textproduct: Central Illinois

KEY MESSAGES

- Periods of rain will persist through the evening hours before departing by Saturday morning.

- Another round of rain is likely (greater than 80% chance) Monday evening into Tuesday morning. Current forecast guidance suggests amounts will generally range between 0.25"-0.5".

- A sharp cold front will push across the area on Wednesday with temperatures slipping into the 20s by Thanksgiving morning.

DISCUSSION

Issued at 1219 PM CST Fri Nov 21 2025

Periods of rain, drizzle and fog will persist through this evening as a loosely-organized frontal system slides out of the Missouri Ozarks and toward the Lower Ohio River Valley. Overall trends in hi-res guidance have shifted the rainfall axis slightly further north as an east-west band of 850-700 mb frontogenesis moves roughly parallel to the I-72 corridor by evening and helps to support a narrow area of moderate rainfall. Total QPF looks greatest in between the I-72 and I-70 corridors where the latest RRFS guidance supports between 0.25"-0.75", with locally higher amounts up to 1.25" east of I-57 (i.e. portions of west-central and southwest IL).

Precip will quickly diminish into Saturday morning as large-scale subsidence works in behind the departing upper-level shortwave and attendant frontal system. An abundance of sunshine will emerge Saturday morning and persist through Monday as surface high pressure builds across the region downwind of an upper ridge axis. Temperatures will respond by warming into the mid- to upper-50s each afternoon Saturday through Monday.

Another frontal system will push across central Illinois Monday evening into Tuesday as a pair of mid-level troughs attempt to phase together over the central US. A strong low-level jet (40+ kts) will veer into our region ahead of the front, giving us a healthy injection of moisture and shear, but the greatest instability and convective chances appear to be confined to the Lower Mississippi Valley ahead of the leading trough. Further north across central Illinois, rain is likely (greater than 80% chance, per NBM guidance). And, poking around the various ensemble and multi-model guidance, the Mean QPF generally ranges from 0.25"-0.5" with this next round of rainfall.

The well-advertised cold snap will arrive on Wednesday and continues through at least Thursday with daily highs in the 40s and overnight lows in the 20s. Breezy northwest winds on Thanksgiving morning will yield wind chill values in the teens, perhaps leading to some limited cold-weather impacts for outdoor events.

An unusual amount of forecast uncertainty then exists Friday onward, and especially into early December. As it stands today, there is about a 1 in 6 chance for wintry precip to occur between Friday and Saturday in areas west of I-55; sources: both 13z NBM and 00z LREF. Then, sometime between the Sunday and Tuesday timeframe of that following week, an impactful winter system is looking increasingly likely. For us here in central Illinois, the compass is pointing most strongly toward being on the warm side of this system, at least for now.

MJA

AVIATION

(For the 00z TAFs through 00z Saturday Evening) Issued at 630 PM CST Fri Nov 21 2025

A low pressure system will pass through southern IL this evening with a band of rain affecting the central IL terminals through the evening before tapering off as the low departs to the east. IFR cigs and MVFR vsbys will continue across most of the area for several hours before improving overnight. The earliest improvements will begin at KPIA and spread southeastward. VFR conditions expected at KPIA by 06Z, to as late as 12Z along the I-72 corridor. Winds NE 6-10 kts, becoming light and variable by 12Z. SW winds 6-10 kts developing by 18Z.

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ILX WATCHES/WARNINGS/ADVISORIES

None.