WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Friday, 04-Sep-2026 05:00 am
 
Today

Sunny
Hot!
Sunny
Hot!
Tonight

Fair
Fair
Saturday

Partly Cloudy
Hot!
Partly Cloudy
Hot!
Saturday
night
Fog late
Fog late
Sunday

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

Sunny
Sunny
Monday
night
Mostly Clear
Mostly Clear
High: 102° Low: 76° High: 99° Low: 71° High: 92° Low: 67° High: 92° Low: 65°
Heat: 110°   Heat: 108°   Heat: 97°      
SSW
4-25
mph
SSW
2-18
mph
W→NNW
4-21
mph
N
3
mph
ENE
6-24
mph
ENE
6-20
mph
E
5-24
mph
ESE
5-19
mph
UV: 8
 Very High 
UV: 7
 High 
UV: 6
 High 
UV: 8
 Very High 

 

Today
 
Sunny. Near record heat. High 102°. Heat index up to 110°. UV index up to 8. Wind south-southwest around 4 mph, gusting to 25 mph.
Tonight
 
Fair. Warm. Low 76°. Wind south-southwest around 2 mph, gusting to 18 mph.
Saturday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Extremely hot. High 99°. Heat index up to 108°. UV index up to 7. Wind west around 4 mph, gusting to 21 mph, in the morning, becoming north-northwest in the afternoon.
Saturday night
 
Fair to partly cloudy in the evening, becoming clear after midnight. Patchy light fog after midnight. Low 71°. Wind north around 3 mph.
Sunday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. Very hot. High 92°. Heat index up to 97°. UV index up to 6. Wind east-northeast around 6 mph, gusting to 24 mph.
Sunday night
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Low 67°. Wind east-northeast around 6 mph, gusting to 20 mph.
Monday
 
Sunny. Very hot. High 92°. UV index up to 8. Wind east around 5 mph, gusting to 24 mph.
Monday night
 
Mostly clear in the evening, becoming clear after midnight. Low 65°. Wind east-southeast around 5 mph, gusting to 19 mph.
Tuesday
 
Sunny. Patchy light fog in the morning. Very hot. High 95°. Heat index up to 98°. UV index up to 7. Wind south-southeast around 4 mph, gusting to 22 mph.
Tuesday night
 
Clear. Low 68°. Wind south-southeast around 6 mph, gusting to 15 mph.
Wednesday
 
Sunny in the morning, becoming mostly sunny in the afternoon. Extremely hot. High 100°. Heat index up to 105°. UV index up to 8. Wind west-southwest around 7 mph, gusting to 23 mph.
Wednesday night
 
Partly cloudy. Low 69°. Wind northeast around 4 mph.
Thursday
 
Partly to mostly sunny in the morning, becoming sunny in the afternoon. Very hot. High 94°. Heat index up to 98°. UV index up to 7. Wind northeast around 5 mph, gusting to 21 mph.
Thursday night
 
Mostly clear. Low 65°. Wind northeast around 7 mph, gusting to 15 mph, in the evening, becoming east-southeast after midnight.

WXSIM forecast formatting script by Saratoga-Weather.org.

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