December weather forecast
Sunnyvale, CA

The perfect blue sky, trees, buildings, and cute water fountain all reflected in the calm pool of water with birds in Sunnyvale, California
The perfect blue sky, trees, buildings, and cute water fountain all reflected in the calm pool of water with birds in Sunnyvale, California

Weather in December

December, the first month of the winter in Sunnyvale, is also a moderate month, with an average temperature fluctuating between 56.8°F (13.8°C) and 44.2°F (6.8°C).

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

The average relative humidity in December in Sunnyvale is 71%.

Rainfall

In Sunnyvale, California, during December, the rain falls for 7.5 days and regularly aggregates up to 0.71" (18mm) of precipitation. In Sunnyvale, during the entire year, the rain falls for 50 days and collects up to 3.9" (99mm) of precipitation.

Daylight

December has the shortest days of the year, with an average of 9h and 38min of daylight.
On the first day of the month, sunrise is at 7:03 am and sunset at 4:50 pm. On the last day of December, in Sunnyvale, sunrise is at 7:22 am and sunset at 5:00 pm PST.

Sunshine

December has the least sunshine of the year in Sunnyvale, 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 rays for average individuals.
Note: The daily maximum UV index of 3 in December interpret into the following advice:
Take precautions - Protection against sunburn is recommended. The Sun's most intense and consequently most harmful UV radiation during midday hours should be decreased by minimizing exposure and seeking shade. 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.
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FAQ

What is the coldest month in Sunnyvale?

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.

What is the average humidity in December in Sunnyvale?

The average relative humidity in December in Sunnyvale is 71%.

How many days does it rain in December in Sunnyvale?

In Sunnyvale, California, in December, during 7.5 rainfall days, 0.71" (18mm) of precipitation is typically accumulated.

What is the month with the shortest days in Sunnyvale?

December has the shortest days of the year in Sunnyvale, with an average of 9h and 38min of daylight.

What is the average length of the day in December in Sunnyvale?

In December, the average day length is 9h and 38min.

When are sunrise and sunset in December in Sunnyvale?

On the first day of December, sunrise is at 7:03 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.

What is the month with the least sunshine in Sunnyvale?

December has the least sunshine of the year in Sunnyvale, with an average of 5.9h of sunshine.

How long on average sun shines in December in Sunnyvale?

In December, the average sunshine duration in Sunnyvale is 5.9h.

What are the months with the lowest UV index in Sunnyvale?

The months with the lowest UV index in Sunnyvale are February, November and December, with an average maximum UV index of 3.

What is the UV index reading in December in Sunnyvale?

In December, the average daily maximum UV index in Sunnyvale, California, is 3. A UV Index estimate of 3 to 5 represents a medium health risk from exposure to Sun's UV rays.

Average temperature in December
Sunnyvale, CA

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).

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Average pressure in December
Sunnyvale, CA

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).

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Average wind speed in December
Sunnyvale, CA

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).

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Average humidity in December
Sunnyvale, CA

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%).

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Average rainfall in December
Sunnyvale, CA

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").

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Average rainfall days in December
Sunnyvale, CA

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).

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Average daylight in December /
Average sunshine in December
Sunnyvale, CA

Average daylight in December / Average sunshine in December - Sunnyvale, CA
  • Average daylight in December: 9h and 38min

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 38min).

  • Average sunshine in December: 5.9h

The month with the most sunshine is July (Average sunshine: 12.1h).
The month with the least sunshine is December (Average sunshine: 5.9h).

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Average sunshine days in December
Sunnyvale, CA

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).

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Average UV index in December
Sunnyvale, CA

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).

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Average cloud cover in December
Sunnyvale, CA

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).

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Average visibility in December
Sunnyvale, CA

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).

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