St. Louis weather in September
September in St. Louis: warm, a little rain, with clean air — one of the best months to visit.
#2 of 12 months in St. Louis · #221 of 897 destinations to visit in September · comfort 89/100 (tier A)
Updated June 2026 · climate normals from ERA5 reanalysis
Traveller notes on St. Louis in September
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St. Louis climate normals — September
| Daytime high | 28°C / 82°F | 🌤 warm |
|---|---|---|
| Nighttime low | 18°C / 64°F | |
| Rainfall | 49 mm / 1.9 in | 🌦 some rain |
| Rainy days | 8 days | |
| Humidity | 67% | 💧 humid |
| Dew point | 15°C / 59°F | |
| Sunshine | 10.4 h/day | |
| Daylight | 12.4 h | |
| Wind | 14 km/h / 9 mph | |
| Air quality (US AQI) | 50 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
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St. Louis in September — FAQ
- Is September a good time to visit St. Louis?
- September in St. Louis: warm, a little rain, with clean air — one of the best months to visit. It ranks #2 of 12 months for St. Louis on SeasonMap's comfort score (89/100).
- What is the weather like in St. Louis in September?
- In September, St. Louis averages a daily high of 27.8°C and a low of 17.9°C, with about 49.4 mm of rain over roughly 7.6 rainy days.
- What is the air quality in St. Louis in September?
- St. Louis has a mean US Air Quality Index of about 50 in September.