Dear Tom,
While in Minnesota, I read a newspaper article about a storm called a “derecho.” The article says the condition is relatively rare. Does this condition hit Chicago and, if so, how often? Bernie Bischoff, Elmhurst, IL
Dear Bernie,
Derechos (pronounced deh-ray’-cho) are no strangers to Chicagoans-nearly all have experienced a derecho but may not be familiar with the term. It was a derecho passing just north of Chicago which set off the seiches along Lake Michigan on May 31.
Produced by fast, often southeastward-moving lines of thunderstorms which may occur 2 to 4 times a year here, derecho applies to the damaging family of downburst winds which gush out of the front of powerful, long-lived squall lines. These often damaging winds can cover hundreds of miles and show up on weather radars as concave shaped “bow echoes.” Derecho means “straight ahead,” distinguishing these winds from a more rotary tornadic wind.
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Tom Skilling is chief meteorologist at WGN-TV. His weather forecasts can be seen Monday through Friday on WGN News at noon and 9 p.m.
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