In July, O'Fallon typically sees daytime highs of 31.8°C and overnight lows around 19.2°C. Compared to the annual average high of 18.9°C, July runs +12.9°C.
July in O'Fallon averages a daytime high of 31.8°C and an overnight low of 19.2°C.
July runs +12.9°C compared to O'Fallon's annual average high of 18.9°C, ranking #1 of 12 months by warmth.
Plan for daytime highs near 31.8°C and cooler evenings around 19.2°C.