textproduct: Central Illinois

KEY MESSAGES

- Lingering showers northwest of the Illinois River should diminish by late afternoon.

- Overall, a tranquil weather pattern will be in place through the weekend, with temperatures fairly typical for the beginning of autumn.

DISCUSSION

Issued at 100 PM CDT Tue Sep 22 2026

Fall begins in a few hours, and cooler temperatures and brisk northwest winds give it that fall feeling. With showers persisting northwest of the Illinois River early this afternoon, temperatures in that area have been confined to the upper 50s. Some breaks in the clouds over east central Illinois have allowed temperatures to reach near 70 in a few areas. Overall the high-res models have not handled this rain especially well, though the HRRR suggests it will persist for a few more hours.

Water vapor imagery shows an upper low centered just southwest of Dubuque, and this low should tighten up a bit as it drops southeast into the Ohio Valley by late Wednesday morning. Another slug of lower clouds will advect in from the east beginning this evening within the circulation, persisting through much of Wednesday. Soundings show a fairly prominent dry layer between 5-8kft, so any precipitation would probably be more in the form of drizzle or sprinkles. Best chances would be in eastern Illinois, as soundings further west have a shallower depth of moisture in the lower levels. With the persistent clouds, temperatures should be held back a bit, though some lower 70s can't be ruled out especially where some sunshine does occur.

Overall, the longer range outlook looks rather tame, as a developing nor'easter off the East Coast slows west-east progression of any storm systems through much of the weekend. Sprawling high pressure over southern Quebec, north of the storm, will keep us in an easterly flow, keeping any significant warming trend at bay through the weekend. High temperatures. It may take until early next week to fully dislodge this eastern low, at which we start getting more of a southerly wind flow. LREF probabilities of high temperatures greater than 80 degrees range from 30-60% Monday and Tuesday from west central to southeast Illinois.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 548 PM CDT Tue Sep 22 2026

Another round of MVFR ceilings currently over Indiana, is forecast to overspread the central IL terminals tonight and Wed morning. Most guidance keeps this around through afternoon, however some erosion on the western edge toward KPIA-KSPI could scatter the ceilings out later in the afternoon. Northeast winds around 10 kt will persist through the forecast.

ILX WATCHES/WARNINGS/ADVISORIES

None.