May in Sioux Falls averages a daily high of 21°C with nights around 8.2°C. Expect roughly 12.3 wet days totalling 93.5mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Sioux Falls is August–September.
Based on SIOUX FALLS FOSS FIELD, SD US (4.9km), 1995–2024. 30 years of May data.