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, having an average high-temperature of 55.4°F (13°C) and an average low-temperature of 43.2°F (6.2°C), is the coldest month.Humidity
The average relative humidity in December is 71%.Rainfall
In Port Costa, in December, it is raining for 8.5 days, with typically 0.79" (20mm) of accumulated precipitation. Throughout the year, there are 56.9 rainfall days, and 4.88" (124mm) of precipitation is accumulated.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 7:06 am and sunset at 4:49 pm. On the last day of the month, sunrise is at 7:24 am and sunset at 4:59 pm PST.
Sunshine
December has the least sunshine of the year, with an average of 5.7h of sunshine.UV index
The months with the lowest UV index are January, February, November and December, with an average maximum UV index of 3. A UV Index of 3 to 5 symbolizes a moderate health risk from unsafe exposure to UV radiation for the ordinary person.Note: The daily high UV index of 3 in December translates into this advice:
Exercise prevention - Protecting skin and eyes from harm is required. The mid-day Sun emits the most powerful UV radiation, so seek shade and minimize exposure. Stay sun-safe with clothing that is both closely woven and worn loosely.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
What is the coldest time of year?
What are December temperatures?
What is the average humidity in December?
How much does it rain in December?
What is the month with the shortest days?
What is the average length of the day in December?
When are sunrise and sunset in December?
What is the month with the least sunshine?
How many hours of sunshine does Port Costa have in December?
When is the lowest UV index?
What is the UV index reading in December?
Average temperature in December
Port Costa, CA
- Average high temperature in December: 55.4°F
The warmest months (with the highest average high temperature) are July and September (80.1°F).
The month with the lowest average high temperature is December (55.4°F).
- Average low temperature in December: 43.2°F
The month with the highest average low temperature is August (56.5°F).
The coldest month (with the lowest average low temperature) is January (43°F).
Average pressure in December
Port Costa, CA
- Average pressure in December: 30.11"Hg
The month with the highest atmospheric pressure is January (30.14"Hg).
The month with the lowest atmospheric pressure is June (29.91"Hg).
Average wind speed in December
Port Costa, CA
- Average wind speed in December: 5.2mph
The windiest month (with the highest average wind speed) is May (7.1mph).
The calmest month (with the lowest average wind speed) is November (4.6mph).
Average humidity in December
Port Costa, CA
- Average humidity in December: 71%
The month with the highest relative humidity is March (75%).
The months with the lowest relative humidity are September and October (60%).
Average rainfall in December
Port Costa, CA
- Average rainfall in December: 0.79"
The wettest month (with the highest rainfall) is February (1.14").
The driest months (with the least rainfall) are July and August (0.04").
Average rainfall days in December
Port Costa, CA
- Average rainfall days in December: 8.5 days
The month with the highest number of rainy days is March (10.2 days).
The month with the least rainy days is August (0.9 days).
Average daylight in December /
Average sunshine in December
Port Costa, CA
- Average daylight in December: 9h and 4min
The month with the longest days is June (Average daylight: 14h and 48min).
The month with the shortest days is December (Average daylight: 9h and 36min).
- Average sunshine in December: 5h and 4min
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 42min).
Average sunshine days in December
Port Costa, CA
- Average sunshine days in December: 20.8 days
The month with the most sunshine days is July (27.2 days).
The month with the least sunshine days is March (18.8 days).
Average UV index in December
Port Costa, 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 January, February, November and December (UV index 3).
Average cloud cover in December
Port Costa, CA
- Average cloud cover in December: 36
The month with the most cloud cover is March (Cloud cover 37).
The month with the least cloud cover is July (Cloud cover 9).
Average visibility in December
Port Costa, 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).
Port Costa, California, USA
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