San Francisco, California Climate Records and Averages

San Francisco, California enjoys a marine–type climate characterized by mild and moderately wet winters and dry, cool summers. Winter rains, occurring from November through March, account for over 80 percent of the annual rainfall and measurable precipitation occurs on an average of 10 days per month during this period. However, there are frequent dry periods lasting well over a week. Severe winter storms with gale winds and heavy rains occur only occasionally. Thunderstorms average two a year and could occur in any month.

The daily and annual range in temperature is small. A few frosty mornings occur during the winter, but the temperature seldom drops below freezing. Winter temperatures generally rise to the high 50s in the early afternoon.

The summer weather is dominated by a cool sea breeze resulting in an average summer wind speed of nearly 15 mph. Winds are light in the early morning but normally reach 20 to 25 mph in the afternoon.

A sea fog, arriving over the city during the late evening or night as a low cloud, is another persistent feature of summer weather. This fog, occasionally producing drizzle or mist, usually disappears during late morning. Despite the morning overcast, summer days are sunny. On the average a total of only 14 days during the four months from June through September are classified as cloudy.

Daytime temperatures are held down both by the morning low overcast and the afternoon strengthening sea breeze, resulting in daily maximum readings averaging about 70 degrees from May through August. September, when the sea breeze becomes less pronounced, is the warmest month with highs in the 70s. Low temperatures during the summer are in the mid–50s.

Temperature + Precipitation

Precipitation

California averages and extremes in precipitation and temperature and Top 10 U.S climate extremes.

Data period is 1948 - 2010, San Francisco Airport. Source: Western Regional Climate Center