December weather forecast
Keystone, SD

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Weather in December

December marks the commencement of the freezing winter season in Keystone, South Dakota. The average high temperature drops to a chilly 29.8°F (-1.2°C), making December one of the coldest months of the year. Snowfall sights become more frequent, blanketing the region with a white layer, while creating a picture-perfect winter wonderland. By the month's end, the city is fully entrenched in the winter climate, with cold temperatures and short hours of daylight being the principal characteristics. As the year wraps up, January brings slightly harsher temperatures, continuing the cycle of Keystone's annual weather pattern.

Temperature

December is the month when Keystone experiences its coldest temperatures, averaging a high of 29.8°F (-1.2°C) and a low of 16.5°F (-8.6°C).

Humidity

In Keystone, the average relative humidity in December is 74%.

Rainfall

In December, the rain falls for 6.3 days. Throughout December, 0.67" (17mm) of precipitation is accumulated. Throughout the year, there are 135.4 rainfall days, and 20.39" (518mm) of precipitation is accumulated.

Snowfall

January through May, September through December are months with snowfall. In Keystone, South Dakota, in December, during 11.5 snowfall days, 4.57" (116mm) of snow is typically accumulated. Throughout the year, there are 75.1 snowfall days, and 40.24" (1022mm) of snow is accumulated.

Daylight

The month with the shortest days in Keystone is December, with an average of 9h and 0min of daylight.
On the first day of the month, sunrise is at 7:08 am and sunset at 4:17 pm. On the last day of December, in Keystone, sunrise is at 7:27 am and sunset at 4:26 pm MST.

Sunshine

In December, the average sunshine in Keystone is 6.2h.

UV index

The months with the lowest UV index are January through March, October through December, with an average maximum UV index of 2. A UV Index reading of 2, and below, represents a low threat to health from unsafe exposure to UV radiation for ordinary individuals.
Note: A daily high UV index of 2 in December leads to these guidelines:
Most individuals can handle sun exposure for up to an hour without burning, but children must always be shielded from sun exposure. Being in direct Sun during midday can be harmful due to intense solar radiation; take precautions. Limit sun-induced ocular harm with sunglasses that feature UVA and UVB filtration. Take careful note! The UV radiation of the Sun can be nearly doubled by snow reflection.
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Frequently asked questions

What is the coldest month in Keystone?

Keystone experiences its lowest temperatures in December, with an average peak of 29.8°F (-1.2°C) and a low of 16.5°F (-8.6°C).

How cold is December in Keystone?

During December, Keystone experiences an average high-temperature of 29.8°F (-1.2°C) and a low-temperature of 16.5°F (-8.6°C). The average heat index (a.k.a. 'real feel', 'apparent temperature'), which takes the relative humidity and factors it into the air temperature reading, in July is evaluated at 82.4°F (28°C).

What is the average humidity in December in Keystone?

The average relative humidity in December is 74%.

How many days does it rain in December in Keystone?

In Keystone, during December, the rain falls for 6.3 days and regularly aggregates up to 0.67" (17mm) of precipitation.

How much does it snow in Keystone in December?

In Keystone, South Dakota, in December, during 11.5 snowfall days, 4.57" (116mm) of snow is typically accumulated.

What is the month with the shortest days in Keystone?

With an average of 9h and 0min of daylight, December has the shortest days of the year in Keystone, South Dakota.

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

The average day length in December in Keystone, South Dakota, is 8h and 58min.

When are sunrise and sunset in December in Keystone?

On the first day of December in Keystone, South Dakota, sunrise is at 7:08 am and sunset at 4:17 pm. On the last day of the month, sunrise is at 7:27 am and sunset at 4:26 pm MST.

How many hours of sunshine does Keystone have in December?

In Keystone, the average sunshine duration in December is 6.2h.

When is the lowest UV index in Keystone?

The months with the lowest UV index in Keystone are January through March, October through December, with an average maximum UV index of 2.

How high is the UV index in December in Keystone?

The average daily maximum UV index in December in Keystone, South Dakota, is 2. A UV Index reading of 2, and below, represents a low health risk from exposure to Sun's UV rays.
Average humidity
Average rainfall days
Average snowfall days
Average daylight
Average sunshine
Average sunshine days
Average UV index
Average cloud cover
Average visibility

Average temperature in December
Keystone, SD

Average temperature in December - Keystone, SD
  • Average high temperature in December: 29.8°F

The warmest month (with the highest average high temperature) is July (81.7°F).
The month with the lowest average high temperature is December (29.8°F).

  • Average low temperature in December: 16.5°F

The month with the highest average low temperature is July (60.4°F).
The coldest month (with the lowest average low temperature) is February (16.2°F).

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Average pressure in December
Keystone, SD

Average pressure in December - Keystone, SD
  • Average pressure in December: 30.12"Hg

The month with the highest atmospheric pressure is January (30.13"Hg).
The month with the lowest atmospheric pressure is June (29.84"Hg).

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Average wind speed in December
Keystone, SD

Average wind speed in December - Keystone, SD
  • Average wind speed in December: 8.9mph

The windiest month (with the highest average wind speed) is April (9.5mph).
The calmest month (with the lowest average wind speed) is August (7mph).

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Average humidity in December
Keystone, SD

Average humidity in December - Keystone, SD
  • Average humidity in December: 74%

The months with the highest relative humidity are January and February (77%).
The months with the lowest relative humidity are August and September (52%).

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Average rainfall in December
Keystone, SD

Average rainfall in December - Keystone, SD
  • Average rainfall in December: 0.67"

The wettest month (with the highest rainfall) is June (3.19").
The driest month (with the least rainfall) is January (0.47").

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Average rainfall days in December
Keystone, SD

Average rainfall days in December - Keystone, SD
  • Average rainfall days in December: 6.3 days

The month with the highest number of rainy days is May (18.6 days).
The month with the least rainy days is November (4.5 days).

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Average snowfall in December
Keystone, SD

Average snowfall in December - Keystone, SD
  • Average snowfall in December: 4.57"

The month with the highest snowfall is April (7.24").
The months with the least snowfall are June, July and August (0").

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Average snowfall days in December
Keystone, SD

Average snowfall days in December - Keystone, SD
  • Average snowfall days in December: 11.5 days

The month with the highest number of snowfall days is February (12.9 days).
The months with the least snowfall days are June, July and August (0 days).

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Average daylight in December /
Average sunshine in December
Keystone, SD

Average daylight in December / Average sunshine in December - Keystone, SD
  • Average daylight in December: 9h and 0min

The month with the longest days is June (Average daylight: 15h and 24min).
The month with the shortest days is December (Average daylight: 9h and 0min).

  • Average sunshine in December: 6h and 1min

The month with the most sunshine is August (Average sunshine: 11h and 42min).
The month with the least sunshine is February (Average sunshine: 6h and 0min).

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Average sunshine days in December
Keystone, SD

Average sunshine days in December - Keystone, SD
  • Average sunshine days in December: 18.1 days

The month with the most sunshine days is November (19.2 days).
The month with the least sunshine days is May (7.8 days).

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Average UV index in December
Keystone, SD

Average UV index in December - Keystone, SD
  • Average UV index in December: 2

The month with the highest UV index is July (UV index 6).
The months with the lowest UV index are January, February, March, October, November and December (UV index 2).

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Average cloud cover in December
Keystone, SD

Average cloud cover in December - Keystone, SD
  • Average cloud cover in December: 34

The month with the most cloud cover is April (Cloud cover 38).
The month with the least cloud cover is August (Cloud cover 17).

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Average visibility in December
Keystone, SD

Average visibility in December - Keystone, SD
  • 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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Keystone, South Dakota, USA

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