textproduct: Central Illinois

KEY MESSAGES

- Slippery morning commute possible due to yesterday's snow and some patchy freezing fog.

- There is medium confidence (30-50%) in additional snowfall by Wednesday evening in areas north of Interstate 72. Our base case is between a dusting and one inch. - The coldest air of the season will settle in Wednesday and Thursday nights. Wind chill values will approach advisory criteria up near Interstate 74.

- A clipper system will push across the Corn Belt this weekend. There is currently a low (20-25%) chance that snowfall will exceed 1 inch.

DISCUSSION

Issued at 329 AM CST Tue Dec 2 2025

A compact shortwave trough is currently lifting north through the lower Ohio River Valley this morning, as indicated by mid-level water vapor imagery. A drier, subsident air mass is settling in behind this feature. Regional model soundings show a shallow pinch of moisture trapped beneath a strong subsidence inversion, which is causing low stratus and pockets of dense fog. The combination of yesterdays snow accumulation and todays patchy freezing fog may result in a continued slippery morning commute.

Afternoon temperatures are expected to remain close to morning lows, as light winds beneath the stubborn subsidence inversion limit mixing and keep skies mostly cloudy. Low clouds will persist into this evening, with temperatures falling into the mid-teens to around 20 degF across the region.

Overnight, a good surge of warm air advection is expected as surface winds shift southerly behind departing surface high pressure. This will cause temperatures to slowly climb into the low-to-mid 30s Wednesday afternoon ahead of an approaching cold front.

There remains a decent signal for scattered snow showers to develop behind the front by early Wednesday afternoon. This is associated with a sharpening band of shallow FGEN (925-850 mb) beneath a pair of phasing jet streaks aloft. The latest 00z RRFS guidance suggests a medium chance (30-50%) for PoPs north of I-72, with the wet-bulb temperature cold enough to support snow. This same guidance also supports a range of QPF from a trace to 0.10 inches. Consequently, our base case forecast is for a dusting to one inch of new snow accumulation in areas north of I-72.

The region will experience the coldest air of the season so far from Wednesday night through Friday morning. Overnight lows will drop into the single digits, and daytime highs will only reach the teens, particularly in areas north of I-70. These conditions are exceptionally cold for early December, running approximately 25-30 degrees below average. Furthermore, wind chill values in our northern areas are expected to approach advisory criteria.

Marginally warmer and continued dry weather will then stretch through late week as the storm system for Friday that we were once concerned about passes well to our south. Nevertheless, there is an emerging signal for another shot of light accumulating snow this weekend as choppy northwest flow brings a clipper-like system across the Corn Belt. Latest guidance from the NBM and Grand Ensemble (GEFS, GEPS and EPS) support a 1 in 4 chance for at least 1 inch, though this probability may be artificially low due to some timing differences that still exist.

MJA

AVIATION

(For the 12z TAFs through 12z Wednesday Morning) Issued at 426 AM CST Tue Dec 2 2025

Low-level stratus remains trapped beneath a strong subsidence inversion, causing mostly IFR conditions across the regional terminals early this morning. Model soundings mostly suggest that this stratus remains intact through at least early afternoon as light winds limit mixing beneath the inversion. Guidance supports an improvement to VFR conditions at KPIA/KSPI/KDEC between 02z-05z, and then at KBMI/KCMI by 05z-08z, as surface winds shift south and increase.

MJA

ILX WATCHES/WARNINGS/ADVISORIES

None.