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
With average high and low temperatures of 33.1°F (0.6°C) and 21.2°F (-6°C) respectively, December is Riley's coldest month.Humidity
December is the most humid month, with an average relative humidity of 83%.Rainfall
The month with the most rainfall is December, when the rain falls for 13.6 days and typically aggregates up to 1.54" (39mm) of precipitation.Snowfall
January through March, November and December are months with snowfall. December is the month with the most snowfall. Snow falls for 3.1 days and accumulates 0.87" (22mm) of snow.Daylight
December has the shortest days of the year, with an average of 9h and 0min of daylight.On the first day of December, sunrise is at 7:12 am and sunset at 4:22 pm. On the last day of the month, sunrise is at 7:31 am and sunset at 4:31 pm PST.
Sunshine
December has the least sunshine of the year, with an average of 5.2h of sunshine.UV index
January through March, November and December, with an average maximum UV index of 2, are months with the lowest UV index. A UV Index of 2, and less, symbolizes a minimal health vulnerability from exposure to the Sun's UV rays for the average person.Note: A maximum high UV index of 2 in December translates into the following recommendations:
The majority are not significantly affected by prolonged sun exposure. Infants, children, and those with fair skin must always have protection. To protect against the Sun's most potent rays, avoid direct exposure around midday. For effective sun eye protection, rely on sunglasses certified for UVA and UVB resistance. Mark this! Snow reflection can nearly double the UV radiation intensity from the Sun.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
What month is the coldest?
How cold is December?
What is the most humid month?
What is the average humidity in December?
What is the wettest month?
How many days does it rain in December?
When does it snow the most in Riley?
How many days does it snow in December?
What is the month with the shortest days?
How many hours of daylight does Riley have in December?
When are sunrise and sunset in December?
What is the month with the least sunshine?
How many hours of sunshine does Riley have in December?
When is the lowest UV index?
What is the UV index intensity in December?
Average temperature in December
Riley, OR
- Average high temperature in December: 33.1°F
The warmest month (with the highest average high temperature) is July (82.9°F).
The month with the lowest average high temperature is December (33.1°F).
- Average low temperature in December: 21.2°F
The month with the highest average low temperature is August (58.1°F).
The coldest month (with the lowest average low temperature) is December (21.2°F).
Average pressure in December
Riley, OR
- Average pressure in December: 30.19"Hg
The month with the highest atmospheric pressure is January (30.22"Hg).
The month with the lowest atmospheric pressure is August (29.94"Hg).
Average wind speed in December
Riley, OR
- Average wind speed in December: 7.9mph
The windiest month (with the highest average wind speed) is April (9.9mph).
The calmest month (with the lowest average wind speed) is August (7.5mph).
Average humidity in December
Riley, OR
- Average humidity in December: 83%
The month with the highest relative humidity is December (83%).
The months with the lowest relative humidity are July and August (33%).
Average rainfall in December
Riley, OR
- Average rainfall in December: 1.54"
The wettest month (with the highest rainfall) is December (1.54").
The driest month (with the least rainfall) is July (0.16").
Average rainfall days in December
Riley, OR
- Average rainfall days in December: 13.6 days
The month with the highest number of rainy days is March (17.7 days).
The month with the least rainy days is August (3.3 days).
Average snowfall in December
Riley, OR
- Average snowfall in December: 0.87"
The month with the highest snowfall is December (0.87").
The months with the least snowfall are April, May, June, July, August, September and October (0").
Average snowfall days in December
Riley, OR
- Average snowfall days in December: 3.1 days
The month with the highest number of snowfall days is December (3.1 days).
The months with the least snowfall days are April, May, June, July, August, September and October (0 days).
Average daylight in December /
Average sunshine in December
Riley, OR
- Average daylight in December: 9h and 0min
The month with the longest days is June (Average daylight: 15h and 24min).
The month with the shortest days is December (Average daylight: 9h and 0min).
- Average sunshine in December: 5h and 1min
The month with the most sunshine is July (Average sunshine: 12h and 6min).
The month with the least sunshine is December (Average sunshine: 5h and 12min).
Average sunshine days in December
Riley, OR
- Average sunshine days in December: 14.5 days
The months with the most sunshine days are July and August (25.3 days).
The month with the least sunshine days is March (11.5 days).
Average UV index in December
Riley, OR
- Average UV index in December: 2
The month with the highest UV index is July (UV index 7).
The months with the lowest UV index are January, February, March, November and December (UV index 2).
Average cloud cover in December
Riley, OR
- Average cloud cover in December: 47
The month with the most cloud cover is December (Cloud cover 47).
The months with the least cloud cover are July and August (Cloud cover 9).
Average visibility in December
Riley, OR
- Average visibility in December: 6mi
The months with the highest visibility are February, March, April, May, June, July, August, September, October, November and December (6mi).
The month with the lowest visibility is January (5mi).
Riley, Oregon, USA
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