O'Fallon Weather Forecast

    • 63
    • 92

    Sunny

    • 63
    • 93

    Mostly Sunny

    • 66
    • 94

    Chance Thunderstorms

    • 64
    • 87

    Chance Thunderstorms

    • 65
    • 88

    Chance Rain Showers

    • 67
    • 88

    Chance Thunderstorms

    • 65
    • 83

    Chance Thunderstorms

Today 16 Sep St. Clair

Sunny. Near steady temperature in the lower 90s. Northeast Winds around 5 Mph.

Tonight 16 Sep St. Clair

Clear. Lows in the lower 60s. Northeast Winds around 5 Mph.

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O'Fallon Temperature Statistics

September Temperature

Belleville, Scott AFB/MidAmerica Airport (4.3 miles)

  • Lowest 8 September, 2025

    44.6 °F

  • Average September

    70.5 °F

  • Highest 14 September, 2025

    98.6 °F

Climate (2020–Present)

Belleville, Scott AFB/MidAmerica Airport (4.3 miles)

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  • Average Low 2020–2025

    47.3 °F

  • Average 2020–2025

    57.2 °F

  • Average High 2020–2025

    67.4 °F
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