Why It's Chilly in San Francisco

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As most of the country swelters this week, San Francisco residents are pulling on their jackets and turning on the heat. The city is experiencing a winter-like chill, with temperatures in the 50s-- about 10 degrees below average. And then there's the fog, which has delayed flights at the city's airport.

We know you've heard this on many occasions, but we also know odds are you've promptly  forgotten it each and every time. So once more -- impress your friends at parties and informal meteorological gatherings! -- here's why it's so frickin' cold in San Francisco:

The chill is in part a result of San Francisco’s location between the ocean and the Central Valley, according to Diana Henderson, a forecaster with the National Weather Service Forecast Office for the San Francisco Bay Area/Monterey. To the west, the marine layer sits above the cold Pacific. To the east, heat in the valley creates thinner air and low pressure.

The valley becomes like a vacuum that wants to be filled by the heavier marine layer. It pulls that layer over San Francisco, which typically makes the city cooler than other parts of California -- and the country -- in the summer.

This week, Henderson said, an additional low-pressure system has moved in from the north, which is keeping cooler air around. She said temperatures should warm up later this week.


Meanwhile, San Francisco residents are bundling up against the chill. Here are some of their tips for dealing with the cold.