textproduct: Central Illinois

KEY MESSAGES

- Strong southerly winds will gust between 30 and 40 mph Tuesday afternoon across central Illinois.

- Widespread rainfall will overspread the region Tuesday evening, with a 50 to 70% chance of rainfall exceeding 1 inch by Wednesday morning.

- An isolated severe storm is possible Tuesday evening primarily south of Interstate 72; sporadic damaging winds are the main threat, though an isolated tornado cannot be completely ruled out.

DISCUSSION

Issued at 321 AM CST Mon Nov 2 2026

/Synoptic Overview and Short Term (Today - Tonight)/

Early morning mid-level water vapor imagery depicts a deep trough carving across the Intermountain West, with lee cyclogenesis well underway. Strong cross-barrier flow and pronounced downslope warming, coupled with vertical vortex stretching east of the Rockies, have sharply tightened the geopotential height gradient and driven rapid mass evacuation across the High Plains. Surface analysis reflects this dynamic response, revealing a deepening 996 mb surface low centered over eastern Colorado with a trailing cold front draped across the Texas Panhandle, where nocturnal, severe convection remains ongoing.

The tightening mass gradient and steep isallobaric falls over eastern Colorado continue to sustain an accelerating 45-55 kt southerly low-level jet rooted off the western Gulf. This robust low-level mass response is driving strong warm and moist isentropic ascent downstream across the Plains and Midwest. In tandem with subtle shortwave impulses ejecting ahead of the parent trough, this forcing mechanism is supporting scattered warm-advection showers across the Plains. Further east into the Midwest, including central Illinois, patchy drizzle persists where moisture remains trapped in a shallow, supercooled boundary layer that currently lacks sufficient cloud ice nuclei.

/Tuesday: Dynamic System, Heavy Rain, and Severe Potential/

Numerical guidance exhibits high confidence regarding the splitting of the synoptic trough this evening. The northern branch of energy will progress across the Northern Plains while the southern stream temporarily detaches over the Southern Plains. By Tuesday, these features will consolidate into a complex, double-barrel surface cyclone moving across the central U.S., driving a vigorous mass response throughout the Mississippi Valley.

In advance of the approaching cold front on Tuesday afternoon, a tightening low-level pressure gradient will produce widespread wind gusts of 30 to 40 mph across the warm sector. Robust poleward moisture transport will pull an expansive Gulf airmass northward, driving surface temperatures into the mid-70s. Immediately along and ahead of the boundary, precipitable water (PWAT) values will climb toward 1.75 inches--nearing the 99th percentile for early November local climatology and signaling a highly efficient precipitation environment.

As the bifurcated upper troughs recombine and force the cold front eastward, widespread rainfall will overspread central Illinois Tuesday evening. NBM guidance indicates a 5070% chance of totals reaching at least 1 inch by 6 AM Wednesday, with 90th percentile suggesting localized amounts over 2 inches in training convection.

A few severe storms cannot be ruled out Tuesday evening, focused primarily south of the Interstate 72 corridor. Dynamic and kinematic fields will be exceptionally robust, characterized by 40 to 50 kts of effective bulk shear. Although model-derived thermodynamics remain modest (MLCAPE < 350 J/kg), a narrow tongue of 60+ degree surface dewpoints is forecast to surge northward ahead of the boundary. Given the high-shear/low-CAPE parameter space, isolated strong to severe storms capable of producing sporadic damaging downdrafts remain the primary concern within any sustained linear segments. However, low-level hodographs exhibit notable clockwise curvature, maintaining a conditional tornado threat should enough low-level buoyancy materialize to promote vertical vortex stretching.

/Wednesday - Thursday: Lingering Gusts and Showers/

Dry slotting will bring an end to the widespread heavy precipitation early Wednesday. However, brisk and breezy conditions will linger as the primary surface cyclone occludes and meanders across the upper Great Lakes. By Thursday, as the parent upper low spins eastward, its associated deformation axis and wrap-around cyclonic moisture will rotate back across central and eastern Illinois, yielding periodic light rain showers.

/Friday - Sunday: Brief Weekend Reprieve Preceding Next System/

Shortwave ridging will expand across the Upper Mississippi Valley and western Great Lakes on Friday and Saturday, shunting the deep trough into New England and providing a dry, mild interlude. Quiet weather will be relatively short-lived, however. Global ensembles remain in decent agreement that another fast-moving shortwave trough will dig into the Corn Belt by Sunday, reintroducing a period of damp, breezy, and unsettled weather to wrap up the weekend.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 450 AM CST Mon Nov 2 2026

A weak atmospheric disturbance rippling atop robust low-level moisture transport is contributing to patchy drizzle and widespread IFR/LIFR ceilings this morning across the central Illinois terminals.

Improvement to MVFR ceilings will be gradual and non- uniform this afternoon. More likely than not, MVFR ceilings will become more common after 00z as drier low-level air mixes in ahead of an impending cold front.

South winds will increase later this morning, occasionally gusting over 25 kts.

ILX WATCHES/WARNINGS/ADVISORIES

None.