People 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. What’s it all about?
In a nutshell, this is a “sub tropical” area, or a place that enjoys a “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 20 inches of rainfall a year and enjoy 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! Most people do NOT have air conditioning here unless they are in a newer home or live in the warmer South County areas of Morgan Hill or Gilroy.
A January day might have a high in the 60s or 50s, depending. 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 (right now we have been asked for a voluntary cutback of 10%). 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 Nino 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.
Because we are on the Pacific, that ocean dominates our weather. Sometimes a freaky cold storm from Alaska barrels down the coast in winter. When that happens, it gets extremely cold. And once in a rare time – perhaps once a decade – it might even snow! When the white stuff does fall in Los Gatos, Saratoga or San Jose, though, it doesn’t usually stay for awhile. It is so rare that it simply feels like magic. Can you imagine the look of snowfall on a palm tree?
Warm weather – or mild, comfortable weather – is the norm from about spring (varies from Feb – April each year) through most of November. Really December and January tend to be the coolest months, but sometimes cold storms can make winter linger longer and forestall spring a bit.
And what of those palm trees? We have LOTS of types of palms here (Royal Palms, Fan Palms, Date Palms, etc.). They do well here when planted right and well nurtured, but they are not indigenous to northern CA. They are native to southern CA but not here. However, if handled well they usually do fine in our slightly cooler climate.
For me, the palm trees are a sign that the climate somewhere is “mild enough”. I often joke with folks, “if the palm trees can live there, so can I….”
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.