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

The same powerful storm that battered Southern California with heavy rain and brought blizzard conditions to the San Bernardino Mountains is putting millions on alert from coast to coast.