Our recent historic rains caused a lot of road closures due to debris flow and water damage. Cyclelicio.us has a nice summary of the closures for the South Bay as of the most recent storm. We are bound to have more rain this winter, and to keep up with road closures throughout the Bay Area I’ve aggregated links by county to make it easier for you to ascertain current conditions. There are at least two interactive online maps that display road closures, one at Localconditions.com and the other at 511.org. But these seem to lack some local data. The California Dept. of Transportation also maintains a closure list but these are state roads and highways and not necessarily local byways or even roads we would usually ride due to traffic. Nonetheless it is quite useful if you don’t mind scrolling through a long list of roads by state highway number.
CA DOT list here.
San Francisco: Localconditions.com
San Mateo: Localconditions.com
Napa (this link also has information about the entire state.)
Marin: the Napa map above also covers Marin County
Sonoma and the Napa map above also covers Sonoma County.
Solano: the Napa map above also covers Solano County.
Santa Clara: Unfortunately you have to phone the county (!) at (408) 494-1382