textproduct: Central Illinois

KEY MESSAGES

- There is a high (50-80%) chance for temperatures to fall below freezing overnight into Tuesday morning in areas roughly north of a Paris to Peoria line. Tender, early-season vegetation will need to be covered to prevent damage.

- An upper disturbance will produce a band of light rain and snow along and south of a Macomb to Decatur to Mattoon line overnight into early Tuesday morning. There is currently a very low (less than 20%) chance of exceeding 1 inch of snow.

- Warmer and wetter conditions return by the back half of the week, though the severe weather potential appears to be delayed until late this weekend or early next week.

DISCUSSION

Issued at 251 PM CDT Mon Apr 6 2026

The primary near-term concern is the potential for freezing temperatures tonight into Tuesday morning. This forecast has been complicated by a developing mesoscale snowfall event stretching from the central Plains to the Mid-Mississippi Valley. A band of frontogenesis (850-700 mb layer) is sharpening from Omaha, Nebraska to Quincy, Illinois, as a mid-level shortwave trough exits the Great Lakes and strong surface high pressure builds in.

Although the heaviest snow and precipitation are expected south and west of our area, the associated broad cloud cover is sufficient to increase tonights minimum temperature forecast by one or two degrees.

Despite this, the latest guidance from the HREF and NBM still indicates a high probability (50-80%) of sub-freezing temperatures overnight along and north of a line from Paris to Peoria, with probabilities decreasing significantly to the south. Based on these high probabilities in the noted guidance, the Freeze Watch has been upgraded to a Freeze Warning. Widespread frost, however, is expected to be prevented by the extensive cloud cover and just enough wind to mix the near- surface air.

Scattered rain and snow showers may gradually lift northward across the forecast area through Tuesday morning as the sharp baroclinic zone loses its punch and begins to lift northward as a pseudo warm front. Seasonably cool temperatures are expected through Tuesday afternoon, remaining in the mid-to-upper 40s across the entire area, according to consistent guidance. A notable warm-up is anticipated on Wednesday, with temperatures reaching the lower 70s, propelled by gusty southerly winds of 20-30 mph.

Unsettled weather is expected from Wednesday night through next weekend as a vigorous mid-level shortwave trough moves across Lake Superior. This system will be accompanied by a cold front that will gradually sag southward into central Illinois, effectively becoming a diffuse stationary boundary. This boundary is expected to be the focus for multiple rounds of rainfall throughout the latter half of the week. However, the chances for thunder, and subsequently for convectively-enhanced rainfall, will be somewhat limited due to poor thermodynamics near the stalled front. As a result, the probability for QPF to exceed one inch west of Interstate 55 remains low, between 20-40%, through Saturday night.

The potential for thunderstorms increases significantly beginning Sunday evening and continues through the middle of next week. This is due to a return of strong southwest flow across the Plains states, which will draw a considerable surge of Gulf moisture northward into the Mid-Mississippi Valley.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1246 PM CDT Mon Apr 6 2026

Northwest winds will gradually veer east through this TAF period as surface high pressure builds into the Great Lakes region overnight. Despite increasing cloudiness tonight developing in the vicinity of a strengthening baroclinic/frontal zone, ceilings are largely anticipated to remain VFR through the period. There could be a brief exception between 07z-15z areawide where short term models support a low (20-40%) chance of lowering into MVFR.

ILX WATCHES/WARNINGS/ADVISORIES

Freeze Warning from 1 AM to 9 AM CDT Tuesday for ILZ029-031- 037-038-043>046-055-057.