In August, O'Fallon typically sees daytime highs of 30.9°C and overnight lows around 18.2°C. Compared to the annual average high of 18.9°C, August runs +12.1°C.
August in O'Fallon averages a daytime high of 30.9°C and an overnight low of 18.2°C.
August runs +12.1°C compared to O'Fallon's annual average high of 18.9°C, ranking #2 of 12 months by warmth.
Plan for daytime highs near 30.9°C and cooler evenings around 18.2°C.