September weather forecast and climate
Helena, MT

The State Capital building of Montana in Helena city, set on a beautiful natural park
The State Capital building of Montana in Helena city, set on a beautiful natural park

Weather in September

The first month of the autumn, September, is still a pleasant month in Helena, Montana, with average temperature varying between 43.9°F (6.6°C) and 68.2°F (20.1°C).

Temperature

In September, the average high-temperature drops, from a warm 78.1°F (25.6°C) in August, to a pleasant 68.2°F (20.1°C). In Helena, the average low-temperature is 43.9°F (6.6°C).

Humidity

The average relative humidity in Helena is 51%.

Rainfall

In Helena, during 8.1 rainfall days, 0.94" (24mm) of precipitation is typically accumulated. In Helena, during the entire year, the rain falls for 123.7 days and collects up to 12.4" (315mm) of precipitation.

Snowfall

Months with snowfall are January through May, September through December. September is the first month it typically snows. Throughout September, in the average 0.7 snowfall days, it receives 1.77" (45mm) of snow. In Helena, during the entire year, snow falls for 80.4 days, and aggregates up to 34.88" (886mm) of snow.

Daylight

In September, the average length of the day is 12.5h.

Sunshine

In Helena, the average sunshine is 9.7h.

UV index

The average daily maximum UV index in Helena is 3. A UV Index reading of 3 to 5 represents a moderate health risk from the exposure to the Sun's UV rays for the ordinary person.
Note: The daily maximum UV index of 3 interpret into the following advice:
Take precautions - Protection against sunburn is recommended. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. A wide-brim hat offers excellent sun protection for eyes, ears, face, and neck. Sunglasses with UVA and UVB protection significantly reduce eye damage from sun exposure. Tightly woven, loose-fitting clothes provide additional protection from the Sun. Beware! The strength of the UV rays is increased nearly double-fold by the reflection of the snow.
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FAQ

What is the temperature in September in Helena?

In September, in Helena, Montana, the average high-temperature is 68.2°F (20.1°C), and the average low-temperature is 43.9°F (6.6°C).

What is the average humidity in September in Helena?

In September, the average relative humidity in Helena, Montana, is 51%.

How much does it rain in Helena in September?

In September, in Helena, Montana, the rain falls for 8.1 days. Throughout September, 0.94" (24mm) of precipitation is accumulated.

When does it start to snow in Helena?

September is the first month it typically snows in Helena, Montana. Throughout September, in the average 0.7 snowfall days, it receives 1.77" (45mm) of snow.

What is the average length of the day in September in Helena?

In September, the average length of the day is 12.5h.

How many hours of sunshine does Helena have in September?

In September, the average sunshine in Helena, Montana, is 9.7h.

What is the UV index reading in September in Helena?

In Helena, Montana, the average daily maximum UV index in September is 3. A UV Index of 3 to 5 symbolizes a moderate health threat from unsafe exposure to the Sun's UV rays.

Average temperature in September
Helena, MT

Average temperature in September - Helena, MT
  • Average high temperature in September: 68.2°F

The warmest month (with the highest average high temperature) is July (80.2°F).
The month with the lowest average high temperature is December (27.7°F).

  • Average low temperature in September: 43.9°F

The month with the highest average low temperature is July (50.4°F).
The coldest month (with the lowest average low temperature) is December (14.2°F).

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Average pressure in September
Helena, MT

Average pressure in September - Helena, MT
  • Average pressure in September: 29.98"

The month with the highest atmospheric pressure is January (30.18").
The month with the lowest atmospheric pressure is June (29.9").

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Average wind speed in September
Helena, MT

Average wind speed in September - Helena, MT
  • Average wind speed in September: 5.9mph

The windiest month (with the highest average wind speed) is November (7.1mph).
The calmest month (with the lowest average wind speed) is August (5mph).

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Average humidity in September
Helena, MT

Average humidity in September - Helena, MT
  • Average humidity in September: 51%

The month with the highest relative humidity is January (85%).
Months with the lowest relative humidity are July and August (46%).

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Average rainfall in September
Helena, MT

Average rainfall in September - Helena, MT
  • Average rainfall in September: 0.94"

The wettest month (with the highest rainfall) is June (2.01").
The driest months (with the least rainfall) are January and December (0.63").

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Average rainfall days in September
Helena, MT

Average rainfall days in September - Helena, MT
  • Average rainfall days in September: 8.1 days

The month with the highest number of rainy days is May (15.8 days).
The month with the least rainy days is November (7 days).

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Average snowfall in September
Helena, MT

Average snowfall in September - Helena, MT
  • Average snowfall in September: 1.77"

The month with the highest snowfall is February (6.18").
Months with the least snowfall are June, July and August (0").

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Average snowfall days in September
Helena, MT

Average snowfall days in September - Helena, MT
  • Average snowfall days in September: 0.7 days

The month with the highest number of snowfall days is February (16.2 days).
Months with the least snowfall days are July and August (0 days).

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

Average daylight in September / Average sunshine in September - Helena, MT
  • Average daylight in September: 12.5h

The month with the longest days is June (Average daylight: 15.8h).
The month with the shortest days is December (Average daylight: 8.6h).

  • Average sunshine in September: 9.7h

The month with the most sunshine is July (Average sunshine: 11.7h).
The month with the least sunshine is January (Average sunshine: 5.6h).

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Average sunshine days in September
Helena, MT

Average sunshine days in September - Helena, MT
  • Average sunshine days in September: 19.3 days

The month with the most sunshine days is July (20.5 days).
The month with the least sunshine days is April (9.8 days).

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Average UV index in September
Helena, MT

Average UV index in September - Helena, 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
Helena, MT

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

The month with the most cloud cover is February (Cloud cover 47).
Months with the least cloud cover are July and August (Cloud cover 15).

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Average visibility in September
Helena, MT

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

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

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