December weather forecastMercer Island, WA
December
Weather in December
The first month of the winter, December, is also a frosty month in Mercer Island, Washington, with an average temperature ranging between min 34.7°F (1.5°C) and max 42.8°F (6°C).Temperature
Mercer Island notes the coldest temperatures in December, with a high average of 42.8°F (6°C) and a low of 34.7°F (1.5°C).Humidity
In December, the average relative humidity is 84%.Rainfall
The month with the most rainfall in Mercer Island is December, when the rain falls for 12.5 days and typically aggregates up to 2.01" (51mm) of precipitation.Snowfall
January through March, November and December are months with snowfall. In Mercer Island, in December, snow falls for 1.1 days, with typically accumulated 0.31" (8mm) of snow. In Mercer Island, Washington, during the entire year, snow falls for 7 days and aggregates up to 3.27" (83mm) of snow.Daylight
December has the shortest days of the year in Mercer Island, Washington, with an average of 8h and 30min of daylight.On the first day of December, sunrise is at 7:36 am and sunset at 4:19 pm. On the last day of the month, sunrise is at 7:56 am and sunset at 4:27 pm PST.
Sunshine
December has the least sunshine of the year, with an average of 4.2h of sunshine.UV index
The months with the lowest UV index are January, February, November and December, with an average maximum UV index of 2. A UV Index of 2, and less, symbolizes a low health risk from unprotected exposure to Sun's UV rays for the average person.Note: In December, an average UV index of 2 transforms into the following instructions:
Unlike children, who always need sun protection, most individuals can remain in the sun for up to an hour without getting burnt. Direct exposure to the Sun during its peak hours around mid-day should be minimized for safety. 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. Forewarned is forearmed! The Sun's UV radiation can be almost doubled in intensity by snow reflection.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in December
Mercer Island, WA
- Average high temperature in December: 42.8°F
The warmest month (with the highest average high temperature) is August (76.6°F).
The month with the lowest average high temperature is December (42.8°F).
- Average low temperature in December: 34.7°F
The month with the highest average low temperature is August (53.4°F).
The coldest month (with the lowest average low temperature) is February (34.5°F).
Average pressure in December
Mercer Island, WA
- Average pressure in December: 30.09"Hg
The month with the highest atmospheric pressure is January (30.1"Hg).
The month with the lowest atmospheric pressure is August (30"Hg).
Average wind speed in December
Mercer Island, WA
- Average wind speed in December: 4.7mph
The windiest month (with the highest average wind speed) is March (5.1mph).
The calmest month (with the lowest average wind speed) is August (3.4mph).
Average humidity in December
Mercer Island, WA
- Average humidity in December: 84%
The month with the highest relative humidity is January (85%).
The month with the lowest relative humidity is July (69%).
Average rainfall in December
Mercer Island, WA
- Average rainfall in December: 2.01"
The wettest month (with the highest rainfall) is December (2.01").
The driest month (with the least rainfall) is July (0.24").
Average rainfall days in December
Mercer Island, WA
- Average rainfall days in December: 12.5 days
The month with the highest number of rainy days is March (13.7 days).
The month with the least rainy days is August (4.1 days).
Average snowfall in December
Mercer Island, WA
- Average snowfall in December: 0.31"
The month with the highest snowfall is February (1.77").
The months with the least snowfall are April, May, June, July, August, September and October (0").
Average snowfall days in December
Mercer Island, WA
- Average snowfall days in December: 1.1 days
The month with the highest number of snowfall days is February (3 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).
Average daylight in December /
Average sunshine in December
Mercer Island, WA
- Average daylight in December: 8h and 30min
The month with the longest days is June (Average daylight: 15h and 54min).
The month with the shortest days is December (Average daylight: 8h and 30min).
- Average sunshine in December: 4h and 12min
The month with the most sunshine is August (Average sunshine: 10h and 42min).
The month with the least sunshine is December (Average sunshine: 4h and 12min).
Average sunshine days in December
Mercer Island, WA
- Average sunshine days in December: 17.4 days
The month with the most sunshine days is August (24.9 days).
The month with the least sunshine days is February (13.8 days).
Average UV index in December
Mercer Island, WA
- Average UV index in December: 2
The month with the highest UV index is July (UV index 6).
The months with the lowest UV index are January, February, November and December (UV index 2).
Average cloud cover in December
Mercer Island, WA
- Average cloud cover in December: 56
The month with the most cloud cover is December (Cloud cover 56).
The month with the least cloud cover is August (Cloud cover 25).
Average visibility in December
Mercer Island, WA
- Average visibility in December: 5mi
The months with the highest visibility are May, June, July, August and September (6mi).
The months with the lowest visibility are January, February, March, April, October, November and December (5mi).
