| WXSIM Forecast for:
O'Fallon Issued by: OFallonweather.com |
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| Updated: Tuesday, 08-Sep-2026 04:00 pm | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Tonight |
Fair to partly cloudy in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Low 68°. Wind south around 6 mph, gusting to 22 mph. |
| Wednesday |
Partly to mostly sunny in the morning, becoming partly to mostly cloudy in the afternoon. A chance of rain. Scattered thunderstorms likely, some possibly severe. Very hot. High 95°. Heat index up to 101°. UV index up to 6. Wind south-southwest around 7 mph, gusting to 23 mph, in the morning, becoming west in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Wednesday night |
Mostly cloudy. Patchy light fog in the evening, then moderate fog after midnight. A chance of rain in the evening, then rain likely after midnight. Scattered thunderstorms likely. Warm. Low 72°. Wind south around 3 mph in the evening, becoming west-northwest after midnight. Chance of precipitation 70 percent. Precipitation mostly around half an inch. |
| Thursday |
Mostly cloudy to cloudy. Light to moderate fog in the morning. A chance of rain in the morning, then a slight chance of rain in the afternoon. Scattered thunderstorms likely. High 81°. UV index up to 5. Wind west-northwest around 3 mph, gusting to 20 mph, in the morning, becoming north-northeast in the afternoon. Chance of precipitation 60 percent. Precipitation mostly less than a quarter of an inch. |
| Thursday night |
Partly to mostly cloudy. Low 68°. Wind north-northeast around 2 mph, gusting to 18 mph, in the evening, becoming east-northeast after midnight. |
| Friday |
Mostly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Warm. High 84°. UV index up to 4. Wind east-southeast around 4 mph, gusting to 21 mph. |
| Friday night |
Clear. Patchy light fog in the evening, then light to moderate fog after midnight. Low 67°. Wind southeast around 4 mph, gusting to 16 mph. |
| Saturday |
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. Hot. High 89°. Heat index up to 95°. UV index up to 7. Wind southwest around 4 mph, gusting to 22 mph. |
| Saturday night |
Partly to mostly cloudy in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Low 69°. Wind east-northeast around 2 mph in the evening, becoming south-southeast after midnight. |
| Sunday |
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Patchy light fog in the morning. Hot. High 89°. Heat index up to 96°. UV index up to 5. Wind south-southeast around 4 mph, gusting to 20 mph. |
| Sunday night |
Partly cloudy. Patchy light fog. Warm. Low 72°. Wind south-southeast around 5 mph, gusting to 15 mph. |
| Monday |
Mostly cloudy in the morning, becoming mostly sunny in the afternoon. A chance of rain. Scattered thundershowers possible. Hot. High 90°. Heat index up to 98°. UV index up to 6. Wind south-southeast around 4 mph, gusting to 15 mph, in the morning, becoming 7 mph, gusting to 24 mph, in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Monday night |
Fair to partly cloudy in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Warm. Low 72°. Wind south around 7 mph, gusting to 17 mph. |
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