Derecho cut path of damage across Tama, Benton Counties 10 years ago Sunday
CEDAR RAPIDS, Iowa (KCRG) - Sunday marks another anniversary of a damaging windstorm called a derecho, this time not too far off of the path of the one that struck August 10, 2020, but at a much different time of day.
The event took place on July 11, 2011, with the most intense winds and resulting damage taking place between Garwin, in Tama County, to Vinton, in Benton County. The storms initially moved into southwest Iowa after about 1:00 a.m., intensifying further as they approached Interstate 35 north of the Des Moines metro area around 3:30 a.m. Unusually unstable air was in place across the state for that time of night, allowing the storms to really gain steam as they moved east, only taking another three hours or so to reach the Mississippi River.
Widespread damage began to take place in and around Marshalltown, where numerous large trees were downed by winds that were likely in the 70 to 90 mph range. A focused, intense corridor of winds developed in northern Tama County, where a path of 100 mph or more took place for nearly 50 miles. Embedded within that path, National Weather Service officials discovered damage to well-built structures, electrical transmission towers, and radio towers to determine that winds were, at times, in the 110 to 130 mph range. Most of this type of damage took place in Garwin and Vinton.
Vinton took significant structural damage to an apartment building downtown, the Iowa Braille School, and other buildings. NWS officials wrote that “nearly every tree was significantly damaged or snapped off.”
Thousands were without power after the storms rolled through, with crews working to replace damaged infrastructure. Damage estimates to property and crops, at the time, were around $11 million. Incredibly, nobody was injured or killed in the storms, in spite of the unusual time of day.
The storms traveled hundreds of miles through the day on July 11, finally weakening toward the Atlantic coast of the U.S.
While storm complexes that meet the technical definition of a derecho are somewhat common, we rarely see them that are of this extreme intensity. In the last 25 years in eastern Iowa, only three such events have taken place: this one in 2011, the June 29, 1998 derecho, and last August.
More information on this particular event is available here:
- Quad Cities National Weather Service write-up of the event.
- A more technical case study from the Storm Prediction Center.
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