| WXSIM Forecast for:
O'Fallon Issued by: OFallonweather.com |
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| Updated: Monday, 20-Jul-2026 04:00 pm | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Tonight |
Partly cloudy. Patchy light fog in the evening, then moderate fog after midnight. Rain likely. Scattered thundershowers possible. Low 77°. Wind south-southwest around 4 mph, gusting to 22 mph. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch. |
| Tuesday |
Partly cloudy. Moderate fog in the morning. Rain likely. Scattered thunderstorms likely. High 90°. Heat index up to 99°. UV index up to 10. Wind northwest around 5 mph, gusting to 19 mph, in the morning, becoming 9 mph, gusting to 22 mph, in the afternoon. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch. |
| Tuesday night |
Fair. Patchy light fog in the evening, then moderate fog after midnight. A chance of rain. Low 70°. Wind north around 7 mph, gusting to 20 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch. |
| Wednesday |
Partly cloudy in the morning, becoming mostly cloudy in the afternoon. Moderate fog in the morning. A chance of rain. High 82°. UV index up to 6. Wind north around 7 mph, gusting to 26 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch. |
| Wednesday night |
Partly to mostly cloudy in the evening, becoming fair after midnight. Patchy light fog after midnight. A slight chance of rain in the evening. Relatively cool. Low 63°. Wind northeast around 5 mph, gusting to 24 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Thursday |
Partly cloudy in the morning, becoming partly to mostly sunny in the afternoon. Patchy light fog in the morning. High 83°. UV index up to 9. Wind east around 5 mph, gusting to 24 mph. |
| Thursday night |
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. A chance of rain after midnight. Relatively cool. Low 63°. Wind east around 4 mph, gusting to 23 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch. |
| Friday |
Mostly cloudy to cloudy in the morning, becoming cloudy in the afternoon. Patchy light fog. Rain very likely. Relatively cool. High 73°. UV index up to 5. Wind east-southeast around 3 mph. Chance of precipitation 80 percent. Precipitation mostly around an inch. |
| Friday night |
Mostly cloudy. Patchy light fog. A chance of rain. Precipitation showery or intermittent. Low 68°. Wind east-southeast around 3 mph, gusting to 15 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch. |
| Saturday |
Partly cloudy. Patchy light fog in the morning. A chance of rain. Precipitation showery or intermittent. High 89°. Heat index up to 94°. UV index up to 7. Wind east-southeast around 4 mph, gusting to 22 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch. |
| Saturday night |
Mostly clear in the evening, becoming partly cloudy after midnight. Light to moderate fog after midnight. Low 70°. Wind east-northeast around 2 mph, gusting to 20 mph, in the evening, becoming east-southeast after midnight. |
| Sunday |
Sunny. Light to moderate fog in the morning. Hot. High 93°. Heat index up to 100°. UV index up to 9. Wind west-southwest around 6 mph, gusting to 22 mph. |
| Sunday night |
Fair to partly cloudy. Patchy light fog after midnight. Low 71°. Wind west-northwest around 3 mph, gusting to 15 mph, in the evening, becoming north after midnight. |
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