| WXSIM Forecast for:
O'Fallon Issued by: OFallonweather.com |
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| Updated: Thursday, 17-Sep-2026 04:00 pm | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Tonight |
Fair to partly cloudy in the evening, becoming fair after midnight. Warm. Low 68°. Wind south-southwest around 5 mph, gusting to 19 mph, in the evening, becoming north-northeast around 2 mph after midnight. |
| Friday |
Sunny in the morning, becoming mostly sunny in the afternoon. Very hot. High 92°. Heat index up to 98°. UV index up to 7. Wind southeast around 3 mph, gusting to 20 mph. |
| Friday night |
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Moderate fog after midnight. A chance of rain. Warm. Low 70°. Wind south-southeast around 4 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Saturday |
Partly to mostly sunny in the morning, becoming mostly cloudy in the afternoon. Moderate fog in the morning. A slight chance of rain in the morning. Very hot. High 91°. Heat index up to 97°. UV index up to 5. Wind south-southwest around 5 mph, gusting to 20 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Saturday night |
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Warm. Low 69°. Wind south-southeast around 3 mph. |
| Sunday |
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Very hot. High 91°. Heat index up to 96°. UV index up to 6. Wind southwest around 4 mph, gusting to 21 mph. |
| Sunday night |
Partly to mostly cloudy in the evening, becoming cloudy after midnight. Patchy light fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Warm. Low 70°. Wind north-northeast around 2 mph in the evening, becoming south-southwest after midnight. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch. |
| Monday |
Cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Patchy light fog in the morning. Rain likely. Precipitation showery or intermittent. High 77°. UV index up to 5. Wind north-northwest near calm in the morning, becoming 5 mph, gusting to 20 mph, in the afternoon. Chance of precipitation 60 percent. Precipitation mostly around a quarter of an inch. |
| Monday night |
Mostly cloudy in the evening, becoming cloudy after midnight. Moderate fog in the evening, then light to moderate fog after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Low 64°. Wind north around 6 mph, gusting to 20 mph. Chance of precipitation 60 percent. Precipitation mostly around a quarter of an inch. |
| Tuesday |
Mostly cloudy to cloudy. Patchy light fog in the morning. A chance of rain. High 71°. Wind north-northeast around 8 mph, gusting to 26 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Tuesday night |
Mostly cloudy to cloudy. Low 59°. Wind north-northeast around 6 mph, gusting to 23 mph. |
| Wednesday |
Mostly cloudy to cloudy in the morning, becoming sunny in the afternoon. High 76°. UV index up to 6. Wind north-northeast around 4 mph, gusting to 23 mph. |
| Wednesday night |
Fair in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. Low 57°. Wind north-northeast around 4 mph, gusting to 17 mph. |
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