A powerful low pressure system over Minnesota pushed a cold front across northern Illinois and northwest Indiana Tuesday morning which aided in the development of strong to severe thunderstorms. Thunderstorms stretched all the way from northern Wisconsin across Illinois and into Missouri. Storms intensified in a line as they crossed northern Illinois just prior to daybreak. Several storms were able to develop rotating updrafts which can lead to wind damage and, in some cases, tornadoes. Numerous reports of damage were received from a variety of areas including Kane, Will, Kankakee, and Iroquois Counties in Illinois and in Porter County in Indiana. Damage assessment teams from the National Weather Service have been dispatched to determine if damage in these areas was caused by straight lines winds or tornadoes, and also determine the strength of the winds.
The radar image below shows the expansive line of showers and thunderstorms associated with the deep low and attendant cold front at 7 AM CDT/8 AM EDT Tuesday. The white circular lines show the strong low pressure which is centered over north central Minnesota in this image.
Below is an image showing the storm relative motion within the morning storms as seen by the WSR-88D radar at the National Weather Service in Romeoville. The circled area depicts a very small circulation (bright red pixels agains bright green pixels) which may have led to a tornado. Damage assessment teams will determine if a tornado did in fact occur. Small scale, short-lived, circulations like this are not uncommon within larger lines of thunderstorms with strong low pressure systems.