textproduct: Central Illinois

KEY MESSAGES

- Above normal temperatures are likely to persist into mid June, with highs generally in the 80s. Humidity values are expected to increase late this week into early next week.

- Storm chances return to the forecast Friday through at least early next week. (30-50% chance).

UPDATE

Issued at 723 PM CDT Mon Jun 1 2026

A couple lines of thunderstorms developed around mid afternoon just south of I-72, and are now pushing into southern Illinois. This was in an area where surface CAPE's reached to around 1500 J/kg, and was near a subtle surface boundary. The bulk of these stayed just west of our forecast area, but isolated convection has developed this evening near I-70 as well. PoP's were updated earlier to address the convection, and will keep a 20-30% mention south of I-70 through sunset.

Otherwise, another period of breezy northeast winds has moved into the area near and north of I-72/US-36, with some gusts 20-30 mph this evening. This should continue a few more hours, though the HRRR suggests some gusts near 20 mph continuing past midnight. This is coinciding with drier air pushing into the forecast area, with dew points in the 40s north of I-74 this hour. Based on upstream trends and coordination with northern neighbors, the dew point grids were adjusted through early Tuesday evening, resulting in humidity levels dropping below 30% Tuesday afternoon.

DISCUSSION

Issued at 245 PM CDT Mon Jun 1 2026

Currently dry conditions prevail across central and southeast IL at mid afternoon with partly to mostly sunny skies with scattered cumulus clouds. Warm temps were in the low to mid 80s. Dewpoints ranged from lower 50s far ne CWA to low to mid 60s from Macomb to Lincoln to Mattoon and Terre Haute sw. Latest HRRR models and some other CAM members still showing isolated convection developing along and south of a Taylorville to Paris line next few hours and pushing into southeast IL early this evening before dissipating at sundown as back door cold front pushes through. Unstable air mass remains south and sw of CWA and SPC Day 1 outlooks keeps marginal to slight risk from far southern IL, southern MO, sw KY and south.

Large Canadian high pressure settling southward from Hudson Bay into the Great Lakes Tue and Ohio river valley Wed, will bring NE flow of drier more stable air into the area with ample sunshine and lower dewpoints into the 40s Tue into Wed. Will also see strengthening upper level ridge into IL during mid week with 500 mb heights rising to near 590 decameter on Wed. Lows overnight in the mid 50s to around 60F, coolest north of I-74. Highs Tue/Wed in the upper 70s/lower 80s with some areas over the IL river valley reaching mid 80s. Seasonably cool lows in the low to mid 50s Tue night and mid to upper 50s Wed night.

Fair weather is expected to continue Thu and much of Thu night, with just 20-30% chance of showers nw of the IL river late Thu night. Return ssw flow on Thu to start to bring back more humid air late this week. Warm highs in the mid to upper 80s Thu with dewpoints in the 50s.

The persistent Omega Block pattern starts to break down late this week with return of more moisture into IL late this week and increasing chances of convection. Convection chances mainly over nw half of CWA on Friday and over most of CWA by Saturday as frontal boundary approaching IL from the upper Midwest. A frontal boundary lurking near central/northern IL early next week to keep chances of convection around. Highs in the 80s overall Fri through Monday with more humid conditions as dewpoints rise into the mid to upper 60s this weekend and upper 60s and lower 70s next Monday.

The Climate Prediction Center 8-14 Day Outlook for June 9-15th has 50-60% chance of above normal temperatures over IL with precipitation trending near normal while pcpn trending above normal se of IL.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1143 PM CDT Mon Jun 1 2026

VFR conditions prevail through the period, along with light northeasterly winds. Sustained winds will generally be less than 10 knots, but a few gusts of 18-20 kts could occur during the afternoon. Aside from some lingering mid clouds at the start of the period, skies will be mostly clear.

ILX WATCHES/WARNINGS/ADVISORIES

None.