In May, O'Fallon typically sees daytime highs of 24.8°C and overnight lows around 12.0°C. Compared to the annual average high of 18.9°C, May runs +5.9°C.
May in O'Fallon averages a daytime high of 24.8°C and an overnight low of 12.0°C.
May runs +5.9°C compared to O'Fallon's annual average high of 18.9°C, ranking #5 of 12 months by warmth.
Plan for daytime highs near 24.8°C and cooler evenings around 12.0°C.