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Two Derechos this past weekend

Derecho, you may or may not have heard this term when it comes to storms during the summer months.

Click here to listen to how the word is pronounced.

It is a fast moving wind storm that produces on and off wind damage from gusts of 58+ mph. In some cases the winds can exceed 100 mph. The damage reports have to continue on and off for at least 240 miles. The damage happens from straight-line winds.

This past weekend (July 19-21) a line of storms moved across the Midwest causing damage from the wind for several miles. One wind storm produced damage from Minnesota southeast to Michigan (about 490 miles). This is the red circled area on the map below.

The other started in South Dakota and moved east across southern Minnesota and northern Iowa on through Wisconsin before weakening in northern Michigan. This produced damage on and off for about 860 miles. This is the blue circled are on the map below.  These both fit the above criteria for being called a derecho.

The National Weather Service forecast office in La Crosse, WI has a radar loop showing what it looked like with both of the derechos

[embedyt] https://www.youtube.com/watch?v=fZH_c6vjypE[/embedyt]

The term derecho was first mentioned by Dr. Gustavus Hinrichs, a physics professor at the University of Iowa. It was in a paper published in 1888. The image below was in that paper talking about a wind storm through Iowa in 1877.

The climatology of derechos shows eastern Iowa to have one every year or two.

Mark Schnackenberg

Chief Meteorologist

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