The dangerous outbreak begins today and will sweep through the Midwest, South and East through the weekend.

Widespread high wind capable of power outages, rapid fire spread and tree damage are expected in the Plains and parts of the Midwest. Blizzard conditions are also possible in the Northern Plains.

They're much more common than tornadoes. Here's why severe thunderstorms are dangerous and why you should take action when a warning is issued.

Tornadoes can have extreme differences in how fast they move. Past history shows they can track as fast as traffic on an interstate, or as slow as someone taking a walk.

There's one key item you should add to your tornado preparedness plan if it's not already there – a helmet. We talked to an expert about why wearing a helmet in a tornado warning matters, and what kinds of helmets can help you avoid injury.