September Weather in Helena, United States

Last updated: June 24, 2025

In September, the average temperature in Helena, United States is a pleasant 25°C (77°F). You can expect temperatures to range from a minimum of 12°C (53°F) to a scorching maximum of 36°C (98°F). With an average humidity of 71% and approximately 92 mm (3.6 in) of precipitation spread over 7 days, it's a month that balances warmth with a touch of moisture.

September Temperature in Helena

In September in Helena, the average temperature is 25°C (77°F). Maximum temperatures can reach 36°C (98°F), while minimums can drop as low as 12°C (53°F). Be sure to pack accordingly to enjoy the warm days and cooler nights!

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 25°C (77°F), with highs reaching up to 36°C (98°F) and lows dropping to around 12°C (53°F).

Data source: Temperature data for Helena generated using information from the Copernicus Climate Change Service.

September Precipitation in Helena

In Helena in September, the precipitation amount is 92 mm (3.6 in) over the course of 7 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 92 mm (3.6 inches) of precipitation spread over approximately 7 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

September Humidity in Helena

In Helena in September humidity is 71%. With an average temperature of 25°C (77°F), this humidity feels like a warm embrace, making outdoor exploration a bit sticky but still enjoyable, especially if you take breaks in shaded areas and stay hydrated.

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 71%, offering insight into how humid the weather typically is during this month.

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 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For 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 9, which falls under the very high exposure category.

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.
	Temperature	Precipitation	Humidity	UV
January Weather	7°C (44°F)	107 mm (4.2 inches)	84%	moderate
February Weather	9°C (48°F)	185 mm (7.3 inches)	83%	high
March Weather	14°C (57°F)	172 mm (6.8 inches)	81%	very high
April Weather	17°C (62°F)	146 mm (5.7 inches)	81%	very high
May Weather	23°C (73°F)	138 mm (5.5 inches)	83%	extreme
June Weather	26°C (79°F)	133 mm (5.2 inches)	83%	extreme
July Weather	28°C (82°F)	124 mm (4.9 inches)	81%	extreme
August Weather	27°C (81°F)	114 mm (4.5 inches)	74%	very high
September Weather	25°C (77°F)	92 mm (3.6 inches)	71%	very high
October Weather	19°C (66°F)	111 mm (4.4 inches)	76%	high
November Weather	11°C (52°F)	82 mm (3.2 inches)	84%	high
December Weather	9°C (49°F)	144 mm (5.7 inches)	88%	moderate