textproduct: Central Illinois

KEY MESSAGES

- Showers and a few thunderstorms will persist south of I-72 today...with a narrow corridor from Paris to Shelbyville potentially picking up greater than 1 inch of rainfall.

- Air quality will become unhealthy for sensitive groups across portions of central Illinois today due to high ozone concentrations.

- No major storm systems are expected to impact the region over the next week. As a result, the severe weather risk will remain very low (less than a 5% chance) through next Tuesday.

DISCUSSION

Issued at 338 AM CDT Wed May 27 2026

*** Showers South of I-72 Today ***

08z/3am radar imagery shows a band of showers and thunderstorms extending from near Paris to Shelbyville. This activity has been lifting slowly northward over the past couple of hours, but is losing some of its momentum as the short-wave trough that triggered it pivots northeastward into Indiana. In addition, the showers will be encountering a considerably drier/more subsident airmass north of the I-72 corridor where current dewpoints are only in the 50s. CAMs seem to have a good handle on the band and suggest it will eventually stall and begin to dissipate near or just south of a Danville to Decatur line by daybreak. After a lull in precip chances by mid to late morning, additional showers and storms will develop across the same area this afternoon before gradually dropping southeastward and exiting into the Ohio River Valley by early evening. While not all locations across east-central and southeast Illinois will see rainfall, a favored corridor from Paris to Shelbyville may see amounts over 1 inch. Meanwhile north of I-72, conditions will remain dry. High temperatures will range from the upper 70s near I-70...to the upper 80s along/northwest of the Illinois River.

*** Poor Air Quality Today ***

Elevated ozone levels in the Chicago area will gradually advect into central Illinois today due to weak northeasterly flow around high pressure over the Upper Midwest. The Illinois Environmental Protection Agency (EPA) indicates air quality will become unhealthy for sensitive groups along/north of I-74. A weak cold front currently over Wisconsin will drop southward through the region tonight, resulting in increasing northeasterly winds which should help disperse the ozone and improve air quality by Thursday.

*** Prolonged Stretch of Quiet Weather ***

An Omega Block will develop across the CONUS...featuring deep upper lows along the West Coast and over New England and a persistent ridge sandwiched between them over the Midwest. This will ensure any approaching short-waves will be shunted S/SW of central Illinois through at least early next week. As a result, am expecting dry conditions Thursday through next next Tuesday with seasonable high temperatures ranging from the upper 70s to the middle 80s.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1222 AM CDT Wed May 27 2026

Primary focus is on the potential for MVFR ceilings and light rain for the corridor from DEC to CMI early this morning. Radar and satellite loops are indicating a northward progression to a area of showers and MVFR clouds along the I-70 corridor. The consensus of solutions from the latest high resolution guidance continue to support DEC and to a lesser extent CMI getting into those conditions. The main changes with this update were to limit CMI rain/MVFR period to just 10-12z, removing the 09z-12z prob30 group. DEC timing was left intact, with MVFR conditions possible from 09z to 14z. Otherwise, SCT-BKN high clouds will affect the region this afternoon and into evening. Any remaining light SE winds will back NE by sunrise this 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.