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December Weather in Sunnyvale, United States

Last updated: June 24, 2025

In December, the average temperature in Sunnyvale, United States hovers around 11°C (52°F). Expect temperatures to range from a chilly -5°C (23°F) to a pleasant 28°C (82°F). With an average precipitation amount of 74 mm (2.9 in) spread over 7 days, and a high humidity level of 87%, be prepared for some damp days.

December Temperature in Sunnyvale

In December in Sunnyvale, the average temperature is 11°C (52°F), with maximums reaching up to 28°C (82°F) and minimums dipping as low as -5°C (23°F). It's essential to pack for a variety of weather conditions while traveling during this month.

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

The chart illustrates December temperature patterns in Sunnyvale, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Sunnyvale, December typically has an average temperature of 11°C (52°F), with highs reaching up to 28°C (82°F) and lows dropping to around -5°C (23°F).
JanFebMarAprMayJunJulAugSepOctNovDec474960657481858479685752
Data source: Temperature data for Sunnyvale 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 Sunnyvale

In Sunnyvale in December, the precipitation amount is 74 mm (2.9 in) over a period of 7 days.

December Precipitation Trends in Sunnyvale

The chart displays monthly precipitation patterns in Sunnyvale, 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 Sunnyvale, December typically receives around 74 mm (2.9 inches) of precipitation spread over approximately 7 days.
JanFebMarAprMayJunJulAugSepOctNovDec65111117138181975697861445574
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in Sunnyvale

In Sunnyvale in December, humidity is 87%. With an average temperature of 11°C (52°F), this humidity feels like a damp chill that can make your clothes cling uncomfortably, leaving you feeling slightly weighed down while exploring the area.

December Average Humidity in Sunnyvale

This chart illustrates the average monthly humidity levels in Sunnyvale, 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 Sunnyvale is approximately 87%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec80%79%78%78%81%78%73%66%65%72%82%87%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in Sunnyvale

In Sunnyvale in December, the maximum UV index reaches 4, which corresponds to a moderate Exposure Category. With a time to burn of 30 minutes, it’s important to take precautions to protect your skin. You can find more details in the Hourly UV Index in Sunnyvale for better planning.

Maximum UV Index Levels in Sunnyvale for December

The chart shows the monthly maximum UV Index (UVI) for Sunnyvale 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 Sunnyvale typically reaches 4, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec478101111111110864
Data source: Sunnyvale 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 Sunnyvale Compares to Other Months

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

This table compares monthly weather conditions in Sunnyvale, showing how December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather8°C (47°F)65 mm (2.6 inches)80%moderate
February Weather10°C (50°F)111 mm (4.4 inches)79%high
March Weather16°C (61°F)117 mm (4.6 inches)78%very high
April Weather18°C (65°F)138 mm (5.4 inches)78%very high
May Weather23°C (75°F)181 mm (7.1 inches)81%extreme
June Weather27°C (82°F)97 mm (3.8 inches)78%extreme
July Weather29°C (85°F)56 mm (2.2 inches)73%extreme
August Weather29°C (85°F)97 mm (3.8 inches)66%extreme
September Weather26°C (80°F)86 mm (3.4 inches)65%very high
October Weather20°C (68°F)144 mm (5.7 inches)72%very high
November Weather14°C (57°F)55 mm (2.2 inches)82%high
December Weather11°C (52°F)74 mm (2.9 inches)87%moderate

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