San Francisco has around 5 months a year of intermittent rain. San Jose, just 50 miles south and nestled between mountains instead of between waters, has perhaps only 1 month of rain. San Francisco also has notably colder winters and summers than San Jose, to a fairly shocking degree.
Geographical differences are three, primarily. First of all, San Francisco is further north, and closer to the Pacific Northwest, but only by 50 miles, or 80 kilometers. Second, San Francisco is surrounded by water, with the San Francisco Bay to the east and the Pacific Ocean to the West, while San Jose is isolated from the Pacific by the Santa Cruz mountains. Third, San Francisco has a far higher population density, with more smog and greenhouse gases as a result, which may or may not be a significant contributor to rain (nucleation sites?).
Why do these two so proximate cities have such different climates?