The highest day temperature in September 2026 was 91°F. The lowest night temperature was 48°F. The average values for day and night temperatures during September were 75.9°F и 59.1°F respectivly.

Most of the days in September are sunny but you can also expect cloudy and gloomy days.

Precipitation total in September for Boise is 0.3 in. It makes september one of the least rainy months of the year.

The average wind speed in September is 6.1 mph. This value is relatively stable throughout the year.

We are using day length and cloud cover information for each day of the month to calculate averages for this chart. Average sunny hours for Boise in September is 10.0 hours.