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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 reaches a warm 26°C (80°F), with a minimum of 13°C (56°F) and a maximum of 38°C (101°F). Expect 99 mm (3.9 in) of rain spread over 11 days, contributing to an average humidity of 82%.

September Temperature in Mount Vernon

In September in Mount Vernon, the average temperature is 26°C (80°F). Maximums can reach 38°C (101°F), and minimums can be as low as 13°C (56°F). Visitors should be prepared for warm weather, with the possibility of cooler evenings, making it an ideal time for both outdoor adventures and leisurely explorations.

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 26°C (80°F), with highs reaching up to 38°C (101°F) and lows dropping to around 13°C (56°F).
JanFebMarAprMayJunJulAugSepOctNovDec515761677580838279725853
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 99 mm (3.9 in) over the course of 11 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 99 mm (3.9 inches) of precipitation spread over approximately 11 days.
JanFebMarAprMayJunJulAugSepOctNovDec83101748284108126119998456124
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 82%. With an average temperature of 26°C (80°F), this humidity feels like a heavy, warm blanket wrapping around you, making outdoor activities feel more exhausting and sweaty, which can be quite challenging 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 82%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec86%84%83%81%81%81%83%81%82%78%86%89%
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 reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more 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 10, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec479101111111110864
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 Weather11°C (52°F)83 mm (3.2 inches)86%moderate
February Weather14°C (57°F)101 mm (4.0 inches)84%high
March Weather16°C (62°F)74 mm (2.9 inches)83%very high
April Weather20°C (68°F)82 mm (3.2 inches)81%very high
May Weather24°C (76°F)84 mm (3.3 inches)81%extreme
June Weather27°C (80°F)108 mm (4.3 inches)81%extreme
July Weather28°C (83°F)126 mm (5.0 inches)83%extreme
August Weather28°C (82°F)119 mm (4.7 inches)81%extreme
September Weather26°C (80°F)99 mm (3.9 inches)82%very high
October Weather22°C (72°F)83 mm (3.3 inches)78%very high
November Weather14°C (58°F)56 mm (2.2 inches)86%high
December Weather12°C (54°F)124 mm (4.9 inches)89%moderate

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