After some patchy early morning dense fog, scattered cumulus clouds and easterly winds will prevail across the Chicago area under high pressure Sunday. However Monday looks to be a different story, as the high pressure shifts off to the east and low pressure develops in the central plains and moves in our direction.
Monday into Tuesday the National Weather Prediction Center has outlooked northern Illinois, most of Indiana, southern Wisconsin and eastern Iowa in a Slight Risk for excessive rainfall (yellow-shaded area on the headlined map), while at the same time the National Storm Prediction Center has our area included in a Marginal Risk for severe storms (dark green-shaded area on the severe weather outlook map below).
Heavy localized flood-producing downpours of 1 to 2-inches or more are expected to accompany showers and embedded thunderstorms across the Chicago area, especially Monday afternoon and evening when the severe weather threat also peaks. The main severe weather threat will be strong winds, but the proximity of a warm front also belies the possibility of tornadoes.
Aided by an extensive low pressure trough aloft, a center of low pressure and associated warm front will move out of the central plains through northern Missouri into western Illinois Monday, passing over the Chicago area Monday night and early Tuesday. A tongue of warm moist unstable air out of the Gulf of Mexico will flow into Illinois and Indiana lifted over the warm front ahead of the approaching low pressure system.
A slow improvement from the west should occur Tuesday, as the low pressure pulls off to the northeast.
Severe Weather Outlook Map for Monday/Monday night…