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September Weather in Janesville, United States

Last updated: June 24, 2025

In September, the average temperature in Janesville, United States is a comfortable 18°C (65°F). However, temperatures can range from a cool 3°C (37°F) to a warm 33°C (92°F). Expect about 137 mm (5.4 in) of precipitation spread over 9 days, and with an average humidity of 75%, you might want to pack an umbrella along with your sunglasses!

September Temperature in Janesville

In September in Janesville, the average temperature is 18°C (65°F), with maximums that can reach 33°C (92°F) and minimums that can drop to as low as 3°C (37°F). Overall, travelers should be prepared for a range of temperatures, ensuring they pack both warm clothing for the cooler evenings and lighter attire for the hotter days.

September Weather in Janesville: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Janesville, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Janesville, September typically has an average temperature of 18°C (65°F), with highs reaching up to 33°C (92°F) and lows dropping to around 3°C (37°F).
JanFebMarAprMayJunJulAugSepOctNovDec171634446072747165493425
Data source: Temperature data for Janesville generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Janesville

In Janesville in September, the total precipitation amount is 137 mm (5.4 in) over the course of 9 days.

September Precipitation Trends in Janesville

The chart displays monthly precipitation patterns in Janesville, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Janesville, September typically receives around 137 mm (5.4 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec34416891140118103119137933644
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Janesville

In Janesville in September, humidity is 75%. With an average temperature of 18°C (65°F), this humidity feels like a warm, enveloping blanket that can make outdoor exploration feel a bit stifling, potentially leading to discomfort during travel activities.

September Average Humidity in Janesville

This chart illustrates the average monthly humidity levels in Janesville, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Janesville is approximately 75%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec82%84%80%81%74%81%80%77%75%80%87%83%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Janesville

In Janesville in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Janesville.

Maximum UV Index Levels in Janesville for September

The chart shows the monthly maximum UV Index (UVI) for Janesville in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Janesville typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec35589101098533
Data source: Janesville September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How September Weather in Janesville Compares to Other Months

Weather in Janesville varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Janesville, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Janesville, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-8°C (17°F)34 mm (1.3 inches)82%moderate
February Weather-9°C (17°F)41 mm (1.6 inches)84%moderate
March Weather1°C (34°F)68 mm (2.7 inches)80%moderate
April Weather7°C (45°F)91 mm (3.6 inches)81%very high
May Weather15°C (60°F)140 mm (5.5 inches)74%very high
June Weather22°C (72°F)118 mm (4.7 inches)80%very high
July Weather23°C (74°F)103 mm (4.1 inches)80%very high
August Weather21°C (71°F)119 mm (4.7 inches)77%very high
September Weather18°C (65°F)137 mm (5.4 inches)75%very high
October Weather9°C (49°F)93 mm (3.7 inches)80%moderate
November Weather1°C (35°F)36 mm (1.4 inches)87%moderate
December Weather-4°C (25°F)44 mm (1.7 inches)83%moderate

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