Average annual temperature is 10.5 °C
Absolute maximum temperature: 39.0 °C
Absolute minimum temperature: -22.4 °C
Number of sunny days: 209 days
Number of rainy days: 130 days
Number of snow days: 26 days
Look at detailed online map of O'Fallons
* Weather data for O'Fallons United States is based on climate observations for 2026 year
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Absolute maximum temperature (°C) | 7.1 | 13.5 | 19.0 | 31.4 | 27.4 | 31.6 | 37.2 | 39.0 | 37.7 | 29.4 | 20.4 | 15.3 |
| Average daytime temperature (°C) | -1.1 | 5.3 | 8.5 | 18.2 | 23.0 | 27.0 | 30.2 | 31.6 | 28.0 | 17.5 | 12.3 | 6.6 |
| Average temperature (°C) | -5.3 | -2.4 | 0.7 | 9.7 | 16.6 | 20.9 | 23.5 | 24.6 | 20.5 | 10.9 | 5.1 | 0.5 |
| Average night temperature (°C) | -8.9 | -7.4 | -4.4 | 2.5 | 10.8 | 15.1 | 17.2 | 18.5 | 14.1 | 5.1 | -0.1 | -3.4 |
| Absolute minimum temperature (°C) | -22.1 | -22.4 | -9.8 | -6.7 | -0.5 | 10.4 | 10.4 | 12.9 | 7.4 | -8.4 | -8.3 | -10.6 |
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daylight maximum duration (h) | 10.0 | 11.0 | 12.0 | 13.0 | 14.0 | 15.0 | 15.0 | 14.0 | 13.0 | 11.0 | 10.0 | 9.0 |
| Daylight mean duration (h) | 9.6 | 10.6 | 11.9 | 13.3 | 14.5 | 15.1 | 14.8 | 13.8 | 12.5 | 11.1 | 9.9 | 9.3 |
| Daylight minimum duration (h) | 9.0 | 10.0 | 11.0 | 12.0 | 13.0 | 14.0 | 14.0 | 13.0 | 11.0 | 10.0 | 9.0 | 9.0 |
| Sunshine mean duration (h) | 5.9 | 8.1 | 8.9 | 10.5 | 10.5 | 12.3 | 12.5 | 12.0 | 10.5 | 8.0 | 7.6 | 5.5 |
| Precipitation (mm) | 59 | 10 | 39 | 6 | 140 | 64 | 51 | 31 | 39 | 48 | 13 | 31 |
| Sunny days | 18 | 18 | 16 | 22 | 8 | 10 | 13 | 21 | 20 | 19 | 22 | 22 |
| Rainy days | 5 | 3 | 10 | 8 | 23 | 20 | 18 | 10 | 10 | 10 | 6 | 7 |
| Snow days | 8 | 7 | 5 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 2 | 2 |
The best time to visit O'Fallons during the most sunny months:
The largest precipitation sum in O'Fallons is at