textproduct: Central Illinois

KEY MESSAGES

- Cooler weather will prevail this week as high temperatures range from the 60s to 70s.

DISCUSSION

Issued at 144 PM CDT Mon Sep 21 2026

Water vapor imagery early this afternoon shows an upper low spinning over eastern Nebraska/western Iowa with ridging on both sides of it. At the surface, a cold/stationary front is draped from the Mid- Atlantic states westward into Arkansas with high pressure centered over Ontario. Widespread cloud cover will remain in place through at least Tuesday morning as low-level moisture remains trapped beneath a temperature inversion, holding temperatures several degrees cooler than normal.

Spotty showers/drizzle are noted on regional radar within the vicinity of the aforementioned upper low from central Iowa into northwest Illinois, and also downwind of Lake Michigan where steady northeast winds are spreading moisture inland. Similar conditions are expected to expand east through Tuesday morning as the upper low positions itself over eastern Iowa/northwest Illinois by daybreak. These should be very light in nature and amount to little accumulation. Temperatures on Tuesday will be similar to today due to widespread cloud cover/precipitation with overnight lows dropping into the low to middle 50s. Subsidence on the backside of the upper low should result in some pockets of clearing across west- central Illinois Tuesday night, potentially opening the door for a few spots to dip down into the upper 40s (20-40% chance).

By midweek, the upper low meanders into the Mid-Atlantic states with subtle ridging building in its wake. Temperatures will remain cool through the end of the week, then gradually warm back into the 70s to low 80s by the latter half of the weekend. Precipitation chances look minimal midweek through the weekend, though a developing low over the Plains states may begin to encroach on the Midwest states later this weekend.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 558 PM CDT Mon Sep 21 2026

The central IL terminals will be dominated by MVFR ceilings over the next 24 hours. There will be periods of breaks for MVFR this evening, particularly at KPIA-KBMI-KCMI as drier air temporarily works in from the northeast. Then again late Tuesday afternoon will be another period that is likely to see ceilings rise above the MVFR threshold area-wide. Northeast winds will be persistent through the forecast around 10 kt.

ILX WATCHES/WARNINGS/ADVISORIES

None.