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San Francisco sits at the tip of a peninsula in Northern California, surrounded on three sides by the Pacific Ocean and San Francisco Bay, at approximately 37.77°N, 122.42°W. It has a cool-summer Mediterranean climate (Köppen Csb, bordering Csc) — mild and dry in summer, mild and wet in winter — with an exceptionally narrow temperature range year-round, moderated by the cold ocean current that also gives the city its famous fog.
Summer, from June to September, is dry but famously cool and foggy rather than hot, with September and October the warmest — average highs only around 20–22°C. The cold California Current chills the air and generates thick banks of fog (nicknamed 'Karl') that pour in through the Golden Gate on summer afternoons and evenings, so July can feel chillier than April — the sea keeps the city cool while inland areas swelter. Rain is essentially absent.
Winter, from December to February, is mild and the wet season, with the coolest months bringing highs around 14°C and lows near 8°C, seldom approaching freezing. Most of the year's rain falls now, arriving on Pacific storms and occasionally as heavy atmospheric-river events, interspersed with clear, mild, pleasant days. Snow is virtually unheard of in the city.
San Francisco receives around 580–600 mm of rain a year, almost all of it in the winter half from November to March, while the summer stays dry; annual totals vary widely with the El Niño cycle. Live rainfall, humidity, and pressure readings for the city are shown in the panels above.
San Francisco's defining weather feature is its summer fog, a product of the cold offshore current and coastal upwelling, which keeps the city cool and grey on summer afternoons even as the inland valleys bake — giving rise to the quip, often misattributed to Mark Twain, about the coldest winter being a summer in San Francisco. Its many hills also create sharp microclimates, with sunny and fog-bound neighbourhoods just a short distance apart.
To follow any single measurement in San Francisco more closely, use our live instruments: the online barometer for atmospheric pressure, the thermometer for temperature, the hygrometer for humidity, the anemometer for wind speed, the wind vane for wind direction, and the rain gauge for rainfall.