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 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 is the coldest month, exhibiting average temperatures of 55.8°F (13.2°C) at the peak and 47.1°F (8.4°C) at the base.Humidity
In Portola Valley, the average relative humidity in December is 72%.Rainfall
In December, in Portola Valley, the rain falls for 8.9 days. Throughout December, 0.79" (20mm) of precipitation is accumulated. In Portola Valley, during the entire year, the rain falls for 57.5 days and collects up to 4.76" (121mm) of precipitation.Daylight
December has the shortest days of the year, with an average of 9h and 36min of daylight.On the first day of December, sunrise is at 7:05 am and sunset at 4:51 pm. On the last day of the month, sunrise is at 7:23 am and sunset at 5:01 pm PST.
Sunshine
December has the least sunshine of the year in Portola Valley, with an average of 5.9h of sunshine.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 reading of 3 to 5 represents a medium health hazard from exposure to the Sun's UV radiation for the ordinary person.Note: A typical high UV index of 3 in December suggests the following recommendations:
Take precautions - Protection against sunburn is recommended. To prevent harmful UV exposure, minimize direct contact with the Sun around midday. Sunglasses that ward off UVA and UVB rays play a pivotal role in reducing solar eye damage.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
What is the coldest month in Portola Valley?
What is the usual temperature for Portola Valley in December?
What is the average humidity in December in Portola Valley?
How many days does it rain in December in Portola Valley?
What is the month with the shortest days in Portola Valley?
How many hours of daylight does Portola Valley have in December?
When is the sunrise / sunset in December in Portola Valley?
What is the month with the least sunshine in Portola Valley?
How long on average sun shines in December in Portola Valley?
When is the lowest UV index in Portola Valley?
How high is the UV index in December in Portola Valley?
Average temperature in December
Portola Valley, CA
- Average high temperature in December: 55.8°F
The warmest month (with the highest average high temperature) is August (73°F).
The month with the lowest average high temperature is December (55.8°F).
- Average low temperature in December: 47.1°F
The months with the highest average low temperature are August and September (56.7°F).
The coldest months (with the lowest average low temperature) are January and February (46.4°F).
Average pressure in December
Portola Valley, CA
- Average pressure in December: 30.11"Hg
The month with the highest atmospheric pressure is January (30.13"Hg).
The month with the lowest atmospheric pressure is September (29.92"Hg).
Average wind speed in December
Portola Valley, CA
- Average wind speed in December: 6.6mph
The windiest month (with the highest average wind speed) is April (7.6mph).
The calmest month (with the lowest average wind speed) is August (5.5mph).
Average humidity in December
Portola Valley, CA
- Average humidity in December: 72%
The month with the highest relative humidity is March (76%).
The month with the lowest relative humidity is October (68%).
Average rainfall in December
Portola Valley, CA
- Average rainfall in December: 0.79"
The wettest month (with the highest rainfall) is February (0.98").
The driest month (with the least rainfall) is June (0.04").
Average rainfall days in December
Portola Valley, CA
- Average rainfall days in December: 8.9 days
The month with the highest number of rainy days is March (10.6 days).
The month with the least rainy days is June (0.9 days).
Average daylight in December /
Average sunshine in December
Portola Valley, CA
- Average daylight in December: 9h and 4min
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 5min
The month with the most sunshine is July (Average sunshine: 12h and 0min).
The month with the least sunshine is December (Average sunshine: 5h and 54min).
Average sunshine days in December
Portola Valley, CA
- Average sunshine days in December: 20.4 days
The months with the most sunshine days are June and July (26.3 days).
The month with the least sunshine days is March (18.3 days).
Average UV index in December
Portola Valley, CA
- Average UV index in December: 3
The months with the highest UV index are June, July, August and September (UV index 5).
The months with the lowest UV index are February, November and December (UV index 3).
Average cloud cover in December
Portola Valley, 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 9).
Average visibility in December
Portola Valley, 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).
Portola Valley, California, USA
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