In September, Naperville typically sees daytime highs of 23.9°C and overnight lows around 11.6°C. Compared to the annual average high of 14.7°C, September runs +9.2°C.
September in Naperville averages a daytime high of 23.9°C and an overnight low of 11.6°C.
September runs +9.2°C compared to Naperville's annual average high of 14.7°C, ranking #4 of 12 months by warmth.
Plan for daytime highs near 23.9°C and cooler evenings around 11.6°C.