June 29th Derecho Radar Snapshot

That’s a composite of radar images that show the path of the huge wind storm Friday. It cranked up in northern Indiana, and then didn’t let up…still generating big gusts hours and hours later as it moved toward the East Coast. Click here for a full size version of the radar summary.

The wild winds of Friday can be attributed to a “derecho” event.

A derecho (pronounced similar to “deh-REY-cho” in English) is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. We couldn’t call it a derecho at first, because to fit that classification the wind damage swath must extend more than 240 miles, in addition to including wind gusts of at least 58 mph or greater along most of its length. Check!

You’ll notice the persistent curve on the radar. That’s a “bow echo.” Storms “bow out” when strong winds associated with the storms reach the surface and spread out. Click here for a discussion and charts about the structure of the derecho.

A 91 mph wind gust was clocked in Fort Wayne and a 62 mph gust was measured in South Bend. Even though the Indianapolis Airport only squeezed .04″ of an inch of rain out of the complex of storms, they still caught the downdraft, measuring a 57 mph gust just before 4pm.

Here’s a chart from the Storm Prediction Center plotting the wind damage reports: