Lake Michigan Mesovortex Radar

June 25, 2008


Referred by: Frank Dempsey
Summary author: Frank Dempsey

On February 20, 2008, mesoscale lake vortices, or “mesovortices”, formed over both Lake Michigan and Lake Huron. They were clearly seen on satellite imagery in the visible wavelengths as cyclonic cloud circulations. The inset radar image shows precipitation in spiral bands in the Lake Michigan mesovortex.

While mesovortices like these form occasionally during winter, the appearance of two visible, distinct mesovortices simultaneously on two Great Lakes was unusual and made a striking image. These phenomena may develop when cold Arctic air flows over the relatively warm and ice-free lake surfaces. Warm, moist air parcels rise from the lakes, their moisture condensing into low-level clouds, but local wind effects further contributed to the circulation in the light wind patterns that were present on February 20th. In addition, thermally driven land breezes created by the temperature contrast between the cold, snow covered land surfaces and the warm, ice free lake surfaces, flow from the land to the lakes and converge. The concave shape of the shoreline helps to impart low-level cyclonic rotation to the clouds. Thanks to Susan Thornton for providing the images.

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