St Helena Weather Forecast

    • 49
    • 74

    Mostly Sunny

    • 50
    • 77

    Mostly Sunny

    • 51
    • 76

    Mostly Sunny

    • 55
    • 84

    Mostly Sunny

    • 56
    • 85

    Partly Sunny

    • 59
    • 83

    Partly Sunny

Today 4 Sep North Bay Interior Valleys

Partly cloudy in the morning then becoming sunny. Patchy fog in the morning. Highs in the mid 60s to upper 70s. West Winds 5 to 10 Mph increasing to 10 to 20 Mph in the afternoon.

Tonight 4 Sep North Bay Interior Valleys

Mostly clear except patchy fog after midnight. Lows in the 40s to mid 50s. West Winds 10 to 20 Mph. Becoming 5 to 10 Mph after midnight.

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St Helena Temperature Statistics

September Temperature

Petaluma Municipal Airport (18 miles)

  • Lowest 1 September, 2026

    53.6 °F

  • Average September

    61.9 °F

  • Highest 1 September, 2026

    75.2 °F

Climate (2021–2026)

Petaluma Municipal Airport (18 miles)

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  • Average Low 2021–2026

    44.7 °F

  • Average 2021–2026

    55.2 °F

  • Average High 2021–2026

    68.5 °F
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