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September Weather in Waterloo, United States

Last updated: June 24, 2025

In September, the average temperature in Waterloo, United States is a pleasant 18°C (65°F). However, temperatures can vary significantly, ranging from a cool 2°C (35°F) to a warm 33°C (92°F). Expect an average of 102 mm (4.0 in) of precipitation over 9 days, contributing to a typically high humidity of 79%. Enjoy the unique climate of this captivating destination!

September Temperature in Waterloo

In September in Waterloo, the average temperature is 18°C (65°F). The maximum can reach 33°C (92°F), while the minimum can drop as low as 2°C (35°F). This diverse climate makes Waterloo a great destination for travelers seeking both warmth and cool, refreshing conditions.

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

The chart illustrates September temperature patterns in Waterloo, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Waterloo, 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 2°C (35°F).
JanFebMarAprMayJunJulAugSepOctNovDec212235465970747165513629
Data source: Temperature data for Waterloo 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 Waterloo

In Waterloo in September, the total precipitation amount is 102 mm (4.0 in) over a span of 9 days.

September Precipitation Trends in Waterloo

The chart displays monthly precipitation patterns in Waterloo, 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 Waterloo, September typically receives around 102 mm (4.0 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec515157101125114102961021154346
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Waterloo

In Waterloo in September, humidity is 79%. With an average temperature of 18°C (65°F), this humidity feels like walking through a warm mist, making traveling slightly uncomfortable and sticky, but offering a refreshing escape when you find moments of shade or a breeze.

September Average Humidity in Waterloo

This chart illustrates the average monthly humidity levels in Waterloo, 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 Waterloo is approximately 79%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%85%85%85%78%80%78%76%79%83%88%82%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Waterloo

In Waterloo 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 Waterloo.

Maximum UV Index Levels in Waterloo for September

The chart shows the monthly maximum UV Index (UVI) for Waterloo 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 Waterloo typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec34589101098532
Data source: Waterloo 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 Waterloo Compares to Other Months

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

This table compares monthly weather conditions in Waterloo, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-6°C (22°F)51 mm (2.0 inches)85%moderate
February Weather-5°C (22°F)51 mm (2.0 inches)85%moderate
March Weather2°C (36°F)57 mm (2.3 inches)85%moderate
April Weather8°C (46°F)100 mm (4.0 inches)85%very high
May Weather15°C (59°F)125 mm (4.9 inches)78%very high
June Weather21°C (70°F)114 mm (4.5 inches)80%very high
July Weather23°C (75°F)102 mm (4.0 inches)78%very high
August Weather22°C (71°F)96 mm (3.8 inches)76%very high
September Weather18°C (65°F)102 mm (4.0 inches)79%very high
October Weather11°C (51°F)115 mm (4.5 inches)83%moderate
November Weather2°C (37°F)43 mm (1.7 inches)88%moderate
December Weather-2°C (29°F)46 mm (1.8 inches)81%low

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