September weather in Lake St. Louis, MO
The average temperature in Lake St. Louis in September is 68.4°F (57.0°F–79.8°F). Average precipitation: 3.50 inches.
September is a fall month in Lake St. Louis, and is warmer than the annual average of 55.2°F. Daily temperatures swing about 22.8°F between overnight low and afternoon high. Expect about 7 days with precipitation. Daylight averages about 12h 14m. For travel, September is one of the best months of the year to visit.
Avg High
79.8°F
Avg Low
57.0°F
Precipitation
3.50 in
Daylight
12h 14m
September records in Lake St. Louis
| Date | Record High | Record Low | Record Precip |
|---|---|---|---|
| September 1 | 99.0°F (2011) | 44.1°F (1987) | 3.10 in (1981) |
| September 2 | 102.0°F (1984) | 44.1°F (1974) | 2.39 in (2014) |
| September 3 | 99.0°F (2011) | 27.0°F (1995) | 2.01 in (1993) |
| September 4 | 98.1°F (2011) | 30.9°F (1995) | 0.91 in (1980) |
| September 5 | 98.1°F (1960) | 46.9°F (1976) | 2.45 in (2008) |
| September 6 | 98.1°F (1960) | 46.0°F (1962) | 0.47 in (2014) |
| September 7 | 99.0°F (1960) | 45.0°F (1962) | 0.52 in (1968) |
| September 8 | 99.0°F (1960) | 33.1°F (1986) | 1.80 in (2018) |
| September 9 | 99.0°F (1960) | 43.0°F (1986) | 2.85 in (1984) |
| September 10 | 97.0°F (2013) | 43.0°F (1976) | 2.56 in (2016) |
| September 11 | 97.0°F (1964) | 45.0°F (1959) | 3.87 in (1984) |
| September 12 | 96.1°F (2013) | 41.0°F (1968) | 1.25 in (2008) |
| September 13 | 95.0°F (1991) | 39.9°F (1974) | 0.45 in (1977) |
| September 14 | 97.0°F (2025) | 37.9°F (1975) | 3.96 in (2008) |
| September 15 | 100.9°F (1971) | 37.9°F (1979) | 1.76 in (1993) |
| September 16 | 93.9°F (1997) | 36.0°F (1984) | 1.39 in (1978) |
| September 17 | 93.0°F (2019) | 39.0°F (1984) | 1.68 in (1969) |
| September 18 | 93.0°F (2025) | 39.9°F (1981) | 2.01 in (1968) |
| September 19 | 96.1°F (2025) | 37.9°F (1991) | 1.44 in (2010) |
| September 20 | 95.0°F (1972) | 34.0°F (1991) | 3.38 in (2002) |
| September 21 | 96.1°F (2022) | 33.1°F (1991) | 1.37 in (2021) |
| September 22 | 93.9°F (2022) | 30.9°F (1983) | 1.45 in (2024) |
| September 23 | 95.0°F (2017) | 28.0°F (1983) | 2.20 in (1993) |
| September 24 | 91.9°F (2017) | 30.0°F (1995) | 3.32 in (2024) |
| September 25 | 91.9°F (2017) | 21.9°F (1989) | 2.41 in (1961) |
| September 26 | 91.0°F (1958) | 28.9°F (1995) | 1.29 in (2012) |
| September 27 | 90.0°F (2017) | 27.0°F (1989) | 1.44 in (2003) |
| September 28 | 90.0°F (2021) | 28.0°F (1989) | 0.69 in (2024) |
| September 29 | 90.0°F (1971) | 28.9°F (1995) | 1.31 in (1974) |
| September 30 | 90.0°F (2023) | 28.0°F (1984) | 1.74 in (1986) |