textproduct: Central Illinois

KEY MESSAGES

- Seasonal and mostly dry weather is expected through at least Tuesday evening over central and southeast IL.

- The next chance for showers and thunderstorms arrives on Wednesday afternoon and Wednesday evening. Some of these thunderstorms could be strong to marginally severe.

DISCUSSION

Issued at 230 PM CDT Sun Aug 23 2026

Nice late summer weather pattern expected through Tuesday across central and southeast IL after a very active weather pattern 1st 3 weeks of the month. Weak 1021 mb surface high pressure over nw MO into central Iowa and upper MS river valley to settle over IL during tonight and into the mid Ohio river valley on Mon and Mon night while ridging back into central/ne IL. This will continue fair wx across the prairie state into Tuesday with dry conditions and more comfortable humidity levels. NW winds 5-15 mph and scattered diurnally driven cumulus clouds over central and ne IL to dissipate after sunset while veil of high clouds over MO and central/se Iowa is clipping west central and sw IL. A disturbance over the central plains to keep chances of convection well sw of IL over central and sw MO tonight into early Monday as it tracks se across the MO valley/Ozarks. Patchy shallow ground fog may develop during overnight into early Mon morning mainly near river valleys and low lying rural ares. HREF only has 15-30% chance of vsbys getting to 5 miles or less over portions of CWA later tonight. HRRR and RAP show very little fog formation with drier air in place while NAM and GFSLamp show some patchy fog development mainly near river valleys. Comfortable night ahead with lows in the mid to upper 50s. Highs Monday around 80F with lower 80s southeast IL and sw CWA, with scattered cumulus clouds developing by midday giving partly to mostly sunny skies. Lows 55-60F Monday night and highs in the low to mid 80s Tuesday. Winds to stay fairly light generally under 10 mph tonight through Tue.

A northern stream upper level shortwave moving over the southern Canadian Prairie Provinces next few days, will track se through the northern Great Lakes Region, sending a cold front se through IL during Wed afternoon and Wed night. This will likely bring our next chance for showers and thunderstorms. Increasing south to SW flow ahead of the cold front to bring in warmer and more humid air into central/se IL on Wed. Highs in the mid to upper 80s Wed and possibly approaching 90F from Springfield sw with dewpoints climbing into the upper 60s/lower 70s. A cap initially in place on Wed could break later in the afternoon and Wed evening allowing thunderstorms to develop in a moderate instability with wind shear environment. Although the better upper forcing will be displaced to our north, a few strong to marginally severe storms could develop later Wednesday afternoon and evening, posing a threat for damaging wind gusts.

Could see lingering low chances of showers/thunderstorms in se IL early Thu, otherwise fair weather with seasonable temperatures to return Thu through at least Friday night as high pressure settles into the region. Strong mid/upper level ridge over the Southwest States through this work week begins to break down/flatten this weekend, and may see disturbance tracking into the midwest during this weekend especially by Sunday. A few model members shows some convection chances as early as Saturday over the IL river valley, while more members wait until Sunday for convection chances, though GEM and Ecmwf are dry thru the weekend. NBM keeps pops low this weekend with 20% pops over IL river valley Sat and Sat evening and 20-40% pops overnight Sat night and Sunday.

The Climate Prediction Center (CPC) 8-14 Day outlook for Aug 31-Sep 6th has a 35-45% chance of above normal temperatures over central/se IL and 33-40% below normal precipitation from Quincy to Danville north and trending near normal south.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 611 PM CDT Sun Aug 23 2026

VFR conditions will prevail at all TAF sites next 24hrs. A few high cirrus will be present overnight, but clear skies will be the rule. Some diurnal CU will develop again tomorrow but under high pressure, that should be limited. Winds will be light and variable overnight through tomorrow.

ILX WATCHES/WARNINGS/ADVISORIES

None.