From the National Weather Service:
Confidence is increasing in a wet weekend for Norcal. Although model timing is in better agreement regarding the onset of rain and mountain snow beginning Saturday and continuing on Sunday, precipitation amounts continue to vary. Showers could linger into Monday. After a break, another weather system may arrive on Wednesday potentially affecting pre-holiday Thanksgiving Day travel.
Slick roads from valley/foothill rain and mountain snow
Roadway spin outs & accidents
Chain controls & travel delays over Sierra Nevada passes
High for wet pattern
Medium for snow levels, rain and snowfall amounts
Medium for timing of weekend system
Timing and Strength
Rain: See Precipitation Forecast
Snow levels: 4000-4500 ft Shasta County mountains Saturday rising to 6000 ft Sunday. 6500-7000 ft Sierra Nevada passes.
Snow amounts: See Snow Forecast
Wind: Southwest mountain wind gusts 50 mph or higher this weekend.