Silicon Valley: A Word About the Climate

Silicon Valley Climate - sub-tropical tempsPeople coming from out of the area to relocate to Silicon Valley might not know what to expect from the weather in the San Jose, Santa Clara County, or Silicon Valley Area.  Does this part of California ever rain? How hot is the summer? What is the climate like?

In a nutshell, this is a “sub-tropical” area, or a place that enjoys a mild “Mediterranean climate” that is most heavily influenced by the close proximity of the shoreline and the Pacific Ocean.  Temps are mild, we get little rainfall compared to many parts of the country.

More specifically, we usually get about 10-20 inches of rainfall a year (less on the east and more on the west) and enjoy as many as 300 sunny days a year. Winters seldom see many hard freezes (but they can happen).

A typical summer day has highs in the mid to upper eighties but very low humidity – so it feels much cooler. Heat waves and heat inversions can run the temps up to the low to mid 100s in the hottest parts of the valley. Luckily it doesn’t happen much, or stay for long! Once in awhile, a rare storm in summer will bring high humidity and thundershowers, but for the most part, summers are dry. The hottest month is typically August.

The coldest month, usually, is December. A January day will often have a high in the 60s or 50s, depending. A cold day here is when it does not get into the 50s (not too common). By February, though, the worst is usually over and it’s even possible to have freak warm days that hit 80 degrees!

Our weather varies from year to year. Some years we get drought conditions and may require water rationing . Other years we get lots of wet weather from the Pacific – temps are warmer but there’s much too much rain: those are the El Niño years. Most often, though, winters aren’t that bad – evenings can be nippy as temps drop into the 20s on the worst nights in December or January. It will make the news that people should cover their citrus trees so they aren’t damaged by the freezing temps. (more…)

Microclimates in Silicon Valley

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.