Locals to the San Jose area (Silicon Valley, Santa Clara County) know, and newcomers often do not, that we have mico-climates here. Our weather is mild everywhere, of course – we enjoy a “sub tropical climate” where citrus grows and palm trees thrive – but it varies a lot nonetheless.
What kind of variation exists in Santa Clara County’s weather?
Consider that our terrain is shaped somewhat like a funnel with the San Francisco Bay on the wide end, and the two mountain ranges making up the sides of the funnel, narrowing at its base (near Morgan Hill).
Together with our funnel shaped valley, the Pacific Ocean and the San Francisco Bay are the major influencers on our climate. The Santa Cruz Mountains are warmer and wetter than the eastern foothills in winter. The Pacific Ocean brings in the rain, fog and winds pulling storms in from the ocean to the valley. Much of the weather stops at or near the coastal mountains, though, and the influence lessens as you go east such that the east foothills are very, very different from the Santa Cruz Mountains. The areas close to the bay get more breezes than those sheltered by smaller valleys or nooks.
In general, the further south you go (Gilroy, Morgan Hill, Almaden Valley), the warmer it gets. The closer to the bay, the cooler it will be. Areas in smaller valleys in the hills may get mini heat inversions, which trap heat, and will generally be hotter in summer than areas not so protected.