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
December comes with a decrease in the average high-temperature, falling from a chilly 48.4°F (9.1°C) in November to a wintry 39°F (3.9°C). In Herndon, December nights witness a steady temperature drop to a freezing cold 28°F (-2.2°C).Humidity
In Herndon, the average relative humidity in December is 81%.Rainfall
In Herndon, in December, it is raining for 11.8 days, with typically 2.2" (56mm) of accumulated precipitation. In Herndon, during the entire year, the rain falls for 165.3 days and collects up to 30.55" (776mm) of precipitation.Snowfall
January through May, October through December are months with snowfall. In December, it is snowing for 7 days. Throughout December, 1.97" (50mm) of snow is accumulated. In Herndon, during the entire year, snow falls for 38.1 days and aggregates up to 17.68" (449mm) of snow.Daylight
With an average of 9h and 18min of daylight, December has the shortest days of the year.On the first day of the month, sunrise is at 7:12 am and sunset at 4:40 pm. On the last day of December, in Herndon, sunrise is at 7:31 am and sunset at 4:50 pm EST.
Sunshine
In Herndon, the average sunshine in December is 4.4h.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 estimate of 2, and below, represents a minimal health hazard from unprotected exposure to Sun's UV rays for the ordinary person.Note: The maximum daily UV index of 2 in December converts into the following recommendations:
Despite most people tolerating extended sun exposure, it is critical to always protect those with sensitive skin, infants, and children. Stay safe from the Sun's strongest UV rays by limiting exposure during midday. For effective sun eye protection, rely on sunglasses certified for UVA and UVB resistance. Be aware! The reflective nature of snow can magnify the Sun's UV radiation almost twofold.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
How cold is December?
What is the average humidity in December?
How much does it rain in December?
How much does it snow in December?
What is the month with the shortest days?
How many hours of daylight does Herndon have in December?
When are sunrise and sunset in December?
How many hours of sunshine does Herndon have in December?
When is the lowest UV index?
How high is the UV index in December?
Average temperature in December
Herndon, PA
- Average high temperature in December: 39°F
The warmest month (with the highest average high temperature) is July (82.4°F).
The month with the lowest average high temperature is January (32.9°F).
- Average low temperature in December: 28°F
The month with the highest average low temperature is July (61.2°F).
The coldest month (with the lowest average low temperature) is January (20.1°F).
Average pressure in December
Herndon, 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
Herndon, PA
- Average wind speed in December: 7mph
The windiest months (with the highest average wind speed) are March and April (7.8mph).
The calmest month (with the lowest average wind speed) is August (4.5mph).
Average humidity in December
Herndon, PA
- Average humidity in December: 81%
The month with the highest relative humidity is February (82%).
The month with the lowest relative humidity is April (76%).
Average rainfall in December
Herndon, PA
- Average rainfall in December: 2.2"
The wettest month (with the highest rainfall) is May (3.35").
The driest months (with the least rainfall) are February and November (2.09").
Average rainfall days in December
Herndon, PA
- Average rainfall days in December: 11.8 days
The month with the highest number of rainy days is May (18.4 days).
The month with the least rainy days is February (9 days).
Average snowfall in December
Herndon, PA
- Average snowfall in December: 1.97"
The month with the highest snowfall is February (5.67").
The months with the least snowfall are June, July, August and September (0").
Average snowfall days in December
Herndon, PA
- Average snowfall days in December: 7 days
The month with the highest number of snowfall days is January (11.3 days).
The months with the least snowfall days are June, July, August and September (0 days).
Average daylight in December /
Average sunshine in December
Herndon, 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 18min).
- Average sunshine in December: 4h and 2min
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 12min).
Average sunshine days in December
Herndon, PA
- Average sunshine days in December: 14.6 days
The month with the most sunshine days is November (16.4 days).
The month with the least sunshine days is May (9.9 days).
Average UV index in December
Herndon, PA
- Average UV index in December: 2
The months with the highest UV index are 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
Herndon, PA
- Average cloud cover in December: 53
The month with the most cloud cover is February (Cloud cover 54).
The month with the least cloud cover is July (Cloud cover 32).
Average visibility in December
Herndon, PA
- Average visibility in December: 5mi
The months with the highest visibility are March, April, June, July and November (6mi).
The months with the lowest visibility are January, February, May, August, September, October and December (5mi).
Herndon, Pennsylvania, USA
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