textproduct: Central Illinois

KEY MESSAGES

- Additional showers and storms are likely this evening into tonight. The best chance for rainfall totals over a quarter inch is south of I-72/Danville (60-80% chance). Severe storms are not expected.

- Below normal temperatures persist through Saturday. Frost is possible Friday night as lows fall into the mid 30s.

DISCUSSION

Issued at 116 AM CDT Tue Apr 28 2026

Active convection departed the ILX CWA around 10pm Mon/03z Tues. A compact shortwave and associated sfc low were positioned near Lake Superior as of 1230am Tues/0530z, with an associated cold front draped southward all the way into IL. This front was nearing the I- 57 corridor as of 1230am Tues. While a stray shower can't be ruled out along the front (a few weak echoes have been noted in KILX radar reflectivity over the last two hours), our thinking is that the chance of additional rain is less than 15% at any one location. Behind the front, an extensive stratus deck (bases between 1-2 kft) is evident in satellite imagery, with overcast skies from the IL River back into NW IA and portions of SE MN. The expectation is this cloud deck will persist and shift southeast into the ILX CWA Tues AM. This cloud deck may start to break up by late morning/early afternoon, but additional mid/high clouds will be streaming in from the west. With plenty of cloud cover today, trended temps a bit cooler than previously forecast.

*** MORE RAIN TONIGHT ***

Another shortwave traversing the central Plains will lead to a sfc low tracking from OK to the Ohio Valley Tues PM. This will lead to increasing southwesterly mid-level flow and ample wind shear. However, the sfc front will remain south of the ILX CWA, resulting in no sfc based instability. Elevated instability values also appear meager, generally less than 500 J/kg, so severe storms continue to appear unlikely for our CWA with this wave. On the other hand, PWAT values are modest, with the ens mean increasing to 1-1.25" south of I-70. Both the NBM and HREF depict a sharp gradient in the QPF probabilities, with a 60-80% chance of over a quarter inch of rain south of I-72/Danville, decreasing quickly to less than 30% north of I-72/Danville. The best chance of exceeding a half inch of rain is south of I-70 (50-60%). The rain will primarily occur after 7 PM Tues night and before daybreak on Wednesday.

*** MID-WEEK THROUGH THE WEEKEND ***

A relatively benign stretch of weather is in store from mid-week through the weekend. The rest of the work week will generally be characterized by upper level troughing over the northern Great Lakes and weak sfc high pressure over the Midwest. This will favor slightly below normal temperatures (highs in the 60s) and mostly dry conditions. The one period to watch for additional rain would be as a shortwave pivots around the main trough Thurs PM (10-15% chance). This wave will be interacting with a relatively dry airmass (ensemble mean PWATs less than 0.5"), so any rainfall that occurs would be light. This system will bring a renewed push of cool air, with highs struggling to reach 60F on Fri and a chance for frost development Fri night as lows drop into the mid/upper 30s. Those with sensitive vegetation may need to take protective action.

Model agreement starts to decrease towards the end of the weekend, but generally favors sfc high pressure sinking south of the region, reestablishing a southerly component to the sfc winds and warming temps. Ens guidance favors highs between the mid 60s and mid 70s into next week, with the deterministic NBM delivering values on the upper end of that range. While some additional rain chances are possible late weekend-early next week, the severe storm potential appears low through at least Monday.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 545 AM CDT Tue Apr 28 2026

MVFR stratus deck is slowly pushing east to KCMI as of 1045z, overcast skies extend all the way west into central Iowa. Ceilings are expected to gradually rise to VFR by midday. Scattered to widespread showers will overspread much of the region tonight (01- 08z), but precip chances decrease as you go further north/west, so only have a PROB30 at KPIA rather than prevailing -SHRA. West- northwest winds this morning will gradually turn to northerly tonight.

ILX WATCHES/WARNINGS/ADVISORIES

None.