The highest day temperature in September 2025 was 104°F. The lowest night temperature was 56°F. The average values for day and night temperatures during September were 88.5°F и 67.8°F respectivly.

Most of the days in September are sunny but you can also expect cloudy and gloomy days.

Precipitation total in September for Saint Charles is 0.5 in. It makes september the least rainy month of the year.

The average wind speed in September is 6.6 mph. It makes September one of the most windless months of the year for Saint Charles.

We are using day length and cloud cover information for each day of the month to calculate averages for this chart. Average sunny hours for Saint Charles in September is 8.9 hours.