December weather forecastSunnyvale, CA
December
Weather in December
December, the final month of the year, witnesses a further dip in temperature, reaching an average high of 56.8°F (13.8°C). Noticing a steep increase in rainfall - up to an average of 0.71" (18mm) - December has the largest number of rainfall days, reaching 7.5. As the daylight hours minimize to 9.6, the sunshine duration also lessens to just 5.9 hours. Maintaining consistent pressure and visibility, December fully embraces the winter season, preparing Sunnyvale for the upcoming festive holiday period.Temperature
With an average high-temperature of 56.8°F (13.8°C) and an average low-temperature of 44.2°F (6.8°C), December is the coldest month.Humidity
In Sunnyvale, the average relative humidity in December is 71%.Rainfall
In Sunnyvale, in December, it is raining for 7.5 days, with typically 0.71" (18mm) of accumulated precipitation. Throughout the year, there are 50 rainfall days, and 3.9" (99mm) of precipitation is accumulated.Daylight
With an average of 9h and 36min of daylight, December has the shortest days of the year.On the first day of December, sunrise is at 7:04 am and sunset at 4:50 pm. On the last day of the month, sunrise is at 7:22 am and sunset at 5:00 pm PST.
Sunshine
With an average of 5.9h of sunshine, December has the least sunshine of the year.UV index
The months with the lowest UV index are February, November and December, with an average maximum UV index of 3. A UV Index estimate of 3 to 5 represents a medium vulnerability from exposure to the Sun's UV rays for ordinary individuals.Note: A daily high UV index of 3 in December leads to these guidelines:
Undertake precautions - Obligation exists to protect against skin and eye damage. Sun exposure should be minimized, especially during midday, to avoid harmful UV radiation. Using UVA and UVB-protective sunglasses and sun-protective clothing is effective against UV radiation.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in December
Sunnyvale, CA
- Average high temperature in December: 56.8°F
The warmest month (with the highest average high temperature) is July (79.9°F).
The month with the lowest average high temperature is December (56.8°F).
- Average low temperature in December: 44.2°F
The month with the highest average low temperature is August (56.8°F).
The coldest months (with the lowest average low temperature) are February and December (44.2°F).
Average pressure in December
Sunnyvale, CA
- Average pressure in December: 30.11"Hg
The month with the highest atmospheric pressure is January (30.13"Hg).
The months with the lowest atmospheric pressure are June and September (29.92"Hg).
Average wind speed in December
Sunnyvale, CA
- Average wind speed in December: 5.3mph
The windiest month (with the highest average wind speed) is April (6.2mph).
The calmest month (with the lowest average wind speed) is September (4.6mph).
Average humidity in December
Sunnyvale, CA
- Average humidity in December: 71%
The month with the highest relative humidity is March (73%).
The months with the lowest relative humidity are September and October (63%).
Average rainfall in December
Sunnyvale, CA
- Average rainfall in December: 0.71"
The wettest months (with the highest rainfall) are February and March (0.75").
The driest month (with the least rainfall) is July (0").
Average rainfall days in December
Sunnyvale, CA
- Average rainfall days in December: 7.5 days
The month with the highest number of rainy days is March (9.6 days).
The month with the least rainy days is August (0.4 days).
Average daylight in December /
Average sunshine in December
Sunnyvale, CA
- Average daylight in December: 9h and 36min
The month with the longest days is June (Average daylight: 14h and 42min).
The month with the shortest days is December (Average daylight: 9h and 36min).
- Average sunshine in December: 5h and 54min
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 54min).
Average sunshine days in December
Sunnyvale, CA
- Average sunshine days in December: 22.4 days
The month with the most sunshine days is August (30.1 days).
The month with the least sunshine days is March (19.9 days).
Average UV index in December
Sunnyvale, CA
- Average UV index in December: 3
The month with the highest UV index is June (UV index 6).
The months with the lowest UV index are February, November and December (UV index 3).
Average cloud cover in December
Sunnyvale, CA
- Average cloud cover in December: 33
The month with the most cloud cover is March (Cloud cover 35).
The month with the least cloud cover is July (Cloud cover 7).
Average visibility in December
Sunnyvale, CA
- Average visibility in December: 6mi
The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
