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September Weather in Saint Charles, United States

Last updated: June 24, 2025

In September, the average temperature in Saint Charles, United States is a pleasant 18°C (64°F). During this month, you can expect temperatures to range from a cool 2°C (36°F) to a warm 32°C (91°F). Rainfall brings 117 mm (4.6 in) over approximately 9 days, while the atmosphere remains comfortably humid with an average humidity of 74%.

September Temperature in Saint Charles

In September in Saint Charles, the average temperature is 18°C (64°F). Maximums can reach 32°C (91°F) and minimums can be as low as 2°C (36°F). It's a great time for travelers to enjoy mild weather while being prepared for both warm days and cooler nights.

September Weather in Saint Charles: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Saint Charles, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Saint Charles, September typically has an average temperature of 18°C (64°F), with highs reaching up to 32°C (91°F) and lows dropping to around 2°C (36°F).
JanFebMarAprMayJunJulAugSepOctNovDec181934445970737064483425
Data source: Temperature data for Saint Charles generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Saint Charles

In Saint Charles in September, the total precipitation amount is 117 mm (4.6 in) spread over a period of 9 days.

September Precipitation Trends in Saint Charles

The chart displays monthly precipitation patterns in Saint Charles, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Saint Charles, September typically receives around 117 mm (4.6 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec364857861521511031261171195243
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Saint Charles

In Saint Charles in September humidity is 74%. With an average temperature of 18°C (64°F), this humidity feels like a warm embrace, making it ideal for leisurely strolls but potentially uncomfortable for extended outdoor activities.

September Average Humidity in Saint Charles

This chart illustrates the average monthly humidity levels in Saint Charles, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Saint Charles is approximately 74%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec84%85%84%83%75%79%75%69%74%79%88%82%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Saint Charles

In Saint Charles in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Saint Charles.

Maximum UV Index Levels in Saint Charles for September

The chart shows the monthly maximum UV Index (UVI) for Saint Charles in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Saint Charles typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec34589101098532
Data source: Saint Charles September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How September Weather in Saint Charles Compares to Other Months

Weather in Saint Charles varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Saint Charles, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Saint Charles, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-8°C (18°F)36 mm (1.4 inches)84%moderate
February Weather-7°C (19°F)48 mm (1.9 inches)85%moderate
March Weather1°C (34°F)57 mm (2.2 inches)84%moderate
April Weather7°C (44°F)86 mm (3.4 inches)83%very high
May Weather15°C (59°F)152 mm (6.0 inches)75%very high
June Weather21°C (71°F)151 mm (5.9 inches)79%very high
July Weather23°C (74°F)103 mm (4.1 inches)75%very high
August Weather21°C (70°F)126 mm (5.0 inches)69%very high
September Weather18°C (64°F)117 mm (4.6 inches)74%very high
October Weather9°C (49°F)118 mm (4.7 inches)79%moderate
November Weather1°C (34°F)52 mm (2.0 inches)88%moderate
December Weather-4°C (26°F)43 mm (1.7 inches)82%low

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