textproduct: Central Illinois

KEY MESSAGES

- Substantial warming occurs Thursday through Sunday, with well above normal temperatures through this period.

- A cold front arrives Sunday, bringing a low chance for rain, followed by a return to cooler, near-normal temperatures early next week.

DISCUSSION

Issued at 112 PM CDT Wed Mar 18 2026

A shortwave passing well north of the region late tonight into Thursday morning will cause a ribbon of moisture increase between 700mb and 500mb, though the sub- cloud layer remains dry. Due to the dry air, light rain is forecast to stay northeast of the local area, with an increase in high to mid level clouds noted over central IL. A period of light winds sets up across the region tonight through much of Thursday as the MSLP gradient briefly relaxes. After morning clouds clear out Thu, PM sun should help to get highs into the 60s.

On Friday, the region enters a period of strong warm air advection on gusty southwesterly wind gusts ahead of the next dry frontal passage. The NBM indicates highs reaching the mid-70s, which is approximately 20 degrees above the climatological normal for mid- March. Unseasonable warmth continues on Saturday, which at this point appears to be the warmest of this stretch. The ECMWF Extreme Forecast Index (EFI) shows values of 0.8 for maximum temperatures, signaling a highly unusual event in a climatological context. Highs around 80F are forecast for the southwest CWA, which would be a few degrees shy of records.

Medium range guidance continues to show a cold frontal passage on Sunday, though timing and moisture return ahead of the front show a range in solutions, which will have a significant impact on the forecast. The faster solutions (ECMWF/GEM), which would limit the window for instability and bring in cold advection by Sunday afternoon. Conversely, the GFS and its ensemble solutions with a slower frontal passage allow dewpoints to surge into the 50s ahead of the front. If the slower solution verifies, a low risk for severe weather could develop as far west as eastern IL Sunday afternoon as CAPE values approach 500 J/kg below increasing deep layer shear. This is noted in a few ML/AI severe outlooks with low SVR probs over eastern IL. Latest NBM only shows 20% PoPs over southeast IL Sunday afternoon.

Behind the front, a period of cold advection will likely drive temperatures a few degrees below normal early next week before moderating again.

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AVIATION

(For the 18z TAFs through 18z Thursday Afternoon) Issued at 1209 PM CDT Wed Mar 18 2026

VFR through the forecast with an increase in high clouds tonight. Southwest winds will be highest east of I-55 this afternoon, gusting 20+ kt at times for KDEC-KCMI. Winds will decrease by early evening with light/variable winds for much of the overnight.

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ILX WATCHES/WARNINGS/ADVISORIES

None.