Fall Weather at San Francisco International Airport California, United StatesDaily high temperatures decrease by 13°F, from 72°F to 59°F, rarely falling below 54°F or exceeding 83°F. The highest daily average high temperature is 72°F on September 12. Daily low temperatures decrease by 9°F, from 57°F to 48°F, rarely falling below 42°F or exceeding 61°F. The highest daily average low temperature is 57°F on September 2. For reference, on September 10, the hottest day of the year, temperatures at San Francisco International Airport typically range from 57°F to 72°F, while on December 31, the coldest day of the year, they range from 45°F to 55°F. The figure below shows you a compact characterization of the hourly average fall temperatures. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day. Anglesea, Victoria, Australia (7,927 miles away) is the far-away foreign place with temperatures most similar to San Francisco International Airport (view comparison). CloudsThe fall at San Francisco International Airport experiences very rapidly increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 11% to 48%. The clearest day of the fall is September 1, with clear, mostly clear, or partly cloudy conditions 89% of the time. For reference, on January 12, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 54%, while on August 7, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 92%. PrecipitationA wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. At San Francisco International Airport, the chance of a wet day over the course of the fall is very rapidly increasing, starting the season at 1% and ending it at 24%. For reference, the year's highest daily chance of a wet day is 29% on February 21, and its lowest chance is -0% on July 23. RainfallTo show variation within the season and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day. The average sliding 31-day rainfall during the fall at San Francisco International Airport is very rapidly increasing, starting the season at 0.1 inches, when it rarely exceeds 0.2 inches or falls below -0.0 inches, and ending the season at 3.0 inches, when it rarely exceeds 6.1 inches or falls below 0.5 inches. SunOver the course of the fall at San Francisco International Airport, the length of the day is very rapidly decreasing. From the start to the end of the season, the length of the day decreases by 3 hours, 11 minutes, implying an average daily decrease of 2 minutes, 8 seconds, and weekly decrease of 14 minutes, 53 seconds. The shortest day of the fall is November 30, with 9 hours, 46 minutes of daylight and the longest day is September 1, with 12 hours, 57 minutes of daylight. The latest sunrise of the fall at San Francisco International Airport is 7:36 AM on November 2 and the earliest sunrise is 59 minutes earlier at 6:37 AM on November 3. The latest sunset is 7:37 PM on September 1 and the earliest sunset is 2 hours, 46 minutes earlier at 4:51 PM on November 30. Daylight saving time (DST) ends at 1:00 AM on November 3, 2024, shifting sunrise and sunset to be an hour earlier. For reference, on June 20, the longest day of the year, the Sun rises at 5:48 AM and sets 14 hours, 46 minutes later, at 8:34 PM, while on December 21, the shortest day of the year, it rises at 7:21 AM and sets 9 hours, 34 minutes later, at 4:54 PM. The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation. MoonThe figure below presents a compact representation of key lunar data for the fall of 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon. HumidityWe 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 chance that a given day will be muggy at San Francisco International Airport is essentially constant during the fall, remaining around 0% throughout. For reference, on September 5, the muggiest day of the year, there are muggy conditions 0% of the time, while on January 1, the least muggy day of the year, there are muggy conditions 0% of the time. WindThis 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 is gradually increasing during the fall, increasing from 8.2 miles per hour to 8.9 miles per hour over the course of the season. For reference, on May 29, the windiest day of the year, the daily average wind speed is 10.1 miles per hour, while on October 4, the calmest day of the year, the daily average wind speed is 7.5 miles per hour. The lowest daily average wind speed during the fall is 7.5 miles per hour on October 4. The wind direction at San Francisco International Airport during the fall is predominantly out of the west from September 1 to November 12 and the north from November 12 to November 30. Water TemperatureSan 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 surface water temperature at San Francisco International Airport is gradually decreasing during the fall, falling by 3°F, from 58°F to 55°F, over the course of the season. The highest average surface water temperature during the fall is 58°F on September 16. Growing SeasonDefinitions 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. 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. The average accumulated growing degree days at San Francisco International Airport are rapidly increasing during the fall, increasing by 864°F, from 1,798°F to 2,662°F, over the course of the season. Solar EnergyThis 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 at San Francisco International Airport is very rapidly decreasing during the fall, falling by 4.4 kWh, from 6.8 kWh to 2.4 kWh, over the course of the season. TopographyFor the purposes of this report, the geographical coordinates of San Francisco International Airport are 37.619 deg latitude, -122.376 deg longitude, and 13 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 SourcesThis 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 PointSan 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 DataAll data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , 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 airports and weather stations are provided by AskGeo.com . Maps are © OpenStreetMap contributors. DisclaimerThe 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. Please review our full terms contained on our Terms of Service page. |