Alta Loma Weather Forecast

    • 68
    • 90

    Mostly Sunny

    • 68
    • 92

    Increasing Clouds

    • 63
    • 85

    Partly Sunny

    • 60
    • 79

    Mostly Sunny

    • 64
    • 85

    Sunny

    • 65
    • 89

    Mostly Sunny

    • 65
    • 90

    Mostly Sunny

Today 25 Sep San Bernardino and Riverside County Valleys-The Inland Empire

Partly cloudy in the morning. Becoming mostly sunny. Highs 87 to 92.

Tonight 25 Sep San Bernardino and Riverside County Valleys-The Inland Empire

Mostly clear this evening. Becoming partly cloudy. Lows 64 to 68. Areas of Winds west to 10 Mph this evening becoming light.

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Alta Loma Temperature Statistics

September Temperature

Ontario International Airport (4.3 miles)

  • Lowest 19 September, 2026

    61.6 °F

  • Average September

    78.8 °F

  • Highest 9 September, 2026

    109.7 °F

Climate (2021–2026)

Ontario International Airport (4.3 miles)

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  • Average Low 2021–2026

    55.8 °F

  • Average 2021–2026

    67.2 °F

  • Average High 2021–2026

    79.3 °F
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