December weather forecast
Johnstown, CA

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Weather in December

December, the first month of the winter in Johnstown, is also an enjoyable month, with an average temperature fluctuating between 63.7°F (17.6°C) and 46.6°F (8.1°C).

Temperature

With average high and low temperatures of 63.7°F (17.6°C) and 46.6°F (8.1°C) respectively, December is Johnstown's coldest month.

Humidity

In Johnstown, the average relative humidity in December is 58%.

Rainfall

In December, the rain falls for 5.1 days. Throughout December, 0.71" (18mm) of precipitation is accumulated. In Johnstown, during the entire year, the rain falls for 49.6 days and collects up to 5.16" (131mm) of precipitation.

Daylight

With an average of 10h and 0min of daylight, December has the shortest days of the year.
On the first day of December, sunrise is at 6:32 am and sunset at 4:41 pm. On the last day of the month, sunrise is at 6:50 am and sunset at 4:51 pm PST.

Sunshine

The month with the least sunshine is December, with an average of 6.7h of sunshine.

UV index

With an average maximum UV index of 3, December is the month with the lowest UV index. A UV Index estimate of 3 to 5 represents a moderate threat to health from exposure to the Sun's UV rays for ordinary individuals.
Note: The maximum UV index of 3 during December translates into these guidelines:
Undertake precautions - Guarding against sun damage is counselled. Being exposed to the midday Sun can have harmful effects due to strong UV radiation; always take precautions. Loose clothes with a tight weave are optimal for safeguarding yourself against the Sun's rays.
Updated: Jul 18, 2024
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate

Frequently asked questions

What is the coldest month?

December, with an average high of 63.7°F (17.6°C) and a low of 46.6°F (8.1°C), signifies the coldest month of the year.

What is the average December temperature?

December temperatures vary between a high-temperature of 63.7°F (17.6°C) and a low-temperature of 46.6°F (8.1°C). In September, the average heat index (a.k.a. 'felt air temperature', 'apparent temperature'), which combines relative humidity and air temperature, is computed to be 86°F (30°C).

What is the average humidity in December?

In Johnstown, the average relative humidity in December is 58%.

How much does it rain in December?

In Johnstown, in December, during 5.1 rainfall days, 0.71" (18mm) of precipitation is typically accumulated.

What is the month with the shortest days?

The month with the shortest days in Johnstown is December, with an average of 10h and 0min of daylight.

What is the average length of the day in December?

The average day length in December is 10h and 2min.

What time are sunrise and sunset in December?

On the first day of December, sunrise is at 6:32 am and sunset at 4:41 pm. On the last day of the month, sunrise is at 6:50 am and sunset at 4:51 pm PST.

What is the month with the least sunshine?

With an average of 6.7h of sunshine, December has the least sunshine of the year.

How many hours of sunshine does Johnstown have in December?

In Johnstown, the average sunshine duration in December is 6.7h.

When is the lowest UV index?

December is the month with the lowest UV index, with an average maximum UV index of 3.

How high is the UV index in December?

In Johnstown, the average daily maximum UV index in December is 3. A UV Index of 3 to 5 symbolizes a moderate vulnerability from exposure to the Sun's UV radiation.
Average humidity
Average rainfall days
Average daylight
Average sunshine
Average sunshine days
Average UV index
Average cloud cover
Average visibility

Average temperature in December
Johnstown, CA

Average temperature in December - Johnstown, CA
  • Average high temperature in December: 63.7°F

The warmest month (with the highest average high temperature) is August (85.5°F).
The month with the lowest average high temperature is December (63.7°F).

  • Average low temperature in December: 46.6°F

The month with the highest average low temperature is August (64.9°F).
The coldest month (with the lowest average low temperature) is February (46°F).

Average pressure in December
Johnstown, CA

Average pressure in December - Johnstown, CA
  • Average pressure in December: 30.06"Hg

The month with the highest atmospheric pressure is January (30.09"Hg).
The month with the lowest atmospheric pressure is June (29.86"Hg).

Average wind speed in December
Johnstown, CA

Average wind speed in December - Johnstown, CA
  • Average wind speed in December: 4.8mph

The windiest months (with the highest average wind speed) are April and May (5.3mph).
The calmest months (with the lowest average wind speed) are August, September and October (4.2mph).

Average humidity in December
Johnstown, CA

Average humidity in December - Johnstown, CA
  • Average humidity in December: 58%

The month with the highest relative humidity is May (65%).
The month with the lowest relative humidity is November (52%).

Average rainfall in December
Johnstown, CA

Average rainfall in December - Johnstown, CA
  • Average rainfall in December: 0.71"

The wettest month (with the highest rainfall) is February (1.06").
The driest month (with the least rainfall) is June (0.04").

Average rainfall days in December
Johnstown, CA

Average rainfall days in December - Johnstown, CA
  • Average rainfall days in December: 5.1 days

The month with the highest number of rainy days is March (6.8 days).
The month with the least rainy days is June (1.4 days).

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

Average daylight in December / Average sunshine in December - Johnstown, CA
  • Average daylight in December: 10h and 0min

The month with the longest days is June (Average daylight: 14h and 18min).
The month with the shortest days is December (Average daylight: 10h and 0min).

  • Average sunshine in December: 6h and 4min

The months with the most sunshine are June and July (Average sunshine: 12h and 6min).
The month with the least sunshine is December (Average sunshine: 6h and 42min).

Average sunshine days in December
Johnstown, CA

Average sunshine days in December - Johnstown, CA
  • Average sunshine days in December: 25.2 days

The month with the most sunshine days is June (28 days).
The month with the least sunshine days is July (20.7 days).

Average UV index in December
Johnstown, CA

Average UV index in December - Johnstown, CA
  • Average UV index in December: 3

The months with the highest UV index are June, July, August and September (UV index 6).
The month with the lowest UV index is December (UV index 3).

Average cloud cover in December
Johnstown, CA

Average cloud cover in December - Johnstown, CA
  • Average cloud cover in December: 23

The months with the most cloud cover are March and December (Cloud cover 23).
The month with the least cloud cover is August (Cloud cover 6).

Average visibility in December
Johnstown, CA

Average visibility in December - Johnstown, 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).

Johnstown, California, USA

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