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Average Weather at San Francisco International Airport California, United States

At San Francisco International Airport, 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 38°F or above 83°F.

Climate Summary

coolcomfortablecoolJanFebMarAprMayJunJulAugSepOctNovDec92%92%46%46%clearovercastprecipitation: 3.7 inprecipitation: 3.7 in0.0 in0.0 inmuggy: 0%muggy: 0%0%0%drydrytourism score: 7.4tourism score: 7.41.01.0
Click on each chart for more information.

Based on the tourism score, the best time of year to visit San Francisco International Airport for warm-weather activities is from late June to early October.

Temperature

The warm season lasts for 4.3 months, from June 11 to October 22, with an average daily high temperature above 69°F. The hottest day of the year is September 11, with an average high of 72°F and low of 57°F.

The cool season lasts for 2.2 months, from December 2 to February 8, with an average daily high temperature below 59°F. The coldest day of the year is January 1, with an average low of 45°F and high of 55°F.

Average High and Low Temperature

Average High and Low Temperature at San Francisco International AirportwarmcoolcoolJanFebMarAprMayJunJulAugSepOctNovDec0°F10°F20°F30°F40°F50°F60°F70°F80°F90°F100°FJan 155°FJan 155°FSep 1172°FSep 1172°F45°F45°F57°F57°FJun 1169°FJun 1169°FOct 2269°FOct 2269°FFeb 859°FFeb 859°F54°F54°F54°F54°F47°F47°F
The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

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

Average Hourly Temperature at San Francisco International AirportJanFebMarAprMayJunJulAugSepOctNovDec12 AM4 AM8 AM12 PM4 PM8 PM12 AMcoldcoldcoolcomfortable
The average hourly temperature, color coded into bands: frigid < 15°F < freezing < 32°F < very cold < 45°F < cold < 55°F < cool < 65°F < comfortable < 75°F < warm < 85°F < hot < 95°F < sweltering. The shaded overlays indicate night and civil twilight.

Anglesea, Australia (7,927 miles away) is the far-away foreign place with temperatures most similar to San Francisco International Airport (view comparison).

Clouds

At San Francisco International Airport, 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 at San Francisco International Airport begins around May 23 and lasts for 5.0 months, ending around October 24. On August 8, 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 7.0 months, ending around May 23. On January 12, the cloudiest day of the year, the sky is overcast or mostly cloudy 54% of the time, and clear, mostly clear, or partly cloudy 46% of the time.

Cloud Cover Categories

Cloud Cover Categories at San Francisco International AirportclearercloudiercloudierJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%Aug 892%Aug 892%Jan 1246%Jan 1246%May 2368%May 2368%Oct 2469%Oct 2469%clearovercastmostly clearpartly cloudymostly cloudy
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds: clear < 20% < mostly clear < 40% < partly cloudy < 60% < mostly cloudy < 80% < overcast.

Precipitation

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days at San Francisco International Airport varies throughout the year.

The wetter season lasts 5.2 months, from November 4 to April 10, with a greater than 15% chance of a given day being a wet day. The chance of a wet day peaks at 29% on February 20.

The drier season lasts 6.8 months, from April 10 to November 4. 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 29% on February 20.

Daily Chance of Precipitation

Daily Chance of Precipitation at San Francisco International AirportwetwetdryJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Feb 2029%Feb 2029%Jul 190%Jul 190%Jan 127%Jan 127%Nov 415%Nov 415%Apr 1015%Apr 1015%rain
The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

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 International Airport experiences significant seasonal variation in monthly rainfall.

The rainy period of the year lasts for 7.3 months, from October 4 to May 13, 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 3.7 inches.

The rainless period of the year lasts for 4.7 months, from May 13 to October 4. The least rain falls around July 31, with an average total accumulation of 0.0 inches.

Average Monthly Rainfall

Average Monthly Rainfall at San Francisco International AirportrainrainJanFebMarAprMayJunJulAugSepOctNovDec0 in1 in2 in3 in4 in5 in6 in7 in8 inFeb 153.7 inFeb 153.7 inJul 310.0 inJul 310.0 inDec 293.5 inDec 293.5 inOct 40.5 inOct 40.5 inMay 130.5 inMay 130.5 in
The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average liquid-equivalent snowfall.

Sun

The length of the day at San Francisco International Airport varies significantly over the course of the year. In 2017, the shortest day is December 21, with 9 hours, 34 minutes of daylight; the longest day is June 20, with 14 hours, 46 minutes of daylight.

Hours of Daylight and Twilight

Hours of Daylight and Twilight at San Francisco International AirportJanFebMarAprMayJunJulAugSepOctNovDec0 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hr12 hr, 7 minMar 2012 hr, 7 minMar 2014 hr, 46 minJun 2014 hr, 46 minJun 2012 hr, 8 minSep 2212 hr, 8 minSep 229 hr, 34 minDec 219 hr, 34 minDec 21nightnightday
The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

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, 44 minutes later at 8:35 PM on June 27.

Daylight saving time (DST) is observed at San Francisco International Airport 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

Sunrise & Sunset with Twilight and Daylight Saving Time at San Francisco International AirportJanFebMarAprMayJunJulAugSepOctNovDec12 AM2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMJun 135:47 AMJun 135:47 AM8:35 PMJun 278:35 PMJun 27Dec 64:50 PMDec 64:50 PM7:38 AMNov 47:38 AMNov 4Mar 12DSTMar 12DSTDSTNov 5DSTNov 5daynightnightnightnightSolarMidnightSolarMidnightSolarNoonSunriseSunset
The solar day over the course of the year 2017. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray. The transitions to and from daylight saving time are indicated by the 'DST' labels.

Humidity

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 at San Francisco International Airport, 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

Humidity Comfort Levels at San Francisco International AirportJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Jan 180%Jan 180%Sep 80%Sep 80%comfortablecomfortabledrydry
The percentage of time spent at various humidity comfort levels, categorized by dew point: dry < 55°F < comfortable < 60°F < humid < 65°F < muggy < 70°F < oppressive < 75°F < miserable.

Wind

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 at San Francisco International Airport experiences mild seasonal variation over the course of the year.

The windier part of the year lasts for 5.5 months, from February 1 to July 17, with average wind speeds of more than 8.8 miles per hour. The windiest day of the year is May 30, with an average hourly wind speed of 10.1 miles per hour.

The calmer time of year lasts for 6.4 months, from July 17 to February 1. The calmest day of the year is October 5, with an average hourly wind speed of 7.5 miles per hour.

Average Wind Speed

Average Wind Speed at San Francisco International AirportwindyJanFebMarAprMayJunJulAugSepOctNovDec0 mph2 mph4 mph6 mph8 mph10 mph12 mph14 mph16 mphMay 3010.1 mphMay 3010.1 mphOct 57.5 mphOct 57.5 mphFeb 18.8 mphFeb 18.8 mphJul 178.8 mphJul 178.8 mph
The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The predominant average hourly wind direction at San Francisco International Airport varies throughout the year.

The wind is most often from the west for 9.0 months, from February 13 to November 13, with a peak percentage of 92% on August 13. The wind is most often from the north for 3.0 months, from November 13 to February 13, with a peak percentage of 35% on January 1.

Wind Direction

Wind Direction at San Francisco International AirportNWNJanFebMarAprMayJunJulAugSepOctNovDec0%100%20%80%40%60%60%40%80%20%100%0%westnorthsoutheast
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions (north, east, south, and west), excluding hours in which the mean wind speed is less than 1 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Water Temperature

San Francisco International Airport 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 3 to October 17, with an average temperature above 57°F. The day of the year with the warmest water is September 16, with an average temperature of 58°F.

The time of year with cooler water lasts for 5.8 months, from December 19 to June 12, with an average temperature below 54°F. The day of the year with the coolest water is May 1, with an average temperature of 53°F.

Average Water Temperature

The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.

Best Time of Year to Visit

To characterize how pleasant the weather is at San Francisco International Airport throughout the year, we compute two travel scores.

The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit San Francisco International Airport for general outdoor tourist activities is from late June to early October, with a peak score in the last week of August.

Tourism Score

Tourism Score at San Francisco International Airportbest timeJanFebMarAprMayJunJulAugSepOctNovDec02468107.47.41.01.0 precipitationprecipitationcloudscloudstemperaturetemperaturetourism score
The tourism score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit San Francisco International Airport for hot-weather activities is from mid August to late September, with a peak score in the first week of September.

Beach/Pool Score

Beach/Pool Score at San Francisco International AirportJanFebMarAprMayJunJulAugSepOctNovDec02468101.61.60.00.0 precipitationprecipitationcloudscloudsbeach/pool score
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

Methodology

For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.

Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.

Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.

Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.

Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.

Growing Season

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

Temperatures at San Francisco International Airport are sufficiently warm year round that it is not entirely meaningful to discuss the growing season in these terms. We nevertheless include the chart below as an illustration of the distribution of temperatures experienced throughout the year.

Time Spent in Various Temperature Bands and the Growing Season

Time Spent in Various Temperature Bands and the Growing Season at San Francisco International AirportJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%100%Jan 15100%Jan 1599%Dec 2699%Dec 26Jun 26100%Jun 26100%coldcoolcomfortablevery coldwarm
The percentage of time spent in various temperature bands: frigid < 15°F < freezing < 32°F < very cold < 45°F < cold < 55°F < cool < 65°F < comfortable < 75°F < warm < 85°F < hot < 95°F < sweltering. The black line is the percentage chance that a given day is within the growing season.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

Growing Degree Days

Growing Degree Days at San Francisco International AirportJanFebMarAprMayJunJulAugSepOctNovDec0°F500°F1,000°F1,500°F2,000°F2,500°F3,000°FFeb 790°FFeb 790°FJun 17900°FJun 17900°FSep 21,800°FSep 21,800°FDec 312,741°FDec 312,741°F
The average growing degree days accumulated over the course of the year, with 25th to 75th and 10th to 90th percentile bands.

Solar Energy

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 7 to August 25, with an average daily incident shortwave energy per square meter above 7.1 kWh. The brightest day of the year is June 27, with an average of 8.4 kWh.

The darker period of the year lasts for 3.5 months, from November 4 to February 17, 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

Average Daily Incident Shortwave Solar Energy at San Francisco International AirportbrightdarkdarkJanFebMarAprMayJunJulAugSepOctNovDec0 kWh1 kWh2 kWh3 kWh4 kWh5 kWh6 kWh7 kWh8 kWh9 kWh10 kWhJun 278.4 kWhJun 278.4 kWhDec 212.2 kWhDec 212.2 kWhMay 77.1 kWhMay 77.1 kWhAug 257.1 kWhAug 257.1 kWhNov 43.4 kWhNov 43.4 kWhFeb 173.4 kWhFeb 173.4 kWh
The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

Topography

For the purposes of this report, the geographical coordinates of San Francisco International Airport are 37.619 deg latitude, -122.376 deg longitude, and 7 ft elevation.

The topography within 2 miles of San Francisco International Airport contains only modest variations in elevation, with a maximum elevation change of 131 feet and an average elevation above sea level of 11 feet. Within 10 miles contains only modest variations in elevation (1,909 feet). Within 50 miles contains very significant variations in elevation (4,318 feet).

The area within 2 miles of San Francisco International Airport is covered by artificial surfaces (51%) and water (46%), within 10 miles by water (45%) and artificial surfaces (30%), and within 50 miles by water (45%) and grassland (17%).

Data Sources

This report illustrates the typical weather at San Francisco International Airport, 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

San Francisco International Airport has a weather station that reported reliably enough during the analysis period that we have included it in our network. When available, historical temperature and dew point measurements are taken directly from this weather station. These records are obtained from NOAA's Integrated Surface Hourly data set, falling back on ICAO METAR records as required.

In the case of missing or erroneous measurements from this station, we fall back on records from nearby stations, adjusted according to typical seasonal and diurnal intra-station differences. For a given day of the year and hour of the day, the fallback station is selected to minimize the prediction error over the years for which there are measurements for both stations.

The stations on which we may fall back include but are not limited to Naval Air Station Alameda (historical), Half Moon Bay Airport, Oakland International Airport, Hayward Air Terminal Airport, Moffett Federal Airfield, Buchanan Field Airport, Norman Y. Mineta San José International Airport, and Livermore Municipal Airport.

Other Data

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.

Disclaimer

The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.

We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.

We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.