San Francisco Weather in December
Overall, December has the rainiest and cloudiest weather in San Francisco, California. But total rainfall for the month varies widely from year to year.
This page gives detailed information on the typical December temperature, precipitation, sun, humidity, wind and storms for San Francisco. The temperature, rainfall, sunshine and wind speed numbers here are historical averages based on climate data gathered in downtown San Francisco near the corner of Buchanan and Hermann Streets. The other measurements are averages at San Francisco International Airport, located south of the city center.
Temperature
| 58 °F | December average high | 14 °C |
| 47 °F | December average low | 8 °C |
The last week of December is among the chilliest of the year at San Francisco. These days have daily highs averaging 57 degrees Fahrenheit (14 degrees Celsius) and the minimum averages 46 °F (8 °C).
| 13 days | 60 °F max. or more (16 °C) |
| 25 days | 50 °F min. or less (10 °C) |
San Francisco warms up to at least 50 °F (10 °C) on most days in December. Temperatures of 70 °F (21 °C) and above rarely occur here this month.
The thermometer dips to 40 °F (4 °C) or below on one or two nights during December. Even in December freezing temperatures are not expected here.
Rain
| 4.8 in | total precipitation | 121 mm |
| 12 days | of rain |
December is the rainiest month in San Francisco. Half the time, the city receives 2.2 to 7.5 inches (56 to 190 mm) of rainfall in December. One in four years has drier weather, while another one in four is wetter.
Sun
| 53 % | sunshine |
| 9 days | clear skies |
The sun's rays reach the ground in San Francisco during 53 percent of daylight hours on average in December, for a total of 158 hours in the month. Typically on 9 days this month the sky is mainly clear, with at most 30 percent cloud cover. December is the cloudiest month for San Francisco.
Sunlight in December at San Francisco averages 9 hours and 35 minutes a day. The shortest days of the year, from around December 17th to 24th, last 9 hours and 33 minutes from sunrise to sunset.
Humidity
| 78 % | December average humidity |
The relative humidity in San Francisco during December usually peaks at 85 percent in the morning then drops to 67 percent by late afternoon.
| Local Time | 1 am | 4 am | 7 am | 10 am | 1 pm | 4 pm | 7 pm | 10 pm |
| Humidity % | 82 | 85 | 85 | 77 | 68 | 67 | 76 | 80 |
Wind
| 6.5 mph | December wind speed average | 10.5 kph |
December is less windy than most other months in San Francisco.
Storms
| 3 days | rainfall of 0.5 inches (13 mm) or more |
| 0 days | with thunderstorms in December |
About once every five years, a thunderstorm passes through San Francisco in December.
Reference
The weather data here are long-term averages provided by the US National Centers for Environmental Information (NCEI). Temperature and precipitation are 1991-2020 normals while humidity and thunderstorms are 1961-1990 normals.