A cold front will turn become stationary over central Illinois during Monday. Isolated showers or thunderstorms will be possible Monday morning and again Monday evening near the front.
Monday night, the front will move slowly northward into north-central Illinois, shifting the chance for scattered t-storms northward with it. The risk for severe storms is low. However, by Tuesday night, the risk for severe storms will be greater.
A low pressure system on the Plains will move into the Midwest Tuesday. Thunderstorms, some of which may be heavy or severe, will develop over Iowa and northern Missouri Tuesday and move east into Illinois Tuesday night. The primary severe weather threats will be large hail and damaging winds.
There is a lingering chance for showers Wednesday before windy and much colder air moves into the area. Expect highs mainly in the upper 30s to mid-40s Thursday through Sunday.