Flat Lake Weather Forecast

    • 48
    • 66

    Rain Showers Likely

    • 47
    • 62

    Rain Showers

    • 47
    • 68

    Partly Sunny

    • 45
    • 71

    Mostly Sunny

    • 42
    • 63

    Mostly Sunny

    • 42
    • 63

    Mostly Cloudy

Today 27 Sep McHenry

Sunny. Highs in the mid 60s. Northwest Winds around 10 Mph.

Tonight 27 Sep McHenry

Mostly cloudy. Showers after midnight. Lows in the upper 40s. East Winds around 10 Mph.

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  • Temperature Forecast NOAA

  • Temperature Real-Time

Flat Lake Temperature Statistics

September Temperature

Harvey Municipal Airport (22.4 miles)

  • Lowest 13 September, 2026

    35.6 °F

  • Average September

    60.9 °F

  • Highest 4 September, 2026

    84.2 °F

Climate (2021–2026)

Harvey Municipal Airport (22.4 miles)

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  • Average Low 2021–2026

    30.4 °F

  • Average 2021–2026

    41.2 °F

  • Average High 2021–2026

    51.8 °F
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