textproduct: Central Illinois

KEY MESSAGES

- Low humidity and seasonable to slightly above normal temperatures will continue through tomorrow, with highs in the low to mid 80s.

- A pattern change will occur late in the week, resulting in increasing humidity and storm chances (30-60%) Friday into next week. Afternoon heat indices may climb into the 90s at times.

DISCUSSION

Issued at 102 PM CDT Tue Jun 2 2026

***** DRY AND WARM NEXT FEW DAYS *****

18z surface analysis reveals a 1028mb high over the Upper Great Lakes, which is maintaining dry easterly flow over central and southeast Illinois early this afternoon. This dry airmass has once again allowed for efficient radiational warming, resulting in temperatures already in the 80s (near the 90th percentile of model guidance for highs) as of 1pm. This dry, seasonably warm pattern will continue into tomorrow, though winds will start to blow from the southeast during the afternoon as that surface high shifts southward into the Ohio Valley.

***** SUMMERLIKE HUMIDITY, STORM CHANCES BEGIN FRIDAY *****

By Thursday, winds will begin to blow from the south-southwest as the surface high shifts into the southeast states and ridging begins to break down over our neck of the woods. This will gradually bring Gulf moisture into the region, allowing dewpoints to climb well into the 60s - highest across west-central Illinois where the Low Resolution Ensemble Forecast (LREF) system even gives a 20-40% chance for 70 or higher - by Friday evening. This will foster sufficient instability (EPS mean MUCAPE ~1000 J/kg) to fuel thunderstorms, though it remains unclear whether forcing associated with a weak midlevel disturbance will be enough to overcome the capping inversion apparent on forecast soundings. As additional weak disturbances ripple through the region into early next week, thunderstorm chances will linger, though again the lackluster forcing makes it tricky to know if, where, and when storms will form. Given weak shear, GEFS/EPS mean PWATs around 1.5-1.75" (above the 90th percentile of ILX raob climatology), and a deep (>10kft) warm cloud layer, any storms will be efficient rain producers, making this weekend a "feast or famine" scenario for needed rain.

By early next work week, substantial model differences become evident in the synoptic pattern, making the forecast increasingly nebulous. Nonetheless, the general trend is for summer-like humidity and warmth. The National Blend of Models (NBM) advertises daily highs/lows in the upper 80s/60s with 20-40% storm chances Monday through Wednesday (June 8-10th).

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 552 PM CDT Tue Jun 2 2026

VFR conditions continue through Wednesday, with just a few high clouds at times. Breezy east winds will drop off some with sunset, then trend more toward the southeast on Wednesday.

ILX WATCHES/WARNINGS/ADVISORIES

None.