From an NWS bulletin:
Sierra Snow with Valley Rain Likely Sunday through Tuesday
Hazardous travel likely across the mountains with chain controls and travel delays.
Locally heavy rain and small hail possible from thunderstorms.
Timing and Strength
1st System: Saturday night through Sunday
A few inches of snow possible above 4000 ft.
2nd System: Tuesday
Shorter duration of snow than 1st system, but potentially higher snowfall rates.
A long period of mostly fair and warm weather will be coming to an end this weekend as a series of low pressure systems moves through Northern California. The greatest impact will likely be to the Sierra, where potentially a foot of snow could fall along the passes over the course of a few days. Given the long stretch of warm weather, many trans-Sierra drivers will likely be ill-prepared for wintry weather; complacency is a major concern.