Brentwood Weather Forecast

    • 68
    • 94

    Mostly Sunny

    • 69
    • 95

    Mostly Sunny

    • 67
    • 92

    Mostly Cloudy

    • 66
    • 85

    Chance Rain Showers

    • 66
    • 86

    Slight Chance Thunderstorms

    • 66
    • 88

    Slight Chance Thunderstorms

    • 67
    • 90

    Mostly Sunny

Today 15 Sep San Bernardino and Riverside County Valleys-The Inland Empire

Mostly sunny. Warmer. Highs 92 to 98. Areas of Winds east to 10 Mph becoming southwest with Gusts to 25 Mph this afternoon.

Tonight 15 Sep San Bernardino and Riverside County Valleys-The Inland Empire

Mostly clear. Lows 64 to 69. Areas of Winds west to 10 Mph this evening becoming light.

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Brentwood Temperature Statistics

September Temperature

Ontario International Airport (8.1 miles)

  • Lowest 12 September, 2025

    62.1 °F

  • Average September

    77.4 °F

  • Highest 2 September, 2025

    102 °F

Climate (2020–Present)

Ontario International Airport (8.1 miles)

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  • Average Low 2020–2025

    55.5 °F

  • Average 2020–2025

    66.7 °F

  • Average High 2020–2025

    79.1 °F
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