| WXSIM Forecast for:
O'Fallon Issued by: OFallonweather.com |
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| Updated: Monday, 31-Aug-2026 04:00 pm | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Tonight |
Clear. Low 72°. Wind south-southwest around 5 mph, gusting to 22 mph. |
| Tuesday |
Sunny. Extremely hot. High 99°. Heat index up to 104°. UV index up to 8. Wind south-southwest around 5 mph, gusting to 22 mph. |
| Tuesday night |
Clear. Low 72°. Wind south around 2 mph in the evening, becoming 6 mph after midnight. |
| Wednesday |
Sunny. Very hot. High 98°. Heat index up to 105°. UV index up to 8. Wind southwest around 6 mph, gusting to 23 mph. |
| Wednesday night |
Mostly clear in the evening, becoming clear after midnight. Low 72°. Wind south around 4 mph. |
| Thursday |
Sunny. Extremely hot. High 99°. Heat index up to 106°. UV index up to 8. Wind southwest around 5 mph, gusting to 23 mph. |
| Thursday night |
Fair in the evening, becoming clear after midnight. Low 72°. Wind south around 4 mph, gusting to 15 mph. |
| Friday |
Sunny. Very hot. High 98°. Heat index up to 107°. UV index up to 8. Wind south-southwest around 4 mph, gusting to 22 mph. |
| Friday night |
Fair to partly cloudy in the evening, becoming mostly clear after midnight. Low 73°. Wind south around 2 mph. |
| Saturday |
Mostly sunny in the morning, becoming partly cloudy in the afternoon. Very hot. High 99°. Heat index up to 108°. UV index up to 7. Wind west-southwest around 3 mph, gusting to 19 mph. |
| Saturday night |
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Moderate fog after midnight. Rain likely. Warm. Low 74°. Wind east-southeast around 2 mph in the evening, becoming 6 mph after midnight. Chance of precipitation 60 percent. Precipitation mostly between a quarter and half an inch. |
| Sunday |
Partly cloudy. Patchy light fog in the morning. Very hot. High 96°. Heat index up to 108°. UV index up to 7. Wind south around 3 mph, gusting to 17 mph. |
| Sunday night |
Partly cloudy in the evening, becoming mostly cloudy to cloudy after midnight. A slight chance of rain. Warm. Low 73°. Wind east-southeast around 8 mph, gusting to 16 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch. |
WXSIM forecast formatting script by Saratoga-Weather.org.