San Francisco does not belong to the California of endless blue skies and slothful warmth. Flanked on three sides by water, it is regularly invigorated by the fresh winds that sweep across the Peninsula. The climate is among the most stable in the world, with a daytime temperature that generally hovers around 15°C (60°F), but can drop much lower at night.
Spring and autumn usually have the sunniest days, while summer often sees heavy fog roll in through the Golden Gate. This thick mist does much to add romance to the city but it can also dash any hopes of tanning at the beach. Winter brings most of the city’s rainfall, sometimes in torrential storms.
Almost everywhere else in the Bay Area is warmer than San Francisco, especially in the summer when the East Bay basks in sunshine, and the Wine Country and other inland valleys are baking hot.
To avoid the crowds, do not come in the summer, although even then the tourist congestion is rarely off-putting. The best time to visit San Francisco is late May or June, when the hills are greenest and covered with wildflowers, or in October and November, when you can be fairly sure of good weather and reduced crowds.