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September Weather in Helena, United States

Last updated: June 24, 2025

In Helena, United States, the average temperature in September hovers around 13°C (55°F). However, be prepared for a range of conditions, as temperatures can drop to a brisk -5°C (23°F) or soar to a sizzling 33°C (91°F). During this month, expect about 44 mm (1.7 in) of precipitation spread over 6 days, with an average humidity of 68% that lends a unique charm to the atmosphere.

September Temperature in Helena

In September in Helena, the average temperature is 13°C (55°F), with maximums reaching up to 33°C (91°F) and minimums dropping as low as -5°C (23°F). Travelers should be prepared for a wide range of temperatures during this time.

September Weather in Helena: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Helena, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Helena, September typically has an average temperature of 13°C (55°F), with highs reaching up to 33°C (91°F) and lows dropping to around -5°C (23°F).
JanFebMarAprMayJunJulAugSepOctNovDec191629364858666555393021
Data source: Temperature data for Helena generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Helena

In Helena in September, the total precipitation amount is 44 mm (1.7 in) spread over 6 days.

September Precipitation Trends in Helena

The chart displays monthly precipitation patterns in Helena, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Helena, September typically receives around 44 mm (1.7 inches) of precipitation spread over approximately 6 days.
JanFebMarAprMayJunJulAugSepOctNovDec2351386788107313444413333
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Helena

In Helena in September humidity is 68%. With an average temperature of 13°C (55°F), this humidity feels like a cool, damp embrace, making outdoor exploration refreshing yet slightly chilly, and travelers should be prepared for a sweater to enjoy their adventures comfortably.

September Average Humidity in Helena

This chart illustrates the average monthly humidity levels in Helena, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Helena is approximately 68%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec87%88%83%78%76%78%77%71%68%72%84%91%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Helena

In Helena in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Helena.

Maximum UV Index Levels in Helena for September

The chart shows the monthly maximum UV Index (UVI) for Helena in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Helena typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec34689111098532
Data source: Helena September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How September Weather in Helena Compares to Other Months

Weather in Helena varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Helena, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Helena, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-7°C (20°F)23 mm (0.9 inches)87%moderate
February Weather-9°C (16°F)51 mm (2.0 inches)88%moderate
March Weather-2°C (29°F)38 mm (1.5 inches)83%high
April Weather2°C (36°F)67 mm (2.7 inches)78%very high
May Weather9°C (48°F)88 mm (3.5 inches)76%very high
June Weather14°C (58°F)107 mm (4.2 inches)78%extreme
July Weather19°C (67°F)31 mm (1.2 inches)77%very high
August Weather18°C (65°F)34 mm (1.3 inches)71%very high
September Weather13°C (55°F)44 mm (1.7 inches)68%very high
October Weather4°C (40°F)41 mm (1.6 inches)72%moderate
November Weather-1°C (30°F)33 mm (1.3 inches)84%moderate
December Weather-6°C (21°F)33 mm (1.3 inches)90%low

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