Average Weather in December in San Francisco Mexico
Daily high temperatures decrease by 4°F, from 78°F to 74°F, rarely falling below 66°F or exceeding 85°F. The lowest daily average high temperature is 74°F on December 28.
Daily low temperatures decrease by 3°F, from 55°F to 52°F, rarely falling below 46°F or exceeding 60°F.
For reference, on July 26, the hottest day of the year, temperatures in San Francisco typically range from 73°F to 101°F, while on January 7, the coldest day of the year, they range from 51°F to 75°F.
Average High and Low Temperature in December
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on December. 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.
Average Hourly Temperature in December
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 month of December in San Francisco experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 34% throughout the month. The highest chance of overcast or mostly cloudy conditions is 34% on December 18.
The clearest day of the month is December 24, with clear, mostly clear, or partly cloudy conditions 67% of the time.
For reference, on July 31, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 37%, while on June 12, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 88%.
Cloud Cover Categories in December
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In San Francisco, the chance of a wet day over the course of December is essentially constant, remaining around 6% throughout.
For reference, the year's highest daily chance of a wet day is 8% on September 7, and its lowest chance is 0% on May 22.
Probability of Precipitation in December
To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day rainfall during December in San Francisco is essentially constant, remaining about 0.5 inches throughout, and rarely exceeding 1.3 inches.
The highest average 31-day accumulation is 0.5 inches on December 8.
Average Monthly Rainfall in December
Over the course of December in San Francisco, the length of the day is essentially constant. The shortest day of the month is December 21, with 10 hours, 24 minutes of daylight and the longest day is December 1, with 10 hours, 31 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month in San Francisco is 7:07 AM on December 1 and the latest sunrise is 17 minutes later at 7:24 AM on December 31.
The earliest sunset is 5:38 PM on December 1 and the latest sunset is 11 minutes later at 5:49 PM on December 31.
Daylight saving time is observed in San Francisco during 2021, but it neither starts nor ends during December, so the entire month is in standard time.
For reference, on June 21, the longest day of the year, the Sun rises at 6:38 AM and sets 13 hours, 54 minutes later, at 8:32 PM, while on December 21, the shortest day of the year, it rises at 7:20 AM and sets 10 hours, 24 minutes later, at 5:43 PM.
Sunrise & Sunset with Twilight in December
The figure below presents a compact representation of key lunar data for December 2021. 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.
Moon Rise, Set & Phases in December
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 chance that a given day will be muggy in San Francisco is essentially constant during December, remaining around 0% throughout.
For reference, on September 8, the muggiest day of the year, there are muggy conditions 29% of the time, while on January 13, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in December
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
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 is essentially constant during December, remaining within 0.1 miles per hour of 8.2 miles per hour throughout.
For reference, on May 29, the windiest day of the year, the daily average wind speed is 10.9 miles per hour, while on August 29, the calmest day of the year, the daily average wind speed is 7.5 miles per hour.
The highest daily average wind speed during December is 8.3 miles per hour on December 11.
Average Wind Speed in December
The hourly average wind direction in San Francisco throughout December is predominantly from the north, with a peak proportion of 62% on December 16.
Wind Direction in December
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 surface water temperature in San Francisco is decreasing during December, falling by 4°F, from 68°F to 64°F, over the course of the month.
Average Water Temperature in December
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 in San Francisco 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 in December
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
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 in San Francisco are increasing during December, increasing by 353°F, from 7,301°F to 7,654°F, over the course of the month.
Growing Degree Days in December
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 in San Francisco is essentially constant during December, remaining within 0.1 kWh of 4.0 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 3.9 kWh on December 18.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of San Francisco are 27.645 deg latitude, -113.419 deg longitude, and 236 ft elevation.
The topography within 2 miles of San Francisco is essentially flat, with a maximum elevation change of 59 feet and an average elevation above sea level of 243 feet. Within 10 miles is essentially flat (1,250 feet). Within 50 miles contains very significant variations in elevation (5,217 feet).
The area within 2 miles of San Francisco is covered by shrubs (100%), within 10 miles by shrubs (100%), and within 50 miles by shrubs (90%).
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.
San Francisco is further than 200 kilometers from the nearest reliable weather station, so the weather-related data on this page were taken entirely from NASA's MERRA-2 satellite-era reanalysis . 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.
The temperature and dew point estimates are corrected for the difference between the reference elevation of the MERRA-2 grid cell and the elevation of San Francisco, according to the International Standard Atmosphere .
All 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.
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 © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.
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.