textproduct: Central Illinois

KEY MESSAGES

- Comfortable and dry weather is anticipated through Saturday, followed by the return of hot and humid conditions early next week.

DISCUSSION

Issued at 1211 PM CDT Thu Aug 27 2026

High pressure stretched north to south over the eastern Plains continues to control regional weather through Friday. HRRR and RAP model soundings display a column dominated by subsidence and dry low-level air, with surface dew points holding in the 60s. Temperatures remain seasonably mild. Highs today and Friday reach the low-mid 80s under mostly sunny skies. Surface winds will be light through Friday with the ridge axis nearby. As the high slides east toward the Mid- Atlantic on Saturday, low- level flow transitions to the south- southeast, initiating warm air advection. Afternoon highs on Saturday warm into the mid 80s, while overnight lows drop comfortably to around 60 the next couple nights.

A synoptic pattern shift occurs Sunday into early next week as an expansive 500 mb ridge amplifies over the central Plains and expands into the Midwest. High confidence exists regarding the substantial temperature surge, while lower confidence surrounds the southern extent of convective tracks riding the ridge perimeter.

Notable model disagreements emerge regarding ridge amplitude and structure as we head through the early to mid portions of next week. More amplified solutions keep the storm track to our north, anchoring the primary track of active weather across Minnesota, Wisconsin, and far northern Illinois. Meanwhile, model solutions favoring a flatter ridge would bring the southern edge of the "ring of fire" into parts of central IL. The forecast relies on the NBM, which favors the amplified solution and lower PoPs, mainly affecting the far northern CWA with slight chance levels (20% or less) through mid next week.

Thermal advection ramps up under the ridge, with 850 mb temperatures climbing near +25 C. NBM guidance projects highs reaching the lower 90s Sunday, then lower to mid 90s Monday through Wednesday. Accompanied by dew points in the upper 60s to lower 70s, peak heat index values range between 100-105 F. Climatologically, the ECMWF Extreme Forecast Index (EFI) highlights this heat wave with maximum temperature EFI values between 0.70 and 0.85 across central Illinois from Monday through Wednesday, signaling an unusually hot airmass for late August to early September. The Climate Prediction Center (CPC) 6-10 Day Outlook reinforces this trend, leaning heavily toward above- normal temperatures across the region with a 70 to 80 percent probability Sept. 1-5.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1211 PM CDT Thu Aug 27 2026

SCT-BKN diurnal cu and NNW winds under 10 kt will dominate the area this afternoon. Winds go calm to light/variable this evening with SKC. Periods of MVFR visibilities in light fog are likely early Friday morning, and have TEMPO groups to account for this.

ILX WATCHES/WARNINGS/ADVISORIES

None.