textproduct: Central Illinois

KEY MESSAGES

- The coldest air of the season will settle in Wednesday night through Thursday night. Wind chill values will approach advisory criteria 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 18z TAFs through 18z Wednesday Afternoon) Issued at 1150 AM CST Tue Dec 2 2025

Low clouds continue to blanket central Illinois late this morning. Most terminals have improved to low MVFR: however, both KBMI and KCMI are hanging on to IFR. 1730z/1130am satellite imagery shows the back edge of the overcast advancing eastward across Iowa/Missouri to the Mississippi River. While satellite trends appear optimistic for clearing across west-central Illinois this afternoon, both NAM and HRRR forecast soundings suggest the clearing line will slow substantially...and may not reach KPIA until around 02z...and not to KCMI until perhaps 14z/15z Wed. Winds are presently light, but will back to SW and increase tonight as a cold front approaches from the northwest. Once the SW flow commences, the low clouds will finally get shoved out of east-central Illinois by late morning Wednesday. As WAA increases over the fresh snow cover, fog will become a concern tonight...particularly east of the I-55 corridor. CAMs are most aggressive with lowered visbys further east in Indiana: however, based on what happened last night into this morning, think fog will develop further west than the models indicate. As a result, have lowered visbys to around 4 miles at KDEC and 2 miles at KCMI between 09z and 13z. Once the low clouds/fog clear the eastern terminals, VFR conditions are expected across the board through midday before the approaching front brings lower clouds and scattered snow-showers by Wednesday afternoon/evening.

Barnes

ILX WATCHES/WARNINGS/ADVISORIES

None.