| WXSIM Forecast for:
O'Fallon Issued by: OFallonweather.com |
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| Updated: Tuesday, 18-Aug-2026 04:00 pm | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Tonight |
Fair to partly cloudy in the evening, becoming mostly cloudy after midnight. Moderate fog after midnight. A slight chance of rain in the evening, then rain likely after midnight. Scattered thundershowers possible. Low 72°. Wind east around 3 mph, gusting to 21 mph. Chance of precipitation 60 percent. Precipitation mostly between a quarter and half an inch. |
| Wednesday |
Mostly cloudy to cloudy in the morning, becoming mostly cloudy in the afternoon. Light to moderate fog in the morning. Rain likely. Scattered thunderstorms likely. High 83°. UV index up to 5. Wind southeast around 2 mph, gusting to 19 mph, in the morning, becoming east-northeast in the afternoon. Chance of precipitation 70 percent. Precipitation mostly around a quarter of an inch. |
| Wednesday night |
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Light to moderate fog in the evening, then moderate fog after midnight. A chance of rain. Scattered thundershowers possible. Low 71°. Wind east-northeast around 3 mph, gusting to 17 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch. |
| Thursday |
Partly to mostly sunny. Moderate fog in the morning. A chance of rain. High 84°. UV index up to 7. Wind northeast around 4 mph, gusting to 23 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Thursday night |
Clear in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Low 67°. Wind northeast around 2 mph, gusting to 18 mph, in the evening, becoming east after midnight. |
| Friday |
Sunny in the morning, becoming mostly sunny in the afternoon. Patchy light fog in the morning. High 87°. UV index up to 7. Wind south around 2 mph, gusting to 19 mph, in the morning, becoming southwest in the afternoon. |
| Friday night |
Fair in the evening, becoming clear after midnight. Light to moderate fog after midnight. Low 69°. Wind west-northwest near calm. |
| Saturday |
Mostly sunny. Light to moderate fog in the morning. High 86°. UV index up to 7. Wind northwest around 7 mph, gusting to 25 mph. |
| Saturday night |
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Patchy light fog after midnight. Low 66°. Wind north around 4 mph, gusting to 18 mph. |
| Sunday |
Partly cloudy. Patchy light fog in the morning. High 85°. UV index up to 8. Wind north around 3 mph, gusting to 21 mph. |
| Sunday night |
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Patchy light fog after midnight. Low 64°. Wind east-northeast around 3 mph, gusting to 17 mph. |
| Monday |
Partly to mostly sunny in the morning, becoming sunny in the afternoon. Patchy light fog in the morning. High 87°. UV index up to 8. Wind east-southeast around 6 mph, gusting to 23 mph. |
| Monday night |
Fair in the evening, becoming mostly cloudy to cloudy after midnight. Low 66°. Wind east-southeast around 5 mph, gusting to 20 mph. |
WXSIM forecast formatting script by Saratoga-Weather.org.