textproduct: Central Illinois

KEY MESSAGES

- Near-record warmth can be expected today and Monday, with afternoon high temperatures in the 80s today and upper 80s to lower 90s Monday. Tuesday looks equally warm south of I-72. - An extended period of rain chances is on track Tuesday night through Thursday. There is a Marginal Risk for severe thunderstorms in west-central IL Tuesday evening, otherwise severe weather potential appears low at this point.

- Colder air will arrive next weekend, although the amount of cooling remains uncertain. Patchy frost could develop Saturday night and Sunday night. Otherwise, temperatures are likely to be below normal.

DISCUSSION

Issued at 240 AM CDT Sun Oct 11 2026

Sunny skies will return today as high pressure builds into central IL. Strong warm advection building this ridge will result in highs surging into the mid 80s today, just a few degrees from record values, and into the lower 90s Monday, exceeding previous record highs. A weak cold front will push into the area Tuesday, bringing some minor cooling to areas north of I-72 and a slight chance for showers or thunderstorms.

Models are in good agreement that precipitation will develop Tuesday night as the stalled frontal zone strengthens, a low level jet develops, and increased gulf moisture arrives. 60 to 80 percent PoPs are included in the current forecast package Tuesday night into Wednesday morning. Precipitation amounts remain uncertain, but 00Z GFS advertises amounts over an inch in much of central IL, while 12Z ECMWF and Canadian models show generally under a half inch. Several hundred J/kg MUCAPE and 30-40 kt bulk shear appear likely Tuesday evening in a corridor extending from northern MO into west-central IL as 12Z ensemble depicts 60+ percent chances for joint probability of shear greater than 30 kts and MUCAPE greater than 500 J/kg, which would support potential for severe storms. SPC has designated a Marginal Risk for severe storms in this area.

Later in the week, a central Rockies low looks to eject eastward and merge with a Canadian low to bring another 70 percent chance for showers and thunderstorms Thursday.

Colder air following Thursday's system will arrive for the weekend, however the trajectory of the coldest air remains uncertain, with models varying considerably. For central IL, 12Z ensembles have around a 40 degree spread for Saturday afternoon. Current forecast reflects roughly a median value, with highs in the upper 50s and lows in the upper 30s Saturday/Saturday night, but a potential for freezing temperatures or frost will have to be monitored for this time period.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1215 AM CDT Sun Oct 11 2026

Area of ceilings just below 3,000 feet is located just southeast of KCMI. Nighttime microphysics satellite data has shown some erosion on the northwest edge, and blended model guidance suggests not much of an additional push northwest. Currently feel that this will not reach KCMI, though it will be a close call, and any MVFR conditions will be transient through about 09z.

In general, VFR conditions will prevail the next 24 hours over central Illinois, with mainly high-based clouds during the beginning and ending portions of the forecast period.

ILX WATCHES/WARNINGS/ADVISORIES

None.