September in St. Louis averages a daily high of 27.4°C with nights around 16.4°C. Expect roughly 7.1 wet days totalling 85.5mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit St. Louis is April–May.
Based on ST LOUIS SCIENCE CENTER, MO US (6.3km), 1995–2024. 20 years of September data.