In September, Great Falls typically sees daytime highs of 21.8°C and overnight lows around 5.3°C. Compared to the annual average high of 13.8°C, September runs +8.1°C.
September in Great Falls averages a daytime high of 21.8°C and an overnight low of 5.3°C.
September runs +8.1°C compared to Great Falls's annual average high of 13.8°C, ranking #4 of 12 months by warmth.
Plan for daytime highs near 21.8°C and cooler evenings around 5.3°C.