In September, Walnut Creek typically sees daytime highs of 26.4°C and overnight lows around 12.1°C. Compared to the annual average high of 20.0°C, September runs +6.5°C.
September in Walnut Creek averages a daytime high of 26.4°C and an overnight low of 12.1°C.
September runs +6.5°C compared to Walnut Creek's annual average high of 20.0°C, ranking #2 of 12 months by warmth.
Plan for daytime highs near 26.4°C and cooler evenings around 12.1°C.