September weather forecast
Boulder, MT

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Weather in September

September, the first month of the autumn in Boulder, is also an enjoyable month, with temperature in the range of an average high of 67.5°F (19.7°C) and an average low of 42.4°F (5.8°C).

Temperature

Start of September brings a shift in the average high-temperature, falling from August's warm 77.5°F (25.3°C) to a refreshing 67.5°F (19.7°C). Despite high daytime temperatures, the average temperature in Boulder, Montana, lowers to an icy 42.4°F (5.8°C) during September nights.

Humidity

The average relative humidity in September is 52%.

Rainfall

In Boulder, Montana, during September, the rain falls for 9.8 days and regularly aggregates up to 1.14" (29mm) of precipitation. Throughout the year, in Boulder, Montana, there are 133.7 rainfall days, and 16.38" (416mm) of precipitation is accumulated.

Snowfall

Months with snowfall in Boulder are January through June, September through December. September is the first month it typically snows. Throughout September, in the average 1.2 snowfall days, it receives 2.01" (51mm) of snow. Throughout the year, in Boulder, Montana, there are 105.8 snowfall days, and 55.12" (1400mm) of snow is accumulated.

Daylight

In Boulder, the average length of the day in September is 12h and 32min.
On the first day of the month, sunrise is at 6:50 am and sunset at 8:06 pm. On the last day of September, in Boulder, sunrise is at 7:26 am and sunset at 7:09 pm MDT.

Sunshine

In September, the average sunshine is 9.8h.

UV index

In Boulder, the average daily maximum UV index in September is 3. A UV Index estimate of 3 to 5 represents a medium vulnerability from exposure to the Sun's UV rays for the average person.
Note: In September, a daily maximum UV index of 3 leads to the following instructions:
Put precautions into practice - Protective measures against sun-induced damage are advised. During midday, the Sun's radiation is strongest, and it's advisable to reduce direct exposure. Always opt for UVA and UVB-resistant sunglasses on radiant days. Take heed! Reflection from the snow can almost amplify the Sun's UV radiation by double.
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Frequently asked questions

What is the average September temperature in Boulder?

The high-temperature, in September, in Boulder, is 67.5°F (19.7°C), while the low-temperature averages to 42.4°F (5.8°C).

What is the average humidity in September in Boulder?

The average relative humidity in September in Boulder is 52%.

How much does it rain in Boulder in September?

In Boulder, Montana, during September, the rain falls for 9.8 days and regularly aggregates up to 1.14" (29mm) of precipitation.

When does it start to snow in Boulder?

September is the first month it typically snows. Throughout September, in the average 1.2 snowfall days, it receives 2.01" (51mm) of snow.

How many hours of daylight does Boulder have in September?

The average day length in September in Boulder, Montana, is 12h and 32min.

When are sunrise and sunset in September in Boulder?

On the first day of September, sunrise is at 6:50 am and sunset at 8:06 pm. On the last day of the month, sunrise is at 7:26 am and sunset at 7:09 pm MDT.

How long on average sun shines in September in Boulder?

In September, the average sunshine duration in Boulder, Montana, is 9.8h.

How high is the UV index in September in Boulder?

In September, the average daily maximum UV index in Boulder is 3. A UV Index estimate of 3 to 5 represents a moderate health threat from unsafe 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 September
Boulder, MT

Average temperature in September - Boulder, MT
  • Average high temperature in September: 67.5°F

The warmest month (with the highest average high temperature) is July (79.7°F).
The month with the lowest average high temperature is December (27°F).

  • Average low temperature in September: 42.4°F

The month with the highest average low temperature is August (48.6°F).
The coldest month (with the lowest average low temperature) is December (12.6°F).

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Average pressure in September
Boulder, MT

Average pressure in September - Boulder, MT
  • Average pressure in September: 29.98"Hg

The month with the highest atmospheric pressure is January (30.19"Hg).
The month with the lowest atmospheric pressure is June (29.91"Hg).

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Average wind speed in September
Boulder, MT

Average wind speed in September - Boulder, MT
  • Average wind speed in September: 5.4mph

The windiest months (with the highest average wind speed) are January and November (6.5mph).
The calmest month (with the lowest average wind speed) is August (4.7mph).

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Average humidity in September
Boulder, MT

Average humidity in September - Boulder, MT
  • Average humidity in September: 52%

The month with the highest relative humidity is January (86%).
The month with the lowest relative humidity is August (46%).

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Average rainfall in September
Boulder, MT

Average rainfall in September - Boulder, MT
  • Average rainfall in September: 1.14"

The wettest month (with the highest rainfall) is June (2.68").
The driest month (with the least rainfall) is December (0.79").

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Average rainfall days in September
Boulder, MT

Average rainfall days in September - Boulder, MT
  • Average rainfall days in September: 9.8 days

The month with the highest number of rainy days is May (18.2 days).
The month with the least rainy days is November (7.5 days).

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Average snowfall in September
Boulder, MT

Average snowfall in September - Boulder, MT
  • Average snowfall in September: 2.01"

The month with the highest snowfall is February (9.72").
The months with the least snowfall are July and August (0").

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Average snowfall days in September
Boulder, MT

Average snowfall days in September - Boulder, MT
  • Average snowfall days in September: 1.2 days

The month with the highest number of snowfall days is February (18 days).
The months with the least snowfall days are July and August (0 days).

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Average daylight in September /
Average sunshine in September
Boulder, MT

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

The month with the longest days is June (Average daylight: 15h and 42min).
The month with the shortest days is December (Average daylight: 8h and 42min).

  • Average sunshine in September: 9h and 5min

The month with the most sunshine is July (Average sunshine: 11h and 42min).
The months with the least sunshine are January and December (Average sunshine: 5h and 36min).

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Average sunshine days in September
Boulder, MT

Average sunshine days in September - Boulder, MT
  • Average sunshine days in September: 17.9 days

The month with the most sunshine days is September (17.9 days).
The month with the least sunshine days is February (8.5 days).

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Average UV index in September
Boulder, MT

Average UV index in September - Boulder, MT
  • Average UV index in September: 3

The month with the highest UV index is July (UV index 6).
The month with the lowest UV index is February (UV index 1).

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Average cloud cover in September
Boulder, MT

Average cloud cover in September - Boulder, MT
  • Average cloud cover in September: 22

The month with the most cloud cover is February (Cloud cover 48).
The month with the least cloud cover is August (Cloud cover 15).

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Average visibility in September
Boulder, MT

Average visibility in September - Boulder, MT
  • Average visibility in September: 6mi

The months with the highest visibility are April, May, June, July, August, September, October and November (6mi).
The months with the lowest visibility are January, February, March and December (5mi).

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Boulder, Montana, USA

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