Weather San Francisco , California
San Francisco is located in California, on the west coast of the United States of America, and is a popular tourist destination, enjoying mild, dry summers and cool, wet winters. With several micro-climates due to its geography, the weather averages can vary greatly across the city and throughout the months.
The hottest month of the year on average is July and the coldest is January, which is also the wettest month. The unpredictable climate means the weather is hard to predict and hot days can occur during the autumn months. The city has many tourist attractions such as the Golden Gate Bridge, Alcatraz, and its alternative, liberal counter-culture that has been a part of city life since the 1960's. The area is susceptible to earthquakes and has had many severe earthquakes in the past. The last major earthquake was in 1989 and measured 6.9 on the Richter scale.
The topography of San Francisco and maritime location at the end of a peninsular, surrounded by the Pacific Ocean and San Francisco Bay, create little year-round temperature variation. The city is also well-known for its foggy conditions, mainly occurring during the summer months, as the hot air rising in California's inland valleys creates low pressure, pulling in winds from the North Pacific and creating the fog.
Summer Weather in San Francisco
Temperature
Summer months in San Francisco, from June to August sees average high temperatures of between 190C in June to 230C in July with overnight lows ranging from 110C to 150C. These mild temperatures are ideal for exploring the city and surrounding area, although bringing a jacket is wise as temperatures can drop quickly.
Sea Temperature
Cool sea temperatures mean swimming is not a popular activity, although August has the one of the highest annual sea temperatures at 150C.
Sunshine Hours
Summer is the sunniest month of the year, with daily hours of sunshine ranging from 12 hours in June and August to an average of 14 hours of sunshine a day in July which is the sunniest month of the year. Summer is also characterized by the persistent fog, which usually rolls in during the afternoon after clear mornings. The warmer bay side tends to be clearer than the cooler Pacific Ocean side and this fog gradually fades by August, leaving only a thin finger of fog moving through the Golden Gate Bridge.
Rain
Summers are dry and see very little rain, with 0-2 days of precipitation throughout June to August.
Autumn Weather in San Francisco
September to November brings gradually cooler weather and fewer sunny days, but this is still a pleasant time to visit San Francisco, as the fog has cleared, the rainfall is low and the temperatures remain mild.
Temperature
Average temperatures are stable at around 140C in September and October, before starting to drop to 130C in November. Daytime temperatures can reach a high of 210C with a night-time low of 120C. The lack of fog can make the days feel even warmer than in summer, and sea temperatures are also the warmest of the year in these months remaining at 150C during September and October. These months often see locals going to the beach and enjoying outdoor activities as the temperatures can be the highest of the year.
Rain
Although autumn is not a wet season, there is increasing rainfall during these months, ranging from 8mm and 2 days of rain in September to 64mm falling over around 7 days in November.
Sunshine Hours
Daily hours of sunshine also begin to decline throughout autumn from 11 hours in September to 8 hours in November.
Winter Weather in San Francisco
Rain
Winter, from December to February, is the wet season in San Francisco, and 80% of rain can fall between November and March. Rainfall can be heavy and persistent with winter storms bringing substantial rain. The heaviest rain is seen in January with 119mm over 11 days, with around 112mm falling in December. February sees less rain at around 97mm as the rainy season gradually comes to an end. Days between these heavy downpours can be crisp and bright as the weather remains unpredictable.
Temperature
Visitors should remember to pack warm clothes as well as their umbrella if travelling to San Francisco during the winter months. Plan for indoor activities at this time of year as, although daytime temperatures are mild compared to other US cities, days can be cold and temperatures can drop to as low as 70C in January. Average temperatures range from 100C to 150C and can drop to 70C at night. Snow is extremely rare and if it does fall, it will not settle.
Sunshine Hours
Expect around 6 to 7 hours of sunshine per day and cold sea temperatures ranging from 120C to 130C.
Spring Weather in San Francisco
Temperature
March, April and May are pleasant months for visiting San Francisco, as the weather remains mild and dry with cloudless skies. It is still fairly cool with temperatures stable at 110C in March and April and increasing gradually to an average of 130C in May. Spring temperatures can reach a high of 170C and drop to a low of 90C.
Rain
Rainfall begins to decrease in spring and there are fewer rainy days during these months. March continues to see the end of the rainy season with an average of 79mm falling over 10 days, but by May the amount of rain decreases to around 18mm over 4 days of the month. Like autumn, this time of year can feel warmer than expected as the fog is not yet keeping the temperatures down.
The weather is variable across the San Francisco Bay area but is generally warmer on the bay side then on the ocean side. It is also foggier on the west side as the fog rolls in from the Pacific Ocean. It is important to pack for all weather conditions when visiting San Francisco, and layering is essential.
The weather can change in an instant as cold winds can blow in from the Pacific Ocean without warning making a warm, sunny day suddenly feel like winter. The fog can be the summer's natural air conditioner as it cools the day considerably as it blankets the city. The highest recorded temperature was 390C in July 1998 and in 2000, while the lowest recorded temperature was -30C in December 1932.
Precipitation varies greatly from year to year depending on the conditions in the Pacific Ocean. El Nio years bring warmer air and above average rainfall, while colder, drier La Nia conditions bring less rain to the city. The summer fog follows a pattern of sunny mornings heating up the land, with low pressure occurring by the middle of the day. As the maritime wind increases, it pushes the fog inland and is unable to evaporate, causing the famous foggy conditions that San Francisco is known for. Take a look at the weather forecast and find out how the averages are calculated here.
