textproduct: Central Illinois

KEY MESSAGES

- There is a Slight Risk (level 2 of 5) for severe weather late Thursday afternoon and evening. The primary hazards will be damaging wind gusts and hail: however, an isolated tornado cannot be ruled out.

- Large temperature swings are in store for the remainder of the week. Readings will soar to record warm levels in the middle to upper 80s on Thursday...then will plunge into the middle to upper 20s by early Saturday morning.

DISCUSSION

Issued at 241 PM CDT Tue Mar 24 2026

Big Warm-up by Thursday...

An unseasonably strong 590dm 500mb high centered over the Desert Southwest will build eastward into the Deep South over the next 48 hours...resulting in rising upper heights and warming temperatures across central Illinois. As the high and its associated warm dome approach, 850mb temps will rise from current readings in the 2-4C range to 18-20C by Thursday afternoon. Given strong WAA and at least partial sunshine, high temperatures will soar well into the 80s. Based on the latest projections, it appears record highs will be tied or broken across all of central and southeast Illinois before an approaching cold front brings clouds and thunderstorms by late afternoon/evening.

Severe Weather Risk Thursday...

A deep upper low anchored over Hudson Bay will pivot slightly southward later in the week, flattening the Deep South ridge and sending a strong cold front into central Illinois Thursday evening. With surface dewpoints progged to climb into the lower to middle 60s within the WAA regime, SBCAPEs will reach 500-1500J/kg by peak heating. 0-6km shear will generally range from 45-55kt...with the strongest shear remaining N/NW of the cold front across Iowa into northern Illinois. Despite the moderately unstable/sheared environment, NAM forecast soundings are showing a strong cap with MLCIN of 200-300J/kg midday Thursday...followed by a slow erosion of the cap immediately along the front as the afternoon progresses. While most CAMs do not quite cover the time range of interest, the 3km NAM and RRFS both suggest convection forming along/behind the boundary after about 4pm. While the initial cells may pose a large hail risk, think the primary hazard will become damaging wind gusts as the storms congeal into a line toward evening. Given 0-3km VGP peaking at 0.4-0.45, think there will be a non-zero risk for a couple QLCS type tornadoes along the line as it sinks southeastward through mid-evening. Once daytime instability wanes, the severe weather risk will diminish by late evening as the storms drop south of I-70.

Plunging Temperatures by the End of the Week...

Once the Thursday night cold front drops south of Illinois, a sharply colder airmass will arrive by the end of the week. GFS/ECMWF are showing 850mb temperatures dropping from 18-20C Thursday afternoon to around -6C by Friday night. As high pressure builds into the region and gusty northwesterly winds subside, radiational cooling will allow temperatures to drop below freezing by early Saturday morning. The 12z NBM suggests a high probability (50-70% chance) of lows colder than 30 degrees and a 15-30% chance of readings dipping below 25 degrees. This may pose a risk to any sensitive plants that may be emerging a couple weeks earlier than usual this spring.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 615 PM CDT Tue Mar 24 2026

VFR conditions are expected through Wednesday. Southeast winds will veer to the south-southwest by morning, becoming breezy by late morning/early afternoon. BKN mid to high clouds will continue to filter through the region overnight then thin out some in spots later in the period.

CLIMATE

Issued at 100 PM CDT Mon Mar 23 2026

Records Highs on Thu/Mar 26...

Charleston.... 84 in 1907 Danville...... 78 in 2007 Galesburg..... 83 in 1991 Lincoln....... 79 in 2007 Normal........ 83 in 2007 Olney......... 85 in 1907 Peoria........ 82 in 1907 and 1991 Springfield... 81 in 1991 Urbana........ 81 in 1907

ILX WATCHES/WARNINGS/ADVISORIES

None.