textproduct: Central Illinois

KEY MESSAGES

- Another round of showers will continue today, with a few thunderstorms along and south of roughly I-70 where there is a low (5-14%) risk for flooding.

- Showery and cool weather will continue through the end of the work week, with the next chance (40-50%) for thunderstorms arriving Saturday night into Sunday. The severe weather risk appears low at this time.

UPDATE

Issued at 1055 AM CDT Tue May 5 2026

Updated the forecast today and evening to adjust chances of showers, with one batch of showers exiting east of I-57 late this morning and another batch of showers spreading into west central IL from central/northern MO. The 2nd batch of showers to spread ENE across central and southeast parts of CWA (mainly se of the IL river) next few hours and HRRR and other CAM members fairly consistent in showing this. Have isolated thunderstorms in southeast IL with additional half to 1 inch of rain expected. SPC Day1 outlook has marginal risk south of CWA into southern reaches of Wabash and Edwards counties for 5% risk of damaging winds. Showers to diminish during mid/late evening. Cold front was in far southeast Lawrence county, just passing through Lawrenceville and will push southeast toward the Ohio river early this evening. Also lowered high temperatures a few degrees over central portions of CWA with a fair amount of low clouds and north to NE winds. Highs mostly in the mid to upper 50s with lower 60s in far southeast IL, a much cooler day than yesterdays highs in mid 70s to lower 80s.

DISCUSSION

Issued at 1241 AM CDT Tue May 5 2026

***** STORMS EARLY THIS MORNING, RAIN TODAY *****

At 1230am, scattered thunderstorms, some approaching severe limits, were ongoing across portions of central Illinois. Given much of this activity is behind an outflow boundary sent out of evening storms, the wind risk should be low, though with some of the taller cores can't fully rule out a microburst or two via precipitation loading. We have received several reports of hail up to 1 inch in diameter recently, which is not surprising given 500-1500 J/kg MLCAPE and 30- 35 kt effective bulk wind shear apparent in the RAP's mesoanalysis. Due to a 40-50 kt LLJ, strongly veering low level winds should sustain storms for at least a few more hours, with nearly 600 m^2/s^2 0-1km SRH evident on both VWX and IND's VAD profilers. Most convective allowing models (CAMs) and Warn on Forecast System (WoFs) members suggest activity will abate with waning instability after 2- 3am or so, but a weak disturbance riding along the front will spark additional rain area-wide and perhaps a few thunderstorms in southeast Illinois near daybreak. Showers are forecast to continue for most of the area (though mainly near/south of I-72) much of the day, with the most persistent activity near and south of roughly I- 72/Danville. Given heavy rainfall (1.25"+ in an hour) with the storms early this morning, and the heavy rain portions of central and southeast Illinois received last week, the threshold for flooding will be lower than normal. With HREF/NBM showing a 10-30% chance for more than 2 inches of rainfall in southeast Illinois, we'll need to keep one eye on this area for flooding, though we suspect the chance is low given at least half of that 2 inches should be spread out over 12+ hours mid morning through late evening. With cloud cover, showers, and low level northerly flow behind the cold front, it'll be a cool and gloomy day with highs in the mid to upper 50s south of roughly I-72/Danville where the rain will be most persistent. Further north, temperatures may top out in the low-mid 60s with any breaks of sunshine, especially north of a Macomb to Bloomington line.

***** STAYING COOL WITH LOW PRECIP CHANCES LATE WEEK *****

Another shortwave will bring a 20-30% chance for light rain tomorrow morning into early afternoon, though rain amounts will be much lighter with NBM giving only a 10-25% chance for a wetting rain (0.10" or more). With a cool airmass aloft (850mb temperatures near/below 0 degC), high temperatures will likely (50-70% chance) fall shy of 60 degF area-wide tomorrow afternoon. This trend for cool and showery weather will continue into the first part of the weekend as the parent upper level trough lingers over Ontario/Quebec to foster continued northwest flow across the Midwest. The deterministic GFS and ECMWF suggest we may get a weak push of warm advection ahead of a shortwave trough to warm the area into the 70s Saturday and provide some instability for showers/storms Saturday night into early Sunday (40-60% chance). Otherwise, conditions look mostly dry next week, with a warming trend apparent in global and ensemble data; by Wednesday, there is a 40-60% chance for high temperatures warmer than 80 degrees from NBM.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1245 PM CDT Tue May 5 2026

Light to moderate rain showers are lifting ENE into west central IL and currently reaching near SPI and sw of PIA. These showers to spread across the central IL airports next 1-2 hours, though likely staying just south/se of PIA where VCSH carried this afternoon. High end MVFR conditions possible along I-72 this afternoon and early evening but generally VFR conditions will dominate. Latest HRRR model has showers diminish from I-55 se between 00-04Z. HRRR shows patchy dense fog east of CMI toward daybreak but other CAMs are limited with fog development overnight. Will need to watch for fog development especially if clouds decrease/scatter out overnight with the light winds expected. An approaching positive tilted trof approaching IL on Wed afternoon will spread 5-10k ft clouds back into central IL between 13-15Z Wed especially from I-55 se. North to NNE winds around 10 kts this afternoon to be north around 5 kts or light and variable tonight and NW 5-10 kts after 14Z Wed.

ILX WATCHES/WARNINGS/ADVISORIES

None.