textproduct: Central Illinois

KEY MESSAGES

- Unseasonably warm temperatures continue through Saturday, with highs reaching the upper 70s to low 80s. There is a 40-70% chance of lows exceeding 60 degrees Saturday night/Sunday morning south of I-74.

- A conditional risk for severe storms exists Sunday afternoon and evening for southeast Illinois. While storm development is uncertain (20-40% chance), any storms that form could become severe, with the primary hazards of damaging winds and large hail.

- A sharp pattern change follows Sunday's cold frontal passage through the region. High temperatures will drop back into the 50s by Monday. However, cooler temperatures are only temporary as we should be back up in the upper 60s to low 70s by Thursday.

DISCUSSION

Issued at 208 AM CDT Sat Mar 21 2026

Today will be very pleasant (albeit toasty/warm) again. Highs today and Sunday will be knocking down the door to 80 degrees. 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. The warmest lows are expected on Saturday night which will only get down into the upper 50s to near 60. The HREF is showing a 40-70% chance of lows exceeding 60 degrees Saturday night/Sunday morning south of I-74.

Sunday night into Monday there is a 20-40% chance of showers and thunderstorms as a cold front passes through. If any of these storms can manage to develop, they could be strong to severe. SPC has a marginal risk (level 1 of 5) for areas near and south of I-70, and a slight risk (level 2 of 5) that reaches only into Lawrence County. Some of the forecast soundings (GFS, NAMNest, GDPS) for southeastern IL are showing an "inverted-v" look. Most of the models are showing MUCAPE values of 1000-1500 J/kg, but then you have the NAMNest that shows nearly 3000 J/kg. DCAPE values are generally around 500-900 J/kg. Effective wind shear has values from 50-60 knots. If we can overcome the 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 be possible. There are decent lapse rates seen in the models for Sunday evening (7.0-8.0 C/km). The CAMs that go out far enough (particularly the NAMNest) show the storms popping early evening around 00z near the I-70 corridor.

Then the aforementioned cold front will move through the forecast area Sunday also bringing a nearly 30 degree temperature change. 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 60s to low 70s by Thursday. Then another cold front will move through late Thursday, bringing the next best chance for for rain (20-50%) 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 Tuesday evening onward.

Copple

AVIATION

(For the 06z TAFs through 06z Saturday Night) Issued at 1201 AM CDT Sat Mar 21 2026

VFR conditions expected through the period, with high-based ceilings gradually eroding early this morning. Northeast winds will trend back around to the south-southwest mid morning through midday.

Geelhart

ILX WATCHES/WARNINGS/ADVISORIES

None.