One has to define northern California. There are the SF bay area, wine country, Lake Tahoe area, Monterey and Eureka area et. al. to name a few. In general, the terrain is hilly to very hilly / mountainous. Even the coast is hilly.
The next matter is the time of year. In general, we have little to no rain from the middle of April through October and the fog and the micro climates dictate temperatures. So it can be very hot inland and in the mountains and cold at the coast in July.
With respect to traffic / road conditions, IMHO, it is pretty good in the Bay area. Motorists are generally courteous but of course there are exceptions. Where we cycle there are usually good bike lanes and the routes that we choose have little traffic. Local knowledge can make or break a cycling vacation.
Hopefully, others will have some tour companies. I do not. I recommend posting this in the Northern California regional forum.
Last edited by Hermes; 08-04-08 at 01:58 PM.