Weather and climate in San Francisco (California)

The climate of San Francisco can be defined as "Mediterranean with cool summers". In fact, both the winter temperatures and the rain pattern remind of the Mediterranean climate, but summer is unusually cool because of the cold current that flows along the coast of California and is able to cause fog in San Francisco Bay, and to function as a natural air conditioner for the city and the surrounding areas.
Here are the average temperatures measured at the international airport, which is located south of the city and overlooks the bay.

However, in the area, there are different microclimates, which must be taken into account by those who plan to move outside of the city proper (for example, you could go to the Yosemite National Park). In general, as you move away from the sea, you will find a more continental climate, a bit colder in winter and much warmer in summer.
Rainfall is not abundant, since it amounts to about 485 millimeters (19 inches) per year, but the period from November to March is quite rainy; in April and October, the rains are quite rare, while from June to September, they are definitely rare and sporadic.
Here is the average precipitation.

Winter, from December to mid-March, is mild and quite rainy. There are, however, sunny and dry periods, sometimes long. Very cold days are rare: at most, the temperature can approach freezing (0 °C or 32 °F) during the night, and only on colder periods it remains about 8/10 °C (46/50 °F) during the day. However, east of the city, in the Sacramento Valley, and more rarely also to the north and the south of the bay, there may be night frosts.
Snow is an extremely rare phenomenon. On February 5, 1976, it snowed also in the city, where, however, the temperature remained above freezing, and the snow accumulated significantly (13 cm or 5 inches) only on the hills, such as in Twin Peaks.
Every so often, fog can form in the city, while this phenomenon is more common in the Sacramento Valley.

Spring, from mid-March to May, is cool or slightly cold at night, while the days become gradually milder, and sometimes pleasantly warm, though with a moderate breeze in the afternoon that lowers the temperature. The rains become increasingly rarer.

Summer, from June to September, is cool, and it is usually foggy in the morning and sunny in the afternoon, with a cool breeze blowing from the sea. September, albeit slightly, is the warmest month. The foggiest districts (and also the windiest in the afternoon) are the westernmost ones (see Sunset District). The rains are rare, especially in July and August, when basically it never rains.
Daytime temperatures from June to September are around 17/19 °C (63/66 °F) in the towns on the Pacific coast (see Half Moon Bay) and in the western districts of San Francisco, around 21/23 °C (70/73 °F) in the eastern districts, 22/24 °C (72/75 °F) in Oakland and Richmond (on the other side of the bay), 25/26 °C (77/79 °F) in the towns on the south shore of the bay (see Palo Alto, Mountain View, Fremont), and up to 28 °C (82 °F) in San José, just south of the bay.
Beware though: it's sufficient to move to the east, in the Sacramento Valley (see Sacramento, Stockton, Modesto), to find very high temperatures, usually about 33/35 °C (91/95 °F), and sometimes even above 40 °C (104 °F).
In the following map, we can see the average maximum temperatures of August in the San Francisco area, which shows the significant differences that occur in it. The city of San Francisco is indicated by a red star.



Every so often, however, hot air from the desert manages to reach the city, so much so that the temperature can reach 35/38 °C (95/100 °F) from May to October. Anyway, these periods of hot weather are very rare (in fact, they may even not occur for a whole year), they do not last long (just one or two days), and the heat is felt only during the day, while it is cooled by the ocean breeze during the evening. For example, in June 14, 2000, the temperature reached 40.6 °C (105.1 °F), but the minimum temperature of the previous night had been 13 °C (55.5 °F), and that of the next night was only 16 °C (61 °F).

Autumn, in October and November, is initially mild, and gradually becomes cooler and rainier. Usually, it begins to get a little cold at night by late October.



The amount of sunshine in San Francisco is acceptable in winter, when there is a moderate amount of sunny days, but also cloudy periods. In spring, sunny days already prevail, while in summer, it's usually sunny in the afternoon, but in the morning, fogs and mists frequently occur. There are around 3,000 hours of sunshine a year.

Owing to the cold current, the sea in San Francisco is cold all year round. In addition, the water temperature remains quite stable, in fact, it ranges from 12 °C (54 °F) between January and June to 14 °C (57 °F) between August and November. Here are the average sea temperatures.

Best Time

The best time to visit San Francisco is the summer, from June to September, since it is the driest and warmest season of the year. However, you have to take into account cool temperatures, and sometimes even a little cold, at night and in the early morning, as well as morning fogs, so it's better to bring a jacket and a sweater.
Usually, in the months of April, May and October, the weather is good as well, in fact, it's often mild and sunny, even though there's a greater chance of rain; in addition, it can be cold at night, especially in April. Moreover, in spring, afternoon breezes are quite intense.

Back to California.

San Francisco - Weather by month

Based on the period 1991-2020

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January, the coldest month of the year, is generally a mild month. The average temperature is of 10.7 °C (51 °F), with a minimum of 6.8 °C (44.2 °F) and a maximum of 14.6 °C (58.2 °F).
On the coldest nights of the month, the temperature usually drops to around 2.5 °C (36.5 °F). However, it dropped to -1 °C (30.2 °F) in January 2001.
On the warmest days of the month, the temperature usually reaches around 18.5 °C (65.5 °F). However, it reached 23.3 °C (73.9 °F) in January 2015.
Precipitation amounts to 100 mm (3.9 in), distributed over 12 days.
The day lasts on average 9 hours and 55 minutes.
There are on average 6 hours of sunshine per day. So, the sun shines 60% of the time.
The average humidity is 79%. Hence, the air is normally humid.
The average wind speed is 11 kph (7 mph).
The average sea temperature is of 12.5 °C (54.5 °F). Therefore, the sea is very cold for swimming.

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February is generally a mild month. The average temperature is of 11.9 °C (53 °F), with a minimum of 7.7 °C (45.9 °F) and a maximum of 16.1 °C (61 °F).
On the coldest nights of the month, the temperature usually drops to around 4 °C (39 °F). However, it dropped to -0.9 °C (30.4 °F) in February 1998.
On the warmest days of the month, the temperature usually reaches around 21 °C (69.5 °F). However, it reached 24.4 °C (75.9 °F) in February 1992.
Precipitation amounts to 95 mm (3.7 in), distributed over 11 days.
The day lasts on average 10 hours and 50 minutes.
There are on average 7.5 hours of sunshine per day. So, the sun shines 68% of the time.
The average humidity is 76%. Hence, the air is normally humid.
The average wind speed is 14 kph (8 mph).
The average sea temperature is of 12 °C (54 °F). Therefore, the sea is very cold for swimming.

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March is generally a mild month. The average temperature is of 13.1 °C (56 °F), with a minimum of 8.5 °C (47.3 °F) and a maximum of 17.7 °C (63.8 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 5 °C (41 °F). However, it dropped to -0.3 °C (31.5 °F) in March 1998.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 23.5 °C (74.5 °F). However, it reached 28.3 °C (82.9 °F) in March 2005.
Precipitation amounts to 65 mm (2.6 in), distributed over 11 days.
The day lasts on average 12 hours and 0 minutes.
There are on average 8.5 hours of sunshine per day. So, the sun shines 72% of the time.
The average humidity is 74%. Hence, the air is normally humid.
The average wind speed is 16 kph (10 mph).
The average sea temperature is of 12 °C (54 °F). Therefore, the sea is very cold for swimming.

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April is generally a mild month. The average temperature is of 14.2 °C (58 °F), with a minimum of 9.4 °C (48.9 °F) and a maximum of 19 °C (66.2 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 6.5 °C (43.5 °F). However, it dropped to 3.9 °C (39 °F) in April 1999.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 27 °C (80.5 °F). However, it reached 33 °C (91.4 °F) in April 2009.
Precipitation amounts to 40 mm (1.6 in), distributed over 7 days.
The day lasts on average 13 hours and 10 minutes.
There are on average 10.5 hours of sunshine per day. So, the sun shines 78% of the time.
The average humidity is 70%. Hence, the air is normally humid.
The average wind speed is 20 kph (13 mph).
The average sea temperature is of 12 °C (53 °F). Therefore, the sea is very cold for swimming.

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May is generally a very mild month. The average temperature is of 15.7 °C (60 °F), with a minimum of 10.9 °C (51.7 °F) and a maximum of 20.5 °C (68.9 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 9 °C (48 °F). However, it dropped to 6.7 °C (44.1 °F) in May 2008.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 29.5 °C (84.5 °F). However, it reached 35.6 °C (96.1 °F) in May 2008.
Precipitation amounts to 12 mm (0.5 in), distributed over 5 days.
The day lasts on average 14 hours and 20 minutes. So the days are long.
There are on average 10.5 hours of sunshine per day. So, the sun shines 73% of the time.
The average humidity is 70%. Hence, the air is normally humid.
The average wind speed is 22 kph (14 mph).
The average sea temperature is of 12 °C (53 °F). Therefore, the sea is very cold for swimming.

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June is generally a very mild month. The average temperature is of 17.2 °C (63 °F), with a minimum of 12 °C (53.6 °F) and a maximum of 22.4 °C (72.3 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 10 °C (50.5 °F). However, it dropped to 8.3 °C (46.9 °F) in June 1991.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 31.5 °C (89 °F). However, it reached 40.6 °C (105.1 °F) in June 2000.
Precipitation amounts to only 4 mm (0.2 in), distributed over 2 days.
The day lasts on average 14 hours and 40 minutes. So the days are long. June 21, the summer solstice, is the longest day of the year in the Northern Hemisphere.
There are on average 10.5 hours of sunshine per day. So, the sun shines 71% of the time.
The average humidity is 69%.
The average wind speed is 22 kph (14 mph).
The average sea temperature is of 12 °C (54 °F). Therefore, the sea is very cold for swimming.

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July is generally a very mild month. The average temperature is of 17.9 °C (64 °F), with a minimum of 13 °C (55.3 °F) and a maximum of 22.8 °C (73 °F).
On the coldest nights of the month, the temperature usually drops to around 11 °C (52 °F). However, it dropped to 9 °C (48.2 °F) in July 1998.
On the warmest days of the month, the temperature usually reaches around 30 °C (86 °F). However, it reached 36.7 °C (98.1 °F) in July 2018.
Precipitation amounts to only 0 mm (0 in), so on average it never rains in the whole month.
The day lasts on average 14 hours and 30 minutes. So the days are long.
There are on average 10 hours of sunshine per day. So, the sun shines 70% of the time.
The average humidity is 73%. Hence, the air is normally humid.
The average wind speed is 21 kph (13 mph).
The average sea temperature is of 13 °C (55.5 °F). Therefore, the sea is very cold for swimming.

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August is generally a warm month. The average temperature is of 18.4 °C (65 °F), with a minimum of 13.5 °C (56.2 °F) and a maximum of 23.2 °C (73.8 °F).
On the coldest nights of the month, the temperature usually drops to around 12 °C (53 °F). However, it dropped to 10 °C (50 °F) in August 1995.
On the warmest days of the month, the temperature usually reaches around 31 °C (87.5 °F). However, it reached 37.8 °C (100 °F) in August 1993.
Precipitation amounts to only 1 mm (0 in), distributed over 2 days.
The day lasts on average 13 hours and 30 minutes.
There are on average 9.5 hours of sunshine per day. So, the sun shines 69% of the time.
The average humidity is 74%. Hence, the air is normally humid.
The average wind speed is 20 kph (12 mph).
The average sea temperature is of 14 °C (57 °F). Therefore, the sea is very cold for swimming.

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September, the warmest month of the year, is generally a warm month. The average temperature is of 18.7 °C (66 °F), with a minimum of 13.3 °C (55.9 °F) and a maximum of 24.2 °C (75.5 °F).
On the coldest nights, which normally occur at the end of the month, the temperature usually drops to around 11 °C (52 °F). However, it dropped to 9.4 °C (48.9 °F) in September 1993.
On the warmest days, which normally occur at the beginning of the month, the temperature usually reaches around 32.5 °C (90.5 °F). However, it reached 40 °C (104 °F) in September 2017.
Precipitation amounts to only 2 mm (0.1 in), distributed over 2 days.
The day lasts on average 12 hours and 25 minutes.
There are on average 9 hours of sunshine per day. So, the sun shines 73% of the time.
The average humidity is 72%. Hence, the air is normally humid.
The average wind speed is 18 kph (11 mph).
The average sea temperature is of 14.5 °C (58 °F). Therefore, the sea is very cold for swimming.

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October is generally a very mild month. The average temperature is of 17.4 °C (63 °F), with a minimum of 11.9 °C (53.4 °F) and a maximum of 22.8 °C (73.1 °F).
On the coldest nights, which normally occur at the end of the month, the temperature usually drops to around 9 °C (48 °F). However, it dropped to 6.1 °C (43 °F) in October 2002.
On the warmest days, which normally occur at the beginning of the month, the temperature usually reaches around 30.5 °C (87 °F). However, it reached 35 °C (95 °F) in October 2014.
Precipitation amounts to 20 mm (0.8 in), distributed over 4 days.
The day lasts on average 11 hours and 10 minutes.
There are on average 8 hours of sunshine per day. So, the sun shines 71% of the time.
The average humidity is 69%.
The average wind speed is 15 kph (9 mph).
The average sea temperature is of 14 °C (57.5 °F). Therefore, the sea is very cold for swimming.

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November is generally a mild month. The average temperature is of 13.6 °C (56 °F), with a minimum of 9.1 °C (48.4 °F) and a maximum of 18.1 °C (64.6 °F).
On the coldest nights, which normally occur at the end of the month, the temperature usually drops to around 5.5 °C (41.5 °F). However, it dropped to 1.7 °C (35.1 °F) in November 1994.
On the warmest days, which normally occur at the beginning of the month, the temperature usually reaches around 24 °C (75 °F). However, it reached 27.8 °C (82 °F) in November 2018.
Precipitation amounts to 50 mm (2 in), distributed over 8 days.
The day lasts on average 10 hours and 5 minutes.
There are on average 6 hours of sunshine per day. So, the sun shines 57% of the time.
The average humidity is 74%. Hence, the air is normally humid.
The average wind speed is 12 kph (7 mph).
The average sea temperature is of 13.5 °C (56.5 °F). Therefore, the sea is very cold for swimming.

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December is generally a mild month. The average temperature is of 10.8 °C (51 °F), with a minimum of 6.9 °C (44.5 °F) and a maximum of 14.7 °C (58.4 °F).
On the coldest nights of the month, the temperature usually drops to around 2.5 °C (37 °F). However, it dropped to -1.4 °C (29.5 °F) in December 1998.
On the warmest days of the month, the temperature usually reaches around 18.5 °C (65.5 °F). However, it reached 22.8 °C (73 °F) in December 2020.
Precipitation amounts to 105 mm (4.1 in), distributed over 11 days.
The day lasts on average 9 hours and 35 minutes. December 21, the winter solstice, is the shortest day of the year in the Northern Hemisphere.
There are on average 5 hours of sunshine per day. So, the sun shines 54% of the time.
The average humidity is 76%. Hence, the air is normally humid.
The average wind speed is 12 kph (7 mph).
The average sea temperature is of 12.5 °C (55 °F). Therefore, the sea is very cold for swimming.