Dolores Park on Sunday is perfect. The beautiful sunshine, the gorgeous view to the downtown, the newly completed children playground swarming with running kids. Everyone is having a blast. What a lovely day it is!
Dolores park (Jamison Wieser)
The only issue, ouch! Barely an hour under the sun is enough to get me sunburn. I know. I should have put on sunscreen. I have a tube with me but I just didn't expect such short exposure will do me any harm. This is a mistake I would have made many times.
But where is the San Francisco fog? The weather condition that the city is so well known for? A city shrouded in dense and cool fog. Foghorn blows the deep and the ghostly sight of cargo ship slowly emerge from the mist. The reputation of San Francisco fog spread so far that sometime visitors would ask for advice to plan around fog. How should they prepare themselves in the foggy weather. Bring umbrella? Trench coat? This is good for building up film noir atmosphere, but what you need in San Francisco is actually sunglasses and sunscreen.
As it turns out, San Francisco is one of the most sunny city in United States. It is not my wishful thinking. It is sunny according to meteorologists' statistics. 160 sunny days a year put it among the top most sunny cities. It even ranks favorably to the sunshine state of Florida, which is actually rather cloudy.
But what about the fog that engulf the city so often? It is of course no illusion. We residents experience it regularly. People who knows about San Francisco may point out to the effect of microclimate. Areas close to each other may experience dramatically different climate due to different geographic features like hills and valley. In general it means the coastal side is far more foggy than the bay side. To a visitor, it means Golden Gate Bridge and Golden Gate Park can be quite foggy, while Union Square, Embarcadero and the gorgeous Dolores Park are a lot less susceptible.
The microclimate explains some of the paradox. But what if I say the west side is also rather sunny? You may laugh at me really hard for saying this. That's pretty much people's response when the city of San Francisco announce plan to build a major solar power system on top of the Sunset Reservoir a few years ago. Everyone knows it is foggy in the Sunset district. To build a solar system there sounds so absurd that it is widely ridiculed. But wouldn't a professional solar developer have better idea then people who make judgment base on gut feeling? Indeed fog does not come all day to Sunset and it does get quite a bit of sun. According to the developer Recurrent Energy, the solar resource in Sunset is on average only 15% lower than the sunniest areas of the City and is consider quite good. With this solar power installation, it more than triple the energy San Francisco generate from the sun.
Sunset Reservoir Solar System (Recurrent Energy)
To make sense of the fog city so sunny paradox, it helps to understand a common bias known as base rate fallacy. Scientists find that people have a tendency, when making judgments of the probability with which an event will occur, to ignore the base rate and to concentrate on other specific information. Overall fog is a rather infrequent phenomenon. But the specific attribute of San Francisco's fogginess affect people's judgment more than the general base rate. To give another example, if city A hails 30 times a year, you will be right to consider it far more prone to hail than other cities. So how likely is it going to hail next Monday? Some people maybe tricked to think it is quite likely. They ignored the fact that hail is a rare phenomenon and even hail prone city A has 326 hail free days.
Let's not get distracted. Meteorologists say San Francisco is a sunny city. Bring sunglasses and sunscreen to enjoy your the visit. Don't get sunburnt like me.
2012.05.07 - comments
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