May in Sioux City averages a daily high of 22.8°C with nights around 9.4°C. Expect roughly 12.3 wet days totalling 101.4mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Sioux City is September–October.
Based on SIOUX CITY AIRPORT, IA US (12.2km), 1995–2024. 30 years of May data.