September Weather in Boise, United States

Last updated: June 24, 2025

The average temperature in Boise, United States during September is a comfortable 20°C (68°F). However, temperatures can vary significantly, with a minimum of 3°C (38°F) and a maximum soaring to 38°C (101°F). Expect a modest precipitation of 10 mm (0.4 in) spread over approximately 2 days, and enjoy an average humidity level of around 48%.

September Temperature in Boise

In September in Boise, the average temperature is 20°C (68°F). Maximum can reach 38°C (101°F) and minimum can be as low as 3°C (38°F). This varied climate makes Boise a great destination for travelers seeking both warm days and cooler nights.

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

The chart illustrates September temperature patterns in Boise, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Boise, September typically has an average temperature of 20°C (68°F), with highs reaching up to 38°C (101°F) and lows dropping to around 3°C (38°F).

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

September Precipitation in Boise

In Boise in September, the precipitation amount is 10 mm (0.4 in) over a period of 2 days.

September Precipitation Trends in Boise

The chart displays monthly precipitation patterns in Boise, 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, September typically receives around 10 mm (0.4 inches) of precipitation spread over approximately 2 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 Boise

In Boise in September humidity is 48%. With an average temperature of 20°C (68°F), this humidity feels like a pleasant and refreshing environment for traveling, creating an ideal atmosphere for exploring and enjoying outdoor activities.

September Average Humidity in Boise

This chart illustrates the average monthly humidity levels in Boise, 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 is approximately 48%, 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 Boise

In Boise 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 Boise.

Maximum UV Index Levels in Boise for September

The chart shows the monthly maximum UV Index (UVI) for Boise 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 typically reaches 8, which falls under the very high exposure category.

Data source: Boise 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 Compares to Other Months

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

This table compares monthly weather conditions in Boise, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	1°C (33°F)	49 mm (1.9 inches)	88%	moderate
February Weather	2°C (36°F)	50 mm (2.0 inches)	89%	moderate
March Weather	8°C (46°F)	38 mm (1.5 inches)	85%	high
April Weather	11°C (52°F)	36 mm (1.4 inches)	79%	very high
May Weather	16°C (61°F)	39 mm (1.5 inches)	71%	very high
June Weather	21°C (71°F)	21 mm (0.8 inches)	71%	extreme
July Weather	27°C (81°F)	1 mm (0.0 inches)	66%	extreme
August Weather	26°C (78°F)	8 mm (0.3 inches)	50%	very high
September Weather	20°C (68°F)	10 mm (0.4 inches)	48%	very high
October Weather	11°C (53°F)	22 mm (0.9 inches)	65%	high
November Weather	6°C (43°F)	32 mm (1.3 inches)	84%	moderate
December Weather	1°C (34°F)	40 mm (1.6 inches)	87%	low