Up to 12 feet of snow heading to California mountains: What to expect

Up to 12 feet of snow is heading to California's Sierra Nevada mountains as a new winter storm bears down on the West Coast.

Winter storm watches have been issued for California, Oregon and Washington.

The storm will begin in the Pacific Northwest on Wednesday and will reach California by Thursday, bringing rain to the San Francisco area and snow to the mountains.

The rain will spread into Southern California from Friday night into Saturday.

The heaviest snow -- 4 to 12 feet -- will hit the Sierra Nevada mountains Friday to Sunday.

Snowfall rates could reach 1 to 3 inches per hour in the mountains. Strong winds are also forecast to cause blowing and drifting snow, which will reduce visibility and make driving in the mountains extremely dangerous.

The winter storm will spread into the Rockies early next week.