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.

The threat of tornadoes moved east into the Mississippi Valley and the south on Saturday, just a day after a massive storm in several central states.

At least three people have died as a powerful system of storms sweeps across a wide swathe of the central and southern of the United States, with another three killed in vehicle crashes as blinding winds whipped through Texas and Oklahoma.