Diamond Bar Weather Forecast

    • 58
    • 78

    Mostly Cloudy

    • 60
    • 82

    Mostly Sunny

    • 66
    • 90

    Sunny

    • 66
    • 90

    Mostly Sunny

    • 67
    • 90

    Mostly Sunny

    • 65
    • 90

    Partly Sunny

    • 62
    • 84

    Mostly Sunny

Today 21 Sep Los Angeles County San Gabriel Valley

Sunny. Highs in the lower to mid 80s.

Tonight 21 Sep Los Angeles County San Gabriel Valley

Partly cloudy in the evening then mostly cloudy. Lows in the mid 50s to mid 60s.

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  • Temperature Forecast NOAA

  • Temperature Real-Time

Diamond Bar Temperature Statistics

September Temperature

Brackett Field Airport (4.3 miles)

  • Lowest 2 September, 2026

    60.8 °F

  • Average September

    78.5 °F

  • Highest 9 September, 2026

    105.8 °F

Climate (2021–2026)

Brackett Field Airport (4.3 miles)

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  • Average Low 2021–2026

    56.1 °F

  • Average 2021–2026

    68.1 °F

  • Average High 2021–2026

    76 °F
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