San Francisco weather is one of the many reasons for the city's popularity as a vacation destination. When everyone else is sweltering, San Francisco is playing it cool. Even in winter the weather is mild. Average winter highs are only 10 degrees (F) cooler than those in the summer.
San Francisco's weather is unique, because the geography of the place is so unusual. The City sits on a peninsula surrounded by the waters of the Pacific Ocean and the San Francisco Bay. All that cool water moderates the climate and keeps temperatures within a fairly narrow range throughout the year.
San Francisco Travel Association photo by Kerrick James
But that's not the whole story. San Francisco is a city of hills, 47 of them to be exact, many of them pretty steep. Those hills create a lot of microclimates, so that the weather can change dramatically as you travel around the city. One area may be warm and sunny, while a short distance away, it's foggy and cool.
The effect is even more noticeable between the east and west sides of the city. The west is much foggier and cooler than the east, which is probably why the powers that be situated the airport on the east side of the city.
The standard advice to San Francisco tourists is to dress in layers, preferably with a light jacket, sweater, or sweatshirt that can be easily tied around your waist or stowed in a backpack when you don't need it. Closed toed shoes are best, your most comfortable pair if you plan to do a lot of walking.
San Francisco weather is at its peak in the Fall. Temperatures are warm; there's very little fog, and rain is highly unlikely. (The rainy season is from November through March.) In fact, September is the warmest month, with average highs of 71 degrees F. San Francisco is rarely hot (usually no more than 75 degrees F.) but in September that's very likely to happen. You may even find that it's warm enough to do a bit of sunbathing at the beach.
Spring is another good time to visit. While not quite as warm as the Fall, the weather is dry and clear. Average high temperatures are in the mid 60's. But remember, even though there's less fog, evenings can still get cool, so don't forget to dress in layers.
San Francisco is famous for its fog, which provides the city with its "natural air conditioning." You'll see exactly what that term means when the fog creeps in and the temperature suddenly drops. You'll be reaching for your sweater or jacket pretty quickly.
During the summer months, the fog typically blankets the city in the early morning, burns off by noon, then rolls back in during the afternoon. However, coastal areas can remain overcast all day, while bayside neighborhoods are clear and sunny.
Although the fog is most common during the summer months, it can occur throughout the year. It's most likely to be dense enough to cause travel problems during the winter months.
Spring in San Francisco sees the return of the lush green hills from the winter rains. The rains continue into March (11 rainy days on average) and begin to taper off in April (only 6 rainy days). Most days are clear and mild with average highs in the mid 60's. Evenings and nights are cool, in the low 50's on average. It's an excellent time to visit San Francisco.
Summer in San Francisco is cool and foggy, just the thing if you're trying to escape the scorching heat of the Central Valley. Average highs are about 68-69 degrees F.
The mornings usually start out with fog blanketing the coastal areas, and sometimes the entire city. It usually burns off by noon, although the coast may remain overcast all day. By late afternoon, the winds off the ocean pick up (usually about 20-30 mph) and the fog starts rolling back in. Temperatures can drop quite suddenly to the 50's, and evenings are usually chilly.
While you'll have to contend with the fog, rain won't be a problem. It's a pretty rare event at this time of year.
Fall brings some glorious weather to the City. The days are usually warm and sunny; bye-bye fog. The rains don't start in earnest until November, with just a smattering in September and October (a "smattering being 2-4 days of rain a month). If there's a time when you can actually sunbathe in San Francisco, this is it.
Without the fog, evenings are actually warmer than they were in the summer. But don't get careless; you'll still want to keep that sweater handy.
Winter is the rainy season in San Francisco (and in most of California for that matter), but in spite of that your chances of enjoying clear crisp days are pretty good. The average number of rainy days ranges from 9 to 11 days a month from November through March.
January is the wettest month, in terms of both the number of days and amount of rainfall. Winter storms tend to bring downpours, so be sure to make a plan B in case you get stuck inside for a day or so.
Winter temperatures are really pretty mild, with average highs ranging from 58-65 degrees F and average lows from 46-49. The lowest recorded temperature was 27 degrees, but you're unlikely to experience anything close to that. If it snows while you're visiting San Francisco, get out your camera, because that's a rare event.
Fog isn't as common as it is in the summer, but when it does creep in it tends to be denser and more likely to cause problems getting around.