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What is a Derecho?

Inarguably, the biggest severe weather event last year was the derecho on August 10th. The meteorological tie to the word derecho was coined right here in Iowa back in 1888. University of Iowa physics professor, Dr. Gustavus Hinrichs, used the term derecho to describe a damaging wind event that happened in 1877. "Derecho" is the Spanish word for "right", "direct" or "straight ahead" -- different from the damaging wind of a tornado.

It's the sounds and images many Eastern Iowans will not soon forget. The powerful line of severe thunderstorms that raced across Iowa, leaving behind a swatch of damage from 60 to 130 mph wind gusts. The peak estimated gust was 140 miles per hour on the southwest side of Cedar Rapids at the Westdale Court apartments, where straight line wind tore off the roof, and destroyed most of the exterior walls.

Starting as a few scattered thunderstorms after 3 am, the storms continued to strengthen and began to form a line just after 7 a.m.

An hour later, the storms moved east of the Missouri river and that's when the damage reports began coming in. The storms continued to strengthen as they moved into central Iowa.

The squall line started tracking through Eastern Iowa around 11:30 AM, with reported winds of 60-80 miles per hour.

Winds of 100-140 miles per hour swept through Tama, Benton, Linn, Cedar and Jones county, damaging anything in the path from crops, to trees and powerlines, to radio towers and hundreds of buildings.

By two o'clock, the derecho moved east of the Mississippi River and continued on through Illinois, Indiana and Ohio before dissipating after seven o'clock.

The total path of the derecho was a whopping 770 miles. A derecho is classified as a group of severe thunderstorms with consistent 60 mile per hour wind gusts that covers at least a distance of 250 mph over a span of six hours or more

The extensive damage prompted Governor Reynolds to declare a disaster emergency. It is estimated the derecho caused 11 billion dollars worth of damage.

That was just one of four billion dollar disasters in Iowa alone, in 2020.

The state is no stranger to derechos. Looking at climatology data, Iowa can get a derecho once per year, or one every two years. The last derecho prior to 2020 moved through northern Iowa in 2019, although not to size or extent of the August derecho.

2004 and 2005 were active years across the US. In 2004, 24 derechos were tracked nationwide, 28 of them in the following year.

Not only was it one of the costliest natural disasters in the U.S. last year, the Iowa derecho is now the costliest thunderstorm event in U.S. history.

That just goes to show its scope -- and Iowans are still cleaning up the debris.

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Kyle Kiel


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