Downtown Fullerton Weather Forecast

    • 66
    • 87

    Decreasing Clouds

    • 64
    • 82

    Becoming Sunny

    • 66
    • 86

    Mostly Sunny

    • 68
    • 86

    Mostly Sunny

    • 70
    • 91

    Mostly Sunny

    • 73
    • 93

    Mostly Sunny

    • 73
    • 96

    Sunny

Today 27 Sep Orange County Inland

Mostly sunny. Highs 93 to 97.

Tonight 27 Sep Orange County Inland

Mostly cloudy this evening. Becoming partly cloudy. Lows 60 to 67. Light Winds.

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Downtown Fullerton Temperature Statistics

September Temperature

Fullerton, Fullerton Municipal Airport (3.1 miles)

  • Lowest 2 September, 2026

    63.6 °F

  • Average September

    77.4 °F

  • Highest 9 September, 2026

    108.6 °F

Climate (2021–2026)

Fullerton, Fullerton Municipal Airport (3.1 miles)

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  • Average Low 2021–2026

    57.1 °F

  • Average 2021–2026

    66.7 °F

  • Average High 2021–2026

    76.9 °F
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