textproduct: Central Illinois

KEY MESSAGES

- Above normal temperatures are likely to persist into mid June, with highs generally in the 80s. Humidity values are expected to increase late this week into early next week.

- Widely scattered showers and storms are possible through Monday, with the best chance (30-40%) being south of a Galesburg to Decatur to Lawrenceville line late tonight into Monday morning. Dry conditions are expected Tuesday through Thursday.

DISCUSSION

Issued at 230 PM CDT Sun May 31 2026

Scattered showers affected areas from I-55 nw today, with isolated showers lingering north of I-74 and lifting northward as they continue to diminish. A small MCS was over east central MO south of St Louis and drifting ESE toward southern tip IL and this convection should pass south of CWA into this evening as it weakens too. Another disturbance/MCS to develop over southern Iowa/northern MO tonight and track se over southern half of IL late tonight into Mon morning. The highest chances of convection appears to be over southern IL, while 30-40% pops in our southern/sw counties and slight pops northern/ne CWA. SPC Day1 and Day2 outlook though Monday night keeps marginal risk sw of CWA where more unstable air mass in sw IL into MO and closer to frontal boundary south and sw of IL. Lows tonight in the lower 60s. The CAMs show much of convection passing se of CWA during midday and afternoon hours on Monday as skies become partly to mostly sunny Monday afternoon. Highs Monday in the lower 80s, with mid 80s over west central IL.

The Omega Block will reposition itself a bit during mid week with large mid/upper level low over New England and mid Atlantic States and northern Rockies into southern CA while narrow upper level ridge from Texas into the upper MS river valley and Ontario Province Tue with upper level ridge shifting over IL on Wed. Large Canadian high pressure to settle southward from Hudson Bay into the Great Lakes on Tue, into the Ohio river valley Wed and mid/southern Atlantic States on Thu. Dry/fair wx expected over central/se IL Mon night through Thu night with a fair amount of sunshine Tue/Wed and partly to mostly sunny Thu. Highs Tue in the lower 80s, warm back into the mid/upper 80s Thu as SSW flow starts and also will increase humidity late this week. A summerlike pattern takes shape over IL late this week into early next week with warm and more humid conditions prevailing along with daily chances of showers and thunderstorms Friday through Monday/June 8th, starting in central IL Fri and in southeast IL too on Saturday.

Climate Prediction Center (CPC) Day 8-14 Outlook for June 8-14 has 55-60% chance of above normal temperatures over central/se IL and 33-40% chance of above normal precipitation. CPC Risk of Hazardous Temperatures shows Slight Risk (20-40%) of Extreme Heat over IL from June 8-11th.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 605 PM CDT Sun May 31 2026

Ceilings through Monday afternoon generally will be at or above 10kft, with east/southeast winds trending back toward the northeast once again on Monday. Clusters of thunderstorms will be tracking southeast across Missouri, and there is some question as to how far east they make it. Currently thinking they should miss the terminals for the most part, though there is enough uncertainty at KSPI to continue a PROB30 mention. Main window of concern would be 10-14z if they did occur.

ILX WATCHES/WARNINGS/ADVISORIES

None.