O'Fallon Climate: Weather by Month and Best Time to Visit
Best months for O'Fallon: September, October, June, August.
Year at a glance
Weather by month
| Month | Avg high | Avg low | Rainfall | Rainy days | Humidity | Sunshine | Score |
|---|---|---|---|---|---|---|---|
| January | 5°C | -4°C | 65 mm | 7 | – | – | 4.9 |
| February | 8°C | -2°C | 61 mm | 8 | – | – | 5.5 |
| March | 14°C | 3°C | 92 mm | 10 | – | – | 6.3 |
| April | 20°C | 9°C | 114 mm | 11 | – | – | 7.1 |
| May | 25°C | 14°C | 123 mm | 13 | – | – | 7.1 |
| June | 29°C | 19°C | 101 mm | 11 | – | – | 7.5 |
| July | 31°C | 21°C | 82 mm | 10 | – | – | 7.1 |
| August | 30°C | 20°C | 76 mm | 9 | – | – | 7.5 |
| September | 27°C | 15°C | 81 mm | 7 | – | – | 8.1 |
| October | 20°C | 9°C | 83 mm | 9 | – | – | 7.7 |
| November | 13°C | 3°C | 89 mm | 8 | – | – | 6.5 |
| December | 7°C | -1°C | 62 mm | 8 | – | – | 5.3 |