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December Weather in California, United States

Last updated: June 24, 2025

In December, the average temperature in California, United States hovers around 3°C (38°F). Expect chilly days, as temperatures can dip as low as -15°C (5°F) and occasionally rise to 19°C (66°F). Prepare for some rain, with a total precipitation of 116 mm (4.6 in) spread over approximately 12 days. Humidity levels are high, averaging at 86%, making the air feel even cooler.

December Temperature in California

In December in California, the average temperature is 3°C (38°F), with maximums reaching 19°C (66°F) and minimums dropping as low as -15°C (5°F). Be prepared for a wide range of weather conditions during your travels, from chilly days to surprisingly warm afternoons.

December Weather in California: Daily Temperature Highs, Lows, and Averages

The chart illustrates December temperature patterns in California, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In California, December typically has an average temperature of 3°C (38°F), with highs reaching up to 19°C (66°F) and lows dropping to around -15°C (5°F).
JanFebMarAprMayJunJulAugSepOctNovDec323643536370757368584337
Data source: Temperature data for California 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 California

In California in December, the precipitation amount is 116 mm (4.6 in) over a span of 12 days.

December Precipitation Trends in California

The chart displays monthly precipitation patterns in California, 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 California, December typically receives around 116 mm (4.6 inches) of precipitation spread over approximately 12 days.
JanFebMarAprMayJunJulAugSepOctNovDec8712411712914917215311012512186116
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in California

In California in December humidity is 86%. With an average temperature of 3°C (38°F), this humidity feels like a damp chill that seeps through your layers, making traveling uncomfortable as breath clouds visibly in the crisp air.

December Average Humidity in California

This chart illustrates the average monthly humidity levels in California, 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 California is approximately 86%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec88%88%88%87%82%84%82%73%74%81%89%86%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in California

In California 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 California, you can check the information here.

Maximum UV Index Levels in California for December

The chart shows the monthly maximum UV Index (UVI) for California 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 California typically reaches 3, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec357910101098643
Data source: California 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 California Compares to Other Months

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

This table compares monthly weather conditions in California, showing how December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather0°C (33°F)87 mm (3.4 inches)88%moderate
February Weather2°C (37°F)124 mm (4.9 inches)88%moderate
March Weather6°C (43°F)117 mm (4.6 inches)88%high
April Weather11°C (53°F)129 mm (5.1 inches)86%very high
May Weather17°C (63°F)149 mm (5.9 inches)82%very high
June Weather21°C (70°F)172 mm (6.8 inches)84%very high
July Weather24°C (75°F)153 mm (6.0 inches)82%very high
August Weather23°C (73°F)110 mm (4.3 inches)73%very high
September Weather20°C (68°F)125 mm (4.9 inches)73%very high
October Weather14°C (58°F)121 mm (4.8 inches)81%high
November Weather6°C (43°F)86 mm (3.4 inches)89%moderate
December Weather3°C (38°F)116 mm (4.6 inches)86%moderate

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