow, bringing enough forcing to support scattered storms through Saturday (Friday having the best chances). Moderately strong instability could support a few stronger storms capable of gusty winds. However, weak vertical wind shear should limit storm longevity and organization. High PWATS and slow storm motions will favor torrential downpours, with the 15.12Z HREF LPMM showing localized pockets of over 2" possible.

Shower and storm chances exist Sunday into the early parts of next week as a few shortwave troughs dive through the Great Lakes Region, sending a couple of cold fronts through the area. The first cold front will arrive on Sunday, stalling out just south of the area before lifting back northward on Monday ahead of the next approaching wave. Although a subtle reprieve from the heat will come for some Sunday into Monday, a more noticeable cool down won't arrive until Tuesday or Wednesday after a stronger upper wave sends a more progressive cold front through the area.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1245 AM CDT Thu Jul 16 2026

Patchy shallow ground fog expected to develop again during overnight and lift between 12-13Z. SPI tends to be more prone to this occurrence past few nights, so will only include a mention there at this point with IFR to MVFR conditions from 10-13Z. Scattered diurnally driven cumulus clouds with 3-5k ft bases to appear by 15Z and dissipate around dusk/02Z. Isolated to scattered thunderstorms expected to develop during mid to late afternoon from SPI and DEC south and dissipate around sunset. Continued PROB30 for MVFR condtions with TSRA at SPI/DEC from 22Z-01Z. Isolated to scattered convection to appear over northeast IL late Thu afternoon until sunset, but this convection should stay ne of the I-74 airports (PIA, BMI, CMI). Another concern is Canadian wildfire smoke which currently near ground smoke and vsbys restrictions should be confined to northeast IL, ne of I-74 though a thin smoke layer aloft at 25k ft could impact the central IL airports especially along I-74.

ILX WATCHES/WARNINGS/ADVISORIES

None.