| WXSIM Forecast for:
O'Fallon Issued by: OFallonweather.com |
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| Updated: Monday, 27-Jul-2026 04:00 pm | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Tonight |
Partly cloudy. Light to moderate fog after midnight. A chance of rain. Thunderstorms very likely, some severe. Low 78°. Wind west-southwest around 5 mph, gusting to 21 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch. |
| Tuesday |
Mostly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Rain likely. Scattered thunderstorms likely. Hot. High 93°. Heat index up to 103°. UV index up to 8. Wind northwest around 5 mph, gusting to 22 mph, in the morning, becoming north-northeast in the afternoon. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch. |
| Tuesday night |
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Light to moderate fog in the evening, then moderate fog after midnight. Rain likely. Low 73°. Wind northeast around 5 mph, gusting to 18 mph. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch. |
| Wednesday |
Mostly sunny in the morning, becoming sunny in the afternoon. Light to moderate fog in the morning. Hot. High 90°. Heat index up to 96°. UV index up to 9. Wind east around 5 mph, gusting to 24 mph. |
| Wednesday night |
Clear. Patchy light fog after midnight. Low 67°. Wind east around 3 mph, gusting to 22 mph. |
| Thursday |
Mostly sunny in the morning, becoming partly to mostly sunny in the afternoon. Patchy light fog in the morning. Hot. High 91°. Heat index up to 96°. UV index up to 8. Wind southeast around 4 mph, gusting to 22 mph. |
| Thursday night |
Partly cloudy. Patchy light fog after midnight. A chance of rain after midnight. Low 69°. Wind east around 5 mph, gusting to 19 mph, in the evening, becoming south-southeast after midnight. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch. |
| Friday |
Mostly cloudy. Light to moderate fog in the morning. A chance of rain in the morning, then rain likely in the afternoon. Precipitation showery or intermittent. High 86°. UV index up to 7. Wind south-southeast around 5 mph, gusting to 22 mph. Chance of precipitation 80 percent. Precipitation mostly between a quarter and half an inch. |
| Friday night |
Mostly cloudy in the evening, becoming cloudy after midnight. Moderate fog in the evening, then light to moderate fog after midnight. Rain. Thunderstorms very likely, some possibly severe. Low 74°. Wind south-southeast around 6 mph, gusting to 19 mph. Chance of precipitation near 100 percent. Precipitation mostly around an inch. |
| Saturday |
Cloudy in the morning, becoming mostly cloudy to cloudy in the afternoon. Light to moderate fog in the morning. A chance of rain in the morning, then rain likely in the afternoon. Thunderstorms very likely, some possibly severe. High 80°. UV index up to 4. Wind east-southeast around 7 mph, gusting to 24 mph, in the morning, becoming north-northeast in the afternoon. Chance of precipitation 70 percent. Precipitation mostly around a quarter of an inch. |
| Saturday night |
Cloudy in the evening, becoming fair to partly cloudy after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. Rain likely. Thunderstorms very likely, some possibly severe. Low 70°. Wind north-northeast around 8 mph, gusting to 22 mph. Chance of precipitation 60 percent. Precipitation mostly less than a tenth of an inch. |
| Sunday |
Sunny. Light to moderate fog in the morning. High 85°. UV index up to 9. Wind north-northeast around 10 mph, gusting to 28 mph. |
| Sunday night |
Clear. Light to moderate fog after midnight. Low 68°. Wind north around 3 mph, gusting to 22 mph. |
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