textproduct: Central Illinois

KEY MESSAGES

- There is a 50-70% chance for scattered thunderstorms through this evening. Some of these storms could be severe, including heavy rainfall. - There is another risk for severe storms late Friday evening through Saturday.

- Much cooler weather returns this weekend. There is a low chance for frost Saturday night north of Interstate 70, and a higher chance areawide Sunday night.

UPDATE

Issued at 753 PM CDT Wed Apr 15 2026

Clusters of strong to severe thunderstorms extend from southern Wisconsin to southwest Missouri early this evening. While the main shortwave is moving through eastern Nebraska, some more subtle impulses are helping to fuel the ongoing storms. Latest HRRR runs have been struggling with some consistency on the overall trends, but the bigger severe threat in our CWA will be west of I-55 into late evening.

Main forecast updates have been to tweak the rain chances through Thursday.

DISCUSSION

Issued at 221 PM CDT Wed Apr 15 2026

A shortwave trough over the central Plains will pivot into western Iowa this evening and serve as one of the main forcing mechanisms for thunderstorm development across a good portion of the central US this evening, including central Illinois. Lingering rain showers will continue to impact parts of eastern and southeast Illinois this afternoon, with a lull in precipitation further west. Several shortwave impulses ahead of the main upper wave may bring periods of showers and storms working across the area from late afternoon into this evening with the latest CAMs showing isolated activity spreading in as early as 21Z/4 pm west of the Illinois River.

Environmental conditions have been slow to improve due to widespread cloud cover from morning storms. RAP forecast analysis suggests SBCAPE will approach 1500 J/kg in western Illinois over the next few hours with deep layer shear up around 40 kts, which is sufficient for storm organization. Although the main surface front remains displaced off to our north, better forcing from the approaching wave should support isolated to scattered thunderstorms through this evening. Hodographs favor supercell/multicellular storm modes, posing a threat for all severe hazards. Although timing and coverage of late afternoon/early evening storms remains low, CAM output becomes more consistent later this evening as a linear MCS works through the area as the surface front nears. Although instability will wane some by then, the threat for damaging winds will still be a threat.

Heavy rain is also a concern through tonight, especially over areas that picked up 1-2"+ this morning (along a Rushville to Bloomington line). Warm cloud depths, high PWATs, and the potential for repeating rounds of storms could lead to a localized flash flooding threat. The 15.12Z HREF 24 hour LPMM shows pockets of 2"+ over parts of the area, though confidence in the exact location of these amounts remains low.

A break from storms is expected on Thursday as large-scale subsidence overspreads the area behind the departing upper shortwave. However, the threat for more thunderstorms returns Friday evening into Saturday as a compact upper shortwave tracks through the Upper Mississippi Valley and sends a cold front through the area. The front looks to approach the Mississippi River Friday evening then work through central Illinois during the overnight hours. The highest risk for severe weather is currently expected just west of here where instability and shear will be strongest during a diurnally favorable time. However, sufficient CAPE/shear parameters through the overnight hours could still support the development of scattered severe storms.

Temperatures turn much cooler by the weekend. Overnight lows Saturday and Sunday nights look to dip down into the middle to upper 30s, which introduces the possibility for frost. Chances are lower Saturday night due to lingering cloud cover and breezier winds, with higher chances Sunday night when winds are lighter.

Temperatures moderate by the middle parts of next week as upper ridging amplifies over the west-central US. Precipitation chances look minimal through much of next week with global models hinting at a wetter pattern setting up by the end of next week into next weekend.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1217 AM CDT Thu Apr 16 2026

Area of rain will exit the eastern terminals over the next hour or so. There is a low (20-40% chance) that MVFR stratocu will develop near/after daybreak, otherwise conditions will be VFR through the forecast. Southwest winds will remain gusty near 25 kt until late afternoon, then go light as surface ridging builds in.

ILX WATCHES/WARNINGS/ADVISORIES

None.