Mark Twain once said, "If you don’t like the weather in New England, wait a few minutes."  In San Francisco, if you don’t like the weather, just drive a few miles. The temperature at both ends of the mile-long Golden Gate Bridge can be 20°F different. Since a city’s average temperature for the year is not helpful to travelers, here is a general breakdown of what to expect.

For the most part, San Francisco’s weather is temperate and, within limits, predictable although it has its own micro climate.  San Francisco temperatures seldom dip below 40°F, or reach or exceed 90°F.  Its summers are famously foggy; but for the summer visitor who hasn’t heard, it’s important to know about The City’s "natural air conditioner" - the fog. But it gives tourists the excuse to buy a souvenir SF sweatshirt or scramble to buy a windbreaker.  It can be in the 80s downtown, and then the fog rolls in in the afternoon, shaving 30 degrees off the top.  It can be in the 50s after the fog comes into The City, even as it’s still in the 90s in the surrounding counties to the north, east and south.  In winter, the ocean and Bay tend to keep The City from getting as cold as other parts of the Bay Area.  It frequently can go below freezing in the surrounding counties, and be 50F in San Francisco. Even within the city limits, the temperature can change from one block to the next. The Mission and Potrero Hill are rumored to be a few degrees warmer than the rest of the city year round, while the Sunset and Richmond districts (surrounding Golden Gate Park) are arguably the coldest, windiest and rainiest.

If you're packing for summer... 

Summer weather often catches visitors off guard.  They are either wearing shorts in 50 degree cold and wind or a jacket and sweater on a beautiful day.  Dress in layers and have a way to carry the layers with you when you peel them off.  As is the case in most of California, a typical summer day starts with fog blanketing the coastline.  It can cover the whole city or only a portion of it.  Most days, the sun will burn the fog back from the east toward the ocean by mid-morning. Most of the day should be nice and temperate. By 4 or 5 pm the winds kick up and the fog often starts rolling back in over the City, and it gets chilly. The clothing layers you put away will come in handy once more.

The Temps & Annual Events Highlights

 

Summer

In the summer months, in the 50s overnight, going up to 75°F in the afternoon. If the fog comes back in, it will drop back into the 50s.  Nearly everyday, by 3 pm, there is a west wind (from the ocean) of 25-30mph.  The wind calms by dark.  In August, there might be a few showers, even one thunderstorm, as the edge of the Southwest’s monsoons reach the Bay Area.

Annual Summer Events:

June:

- Gay Pride Parade, the largest of its kind in the United States 

July:

- Fourth of July fireworks displays are set off and viewable from several locations along the Bay-side waterfront, including the Ferry Building, Fisherman's Wharf and Chrissy Field.

- Fillmore Street Jazz Festival (multiple stages and hundreds of arts and crafts vendors)

- North Beach Jazz Festival (40+ clubs participate, look for free concerts in Washington Square Park)

August:

- The Nihonmachi Street Fair in JapanTown features cultural and musical performances

- San Francisco Shakespeare Festival 

Autumn

Autumn weather is the most dependable.  Warm (80°F in The City, 90-100°F in the East, South or North bay cities) and dry "Indian Summer" days prevail in October, when there’s least likely to be any fog or rain.  Still, it can be in the 50s at night.  Some say this is the best time of year to visit The City, and that the real summer here happens in September & October. 

Annual Autumn Events:

September:

- Ghirardelli Square Chocolate Festival

- Autumn Moon Festival and Street Fair (held in September or October) celebrates music, cuisine and culture in Chinatown.

- Opera Season opens with a ball at the War Memorial Opera House.

- The San Francisco Blues Festival at Fort Mason. 

- Folsom Street Fair in SoMA (warning: geared towards adults who don't mind leather and lots of skin!) 

October:

- Fleet Week means all kinds of watercraft on the Bay (and fly-overs from the Blue Angels) 

- Litquake is San Francisco's literary festival

- San Francisco's Jazz Festival, which runs through mid-December, takes place at venues all over the city, including Herbst Theater, Paramount Theater, the War Memorial, and the Palace of Fine Arts. Of note the new 35,000 sq ft SFJAZZ Center (at Franklin and Fell streets) is scheduled to open in 2012.

- Castro Street Fair - crafts, music, dancing and food

- Oktoberfest by the Bay - singing, dancing, food and lots of beer 

November: 

- The Day of the Dead procession (Dia de los Muertos) is held in the Mission district neighborhood, usually a day or two after Halloween. It's a community-wide, alcohol-free event that honors the dead.

- The Embarcadero Center Ice Rink opens for the holiday season at Justin Herman Plaza (end of Market St, opposite the Ferry Building) 

- The outlines of the buildings that comprise the Embarcadero Center (retail and commercial high rises near the waterfront) are all aglow with holday lights

- Macy's Union Square Tree Lighting Ceremony (usually the last weekend in November). Also check out the multi-story tree that Neiman Marcus puts up every year in its atrium. Neiman's faces Union Square at the southeast corner.

- Annual Tree Lighting Ceremony at Ghirardelli Square (usually the last weekend in November) 

- Holiday Festival of Lights at Fisherman's Wharf

- Great Dickens Christmas Fair (Cow Palace) 

Winter

The rains can be heaviest in November-December.  These are cool winter storms from the Pacific, not monsoons.  December also usually brings fog, which may burn off in the morning or linger all day.  It can make driving dangerous at night (and treacherous on Interstates 580 and 5 anytime it's present).  Usually these months are usually just cold - by San Franciscans’ standards - and clear.  It may not get above 50F in San Francisco, or above 40F in the suburbs.  Snow is very rare, except for occasional light dustings atop the nearby peaks of Mt. Tamalpais, Mt. Diablo, and Mt. Hamilton.  The Santa Cruz mountains may share the snow at these times.  Once every few years, snow flurries may reach San Francisco proper for a few minutes, but seeing snow on the ground here is such a rare event, you'd be hard pressed to find a local who's seen it happen.

Annual Winter Events:

December:

- Nob Hill - Huntington Park Tree Lighting Ceremony, including festivities at Grace Cathedral

- Holiday teas all over the city, especially at hotels near Union Square

- San Francisco Bowl (football): New Year's Eve at AT&T Park 

January:

- Ballet season opens at the War Memorial

- Dine About Town features hundreds of participating (and amazing) restaurants

February: 

- Chinese New Year Parade is a spectacular display of music, dragons, children and culture

- Crab Festival (multiple neighborhoods and venues participate) 

Spring

The rains usually return heavily in March.  Then April weather is the most uncertain of the year.  There can be a freak dry heat wave in the 80s for a few days, and a week later it can rain. By now, the surrounding hills are a vibrant green.  May can be sunny and mild, or there can be sustained overcast with temperatures usually in the 60s and 70s. The summer pattern and golden hills return in May or June.

All in all, in comparison with most places in the United States, San Francisco's climate is one of the most even and predictable. This quality is also what makes it one of the most abnormal climates in the entire country.   

The city averages a little over 300 days of sunshine per year.  San Francisco has a reputation of being windy, due to its location near cold ocean waters and its topography which funnels the winds through the city, so you'll want to have at least a jacket.  Layers of clothes will ultimately serve most practical. Ocean water temperatures are typically in the 50s and 60s.

Annual Spring Events:

March:

- Cherry Blosson Festival at the Japanese Tea Garden in Golden Gate Park 

April: 

- San Francisco International Film Festival features up and coming film makers 

May:

- Cinco de Mayo celebration: various venues and neighborhoods participate, but the Mission District is the center of the action.

- Bay to Breakers: more city-wide costume party than foot race, this nearly 100-year-old San Francisco tradition is very fun for participants but wreaks havoc on major roads. Watch for it the third Sunday in May. If you want to lace up your running shoes, the 7.46 mile (12k) distance isn't bad, but the hills, crowds and long walk back to the starting line might be.

Air conditioning in San Francisco?

In San Francisco, air conditioning is not present in many of the residences, offices, theaters as well as older, boutique style hotels. According to weather.com, the warmest month on average is September with an average high of 71°F and low of 56°F. San Francisco gets about 15 days per year with a temp over 90°F. Typically, there are not more than 3 over 90 degree days in a row.  Most importantly, even in the heat waves, it always cools down at night.  People will find that the lack of A/C is not an issue 99.9% of the time.  If air conditioning is important to you, double check the hotel, because not all properties have it.