December in Waterloo averages a daily high of 0.7°C with nights around -8.8°C. Expect roughly 8.3 wet days totalling 36.6mm. A hard month to visit for comfort alone.
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 December data.