textproduct: Central Illinois

KEY MESSAGES

- There is a level 3 of 5 (enhanced) risk for severe weather this evening. Damaging winds, large hail, a couple tornadoes, and flash flooding are all concerns, especially near and south of I-70.

- There is a 30-50% chance for frost Friday night. Tender vegetation may need to be covered in order to prevent damage.

DISCUSSION

Issued at 226 PM CDT Mon Apr 27 2026

***** SEVERE WEATHER THIS EVENING *****

Mid level water vapor satellite reveals a negatively tilted upper level trough spinning over the Midwest. At the surface, WPC has analyzed a 996mb low in eastern Iowa which is forecast to lift northeastward across Wisconsin this evening. Much of the warm sector has been worked over at this point via a morning-early afternoon MCS, but these storms left an outflow boundary near/south of the I- 70 corridor which will serve as a differential heating/convergence zone for renewed storms later this afternoon. A wake low continues to foster wind gusts up to 35mph from the southeast, which should help maintain stable low levels further north. Nonetheless, a few elevated storms could generate locally severe hail and wind in those areas. Meanwhile, south of the I-70 corridor, dewpoints should surge into the mid-upper 60s while a 50 kt LLJ maintains 40-55 kt effective bulk wind shear and 400-700 (679 on the VWX vad profiler) m^2/s^2 0-3km SRH via strongly cyclonically curved hodographs. CAMs generally suggest convective activity developing upstream over the next couple hours and moving through this environment during the evening will start discrete and eventually grow upscale into another MCS. Hence, the initial hazards will be very large hail and tornadoes, with the risk transitioning to damaging winds, locally severe hail, and QLCS tornadoes with time. Training storms will pose a risk for flash flooding (REFS and HREF ensemble max precip have swaths of 4+ inches of rain falling in <6 hours), for which we have issued a Flood Watch which extends through 10pm. A Tornado Watch is in effect for Effingham to Crawford Counties and areas further south, where the chance of surface based (and hence potentially tornadic) storms is highest. Storms should exit the ILX County Warning area by 11pm, while a cooler and more stable airmass arrives from the west-northwest behind a cold front.

***** DRY CONDITIONS LIKELY WEDNESDAY AND BEYOND *****

Another shortwave will lift northeast through the area tomorrow night, bringing another opportunity for some rain and perhaps a rumble of thunder. Thankfully QPF with this system is lighter, with a low (<20%) chance for an additional inch of rainfall. Since this will occur around 24 hours after this evening's heavy rainfall in southeast Illinois, the ground may have some time to absorb the water, though we'll still be keeping one eye on it.

By Wednesday morning, a drier pattern should take hold of the region, with less than a 20% chance for rain through the weekend. High temperatures each day are forecast in the 60s, with locations near and north of the I-74 corridor potentially (60% chance) not climbing out of the 50s on Friday. The National Blend of Models (NBM) indicates a 30-50% chance temperatures fall below 37 degF Friday night into Saturday morning, which should be cold enough for frost given the expected light winds.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1258 PM CDT Mon Apr 27 2026

A thunderstorm complex will move east of the airfields over the next couple hours, with a 30-40% chance of redevelopment north to impact BMI and PIA (higher chances at the other airfields) after 22z. In the wake of the morning storms, a brief period of southeast wind gusts to 40 kt are possible (20-30% chance); TAFs will be amended for this as necessary. Otherwise, winds will blow from the south-southeast around 15-20 kt with gusts up to 30 kt through late afternoon, veering to southwesterly and easing this evening, and then veering more sharply to a west- northwesterly direction tonight behind a cold front. There will also be a 50-60% chance for MVFR ceilings behind that front after around 06z.

ILX WATCHES/WARNINGS/ADVISORIES

Flood Watch until 10 PM CDT this evening for ILZ052>057- 061>063-066>068-071>073.