Southern Great Lakes Derecho of 1991

It lasted 17 hours and raced from southeast South Dakota through southern Michigan before dying out over Western Pennsylvania.

Thousands of acres of corn and soybean crops were flattened causing $60 million in damage (1991 dollars).The strongest wind gust—103 mph (170 km/h) -- was recorded at Sioux Center, Iowa.

Dane, Jefferson, Waukesha, Washington, and Ozaukee counties were declared Federal Disaster Areas by FEMA.

After crossing lower Michigan, the derecho moved into the Windsor area of Ontario around 9:30pm EDT.

The bow echo system then crossed over Lake Erie and dissipated over Western Pennsylvania (including metro Pittsburgh) at around 2 A.M. EDT on July 8.

Map of the Southern Great Lakes Derecho of 1991 (courtesy of NOAA)