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September Weather in Helena, United States

Last updated: June 24, 2025

In September, the average temperature in Helena, United States is a warm 26°C (80°F). Expect a comfortable minimum of 13°C (56°F) and the possibility of rising to a sizzling 38°C (101°F). During this month, 107 mm (4.2 in) of precipitation may fall over 11 days, and you can anticipate an average humidity level of 83%, making for a lush but steamy atmosphere.

September Temperature in Helena

In September in Helena, the average temperature is 26°C (80°F). Maximums can reach 38°C (101°F), and minimums can be as low as 13°C (56°F). Visitors should be prepared for warm weather, with the possibility of cooler evenings, making it an ideal time for both outdoor adventures and leisurely explorations.

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 26°C (80°F), with highs reaching up to 38°C (101°F) and lows dropping to around 13°C (56°F).
JanFebMarAprMayJunJulAugSepOctNovDec525761677580838279725854
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 precipitation amount is 107 mm (4.2 in) spread over a period of 11 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 107 mm (4.2 inches) of precipitation spread over approximately 11 days.
JanFebMarAprMayJunJulAugSepOctNovDec831077888721031181061078953126
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 83%. With an average temperature of 26°C (80°F), this humidity feels like a warm, enveloping blanket that can make traveling quite uncomfortable; you may find yourself needing frequent breaks for hydration and cool shade as the thick air clings to your skin.

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 83%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%82%80%76%73%74%80%79%83%77%84%88%
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 reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more detailed information, you can check 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 10, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec479101111111110864
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 Weather11°C (52°F)83 mm (3.2 inches)85%moderate
February Weather14°C (58°F)107 mm (4.2 inches)82%high
March Weather16°C (62°F)78 mm (3.1 inches)80%very high
April Weather20°C (67°F)88 mm (3.4 inches)76%very high
May Weather24°C (76°F)72 mm (2.8 inches)73%extreme
June Weather27°C (80°F)103 mm (4.1 inches)74%extreme
July Weather28°C (83°F)118 mm (4.6 inches)80%extreme
August Weather28°C (82°F)106 mm (4.2 inches)79%extreme
September Weather26°C (80°F)107 mm (4.2 inches)83%very high
October Weather22°C (72°F)89 mm (3.5 inches)77%very high
November Weather14°C (58°F)53 mm (2.1 inches)84%high
December Weather12°C (54°F)126 mm (4.9 inches)88%moderate

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