O'Fallon Weather Forecast

    • 68
    • 86

    Mostly Sunny

    • 64
    • 85

    Mostly Sunny

    • 64
    • 82

    Partly Sunny

    • 66
    • 80

    Partly Sunny

    • 68
    • 84

    Partly Sunny

    • 66
    • 86

    Slight Chance Thunderstorms

Today 21 Aug St. Charles

Sunny. Highs in the mid 80s. East Winds around 5 Mph, becoming west around 5 Mph this afternoon.

Tonight 21 Aug St. Charles

Mostly clear in the Evening, then becoming partly cloudy. Lows in the upper 60s. Southwest Winds around 5 Mph.

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O'Fallon Temperature Statistics

August Temperature

St. Louis, Spirit Of St. Louis Airport (10.6 miles)

  • Lowest 3 August, 2026

    62.7 °F

  • Average August

    79.5 °F

  • Highest 11 August, 2026

    95.6 °F

Climate (2021–2026)

St. Louis, Spirit Of St. Louis Airport (10.6 miles)

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  • Average Low 2021–2026

    46.1 °F

  • Average 2021–2026

    57.5 °F

  • Average High 2021–2026

    68.9 °F
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