A powerful storm system that tore across the United States in recent days is poised to move offshore into the Atlantic Monday, but in its wake are devastated communities across multiple states that were hit with violent tornadoes,

The dynamic storm from Friday through Sunday had earned an unusual “high risk” designation from weather forecasters.

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.