We learned a new word on Saturday, thanks to Korva's post about the devastating storm that has left millions without power from Ohio east through the mid-Atlantic states:
Now, we'd never heard that word before so we went in search of more about it. According to the National Oceanic and Atmospheric Administration's Derecho Facts Page:
-- "A derecho (pronounced similar to "deh-REY-cho" in English ... ) is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. Although a derecho can produce destruction similar to that of tornadoes, the damage typically is directed in one direction along a relatively straight swath. As a result, the term 'straight-line wind damage' sometimes is used to describe derecho damage. By definition, if the wind damage swath extends more than 240 miles ... and includes wind gusts of at least 58 mph ... or greater along most of its length, then the event may be classified as a derecho. "
-- "The word 'derecho' was coined by Dr. Gustavus Hinrichs, a physics professor at the University of Iowa, in a paper published in the American Meteorological Journal in 1888."
-- "Derechos are associated with bands of showers or thunderstorms (collectively referred to as 'convection') that assume a curved or bowed shape. The bow-shaped storms are called bow echoes. ... Derecho winds are the product of what meteorologists call 'downbursts.' A downburst is a concentrated area of strong wind produced by a convective downdraft. Downbursts have horizontal dimensions of about 4 to 6 miles (8 to 10 kilometers), and may last for several minutes."
-- "Derechos in the United States are most common in the late spring and summer (May through August), with more than 75% occurring between April and August. ... [They] most commonly occur along two axes. One extends along the 'Corn Belt' from the upper Mississippi Valley southeast into the Ohio Valley, and the other from the southern Plains northeast into the mid Mississippi Valley."
As for the term itself, according to a paper written by retired National Weather Service forecaster Robert Johns, the University of Iowa's Hinrichs "decided to use the term derecho (Spanish for 'direct or straight ahead') to define these non-tornadic events since this term could be considered as an analog to the term tornado which is also of Spanish origin."
Update at 2:45 p.m. ET. Like Having "30-plus Weak Tornadoes":
Jeff Masters, director of meteorology for Wunderground.com, a weather website, just told All Things Considered host Melissa Block that during the derecho, "we had over 30 thunderstorms with wind gusts of 80 miles per hour. ... It's kind of the equivalent to having 30-plus weak tornadoes on the ground."
As for how a derecho forms, he said that if enough thunderstorms develop "in the same location ... they have the opportunity to work together and form a complex or a greater whole."
More from his conversation with Melissa is due on All Things Considered later today. Click here to find an NPR station that broadcasts or streams the show. Later, we'll add the as-broadcast version of the interview to this post.
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