O KLAHOMA CITY — The threat of violent tornadoes in parts of the U.S. proved deadly as well as destructive as whipping winds moved east into the Mississippi Valley and Deep South on Saturday, with at least 16 people killed and scores of homes decimated.

A powerful storm system roared across the Midwest and South Friday night, unleashing a series of tornadoes that carved paths of destruction and left at least three dead in Missouri.

An "outbreak" of tornadoes and severe thunderstorms is expected through Saturday night in Alabama, Mississippi, Louisiana, and other southern states.

The National Weather Service issued tornado watches for more than 2 million people on Saturday. An "outbreak" of tornadoes and severe thunderstorms is expected through Saturday night in Alabama, Mississippi, Louisiana, western Georgia, southern Tennessee, the Florida Panhandle and southern Arkansas.

A line of severe thunderstorms, the first extreme weather event of the year, will hit the Chicago area around midnight Friday, according to the National Weather Service.

Most of the rest of north Alabama will have a Level 2 risk, and a small area in the northeast corner of the state will have a Level 1 risk. If storms can develop they have the potential to be intense, especially west of Interstate 65. Tornadoes, damaging winds and hail will be possible.

We all hear the terms when there's a threat of severe weather. But what does each alert mean, and how does it affect you?

Round one of storms has ended, and round two of storms is setting up along the Mississippi River. This round is expected to impact West Alabama as early as noon today.