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.

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? More often, though, we get a dusting of snow on the east foothills. Most of the time it’s too warm on the Pacific Ocean side of the valley for snow to stay there, but a couple of times a year that will happen and last a day or two.

Warm weather – or mild, comfortable weather – is the norm from about spring and even late “winter”, 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.

Silicon Valley’s micro-climates

Silicon Valley does have micro-climates,  with areas closest to the coastal range getting more rainfall than those closer to the Central Valley / Calaveras range.

Areas near the passes to the coast will get more wind as the fog pushes through (such as in downtown Los Gatos). Areas in small valleys will be more protected and get hotter in summer than those which can catch more of a breeze.

Wind tends to blow each afternoon from the San Francisco Bay along the east foothills (Fremont, North San Jose / Berryessa, Alum Rock, South San Jose, Morgan Hill, etc.).

Golden Gate Bridge San Francisco with Mark Twain quote about the city's cold summersAreas close to the bay will be a little cooler than those further from it in summer.  The Peninsula (San Mateo County) gets more fog and wind than the South Bay (Santa Clara County) and is generally cooler in summer.

San Francisco is not part of Silicon Valley, but many people live there and work here or vice versa, so it is worth mentioning that San Francisco’s summers are notoriously cold and foggy. Many San Franciscans used to have “summer homes” in Los Gatos, Menlo Park, and sunnier areas nearby just to escape the gloomy cold summers there.

Palm trees, redwood trees, citrus trees, fruit & nut trees

Many of the trees here rely on the mild sub-tropical or Mediterranean weather: palm trees, redwood trees, fruit (esp citrus) and nut trees all thrive on weather patterns that are not too hot, not too cold, not too wet, not too dry.

Until recently, at my house we had a prolific orange tree* which made fresh citrus available to us for much of the year. My husband would relish the opportunity to serve fresh squeezed orange juice to family and friends visiting from colder climates such as Boston, DC, or Chicago. It’s not at all uncommon for those of us in the Santa Clara Valley or nearby areas to have our own citrus trees and to be able to serve up juice on demand. Most popular seems to be lemon trees, which also can keep the fruit on them for the majority of the year. The climate here is extremely favorable for fruits, nuts, and vegetables, and very few yards here have no produce growing in them. 

Redwood trees only grow in about a 300 mile region of coastal California. They cleverly take the fog that condenses on their needles and the water drops nourish the roots, which lie close to the surface. While there are large forests of them in the Los Gatos or Santa Cruz Mountains, you can find them all over the San Francisco Bay Area. Stanford University’s unofficial mascot is a redwood tree (actually part of its marching band, but you’ll see the shape of the tree in the university’s logo).

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, which is warmer and more arid. 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….”

*The orange tree: it was apparently too close to the lawn, received too much water, and died of root rot – a new one is planted but it will take awhile before it will produce oranges

Some Silicon Valley climate resources:

Wunderground for San Jose

Relocating to Silicon Valley? We have micro-climates! (my main blog – older post, to be updated soon)