Weather in Silicon Valley and the San Francisco Bay area

November 8, 2011 at 7:20 pm | Posted in Uncategorized | Leave a comment
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Once we decided to move to California, I started looking at the weather in detail to help choose a place to live. This actually turned out to be very complicated (but very interesting) because the Bay area has many microclimates. (According to Wikipedia, a microclimate is a local atmospheric zone where the climate differs from the surrounding area.)

A warning: this whole post is about weather. If you aren’t interested in weather, you may want to just give this one a miss.

For example, let’s look at three different cities that span all of Silicon Valley:

San Francisco – 22 inches of rain per year:

Mountain View – 15 inches of rain per year:

San Jose – 15 inches of rain per year:

The differences are especially noticeable in the summer: in August, San Francisco’s average high is only 69 compared to Mountain View’s 79 and to San Jose’s 87. Which might not seem that unreasonable until you realize how close they all are — SF and SJ are only an hour apart and have a difference of almost twenty degrees!

So what’s going on? Why the microclimates, and how can we use this information to make sure we live someplace warm?

Well, let’s look at a map of the area:


As I mentioned in my last post, the term “Silicon Valley” generally refers to the area between San Francisco and San Jose. Now let’s look at the terrain version of this map with some added notes:

Even though this is labeled, I’ll describe it anyway:

  • The Santa Cruz mountain range (yellow arrows) runs NW and SE. On the map you can see that the southern “side” of it is all green with plants, whereas the northern side is much more brownish gray.
  • Silicon Valley is the area between the red arrows.
  • The San Francisco Bay is specified with blue arrows. The Golden Gate bridge is at its mouth to the Pacific on the west.
  • The area on the NE side of the Bay is generally called the “east bay,” (green arrows) and several people have told us that it’s kind of a crappy area.

Now it just so happens that the weather in this part of the world generally comes up from the ocean to the southwest. So when cold and rain and clouds and etc. are blowing NE towards Silicon Valley, an interesting thing happens: they hit the Santa Cruz mountains. And just like a stunt motorcyclist who rides up a ramp, all the weather and precipitation from the ocean shoots way high up in the atmosphere and continues its northeast-ward path too far up to cause any rain. You can see evidence of this on the mountains themselves: on the ocean side, they’re all green and lush from where the rain constantly hits them. On the land side, though, it’s actually quite dry. (This area is called a rain shadow.)

Over time, of course, the weather drifts back down and begins raining on land, but by this time it has moved even further northeast and has missed Silicon Valley entirely. (A similar thing happens in Seattle, actually — downtown Seattle is in the rain shadow of mountains to the west, so it gets far less rain than many of its more easterly suburbs.)

But this is certainly not the only effect. Let’s look at another one:

As I said, the weather is heading NE from the Pacific. At the bottom of this image, you can see the last effect I discussed: the red arrows show the cold air moving NE and the orange arrows show the weather shooting up when it hits the mountains. But take another look at that mountain range: it pretty much stops at the town of Pacifica (slightly below the blue arrows near the middle of the map). This means that unlike Silicon Valley, San Francisco really has nothing to shield it from the chilly Pacific air. Consequently it is actually a pretty cool city (and it is even colder than Seattle some of the time even though SF is at a much lower latitude).

Once the cold air passes through San Francisco, it continues right across the Bay without any obstacles in its path. Then it hits the east bay and makes them colder and wetter as well. Not as cold, of course, because that weather has been warming up a little over the land, but still much colder than sheltered Silicon Valley.

Along similar lines, once that weather has come inland north of the Santa Cruz mountains, some of it will reach the northern part of Silicon Valley. In particular, San Bruno (where we are staying right now), Burlingame, and San Mateo are much cooler than San Jose (which is at the southeastern edge of Silicon Valley and can be seen two maps up from this one).

There are other effects at work here as well, but these are the main ones I’ve been able to find. I know practically nothing about weather, but this post is what I’ve been able to put together from an evening of reading various weather blogs. And I’m half writing this because nobody seems to have written an article like this before — this is the article I was trying to find and didn’t seem to exist. =)

So to generalize: San Francisco and the east bay are cold and wet. San Jose is warm and dry. The Silicon Valley cities between them vary more or less linearly.

We’re hoping to find an apartment in Foster City, which is still pretty warm despite being close to chilly San Bruno. Driving to Mountain View these days is lovely — I keep my top down all day and drive around without a coat and it almost makes me forget that there even is a cold Seattle where I couldn’t go jacket-free all summer long. It’s nice. =)

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Earthquakes, earthquakes everywhere!

November 5, 2011 at 6:13 pm | Posted in Uncategorized | 1 Comment
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I have never felt an earthquake. I’ve always wanted to, but they somehow elude me.  When I was four or five I remember coming home from school and being told an earthquake had just happened, but I was in the car and missed it. This has happened quite a lot, most recently this past October 20th — the very night we arrived in California from Seattle. We didn’t feel a thing. Furthermore, that earthquake was a magnitude 4 and it happened barely 20 miles away in Berkeley, CA, and we still missed it. Life is so unfair!

So tonight I decided to look at the earthquake record and see if there had been any more that we’d missed. Here is what I found:

352 earthquakes! And what’s more, that’s one week’s worth! I don’t know if everybody else knew about this, but I certainly didn’t. Not only that, a whole bunch of them were right here in the Bay area. (You can see the Bay on the map above on California’s coast about halfway between 35° and 40°.)  There are at least ten or twelve there. Come on! Here’s a close up:

"ten or twelve." Ha. More like 94.

Everybody keeps telling me it’s inevitable, which I’m sure is true since we plan to live here for a good long while. But it is frustrating to think that there are so many and we haven’t even been able to notice them.

Also, in case any of you noticed that those two images have two different dates, it’s because one is showing UTC and the other is showing Pacific time.

Oh, and in unrelated news, I recently discovered that my blog contains ads. Those ads don’t show up for me as the owner of the blog, so I didn’t know about them til I looked at my own post on my phone just now. I wanted to let you all know that I’m not making money on you guys from those ads — this is a free WordPress blog, and they show their own ads and they get the money. Just so you know.

Finally, if you’d like to look at the earthquake record for your area, you can do so here: USGS Real-time Earthquake Record. Just click on the map for your state and see what’s been happening (or hasn’t been happening) near you.

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