In September, Thornton typically sees daytime highs of 26.2°C and overnight lows around 8.4°C. Compared to the annual average high of 18.6°C, September runs +7.6°C.
September in Thornton averages a daytime high of 26.2°C and an overnight low of 8.4°C.
September runs +7.6°C compared to Thornton's annual average high of 18.6°C, ranking #4 of 12 months by warmth.
Plan for daytime highs near 26.2°C and cooler evenings around 8.4°C.