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.

As heavy rain from a large storm subsided, officials in Southern California said rock and mudslides remain a threat.

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