December weather forecast and climate
Half Moon Bay, CA

A warm and sunny day on a scenic beach in Half Moon Bay, California
A warm and sunny day on a scenic beach in Half Moon Bay, California

Weather in December

December, the first month of the winter, in Half Moon Bay, is also a moderate month, with average temperature fluctuating between 55.6°F (13.1°C) and 49.3°F (9.6°C).

Temperature

December is the coldest month, with an average high-temperature of 55.6°F (13.1°C) and an average low-temperature of 49.3°F (9.6°C).

Humidity

Months with the lowest humidity are November and December, with an average relative humidity of 72%.

Rainfall

In Half Moon Bay, during December, the rain falls for 8.4 days and regularly aggregates up to 1.5" (38mm) of precipitation. In Half Moon Bay, during the entire year, the rain falls for 76.8 days and collects up to 8.54" (217mm) of precipitation.

Daylight

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

Sunshine

December has the least sunshine of the year in Half Moon Bay, with an average of 5.7h of sunshine.

UV index

January through May, July, October through December, with an average maximum UV index of 4, are months with the lowest UV index. A UV Index estimate of 3 to 5 represents a medium health hazard from unsafe exposure to the UV radiation for average individuals.
Note: In December, the average maximum UV index of 4 translate into the following recommendations:
Take precautions. Light skin individuals may get burned in less than 30 minutes. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. 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 Half Moon Bay?

With an average high-temperature of 55.6°F (13.1°C) and an average low-temperature of 49.3°F (9.6°C), December is the coldest month.

What is the temperature in December in Half Moon Bay?

The average high-temperature, in December, in Half Moon Bay, California, is 55.6°F (13.1°C), while the average low-temperature is 49.3°F (9.6°C).

What are the least humid months in Half Moon Bay?

November and December, with an average relative humidity of 72%, are the least humid months.

What is the average humidity in December in Half Moon Bay?

In Half Moon Bay, the average relative humidity in December is 72%.

How much does it rain in Half Moon Bay in December?

In Half Moon Bay, California, in December, during 8.4 rainfall days, 1.5" (38mm) of precipitation is typically accumulated.

What is the month with the shortest days in Half Moon Bay?

The month with the shortest days is December, with an average of 9.6h of daylight.

What is the average length of the day in December in Half Moon Bay?

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

What is the month with the least sunshine in Half Moon Bay?

With an average of 5.7h of sunshine, December has the least sunshine of the year.

How long on average sun shines in December in Half Moon Bay?

In December, the average sunshine is 5.7h.

What is the month with the lowest UV index in Half Moon Bay?

January through May, July, October through December, with an average maximum UV index of 4, are months with the lowest UV index in Half Moon Bay, California.

How high is the UV index in December in Half Moon Bay?

In December, the average daily maximum UV index is 4. A UV Index estimate of 3 to 5 represents a moderate vulnerability from unprotected exposure to the UV radiation.

Average temperature in December
Half Moon Bay, CA

Average temperature in December - Half Moon Bay, CA
  • Average high temperature in December: 55.6°F

The warmest month (with the highest average high temperature) is September (66.9°F).
The month with the lowest average high temperature is December (55.6°F).

  • Average low temperature in December: 49.3°F

The month with the highest average low temperature is September (56.7°F).
The coldest month (with the lowest average low temperature) is February (48.7°F).

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Average pressure in December
Half Moon Bay, CA

Average pressure in December - Half Moon Bay, CA
  • Average pressure in December: 30.1"

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
Half Moon Bay, CA

Average wind speed in December - Half Moon Bay, CA
  • Average wind speed in December: 8.4mph

The windiest month (with the highest average wind speed) is April (9.6mph).
The calmest month (with the lowest average wind speed) is August (6.6mph).

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Average humidity in December
Half Moon Bay, CA

Average humidity in December - Half Moon Bay, CA
  • Average humidity in December: 72%

The month with the highest relative humidity is August (82%).
Months with the lowest relative humidity are November and December (72%).

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Average rainfall in December
Half Moon Bay, CA

Average rainfall in December - Half Moon Bay, CA
  • Average rainfall in December: 1.5"

The wettest month (with the highest rainfall) is February (1.61").
The driest months (with the least rainfall) are June and July (0.12").

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Average rainfall days in December
Half Moon Bay, CA

Average rainfall days in December - Half Moon Bay, CA
  • Average rainfall days in December: 8.4 days

The month with the highest number of rainy days is March (10.8 days).
The month with the least rainy days is June (3 days).

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Average daylight in December /
Average sunshine in December
Half Moon Bay, CA

Average daylight in December / Average sunshine in December - Half Moon Bay, 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: 5.7h

The month with the most sunshine is July (Average sunshine: 11.4h).
The month with the least sunshine is December (Average sunshine: 5.7h).

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Average sunshine days in December
Half Moon Bay, CA

Average sunshine days in December - Half Moon Bay, CA
  • Average sunshine days in December: 21.1 days

The month with the most sunshine days is October (24.6 days).
Months with the least sunshine days are March and August (18.8 days).

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Average UV index in December
Half Moon Bay, CA

Average UV index in December - Half Moon Bay, CA
  • Average UV index in December: 4

Months with the highest UV index are June, August and September (UV index 5).
Months with the lowest UV index are January, February, March, April, May, July, October, November and December (UV index 4).

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Average cloud cover in December
Half Moon Bay, CA

Average cloud cover in December - Half Moon Bay, CA
  • Average cloud cover in December: 36

The month with the most cloud cover is March (Cloud cover 38).
The month with the least cloud cover is September (Cloud cover 18).

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Average visibility in December
Half Moon Bay, CA

Average visibility in December - Half Moon Bay, 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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