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.

California braced for the arrival of a massive storm on Wednesday, evacuating residents in areas at risk of mudslides and debris flows.

The storm, which forecasters said could produce tornadoes, is expected to strengthen Friday and move towards the central US.