| WXSIM Forecast for:
O'Fallon Issued by: OFallonweather.com |
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| Updated: Wednesday, 16-Sep-2026 04:00 pm | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Tonight |
Partly cloudy in the evening, becoming fair after midnight. Patchy light fog in the evening, then moderate fog after midnight. A slight chance of rain. Warm. Low 73°. Wind south around 3 mph, gusting to 17 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch. |
| Thursday |
Mostly sunny. Moderate fog in the morning. Extremely hot. High 96°. Heat index up to 106°. UV index up to 7. Wind southwest around 5 mph, gusting to 23 mph. |
| Thursday night |
Fair in the evening, becoming clear after midnight. Patchy light fog after midnight. Warm. Low 70°. Wind west-southwest near calm in the evening, becoming north-northeast after midnight. |
| Friday |
Sunny in the morning, becoming partly to mostly sunny in the afternoon. Patchy light fog in the morning. Very hot. High 93°. Heat index up to 99°. UV index up to 6. Wind east-northeast around 3 mph, gusting to 20 mph, in the morning, becoming south-southeast in the afternoon. |
| Friday night |
Fair in the evening, becoming partly cloudy after midnight. Warm. Low 69°. Wind south-southeast around 4 mph. |
| Saturday |
Partly cloudy. Light to moderate fog in the morning. Very hot. High 94°. Heat index up to 100°. UV index up to 6. Wind south-southwest around 5 mph, gusting to 20 mph. |
| Saturday night |
Partly cloudy. Warm. Low 69°. Wind south around 2 mph in the evening, becoming southwest after midnight. |
| Sunday |
Partly cloudy in the morning, becoming partly to mostly sunny in the afternoon. Very hot. High 93°. Heat index up to 97°. UV index up to 7. Wind north around 3 mph, gusting to 21 mph, in the morning, becoming northwest in the afternoon. |
| Sunday night |
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Low 65°. Wind north-northeast around 4 mph. |
| Monday |
Mostly cloudy in the morning, becoming partly to mostly sunny in the afternoon. Moderate fog in the afternoon. A slight chance of rain in the morning, then rain likely in the afternoon. Warm. High 83°. UV index up to 7. Wind north-northeast around 5 mph, gusting to 23 mph, in the morning, becoming northwest in the afternoon. Chance of precipitation 70 percent. Precipitation mostly around half an inch. |
| Monday night |
Moderate fog. A chance of rain in the evening, then a slight chance of rain after midnight. Low 61°. Wind north around 6 mph, gusting to 15 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch. |
| Tuesday |
Partly to mostly sunny in the morning, becoming mostly cloudy in the afternoon. Light to moderate fog in the morning. High 78°. UV index up to 4. Wind north-northwest around 6 mph, gusting to 23 mph. |
| Tuesday night |
Fair to partly cloudy in the evening, becoming clear after midnight. Light to moderate fog after midnight. Low 55°. Wind north around 5 mph, gusting to 16 mph. |
WXSIM forecast formatting script by Saratoga-Weather.org.