| WXSIM Forecast for:
O'Fallon Issued by: OFallonweather.com |
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| Updated: Tuesday, 11-Aug-2026 04:00 pm | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Tonight |
Partly cloudy. Patchy light fog in the evening, then light to moderate fog after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thunderstorms likely, some possibly severe. Low 77°. Wind south around 6 mph, gusting to 21 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch. |
| Wednesday |
Partly cloudy. Light to moderate fog in the morning. A chance of rain. Scattered thunderstorms likely. Hot. High 92°. Heat index up to 103°. UV index up to 7. Wind west around 6 mph, gusting to 21 mph, in the morning, becoming south-southwest in the afternoon. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch. |
| Wednesday night |
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Moderate fog in the evening, then moderate to dense fog after midnight. A chance of rain. Scattered thunderstorms likely. Low 76°. Wind east-southeast around 5 mph, gusting to 16 mph, in the evening, becoming south after midnight. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch. |
| Thursday |
Partly to mostly cloudy in the morning, becoming partly cloudy in the afternoon. Light to moderate fog in the morning. A chance of rain. Scattered thunderstorms likely. Hot. High 94°. Heat index up to 107°. UV index up to 7. Wind south around 5 mph, gusting to 22 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch. |
| Thursday night |
Mostly clear in the evening, becoming partly cloudy after midnight. Low 76°. Wind southeast around 5 mph, gusting to 17 mph, in the evening, becoming southwest after midnight. |
| Friday |
Partly cloudy. Very hot. High 96°. Heat index up to 106°. UV index up to 7. Wind east-southeast around 4 mph, gusting to 22 mph. |
| Friday night |
Fair in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Low 72°. Wind east-southeast around 4 mph, gusting to 17 mph. |
| Saturday |
Sunny. Very hot. High 100°. Heat index up to 109°. UV index up to 8. Wind southwest around 4 mph, gusting to 21 mph. |
| Saturday night |
Clear. Low 73°. Wind south around 4 mph. |
| Sunday |
Sunny in the morning, becoming partly to mostly sunny in the afternoon. Very hot. High 101°. Heat index up to 108°. UV index up to 9. Wind west-southwest around 7 mph, gusting to 24 mph. |
| Sunday night |
Partly cloudy. Low 70°. Wind north around 5 mph, gusting to 16 mph. |
| Monday |
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Hot. High 92°. Heat index up to 96°. UV index up to 8. Wind north-northeast around 5 mph, gusting to 24 mph. |
| Monday night |
Partly to mostly cloudy in the evening, becoming clear after midnight. Patchy light fog after midnight. Low 65°. Wind northeast around 6 mph, gusting to 20 mph, in the evening, becoming east after midnight. |
WXSIM forecast formatting script by Saratoga-Weather.org.