textproduct: Central Illinois

KEY MESSAGES

- Heat Returns Midweek: Hot and muggy conditions return Tuesday and Wednesday. Temperatures will top out in the 90s both days, with an influx of moisture pushing heat indices to around 100 degrees south of I-72 Wednesday afternoon.

- Midweek Storm Potential: A passing front brings a 40-60% chance for scattered showers and thunderstorms on Wednesday, primarily across the Illinois River Valley.

- Higher Storm Chances Late Week: Confidence is higher (60% to 80% chance) for widespread thunderstorms Wednesday night into Thursday morning, especially along and south of I-72.

LONG TERM

(Tuesday through Friday) The respite from the heat will be short-lived as summer-like conditions return mid-week. An upper-level low currently over the Pacific Northwest is projected to track eastward into the Canadian Prairies Monday night into Tuesday, flattening the central U.S. ridge and spreading its eastern periphery back across the Midwest. A corresponding 850mb thermal ridge (with temperatures climbing to 22-24C, reminiscent of the recent heat wave) will shift east over central Illinois on Tuesday, lingering over southern Illinois into Wednesday. Consequently, afternoon highs will surge back into the 90s across most of central Illinois on Tuesday. Fortunately, deep boundary layer mixing on Tuesday afternoon should keep dewpoints relatively dry -- generally in the upper 50s to mid-60s -- which will keep heat indices in check. Moisture returns in earnest on Wednesday as southwesterly flow strengthens ahead of an approaching cold front. This flow will transport a muggier airmass, boosting dewpoints into the upper 60s to mid-70s. Combined with temperatures in the 90s, heat indices are expected to exceed 100 degrees in several locations Wednesday afternoon, particularly south of the I-72 corridor.

The trailing cold front is modeled to sag south-southeastward into central Illinois on Wednesday in response to the parent surface low lifting across Manitoba and toward Hudson Bay. Although National Blended of Models (NBM) PoPs have trended upward (now around 60% in the Illinois River Valley with frontal passage), model guidance remains split on how far southeast the initial precipitation band will penetrate. The primary limiting factors for widespread rainfall Wednesday afternoon include weak low-level convergence near the frontal zone (as central Illinois sits near a col/neutral point) and a lack of strong upper-level support, with the primary 500mb trough axis tracking well to our north across the Great Lakes. Higher confidence precipitation chances (60-80% PoPs, especially along and south of I-72) are expected Wednesday night into Thursday morning. This convective signal is driven by a strengthening low-level jet which will overrun the stalling frontal boundary and trigger renewed, widespread thunderstorm development. Behind this front, temperatures will trend cooler and more comfortable, retreating back into the 80s for the remainder of the work week.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 555 PM CDT Sun Sep 6 2026

An expanding upper ridge will suppress any active weather across the central Illinois terminals through Monday. Skies will remain mostly clear with lights winds through the TAF period.

ILX WATCHES/WARNINGS/ADVISORIES

None.