Average Weather in December in San Francisco Mexico
Daily high temperatures are around 84°F, rarely falling below 81°F or exceeding 88°F.
Daily low temperatures are around 61°F, rarely falling below 57°F or exceeding 66°F.
For reference, on May 8, the hottest day of the year, temperatures in San Francisco typically range from 66°F to 89°F, while on January 24, the coldest day of the year, they range from 60°F to 85°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
Goiânia, Brazil (4,129 miles away); Montes Claros, Brazil (4,439 miles); and Kilimatinde, Tanzania (9,262 miles) are the far-away foreign places with temperatures most similar to San Francisco (view comparison).
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 44% throughout the month.
The clearest day of the month is December 14, with clear, mostly clear, or partly cloudy conditions 57% of the time.
For reference, on September 14, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 93%, while on February 24, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 72%.
Cloud Cover Categories in December
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 1% throughout.
For reference, the year's highest daily chance of a wet day is 71% on September 13, and its lowest chance is 1% on December 8.
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 0.1 inches throughout, and rarely exceeding 0.8 inches or falling below -0.0 inches.
The lowest average 31-day accumulation is 0.1 inches on December 11.
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 11 hours, 7 minutes of daylight and the longest day is December 1, with 11 hours, 11 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month in San Francisco is 6:50 AM on December 1 and the latest sunrise is 16 minutes later at 7:06 AM on December 31.
The earliest sunset is 6:01 PM on December 1 and the latest sunset is 12 minutes later at 6:14 PM on December 31.
Daylight saving time is observed in San Francisco during 2018, 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 7:04 AM and sets 13 hours, 9 minutes later, at 8:13 PM, while on December 21, the shortest day of the year, it rises at 7:01 AM and sets 11 hours, 7 minutes later, at 6:08 PM.
Sunrise & Sunset with Twilight 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 very rapidly decreasing during December, falling from 59% to 34% over the course of the month.
For reference, on September 12, the muggiest day of the year, there are muggy conditions 98% of the time, while on March 12, the least muggy day of the year, there are muggy conditions 23% of the time.
Humidity Comfort Levels in December
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 0.2 miles per hour of 5.1 miles per hour throughout.
For reference, on March 31, the windiest day of the year, the daily average wind speed is 6.4 miles per hour, while on October 20, the calmest day of the year, the daily average wind speed is 4.9 miles per hour.
Average Wind Speed in December
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 essentially constant during December, remaining within 1°F of 84°F throughout.
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
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 rapidly increasing during December, increasing by 641°F, from 8,078°F to 8,719°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 around 4.8 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 4.8 kWh on December 23.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of San Francisco are 17.006 deg latitude, -99.283 deg longitude, and 2,103 ft elevation.
The topography within 2 miles of San Francisco contains large variations in elevation, with a maximum elevation change of 2,073 feet and an average elevation above sea level of 2,070 feet. Within 10 miles contains large variations in elevation (3,724 feet). Within 50 miles also contains extreme variations in elevation (9,685 feet).
The area within 2 miles of San Francisco is covered by cropland (72%) and trees (19%), within 10 miles by cropland (73%) and trees (22%), and within 50 miles by trees (36%) and cropland (29%).
This report illustrates the typical weather in San Francisco year round, 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 is only a single weather station, General Juan N. Álvarez International Airport, in our network suitable to be used as a proxy for the historical temperature and dew point records of San Francisco.
At a distance of 57 kilometers from San Francisco, closer than our threshold of 150 kilometers, this station is deemed sufficiently nearby to be relied upon as our primary source for temperature and dew point records.
The station records are corrected for the elevation difference between the 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.
Please note that the station records themselves may additionally have been back-filled using other nearby stations or the MERRA-2 reanalysis.
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.
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.