textproduct: Central Illinois

KEY MESSAGES

- Unseasonably warm temperatures continue for most of central IL and all of southeastern IL today, with highs in the 70s to upper 80s today. Temperatures turn cooler for the start of the work week, with highs in the low to mid 50s tomorrow.

- Gusty (30-40 mph) north winds will usher a seasonably cool airmass into the region late today, with lows in the low-mid 30s by Monday morning. Temperatures will then slowly rebound, with a 30-50% chance for highs in the 80s again by Thursday.

- Ahead of the cold front this evening, areas near and south of I-70 have a 50-70% chance for seeing thunderstorms. There is a level 1 of 5 (marginal) risk for damaging winds and large hail with those storms.

- Another chance (30-50%) for showers and storms will accompany a cold front sometime Wednesday into Friday. Confidence is low in whether a severe risk or hydro risk will materialize.

DISCUSSION

Issued at 214 AM CDT Sun Mar 22 2026

Today a pattern change will occur. The cold front that will move through the forecast area today is currently located across central Iowa. Daytime temperatures will drop by 30 degrees by tomorrow. Strong (possibly severe) storms are possible across southeastern IL this evening. Strong gradient winds out of the south will pick up this morning, briefly relaxing as the front passes, then picking back up out of the north behind it.

Highs today will depend on the timing of the cold front this morning/afternoon. The daytime temperatures have been overachieving the last few days, so highs were bumped up a few degrees with this forecast package to encompass the warmer temperatures where the cold front will arrive later in the day. There is a 20+ degree spread from NW to SE across the CWA. Galesburg has a forecast high of 64 degrees and Lawrenceville has a forecast high of 86 degrees.

Southerly winds will begin to gust to 25-35 knots by late morning north of I-72, with the strong gusts expanding south from there into the afternoon. Winds will spin abruptly out of the north behind the cold front this morning into afternoon. The northwestern counties will have FROPA by 12-14z this morning. The front will continue across central and southeastern IL throughout the day, exiting the southeast by 00z. Wind gusts will decrease to 15-20 knots starting from the NW around 06z tonight to the SE by 12z tomorrow. There is a 30-50% chance of gusts exceeding 40 mph this morning from now until 12z north of I-72. Then there is a 30-60% chance of exceeding 40 mph this evening (23z-03z) for eastern IL (east of I-55).

Tonight into Monday, there is a 40-70% chance of showers and thunderstorms as a cold front passes through, focused along and east of I-57. The greatest risk for severe storms is concentrated near and south of the I-70 corridor. SPC has maintained a marginal risk (level 1 of 5) for areas southeast of a Pana to Danville line, and a slight risk (level 2 of 5) that extends east of a Olney to Robinson line. The CAMs generally depict the storms developing/strengthening early evening around 23-00z near the I-70 corridor, then exiting pretty quickly to the south by 03-04z. The forecast soundings (GFS, NAMNest, GDPS, HRRR) for southeastern IL are showing an "inverted-v" profile. Most of the models are showing MUCAPE values of 1500-2000 J/kg, but then you have the NAMNest that shows nearly 3000 J/kg. DCAPE values are generally around 900-1000 J/kg. Effective wind shear has values of 30-40 knots. If we can overcome the decent capping in place and if we can moisten the atmosphere sufficiently, then we could see several severe storms. Based off the forecast soundings, it appears the primary risk would be for damaging winds but large hail could also be possible. Decent midlevel lapse rates are seen in the models with 8.0-8.5 C/km.

Behind the front, there is a nearly 30 degree temperature change starting overnight tonight. Lows tonight and tomorrow night will dip into the low to mid 30s. Highs on Monday will only top out in the low to mid 50s. These cooler daytime temperatures don't last long as we should be back up in the upper 70s to low 80s by Thursday. Then another cold front will move through late Thursday, bringing the next best chance for for rain (30-50%) and cooler temperatures (low to mid 50s) for the end of the week. Though the NBM threw in some low chance (10-20%) pops from Wednesday morning onward. This next system Thursday night may have some hydro concerns but for now we will continue to monitor trends as we move into the new week.

Copple

AVIATION

(For the 06z TAFs through 06z Sunday Night) Issued at 1223 AM CDT Sun Mar 22 2026

VAD wind profiles from regional Doppler radars show that the low level wind shear has developed ahead of schedule, with a 50-knot jet extending from near Kansas City to Chicago. Recent ACARS sounding data from KMDW suggests the core of the jet is a little lower as well. Thus, the new TAF set will bring the LLWS mention at the start, with height lowered to about 1500 feet. The jet will settle south of the TAF sites shortly after 12z, as a cold front drops into the area. This front will also result in winds shifting to the north and then northeast by midday, with gusts increasing to 25-30 knots. These stronger winds will persist into the evening.

VFR conditions will prevail through the period, with ceilings mainly 15kft or higher. With the northeast wind, there is some concern for sub-3000 foot ceilings to advect southwest from Lake Michigan Sunday night. Main impacts of this look to be after the current TAF period, and mainly at KCMI/KBMI, with HREF probabilities of MVFR ceilings ranging from 50-60% by 12z Monday.

Geelhart

ILX WATCHES/WARNINGS/ADVISORIES

None.