Average Weather in San Francisco California, United States
In San Francisco, the summers are long, comfortable, arid, and mostly clear and the winters are short, cold, wet, and partly cloudy. Over the course of the year, the temperature typically varies from 45°F to 72°F and is rarely below 39°F or above 83°F.
The warm season lasts for 4.4 months, from June 12 to October 25, with an average daily high temperature above 69°F. The hottest day of the year is September 20, with an average high of 72°F and low of 58°F.
The cool season lasts for 2.0 months, from December 4 to February 5, with an average daily high temperature below 59°F. The coldest day of the year is January 3, with an average low of 45°F and high of 56°F.
Average High and Low Temperature
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature
In San Francisco, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in San Francisco begins around May 21 and lasts for 5.1 months, ending around October 24. On July 20, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 92% of the time, and overcast or mostly cloudy 8% of the time.
The cloudier part of the year begins around October 24 and lasts for 6.9 months, ending around May 21. On January 11, the cloudiest day of the year, the sky is overcast or mostly cloudy 55% of the time, and clear, mostly clear, or partly cloudy 45% of the time.
Cloud Cover Categories
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in San Francisco varies significantly throughout the year.
The wetter season lasts 5.1 months, from November 5 to April 8, with a greater than 16% chance of a given day being a wet day. The chance of a wet day peaks at 31% on February 20.
The drier season lasts 6.9 months, from April 8 to November 5. The smallest chance of a wet day is 0% on July 19.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 31% on February 20.
Daily Chance of Precipitation
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. San Francisco experiences significant seasonal variation in monthly rainfall.
The rainy period of the year lasts for 7.3 months, from October 4 to May 14, with a sliding 31-day rainfall of at least 0.5 inches. The most rain falls during the 31 days centered around February 15, with an average total accumulation of 3.9 inches.
The rainless period of the year lasts for 4.7 months, from May 14 to October 4. The least rain falls around July 31, with an average total accumulation of 0.0 inches.
Average Monthly Rainfall
The length of the day in San Francisco varies significantly over the course of the year. In 2017, the shortest day is December 21, with 9 hours, 33 minutes of daylight; the longest day is June 20, with 14 hours, 47 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:47 AM on June 13, and the latest sunrise is 1 hour, 51 minutes later at 7:38 AM on November 4. The earliest sunset is at 4:50 PM on December 6, and the latest sunset is 3 hours, 45 minutes later at 8:35 PM on June 27.
Daylight saving time (DST) is observed in San Francisco during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.
Sunrise & Sunset with Twilight and Daylight Saving Time
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
The perceived humidity level in San Francisco, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, remaining a virtually constant 0% throughout.
Humidity Comfort Levels
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed in San Francisco experiences mild seasonal variation over the course of the year.
The windier part of the year lasts for 5.7 months, from February 2 to July 23, with average wind speeds of more than 4.5 miles per hour. The windiest day of the year is May 31, with an average hourly wind speed of 5.2 miles per hour.
The calmer time of year lasts for 6.2 months, from July 23 to February 2. The calmest day of the year is October 21, with an average hourly wind speed of 3.9 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in San Francisco varies throughout the year.
The wind is most often from the west for 9.1 months, from February 12 to November 14, with a peak percentage of 93% on August 10. The wind is most often from the north for 2.9 months, from November 14 to February 12, with a peak percentage of 36% on January 1.
San Francisco is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.
The average water temperature experiences some seasonal variation over the course of the year.
The time of year with warmer water lasts for 2.5 months, from August 4 to October 19, with an average temperature above 57°F. The day of the year with the warmest water is September 17, with an average temperature of 58°F.
The time of year with cooler water lasts for 5.9 months, from December 18 to June 15, with an average temperature below 54°F. The day of the year with the coolest water is May 2, with an average temperature of 53°F.
Average Water Temperature
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy experiences extreme seasonal variation over the course of the year.
The brighter period of the year lasts for 3.6 months, from May 6 to August 26, with an average daily incident shortwave energy per square meter above 7.1 kWh. The brightest day of the year is June 28, with an average of 8.4 kWh.
The darker period of the year lasts for 3.5 months, from November 3 to February 18, with an average daily incident shortwave energy per square meter below 3.4 kWh. The darkest day of the year is December 21, with an average of 2.2 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of San Francisco are 37.775 deg latitude, -122.419 deg longitude, and 59 ft elevation.
The topography within 2 miles of San Francisco contains significant variations in elevation, with a maximum elevation change of 597 feet and an average elevation above sea level of 128 feet. Within 10 miles contains significant variations in elevation (1,270 feet). Within 50 miles contains very significant variations in elevation (3,894 feet).
The area within 2 miles of San Francisco is covered by artificial surfaces (82%) and water (15%), within 10 miles by water (62%) and artificial surfaces (29%), and within 50 miles by water (41%) and grassland (20%).
This report illustrates the typical weather in San Francisco, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 2 weather stations near enough to contribute to our estimation of the temperature and dew point in San Francisco.
For each station, the records are corrected for the elevation difference between that station and San Francisco according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at San Francisco is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between San Francisco and a given station.
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , by Jean Meeus.
All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.
Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.
Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.
Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .
Time zones for aiports and weather stations are provided by AskGeo.com .
Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.