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.

Southern California, which was scorched by wildfires in January, was hit by more extreme weather. A rare tornado touched down in Pico Rivera, which is in the L.A. area. Meanwhile, in Riverside County,