textproduct: Central Illinois

KEY MESSAGES

- Comfortable, low-impact weather persists through Tuesday.

- Thunderstorm chances (20-40%) return Wednesday evening, with damaging winds and hail as the main threats. Flash flooding is not a risk.

- Pleasant and dry weather is anticipated from Thursday into Saturday, followed by an approaching heat dome early next week that could drive heat index values up to 100 degrees.

DISCUSSION

Issued at 1219 PM CDT Mon Aug 24 2026

Quiet and low-impact weather will persist through Tuesday under the influence of a mid-level ridge and building surface high pressure over the Great Lakes region. Temperatures will remain typical for late August, featuring afternoon highs in the low 80s. Low relative humidity levels will allow overnight lows to drop into the 50s, creating pleasant evening conditions.

A pattern shift is expected by Wednesday as a well-defined shortwave trough and associated surface cold front track out of the Canadian Prairies and across the Great Lakes. Southerly surface winds ahead of the advancing frontal boundary will drive Wednesday afternoon temperatures into the mid-80s. Moderate instability is anticipated in the boundary layer, supported by a narrow plume of low-70s dewpoints pooling ahead of the front that will help yield MLCAPE values around 2500 J/kg. Overlapping with approximately 30 knots of bulk shear, this buoyancy will favor organized supercellular structures along and ahead of the front. Forecast mesoscale soundings for Wednesday afternoon feature straight or subtle veer-back-veer hodographs, indicating primary threats of hail and damaging winds over a tornado risk. High-resolution CAM guidance shows mixed signals regarding convective coverage. This uncertainty stems from the strength of synoptic forcing over central Illinois, as the primary shortwave displacement well to the north may keep overall forcing and storm coverage limited.

Limited moisture return ahead of Wednesday's front is keeping QPF down. With forecast PWATs around 1.5 inches, and progressive atmospheric flow, the flash flood risk from convective precip is quite low.

Following the passage of the front, dry and less humid conditions will take hold Thursday through Saturday as an elongated central U.S. upper ridge promotes the gradual build of a continental polar (cP) airmass across the Midwest and Great Lakes. Daytime highs will hover around 80F, with overnight lows dipping into the 50s for the remainder of the workweek.

By early next week, medium-range global ensembles indicate a notable warming trend as a strong upper trough makes landfall in the Pacific Northwest, driving the ridge axis eastward into the Midwest. The combined presence of a 588-594 mb ridge core and weak low-level return flow on its western flank will heighten the potential for triple-digit heat indices early next week.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 639 PM CDT Mon Aug 24 2026

VFR conditions will prevail at all TAF sites next 24hrs. Skies will become clear this evening and continue into the overnight hours. Expecting more CU to develop again tomorrow, but think it will be FEW and not SCT. Winds will be light and variable through the period. Light fog is possible at each site in the morning, so have TEMPO group at all sites for 5sm BR from 09-13z.

ILX WATCHES/WARNINGS/ADVISORIES

None.