textproduct: Central Illinois

KEY MESSAGES

- No significant weather is expected across central Illinois over the next week.

DISCUSSION

Issued at 239 AM CDT Wed Sep 23 2026

07z/2am surface analysis shows a sprawling ridge of high pressure extending from Quebec southwestward into the mid-Mississippi River Valley. Despite synoptic subsidence beneath the ridge and dry northeasterly flow from the Great Lakes, ample boundary layer moisture remains trapped beneath an inversion. While skies partially cleared yesterday afternoon, the low overcast has returned everywhere along/east of a Peoria to Springfield line early this morning. While the westward advance of the cloud shield has slowed somewhat over the past hour or two, think overcast conditions will exist across the entire KILX CWA by sunrise. Forecast soundings strongly suggest the low-level moisture will remain locked in place today: however, the RRFS sky forecast once again offers hope for some partial sunshine this afternoon...particularly along/west of the I-55 corridor. Given cloud cover and a cool NE breeze, high temperatures will remain below normal for this time of year in the upper 60s to around 70 degrees. Any partial clearing that occurs will vanish by tonight as low clouds once again spread and/or develop westward across the area after dark.

The upper air pattern currently features a weak Rex Block with a high over southern Canada and a low across central Illinois into the Ohio River Valley. Models continue to show the block gradually shifting eastward and breaking down as the low deepens over the Mid-Atlantic region. With an increasingly strong upper low to the east essentially blocking the progress of any systems across the central/eastern CONUS, a narrow upper ridge will form over the Midwest and remain in place through early next week. Despite the presence of the ridge, cloud cover will be slow to clear from central Illinois as boundary layer flow remains E/NE into the weekend. Am therefore expecting mostly cloudy skies again on Thursday before partial sunshine finally returns by Friday.

A short-wave trough crossing the Rockies into the Plains will run into the blocking pattern and come to a halt over the weekend. This system will come close enough to cause an increase in cloud cover and perhaps some light showers west of the I-55 corridor Saturday/Sunday. All models eventually weaken the wave as the narrow ridge axis holds firm. As a result, any rain chances across the western KILX CWA will come to an end by Sunday afternoon/Monday as temperatures climb back to seasonal normals in the middle to upper 70s. After that, the Mid-Atlantic upper low is progged to weaken and eject northeastward as a prominent trough swings across the Plains by early next week. As this wave and its associated cold front approach, boundary layer flow will become S/SW and temps will soar into the 80s by next Tuesday. The next significant chance for precipitation will arrive with the front, which is currently projected to push into central Illinois Tuesday night into Wednesday.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 542 AM CDT Wed Sep 23 2026

10z/5am satellite imagery/local obs reveal MVFR ceilings along/south of a KAAA to KCMI line. Further north, drier boundary layer advecting into the area from the Great Lakes has resulted in VFR ceilings at both KPIA and KBMI early this morning. Based on satellite trends and the latest HRRR/CONSSHORT, it appears the low overcast will scatter and/or lift to VFR at KSPI by around 16z...but should remain MVFR further east at KDEC/KCMI through the remainder of the 12z TAF period. Models are consistently showing the low clouds re-developing and spreading back westward later today into tonight, resulting in a return to MVFR at KBMI by 17z, at KPIA by 23z, and at KSPI by 00z. Winds will be NE at 10-15kt.

ILX WATCHES/WARNINGS/ADVISORIES

None.