Derechos Are a Major Danger With Destructive Winds. Here's What to Know About Them

 Chris Dolce and Jonathan Erdman

Published: July 28, 2021

Derechos are large clusters of thunderstorms that most commonly form in late spring and summer and cause widespread destruction to trees, power lines and sometimes structures.

From the Spanish word for "straight", these windstorms leave wide, long areas of straight-line wind damage. The winds can be as strong as 60 to 100 mph or higher in extreme cases. They're usually produced by one or more curved lines of thunderstorms known as a bow echo or squall line.

A single severe thunderstorm may produce an area of damaging winds only a mile or two wide and a few miles long, but derechos can produce damage tens of miles wide and hundreds of miles long. They should cover a distance of at least 250 miles, according to a 2005 study by Walker Ashley and Thomas Mote.

Cleanup from the extensive damage from a derecho can take days to weeks. In the worst derecho events, sometimes relief workers from other states are needed to aid in these efforts.

Derechos in the U.S. are most numerous during the late spring and summer. More than 60% of them occur between May and July, according to NOAA's Storm Prediction Center.

The study from Ashley and Mote found that both May and July average over four derechos per year. June is nearly as active with three to four derechos per year.

Derechos are a potential threat for many states east of the Rockies. But they are most common in parts of the Great Plains, Midwest and South.

They can occur during the daytime or in the overnight and early-morning hours when people are sleeping.

Ashley and Mote found derechos claimed 153 lives in the 18-year period of their study. Interestingly, three northern states - New York (23), Michigan (17) and Ohio (16) - comprised over a third of all derecho deaths. 

Almost 70% of derecho fatalities occurred in areas other than a permanent building, including in vehicles (30 percent), in boats (19 percent), under trees (11 percent) and camping (9 percent). 

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.