December weather forecast and climate
Grass Valley, CA

Weather in December

December, the first month of the winter, in Grass Valley, is still a cool month, with average temperature fluctuating between 37.2°F (2.9°C) and 51.3°F (10.7°C).

Temperature

With an average high-temperature of 51.3°F (10.7°C) and an average low-temperature of 37.2°F (2.9°C), December is the coldest month.

Humidity

In Grass Valley, the average relative humidity in December is 68%.

Rainfall

In Grass Valley, California, during 10.7 rainfall days, 5.35" (136mm) of precipitation is typically accumulated. Throughout the year, there are 82 rainfall days, and 33.11" (841mm) of precipitation is accumulated.

Snowfall

Months with snowfall in Grass Valley are January through May, November and December. In Grass Valley, during December, snow falls for 0.5 days and regularly aggregates up to 0.71" (18mm) of snow. Throughout the year, in Grass Valley, there are 6.8 snowfall days, and 14.41" (366mm) of snow is accumulated.

Daylight

December has the shortest days of the year in Grass Valley, with an average of 9.5h of daylight.

Sunshine

In December, the average sunshine in Grass Valley is 5.8h.

UV index

In Grass Valley, the average daily maximum UV index is 3. A UV Index of 3 to 5 symbolizes a medium vulnerability from unprotected exposure to the Sun's UV rays for ordinary individuals.
Note: The average daily UV index of 3 in December transform into the following instructions:
Take precautions - Protection against sun damage is advised. The Sun's most intense and consequently most harmful UV radiation during midday hours should be decreased by minimizing exposure and seeking shade. 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. Beware! The strength of the UV rays is increased nearly double-fold by the reflection of the snow.
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FAQ

What is the coldest month in Grass Valley?

With an average high-temperature of 51.3°F (10.7°C) and an average low-temperature of 37.2°F (2.9°C), December is the coldest month in Grass Valley, California.

What is the temperature in December in Grass Valley?

In Grass Valley, in December, the average high-temperature is 51.3°F (10.7°C), and the average low-temperature is 37.2°F (2.9°C).

What is the average humidity in December in Grass Valley?

In Grass Valley, California, the average relative humidity in December is 68%.

How many days does it rain in December in Grass Valley?

In Grass Valley, California, in December, it is raining for 10.7 days, with typically 5.35" (136mm) of accumulated precipitation.

How many days does it snow in December in Grass Valley?

In Grass Valley, in December, during 0.5 snowfall days, 0.71" (18mm) of snow is typically accumulated.

What is the month with the shortest days in Grass Valley?

The month with the shortest days is December, with an average of 9.5h of daylight.

What is the average length of the day in December in Grass Valley?

In Grass Valley, the average length of the day in December is 9.5h.

How long on average sun shines in December in Grass Valley?

In December, the average sunshine in Grass Valley is 5.8h.

What is the UV index reading in December in Grass Valley?

In December, the average daily maximum UV index in Grass Valley is 3. A UV Index estimate of 3 to 5 represents a moderate vulnerability from the exposure to the Sun's UV radiation.

Average temperature in December
Grass Valley, CA

Average temperature in December - Grass Valley, CA
  • Average high temperature in December: 51.3°F

The warmest month (with the highest average high temperature) is July (90.1°F).
The month with the lowest average high temperature is December (51.3°F).

  • Average low temperature in December: 37.2°F

The month with the highest average low temperature is July (60.1°F).
The coldest month (with the lowest average low temperature) is December (37.2°F).

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Average pressure in December
Grass Valley, CA

Average pressure in December - Grass Valley, CA
  • Average pressure in December: 30.14"

The month with the highest atmospheric pressure is January (30.17").
The month with the lowest atmospheric pressure is June (29.9").

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Average wind speed in December
Grass Valley, CA

Average wind speed in December - Grass Valley, CA
  • Average wind speed in December: 5.3mph

The windiest month (with the highest average wind speed) is February (6mph).
The calmest month (with the lowest average wind speed) is August (4.8mph).

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Average humidity in December
Grass Valley, CA

Average humidity in December - Grass Valley, CA
  • Average humidity in December: 68%

The month with the highest relative humidity is March (75%).
The month with the lowest relative humidity is July (37%).

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Average rainfall in December
Grass Valley, CA

Average rainfall in December - Grass Valley, CA
  • Average rainfall in December: 5.35"

The wettest month (with the highest rainfall) is March (6.57").
The driest months (with the least rainfall) are July and August (0.04").

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Average rainfall days in December
Grass Valley, CA

Average rainfall days in December - Grass Valley, CA
  • Average rainfall days in December: 10.7 days

The month with the highest number of rainy days is March (15.1 days).
The month with the least rainy days is July (1.1 days).

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Average snowfall in December
Grass Valley, CA

Average snowfall in December - Grass Valley, CA
  • Average snowfall in December: 0.71"

The month with the highest snowfall is February (6.42").
Months with the least snowfall are June, July, August, September and October (0").

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Average snowfall days in December
Grass Valley, CA

Average snowfall days in December - Grass Valley, CA
  • Average snowfall days in December: 0.5 days

The month with the highest number of snowfall days is March (2.4 days).
Months with the least snowfall days are June, July, August, September and October (0 days).

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Average daylight in December /
Average sunshine in December
Grass Valley, CA

Average daylight in December / Average sunshine in December - Grass Valley, CA
  • Average daylight in December: 9.5h

The month with the longest days is June (Average daylight: 14.9h).
The month with the shortest days is December (Average daylight: 9.5h).

  • Average sunshine in December: 5.8h

The month with the most sunshine is July (Average sunshine: 12.2h).
The month with the least sunshine is January (Average sunshine: 5.7h).

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Average sunshine days in December
Grass Valley, CA

Average sunshine days in December - Grass Valley, CA
  • Average sunshine days in December: 19.1 days

The month with the most sunshine days is July (29.8 days).
The month with the least sunshine days is March (14.8 days).

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Average UV index in December
Grass Valley, CA

Average UV index in December - Grass Valley, CA
  • Average UV index in December: 3

The month with the highest UV index is July (UV index 7).
The month with the lowest UV index is November (UV index 2).

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Average cloud cover in December
Grass Valley, CA

Average cloud cover in December - Grass Valley, CA
  • Average cloud cover in December: 35

The month with the most cloud cover is March (Cloud cover 41).
The month with the least cloud cover is July (Cloud cover 4).

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Average visibility in December
Grass Valley, CA

Average visibility in December - Grass Valley, 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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