Tornado, blizzard warning as new storm looms over much of US

Cars sit in traffic backed up for miles on Arizona’s Interstate 40 after a fresh dumping of snow - (AP)

A powerful storm system threatens to unleash a cascade of severe weather across the United States this week, from heavy rain and potential flooding in the West to tornadoes in the South and blizzard conditions across the Great Plains and Upper Midwest.

The latest threat follows a weekend of severe weather in Texas, where thunderstorms on Saturday caused havoc on Interstate 35.