textproduct: Central Illinois

KEY MESSAGES

- A frost threat exists tonight and Thursday night across our far northern counties, expanding to include areas north of I-72 Friday night.

- Light rain arrives Thursday afternoon and evening.

- Temperatures remain well below normal through Saturday before a warming trend begins early next week.

DISCUSSION

Issued at 1244 PM CDT Wed Apr 29 2026

Surface high pressure continues to build across the Plains this afternoon. MSLP gradient east of the ridge will produce northwest winds gusting 20-30 mph this afternoon, then quickly diminish this evening. RAP and HRRR soundings show a dry column tonight. The clear skies and light winds will promote good radiational cooling, and with temps dropping into the upper 30s over the northern CWA, outlying areas will have a risk for patchy frost development, particularly north of I-74.

A mid-level shortwave traverses the region Thursday afternoon and evening. HREF members depict light rain developing by mid- afternoon and persisting into the overnight hours. Rainfall totals are forecast to be light, generally between 0.05 and 0.15 inches. Forecast sounding show just enough elevated instability for a slight chance of thunder mention for the central to eastern CWA mid afternoon into evening. A dry sub-cloud layer (below 800 mb) will support gusty winds under any shower, potentially up to 40-50 mph as depicted by latest runs of the HRRR.

Temperatures will remain 10 to 15 degrees below seasonal averages behind this system for Friday and Saturday. Friday night and early Saturday morning represent the highest confidence for widespread frost, based on lows in the mid to upper 30s. However, will need to watch the potential for mid level clouds associated with a weak shortwave rotating through the upper trough, that could diminish the frost potential.

Sunday through Tuesday... A transition in the synoptic pattern occurs as the surface high shifts east and the upper trough departs. High confidence exists in a warming trend, though model disagreement persists regarding the timing of the next precipitation- producing systems. The GFS shows a faster return of moisture by Sunday night and Monday, whereas the ECMWF and ECMWF- AI keep the region dry until Tuesday night. Blended guidance returns low chance PoPs to the region Sunday night and Monday, and likely PoPs for Tuesday night and Wednesday.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 618 PM CDT Wed Apr 29 2026

Northwest winds will subside overnight, becoming light as high pressure slides through the middle Mississippi Valley. A quick passing surface low/cold front will bring scattered showers Thursday afternoon though coverage should be pretty sparse. West winds become breezy ahead of FROPA, with occasional gusts up to 30-35 kts possible with any shower. Otherwise, VFR conditions are expected with cloud cover increasing later in the period.

ILX WATCHES/WARNINGS/ADVISORIES

None.