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December Weather in Fairfax, United States

Last updated: June 24, 2025

In December, the average temperature in Fairfax, United States is a crisp 6°C (43°F). Visitors can expect a range, with minimums dipping to -10°C (14°F) and maximums soaring to 25°C (78°F). During this time, the region receives about 35 mm (1.4 in) of precipitation, typically spread over 4 days. Humidity levels hover around a comfortable 85%, making for a unique climate experience.

December Temperature in Fairfax

In December in Fairfax, the average temperature is 6°C (43°F), with maximums reaching 25°C (78°F) and minimums dropping as low as -10°C (14°F). Be sure to pack layers to accommodate the wide temperature range during your travels.

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

The chart illustrates December temperature patterns in Fairfax, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Fairfax, December typically has an average temperature of 6°C (43°F), with highs reaching up to 25°C (78°F) and lows dropping to around -10°C (14°F).
JanFebMarAprMayJunJulAugSepOctNovDec373952586979828075614942
Data source: Temperature data for Fairfax 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 Fairfax

In Fairfax in December, the precipitation amount is 35 mm (1.4 in) over a span of 4 days.

December Precipitation Trends in Fairfax

The chart displays monthly precipitation patterns in Fairfax, 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 Fairfax, December typically receives around 35 mm (1.4 inches) of precipitation spread over approximately 4 days.
JanFebMarAprMayJunJulAugSepOctNovDec57449710416010281103881213435
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in Fairfax

In Fairfax in December, humidity is 85%. With an average temperature of 6°C (43°F), this humidity feels like a damp chill that seeps into your bones, making travel feel more uncomfortable and limiting your enjoyment of the sights as you navigate the wet, brisk air.

December Average Humidity in Fairfax

This chart illustrates the average monthly humidity levels in Fairfax, 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 Fairfax is approximately 85%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec77%76%71%74%83%83%81%73%67%72%82%85%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in Fairfax

In Fairfax 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 Fairfax, you can check the information here.

Maximum UV Index Levels in Fairfax for December

The chart shows the monthly maximum UV Index (UVI) for Fairfax 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 Fairfax typically reaches 3, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec36710101111109753
Data source: Fairfax 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 Fairfax Compares to Other Months

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

This table compares monthly weather conditions in Fairfax, showing how December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather3°C (38°F)57 mm (2.3 inches)77%moderate
February Weather4°C (39°F)43 mm (1.7 inches)76%high
March Weather11°C (52°F)97 mm (3.8 inches)71%high
April Weather15°C (59°F)104 mm (4.1 inches)73%very high
May Weather20°C (69°F)160 mm (6.3 inches)83%very high
June Weather26°C (79°F)101 mm (4.0 inches)83%extreme
July Weather28°C (82°F)80 mm (3.2 inches)81%extreme
August Weather27°C (80°F)103 mm (4.1 inches)73%very high
September Weather24°C (76°F)88 mm (3.4 inches)67%very high
October Weather16°C (61°F)121 mm (4.8 inches)72%high
November Weather9°C (49°F)34 mm (1.3 inches)82%moderate
December Weather6°C (43°F)35 mm (1.4 inches)85%moderate

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