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

Tornadoes whipped through Missouri on Friday night, ripping apart homes, businesses, and the electrical system. Gov. Mike Kehoe’s Office says at least 12 people have been killed and one person is still missing from the severe weather.

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.