textproduct: Central Illinois

KEY MESSAGES

- Dank, blustery conditions will persist through Thursday before a strong cold front sweeps through Thursday night.

- Frosty temperatures in the 30s will impact the region Friday night and Saturday night.

DISCUSSION

Issued at 236 AM CST Wed Nov 4 2026

Short Term...Today through Thursday Night

Water vapor imagery shows rapid dry-slot entrainment carving northeastward into the Mid-Mississippi Valley early this morning, effectively shutting off widespread stratiform precipitation across central Illinois. In the wake of the departing warm conveyor belt, brisk and breezy conditions will persist through the daylight hours as a stacked 998 mb surface low occludes and meanders across the upper Great Lakes. A tight cyclonic surface pressure gradient will support sustained southwest-to-west winds around 15 to 20 mph with gusts near 30 mph.

Despite the lack of deep-layer saturation, regional RAP forecast soundings indicate a resilient stratus deck trapped beneath a steep subsidence inversion, maintaining ample low- level (0-1.5 km) moisture through this evening. Weak, sporadic periods of upward omega within this boundary layer will support patchy drizzle and occasional mist across the CWA. Have maintained patchy drizzle in the gridded forecast through tonight as a result.

By Thursday, attention turns to a potent 500 mb shortwave trough digging equatorward out of Ontario and into the Great Lakes basin. As this vorticity maxima phases with the broader cyclonic gyre, the lingering, slow-moving surface low will pivot its associated wrap-around moisture plume and deformation axis back southwestward across central and eastern Illinois. This will reinforce overcast skies and yield scattered to periodic light rain showers, primarily east of the I-55 corridor.

Thursday night, a sharpening baroclinic zone and attendant cold frontal boundary will advance southward across the state. In its wake, strong cold air advection will usher in a significantly cooler, drier continental polar (cP) air mass to close out the workweek.

Long Term...Friday through Tuesday

Deep-layer northwesterly flow behind the departing trough will quickly scour remaining low-level moisture by Friday morning. A sprawling 1028 mb surface high centered over the Canadian Prairies will build southeastward into the Midwest for the weekend, setting the stage for a prolonged stretch of quiet autumn weather.

Thermal profiles will start out chilly by Friday morning, with 850 mb temperatures bottoming out near -2C to 0C. Weekend sensible weather will feature crisp daytime highs generally in the low-to-mid 50s under mostly sunny skies. Efficient nocturnal radiational cooling--aided by slackening winds and a clear, dry boundary layer--will promote widespread frosty conditions, with overnight lows dipping into the 30s across the area. Agricultural and late-season gardening interests should anticipate widespread frost/freeze potential Friday night and Saturday night.

Heading into next week, ensemble consensus (GEFS/EPS) remains in strong agreement regarding an amplified synoptic pattern featuring persistent mid/upper-level ridging over the central CONUS, flanked by an anomalous cut-off low meandering across the Deep South/Gulf Coast region. This blocking configuration will effectively shut off poleward transport of Gulf moisture, locking dry and tranquil conditions in place through mid-week. Under continuous air mass modification and rising 500 mb heights, temperatures will gradually trend warmer, returning into the 60s from Monday onward.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 516 AM CST Wed Nov 4 2026

MVFR conditions will be most common throughout this TAF period, though occasional periods of IFR are also forecast, as a large frontal system loiters. Blustery southwest winds will persist, occasionally gusting between 20-25 kts today before diminishing this evening.

ILX WATCHES/WARNINGS/ADVISORIES

None.