December weather forecast and climate
Roy, MT

The first month of the winter, December, is still a freezing cold month in Roy, Montana, with average temperature varying between 29.1°F (-1.6°C) and 16°F (-8.9°C).

Temperature

The coldest months are February and December, with an average high-temperature of 29.1°F (-1.6°C).

Humidity

The average relative humidity in Roy is 77%.

Rainfall

The month with the least rainfall in Roy is December when the rain falls for 6 days and typically collects 0.71" (18mm) of precipitation.

Snowfall

January through June, September through December are months with snowfall. In Roy, during 13.5 snowfall days, 4.88" (124mm) of snow is typically accumulated. Throughout the year, there are 83.4 snowfall days, and 45.51" (1156mm) of snow is accumulated.

Daylight

The month with the shortest days is December, with an average of 8.5h of daylight.

Sunshine

In December, the average sunshine in Roy, Montana, is 5.6h.

UV index

Months with the lowest UV index in Roy, Montana, are January through April, October through December, with an average maximum UV index of 2. A UV Index estimate of 2, and below, represents a minimal health vulnerability from unsafe exposure to the UV radiation for the average person.
Note: The daily maximum UV index of 2 in December interpret into the following advice:
Extended sun exposure is not an issue for the majority. Children, infants, and fair-skinned individuals always need to be protected. 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. Beware! The strength of the UV rays is increased nearly double-fold by the reflection of the snow.

What is the coldest month in Roy?

February and December, with an average high-temperature of 29.1°F (-1.6°C), are the coldest months in Roy.

What is the temperature in December in Roy?

In December, in Roy, the average high-temperature is 29.1°F (-1.6°C), and the average low-temperature is 16°F (-8.9°C).

What is the average humidity in December in Roy?

In Roy, Montana, the average relative humidity in December is 77%.

How much does it rain in Roy in December?

In Roy, Montana, in December, during 6 rainfall days, 0.71" (18mm) of precipitation is typically accumulated.

What is the driest month in Roy?

December is the month with the least rainfall in Roy. Rain falls for 6 days and accumulates 0.71" (18mm) of precipitation.

How many days does it snow in December in Roy?

In Roy, Montana, during December, snow falls for 13.5 days and regularly aggregates up to 4.88" (124mm) of snow.

What is the month with the shortest days in Roy?

With an average of 8.5h of daylight, December has the shortest days of the year in Roy, Montana.

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

In December, the average length of the day is 8.5h.

How many hours of sunshine does Roy have in December?

In Roy, Montana, the average sunshine in December is 5.6h.

What are the months with the lowest UV index in Roy?

Months with the lowest UV index in Roy, Montana, are January through April, October through December, with an average maximum UV index of 2.

What is the UV index intensity in December in Roy?

In December, the average daily maximum UV index in Roy, Montana, is 2. A UV Index value of 2, and less, symbolizes a low health threat from the exposure to the Sun's UV radiation.
Average temperature in December - Roy, MT
  • Average high temperature in December: -1.6°C

The warmest month (with the highest average high temperature) is July (26°C).
Months with the lowest average high temperature are February and December (-1.6°C).

  • Average low temperature in December: -8.9°C

The month with the highest average low temperature is August (12.5°C).
The coldest month (with the lowest average low temperature) is February (-9.3°C).

Average pressure in December - Roy, MT
  • Average pressure in December: 1020mbar

The month with the highest atmospheric pressure is January (1020.3mbar).
The month with the lowest atmospheric pressure is June (1010.9mbar).

Average wind speed in December - Roy, MT
  • Average wind speed in December: 15.3km/h

The windiest months (with the highest average wind speed) are January, April and October (15.9km/h).
The calmest month (with the lowest average wind speed) is August (11.9km/h).

Average humidity in December - Roy, MT
  • Average humidity in December: 77%

The month with the highest relative humidity is February (79%).
The month with the lowest relative humidity is August (47%).

Average rainfall in December - Roy, MT
  • Average rainfall in December: 18mm

The wettest month (with the highest rainfall) is May (86mm).
The driest month (with the least rainfall) is December (18mm).

Average rainfall days in December - Roy, MT
  • Average rainfall days in December: 6 days

The month with the highest number of rainy days is May (19.3 days).
The month with the least rainy days is January (5.4 days).

Average snowfall in December - Roy, MT
  • Average snowfall in December: 124mm

The month with the highest snowfall is April (232mm).
Months with the least snowfall are July and August (0mm).

Average snowfall days in December - Roy, MT
  • Average snowfall days in December: 13.5 days

The month with the highest number of snowfall days is February (15.2 days).
Months with the least snowfall days are July and August (0 days).

Average daylight in December / Average sunshine in December - Roy, MT
  • Average daylight in December: 8.5h

The month with the longest days is June (Average daylight: 15.9h).
The month with the shortest days is December (Average daylight: 8.5h).

  • Average sunshine in December: 5.6h

The month with the most sunshine is July (Average sunshine: 11.8h).
The month with the least sunshine is February (Average sunshine: 5.5h).

Average sunshine days in December - Roy, MT
  • Average sunshine days in December: 16 days

The month with the most sunshine days is September (19.3 days).
The month with the least sunshine days is April (8.3 days).

Average UV index in December - Roy, MT
  • Average UV index in December: 2

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

Average cloud cover in December - Roy, MT
  • Average cloud cover in December: 41

The month with the most cloud cover is February (Cloud cover 45).
The month with the least cloud cover is July (Cloud cover 16).

Average visibility in December - Roy, MT
  • Average visibility in December: 9km

Months with the highest visibility are June, July, August and September (10km).
Months with the lowest visibility are January, February, March, April, May, October, November and December (9km).