textproduct: Central Illinois

KEY MESSAGES

- Dense fog reducing visibility to a quarter mile or less is possible (50-80% confidence) overnight into Monday morning across most of central Illinois.

- There is a greater than 90% chance for rain Monday evening and overnight. 25th-75th percentile rainfall ranges from 0.05-0.35 in the northwestern counties to 0.25-0.75 in the southeast.

- Winds gusting 30-40 mph Wednesday will usher in cooler temperatures to end the week with widespread lows in the lower to mid 20s Thursday morning with Wind Chill Values in the teens.

DISCUSSION

Issued at 124 PM CST Sun Nov 23 2025

This afternoon, water vapor imagery reveals a closed upper low over the Four Corners region which is progged to lift across the central Great Plains tonight, then across central Illinois late Monday night. At the surface, high pressure is analyzed over the mid Mississippi Valley with ridging extending north across the Upper Midwest. The ridge axis will shift east across central Illinois this evening, with a modest southerly gradient overspreading central Illinois from the west in its wake. Despite the 5-8kt southerly wind developing late tonight, guidance is once again hinting at widespread fog potential overnight into Monday morning. 12Z HREF probabilities for dense fog (quarter or mile less visibility) runs roughly 50-80% with the highest confidence along the I-74 corridor and across portions of east central Illinois (closest to the ridge axis).

Meanwhile, as the upper low approaches the region through the day Monday, expect cloud cover to be on the increase followed by precip chances starting late in the afternoon. PoPs peak Monday evening and overnight in the 80-95 percent range within the strong warm air advection ahead of the low. A few additional scattered showers (30% coverage) Tuesday morning and early afternoon are expected as the main upper wave passes over central Illinois.

A northern stream shortwave trough is expected to move onshore over the Pacific Northwest Monday and dig across the Upper Midwest and Great Lakes late Tuesday into early Wednesday. A surface low will deepen in response and push a strong cold front across central Illinois Tuesday night. Warm air advection ahead of the low may drive some very light rain or drizzle Tuesday but precip is not expected with the cold front. Instead, a tight pressure gradient associated with the deepening low and steep low level lapse rates from the cold air advection will result in moderately strong winds across central Illinois Tuesday night and Wednesday. NBM probability of 24-hr peak gusts exceeding 30 mph is greater than 90% and around 50-60% to exceed 40 mph. Much cooler air will overspread central Illinois with highs near 60 degrees Tuesday giving way to highs only in the upper 30s to mid 40s the remainder of the week. Overnight lows in the 20s are likely with wind chill values dipping into the teens at times Thursday through Saturday mornings.

Next weekend, a very dynamic setup may take shape across the region which would be capable of producing impactful winter weather across portions of central Illinois. While it's a bit far out to get into details, accumulating snow changing to freezing rain/rain through the day Saturday are advertised by some of the latest models, so this period will bear watching as the details come into better focus.

Deubelbeiss

AVIATION

(For the 18z TAFs through 18z Monday Afternoon) Issued at 1122 AM CST Sun Nov 23 2025

The fog and low stratus from earlier this morning has largely mixed out, with VFR conditions now observed across the board. We are monitoring a patch of persistent LIFR conditions ongoing across central Missouri early this afternoon. Most short-term models support this area expanding and lifting into central Illinois sometime between 04z-07z, and then persisting through late Monday morning before scattering-out. Confidence is currently high enough to have added mention of such conditions in this TAF cycle, and we will continue to monitor trends and developments throughout this evening.

MJA

ILX WATCHES/WARNINGS/ADVISORIES

None.