Last updated: June 24, 2025
In Saint Charles, United States, the average temperature in September hovers around 18°C (65°F). However, be prepared for a range, with minimums dipping to 1°C (35°F) and maximums soaring to 35°C (95°F). During the month, expect approximately 101 mm (4.0 in) of precipitation over about 10 days, accompanied by an average humidity of 80%. Stay ready for varied weather as you plan your activities!
In September in Saint Charles, the average temperature is 18°C (65°F). Maximums can reach 35°C (95°F), and minimums can be as low as 1°C (35°F). This diverse temperature range makes Saint Charles an ideal destination for travelers seeking both warm and cool experiences.
In Saint Charles in September, the precipitation amount is 101 mm (4.0 in) spread over the course of 10 days.
In Saint Charles in September, humidity is 80%. With an average temperature of 18°C (65°F), this humidity feels like wandering through a warm, damp blanket, making every step slightly heavy and resulting in a constant sheen of sweat, which can be both refreshing and exhausting for travelers.
In Saint Charles in September, the maximum UV index is 7, which corresponds to the high Exposure Category. This means that the time to burn is approximately 25 minutes. For more detailed information, you can check the Hourly UV Index in Saint Charles.
UV Risk Categories
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.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | -4°C (25°F) | 59 mm (2.3 inches) | 88% | low |
| February Weather | -3°C (26°F) | 63 mm (2.5 inches) | 87% | moderate |
| March Weather | 2°C (36°F) | 61 mm (2.4 inches) | 85% | moderate |
| April Weather | 8°C (46°F) | 88 mm (3.4 inches) | 86% | very high |
| May Weather | 15°C (59°F) | 115 mm (4.5 inches) | 80% | very high |
| June Weather | 21°C (70°F) | 121 mm (4.8 inches) | 80% | very high |
| July Weather | 23°C (75°F) | 66 mm (2.6 inches) | 80% | very high |
| August Weather | 22°C (72°F) | 76 mm (3.0 inches) | 80% | very high |
| September Weather | 18°C (65°F) | 101 mm (4.0 inches) | 80% | high |
| October Weather | 11°C (53°F) | 112 mm (4.4 inches) | 84% | moderate |
| November Weather | 3°C (38°F) | 60 mm (2.4 inches) | 89% | moderate |
| December Weather | 0°C (32°F) | 60 mm (2.4 inches) | 86% | low |