WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Wednesday, 16-Sep-2026 05:00 am
 
Today

Partly Cloudy
Hot!
Partly Cloudy
Hot!
Tonight

Fog late
Fog late
Thursday

Fog a.m.
Hot!
Fog a.m.
Hot!
Thursday
night
Partly Cloudy
Partly Cloudy
Friday

Mostly Sunny
Hot!
Mostly Sunny
Hot!
Friday
night
Fog late
Fog late
Saturday

Partly Cloudy
Hot!
Partly Cloudy
Hot!
Saturday
night
Partly Cloudy
Partly Cloudy
High: 100° Low: 71° High: 100° Low: 70° High: 95° Low: 67° High: 96° Low: 69°
Heat: 108°   Heat: 108°   Heat: 101°   Heat: 100°  
SSW
4-24
mph
SSW
4-16
mph
WSW
5-24
mph
WSW→NNE
2
mph
ENE→SSE
3-22
mph
SE
5-15
mph
SW
6-23
mph
SW
3
mph
UV: 6
 High 
UV: 7
 High 
UV: 7
 High 
UV: 6
 High 

 

Today
 
Partly cloudy. Near record heat. High 100°. Heat index up to 108°. UV index up to 6. Wind south-southwest around 4 mph, gusting to 24 mph.
Tonight
 
Partly cloudy in the evening, becoming clear after midnight. Patchy light fog after midnight. Warm. Low 71°. Wind south-southwest around 4 mph, gusting to 16 mph.
Thursday
 
Sunny in the morning, becoming mostly sunny in the afternoon. Patchy light fog in the morning. Near record heat. High 100°. Heat index up to 108°. UV index up to 7. Wind west-southwest around 5 mph, gusting to 24 mph.
Thursday night
 
Fair to partly cloudy in the evening, becoming clear after midnight. Warm. Low 70°. Wind west-southwest around 2 mph in the evening, becoming north-northeast after midnight.
Friday
 
Sunny in the morning, becoming mostly sunny in the afternoon. Very hot. High 95°. Heat index up to 101°. UV index up to 7. Wind east-northeast around 3 mph, gusting to 22 mph, in the morning, becoming south-southeast in the afternoon.
Friday night
 
Fair. Patchy light fog after midnight. Low 67°. Wind southeast around 5 mph, gusting to 15 mph.
Saturday
 
Partly cloudy. Extremely hot. High 96°. Heat index up to 100°. UV index up to 6. Wind southwest around 6 mph, gusting to 23 mph.
Saturday night
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Warm. Low 69°. Wind southwest around 3 mph.
Sunday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Extremely hot. High 96°. UV index up to 6. Wind south-southwest around 2 mph, gusting to 22 mph, in the morning, becoming northwest in the afternoon.
Sunday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Low 66°. Wind northeast around 4 mph.
Monday
 
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. A slight chance of rain. Unusually hot. High 88°. UV index up to 5. Wind northwest around 4 mph, gusting to 24 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Monday night
 
Clear. Light to moderate fog after midnight. Low 60°. Wind north around 3 mph, gusting to 19 mph.
Tuesday
 
Sunny in the morning, becoming mostly sunny in the afternoon. Light to moderate fog in the morning. Warm. High 85°. UV index up to 6. Wind north around 2 mph, gusting to 21 mph, in the morning, becoming east-southeast in the afternoon.
Tuesday night
 
Partly cloudy in the evening, becoming fair after midnight. Light to moderate fog after midnight. Low 62°. Wind south-southeast around 4 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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