A powerful winter storm system is rolling into California tonight and will last through Tuesday, bringing extremely cold air out of Canada. There is the potential for accumulating snows on the valley floors in northern and central California on Monday, and in low elevations/valleys on Monday night and Tuesday in Southern California.

Here is a snippet from NWS Sacramento:

...POTENTIAL CONTINUES FOR VERY HEAVY SNOWFALL ACCUMULATIONS OVER THE WEST SLOPES OF THE NORTHERN SIERRA NEVADA AND FOOTHILLS MONDAY. THERE IS ALSO SOME POTENTIAL FOR ACCUMULATING SNOW ON MONDAY IN THE SOUTHERN PORTION OF THE SACRAMENTO VALLEY AND NORTHERN SAN JOAQUIN VALLEY. SNOW LEVELS WILL BE VERY LOW...LESS THAN 1000 FEET...

How low the snow falls in Southern California will be monitored closely as the cold air makes its way closer. Winter storm watches are in effect for all the mountain regions in SoCal with snow accumulations of 3 feet or more a certainty at resort levels.