A powerful storm dropping drenching rain on flood-prone Southern California is raising concern among forecasters that it could produce a dangerous, widespread outbreak of tornadoes, damaging winds and fires along with a blizzard as it crosses the entire United States in the coming days.

Over the next week, tens of millions of Americans will be at risk of severe weather as a colossal storm marches across the country, threatening hurricane-force winds, major flooding, blizzard conditions and a possible tornado outbreak.

Dirk Verdoorn breaks down active weather on March 13 at 12:50 p.m. and looks ahead an how much more rain and snow to expect.