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Average weather, temperature, rainfall, sunshine hours
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.
The city is located in the central part of
California, at almost 38 degrees north latitude, on the Pacific Ocean coast.
At the international airport, which is located south of the city and overlooks the bay,
daytime temperatures are around 14/15 °C (57/59 °F) in December and January and 23/24 °C (73/75 °F) from July to October.
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.
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.
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.
San Francisco - Climate data
In San Francisco, the
average temperature of the coldest month (January) is of
10.7 °C, that of the warmest month (September) is of
18.7 °C. Here are the average temperatures.
San Francisco - Average temperatures (1991-2020) |
| Month | Min | Max | Mean |
|---|
| January | 6.8 | 14.6 | 10.7 |
|---|
| February | 7.7 | 16.1 | 11.9 |
|---|
| March | 8.5 | 17.7 | 13.1 |
|---|
| April | 9.4 | 19 | 14.2 |
|---|
| May | 10.9 | 20.5 | 15.7 |
|---|
| June | 12 | 22.4 | 17.2 |
|---|
| July | 13 | 22.8 | 17.9 |
|---|
| August | 13.5 | 23.2 | 18.4 |
|---|
| September | 13.3 | 24.2 | 18.7 |
|---|
| October | 11.9 | 22.8 | 17.4 |
|---|
| November | 9.1 | 18.1 | 13.6 |
|---|
| December | 6.9 | 14.7 | 10.8 |
|---|
| Year | 10.3 | 19.7 | 14.95 |
|---|
amounts to
490 millimeters per year: it is therefore quite scarce. It ranges from
0.1 millimeters in the driest month (July) to
105 millimeters in the wettest one (December). Here is the average precipitation.
San Francisco - Average precipitation| Month | Days |
|---|
| January | 100 | 12 |
|---|
| February | 95 | 11 |
|---|
| March | 65 | 11 |
|---|
| April | 40 | 7 |
|---|
| May | 12 | 5 |
|---|
| June | 4 | 2 |
|---|
| July | 0 | 1 |
|---|
| August | 1 | 2 |
|---|
| September | 2 | 2 |
|---|
| October | 20 | 4 |
|---|
| November | 50 | 8 |
|---|
| December | 105 | 11 |
|---|
| Year | 490 | 75 |
|---|
The
sea temperature ranges from
12 °C in February, March, April, May, June to
14.5 °C in September. Here are the average sea temperatures.
San Francisco - Sea temperature| Month |
|---|
| January | 12.5 |
|---|
| February | 12 |
|---|
| March | 12 |
|---|
| April | 12 |
|---|
| May | 12 |
|---|
| June | 12 |
|---|
| July | 13 |
|---|
| August | 14 |
|---|
| September | 14.5 |
|---|
| October | 14 |
|---|
| November | 13.5"> |
|---|
| December | 12.5 |
|---|
| Year | 12.9 |
|---|
There are on average around 3065
sunshine hours per year. Here are the average hours of sunshine per day.
San Francisco - Sunshine hours| Month | Average | Total |
|---|
| January | 6 | 185 |
|---|
| February | 7.5 | 210 |
|---|
| March | 8.5 | 270 |
|---|
| April | 10.5 | 310 |
|---|
| May | 10.5 | 325 |
|---|
| June | 10.5 | 310 |
|---|
| July | 10 | 315 |
|---|
| August | 9.5 | 285 |
|---|
| September | 9 | 270 |
|---|
| October | 8 | 245 |
|---|
| November | 6 | 175 |
|---|
| December | 5 | 160 |
|---|
| Year | 8.4 | 3065 |
|---|
San Francisco - Weather by month
Based on the period 1991-2020
January, the coldest month of the year, is generally a mild month. The average temperature is of
10.7 °C, with a minimum of
6.8 °C and a maximum of
14.6 °C.
On the coldest nights of the month, the temperature usually drops to around
2.5 °C. However, it dropped to
-1 °C in January 2001.
On the warmest days of the month, the temperature usually reaches around
18.5 °C. However, it reached
23.3 °C in January 2015.
Precipitation amounts to
100 mm, 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 of
10.8 kph.
The average sea temperature is of
12.4 °C. Therefore, the sea is very cold for swimming.
February is generally a mild month. The average temperature is of
11.9 °C, with a minimum of
7.7 °C and a maximum of
16.1 °C.
On the coldest nights of the month, the temperature usually drops to around
4 °C. However, it dropped to
-0.9 °C in February 1998.
On the warmest days of the month, the temperature usually reaches around
21 °C. However, it reached
24.4 °C in February 1992.
Precipitation amounts to
95 mm, 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 of
13.6 kph.
The average sea temperature is of
12.2 °C. Therefore, the sea is very cold for swimming.
March is generally a mild month. The average temperature is of
13.1 °C, with a minimum of
8.5 °C and a maximum of
17.7 °C.
On the coldest nights of the month, the temperature usually drops to around
5 °C. However, it dropped to
-0.3 °C in March 1998.
On the warmest days of the month, the temperature usually reaches around
23.5 °C. However, it reached
28.3 °C in March 2005.
Precipitation amounts to
65 mm, 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 of
16.2 kph.
The average sea temperature is of
12.2 °C. Therefore, the sea is very cold for swimming.
April is generally a mild month. The average temperature is of
14.2 °C, with a minimum of
9.4 °C and a maximum of
19 °C.
On the coldest nights of the month, the temperature usually drops to around
6.5 °C. However, it dropped to
3.9 °C in April 1999.
On the warmest days of the month, the temperature usually reaches around
27 °C. However, it reached
33 °C in April 2009.
Precipitation amounts to
40 mm, 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 of
20.2 kph.
The average sea temperature is of
11.8 °C. Therefore, the sea is very cold for swimming.
May is generally a very mild month. The average temperature is of
15.7 °C, with a minimum of
10.9 °C and a maximum of
20.5 °C.
On the coldest nights of the month, the temperature usually drops to around
9 °C. However, it dropped to
6.7 °C in May 2008.
On the warmest days of the month, the temperature usually reaches around
29.5 °C. However, it reached
35.6 °C in May 2008.
Precipitation amounts to
12.2 mm, 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 of
21.9 kph.
The average sea temperature is of
11.8 °C. Therefore, the sea is very cold for swimming.
June is generally a very mild month. The average temperature is of
17.2 °C, with a minimum of
12 °C and a maximum of
22.4 °C.
On the coldest nights of the month, the temperature usually drops to around
10 °C. However, it dropped to
8.3 °C in June 1991.
On the warmest days of the month, the temperature usually reaches around
31.5 °C. However, it reached
40.6 °C in June 2000.
Precipitation amounts to only
3.6 mm, 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 of
22.1 kph.
The average sea temperature is of
12.2 °C. Therefore, the sea is very cold for swimming.
July is generally a very mild month. The average temperature is of
17.9 °C, with a minimum of
13 °C and a maximum of
22.8 °C.
On the coldest nights of the month, the temperature usually drops to around
11 °C. However, it dropped to
9 °C in July 1998.
On the warmest days of the month, the temperature usually reaches around
30 °C. However, it reached
36.7 °C in July 2018.
Precipitation amounts to only
0.1 mm, and all occurs in one day.
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 of
20.6 kph.
The average sea temperature is of
13.1 °C. Therefore, the sea is very cold for swimming.
August is generally a warm month. The average temperature is of
18.4 °C, with a minimum of
13.5 °C and a maximum of
23.2 °C.
On the coldest nights of the month, the temperature usually drops to around
12 °C. However, it dropped to
10 °C in August 1995.
On the warmest days of the month, the temperature usually reaches around
31 °C. However, it reached
37.8 °C in August 1993.
Precipitation amounts to only
1.1 mm, 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 of
19.8 kph.
The average sea temperature is of
14 °C. Therefore, the sea is very cold for swimming.
September, the warmest month of the year, is generally a warm month. The average temperature is of
18.7 °C, with a minimum of
13.3 °C and a maximum of
24.2 °C.
On the coldest nights of the month, the temperature usually drops to around
11 °C. However, it dropped to
9.4 °C in September 1993.
On the warmest days of the month, the temperature usually reaches around
32.5 °C. However, it reached
40 °C in September 2017.
Precipitation amounts to only
1.8 mm, 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 of
17.8 kph.
The average sea temperature is of
14.4 °C. Therefore, the sea is very cold for swimming.
October is generally a very mild month. The average temperature is of
17.4 °C, with a minimum of
11.9 °C and a maximum of
22.8 °C.
On the coldest nights of the month, the temperature usually drops to around
9 °C. However, it dropped to
6.1 °C in October 2002.
On the warmest days of the month, the temperature usually reaches around
30.5 °C. However, it reached
35 °C in October 2014.
Precipitation amounts to
20 mm, 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 of
14.6 kph.
The average sea temperature is of
14.2 °C. Therefore, the sea is very cold for swimming.
November is generally a mild month. The average temperature is of
13.6 °C, with a minimum of
9.1 °C and a maximum of
18.1 °C.
On the coldest nights of the month, the temperature usually drops to around
5.5 °C. However, it dropped to
1.7 °C in November 1994.
On the warmest days of the month, the temperature usually reaches around
24 °C. However, it reached
27.8 °C in November 2018.
Precipitation amounts to
50 mm, 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 of
11.8 kph.
The average sea temperature is of
13.6 °C. Therefore, the sea is very cold for swimming.
December is generally a mild month. The average temperature is of
10.8 °C, with a minimum of
6.9 °C and a maximum of
14.7 °C.
On the coldest nights of the month, the temperature usually drops to around
2.5 °C. However, it dropped to
-1.4 °C in December 1998.
On the warmest days of the month, the temperature usually reaches around
18.5 °C. However, it reached
22.8 °C in December 2020.
Precipitation amounts to
105 mm, 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 of
11.6 kph.
The average sea temperature is of
12.7 °C. Therefore, the sea is very cold for swimming.