Last updated: June 24, 2025
In December, the average temperature in Fairfax, United States hovers around -1°C (30°F), with the possibility of experiencing extreme lows of -22°C (-8°F) and highs reaching up to 22°C (72°F). The region sees about 44 mm (1.7 in) of precipitation over 5 days, and with an average humidity of 84%, the atmosphere can feel quite chilly and damp.
In December in Fairfax, the average temperature is -1°C (30°F), with maximums reaching 22°C (72°F) and minimums dropping as low as -22°C (-8°F). Travelers should be prepared for a wide range of temperatures, from chilly to pleasantly warm, so it's best to pack layers.
In Fairfax in December, the precipitation amount is 44 mm (1.7 in) over the course of 5 days.
In Fairfax in December, humidity is 84%. With an average temperature of -1°C (30°F), this humidity feels like a sharp chill that seeps into your bones, making travel uncomfortable as the wetness in the air intensifies the cold, leaving you yearning for warmth and shelter.
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.
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 | -6°C (21°F) | 47 mm (1.9 inches) | 81% | moderate |
| February Weather | -5°C (23°F) | 56 mm (2.2 inches) | 81% | moderate |
| March Weather | 3°C (38°F) | 73 mm (2.9 inches) | 81% | high |
| April Weather | 9°C (48°F) | 81 mm (3.2 inches) | 82% | very high |
| May Weather | 16°C (62°F) | 160 mm (6.3 inches) | 78% | very high |
| June Weather | 23°C (73°F) | 134 mm (5.3 inches) | 81% | extreme |
| July Weather | 24°C (76°F) | 85 mm (3.3 inches) | 79% | very high |
| August Weather | 22°C (73°F) | 77 mm (3.0 inches) | 77% | very high |
| September Weather | 19°C (67°F) | 127 mm (5.0 inches) | 78% | very high |
| October Weather | 11°C (53°F) | 140 mm (5.5 inches) | 78% | high |
| November Weather | 3°C (38°F) | 47 mm (1.9 inches) | 87% | moderate |
| December Weather | -1°C (30°F) | 44 mm (1.7 inches) | 84% | moderate |