UPDATE: 3:30pm Tuesday: Tornado causes damage in Oregon. The active weather pattern in the West is just getting started and won't reach central California until the end of the week.
The second half of December is likely to be wet along the Pacific coast. Below is a computer model forecast of precipitation from now through December 30. The purple spot is 12 to 14" of rain and melted snow during that period.
Much of California has experienced drier than average weather the last few years, so the rain is good news. The Sierra reports moisture already 167% of normal even before this next wet period begins. AccuWeather is also covering the story.