Marin's Mediterranean Climate
California and Marin County experiences profound seasonal changes in weather. This seasonal variation in weather conditions produces the wet winters and arid summers pattern that geographers classify as a "Mediterranean climate".Marin and especially Kentfield, receives about twice as much rainfall as that received in San Francisco only 15 miles to the south. This is a great example of the "orographic effects" of topography on airmasses. Mt. Tamalpais is the major contributor to this "lifting" of the moisture-rich air masses coming into the area along this section of the California coast.
You can check this during the winter rainy season by comparing the current monthly rainfall in Kentfield to that in San Francisco and in the following summary climographs derived from http://maps.esri.com/climo/climograph.html.
A graph of the '97-'98 El Nino rain season (83.44 inches of rainfall at the Kentfield Campus).
This
effect can be seen in this
photo of Mt. Tamalpais taken during a winter storm from the East Bay.
This lifting causes more cooling, more cooling causes more condensation,
and more condensation causes more rain. With no big hills in San Francisco,
the air masses are not lifted and cooled as much and, as a consequence,
produce less rain.
