Climate almanac
O'Fallon
Illinois, United States · 38.59°, -89.91°
What is the weather like in O'Fallon in May?
In May, O'Fallon is typically 78°F (25°C) during the day and 60°F (15°C) at night. The month brings about 5.4 in (137 mm) of precipitation in total.
- Average high78°F (25°C)
- Average low60°F (15°C)
- Precipitation5.4 in (137 mm)
- Clear or mostly clear days8
- Based on2016-2025 daily ERA5 reanalysis data (10-year normals)