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December Weather in South San Francisco, United States

Last updated: June 24, 2025

In December, the average temperature in South San Francisco, United States hovers around 11°C (52°F). You can expect temperatures to fluctuate between a minimum of 4°C (40°F) and a maximum of 20°C (69°F). Throughout the month, precipitation typically amounts to 95 mm (3.7 in) over about 9 days, contributing to an average humidity level of 79%. Stay prepared for a mix of mild weather and occasional rain!

December Temperature in South San Francisco

In December in South San Francisco, the average temperature is 11°C (52°F), with maximums reaching 20°C (69°F) and minimums dropping as low as 4°C (40°F). This mild climate makes South San Francisco an ideal destination for travelers looking to explore comfortably.

December Weather in South San Francisco: Daily Temperature Highs, Lows, and Averages

The chart illustrates December temperature patterns in South San Francisco, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In South San Francisco, December typically has an average temperature of 11°C (52°F), with highs reaching up to 20°C (69°F) and lows dropping to around 4°C (40°F).
JanFebMarAprMayJunJulAugSepOctNovDec515253555659596162605552
Data source: Temperature data for South San Francisco generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

December Precipitation in South San Francisco

In South San Francisco in December, the precipitation amount is 95 mm (3.7 in) over the course of 9 days.

December Precipitation Trends in South San Francisco

The chart displays monthly precipitation patterns in South San Francisco, with values for each month alongside December’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how December’s conditions compare to those of other months. In South San Francisco, December typically receives around 95 mm (3.7 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec1061097835203322305095
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in South San Francisco

In South San Francisco in December humidity is 79%. With an average temperature of 11°C (52°F), this humidity feels like a damp chill that seeps through your clothes, making prolonged outdoor activities uncomfortable for travelers.

December Average Humidity in South San Francisco

This chart illustrates the average monthly humidity levels in South San Francisco, with December’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In December, average humidity in South San Francisco is approximately 79%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%82%82%79%83%84%87%87%86%80%79%79%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in South San Francisco

In South San Francisco in December, the maximum UV index is 3, which corresponds to a moderate Exposure Category. The time to burn is approximately 30 minutes. For more details on the hourly UV index in South San Francisco, you can check the information here.

Maximum UV Index Levels in South San Francisco for December

The chart shows the monthly maximum UV Index (UVI) for South San Francisco in December, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In December, the maximum UV index in South San Francisco typically reaches 3, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec3589101111109743
Data source: South San Francisco December UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How December Weather in South San Francisco Compares to Other Months

Weather in South San Francisco varies notably across the year, with each month offering distinct climate conditions. This page compares December’s weather to other months in South San Francisco, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in South San Francisco, showing how December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather11°C (52°F)106 mm (4.2 inches)85%moderate
February Weather11°C (52°F)109 mm (4.3 inches)82%moderate
March Weather12°C (53°F)78 mm (3.1 inches)82%very high
April Weather13°C (55°F)35 mm (1.4 inches)79%very high
May Weather14°C (57°F)20 mm (0.8 inches)83%very high
June Weather15°C (60°F)3 mm (0.1 inches)84%extreme
July Weather15°C (60°F)3 mm (0.1 inches)87%extreme
August Weather16°C (61°F)2 mm (0.1 inches)87%very high
September Weather17°C (63°F)2 mm (0.1 inches)86%very high
October Weather16°C (60°F)30 mm (1.2 inches)80%high
November Weather13°C (56°F)50 mm (2.0 inches)79%moderate
December Weather11°C (52°F)95 mm (3.7 inches)79%moderate

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