WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Tuesday, 11-Aug-2026 05:00 am
 
Today

Thunder storm
Hot!
Thunder storm
Hot!
Tonight

Partly Cloudy
Partly Cloudy
Wednesday

Thunder storm
Hot!
Thunder storm
Hot!
Wednesday
night
Thunder storm
Thunder storm
Thursday

Thunder storm
Hot!
Thunder storm
Hot!
Thursday
night
Thunder storm
Thunder storm
Friday

Fog a.m.
Hot!
Fog a.m.
Hot!
Friday
night
Fog late
Fog late
<.1 in. .1 in. <.1 in. <.1 in. <.1 in.
High: 98° Low: 79° High: 96° Low: 78° High: 94° Low: 76° High: 95° Low: 73°
Heat: 112°   Heat: 111°   Heat: 107°   Heat: 106°  
SW
7-27
mph
SW
5-20
mph
SW
7-25
mph
SSE→SW
3
mph
NE→SSE
4-22
mph
ESE
4-17
mph
ESE
4-23
mph
SE
6-20
mph
UV: 8
 Very High 
UV: 8
 Very High 
UV: 7
 High 
UV: 7
 High 

 

Today
 
Partly to mostly sunny. A chance of rain. Scattered thunderstorms likely. Very hot. High 98°. Heat index up to 112°. UV index up to 8. Wind southwest around 7 mph, gusting to 27 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Tonight
 
Fair to partly cloudy. Warm. Low 79°. Wind southwest around 5 mph, gusting to 20 mph.
Wednesday
 
Partly cloudy. A chance of rain. Scattered thunderstorms likely, some possibly severe. Very hot. High 96°. Heat index up to 111°. UV index up to 8. Wind southwest around 7 mph, gusting to 25 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Wednesday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. A chance of rain. Scattered thunderstorms likely. Warm. Low 78°. Wind south-southeast around 3 mph in the evening, becoming southwest after midnight. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Thursday
 
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. A chance of rain. Scattered thunderstorms likely, some possibly severe. Hot. High 94°. Heat index up to 107°. UV index up to 7. Wind northeast around 4 mph, gusting to 22 mph, in the morning, becoming south-southeast in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Thursday night
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. A chance of rain. Scattered thunderstorms likely. Low 76°. Wind east-southeast around 4 mph, gusting to 17 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Friday
 
Partly cloudy. Patchy light fog in the morning. Very hot. High 95°. Heat index up to 106°. UV index up to 7. Wind east-southeast around 4 mph, gusting to 23 mph.
Friday night
 
Clear in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Low 73°. Wind southeast around 6 mph, gusting to 20 mph.
Saturday
 
Sunny. Patchy light fog in the morning. Very hot. High 99°. Heat index up to 109°. UV index up to 8. Wind south-southwest around 6 mph, gusting to 22 mph.
Saturday night
 
Clear. Low 73°. Wind southeast around 4 mph in the evening, becoming south after midnight.
Sunday
 
Mostly sunny in the morning, becoming partly to mostly sunny in the afternoon. Very hot. High 101°. Heat index up to 108°. UV index up to 9. Wind southwest around 9 mph, gusting to 27 mph, in the morning, becoming west in the afternoon.
Sunday night
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Light to moderate fog after midnight. A chance of rain. Scattered thundershowers possible. Low 71°. Wind north-northeast around 5 mph, gusting to 16 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Monday
 
Sunny in the morning, becoming partly cloudy in the afternoon. Light to moderate fog in the morning. Hot. High 91°. Heat index up to 96°. UV index up to 8. Wind northeast around 7 mph, gusting to 25 mph.
Monday night
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. Low 68°. Wind east around 5 mph, gusting to 22 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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