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September Weather in Mercersburg, United States

Last updated: June 24, 2025

In September, the average temperature in Mercersburg, United States hovers around 21°C (69°F). While you might experience a refreshing minimum of 3°C (38°F), be prepared for sizzling highs of 35°C (95°F). Rain is not uncommon, with 122 mm (4.8 in) expected over approximately 9 days. The average humidity stands at a comfortable 68%, adding a touch of warmth to the vibrant atmosphere.

September Temperature in Mercersburg

In September in Mercersburg, the average temperature is 21°C (69°F). The maximum can reach 35°C (95°F), and the minimum can be as low as 3°C (38°F). Be prepared for a wide range of temperatures when traveling to Mercersburg this month!

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

The chart illustrates September temperature patterns in Mercersburg, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Mercersburg, September typically has an average temperature of 21°C (69°F), with highs reaching up to 35°C (95°F) and lows dropping to around 3°C (38°F).
JanFebMarAprMayJunJulAugSepOctNovDec333743546472787569594437
Data source: Temperature data for Mercersburg 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 Mercersburg

In Mercersburg in September, the precipitation amount is 122 mm (4.8 in) over a span of 9 days.

September Precipitation Trends in Mercersburg

The chart displays monthly precipitation patterns in Mercersburg, 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 Mercersburg, September typically receives around 122 mm (4.8 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec6396871071261051301071221107696
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Mercersburg

In Mercersburg in September humidity is 68%. With average temperature 21°C (69°F), this humidity feels like a warm embrace, making it essential for travelers to stay hydrated and take breaks in the shade while exploring the local sights.

September Average Humidity in Mercersburg

This chart illustrates the average monthly humidity levels in Mercersburg, 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 Mercersburg is approximately 68%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec86%86%86%84%78%79%70%59%68%80%87%85%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Mercersburg

In Mercersburg 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 Mercersburg.

Maximum UV Index Levels in Mercersburg for September

The chart shows the monthly maximum UV Index (UVI) for Mercersburg 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 Mercersburg typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec357910101098743
Data source: Mercersburg 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 Mercersburg Compares to Other Months

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

This table compares monthly weather conditions in Mercersburg, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather1°C (34°F)63 mm (2.5 inches)86%moderate
February Weather3°C (37°F)95 mm (3.8 inches)86%moderate
March Weather6°C (43°F)87 mm (3.4 inches)86%high
April Weather12°C (54°F)107 mm (4.2 inches)84%very high
May Weather18°C (64°F)126 mm (5.0 inches)78%very high
June Weather22°C (72°F)105 mm (4.1 inches)79%very high
July Weather25°C (78°F)130 mm (5.1 inches)70%very high
August Weather24°C (75°F)107 mm (4.2 inches)59%very high
September Weather21°C (69°F)122 mm (4.8 inches)68%very high
October Weather15°C (59°F)110 mm (4.3 inches)80%high
November Weather6°C (44°F)76 mm (3.0 inches)86%moderate
December Weather3°C (38°F)96 mm (3.8 inches)85%moderate

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