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September Weather in Boise City, United States

Last updated: June 24, 2025

In Boise City, United States, the average temperature in September hovers around 22°C (71°F), but be prepared for a range that can dip to a chilly 1°C (34°F) and soar to a scorching 40°C (104°F). Expect a modest precipitation of 32 mm (1.3 in) spread over 5 days, accompanied by a high average humidity of 80%. Whether you enjoy the warmth or prefer cooler days, this month offers a diverse climate experience!

September Temperature in Boise City

In September in Boise City, the average temperature is 22°C (71°F), with maximums reaching up to 40°C (104°F) and minimums dropping as low as 1°C (34°F). Be prepared for a wide range of temperatures to ensure a comfortable travel experience.

September Weather in Boise City: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Boise City, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Boise City, September typically has an average temperature of 22°C (71°F), with highs reaching up to 40°C (104°F) and lows dropping to around 1°C (34°F).
JanFebMarAprMayJunJulAugSepOctNovDec363748556475797671564739
Data source: Temperature data for Boise City 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 Boise City

In Boise City in September, the precipitation amount is 32 mm (1.3 in) over the course of 5 days.

September Precipitation Trends in Boise City

The chart displays monthly precipitation patterns in Boise City, 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 Boise City, September typically receives around 32 mm (1.3 inches) of precipitation spread over approximately 5 days.
JanFebMarAprMayJunJulAugSepOctNovDec16113641603744553234715
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Boise City

In Boise City in September, humidity is 80%. With an average temperature of 22°C (71°F), this humidity feels like a warm, enveloping blanket, making travel slightly uncomfortable as skin becomes clammy and sweat clings to clothes.

September Average Humidity in Boise City

This chart illustrates the average monthly humidity levels in Boise City, 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 Boise City is approximately 80%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec73%76%64%61%71%75%75%80%80%78%76%78%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Boise City

In Boise City 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 Boise City.

Maximum UV Index Levels in Boise City for September

The chart shows the monthly maximum UV Index (UVI) for Boise City 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 Boise City typically reaches 10, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec468101112121110753
Data source: Boise City 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 Boise City Compares to Other Months

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

This table compares monthly weather conditions in Boise City, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather2°C (36°F)16 mm (0.6 inches)73%moderate
February Weather3°C (37°F)11 mm (0.4 inches)76%high
March Weather9°C (49°F)36 mm (1.4 inches)64%very high
April Weather13°C (55°F)41 mm (1.6 inches)61%very high
May Weather18°C (64°F)60 mm (2.4 inches)71%extreme
June Weather24°C (76°F)37 mm (1.5 inches)75%extreme
July Weather26°C (79°F)44 mm (1.7 inches)75%extreme
August Weather25°C (77°F)55 mm (2.2 inches)80%extreme
September Weather22°C (71°F)32 mm (1.3 inches)80%very high
October Weather13°C (56°F)34 mm (1.3 inches)78%high
November Weather8°C (47°F)7 mm (0.3 inches)76%moderate
December Weather4°C (39°F)15 mm (0.6 inches)78%moderate

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