Janesville Weather Forecast

    • 63
    • 81

    Chance Thunderstorms

    • 58
    • 75

    Rain Showers Likely

    • 61
    • 76

    Chance Rain Showers

    • 59
    • 78

    Chance Thunderstorms

    • 59
    • 79

    Slight Chance Thunderstorms

    • 57
    • 75

    Slight Chance Thunderstorms

    • 55
    • 75

    Mostly Sunny

Today 18 Sep Bremer

Partly sunny with a chance of Showers and Thunderstorms. Highs in the lower 80s. South Winds 5 to 10 Mph. Chance of rain 40 percent.

Tonight 18 Sep Bremer

A chance of Thunderstorms. A chance of Showers Early, then Showers likely. Patchy fog after midnight. Humid with Lows in the lower 60s. South Winds 5 to 10 Mph. Chance of rain 60 percent.

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Janesville Temperature Statistics

September Temperature

Waterloo, Waterloo Municipal Airport (6.8 miles)

  • Lowest 7 September, 2025

    39.9 °F

  • Average September

    66.3 °F

  • Highest 13 September, 2025

    93.9 °F

Climate (2020–Present)

Waterloo, Waterloo Municipal Airport (6.8 miles)

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  • Average Low 2020–2025

    40.1 °F

  • Average 2020–2025

    50.9 °F

  • Average High 2020–2025

    61.6 °F
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