Dear Tom,
What is a derecho? Is it a thunderstorm?
Ted Maiten
Dear Ted,
It’s much, much more than that. A derecho (in Spanish, meaning “direct” or “straight ahead”) is a widespread, thunderstorm–induced windstorm with straight–line winds (as contrasted to the rotary winds of tornadoes) sometimes exceeding 100 m.p.h. Derechoes invariably occur with southeast-moving or east-moving thunderstorm lines, sometimes producing damage areas hundreds of miles in length. They are summertime phenomena, occurring mainly in a corridor extending from the northern Great Plains southeast across the Midwest into the Ohio Valley, and they have visited Chicago as well. The causative thunderstorm lines–squall lines–are exceedingly fastmoving, often surging ahead in excess of 50 m.p.h., and they are long-lasting (10-30 hours).
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
