In September, Janesville typically sees daytime highs of 23.2°C and overnight lows around 10.5°C. Compared to the annual average high of 13.9°C, September runs +9.3°C.
September in Janesville averages a daytime high of 23.2°C and an overnight low of 10.5°C.
September runs +9.3°C compared to Janesville's annual average high of 13.9°C, ranking #4 of 12 months by warmth.
Plan for daytime highs near 23.2°C and cooler evenings around 10.5°C.