Climate averages 1991–2020
St. Louis weather
in September.
A warm, moderately wet month: the 4th warmest and the 5th driest of the year. Meets the pleasant-weather rule
Long-term climate patterns, not a forecast for a particular trip.
September is a warm month in St. Louis: daytime highs average 26.4°C and nights cool to about 16.6°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 83 mm of rain on roughly 8 days, which makes September a moderately wet month (the 5th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 29 min on an average September day.
The nearest other city in this atlas is O'Fallon (48 km away). In September its highs average 26.0°C, about as warm as St. Louis, with 81 mm of rain.
Among the 498 cities listed in the United States, St. Louis ranks joint 263rd of 498 for the warmest September highs and joint 294th of 498 for the driest September (rainfall, lowest first). The mean September high of those 498 cities is 26.9°C; St. Louis is 0.5°C cooler than that mean.
From September to October, average highs fall by 6.5°C to 19.9°C, and monthly rainfall rises from 83 mm to 87 mm.
The annual picture
September in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
St. Louis climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 4.3°C-4.3°C | -4.3°C | 70 | 8.2 | 9.810 h |
| February | 7.2°C-2.5°C | -2.5°C | 63 | 7.8 | 10.711 h |
| March | 13.0°C2.6°C | 2.6°C | 94 | 10.5 | 11.912 h |
| April | 19.1°C8.4°C | 8.4°C | 117 | 11.2 | 13.213 h |
| May | 24.3°C14.3°C | 14.3°C | 128 | 13.4 | 14.314 h |
| June | 29.1°C19.3°C | 19.3°C | 106 | 11.0 | 14.815 h |
| July | 31.0°C21.6°C | 21.6°C | 86 | 9.9 | 14.615 h |
| August | 30.4°C20.9°C | 20.9°C | 74 | 9.1 | 13.714 h |
| September, selected | 26.4°C16.6°C | 16.6°C | 83 | 7.6 | 12.512 h |
| October | 19.9°C10.3°C | 10.3°C | 87 | 8.4 | 11.211 h |
| November | 12.3°C3.6°C | 3.6°C | 93 | 8.6 | 10.110 h |
| December | 6.3°C-1.7°C | -1.7°C | 65 | 8.2 | 9.510 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- O'Fallon in SeptemberUnited States · 48 kmHigh 26.0°C · Low 16.7°C · 81 mm rain
- Springfield (Illinois), United States in SeptemberUnited States · 139 kmHigh 25.2°C · Low 15.5°C · 80 mm rain
- Decatur in SeptemberUnited States · 172 kmHigh 25.0°C · Low 15.4°C · 82 mm rain
- Columbia (Missouri), United States in SeptemberUnited States · 189 kmHigh 26.1°C · Low 16.5°C · 86 mm rain
- Bloomington (Illinois), United States in SeptemberUnited States · 231 kmHigh 24.3°C · Low 14.8°C · 77 mm rain
- Peoria (Illinois), United States in SeptemberUnited States · 236 kmHigh 24.4°C · Low 15.4°C · 76 mm rain
- Champaign in SeptemberUnited States · 236 kmHigh 24.7°C · Low 14.9°C · 77 mm rain
- Evansville in SeptemberUnited States · 242 kmHigh 26.7°C · Low 17.5°C · 82 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for St. Louis) is explained once on the St. Louis year overview and on the Sources, method and limits page.