What's a derecho? The violent weather phenomenon you've probably never heard of

It's a type of severe weather that doesn't come up often, but it can be just as threatening as a tornado. It's called a derecho.

Derechos are clusters of violent storms spanning at least 240 miles. They are characterized by winds surpassing 100 m.p.h., thunderstorms and fast-moving showers.

These storms typically move in a straight line, making the name appropriate ("straight ahead" in Spanish). Because of this, derechos leave behind destruction: uprooted trees, flipped boats and destroyed homes. A 2012 derecho left millions of Americans from the Midwest through Washington D.C., without power for more than a week. A 1969 derecho caused flash flooding that led to 18 deaths.

Though they are known as "inland hurricanes," derechos are not as common. They occur more than once a year only in a small portion of the country.

If a derecho hits your area, don't drive, and keep an eye out for fallen trees and power lines.