textproduct: Central Illinois

KEY MESSAGES

- Mild conditions are forecast during the work week with daily highs generally in the 50s. Seasonably cool weather will return this weekend, with a 40-60% chance of high temperatures below freezing by Sunday.

- Beneficial rain is forecast (70-90% chance) Thursday into Friday. Chances for more than a half inch of rainfall are as high as 60-70% in east-central IL, where the ongoing drought is most severe.

DISCUSSION

Issued at 149 AM CST Mon Jan 5 2026

***** CLOUDY BUT MILD THROUGH TOMORROW *****

Early Monday morning, 10-15 mph south-southwest winds were holding temperatures in the low to mid 30s across central and southeast IL as a surface low passes to our north in Wisconsin and Lower Michigan. Already, scattered high clouds are returning on westerlies streaming off the Pacific, though these shouldn't have too big an impact on highs today which, thanks to ridging expanding into the region, should climb into the upper 40s to low 50s. Energy emanating from the Four Corners Region will result in a lee cyclone which will meander into northern IL tonight into tomorrow morning. This will keep temperatures mild tonight, but may also result in some patchy fog or drizzle. In general, guidance has backed off on the drizzle potential for our area, though, as moisture convergence with the low is to our north, wrap around moisture is to our west, and warm advection lift is focused to our east. In any case, HREF suggests medium-high confidence (60-80% chances) low clouds will stick around through the day tomorrow north of I-70 where temperatures may run a bit cooler (upper 40s, vs upper 50s to around 60 south of I-70) and west winds will gust to 20+ mph.

***** RAIN LIKELY (70-90% CHANCE) LATE WEEK *****

Conditions are forecast to remain mild through at least Thursday, after which time ridging will begin to shift east as a more potent upper level trough approaches. Global models and their respective ensembles continue to differ in the evolution and track of a surface low developing in the left exit region of a 90+ kt 500mb jet streak, however the trend has been a bit slower and further west; this is reflected in NBM's maxT forecast for Friday, which climbed 4-7 degrees (highest in our southeast) from its last cycle. As a consequence, rain chances have come up considerably over our area, with two possible waves: one Thursday into Thursday night, and another with the main trough/cold front Friday into Friday night. Between these two waves, raw ensemble guidance (LREF) gives 60-70% chances for more than a half inch of rainfall over east-central and southeast IL, with those probabilities tapering to 30-50% west of roughly I-55; chances for over an inch are generally 20-35% east of I-55, highest in southeast IL where instability is most likely to be high enough for some thunderstorms. On the topic, uncertainty remains high in whether a severe weather risk will materialize over us, with two perplexing factors: (1) the possible development of a forerunning shortwave Thursday (night), which could leave our area less warm and unstable going into Friday; and (2) the slower, further west surface low on Friday, which could bring the triple point through a portion of our area - increasing the risk for severe storms. At this point, it wouldn't be surprising to get locally severe hail with elevated storms along the warm front with either wave, but if we destabilize more than currently forecast ahead of the surface low on Friday, all hazards would be plausible; based on various ML forecasts and ensemble surface low tracks, that outcome seems most likely (5-15% chance) southeast of a roughly Shelbyville to Danville line, but again lots is subject to change between now and then. Stay tuned.

***** TURNING SEASONABLY COOL AGAIN THIS WEEKEND *****

Behind the cold front, conditions will turn seasonably breezy then cooler Saturday into Sunday. NBM suggests a 40-50% chance of high temperatures in the 20s on Sunday. In addition, about 15-30% (highest north) of LREF guidance is advertising measurable snow from wrap around moisture Saturday evening-night, though fortunately only a couple members (out of 100) are showing accumulations higher than an inch as a drier airmass gets pulled southeast into our area.

Bumgardner

AVIATION

(For the 12z TAFs through 12z Tuesday Morning) Issued at 541 AM CST Mon Jan 5 2026

South-southwesterly winds around 10 kt will back and blow from the southeast ahead of an approaching low pressure system this evening. When that system arrives early Tuesday morning, expect deteriorating visibilities and especially ceilings, with perhaps some periods of drizzle by the end of the forecast period. At that time, HREF suggests a medium-high (50-80%) chance of MVFR ceilings, with increasing probabilities of IFR ceilings after 12z.

There is a low (10-20%) chance that the MVFR ceilings sinking southward across southern Wisconsin early this morning will reach the northern airfields (PIA, BMI) by lunchtime, but thinking is that the southerly winds will keep that further north, near I-80, with chances too low to warrant even a prob30 group at this juncture.

Bumgardner

ILX WATCHES/WARNINGS/ADVISORIES

None.