Last updated: June 24, 2025
In September, the average temperature in Waterloo, United States hovers around 18°C (65°F). However, be prepared for a range, with minimums dipping to 3°C (38°F) and maximums soaring to 33°C (92°F). Expect about 82 mm (3.2 in) of precipitation spread over 9 days, contributing to an average humidity of 78%. Whether you're planning outdoor adventures or cozy indoor activities, this climate offers a little something for everyone!
In September in Waterloo, the average temperature is 18°C (65°F). Maximum temperatures can reach 33°C (92°F), while minimums can drop as low as 3°C (38°F). This diverse temperature range makes Waterloo an interesting destination for travelers seeking both warm days and cooler nights.
In Waterloo in September, the total precipitation amount is 82 mm (3.2 in), occurring over a span of 9 days.
In Waterloo in September, humidity is 78%. With an average temperature of 18°C (65°F), this humidity feels like a warm, enveloping blanket, making travel quite muggy and potentially uncomfortable, as it can leave you feeling sticky and fatigued more quickly than usual.
In Waterloo in September, the maximum UV index is 7, which corresponds to the high Exposure Category. This means that the time to burn is approximately 25 minutes. For more detailed information, you can check the Hourly UV Index in Waterloo.
UV Risk Categories
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.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | -3°C (27°F) | 89 mm (3.5 inches) | 90% | low |
| February Weather | -2°C (29°F) | 88 mm (3.5 inches) | 90% | moderate |
| March Weather | 2°C (35°F) | 81 mm (3.2 inches) | 87% | high |
| April Weather | 8°C (46°F) | 119 mm (4.7 inches) | 88% | very high |
| May Weather | 14°C (58°F) | 116 mm (4.6 inches) | 82% | very high |
| June Weather | 20°C (67°F) | 86 mm (3.4 inches) | 79% | very high |
| July Weather | 23°C (73°F) | 153 mm (6.0 inches) | 78% | very high |
| August Weather | 22°C (72°F) | 108 mm (4.3 inches) | 76% | very high |
| September Weather | 18°C (65°F) | 82 mm (3.2 inches) | 78% | high |
| October Weather | 12°C (55°F) | 154 mm (6.1 inches) | 84% | high |
| November Weather | 4°C (40°F) | 97 mm (3.8 inches) | 89% | moderate |
| December Weather | 0°C (33°F) | 101 mm (4.0 inches) | 86% | low |