September in Waterloo averages a daily high of 24.9°C with nights around 11°C. Expect roughly 7.9 wet days totalling 74mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Waterloo is August–September.
Based on WATERLOO MUNICIPAL AIRPORT, IA US (8.4km), 1995–2024. 30 years of September data.