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September Weather in Great Falls, United States

Last updated: June 24, 2025

In September, the average temperature in Great Falls, United States is a delightful 24°C (76°F). However, you might experience a range from a cool 10°C (51°F) to a warm 36°C (96°F). Be prepared for some rain, as the area sees an average precipitation of 102 mm (4.0 in) over approximately 8 days. With an average humidity of 75%, the atmosphere can feel quite tropical!

September Temperature in Great Falls

In September in Great Falls, the average temperature is 24°C (76°F), with maximums reaching up to 36°C (96°F) and minimums dropping as low as 10°C (51°F). This makes it an ideal destination for travelers seeking warm weather while still enjoying cooler evenings.

September Weather in Great Falls: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Great Falls, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Great Falls, September typically has an average temperature of 24°C (76°F), with highs reaching up to 36°C (96°F) and lows dropping to around 10°C (51°F).
JanFebMarAprMayJunJulAugSepOctNovDec475256647277817976675449
Data source: Temperature data for Great Falls 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 Great Falls

In Great Falls in September, the precipitation amount is 102 mm (4.0 in) over the course of 8 days.

September Precipitation Trends in Great Falls

The chart displays monthly precipitation patterns in Great Falls, 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 Great Falls, September typically receives around 102 mm (4.0 inches) of precipitation spread over approximately 8 days.
JanFebMarAprMayJunJulAugSepOctNovDec89124831011121011241291027785131
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Great Falls

In Great Falls in September, humidity is 75%. With an average temperature of 24°C (76°F), this humidity feels like a warm embrace, making travel somewhat stifling but also richly invigorating, as the air seems to wrap around you, heightening the experience of the local sights and sounds.

September Average Humidity in Great Falls

This chart illustrates the average monthly humidity levels in Great Falls, 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 Great Falls is approximately 75%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec86%85%84%82%83%82%80%74%75%79%87%87%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Great Falls

In Great Falls 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 Great Falls.

Maximum UV Index Levels in Great Falls for September

The chart shows the monthly maximum UV Index (UVI) for Great Falls 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 Great Falls typically reaches 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec47810101111109864
Data source: Great Falls 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 Great Falls Compares to Other Months

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

This table compares monthly weather conditions in Great Falls, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather8°C (47°F)89 mm (3.5 inches)86%moderate
February Weather11°C (52°F)124 mm (4.9 inches)85%high
March Weather13°C (56°F)83 mm (3.3 inches)84%very high
April Weather18°C (64°F)101 mm (4.0 inches)82%very high
May Weather22°C (72°F)112 mm (4.4 inches)83%very high
June Weather25°C (78°F)101 mm (4.0 inches)82%extreme
July Weather27°C (81°F)124 mm (4.9 inches)80%extreme
August Weather26°C (80°F)129 mm (5.1 inches)74%very high
September Weather24°C (76°F)102 mm (4.0 inches)75%very high
October Weather20°C (68°F)77 mm (3.0 inches)79%very high
November Weather12°C (54°F)85 mm (3.3 inches)87%high
December Weather10°C (50°F)131 mm (5.1 inches)87%moderate

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