| WXSIM Forecast for:
O'Fallon Issued by: OFallonweather.com |
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| Updated: Wednesday, 12-Aug-2026 04:00 pm | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Tonight |
Partly to mostly cloudy in the evening, becoming partly cloudy after midnight. Patchy light fog in the evening, then moderate fog after midnight. Rain likely. Thunderstorms very likely, some severe. Low 76°. Wind south-southeast around 3 mph. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch. |
| Thursday |
Partly to mostly cloudy in the morning, becoming partly to mostly sunny in the afternoon. Light to moderate fog in the morning. Rain likely. Scattered thunderstorms likely. Hot. High 92°. Heat index up to 103°. UV index up to 8. Wind east around 4 mph, gusting to 19 mph, in the morning, becoming south-southeast in the afternoon. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch. |
| Thursday night |
Partly cloudy. Light to moderate fog in the evening, then moderate fog after midnight. Rain likely. Scattered thundershowers possible. Low 76°. Wind east-southeast around 4 mph in the evening, becoming south after midnight. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch. |
| Friday |
Partly cloudy in the morning, becoming mostly sunny in the afternoon. Patchy light fog in the morning. A chance of rain. Scattered thundershowers possible. Hot. High 94°. Heat index up to 108°. UV index up to 8. Wind south around 4 mph, gusting to 18 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch. |
| Friday night |
Mostly clear in the evening, becoming clear after midnight. Low 75°. Wind south around 5 mph. |
| Saturday |
Partly to mostly sunny in the morning, becoming sunny in the afternoon. Very hot. High 99°. Heat index up to 111°. UV index up to 8. Wind southwest around 6 mph, gusting to 21 mph. |
| Saturday night |
Clear in the evening, becoming fair after midnight. Low 75°. Wind south-southwest around 4 mph. |
| Sunday |
Sunny. Very hot. High 98°. Heat index up to 107°. UV index up to 9. Wind southwest around 6 mph, gusting to 24 mph, in the morning, becoming west-northwest in the afternoon. |
| Sunday night |
Partly cloudy in the evening, becoming mostly cloudy after midnight. Light to moderate fog after midnight. A chance of rain in the evening, then rain likely after midnight. Scattered thundershowers possible. Low 71°. Wind north around 4 mph, gusting to 16 mph. Chance of precipitation 80 percent. Precipitation mostly between a quarter and half an inch. |
| Monday |
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Moderate fog in the morning. Rain likely in the morning, then a chance of rain in the afternoon. Precipitation showery or intermittent. High 88°. Heat index up to 93°. UV index up to 6. Wind north around 5 mph, gusting to 23 mph. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch. |
| Monday night |
Partly cloudy. Patchy light fog after midnight. Low 68°. Wind northeast around 4 mph, gusting to 21 mph. |
| Tuesday |
Partly to mostly sunny in the morning, becoming sunny in the afternoon. Patchy light fog in the morning. Hot. High 90°. Heat index up to 95°. UV index up to 8. Wind east-southeast around 4 mph, gusting to 21 mph. |
| Tuesday night |
Mostly clear in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. Low 68°. Wind east around 6 mph, gusting to 19 mph. |
WXSIM forecast formatting script by Saratoga-Weather.org.
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