Saint Charles Weather Forecast
- 79
- 99
Hot
- 78
- 100
Hot
- 75
- 99
Hot
- 70
- 95
Mostly Sunny
- 71
- 94
Mostly Sunny
- 78
- 99
Hot
- 77
- 100
Slight Chance Thunderstorms
Today 3 Sep St. Charles
Mostly sunny. Hot. Near steady temperature in the upper 90s. Southwest Winds 5 to 10 Mph. Heat index Values up to 106.
Tonight 3 Sep St. Charles
Mostly clear. Lows in the mid 70s. South Winds around 5 Mph. Heat index Values up to 104 early this evening.
Saint Charles Temperature Statistics
September Temperature
St. Louis Lambert International Airport (6.2 miles)
Lowest 1 September, 2026
80.1 °FAverage September
89 °FHighest 1 September, 2026
99 °F
Climate (2021–2026)
St. Louis Lambert International Airport (6.2 miles)
Average Low 2021–2026
50.6 °FAverage 2021–2026
60.1 °FAverage High 2021–2026
69.7 °F