Interstate 5, the largest highway leading north out of the city, remained closed at the steep grade known as the Grapevine due to heavy snow, while several more southern points of the freeway in and around Los Angeles were closed due to flooding, the California Department of Transportation said.

    In Northern California, San Francisco was expected to experience record cold temperatures on Saturday, and the National Weather Service warned residents of the state capital of Sacramento to avoid travel from Sunday through Wednesday as rain and snow started up again after a reprieve on Saturday.

    A massive low-pressure system driven from the Arctic was responsible for the unusual conditions, said Bryan Jackson, a forecaster at the NWS Weather Prediction Center in College Park, Maryland.

    In Southern California, "this is a rare case of a cold, significant storm event," Jackson said.

    In a sight that must have delighted many Angelenos on Friday, snowflakes even fell around the Hollywood sign atop Mount Lee in the hills above the city, known for its sunny days and palm trees.

    On Saturday, scattered showers and isolated thunderstorms were expected to bring rain, hail and a mixture of snow and moisture called "graupel" to the area, the National Weather Service said.

    A separate storm that clobbered the U.S. Plains, Midwest and Great Lakes regions earlier this week blew out to the Atlantic on Friday after passing over New England, the weather service said. More than 400,000 customers of Detroit based DTE Energy (DTE.N) remained without power on Saturday, the Detroit News reported.

    Even before the latest storm, much of California had experienced an unusually rainy, chilly winter, starting with a spate of deadly "atmospheric river" storms that unleashed widespread flooding, felled trees and triggered mudslides in a state long plagued by drought and wildfires.