Grand Lake Saint Marys State Park Weather Forecast

    • 61
    • 81

    Decreasing Clouds

    • 54
    • 75

    Mostly Sunny

    • 49
    • 69

    Mostly Sunny

    • 48
    • 69

    Mostly Sunny

    • 52
    • 71

    Mostly Sunny

    • 55
    • 75

    Partly Sunny

Today 23 Aug Mercer

Partly cloudy. Highs in the lower 80s. Light and variable Winds, becoming west 5 to 10 Mph this late morning and afternoon.

Tonight 23 Aug Mercer

Partly cloudy. Lows in the upper 50s. West Winds around 5 Mph.

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Grand Lake Saint Marys State Park Temperature Statistics

August Temperature

Versailles Darke County Airport (22.4 miles)

  • Lowest 3 August, 2025

    55.4 °F

  • Average August

    74.2 °F

  • Highest 8 August, 2025

    87.8 °F

Climate (2020–Present)

Versailles Darke County Airport (22.4 miles)

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  • Average Low 2020–2025

    43.4 °F

  • Average 2020–2025

    52.4 °F

  • Average High 2020–2025

    61.5 °F
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