textproduct: Central Illinois

KEY MESSAGES

- Scattered rain showers across central and southeast Illinois will diminish late this afternoon.

- Unseasonably warm conditions return Saturday through Tuesday, sending afternoon temperatures into the upper 80s and lower 90s.

DISCUSSION

Issued at 1240 PM CDT Thu Sep 10 2026

A shortwave trough and associated frontal boundary currently traversing the area has brought widespread rain showers to central and southeast Illinois through midday. Synoptic scale ascent has weakened over the past few hours and this trend is expected to continue, causing the showers to scatter out and eventually diminish by early evening over southeast IL.

Sinking motion and surface high pressure building across the Great Lakes will promote clearing skies tonight and Friday morning. High temperatures on Friday rebound into the lower to mid 80s as broad southeasterly flow resumes.

Two low chances of rain develop for late Friday through Sunday. The first is associated with a weak upper wave passing to our south, which could spread scattered showers as far north as southeast to east central IL Friday afternoon and Friday night. Separately, a frontal boundary over the upper Midwest makes some progress southeast on Saturday night into Sunday, and this brings low chance PoPs into the western CWA.

High confidence resides in a substantial warming trend Saturday through Tuesday (Sep 12-15). An upper-level ridge amplifies across the central to eastern CONUS, supported by strong agreement between deterministic and ensemble mean guidance. NBM blended guidance projects daily high temperatures climbing into the upper 80s to lower 90s through this period. The ECMWF Extreme Forecast Index (EFI) highlights maximum temperature values ranging from 0.70 to 0.85 across central Illinois, indicating climatologically unusual warmth for mid- September. Guidance supports dew points generally in the 60s though this stretch, which would keep daily peak heat indices below 100 degrees.

The next chance for appreciable rain holds off until some point next week when the next cold front moves into the Midwest. The guidance envelope shows a large spread in timing, which is expected as the system is moving into a strong ridge. As a result, NBM's chance to likely PoPs stretch through Mon-Thu. ML/AI severe outlook produce show a low (5%) risk area centered around Tuesday.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 618 PM CDT Thu Sep 10 2026

Low and mid-level clouds will quickly lift and break after sunset, but only for a brief time. By 06z, or just after, a strong signal for dense fog develops across west central Illinois and builds eastward toward the KSPI/KPIA/KDEC terminals. In the process, occasional LIFR conditions are forecast overnight into Thursday morning across these TAF sites. Model guidance is then steadfast in the fog mixing away by about 13z. Further east at KBMI/KCMI, fog may be more patchy and transient, and have therefore went less aggressive on visibility reductions.

ILX WATCHES/WARNINGS/ADVISORIES

None.