With a hot (90-degree-plus temps) humid (dew points 70 – 75 degrees) rather unstable air mass in place, a weak upper-level disturbance may be enough to trigger the movement of a few showers/t-storms eastward across the Chicago area this Sunday afternoon/early evening. Some of the stronger storms could produce gusty winds, lightning and brief heavy downpours. The thunderstorm probability map below has us in the 10 to 30% chance of storms within 12 miles of a given location.
A slim chance of storms will continue this evening, with a better likelihood of thunderstorms associated with a mesoscale convective system expected to develop over Minnesota and move southeast ahead of a slow-moving cold front – the complex of storms spreading into our area from the northwest after midnight tonight and moving across our area early Monday morning. Note higher thunderstorm probability here (greater than 40% depicted on the map below).
Thunderstorms could redevelop during the day Monday as the cold front moves south and east across northern Illinois into NW Indiana.