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
Average temperature in September - Helena, MT
  • Average high temperature in September: 22.6°C

The warmest month (with the highest average high temperature) is July (29.8°C).
The month with the lowest average high temperature is December (-0.2°C).

  • Average low temperature in September: 6.2°C

The month with the highest average low temperature is July (12.4°C).
The coldest month (with the lowest average low temperature) is December (-11.2°C).

Average humidity in September - Helena, MT
  • Average humidity in September: 54.5%

The month with the highest relative humidity is December (68.1%).
The month with the lowest relative humidity is July (46.4%).

Average rainfall in September - Helena, MT
  • Average rainfall in September: 27.9mm

The wettest month (with the highest rainfall) is June (52.3mm).
The driest month (with the lowest rainfall) is February (7.6mm).

Average rainfall days in September - Helena, MT
  • Average rainfall days in September: 6.1 days

The month with the highest number of rainy days is June (11.2 days).
The month with the lowest number of rainy days is February (5.9 days).

Average snowfall in September - Helena, MT
  • Average snowfall in September: 33mm

The month with the highest snowfall is December (185.4mm).
Months with the lowest snowfall are June and July (0mm).

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 December (6 days).
The month with the lowest number of snowfall days is July (0 days).

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 shortest days is December (Average daylight: 8.6h).

  • Average sunshine in September: 8.5h

The month with most sunshine is July (Average sunshine: 11.9h).
The month with least sunshine is December (Average sunshine: 3.2h).

Average UV index in September - Helena, MT
  • Average UV index in September: 5

The month with the highest UV index is July (UV index 9).
Months with the lowest UV index are January, November and December (UV index 1).

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