Contents
- Weather in December
- Frequently asked questions
- Average temperature in December
- Average pressure in December
- Average wind speed in December
- Average humidity in December
- Average rainfall in December
- Average rainfall days in December
- Average snowfall in December
- Average snowfall days in December
- Average daylight in December
- Average sunshine in December
- Average sunshine days in December
- Average UV index in December
- Average cloud cover in December
- Average visibility in December
Weather in December
Temperature
In December, the average high-temperature decreases from a chilly 49.5°F (9.7°C) in November to an icy 40.3°F (4.6°C). Mount Gretna experiences an average low-temperature of 29.3°F (-1.5°C) in the month of December.Humidity
In December, the average relative humidity is 80%.Rainfall
In Mount Gretna, Pennsylvania, during December, the rain falls for 9.2 days and regularly aggregates up to 1.1" (28mm) of precipitation. Throughout the year, there are 137.4 rainfall days, and 16.26" (413mm) of precipitation is accumulated.Snowfall
January through May, October through December are months with snowfall. In Mount Gretna, during December, snow falls for 3.3 days and regularly aggregates up to 0.98" (25mm) of snow. In Mount Gretna, during the entire year, snow falls for 19.5 days and aggregates up to 6.69" (170mm) of snow.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 7:09 am and sunset at 4:40 pm. On the last day of December, sunrise is at 7:28 am and sunset at 4:50 pm EST.
Sunshine
The average sunshine in December is 4.6h.UV index
The months with the lowest UV index are January through March, November and December, with an average maximum UV index of 2. A UV Index value of 2, and less, symbolizes a low threat to health from unsafe exposure to UV radiation for ordinary individuals.Note: In December, the maximum UV index of 2 transforms into these recommendations:
Protection from prolonged sun exposure is necessary for babies, children, and individuals with sensitive skin. Solar radiation is at its peak intensity during midday, so it's advisable to stay indoors or in the 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. Take careful note! The UV radiation of the Sun can be nearly doubled by snow reflection.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
How cold is it in December?
What is the average humidity in December?
How many days does it rain in December?
How much does it snow in December?
What is the month with the shortest days?
What is the average length of the day in December?
When is the sunrise / sunset in December?
How long on average sun shines in December?
What is the month with the lowest UV index?
What is the UV index reading in December?
Average temperature in December
Mount Gretna, PA
- Average high temperature in December: 40.3°F
The warmest month (with the highest average high temperature) is July (82°F).
The month with the lowest average high temperature is January (33.8°F).
- Average low temperature in December: 29.3°F
The month with the highest average low temperature is July (63.1°F).
The coldest month (with the lowest average low temperature) is January (21.6°F).
Average pressure in December
Mount Gretna, PA
- Average pressure in December: 30.1"Hg
The month with the highest atmospheric pressure is November (30.13"Hg).
The month with the lowest atmospheric pressure is June (29.94"Hg).
Average wind speed in December
Mount Gretna, PA
- Average wind speed in December: 8mph
The windiest month (with the highest average wind speed) is March (8.8mph).
The calmest month (with the lowest average wind speed) is August (4.8mph).
Average humidity in December
Mount Gretna, PA
- Average humidity in December: 80%
The months with the highest relative humidity are February, May and October (81%).
The month with the lowest relative humidity is April (76%).
Average rainfall in December
Mount Gretna, PA
- Average rainfall in December: 1.1"
The wettest month (with the highest rainfall) is August (2.13").
The driest month (with the least rainfall) is February (0.94").
Average rainfall days in December
Mount Gretna, PA
- Average rainfall days in December: 9.2 days
The month with the highest number of rainy days is May (15.9 days).
The month with the least rainy days is January (6.7 days).
Average snowfall in December
Mount Gretna, PA
- Average snowfall in December: 0.98"
The month with the highest snowfall is January (1.97").
The months with the least snowfall are June, July, August and September (0").
Average snowfall days in December
Mount Gretna, PA
- Average snowfall days in December: 3.3 days
The month with the highest number of snowfall days is January (5.2 days).
The months with the least snowfall days are June, July, August and September (0 days).
Average daylight in December /
Average sunshine in December
Mount Gretna, PA
- Average daylight in December: 9h and 2min
The month with the longest days is June (Average daylight: 15h and 0min).
The month with the shortest days is December (Average daylight: 9h and 24min).
- Average sunshine in December: 4h and 4min
The month with the most sunshine is July (Average sunshine: 10h and 24min).
The month with the least sunshine is February (Average sunshine: 4h and 30min).
Average sunshine days in December
Mount Gretna, PA
- Average sunshine days in December: 18.7 days
The month with the most sunshine days is January (20.3 days).
The month with the least sunshine days is May (11.5 days).
Average UV index in December
Mount Gretna, 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).
Average cloud cover in December
Mount Gretna, PA
- Average cloud cover in December: 51
The months with the most cloud cover are February and December (Cloud cover 51).
The month with the least cloud cover is July (Cloud cover 32).
Average visibility in December
Mount Gretna, PA
- Average visibility in December: 6mi
The months with the highest visibility are January, February, March, April, June, July, November and December (6mi).
The months with the lowest visibility are May, August, September and October (5mi).
Mount Gretna, Pennsylvania, USA
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