textproduct: Central Illinois

KEY MESSAGES

- There is a greater than 90% chance for rain Monday evening and overnight. 25th-75th percentile rainfall amounts range from 0.10-0.40 in the northwestern counties to 0.25-0.75 in the southeast.

- Above normal temperatures through Tuesday will turn sharply colder midweek with widespread low to mid 20s in the forecast Thursday morning.

DISCUSSION

Issued at 109 PM CST Sat Nov 22 2025

This afternoon, a ridge of high pressure extends from the eastern Great Lakes across the mid Mississippi Valley into the southern Great Plains. Further north, low pressure is tracking east into Ontario while a trailing cold front stretches south into the Upper Midwest. Locally, southwest winds will freshen ahead of the front late this evening, then will veer to a northwesterly direction overnight behind the front. No precip is expected with frontal passage. Winds drop off again late tonight behind the front as high pressure builds back into the region. This may allow enough time for fog to form once again, especially near the lower Illinois River Valley. Sunday will be sunny with light winds under the influence of high pressure.

Meanwhile, a closed upper low over SoCal today is progged to lift into the central Great Plains Sunday night then across central Illinois late Monday as the wave opens up. A weak surface reflection will eject from the Front Range of the Rockies Sunday night, tracking east across Kansas City Monday evening. Ahead of the low, warm air advection will drive the next round of precip across central Illinois late Monday afternoon through Monday night with additional showers possible late Monday night into Tuesday morning with passage of the upper wave. A few embedded convective elements appear possible with very weak but non-zero elevated CAPE values rooted around 700mb, but forecast soundings show the depth of the instability may not be sufficient to allow thunderstorms. NBM mean QPF ranges from roughly a third of an inch in the NW CWA to around half an inch in the SE. 25th-75th percentile values range from 0.10-0.40 near Galesburg to 0.25-0.75 near Lawrenceville. A few isolated (10%) swaths of just over an inch are possible for any embedded convection that develops with this chance greatest along and south of I-70.

A fast moving northern stream wave will be right behind our early week system and will result in a deepening low over the Upper Midwest and western Great Lakes late Tuesday into Wednesday. A strong cold front will push across central Illinois Tuesday night. Precip looks to stay very limited in both probabilities (30%) and amounts (<0.10 in) but a big swing in temperatures is likely. Highs on Tuesday ahead of the front will top out in the upper 50s to mid 60s, but by Wednesday night behind the front, temps will fall into the 20s area-wide, ushered in by strong west/northwest winds gusting up to around 35 mph. Highs will generally range in the upper 30s to mid 40s through the second half of the week.

Deubelbeiss

AVIATION

(For the 00z TAFs through 00z Sunday Evening) Issued at 502 PM CST Sat Nov 22 2025

A dry cold front will cross the central IL terminals late this evening. The main impact will be a narrow band of mid-level cloud cover around 8-10 kft and a shift in winds. Patchy fog may develop from around 10Z-14Z bringing MVFR vsby or locally worse. Surface winds SW 6-10 kts until 07Z-09Z then becoming NW 5-8 kts and diminishing to light and variable by 16Z.

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ILX WATCHES/WARNINGS/ADVISORIES

None.