textproduct: Central Illinois

KEY MESSAGES

- Sunny mild days and cool nights persist across central and southeast Illinois through Sunday, with highs in the mid- upper 70s and lows in the 40s.

- A cold front moves across the region early next week, bringing prospects for light rain, followed by cooler temperatures.

DISCUSSION

Issued at 1211 PM CDT Wed Oct 21 2026

Surface ridge axis centered across the area provides quiet, clear conditions across central and southeast Illinois. Dry air and subsidence will continue to produce mainly clear skies and large diurnal temperature swings over the next several days.

Mid-level heights build across the Mississippi Valley Friday and this weekend as the surface high slips farther east. Models show strong consensus on establishing persistent southerly return flow. 850-hPa temperatures in the lower teens C, along with deeper mixing support afternoon highs around 80F on Sunday, around 15 degrees above climatological averages.

Medium-range deterministic solutions (ECMWF, ECMWF-AI, and GFS) and the ensemble suite diverge early next week regarding the progression of an upstream longwave trough and associated surface cold front. The deterministic GFS exhibits a faster frontal transit across central Illinois Monday evening with stronger pre-frontal 850-hPa flow (4050 kt). Conversely, the ECMWF and ECMWF-AI are roughly 6 to 12 hours slower, maintaining a broader frontal structure and tracking the primary boundary through the forecast area Tuesday. GEFS and ECMWF ensemble members favor this slower progression. Latest NBM run has lowered PoPs below mentionable levels, but this will likely change as the system develops. Behind the front, a shot of cooler air will move in, returning temperatures to more seasonable levels Tue-Wed.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1211 PM CDT Wed Oct 21 2026

Another cycle of VFR conditions and light/variable winds with high pressure in control.

ILX WATCHES/WARNINGS/ADVISORIES

None.