You could keep an eye on the weather forecasts. It can be very nice in most of California for a week or more at a time in December, January, February -- sometimes for several weeks at a time. There is a lot of absolutely beautiful weather during these months. There will be storms, but also many days that are just fine.
The farther south you go, the less rain. Much of Southern California is very fine during most of the winter. It is interspersed with storms, but the weather is mostly fine, and better than heat and intense sun any day. The riding is good in the cool weather (as long as you dress for it) and the lower sun angles. There is a lot of desert when you go inland in Southern and Central California.
Much of Nevada is colder, but the high desert can be a beautiful place to spend some time. The leeward side of the Sierras is considered a rain shadow: most of the precipitation is squeezed out by the mountain range.
If you watch the ten-day forecasts, you can probably find some good chunks of time when there will be nice weather in other areas that might interest you as well.
Last edited by Niles H.; 10-06-12 at 11:53 AM.