St. Louis weather in September: St. Louis, Missouri: normal highs, lows, rain and records for September
St. Louis in September has a normal high of 81°F and a normal low of 61°F, a daily mean of 71°F, falling from 86°F on the 1st to 76°F by the 30th. Measurable precipitation falls on 7 days in a normal September, 2.96 inches in all. (NOAA 1991-2020 normals)
In metric: a normal high of 27°C and low of 16°C, 75 mm of precipitation in September.
- NOAA stationSt Louis Lambert International Airport
- Station IDUSW00013994
- Location38.75°N 90.37°W
- Elevation531 ft (162 m)
- From the center11 miles
- Population279,695
- Jan 40° 24°
- Feb 46° 28°
- Mar 57° 37°
- Apr 68° 47°
- May 77° 58°
- Jun 86° 67°
- Jul 90° 71°
- Aug 88° 69°
- Sep 81° 61°
- Oct 69° 49°
- Nov 56° 37°
- Dec 45° 29°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
How warm is St. Louis in September?
The normal high is 81°F and the normal low 61°F, for a daily mean of 71.0°F. September is 7.8°F cooler than August and 11.9°F warmer than October. September is the 4th warmest month of the year in St. Louis and the 9th wettest. Across the month the normal high falls 10°F, from 86°F on September 1 to 76°F on September 30. From one year to the next September's mean temperature typically moves about 2.9°F either way (NOAA's standard deviation), so roughly two Septembers in three average between 68°F and 74°F.
Bars above: each day's normal high to low. Columns below: the chance of 0.01 inch or more of precipitation that day, on a scale of 0 to 100% (highest 26%).
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in |
|---|---|---|---|---|
| September 1 | 86°F | 66°F | 26% | 16% |
| September 8 | 84°F | 64°F | 25% | 16% |
| September 15 | 81°F | 61°F | 25% | 15% |
| September 22 | 79°F | 59°F | 25% | 15% |
| September 30 | 76°F | 55°F | 25% | 15% |
Every day of September: normal high, low and chance of precipitation (warmest afternoon September 1, coldest night September 30)
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in | Daylight |
|---|---|---|---|---|---|
| September 1 | 86°F | 66°F | 26% | 16% | 13 h |
| September 2 | 86°F | 66°F | 26% | 16% | 13 h |
| September 3 | 85°F | 65°F | 25% | 16% | 13 h |
| September 4 | 85°F | 65°F | 25% | 16% | 13 h |
| September 5 | 85°F | 65°F | 25% | 16% | 12 h 50 min |
| September 6 | 84°F | 65°F | 25% | 16% | 12 h 50 min |
| September 7 | 84°F | 64°F | 25% | 16% | 12 h 50 min |
| September 8 | 84°F | 64°F | 25% | 16% | 12 h 50 min |
| September 9 | 83°F | 63°F | 25% | 16% | 12 h 40 min |
| September 10 | 83°F | 63°F | 25% | 16% | 12 h 40 min |
| September 11 | 83°F | 63°F | 25% | 16% | 12 h 40 min |
| September 12 | 83°F | 62°F | 25% | 16% | 12 h 40 min |
| September 13 | 82°F | 62°F | 25% | 16% | 12 h 40 min |
| September 14 | 82°F | 62°F | 25% | 15% | 12 h 30 min |
| September 15 | 81°F | 61°F | 25% | 15% | 12 h 30 min |
| September 16 | 81°F | 61°F | 25% | 15% | 12 h 30 min |
| September 17 | 81°F | 60°F | 25% | 15% | 12 h 30 min |
| September 18 | 80°F | 60°F | 25% | 15% | 12 h 20 min |
| September 19 | 80°F | 60°F | 25% | 15% | 12 h 20 min |
| September 20 | 80°F | 59°F | 25% | 15% | 12 h 20 min |
| September 21 | 79°F | 59°F | 25% | 15% | 12 h 20 min |
| September 22 | 79°F | 59°F | 25% | 15% | 12 h 10 min |
| September 23 | 79°F | 58°F | 25% | 15% | 12 h 10 min |
| September 24 | 78°F | 58°F | 25% | 15% | 12 h 10 min |
| September 25 | 78°F | 57°F | 25% | 15% | 12 h 10 min |
| September 26 | 77°F | 57°F | 25% | 15% | 12 h |
| September 27 | 77°F | 57°F | 25% | 15% | 12 h |
| September 28 | 77°F | 56°F | 25% | 15% | 12 h |
| September 29 | 76°F | 56°F | 25% | 15% | 12 h |
| September 30 | 76°F | 55°F | 25% | 15% | 11 h 50 min |
- Normal high
- 81°FSeptember average
- Normal low
- 61°FSeptember average
- Precipitation
- 2.96 inmonth total
- Days with precipitation
- 70.01 inch or more
- Days at 90°F or more
- 5
- Daylight
- 13 h to 11 h 50 minSeptember 1 to September 30
- Days at 70°F or more
- 27
- Days at 80°F or more
- 17
- Sunshine
- 81%of clear-sky sunlight (NASA)
Source: NOAA NCEI 1991-2020 daily normals, station USW00013994; monthly normals. Daylight is computed from the place's latitude with NOAA's solar equations.
Does it rain in St. Louis in September?
On a given September day the chance of 0.01 inch or more is 25% on average, highest around September 1 (26%). In all, 2.96 in falls on 7 days of a normal September, 1 of them with an inch or more.
In a normal September in St. Louis, 5 days reach 90°F.
Source: NOAA NCEI 1991-2020 daily and monthly normals, station USW00013994.
How humid and windy is St. Louis in September?
At 3 p.m. the normal temperature is 74°F with 44% relative humidity and a dew point of 51°F; at 6 a.m. it is 58°F with 80% humidity. The wind averages 7.8 mph, most often from the west-southwest in the afternoon.
| Time | Temperature | Dew point | Humidity | Wind | Clear or few clouds |
|---|---|---|---|---|---|
| 6 a.m. | 58°F | 52°F | 80% | 6.0 mph | 42% |
| 9 a.m. | 65°F | 53°F | 64% | 8.7 mph | 49% |
| noon | 72°F | 52°F | 49% | 9.8 mph | 42% |
| 3 p.m. | 74°F | 51°F | 44% | 10.2 mph | 46% |
| 6 p.m. | 70°F | 52°F | 52% | 7.9 mph | 42% |
| 9 p.m. | 65°F | 53°F | 64% | 6.9 mph | 65% |
Source: NOAA NCEI 1991-2020 hourly normals, station USW00013994. Hourly normals exist only for NOAA's first-order stations; a dash where NOAA publishes no value for that hour (the sky at some hours).
What are the records for September in St. Louis?
The warmest September temperature on St. Louis's official record (since 1874) is 104°F, on September 4, 1954; the coldest is 32°F, on September 28, 1942. The wettest September brought 10.04 in (1945).
The September mean against the 1991-2020 normal of 71.0°F: 2021 74.9°F (+3.9), 2022 71.4°F (+0.4), 2023 74.2°F (+3.2), 2024 73.5°F (+2.5), 2025 73.6°F (+2.6), 2026 78.4°F (+7.4). 6 of 6 ran warmer than normal.
| September | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 74.9°F | +3.9°F | 3.04 in |
| 2022 | 71.4°F | +0.4°F | 1.73 in |
| 2023 | 74.2°F | +3.2°F | 2.67 in |
| 2024 | 73.5°F | +2.5°F | 5.75 in |
| 2025 | 73.6°F | +2.6°F | 0.74 in |
| 2026 | 78.4°F | +7.4°F | 1.38 in |
Source: records: ACIS, NWS threaded record STLthr; recent months: ACIS, station USW00013994. Records and recent months use complete months only.
How does September in St. Louis compare across Missouri?
Across the 134 places PlainClimate covers in Missouri, September normal highs run from 76°F in Unionville to 85°F in Kennett; St. Louis's is 81°F.
Source: NOAA NCEI 1991-2020 monthly normals for every station in the state.