We’re in the grips of a weird weather pattern known in Southern California as Santa Ana conditions. Along the coast of California the normal pattern is for high-pressure regions to develop over the ocean, where it’s cool, and low pressure over the interior valleys and deserts, where it’s warm. Air flows from high to low pressure in the form of winds, so the pressure differential pulls sea breezes and often fog into the hot interior valleys, cooling off the whole region. In Santa Ana conditions, a strong high-pressure region develops over the interior and the air flow is reversed, so we experience hot, often very dry winds from the east. In the autumn, when the hills are brown and dry, these desert winds can fuel devastating wild fires, like the Oakland Hills fire in 1991. But in San Francisco this translates into beach weather, where tourists and locals alike can frolic in bathing suits at Chrissy Field across from the Exploratorium (I took this picture this morning and it was 75 degrees and gorgeous at the beach… making it tough to stay in the office).

I became a weather weenie a few years ago when I wrote the book… err, wrote a book, about weather and atmospheric physics called “Watching Weather”. Since we usually have the ocean as a natural air conditioner, most people who live in coastal parts of the bay area don’t have central air. We depend on sea breezes and maybe a fan to help move air around and cool our houses and offices. But I’ve often wondered whether it’s better to place a fan so that it sucks hot air out of a room or pulls cool air into a room. An unscientific poll of physicists around the Exploratorium concludes that it’s better to push hot air out, since pulling in cool air doesn’t uniformly displace the hot air, especially in the corners of the room. That’s of course assuming that it’s colder outside than inside a room, which is usually the case in the evening when the house is much hotter than the outside air. If you have a better rationale for how to cool a room, send a comment.

If you’re a weather weenie too, here’s a link to our current weather information and rooftop cam (you can point the cam to see conditions at Chrissy Field, especially useful for wind and kite surfers).