December weather forecastRock Island, WA
December
Weather in December
The first month of the winter, December, is also an icy month in Rock Island, Washington, with an average temperature ranging between min 20.7°F (-6.3°C) and max 32.4°F (0.2°C).Temperature
The coldest time of the year is December, with temperatures averaging a high of 32.4°F (0.2°C) and a low of 20.7°F (-6.3°C).Humidity
In Rock Island, the average relative humidity in December is 87%.Rainfall
The wettest months are January and December, with an average 1.57" (40mm) of rainfall.Snowfall
Months with snowfall are January through April, September, November and December. December is the month with the most snowfall in Rock Island, Washington. Snow falls for 9.5 days and accumulates 5.98" (152mm) of snow.Daylight
The month with the shortest days is December, with an average of 8h and 30min of daylight.On the first day of the month, sunrise is at 7:27 am and sunset at 4:11 pm. On the last day of December, sunrise is at 7:47 am and sunset at 4:20 pm PST.
Sunshine
In Rock Island, Washington, the average sunshine in December is 4.9h.UV index
The months with the lowest UV index in Rock Island are January, February, November and December, with an average maximum UV index of 2. A UV Index estimate of 2, and below, represents a low threat to health from unsafe exposure to UV radiation for ordinary individuals.Note: A typical high UV index of 2 in December suggests the following recommendations:
Sun exposure does not present considerable issues for many, yet infants, fair-skinned people, and children necessitate constant protection. Being exposed to the midday Sun can have harmful effects due to strong UV radiation; always take precautions. Counter UV radiation's ill effects with clothing designed for sun safety and UV-resistant eyewear. Notice! The UV radiation of the Sun can be intensified nearly twofold due to the reflective quality of snow.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in December
Rock Island, WA
- Average high temperature in December: 32.4°F
The warmest month (with the highest average high temperature) is July (83.1°F).
The month with the lowest average high temperature is December (32.4°F).
- Average low temperature in December: 20.7°F
The month with the highest average low temperature is August (56.3°F).
The coldest month (with the lowest average low temperature) is December (20.7°F).
Average pressure in December
Rock Island, WA
- Average pressure in December: 30.14"Hg
The month with the highest atmospheric pressure is January (30.15"Hg).
The month with the lowest atmospheric pressure is August (29.93"Hg).
Average wind speed in December
Rock Island, WA
- Average wind speed in December: 3.7mph
The windiest month (with the highest average wind speed) is June (6.5mph).
The calmest month (with the lowest average wind speed) is December (3.7mph).
Average humidity in December
Rock Island, WA
- Average humidity in December: 87%
The month with the highest relative humidity is January (88%).
The months with the lowest relative humidity are July and August (44%).
Average rainfall in December
Rock Island, WA
- Average rainfall in December: 1.57"
The wettest months (with the highest rainfall) are January and December (1.57").
The driest months (with the least rainfall) are July and August (0.24").
Average rainfall days in December
Rock Island, WA
- Average rainfall days in December: 9.7 days
The month with the highest number of rainy days is March (13.8 days).
The month with the least rainy days is August (3.8 days).
Average snowfall in December
Rock Island, WA
- Average snowfall in December: 5.98"
The month with the highest snowfall is December (5.98").
The months with the least snowfall are May, June, July, August and October (0").
Average snowfall days in December
Rock Island, WA
- Average snowfall days in December: 9.5 days
The month with the highest number of snowfall days is December (9.5 days).
The months with the least snowfall days are May, June, July, August and October (0 days).
Average daylight in December /
Average sunshine in December
Rock 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 54min
The month with the most sunshine is August (Average sunshine: 12h and 6min).
The month with the least sunshine is January (Average sunshine: 4h and 42min).
Average sunshine days in December
Rock Island, WA
- Average sunshine days in December: 15.7 days
The month with the most sunshine days is July (25.5 days).
The month with the least sunshine days is February (12.6 days).
Average UV index in December
Rock 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
Rock Island, WA
- Average cloud cover in December: 47
The month with the most cloud cover is January (Cloud cover 49).
The months with the least cloud cover are July and August (Cloud cover 11).
Average visibility in December
Rock Island, WA
- Average visibility in December: 4mi
The months with the highest visibility are March, April, May, June, July, August, September, October and November (6mi).
The months with the lowest visibility are January and December (4mi).
