I'm looking to do a century etc in January. I live in the northwest and wanting to make a trek to some favorable weather.
No centuries in NorCal until April - the riding's good but the weather's unpredictable and the organizers of centuries like predictability good weather.
Yes, come out here, like all the guys at work tell me, why sign up for a century, do your own. There are lots of great rides around here and stores the whole way you can use for support. Taxis make great SAG support, do it.
If you're looking for favorable weather I'd continue down I-5 until you hit So Cal
You did say California in your title and not just NorCal, so I would point out Tour de Palm Springs: http://www.tourdepalmsprings.com/
It is in February, so hopefully it is not too late for you. I am considering going.
Your son wishes to do some fixed gear riding in SF and you wish to encourage this? I don't understand.
San Francisco Randonneurs organize a Populaire (115K) from San Francisco to Point Reyes Station on Jan 11 with a picnic lunch at the end, also a harder 200K ride to Point Reyes Lighthouse on Jan 25. These are rain or shine, and it will often be cold or rainy at some point in the ride.
Since 2009 I've been doing Winter Soltice Century. It's very low key and often times the date is moved far from the actual solstice.
As it happens the 2013 Solstice ride will actually happen next year on 1/18/14