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 /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 553 AM CDT Wed May 27 2026

1030z/530am radar imagery shows a band of showers along/south of a KCMI to KDEC line. The band has become nearly stationary and is expected to gradually dissipate over the next few hours. Based on latest obs and HRRR/RAP guidance, have carried predominant showers at both KCMI and KDEC through 15z. The big question will be how low ceilings will drop at those sites as the rain falls. KCMI has occasionally dipped to MVFR: however, KDEC and KTAZ have remained VFR. HRRR ceiling forecast keeps the low clouds locked in place, then gradually shifts them E/SE by mid-morning. As a result, have opted to go with an MVFR overcast at KCMI through 15z, but keep KDEC low VFR. Once the low clouds/showers depart, skies will gradually clear from northwest to southeast across the area this afternoon. Winds will remain light from the NE at 5-10kt through the entire 12z TAF period, but may increase and become gusty at the I-74 terminals after 09z as a cold front drops southward through the region late tonight.

ILX WATCHES/WARNINGS/ADVISORIES

None.