O'Fallon Weather Forecast
- 59
- 60
Cloudy
- 20
- 71
Rain
- 18
- 27
Blustery
- 25
- 33
Partly Sunny
- 23
- 43
Partly Sunny
- 15
- 34
Partly Sunny
Today 27 Dec St. Clair
Cloudy. A chance of rain with a slight chance of Thunderstorms in the Morning, then rain with a chance of Thunderstorms in the afternoon. Breezy and not as cool with Highs around 70. Temperature falling into the lower 50s in the afternoon. South Winds 10 to 15 Mph with Gusts up to 30 Mph, becoming southwest 15 to 25 Mph with Gusts up to 40 Mph in the afternoon. Chance of rain 80 percent.
Tonight 27 Dec St. Clair
Mostly cloudy with a chance of rain in the Evening, then partly cloudy after midnight. Breezy and much cooler with Lows around 19. Northwest Winds 20 to 25 Mph. Gusts up to 45 Mph in the evening. Chance of rain 50 percent. Wind chill Values as low as 2 above after midnight.
O'Fallon Temperature Statistics
December Temperature
Belleville, Scott AFB/MidAmerica Airport (4.3 miles)
Lowest 14 December, 2025
7.5 °FAverage December
35.8 °FHighest 23 December, 2025
70.7 °F
Climate (2020–Present)
Belleville, Scott AFB/MidAmerica Airport (4.3 miles)
Average Low 2020–2025
47.6 °FAverage 2020–2025
57.4 °FAverage High 2020–2025
67.6 °F