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September Weather in Fairfax, United States

Last updated: June 24, 2025

The average temperature in Fairfax, United States during September is a pleasant 22°C (71°F). However, temperatures can range from a cool 6°C (43°F) to a warm 35°C (95°F). Expect about 85 mm (3.3 in) of precipitation over 8 days, and with an average humidity of 75%, it's a great time to enjoy the climate!

September Temperature in Fairfax

In September in Fairfax, the average temperature is 22°C (71°F), with maximums reaching 35°C (95°F) and minimums dropping to as low as 6°C (43°F). This makes it an ideal destination for travelers seeking pleasant weather and a range of outdoor activities.

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

The chart illustrates September 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, September typically has an average temperature of 22°C (71°F), with highs reaching up to 35°C (95°F) and lows dropping to around 6°C (43°F).
JanFebMarAprMayJunJulAugSepOctNovDec282944526577797571554234
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.

September Precipitation in Fairfax

In Fairfax in September, the precipitation amount is 85 mm (3.3 in) over the course of 8 days.

September Precipitation Trends in Fairfax

The chart displays monthly precipitation patterns in Fairfax, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Fairfax, September typically receives around 85 mm (3.3 inches) of precipitation spread over approximately 8 days.
JanFebMarAprMayJunJulAugSepOctNovDec36329284157119112120851293732
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Fairfax

In Fairfax in September, humidity is 75%. With an average temperature of 22°C (71°F), this humidity feels like a warm embrace, making traveling a bit sticky but also invigorating, as the air surrounds you with a heavy yet refreshing sensation that highlights the vibrant atmosphere of your surroundings.

September Average Humidity in Fairfax

This chart illustrates the average monthly humidity levels in Fairfax, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Fairfax is approximately 75%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec76%80%73%75%78%82%83%81%75%75%82%83%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Fairfax

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.

Maximum UV Index Levels in Fairfax for September

The chart shows the monthly maximum UV Index (UVI) for Fairfax in September, 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 September, the maximum UV index in Fairfax typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec356910111098643
Data source: Fairfax September 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 September 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 September’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 September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-2°C (28°F)36 mm (1.4 inches)76%moderate
February Weather-2°C (29°F)32 mm (1.2 inches)80%moderate
March Weather7°C (44°F)92 mm (3.6 inches)73%high
April Weather11°C (53°F)84 mm (3.3 inches)74%very high
May Weather18°C (65°F)157 mm (6.2 inches)78%very high
June Weather25°C (77°F)119 mm (4.7 inches)82%extreme
July Weather26°C (79°F)112 mm (4.4 inches)83%very high
August Weather24°C (76°F)120 mm (4.7 inches)80%very high
September Weather22°C (71°F)85 mm (3.3 inches)75%very high
October Weather13°C (55°F)129 mm (5.1 inches)75%high
November Weather6°C (42°F)37 mm (1.5 inches)82%moderate
December Weather1°C (35°F)32 mm (1.3 inches)83%moderate

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