| WXSIM Forecast for:
O'Fallon Issued by: OFallonweather.com |
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| Updated: Thursday, 20-Aug-2026 04:00 pm | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Tonight |
Fair to partly cloudy in the evening, becoming fair after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. A chance of rain. Low 68°. Wind northeast around 3 mph, gusting to 19 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch. |
| Friday |
Mostly sunny. Light to moderate fog in the morning. Hot. High 87°. Heat index up to 91°. UV index up to 7. Wind south-southeast around 2 mph, gusting to 21 mph, in the morning, becoming west-southwest in the afternoon. |
| Friday night |
Fair in the evening, becoming fair to partly cloudy after midnight. Patchy light fog after midnight. A slight chance of rain after midnight. Low 68°. Wind west around 3 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch. |
| Saturday |
Partly to mostly sunny in the morning, becoming sunny in the afternoon. Light to moderate fog in the morning. A chance of rain. High 86°. UV index up to 7. Wind northwest around 5 mph, gusting to 22 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Saturday night |
Clear. Patchy light fog after midnight. Low 65°. Wind north around 4 mph, gusting to 18 mph. |
| Sunday |
Sunny in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. High 84°. UV index up to 7. Wind north around 3 mph, gusting to 22 mph. |
| Sunday night |
Partly cloudy. Patchy light fog after midnight. A slight chance of rain. Low 64°. Wind east around 2 mph, gusting to 17 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch. |
| Monday |
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Patchy light fog in the morning. A slight chance of rain in the morning, then a chance of rain in the afternoon. Precipitation showery or intermittent. High 83°. UV index up to 7. Wind east around 5 mph, gusting to 23 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch. |
| Monday night |
Partly cloudy. Moderate fog. A chance of rain in the evening, then rain likely after midnight. Low 67°. Wind east around 6 mph, gusting to 17 mph. Chance of precipitation 70 percent. Precipitation mostly between half an inch and one inch. |
| Tuesday |
Mostly cloudy to cloudy. Moderate fog in the morning. A chance of rain. Precipitation showery or intermittent. High 83°. UV index up to 5. Wind east-southeast around 5 mph, gusting to 19 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Tuesday night |
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Low 70°. Wind southeast around 2 mph. |
| Wednesday |
Partly to mostly cloudy in the morning, becoming mostly cloudy in the afternoon. A chance of rain. Scattered thunderstorms likely. High 85°. UV index up to 6. Wind west around 3 mph, gusting to 17 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Wednesday night |
Fair in the evening, becoming clear after midnight. Patchy light fog in the evening, then moderate fog after midnight. Low 67°. Wind west-northwest around 3 mph, gusting to 15 mph, in the evening, becoming north-northwest after midnight. |
WXSIM forecast formatting script by Saratoga-Weather.org.
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