| WXSIM Forecast for:
O'Fallon Issued by: OFallonweather.com |
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| Updated: Sunday, 13-Sep-2026 04:00 pm | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Tonight |
Partly cloudy in the evening, becoming fair after midnight. Patchy light fog after midnight. Low 59°. Wind northeast around 5 mph, gusting to 21 mph. |
| Monday |
Partly to mostly sunny in the morning, becoming mostly sunny in the afternoon. Patchy light fog in the morning. Hot. High 86°. UV index up to 7. Wind east-southeast around 8 mph, gusting to 26 mph. |
| Monday night |
Partly cloudy in the evening, becoming mostly clear after midnight. Low 62°. Wind southeast around 8 mph, gusting to 21 mph. |
| Tuesday |
Mostly sunny in the morning, becoming partly to mostly cloudy in the afternoon. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thunderstorms likely. Unusually hot. High 90°. UV index up to 5. Wind south-southwest around 6 mph, gusting to 19 mph, in the morning, becoming west-southwest in the afternoon. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch. |
| Tuesday night |
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 thundershowers possible. Low 66°. Wind east-northeast around 2 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch. |
| Wednesday |
Partly to mostly sunny. Light to moderate fog in the morning. A slight chance of rain. Scattered thundershowers possible. Very hot. High 91°. Heat index up to 96°. UV index up to 6. Wind east-northeast around 3 mph, gusting to 18 mph, in the morning, becoming south in the afternoon. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch. |
| Wednesday night |
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Light to moderate fog. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thundershowers possible. Low 69°. Wind south around 4 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Thursday |
Partly cloudy. A chance of rain. Scattered thundershowers possible. Very hot. High 93°. Heat index up to 99°. UV index up to 6. Wind southwest around 4 mph, gusting to 20 mph, in the morning, becoming west-northwest in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Thursday night |
Partly cloudy. Light to moderate fog after midnight. A slight chance of rain. Scattered thundershowers possible. Low 67°. Wind northeast around 2 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch. |
| Friday |
Mostly sunny in the morning, becoming sunny in the afternoon. Light to moderate fog in the morning. Unusually hot. High 89°. Heat index up to 94°. UV index up to 7. Wind east around 3 mph. |
| Friday night |
Partly cloudy in the evening, becoming fair after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. A slight chance of rain. Scattered thundershowers possible. Low 67°. Wind east around 4 mph in the evening, becoming southeast after midnight. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch. |
| Saturday |
Mostly sunny in the morning, becoming partly to mostly sunny in the afternoon. Patchy light fog in the morning. Very hot. High 94°. Heat index up to 99°. UV index up to 5. Wind southwest around 8 mph, gusting to 23 mph. |
| Saturday night |
Partly cloudy. A slight chance of rain. Scattered thundershowers possible. Low 66°. Wind northwest around 4 mph in the evening, becoming north-northeast after midnight. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch. |
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