“A deadly derecho slammed Nashville with 70 mph winds Sunday, snapping trees and knocking out power”
The Washington Post, May 4, 2020
Capital Weather Gang
By Matthew Cappucci
“The damage path stretched from Kansas to Tennessee.”
Residents in the Tennessee Valley are cleaning up after a long-lived line of thunderstorms, known as a derecho, brought severe wind gusts on Sunday. The intense storms caused straight-line wind damage along a path that stretched for more than 600 miles, and in Nashville, the winds were clocked at up to 71 mph.
“The word ‘widespread’ doesn’t even begin to cover the amount of damage we had,” said Scott Unger, meteorologist-in-charge at the National Weather Service in Nashville. The storms knocked out power to more than 100,000 customers, and the local power company is warning residents they could be without electricity for up to two weeks due to the extent of the damage.
A derecho is an arced, curving line of thunderstorms that produces damaging winds as it fans outward. It’s not unusual for the force of winds in a derecho to rival those found in a weak tornado — up to 90 mph. For a storm to be classified as a derecho, its persistence must match its potency — true derechos sweep their winds along a stretch of at least 400 miles. Derechos arrive fast, racing forward at highway speeds.
Derechos are a staple of the summertime, feeding off the oppressive atmosphere found on humid June or July days. May typically features a couple of derechos, but having one this intense and early is noteworthy.
“Derecho science: The debate about what a derecho is and what it isn’t“
The Washington Post, June 22, 2016
Capital Weather Gang
By Jeff Halverson
Derecho – A widespread convectively induced straight-line windstorm.
(American Meteorological Society, Glossary of Meteorology)
Specifically, the term is defined as any family of particularly damaging downburst clusters produced by a mesoscale convective system. Such systems have sustained bow echoes with book-end vortices and/or rear-inflow jets and can generate considerable damage from straight-line winds. Damage must be incurred either continuously or intermittently over a swath of at least 650 km (~400 mi) and a width of approximately 100 km (~60 mi) or more.The term derecho derives from a Spanish word that can be interpreted as “straight ahead” or “direct” and was chosen to discriminate between wind damage caused by tornadoes, which have rotating flow, from straight-line winds. More specific guidelines for identifying derechos are suggested in the references below. These guidelines are subject to change with improvements in observing systems, particularly with severe wind measuring and reporting capabilities.
(Part of the NOAA-NWS-NCEP Storm Prediction Center web site)
Everything you ever wanted to know about Derechos, and somethings you didn’t know you wanted to know…