April in Waterloo averages a daily high of 15.6°C with nights around 2.6°C. Expect roughly 11.1 wet days totalling 94.4mm. Generally workable, with some weather to plan around.
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 April data.