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December Weather in Mercersburg, United States

Last updated: June 24, 2025

In December, the average temperature in Mercersburg, United States hovers around 3°C (38°F), with minimums dipping to a chilly -13°C (9°F) and highs reaching a pleasant 19°C (67°F). Rainfall can be expected, with 96 mm (3.8 in) over 9 days, while the air remains humid, averaging 85%. Prepare for a mix of cool days and the potential for rain!

December Temperature in Mercersburg

In December in Mercersburg, the average temperature is 3°C (38°F). The maximum can reach 19°C (67°F), while the minimum can drop as low as -13°C (9°F). Be prepared for a range of temperatures and pack accordingly for your trip.

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

The chart illustrates December 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, December typically has an average temperature of 3°C (38°F), with highs reaching up to 19°C (67°F) and lows dropping to around -13°C (9°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.

December Precipitation in Mercersburg

In Mercersburg in December, the total precipitation amount is 96 mm (3.8 in) spread over a period of 9 days.

December Precipitation Trends in Mercersburg

The chart displays monthly precipitation patterns in Mercersburg, with values for each month alongside December’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how December’s conditions compare to those of other months. In Mercersburg, December typically receives around 96 mm (3.8 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec6396871071261051301071221107696
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in Mercersburg

In Mercersburg in December, humidity is 85%. With an average temperature of 3°C (38°F), this humidity feels like a damp chill that seeps into your bones, making outdoor activities uncomfortable and travel less enjoyable as you contend with the heavy, cold air surrounding you.

December Average Humidity in Mercersburg

This chart illustrates the average monthly humidity levels in Mercersburg, with December’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In December, average humidity in Mercersburg is approximately 85%, 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 December generated using information from the Copernicus Climate Change Service.

December UV Index in Mercersburg

In Mercersburg in December, the maximum UV index is 3, which corresponds to a moderate Exposure Category. The time to burn is approximately 30 minutes. For more details on the hourly UV index in Mercersburg, you can check the information here.

Maximum UV Index Levels in Mercersburg for December

The chart shows the monthly maximum UV Index (UVI) for Mercersburg in December, 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 December, the maximum UV index in Mercersburg typically reaches 3, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec357910101098743
Data source: Mercersburg December 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 December 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 December’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 December’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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