Millions of Americans across the country are on alert for a severe weather outbreak as violent, long-track tornadoes with damaging winds of up to 80 mph and large hail are expected across the Midwest and South with the cross-country storm moveing east.

Tornado activity has picked up in March, which is traditionally the start of tornado season, but the areas of activity have expanded in recent years.

A severe weather system spawned intense, long-duration tornadoes that struck parts of Arkansas, Mississippi and Missouri, leaving some communities in tatters.

At least 18 people have been killed in a monster storm sweeping across much of the U.S. As of Saturday afternoon, Missouri had recorded more fatalities than any other state