O'Fallon Weather Forecast

    • 77
    • 96

    Chance Thunderstorms

    • 77
    • 97

    Hot

    • 73
    • 97

    Hot

    • 69
    • 88

    Slight Chance Thunderstorms

    • 72
    • 89

    Partly Sunny

    • 72
    • 94

    Slight Chance Thunderstorms

Today 14 Aug St. Clair

Partly sunny with a chance of Showers and Thunderstorms this Morning, then sunny this afternoon. Hot with Highs in the mid 90s. South Winds around 5 Mph. Chance of rain 30 percent. Heat index Values up to 113 this afternoon.

Tonight 14 Aug St. Clair

Mostly clear in the Evening, then becoming partly cloudy. Humid with Lows in the upper 70s. Southeast Winds around 5 Mph. Heat index Values up to 113 early in the evening.

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O'Fallon Temperature Statistics

August Temperature

Belleville, Scott AFB/MidAmerica Airport (4.3 miles)

  • Lowest 3 August, 2026

    64.8 °F

  • Average August

    78.4 °F

  • Highest 11 August, 2026

    95.7 °F

Climate (2021–2026)

Belleville, Scott AFB/MidAmerica Airport (4.3 miles)

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  • Average Low 2021–2026

    47.9 °F

  • Average 2021–2026

    57.9 °F

  • Average High 2021–2026

    68.1 °F
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