textproduct: Central Illinois

KEY MESSAGES

- Light snow is possible (20% chance) late tonight through Tuesday morning, primarily near the I-74 and I-70 corridors. Any accumulations will be very minor, with a 20 to 40% chance of a half-inch of snow east of I-57.

- Mild temperatures return late this week. There is over 80% probability of temperatures rising above freezing west of I-55 Thursday and over 90% probability across the entire Friday.

DISCUSSION

Issued at 104 PM CST Mon Feb 2 2026

Quiet weather is expected for the remainder of today and tonight as Central Illinois finds itself within a low-level col area, and within general subsidence beneath an area of strong mid-level height rises.

Our focus shifts late tonight into Tuesday morning as a shortwave trough currently over the Dakotas causes a subtle buckle in the mid-level ridge. A couple of regional models (NAM/GEM) are hinting at a corridor of strong mid-level frontogenesis translating southeast near/along the I-74 corridor. NAM forecast soundings, however, reveal that the strongest forcing will initially be spent on saturating the very dry low and mid-levels of the atmosphere, with forcing weakening considerably by the time the column supports snow reaching the surface. Given the inconsistencies between the regional and global models and the concern over the extremely dry antecedent airmass, we will maintain only low-end PoPs (20%) north of I-74 tonight associated with this feature.

Further south, near the I-70 corridor, mid-level warm air advection (WAA) will increase late tonight ahead of the approaching shortwave, followed by peak positive differential cyclonic vorticity advection (dCVA) during the Tuesday morning and early afternoon hours. Similar concerns exist regarding the dry air across the southeastern counties. However, forcing is expected to persist a few hours longer once saturation is achieved, which should allow for some very minor accumulations. The NBM probability for 1 inch of snow is low (10-20%) east of I-57, with a slightly higher 20 to 40 percent chance of at least a half-inch of snow.

A broad 1030mb high pressure system centered over the northern Great Plains and Upper Midwest Tuesday evening will slowly inch toward and across Central Illinois Wednesday and Thursday. This will keep the weather dry but initially colder, with highs only in the 20s Wednesday. Overnight lows will drop into the single digits or low teens Wednesday morning and Wednesday night.

Looking beyond midweek, a significant downsloping event is forecast to develop lee of the northern Rockies, with 850mb temperatures warming substantially to 10-15C across Alberta and Montana. This much warmer airmass will translate southeast and clip portions of Central Illinois starting Thursday into early Friday ahead of an approaching cold front. Widespread temperatures above the freezing mark are expected (NBM 80-95% probability) west of I-55 Thursday, becoming areawide (NBM >90% probability) early Friday before the front pushes through. The downsloping effect will not only produce warmer temperatures but also an extremely dry airmass, keeping the probability of any precipitation with the frontal passage quite low (10%). Non- diurnal temperature trends will be possible if the front moves through early during the day Friday.

Deubelbeiss

AVIATION

(For the 00z TAFs through 00z Tuesday Evening) Issued at 505 PM CST Mon Feb 2 2026

A narrow corridor of MVFR ceilings is expected to persist a good portion of the evening across central Illinois, most concentrated from KSPI-KCMI. After that, ceilings of 5-8kft should be common overnight through much of Tuesday. Winds will quickly turn north/northeast this evening, and will be close to 10 knots late Tuesday morning into the afternoon.

Geelhart

ILX WATCHES/WARNINGS/ADVISORIES

None.