December weather forecast
Mercersburg, PA

Weather in December

December, the first month of the winter in Mercersburg, is still a cold month, with temperature in the range of an average low of 28.9°F (-1.7°C) and an average high of 40.8°F (4.9°C).

Temperature

In Mercersburg, the average high-temperature in December drops from a cool 50.4°F (10.2°C) in November to a cold 40.8°F (4.9°C). In Mercersburg, in December, the average low-temperature is 28.9°F (-1.7°C).

Humidity

February, May, October and December, with an average relative humidity of 79%, are the most humid months.

Rainfall

In Mercersburg, during December, the rain falls for 11.1 days and regularly aggregates up to 2.52" (64mm) of precipitation. In Mercersburg, Pennsylvania, during the entire year, the rain falls for 170.5 days and collects up to 31.02" (788mm) of precipitation.

Snowfall

Months with snowfall in Mercersburg are January through April, October through December. In Mercersburg, in December, during 5.9 snowfall days, 2.52" (64mm) of snow is typically accumulated. Throughout the year, there are 33.6 snowfall days, and 17.91" (455mm) of snow is accumulated.

Daylight

December has the shortest days of the year, with an average of 9h and 24min of daylight.
On the first day of the month, sunrise is at 7:13 am and sunset at 4:47 pm. On the last day of December, sunrise is at 7:32 am and sunset at 4:56 pm EST.

Sunshine

In December, the average sunshine is 4.7h.

UV index

January through March, November and December, with an average maximum UV index of 2, are months with the lowest UV index in Mercersburg. A UV Index value of 2, and less, symbolizes a minimal health hazard from unprotected exposure to Sun's UV rays for the ordinary person.
Note: In December, the average maximum UV index of 2 translate into the following recommendations:
Extended sun exposure is not an issue for the majority. Children, infants, and fair-skinned individuals always need to be protected. The Sun's most intense and consequently most harmful UV radiation during midday hours should be decreased by minimizing exposure and seeking shade. On bright days sunglasses that block both UVA and UVB rays should be worn. A hat with a wide brim is extremely helpful, as it can prevent roughly 50% of UV radiation from reaching the eyes. Caution! The reflection of snow can nearly double the intensity of the Sun's UV radiation.
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FAQ

What is the most humid month in Mercersburg?

The months with the highest humidity in Mercersburg, Pennsylvania, are February, May, October and December, with an average relative humidity of 79%.

What is the average humidity in December in Mercersburg?

The average relative humidity in December in Mercersburg, Pennsylvania, is 79%.

How many days does it rain in December in Mercersburg?

In Mercersburg, Pennsylvania, in December, during 11.1 rainfall days, 2.52" (64mm) of precipitation is typically accumulated.

How many days does it snow in December in Mercersburg?

In December, in Mercersburg, Pennsylvania, it is snowing for 5.9 days. Throughout December, 2.52" (64mm) of snow is accumulated.

What is the month with the shortest days in Mercersburg?

The month with the shortest days in Mercersburg is December, with an average of 9h and 24min of daylight.

What is the average length of the day in December in Mercersburg?

The average day length in December is 9h and 24min.

When is the sunrise / sunset in December in Mercersburg?

On the first day of December, sunrise is at 7:13 am and sunset at 4:47 pm. On the last day of the month, sunrise is at 7:32 am and sunset at 4:56 pm EST.

How long on average sun shines in December in Mercersburg?

The average sunshine duration in December in Mercersburg, Pennsylvania, is 4.7h.

What are the months with the lowest UV index in Mercersburg?

January through March, November and December, with an average maximum UV index of 2, are months with the lowest UV index in Mercersburg, Pennsylvania.

What is the UV index reading in December in Mercersburg?

In Mercersburg, Pennsylvania, the average daily maximum UV index in December is 2. A UV Index value of 2, and less, symbolizes a minimal health vulnerability from exposure to Sun's UV rays.

Average temperature in December
Mercersburg, PA

Average temperature in December - Mercersburg, PA
  • Average high temperature in December: 40.8°F

The warmest month (with the highest average high temperature) is July (84.7°F).
The month with the lowest average high temperature is January (35.2°F).

  • Average low temperature in December: 28.9°F

The month with the highest average low temperature is July (62.6°F).
The coldest month (with the lowest average low temperature) is January (22.1°F).

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Average pressure in December
Mercersburg, PA

Average pressure in December - Mercersburg, PA
  • Average pressure in December: 30.11"Hg

The month with the highest atmospheric pressure is November (30.14"Hg).
The month with the lowest atmospheric pressure is June (29.95"Hg).

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Average wind speed in December
Mercersburg, PA

Average wind speed in December - Mercersburg, PA
  • Average wind speed in December: 6.8mph

The windiest month (with the highest average wind speed) is January (7.5mph).
The calmest month (with the lowest average wind speed) is August (4.3mph).

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Average humidity in December
Mercersburg, PA

Average humidity in December - Mercersburg, PA
  • Average humidity in December: 79%

The months with the highest relative humidity are February, May, October and December (79%).
The months with the lowest relative humidity are April and July (75%).

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Average rainfall in December
Mercersburg, PA

Average rainfall in December - Mercersburg, PA
  • Average rainfall in December: 2.52"

The wettest month (with the highest rainfall) is May (3.19").
The driest month (with the least rainfall) is September (2.05").

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Average rainfall days in December
Mercersburg, PA

Average rainfall days in December - Mercersburg, PA
  • Average rainfall days in December: 11.1 days

The month with the highest number of rainy days is May (18.8 days).
The month with the least rainy days is November (9.9 days).

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Average snowfall in December
Mercersburg, PA

Average snowfall in December - Mercersburg, PA
  • Average snowfall in December: 2.52"

The month with the highest snowfall is January (5.2").
The months with the least snowfall are May, June, July, August and September (0").

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Average snowfall days in December
Mercersburg, PA

Average snowfall days in December - Mercersburg, PA
  • Average snowfall days in December: 5.9 days

The month with the highest number of snowfall days is January (9.9 days).
The months with the least snowfall days are May, June, July, August and September (0 days).

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Average daylight in December /
Average sunshine in December
Mercersburg, PA

Average daylight in December / Average sunshine in December - Mercersburg, PA
  • Average daylight in December: 9h and 24min

The month with the longest days is June (Average daylight: 14h and 57min).
The month with the shortest days is December (Average daylight: 9h and 24min).

  • Average sunshine in December: 4.7h

The month with the most sunshine is July (Average sunshine: 10.5h).
The month with the least sunshine is January (Average sunshine: 4.6h).

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Average sunshine days in December
Mercersburg, PA

Average sunshine days in December - Mercersburg, PA
  • Average sunshine days in December: 15.1 days

The month with the most sunshine days is November (18 days).
The month with the least sunshine days is May (10.3 days).

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Average UV index in December
Mercersburg, PA

Average UV index in December - Mercersburg, PA
  • Average UV index in December: 2

The months with the highest UV index are May, June and July (UV index 6).
The months with the lowest UV index are January, February, March, November and December (UV index 2).

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Average cloud cover in December
Mercersburg, PA

Average cloud cover in December - Mercersburg, PA
  • Average cloud cover in December: 50

The months with the most cloud cover are January, February and December (Cloud cover 50).
The month with the least cloud cover is July (Cloud cover 31).

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Average visibility in December
Mercersburg, PA

Average visibility in December - Mercersburg, PA
  • Average visibility in December: 5mi

The months with the highest visibility are April, June, July and November (6mi).
The months with the lowest visibility are January, February, March, May, August, September, October and December (5mi).

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