Why is San Francisco so Cold?

By Teo Spengler

Chilling in San Francisco: Weather clues to use in the City by the Bay

Why is San Francisco so Cold?

Residents and tourists alike complain about San Francisco's summer weather. Visitors from overseas arrive expecting to spend July sunbathing on Ocean Beach, but their bathing suits often don't see the light of day. Instead, surfers don full-body wet suits, gloves and foot cover before venturing into the waves, while morning beachcombers wear hoodies and knit caps.

San Francisco is part of sunny California, so what's going on here?

Why is San Francisco so darn cold?

Poet Carl Sandburg romanticized fog, writing that it comes on little cat feet. In the City by the Bay, those feet aren't so little. They show up most mornings and evenings in summer, and occasionally in other months as well. That fog, caused by icy Pacific water meeting warmer air, is cold and damp, often blown in on a chilly ocean breeze.

That explains why San Francisco neighborhoods near the Pacific, like the Richmond and Sunset districts, have the reputation of being cold. Many days the fog blows off in early afternoon, leaving a blue sky and sun, but in the evenings, it tiptoes back again. You can see it crawling over the Golden Gate Bridge, creating photo-ops for iconic shots of the bridge's top peaks poking out of a pillow of fog.

San Francisco neighborhoods located away from the water don't see as much fog. Areas like Nob Hill, the Castro and South of Market are often sunny and bright from dawn to nightfall, but given the foggy fringe, temperatures within the city stay cooler than those of other inland communities.

Are there seasons in the sun?

Is there one season in San Francisco when it's always sunny? Not really, although autumn comes closest.

Many people who live in this popular city come to love or at least accept the cooler summer temperatures. Those who hate them are likely to move to warmer options in the East Bay where housing is also less expensive.

Summer temperatures are generally higher than winter temperatures. Average San Francisco temperatures peak at around 70 degrees F, with September being the warmest month. Individual days may see higher temperatures, of course. The lowest monthly average high temperature is 55 degrees F in December. December also has the lowest average minimum temperatures of around 40 degrees F.

San Francisco is a year-round tourist destination, so you aren't likely to avoid all crowds by visiting in winter. But peak season is summer, and that's when the crowds are most dense and the prices are highest. Many find fall the best season to visit, and it's often the warmest, too.

Packing for uncertainty

Given San Francisco's changing weather, you'll do best to play the chameleon yourself. Pack clothing you can layer up for chilly mornings, then layer down for warmer afternoons. You'll need a warm coat, too, for going out after sunset and comfortable shoes for tackling all those hills. You may well need rain gear in the winter, which includes rain boots.

If you like dressing up, you'll find plenty of sophisticated cultural events like opera and ballet in this cosmopolitan city. It's also scattered with elegant, top-ranked restaurants. The general fashion mode in San Francisco is somewhat low-key, so casual traveling clothes will also work almost anywhere.

About the Author

Teo Spengler earned a J.D. from U.C. Berkeley's Boalt Hall. As an Assistant Attorney General in Juneau, she practiced before the Alaska Supreme Court and the U.S. Supreme Court before opening a plaintiff's personal injury practice in San Francisco. She holds both an M.A. and an M.F.A in creative writing and enjoys writing legal blogs and articles. Spengler splits her time between French Basque Country and California.