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.

Wind gusts were forecast to top 50 mph in some areas. In Pico Rivera, a tornado with wind speeds reaching 85 mph traveled about a mile through a residential area of the city.

A colossal storm is threatening to bring severe weather to much of California this week and could impact travel over the Grapevine. Here's what to know.