Last updated: June 24, 2025
In Fairfax, United States, the average temperature in December is a chilly -4°C (24°F), with extremes dropping as low as -25°C (-12°F) and occasionally rising to a mild 15°C (59°F). During this month, you can expect about 40 mm (1.6 in) of precipitation over approximately 6 days, accompanied by an average humidity of 84%.
In December in Fairfax, the average temperature is -4°C (24°F). Maximum temperatures can reach 15°C (59°F), while minimums can drop as low as -25°C (-12°F). Be sure to dress warmly and be prepared for a wide range of temperatures if you're planning to travel during this time.
In Fairfax in December, the precipitation amount is 40 mm (1.6 in) over the course of 6 days.
In Fairfax in December humidity is 84%. With an average temperature of -4°C (24°F), this humidity feels like an uninviting chill that seeps into your bones, making outdoor activities uncomfortable and travel quite challenging.
In Fairfax in December, the maximum UV index is 2, which corresponds to a low exposure category. With this level of UV radiation, the time to burn is approximately 45 minutes. To learn more about the hourly UV index in Fairfax, you can visit Hourly UV Index in Fairfax.
UV Risk Categories
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.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | -9°C (16°F) | 26 mm (1.0 inches) | 87% | moderate |
| February Weather | -9°C (16°F) | 27 mm (1.1 inches) | 90% | moderate |
| March Weather | 0°C (33°F) | 62 mm (2.5 inches) | 85% | moderate |
| April Weather | 6°C (43°F) | 80 mm (3.1 inches) | 84% | very high |
| May Weather | 15°C (60°F) | 124 mm (4.9 inches) | 78% | very high |
| June Weather | 22°C (72°F) | 106 mm (4.2 inches) | 80% | very high |
| July Weather | 23°C (74°F) | 123 mm (4.8 inches) | 81% | very high |
| August Weather | 21°C (71°F) | 124 mm (4.9 inches) | 81% | very high |
| September Weather | 18°C (65°F) | 118 mm (4.6 inches) | 81% | very high |
| October Weather | 9°C (48°F) | 97 mm (3.8 inches) | 84% | moderate |
| November Weather | 1°C (34°F) | 30 mm (1.2 inches) | 88% | moderate |
| December Weather | -4°C (24°F) | 40 mm (1.6 inches) | 84% | low |