December weather forecast and climate
San Bruno, CA

Weather in December

The first month of the winter, December, is also a moderate month in San Bruno, California, with average temperature varying between 47.7°F (8.7°C) and 55.8°F (13.2°C).

Temperature

December is the coldest month, with an average high-temperature of 55.8°F (13.2°C) and an average low-temperature of 47.7°F (8.7°C).

Humidity

In December, the average relative humidity in San Bruno is 72%.

Rainfall

In San Bruno, during December, the rain falls for 11 days and regularly aggregates up to 2.28" (58mm) of precipitation. Throughout the year, there are 81.8 rainfall days, and 13.46" (342mm) of precipitation is accumulated.

Daylight

With an average of 9.6h of daylight, December has the shortest days of the year in San Bruno.

Sunshine

The month with the least sunshine is December, with an average of 5.8h of sunshine.

UV index

Months with the lowest UV index in San Bruno are 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 unprotected exposure to the Sun's UV rays for the ordinary person.
Note: The average daily UV index of 3 transform into the following instructions:
Take precautions - Protection against the skin and eye damage is obliged. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. Sun-protective clothing, a long-sleeved shirt and pants, a wide-brimmed hat, and UVA and UVB-blocking sunglasses are particularly helpful in blocking UV radiation's harmful effects.
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FAQ

What is the coldest month in San Bruno?

With an average high-temperature of 55.8°F (13.2°C) and an average low-temperature of 47.7°F (8.7°C), December is the coldest month.

What is the temperature in December in San Bruno?

In December, in San Bruno, the average high-temperature is 55.8°F (13.2°C), and the average low-temperature is 47.7°F (8.7°C).

What is the average humidity in December in San Bruno?

The average relative humidity in December is 72%.

How much does it rain in San Bruno in December?

In December, in San Bruno, California, the rain falls for 11 days. Throughout December, 2.28" (58mm) of precipitation is accumulated.

What is the month with the shortest days in San Bruno?

December has the shortest days of the year in San Bruno, California, with an average of 9.6h of daylight.

What is the average length of the day in December in San Bruno?

In San Bruno, the average length of the day in December is 9.6h.

What is the month with the least sunshine in San Bruno?

December has the least sunshine of the year in San Bruno, California, with an average of 5.8h of sunshine.

How many hours of sunshine does San Bruno have in December?

In December, the average sunshine in San Bruno is 5.8h.

When is the lowest UV index in San Bruno?

Months with the lowest UV index in San Bruno, California, are February, November and December, with an average maximum UV index of 3.

How high is the UV index in December in San Bruno?

The average daily maximum UV index in December is 3. A UV Index of 3 to 5 symbolizes a moderate vulnerability from unprotected exposure to the UV radiation.

Average temperature in December
San Bruno, CA

Average temperature in December - San Bruno, CA
  • Average high temperature in December: 55.8°F

The warmest month (with the highest average high temperature) is September (69.8°F).
The month with the lowest average high temperature is December (55.8°F).

  • Average low temperature in December: 47.7°F

The month with the highest average low temperature is September (56.5°F).
The coldest month (with the lowest average low temperature) is December (47.7°F).

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Average pressure in December
San Bruno, CA

Average pressure in December - San Bruno, CA
  • Average pressure in December: 30.11"

The month with the highest atmospheric pressure is January (30.13").
The month with the lowest atmospheric pressure is September (29.92").

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Average wind speed in December
San Bruno, CA

Average wind speed in December - San Bruno, CA
  • Average wind speed in December: 7.4mph

The windiest month (with the highest average wind speed) is April (8.5mph).
The calmest months (with the lowest average wind speed) are August and September (6.3mph).

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Average humidity in December
San Bruno, CA

Average humidity in December - San Bruno, CA
  • Average humidity in December: 72%

The month with the highest relative humidity is August (79%).
Months with the lowest relative humidity are October and November (71%).

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Average rainfall in December
San Bruno, CA

Average rainfall in December - San Bruno, CA
  • Average rainfall in December: 2.28"

The wettest month (with the highest rainfall) is February (2.72").
The driest months (with the least rainfall) are July and August (0.04").

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Average rainfall days in December
San Bruno, CA

Average rainfall days in December - San Bruno, CA
  • Average rainfall days in December: 11 days

The month with the highest number of rainy days is March (13.3 days).
Months with the least rainy days are July and August (2.2 days).

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Average daylight in December /
Average sunshine in December
San Bruno, CA

Average daylight in December / Average sunshine in December - San Bruno, CA
  • Average daylight in December: 9.6h

The month with the longest days is June (Average daylight: 14.7h).
The month with the shortest days is December (Average daylight: 9.6h).

  • Average sunshine in December: 5.8h

The month with the most sunshine is July (Average sunshine: 11.8h).
The month with the least sunshine is December (Average sunshine: 5.8h).

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Average sunshine days in December
San Bruno, CA

Average sunshine days in December - San Bruno, CA
  • Average sunshine days in December: 19.1 days

The month with the most sunshine days is July (27.3 days).
The month with the least sunshine days is March (16.3 days).

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Average UV index in December
San Bruno, CA

Average UV index in December - San Bruno, CA
  • Average UV index in December: 3

Months with the highest UV index are June, July, August and September (UV index 5).
Months with the lowest UV index are February, November and December (UV index 3).

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Average cloud cover in December
San Bruno, CA

Average cloud cover in December - San Bruno, CA
  • Average cloud cover in December: 35

The month with the most cloud cover is March (Cloud cover 37).
The month with the least cloud cover is September (Cloud cover 16).

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Average visibility in December
San Bruno, CA

Average visibility in December - San Bruno, CA
  • Average visibility in December: 6mi

Months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
Months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).

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