In January, O'Fallon typically sees daytime highs of 3.5°C and overnight lows around -7.1°C. Compared to the annual average high of 18.9°C, January runs -15.3°C.
January in O'Fallon averages a daytime high of 3.5°C and an overnight low of -7.1°C.
January runs -15.3°C compared to O'Fallon's annual average high of 18.9°C, ranking #12 of 12 months by warmth.
Plan for daytime highs near 3.5°C and cooler evenings around -7.1°C.