Most people have heard of tornadoes and hurricanes. Fewer know about derechos - a different kind of severe windstorm that can be just as destructive. The word means “straight” in Spanish, and that’s the key feature: derecho winds blow in a straight line, not rotating like a tornado.
A derecho forms inside a long line of severe thunderstorms (called a bow echo on radar because it looks bowed). As the storms move, they push out a powerful wave of straight-line wind ahead of them. To officially count as a derecho, the windstorm has to produce sustained winds of at least 58 mph along a path of at least 250 miles.
In August 2020, a derecho swept across the U.S. Midwest, particularly devastating Iowa. It traveled about 770 miles in 14 hours, with winds clocked up to 140 mph in some areas - equivalent to a Category 4 hurricane. Crops were flattened across millions of acres, power was knocked out for over a million people, and damage estimates topped $11 billion. Derechos don’t have the spectacular twirl of a tornado, but they cause some of the worst inland wind damage on the continent.
