In September, Boise typically sees daytime highs of 24.6°C and overnight lows around 7.0°C. Compared to the annual average high of 15.8°C, September runs +8.7°C.
September in Boise averages a daytime high of 24.6°C and an overnight low of 7.0°C.
September runs +8.7°C compared to Boise's annual average high of 15.8°C, ranking #4 of 12 months by warmth.
Plan for daytime highs near 24.6°C and cooler evenings around 7.0°C.