O'Fallon Weather Forecast

    • 55
    • 74

    Chance Thunderstorms

    • 66
    • 81

    Chance Thunderstorms

    • 66
    • 84

    Chance Thunderstorms

    • 70
    • 89

    Mostly Sunny

    • 72
    • 90

    Chance Thunderstorms

    • 64
    • 87

    Rain Showers Likely

    • 60
    • 80

    Chance Thunderstorms

Today 14 May St. Clair

Sunny. Near steady temperature in the lower 70s. Southeast Winds 5 to 10 Mph.

Tonight 14 May St. Clair

Partly cloudy this Evening, then mostly cloudy with a chance of Showers and Thunderstorms after midnight. Lows in the mid 50s. Southeast Winds 5 to 10 Mph with Gusts up to 20 Mph. Chance of rain 50 percent.

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  • Temperature Forecast NOAA

  • Temperature Real-Time

O'Fallon Temperature Statistics

May Temperature

Belleville, Scott AFB/MidAmerica Airport (4.3 miles)

  • Lowest 7 May, 2026

    40.1 °F

  • Average May

    61 °F

  • Highest 12 May, 2026

    81.3 °F

Climate (2021–Present)

Belleville, Scott AFB/MidAmerica Airport (4.3 miles)

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  • Average Low 2021–2026

    47.8 °F

  • Average 2021–2026

    57.8 °F

  • Average High 2021–2026

    68.1 °F
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