Meteorology lesson: Derecho
Another storm formation with furious winds is demolishing these areas. It is not a tornado, but a derecho. Wiki has an extensive definition of a derecho, but here is a summary of a derecho, compared to a tornado.
Unlike a tornado which high spinning winds in a narrow area for a short time, a derecho covers a wide area of strong windstorms lasting a long time. Winds in a derecho can blow from 57 to 130 mph, not as strong as a tornado. However, the devastating effects of a derecho is that they cover a wide area (up to 250 miles wide and 800 miles long) and last much longer than a tornado.
Here's a video of a derecho, which includes recent footage of derechos devastating Texas, Louisiana, Mississippi, Alabama, and Gerogia.
And the actual results of a derecho? Let's look at Rusk, TX.
Derecho, not tornado, hits south of Rusk
Heavy rains and hurricane-force winds caused havoc on Sunday morning, uprooting trees and causing power outages across Cherokee County.
"We heard reports that there was a funnel cloud in the area," said DPS Trooper Steven Crosby. "The whole weather system seemed to maintain just a thin path about six to eight miles between Rusk and Alto."
Though there were no confirmed tornados, the National Weather Service Forecast Office in Shreveport, La. said that a derecho (pronounced deh-REY-cho), or large thunderstorm complex, caused winds in excess of 70 miles per hour, causing damage to trees and powerlines.
Derechos are most common in the warm season and are caused by storms called bow echoes. A bow echo is a band of showers or thunderstorms that are curved in shape. For a storm system to be considered a derecho, winds must be greater than 57 miles per hour.
At one point early Sunday morning, the bow echo stretched from Franklin County in upper Northeast Texas to Trinity, Polk, Tyler and Jasper counties, a distance of approximately 216 miles.
Some locations in the Shreveport region, which includes East Texas, southwestern Arkansas and most of northern Louisiana received up to six inches of rain.
The storm system caused four tornadoes in four counties: Bowie, Cass and Camp counties in Texas and Miller County in Arkansas. Only three injuries and no fatalities were reported.
Another derecho hits Alabama.
Alabama Storm Damage Caused By “Derecho”
The National Weather Service says a not very common weather phenomenon, called a “derecho” (duh-RAY’-choh), moved across central Alabama, causing damage and knocking out power in several counties from Mississippi to Georgia. Alabama Power said Monday 48,000 customers were without power at its peak, but all have had power restored. More storms Monday knocked out power to another 2,500.
Weather officials said a derecho is a widespread and long-lived straight line wind storm associated with a fast-moving squall line, producing winds over 58 mph. Its gust front moved across the state Sunday afternoon. The storm knocked thousands of trees down south of Interstate 20.
Mark Linhares, a meteorologist with the National Weather Service in Birmingham, said derechos are more prevalent in the north, but Alabama may get one once a year.