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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 21°C (70°F), offering a perfect balance for outdoor activities. Temperatures can vary widely, with a minimum of 5°C (41°F) and a maximum soaring to 36°C (98°F). Expect 83 mm (3.3 in) of precipitation spread across 9 days, contributing to an average humidity level of 75% that adds a touch of tropical feel to the atmosphere.

September Temperature in Waterloo

In September in Waterloo, the average temperature is 21°C (70°F). Maximums can reach 36°C (98°F) and minimums can be as low as 5°C (41°F). This variation makes it essential for travelers to pack accordingly for both warm and cooler weather during their visit.

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 21°C (70°F), with highs reaching up to 36°C (98°F) and lows dropping to around 5°C (41°F).
JanFebMarAprMayJunJulAugSepOctNovDec252541506376787570534031
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 precipitation amount is 83 mm (3.3 in) over the course 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 83 mm (3.3 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec3330975414612674101831153140
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 75%. With an average temperature of 21°C (70°F), this humidity feels like a warm, enveloping blanket that makes exploring the area feel slightly sticky, requiring travelers to stay hydrated and take occasional breaks in the shade to fully enjoy their adventures.

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 75%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec76%80%73%75%78%82%83%81%75%75%82%83%
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.
JanFebMarAprMayJunJulAugSepOctNovDec356810101098642
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-4°C (25°F)32 mm (1.3 inches)76%moderate
February Weather-4°C (26°F)30 mm (1.2 inches)80%moderate
March Weather5°C (41°F)97 mm (3.8 inches)73%high
April Weather10°C (51°F)54 mm (2.1 inches)74%very high
May Weather17°C (63°F)146 mm (5.8 inches)78%very high
June Weather24°C (76°F)126 mm (5.0 inches)82%very high
July Weather26°C (78°F)74 mm (2.9 inches)83%very high
August Weather24°C (75°F)100 mm (4.0 inches)80%very high
September Weather21°C (70°F)83 mm (3.3 inches)75%very high
October Weather11°C (53°F)115 mm (4.5 inches)75%high
November Weather5°C (40°F)31 mm (1.2 inches)82%moderate
December Weather0°C (32°F)40 mm (1.6 inches)83%low

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