St. Louis, MO weather in September
September in St. Louis: warm, with some rain. Highs 81°F, lows 61°F, rain on about 7 days. A good month for most outdoor plans.
- Normal high
- 81°F
- Normal low
- 61°F
- Wet days
- 7
- 3.0 in total
- Muggy days
- 8
- dew point 65°F+
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 86°F | 76°F |
| Normal low | 66°F | 55°F |
| Chance of a wet day | 25% | 25% |
| Sunrise / sunset | 6:30 am / 7:31 pm | 6:55 am / 6:45 pm |
| Daylight | 13.0 h | 11.8 h |
Chance of a wet day: average for the first and last 7 days of the month. Times are local clock time (Central Time).
A typical September day
- 6 am63°Fdew point 58°F
- 9 am71°Fdew point 59°F
- Noon77°Fdew point 58°F
- 3 pm79°Fdew point 57°F
- 6 pm76°Fdew point 57°F
- 9 pm70°Fdew point 58°F
NOAA hourly normals (local standard time) from St Louis Lambert Intl Airport (13 mi away); average wind 7 mph; clear or few clouds in 39% of daytime hours, mostly cloudy or overcast in 39%.
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F10 of 30
- Hot dayshigh 90°F or more5 of 30
- Muggy daysdaily mean dew point 65°F or more8 of 30
- Wet daysat least 0.01 in of rain or melted snow7 of 30
- Notable rainat least 0.10 in5 of 30
- Freezing nightslow 32°F or below0 of 30
- Snow on the groundsnow depth 1 in or more0 of 30
Average days per September, counted from daily records for each year 1991-2020.
Rain in September
Normal precipitation is 3.0 in; a dry September brings about 1.7 in and a wet one about 3.2 in (25th and 75th percentiles). About 2 days bring half an inch or more, and about 1 an inch or more.
How September varies from year to year
- Warmest September, 1991-20202019: average high 87°F
- Coolest September1993: average high 74°F
- Wettest September2008: 9.8 in
- Driest September2004: 0.2 in
- Highest reading104°F (September 1, 2011)
- Lowest reading40°F (September 23, 1995)
From the station's daily records with NOAA quality flags removed; most recent date shown when a reading repeats.
September compared with August and October
| August | September | October | |
|---|---|---|---|
| Normal high | 88°F | 81°F | 69°F |
| Normal low | 69°F | 61°F | 49°F |
| Wet days | 8 | 7 | 9 |
| Comfortable days | 2 | 10 | 14 |
| Daylight | 13.6 h | 12.4 h | 11.2 h |
Highs change by -7°F from August and -12°F into October.
Nearby alternatives in September
- Cooler: Aurora, IL238 mi · high 76°F · 8 wet days
How St. Louis ranks in September
- Normal high185th warmest of 378 cities; 3rd of 7 in Missouri
- Wet days166th driest of 378
- Comfortable days152nd most of 342
Heating and cooling
September has 32 heating degree days and 212 cooling degree days (base 65°F), 4% of the year's total heating and cooling demand.
Questions
How hot is St. Louis in September?
The normal high is 81°F and the normal low is 61°F. From 1991 to 2020 the hottest September reading was 104°F (September 1, 2011).
Does it rain a lot in St. Louis in September?
About 7 days in September have at least 0.01 in of precipitation, and the normal total is 3.0 in. The wettest September in 1991-2020 was in 2008 (9.8 in); the driest was in 2004 (0.2 in).
Is September a good time to visit St. Louis?
September ranks 4th of 12 months on our comfort score for St. Louis (60 out of 100). It has about 10 comfortable days and about 5 days at 90°F or hotter. The best months are April and May.
Where the numbers come from
- Temperature, rain, snowfall, snow depth, humidity and wind by hour and cloud cover: St Louis Lambert Intl Airport (USW00013994), 13 mi NW of the city center, 531 ft (67 ft higher than the city). NOAA normals and daily records, 1991-2020.
- Frost dates: Cahokia St Louis Airport (USW00003960), 4.4 mi SSE of the city center, 413 ft (51 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Daily humidity and wind: Lambert-St Louis International Airport (724340-13994), 13 mi NW of the city center, 531 ft (67 ft higher than the city). Hourly observations, 1991-2020.