At midday a line of thunderstorms along and ahead of an approaching cold front was moving into the northwest corner of Illinois. This line of storms is expected to intensify as it moves east – reaching western portions of the Chicago area by mid-afternoon.
A Severe Thunderstorm Watch (blue-shaded counties on the map below) will be in effect for western Illinois as well as portions of eastern Iowa and Missouri until 6PM CST this Tuesday evening. If storms intensify as expected, a Severe Thunderstorm Watch will likely cover at least portions of the northeast Illinois into NW Indiana later this afternoon/early evening.
Displayed below are maps showing the western portion of the Chicago area with a better than 40% chance of thunderstorms within 12 miles of a given location between 2 and 6PM CST and a similar probability for eastern portions of our area between 6PM and 10PM CST.
The last map below is a Regional Weather Radar Mosaic. Note to the west of the line of thunderstorms are freezing rain (Pink shading) and snow (blue-shading).