WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Thursday, 03-Sep-2026 04:00 pm
 
Tonight

Clear
Clear
Friday

Sunny
Hot!
Sunny
Hot!
Friday
night
Mostly Clear
Mostly Clear
Saturday

Mostly Sunny
Hot!
Mostly Sunny
Hot!
Saturday
night
Clear
Clear
Sunday

Fog a.m.
Fog a.m.
Sunday
night
Partly Cloudy
Partly Cloudy
Monday

Partly Cloudy
Partly Cloudy
Low: 74° High: 98° Low: 73° High: 96° Low: 70° High: 92° Low: 67° High: 90°
  Heat: 107°   Heat: 104°   Heat: 97°    
S
5-22
mph
SSW
5-24
mph
S
3
mph
W→NNW
4-19
mph
NE
3
mph
NE
5-24
mph
ENE
6-19
mph
E
5-24
mph
UV: 7
 High 
UV: 6
 High 
UV: 7
 High 
UV: 8
 Very High 

 

Tonight
 
Fair in the evening, becoming clear after midnight. Warm. Low 74°. Wind south around 5 mph, gusting to 22 mph.
Friday
 
Sunny. Extremely hot. High 98°. Heat index up to 107°. UV index up to 7. Wind south-southwest around 5 mph, gusting to 24 mph.
Friday night
 
Mostly clear in the evening, becoming fair after midnight. Warm. Low 73°. Wind south around 3 mph.
Saturday
 
Partly to mostly sunny. Very hot. High 96°. Heat index up to 104°. UV index up to 6. Wind west around 4 mph, gusting to 19 mph, in the morning, becoming north-northwest in the afternoon.
Saturday night
 
Fair in the evening, becoming clear after midnight. Low 70°. Wind northeast around 3 mph.
Sunday
 
Sunny. Patchy light fog in the morning. Very hot. High 92°. Heat index up to 97°. UV index up to 7. Wind northeast around 5 mph, gusting to 24 mph.
Sunday night
 
Fair to partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Low 67°. Wind east-northeast around 6 mph, gusting to 19 mph.
Monday
 
Partly cloudy in the morning, becoming sunny in the afternoon. Hot. High 90°. UV index up to 8. Wind east around 5 mph, gusting to 24 mph.
Monday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Low 65°. Wind east around 5 mph, gusting to 19 mph.
Tuesday
 
Partly to mostly sunny in the morning, becoming sunny in the afternoon. Very hot. High 94°. UV index up to 7. Wind southeast around 5 mph, gusting to 22 mph.
Tuesday night
 
Mostly clear in the evening, becoming clear after midnight. Low 67°. Wind southeast around 7 mph, gusting to 16 mph, in the evening, becoming south after midnight.
Wednesday
 
Sunny in the morning, becoming partly to mostly cloudy in the afternoon. Extremely hot. High 99°. Heat index up to 103°. UV index up to 5. Wind west-southwest around 9 mph, gusting to 23 mph.
Wednesday night
 
Mostly clear in the evening, becoming clear after midnight. Low 68°. Wind east-northeast around 5 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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