textproduct: Central Illinois

KEY MESSAGES

- Dry conditions and tranquil weather prevail across central and southeast Illinois through this weekend.

- Above normal temperatures will dominate the region, with afternoon highs climbing into the mid to upper 70s.

DISCUSSION

Issued at 1233 PM CDT Tue Oct 20 2026

Expansive surface high pressure centered south of James Bay extends southwest into the mid and lower Mississippi Valley this afternoon. Broad subsidence and very dry air below 500 mb will lead to clear skies through tonight. High temperatures to peak in the lower 70s today, followed by overnight lows in the mid 40s.

A moderating trend begins Wednesday and continues through this weekend as upper level ridging amplifies overhead. Suite of model guidance indicates 850 hPa temperatures warming to +11C to +13C through this period. Afternoon mix-down of this air will lead to daily highs in the mid 70s through Friday, then upper 70s to around 80F this weekend when southwest low level flow becomes better established. Forecast soundings show daytime boundary layer mixing reducing afternoon dewpoints into the 40s, yielding minimum relative humidity values between 30 and 40 percent. Normally in late October this would result in an enhanced risk of fire spread, but a weak MSLP gradient will promote light winds under 10 mph through Friday.

A transition in the upper air pattern begins Monday into Tuesday as a potent upper-level trough traverses the northern Plains and lifts toward the Upper Midwest. The ECMWF-AI and operational ECMWF-Ens have remained consistent with a slightly slower frontal passage than the GEFS members, bringing the attendant cold front into western Illinois Monday evening and clearing southeast Illinois Tuesday afternoon. The NBM introduces slight chance PoPs (15 percent) west of the Illinois River Monday afternoon. With a lack of upper level support and projected dry airmass, models generally show a dry frontal passage for the remainder of the CWA.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 602 PM CDT Tue Oct 20 2026

VFR conditions continue. High pressure will keep winds light and somewhat variable the next 24 hours.

ILX WATCHES/WARNINGS/ADVISORIES

None.