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September Weather in Mount Vernon, United States

Last updated: June 24, 2025

In September, the average temperature in Mount Vernon, United States is a pleasant 22°C (72°F), making it an inviting destination. Temperatures can fluctuate, with a minimum of 7°C (45°F) and a maximum reaching up to 36°C (97°F). While exploring, expect about 121 mm (4.7 in) of precipitation over roughly 10 days, and enjoy the moderate 67% humidity that accompanies this beautiful season.

September Temperature in Mount Vernon

In September in Mount Vernon, the average temperature is 22°C (72°F), with maximums reaching 36°C (97°F) and minimums dropping as low as 7°C (45°F). This makes it a great time for travelers to enjoy a range of outdoor activities while also being prepared for cooler evenings.

September Weather in Mount Vernon: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Mount Vernon, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Mount Vernon, September typically has an average temperature of 22°C (72°F), with highs reaching up to 36°C (97°F) and lows dropping to around 7°C (45°F).
JanFebMarAprMayJunJulAugSepOctNovDec374349576773787671614642
Data source: Temperature data for Mount Vernon 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 Mount Vernon

In Mount Vernon in September, the precipitation amount is 121 mm (4.7 in) over a span of 10 days.

September Precipitation Trends in Mount Vernon

The chart displays monthly precipitation patterns in Mount Vernon, 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 Mount Vernon, September typically receives around 121 mm (4.7 inches) of precipitation spread over approximately 10 days.
JanFebMarAprMayJunJulAugSepOctNovDec9918213913512814910511712111880139
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Mount Vernon

In Mount Vernon in September humidity is 67%. With an average temperature of 22°C (72°F), this humidity feels like a warm embrace, creating a tropical ambiance that can be both refreshing and slightly stifling for traveling.

September Average Humidity in Mount Vernon

This chart illustrates the average monthly humidity levels in Mount Vernon, 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 Mount Vernon is approximately 67%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec88%88%87%84%84%83%79%66%67%76%89%88%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Mount Vernon

In Mount Vernon in September, the maximum UV index is 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For detailed information, you can check the Hourly UV Index in Mount Vernon.

Maximum UV Index Levels in Mount Vernon for September

The chart shows the monthly maximum UV Index (UVI) for Mount Vernon 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 Mount Vernon typically reaches 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec3679111111109753
Data source: Mount Vernon 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 Mount Vernon Compares to Other Months

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

This table compares monthly weather conditions in Mount Vernon, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather3°C (38°F)99 mm (3.9 inches)88%moderate
February Weather6°C (43°F)182 mm (7.2 inches)88%high
March Weather10°C (49°F)139 mm (5.5 inches)87%high
April Weather14°C (57°F)135 mm (5.3 inches)84%very high
May Weather20°C (68°F)128 mm (5.0 inches)84%extreme
June Weather23°C (73°F)148 mm (5.8 inches)83%extreme
July Weather25°C (78°F)105 mm (4.1 inches)79%extreme
August Weather24°C (76°F)117 mm (4.6 inches)66%very high
September Weather22°C (72°F)121 mm (4.7 inches)67%very high
October Weather16°C (61°F)118 mm (4.6 inches)76%high
November Weather8°C (46°F)80 mm (3.1 inches)89%moderate
December Weather6°C (43°F)139 mm (5.5 inches)88%moderate

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