Last updated: June 24, 2025
In St. Charles, United States, the average temperature in May hovers around 19°C (67°F), offering a comfortable climate. However, temperatures can range from a cool 4°C (39°F) to a warm 34°C (93°F). Expect 118 mm (4.6 in) of precipitation spread over 11 days, contributing to an average humidity of 78%. This combination of weather elements creates a unique atmosphere for visitors and residents alike.
In May in St. Charles, the average temperature is 19°C (67°F) with maximums reaching up to 34°C (93°F) and minimums dropping as low as 4°C (39°F). Travelers should prepare for a wide range of temperatures and pack accordingly for both warm and cool experiences.
In St. Charles in May, the precipitation amount is 118 mm (4.6 in) over the course of 11 days.
In St. Charles in May humidity is 78%. With an average temperature of 19°C (67°F), this humidity feels like a warm, heavy blanket enveloping you, making traveling feel both sticky and sluggish as you navigate through the day.
In St. Charles in May, the maximum UV index reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more detailed information, you can check the Hourly UV Index in St. Charles.
UV Risk Categories
Weather in St. Charles varies notably across the year, with each month offering distinct climate conditions. This page compares May’s weather to other months in St. Charles, focusing on differences in temperature, rainfall, humidity, and UV levels.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | 4°C (39°F) | 62 mm (2.4 inches) | 84% | moderate |
| February Weather | 6°C (42°F) | 93 mm (3.7 inches) | 83% | moderate |
| March Weather | 9°C (48°F) | 77 mm (3.0 inches) | 83% | high |
| April Weather | 14°C (58°F) | 99 mm (3.9 inches) | 81% | very high |
| May Weather | 19°C (67°F) | 118 mm (4.6 inches) | 78% | very high |
| June Weather | 24°C (76°F) | 106 mm (4.2 inches) | 79% | very high |
| July Weather | 27°C (81°F) | 122 mm (4.8 inches) | 74% | very high |
| August Weather | 26°C (79°F) | 151 mm (5.9 inches) | 72% | very high |
| September Weather | 23°C (73°F) | 91 mm (3.6 inches) | 75% | very high |
| October Weather | 17°C (64°F) | 108 mm (4.2 inches) | 81% | high |
| November Weather | 9°C (49°F) | 78 mm (3.1 inches) | 85% | moderate |
| December Weather | 6°C (43°F) | 86 mm (3.4 inches) | 84% | moderate |