Residents are surveying damage from unusually vicious weather in multiple U.S. states where violent twisters, blinding dust storms and fast-moving wildfires decimated entire neighborhoods.

In some extreme cases, thunderstorms can spawn a derecho, a long-lived windstorm with gusts over 100 mph, strong enough to cause widespread destruction. If a severe thunderstorm warning mentions damaging winds or a derecho, take cover immediately—just as you would for a tornado.

At least 20 people have died, including 12 in Missouri, as a storm outbreak has produced tornadoes, high winds and fires in the South and threatens to cause flooding and further storms throughout the weekend.