textproduct: Central Illinois

KEY MESSAGES

- Slow-moving showers are likely south of I-72/Danville (40-70% chance) tonight into Wednesday morning. A narrow, localized corridor of heavy rain is possible (10-30% chance of over 1").

- Air quality may become unhealthy for sensitive groups across portions of central Illinois on Wednesday due to ozone concentrations.

- Precipitation chances are low (less than 15%) Wednesday night through the weekend.

DISCUSSION

Issued at 231 PM CDT Tue May 26 2026

Forecast largely remains on track, with a mostly quiet forecast into this weekend aside from rain chances during the next 24 hours. A weak upper level disturbance continues to lift out of the southern Plains, just north of the ArkLaxTex per latest IR satellite imagery. Regional radar and sfc obs show light rain extending as far north as areas just south of I-70, but precip coverage is much greater over southern MO. These light showers may gradually expand northward in the coming hours, but a more concentrated chance for showers seems to be tied to a low-level FGEN band that pivots northward into the ILX CWA after 06z/1am Wed. There is still some uncertainty in the exact placement of this narrow band, but CAMs generally focus it somewhere between a Shelbyville to Paris line and the I-70 corridor. With forecast PWAT values around 1.75" and weak cloud layer winds resulting in slow-moving showers, there could be some very localized pockets of 1-3" of rain. Due to high-res model differences in the exact placement, the ensemble probability of exceeding 1" came in at just 10-30% south of that aforementioned Shelbyville to Paris line. CAMs also trended slower on the departure of that wave, so kept the rain chances lingering across SE IL through Wed afternoon.

The upper levels will feature a blocking pattern, with a cut-off low over the SW US and a building ridging over the central Plains and portions of the Midwest. A sfc high shifts south towards the Great Lakes tomorrow, sending a backdoor cold front into IL. As this front advects air from Chicagoland towards central IL, the IL EPA has indicated that air quality may temporarily become unhealthy for sensitive groups owing to ozone concentrations. These potential air quality impacts are not expected to persist beyond Wednesday.

Sfc high pressure over the Great Lakes will remain a dominant feature into the weekend. Precip chances are expected to stay south and west of the ILX CWA, with persistent northeasterly flow favoring drier than normal conditions in the low-levels (dewpoints in the low to mid 50s Friday into the weekend). Winds will generally be on the light side as well (gusts less than 20 mph), which stymies any concerns about blowing dust or fire danger. Forecast highs remain in the upper 70s to mid 80s through the end of May, and given this pattern the severe thunderstorm potential is very low locally into early June.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 550 PM CDT Tue May 26 2026

Main concern is -SHRA and MVFR ceilings over southern IL that are forecast to expand north across east central IL later tonight. Most of the high-resolution guidance keeps this just southeast of KDEC-KCMI, but it will be a close call so kept PROB30 mention from 09-14z. Otherwise, SCT-BKN high clouds will affect the region through Wed afternoon. Light SE winds will back NE late tonight and Wed morning as a cool front moves through from the northeast. A brief period of 10-18 kt gusts is possible immediately behind the front, but winds should generally be under 10 kt through the forecast.

ILX WATCHES/WARNINGS/ADVISORIES

None.