The term ‘derecho’ disappeared for nearly a century. They strike eastern SD every other year
While meteorologists say a second derecho this summer can't be ruled out, it's unlikely another one would strike in the magnitude as last Thursday's storm.
SIOUX FALLS — Last Thursday’s derecho quite literally swept across eastern South Dakota, bringing straight-line winds of over 100 mph that damaged everything from trees and outbuildings to homes and grain bins.
The National Weather Service in Sioux Falls classified the storm system as a derecho — a meteorological phenomenon not centered around South Dakota since June 2020, when a derecho developed in Colorado and moved across the state before fizzling off in eastern North Dakota.
What exactly is a derecho? Could another derecho happen this summer?
The Iowa derecho of 1877
The first named derecho in the United States took place in July 1877 in southeastern Iowa. According to the National Oceanic and Atmospheric Administration, the term was coined by Danish-born Gustavus Hinrichs, who was a professor of physical sciences at the University of Iowa in 1864.
In his article " Tornadoes and Derechos," published in the American Meteorological Journal’s November 1888 edition, Hinrichs described the event as a “straight blow of the prairies," a contrast to the circulation of air columns in a tornado. He noted the phenomenon was caused by a “violently progressing mass of cold air, moving destructively onward in slightly diverging straight lines.” When translated from Spanish to English, “derecho” means “straight.”
A term unused for nearly a century
Though Hinrichs first published the word “derecho” in 1888, he eventually lost his meteorological post in Iowa and moved to St. Louis to instead teach chemistry. Beyond the weather world’s loss of Hinrichs, the responsibility for weather research was moved from the U.S. Army Signal Corps (a precursor to the modern-day National Weather Service) to a division of the U.S. Department of Agriculture, where Secretary Julius Morton continued the discouragement of extensive research on severe storms. Those policies continued for roughly five decades.
As American military and aviation needs expanded in the 1940s, so did the need for the advancement of weather prediction and other associated research.
“Although research about convective storms and tornadoes advanced rapidly in the 1940s and 1950s, research and knowledge about non-tornadic severe winds associated with thunderstorms advanced more slowly,” wrote Robert Johns, a former forecaster for the National Weather Service’s Storm Prediction Center.
In the 1980s, when Johns served as a forecaster in Kansas City, Missouri, he was struggling to best describe a particularly strange series of storms that consisted of relatively long paths of progressive straight-line wind damage. One day, Joe Galway, one of the first severe storms lead forecasters, popped into his office and mentioned it could be described as a derecho.
He decided to use the term, and noted in his 2007 research paper, “Origin and Evolution of the Term ‘Derecho’ as a Severe Weather Event,” that the term has since been much more commonly used by forecasters and other weather officials.
Could another derecho strike this summer?
Derechos more common East River
According to the National Weather Service, derechos strike eastern South Dakota roughly twice as often as western South Dakota, averaging one derecho every two years to the east of the Missouri River Valley.
They’re more common, however, in other areas of the eastern United States. The area surrounding the tri-state border of Arkansas, Missouri and Oklahoma typically averages four derechos every year.
Derechos in South Dakota are most often seen in the convective season — generally ranging from May to August. Though one every two years is the historical average rate of occurrence, meteorologists at the National Weather Service in Sioux Falls say it’s too early in the convective season to predict whether or not a second derecho could strike the state this summer.
May 12 derecho was significantly severe
Even if another derecho were to strike South Dakota this summer, it’s unlikely the storm would reach the severity seen and felt by residents on May 12.
Last week’s storm saw severe thunderstorm and tornado warnings stretching from central Kansas as far as Duluth, Minnesota. Over 30 South Dakota counties were under some form of severe weather warning as winds reached 107 mph near Tripp, 96 mph near Madison and 89 mph near Yankton while multiple tornadoes spawned in the state.
Predictions of a widespread path of significant destruction led the National Weather Service to issue a particularly dangerous situation (PDS) severe thunderstorm watch ahead of the storm — the first issuance of a PDS since 2015 and the largest PDS watch since 2008.
After the storms had passed, law enforcement and other damage surveyors hit the ground, discovering imploded grain bins near Tripp, roofs off buildings in Salem, a school rendered useless in Castlewood and countless overturned vehicles across the region.
“The collection of storms will be considered a derecho, which by definition is a long lasting storm system capable of producing extreme winds and damage over an extended area of space and time,” the NWS wrote in a storm report. “Significant damage to residential, commercial, and agricultural areas was reported in many communities across the tri-state area.”
After county commissions across the area held emergency meetings to declare a disaster, Gov. Kristi Noem signed a disaster declaration in many areas of eastern South Dakota, making available additional funds to support those affected by the derecho while also ordering state personnel to assist.
Though storms in the Midwest can rapidly develop and remain ever-changing, the National Weather Service’s Storm Prediction Center works 24/7 to provide notice to residents of areas that are at-risk of storms, while the National Weather Service’s field office in Sioux Falls provides constant updates during severe weather.