There will be wind, mostly cold fronts with Southerly wind direction. Winds shift without warning, and it can blow between 10 to 30 easily. Expect a lot of rain, bring minimum 4/3 wetsuit, booties gloves, and head gear depending on your tolerance to the cold fronts.
Days and sessions are short, people tend to kite between 2 to 5 pm, kite sizes between 5 to 9 meters, when the wind blows, be prepared to drop everything and drive to where it blows.
Typical rideable spots for flat water:
3rd Avenue (Foster City/San Mateo Bridge): NorthWest wind direction
Alameda, CA: NorthWest, West, South, SouthWest wind direction
Half Moon Bay by the harbor: SouthWest Wind direction
Wave spots: Waddell Creek (Davenport, CA): NorthWest wind direction
Search bayareakiteboarding.com and you will find lots of post about winter kiting in Northern California:
http://bayareakiteboarding.com/index...php&f=1&t=6348
It is a lot of fun, doable, locals are friendly and will help you if you get in trouble, but you are expected to be self sufficient and know how to rescue yourself. People travel away from Northern California at this time of the year to warmer kiteboarding destination spots.
If you are going kitesurfing in the ocean, avoid dropping your kite in the water if possible. Wind and waves here are heavy in the winter.
Check the conditions and talk to the locals before riding, especially in open water. Big waves, gnarly ocean, fish with big teeth:
http://topp.org/species/white_shark
Looking at my log book last year, I was able to kite 8 sessions in October, 6 sessions in November, and 4 sessions in December. I could have probably had more sessions, but opted to sit out and help other people instead because the conditions were probably too gnarly for me.
Plan on getting some surfing sessions instead, you will guaranteed not to get skunked surfing.
Hope this helps