textproduct: Central Illinois

KEY MESSAGES

- Scattered showers and a few thunderstorms will diminish south of I-70 through early evening.

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

DISCUSSION

Issued at 338 PM CDT Wed May 27 2026

Scattered showers and isolated thunderstorms south of a Paris to Shelbyville to Litchfield line were along and ahead of a weak surface boundary near I-70. This boundary and its associated convection to gradually push SE the next few hours, exiting far southeast IL during early evening/by sunset. Scattered to broken low/mid clouds from I-72 south will decrease from NW to SE into this evening. Latest CAMs show patchy fog (locally dense) developing in southeast IL during overnight and lifting by mid Thu morning. Lows overnight in the lower 60s. Warm highs Thu in the low to mid 80s with stronger NE winds behind the cold front bringing drier air into areas from I-72 north Thu afternoon as dewpoints slip into the low to mid 50s by late Thu afternoon.

Elevated ozone levels in the Chicago metro area will gradually advect slowly southwest toward central Illinois this afternoon with northeast flow, but mostly stay northeast of I-74. The Illinois Environmental Protection Agency indicates air quality will become unhealthy for sensitive groups northeast of I-74. A weak cold front currently over northeast IL will drop southwest toward central IL overnight into Thursday morning, resulting in increasing northeast winds which should help disperse the ozone and increase air quality by Thursday.

An omega block will develop across the country with deep upper lows along the western U.S. and over New England, and a persistent upper level ridge in between them over the Midwest including Illinois. This will keep any approaching shortwaves shunted S/SW of central Illinois through at least early next work week, along with deeper Gulf moisture south of IL. Therefore dry conditions should prevail over central/SE IL tonight through next Wednesday, with seasonable high temperatures ranging from the upper 70s to mid 80s (warmest temperatures over the Illinois River Valley).

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1230 PM CDT Wed May 27 2026

Aside from brief periods of MVFR ceilings at DEC and CMI til 20Z/3 pm, expect VFR conditions to prevail across the central IL airports through 18Z/1 pm Thu. Isolated showers and thunderstorms to be south of I-72 and push se through southeast IL during this afternoon. Scattered to broken cumulus clouds with MVFR ceilings 2-3k ft near DEC and CMI and se to push se of these taf sites next few hours. NE winds 5-10 kts to prevail this afternoon and be a bit lighter tonight and increase to 8-13 kts on Thu morning.

ILX WATCHES/WARNINGS/ADVISORIES

None.