September weather forecast
Big Sky, MT

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Vast fields and planted forests near the scenic mountainous region in Big Sky, Montana
Vast fields and planted forests near the scenic mountainous region in Big Sky, Montana

Weather in September

September ushers in autumn in Big Sky, adorned by the fall colors painting the Montana landscape. A clear drop in temperatures signifies the departure of summer. Still, it optimizes the comfortable condition between summer's heat and winter's chill. The landscape transforms into a canvas of colors, with green giving way to hues of yellow, orange, and red. September's weather forms a picturesque ambiance for outdoor adventures, making it a prime choice for those looking for a stunning nature expedition.

Temperature

September brings a decrease in the average high-temperature, shifting from a pleasant 72.7°F (22.6°C) in August to a comfortable 63.5°F (17.5°C). During the nights in September, Big Sky records a pronounced shift from the daytime warmth, with a consistent average temperature of 39.6°F (4.2°C).

Humidity

The average relative humidity in September in Big Sky is 57%.

Rainfall

In Big Sky, in September, it is raining for 11.1 days, with typically 1.81" (46mm) of accumulated precipitation. In Big Sky, during the entire year, the rain falls for 116.1 days and collects up to 23.5" (597mm) of precipitation.

Snowfall

Months with snowfall in Big Sky are January through December. In Big Sky, during September, snow falls for 3.6 days and regularly aggregates up to 5.04" (128mm) of snow. In Big Sky, during the entire year, snow falls for 151.6 days and aggregates up to 124.06" (3151mm) of snow.

Daylight

The average length of the day in September in Big Sky is 12h and 31min.
On the first day of September in Big Sky, sunrise is at 6:47 am and sunset at 8:01 pm. On the last day of the month, sunrise is at 7:23 am and sunset at 7:06 pm MDT.

Sunshine

In Big Sky, the average sunshine in September is 9.8h.

UV index

In September, the average daily maximum UV index is 3. A UV Index of 3 to 5 symbolizes a moderate health risk from unsafe exposure to UV radiation for average individuals.
Note: The UV index of 3 during September leads to these advisories:
Undertake protective steps - Obligation to safeguard skin and eyes from harm is in place. Solar radiation is at its peak intensity during midday, so it's advisable to stay indoors or in the shade. Sunglasses that ward off UVA and UVB rays play a pivotal role in reducing solar eye damage. Caution! The reflection of snow can nearly double the intensity of the Sun's UV radiation.
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Frequently asked questions

What is the temperature in September in Big Sky?

September temperatures vary between a high-temperature of 63.5°F (17.5°C) and a low-temperature of 39.6°F (4.2°C).

What is the average humidity in September in Big Sky?

The average relative humidity in September in Big Sky, Montana, is 57%.

How much does it rain in Big Sky in September?

In Big Sky, during September, the rain falls for 11.1 days and regularly aggregates up to 1.81" (46mm) of precipitation.

How many days does it snow in September in Big Sky?

In Big Sky, Montana, in September, snow falls for 3.6 days, with typically accumulated 5.04" (128mm) of snow.

What is the average length of the day in September in Big Sky?

The average day length in September in Big Sky is 12h and 31min.

What time are sunrise and sunset in September in Big Sky?

In September, on the first day of the month, sunrise is at 6:47 am and sunset at 8:01 pm. On the last day of the month, in Big Sky, sunrise is at 7:23 am and sunset at 7:06 pm MDT.

How many hours of sunshine does Big Sky have in September?

The average sunshine duration in September in Big Sky, Montana, is 9.8h.

What is the UV index reading in September in Big Sky?

In Big Sky, Montana, the average daily maximum UV index in September is 3. A UV Index estimate of 3 to 5 represents a moderate health threat from exposure to the Sun's UV radiation.
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 September
Big Sky, MT

Average temperature in September - Big Sky, MT
  • Average high temperature in September: 63.5°F

The warmest month (with the highest average high temperature) is July (74.8°F).
The month with the lowest average high temperature is December (22.5°F).

  • Average low temperature in September: 39.6°F

The month with the highest average low temperature is August (45.1°F).
The coldest month (with the lowest average low temperature) is December (7.9°F).

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Average pressure in September
Big Sky, MT

Average pressure in September - Big Sky, MT
  • Average pressure in September: 29.99"Hg

The month with the highest atmospheric pressure is January (30.22"Hg).
The month with the lowest atmospheric pressure is June (29.91"Hg).

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Average wind speed in September
Big Sky, MT

Average wind speed in September - Big Sky, MT
  • Average wind speed in September: 5.2mph

The windiest month (with the highest average wind speed) is January (7.1mph).
The calmest month (with the lowest average wind speed) is August (4.8mph).

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Average humidity in September
Big Sky, MT

Average humidity in September - Big Sky, MT
  • Average humidity in September: 57%

The months with the highest relative humidity are January and February (90%).
The month with the lowest relative humidity is August (51%).

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Average rainfall in September
Big Sky, MT

Average rainfall in September - Big Sky, MT
  • Average rainfall in September: 1.81"

The wettest months (with the highest rainfall) are April and May (2.91").
The driest month (with the least rainfall) is July (1.18").

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Average rainfall days in September
Big Sky, MT

Average rainfall days in September - Big Sky, MT
  • Average rainfall days in September: 11.1 days

The month with the highest number of rainy days is June (16.6 days).
The month with the least rainy days is February (4.3 days).

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Average snowfall in September
Big Sky, MT

Average snowfall in September - Big Sky, MT
  • Average snowfall in September: 5.04"

The month with the highest snowfall is April (19.88").
The month with the least snowfall is August (0.08").

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Average snowfall days in September
Big Sky, MT

Average snowfall days in September - Big Sky, MT
  • Average snowfall days in September: 3.6 days

The month with the highest number of snowfall days is March (21 days).
The month with the least snowfall days is August (0.3 days).

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Average daylight in September /
Average sunshine in September
Big Sky, MT

Average daylight in September / Average sunshine in September - Big Sky, MT
  • Average daylight in September: 12h and 3min

The month with the longest days is June (Average daylight: 15h and 36min).
The month with the shortest days is December (Average daylight: 8h and 48min).

  • Average sunshine in September: 9h and 5min

The month with the most sunshine is July (Average sunshine: 11h and 42min).
The month with the least sunshine is January (Average sunshine: 4h and 42min).

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Average sunshine days in September
Big Sky, MT

Average sunshine days in September - Big Sky, MT
  • Average sunshine days in September: 14.5 days

The month with the most sunshine days is September (14.5 days).
The month with the least sunshine days is May (5.7 days).

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Average UV index in September
Big Sky, MT

Average UV index in September - Big Sky, MT
  • Average UV index in September: 3

The month with the highest UV index is July (UV index 5).
The months with the lowest UV index are January and February (UV index 1).

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Average cloud cover in September
Big Sky, MT

Average cloud cover in September - Big Sky, MT
  • Average cloud cover in September: 23

The month with the most cloud cover is February (Cloud cover 60).
The month with the least cloud cover is July (Cloud cover 17).

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Average visibility in September
Big Sky, MT

Average visibility in September - Big Sky, MT
  • Average visibility in September: 6mi

The months with the highest visibility are June, July, August, September and October (6mi).
The months with the lowest visibility are January, February, March, April and December (4mi).

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Big Sky, Montana, USA

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