O'Fallon Weather Forecast
- 70
- 85
Chance Thunderstorms
- 74
- 87
Chance Thunderstorms
- 76
- 93
Slight Chance Thunderstorms
- 75
- 94
Chance Thunderstorms
- 77
- 95
Slight Chance Thunderstorms
- 77
- 97
Hot
Today 17 Jul St. Charles
Partly sunny. A slight chance of Showers and Thunderstorms in the Morning, then a chance of Showers and Thunderstorms in the afternoon. Humid with Highs in the upper 80s. North Winds around 5 Mph. Chance of rain 50 percent. Heat index Values up to 100.
Tonight 17 Jul St. Charles
Mostly cloudy with a chance of Showers and Thunderstorms. Lows in the lower 70s. Northeast Winds around 5 Mph. Chance of rain 50 percent.
O'Fallon Temperature Statistics
July Temperature
St. Louis, Spirit Of St. Louis Airport (10.6 miles)
Lowest 2 July, 2025
62.1 °FAverage July
79.5 °FHighest 4 July, 2025
93.7 °F
Climate (2020–Present)
St. Louis, Spirit Of St. Louis Airport (10.6 miles)
Average Low 2020–2025
45.8 °FAverage 2020–2025
56.8 °FAverage High 2020–2025
68 °F