Numerous roll clouds around Chicago Wednesday morning

A line of severe thunderstorms brought 50-60mph winds across the Chicago area late Tuesday night followed by a decaying line of showers and thunderstorms early Wednesday morning.

Because of the long duration of the storms and overall favorable environmental wind shear, the rain-cooled air that built underneath the storm complex became large and spread out ahead of the storms. This is common underneath organized areas of storms, with the front edge being detectable by radar and visible as a roll cloud.

Many people, even us meteorologists, can sometimes get mixed up in determining the difference between a roll cloud and shelf cloud.

A roll cloud is a low, horizontal tube-shaped arcus cloud associated with a thunderstorm gust front (or sometimes with a cold front). Roll clouds are relatively rare; they are completely detached from the thunderstorm base or other cloud features, thus differentiating them from the more familiar shelf clouds. Roll clouds usually appear to be "rolling" about a horizontal axis, but should not be confused with funnel clouds.

A shelf cloud is a low, horizontal wedge-shaped cloud, associated with a thunderstorm gust front (or occasionally with a cold front, even in the absence of thunderstorms). A rising cloud motion often can be seen in the leading part of the shelf cloud, while the underside often appears turbulent, boiling, and wind-torn.

What made Wednesday morning's outflow more unique was that there were numerous outflow edges on radar and associated roll clouds.