O'Fallon Weather Forecast

    • 51
    • 70

    Rain Showers Likely

    • 50
    • 76

    Mostly Sunny

    • 49
    • 74

    Sunny

    • 54
    • 78

    Mostly Sunny

    • 58
    • 83

    Mostly Sunny

    • 62
    • 88

    Mostly Sunny

Today 5 Sep St. Charles

Mostly sunny in the Morning, then mostly cloudy with a chance of Showers in the afternoon. Highs in the lower 70s. Temperature falling into the upper 60s in the afternoon. Northwest Winds 10 to 15 Mph. Chance of rain 50 percent.

Tonight 5 Sep St. Charles

Mostly cloudy. A chance of Showers, mainly in the evening. Lows in the lower 50s. Northwest Winds 5 to 10 Mph. Chance of rain 50 percent.

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  • Temperature Forecast NOAA

  • Temperature Real-Time

O'Fallon Temperature Statistics

September Temperature

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

  • Lowest 1 September, 2025

    57 °F

  • Average September

    68.8 °F

  • Highest 1 September, 2025

    81 °F

Climate (2020–Present)

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

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  • Average Low 2020–2025

    45.8 °F

  • Average 2020–2025

    56.9 °F

  • Average High 2020–2025

    68.1 °F
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