Last updated: June 24, 2025
In Fairfax, United States, the average temperature in September hovers around 19°C (67°F). You'll experience a range from a chilly 3°C (37°F) to a warm 34°C (93°F). Expect around 127 mm (5.0 in) of precipitation spread over 9 days, with an average humidity of 78%. Whether you're planning a cozy outing or gearing up for a rainy day, be prepared for the variations this month brings!
In September in Fairfax, the average temperature is 19°C (67°F). The maximum can reach 34°C (93°F), while the minimum can drop as low as 3°C (37°F). This makes it an ideal time for travelers to enjoy a variety of outdoor activities, from warm afternoons to cool evenings.
In Fairfax in September, the precipitation amount is 127 mm (5.0 in) over a span of 9 days.
In Fairfax in September humidity is 78%. With an average temperature of 19°C (67°F), this humidity feels like a warm, heavy blanket enveloping you, making traveling feel both sticky and sluggish as you navigate through the day.
In Fairfax in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the 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 September’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 |