In September, Napa typically sees daytime highs of 28.6°C and overnight lows around 11.0°C. Compared to the annual average high of 21.5°C, September runs +7.0°C.
September in Napa averages a daytime high of 28.6°C and an overnight low of 11.0°C.
September runs +7.0°C compared to Napa's annual average high of 21.5°C, ranking #3 of 12 months by warmth.
Plan for daytime highs near 28.6°C and cooler evenings around 11.0°C.