WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Sunday, 09-Aug-2026 05:00 am
 
Today

Chance rain
Hot!
Chance rain
Hot!
Tonight

Fog late
Fog late
Monday

Fog a.m.
Hot!
Fog a.m.
Hot!
Monday
night
Thunder storm
Thunder storm
Tuesday

Mostly Sunny
Hot!
Mostly Sunny
Hot!
Tuesday
night
Partly Cloudy
Partly Cloudy
Wednesday

Mostly Sunny
Hot!
Mostly Sunny
Hot!
Wednesday
night
Thunder storm
Thunder storm
.1 in. <.1 in. .1 in.
High: 94° Low: 75° High: 96° Low: 76° High: 96° Low: 74° High: 99° Low: 74°
Heat: 102°   Heat: 108°   Heat: 107°   Heat: 107°  
SSW
5-25→8-25
mph
SSW
6-19
mph
SSW
8-23
mph
SSW
5-17
mph
SSW
7-25
mph
SSW
6-18
mph
WSW
6-25
mph
WNW→NE
2-16
mph
UV: 8
 Very High 
UV: 8
 Very High 
UV: 8
 Very High 
UV: 9
 Very High 

 

Today
 
Partly cloudy in the morning, becoming partly to mostly sunny in the afternoon. A chance of rain. Hot. High 94°. Heat index up to 102°. UV index up to 8. Wind south-southwest around 5 mph, gusting to 25 mph, in the morning, becoming 8 mph, gusting to 25 mph, in the afternoon. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Tonight
 
Fair in the evening, becoming fair to partly cloudy after midnight. Patchy light fog after midnight. Low 75°. Wind south-southwest around 6 mph, gusting to 19 mph.
Monday
 
Partly cloudy. Patchy light fog in the morning. Very hot. High 96°. Heat index up to 108°. UV index up to 8. Wind south-southwest around 8 mph, gusting to 23 mph.
Monday night
 
Partly cloudy. Patchy light fog after midnight. A chance of rain. Scattered thundershowers possible. Low 76°. Wind south-southwest around 5 mph, gusting to 17 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Tuesday
 
Mostly sunny in the morning, becoming sunny in the afternoon. Very hot. High 96°. Heat index up to 107°. UV index up to 8. Wind south-southwest around 7 mph, gusting to 25 mph.
Tuesday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Low 74°. Wind south-southwest around 6 mph, gusting to 18 mph.
Wednesday
 
Partly to mostly sunny. Very hot. High 99°. Heat index up to 107°. UV index up to 9. Wind west-southwest around 6 mph, gusting to 25 mph.
Wednesday night
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Scattered thunderstorms likely. Low 74°. Wind west-northwest around 2 mph, gusting to 16 mph, in the evening, becoming northeast after midnight. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Thursday
 
Partly to mostly cloudy. Patchy light fog in the morning. A chance of rain in the morning, then a slight chance of rain in the afternoon. Scattered thunderstorms likely. Hot. High 90°. Heat index up to 97°. UV index up to 7. Wind east-northeast around 5 mph, gusting to 22 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Thursday night
 
Partly to mostly cloudy. Light to moderate fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Scattered thunderstorms likely. Low 72°. Wind east around 7 mph, gusting to 20 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Friday
 
Partly to mostly cloudy in the morning, becoming partly cloudy in the afternoon. Light to moderate fog in the morning. A slight chance of rain. Scattered thundershowers possible. Hot. High 90°. Heat index up to 97°. UV index up to 6. Wind east around 5 mph, gusting to 22 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Friday night
 
Partly cloudy in the evening, becoming mostly cloudy after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thundershowers possible. Low 70°. Wind east around 8 mph, gusting to 21 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Saturday
 
Cloudy in the morning, becoming partly to mostly cloudy in the afternoon. A chance of rain. Precipitation showery or intermittent. High 85°. UV index up to 6. Wind east around 7 mph, gusting to 22 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Saturday night
 
Partly cloudy in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Relatively cool. Low 65°. Wind east around 6 mph, gusting to 20 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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