The term “derecho” was unknown to many Iowans on the day of the Aug. 10, 2020 storm, but it was actually first used in 1878 to describe a windstorm that blew across Iowa in July of 1877. The man who first coined the term was Gustavus Hinrichs, a German physicist who emigrated to Iowa in 1861. Hinrichs noticed the longevity of these storms and the orientation of the winds were a lot different than the widely known “tornado.”
John P. Finley, an officer with the U.S. Army Signal Corps, was conducting extensive research on tornadoes around this time and classified almost all strong storms as tornadoes. Hinrichs wrote an article in the American Meteorological Journal in 1888 to show the difference between tornadoes and derechos.
Hinrichs noticed that tornado was Spanish meaning “twister” for the way the winds twisted. To keep the parallel between these two different types of storms, he named the straight-line wind storm, “derecho,” which in Spanish means “straight ahead.” But when Hinrichs moved to St. Louis, Missouri, in 1889, the use of the term was nearly lost.
Ray Wolf, the science and operations officer at the National Weather Service in the Quad Cities has done extensive research on Hinrichs. He said, “It wasn’t until later in the 1970s that Bob Johns, a forecaster at the predecessor to the Storm Prediction Center, picked up the term and used that in published research on derechos.”
Even by the 1990s it wasn’t widely known with the public. A derecho of lesser magnitude than the 2020 storm spanned from Iowa to Ohio on June 29, 1998.
Brad Small, a lead meteorologist with the National Weather Service in Des Moines, said, “The term derecho in 1998 wasn’t really well known, so that’s probably why it wasn’t classified as such so prevalently, then the term mesocyclone was thrown around in ’98, some people remember it as the mesocyclone of ’98 versus the derecho.”
Predicting a derecho is quite a bit different than predicting your average chance of a severe thunderstorm. For starters, derechos have to meet a certain criteria to even be called one. “It has to go at least 250 miles, and that’s about the width of Iowa from approximately Omaha to the Quad Cities, and then the winds have to be a minimum and often 58 miles per hour or greater, and interspersed with that they have to be 75 miles per hour or greater,” says Small.
Derechos typically occur in Iowa every other year, but the derecho of 2020 was particularly strong. “Derechos are already the high end of these lines of thunderstorms that produce damaging wind. We’re talking like the top 5% or less of events. So now if you take a look at the one that moved across Iowa last August, that’s like the top of the top, so you’re definitely into almost record territory as far as derechos go,” Wolf said.
Those who experienced the 2020 derecho are likely to remember it forever. “The sheer volume of area that the 2020 one encompassed was much greater and it hit the Cedar Rapids area head on, so that certainly had a great deal of impact,” said Small.
The storm spanned 770 miles and caused over $11 billion in damage, which makes it the most costly thunderstorm event in modern U.S. History. Six million acres of corn and soybeans were either damaged or destroyed, 4.4 million trees were lost, and in Cedar Rapids, 90% of homes sustained some type of damage.
Because of the derecho’s incredible strength, all severe thunderstorms that have 80 mph wind gusts and higher and/or baseball sized hail will trigger a Wireless Emergency Alert on your cell phone.