WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Friday, 24-Jul-2026 04:00 pm
 
Tonight

Chance rain
Chance rain
Saturday

Thunder storm
Thunder storm
Saturday
night
Chance rain
Chance rain
Sunday

Fog a.m.
Hot!
Fog a.m.
Hot!
Sunday
night
Fog late
Fog late
Monday

Fog a.m.
Hot!
Fog a.m.
Hot!
Monday
night
Clear
Clear
Tuesday

Partly Cloudy
Hot!
Partly Cloudy
Hot!
<.25 in. .1 in. .1 in. <.1 in.
Low: 67° High: 89° Low: 72° High: 94° Low: 74° High: 97° Low: 73° High: 97°
  Heat: 95°   Heat: 104°   Heat: 108°   Heat: 103°
S
5-20
mph
S
4-22
mph
ESE→S
2
mph
SW
3-19
mph
SSW
3
mph
SW
6-21→10-25
mph
WSW→NW
5-17
mph
NW
6-24
mph
UV: 8
 Very High 
UV: 9
 Very High 
UV: 9
 Very High 
UV: 9
 Very High 

 

Tonight
 
Mostly cloudy to cloudy in the evening, becoming partly to mostly cloudy after midnight. Light to moderate fog after midnight. A chance of rain. Precipitation showery or intermittent. Relatively cool. Low 67°. Wind south around 5 mph, gusting to 20 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Saturday
 
Mostly cloudy to cloudy in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. A chance of rain. Scattered thundershowers possible. High 89°. Heat index up to 95°. UV index up to 8. Wind south around 4 mph, gusting to 22 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Saturday night
 
Partly cloudy in the evening, becoming mostly cloudy after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. A chance of rain. Low 72°. Wind east-southeast around 2 mph in the evening, becoming south after midnight. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Sunday
 
Partly to mostly sunny. Light to moderate fog in the morning. A chance of rain. Hot. High 94°. Heat index up to 104°. UV index up to 9. Wind southwest around 3 mph, gusting to 19 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Mostly clear in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. Low 74°. Wind south-southwest around 3 mph.
Monday
 
Sunny. Patchy light fog in the morning. Very hot. High 97°. Heat index up to 108°. UV index up to 9. Wind southwest around 6 mph, gusting to 21 mph, in the morning, becoming 10 mph, gusting to 25 mph, in the afternoon.
Monday night
 
Clear. Low 73°. Wind west-southwest around 5 mph, gusting to 17 mph, in the evening, becoming northwest after midnight.
Tuesday
 
Sunny in the morning, becoming partly cloudy in the afternoon. Very hot. High 97°. Heat index up to 103°. UV index up to 9. Wind northwest around 6 mph, gusting to 24 mph.
Tuesday night
 
Partly to mostly cloudy in the evening, becoming partly cloudy after midnight. Low 70°. Wind northeast around 4 mph, gusting to 21 mph, in the evening, becoming east after midnight.
Wednesday
 
Sunny. Hot. High 93°. Heat index up to 98°. UV index up to 9. Wind east-northeast around 3 mph, gusting to 21 mph.
Wednesday night
 
Clear in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Relatively cool. Low 67°. Wind east-northeast around 3 mph, gusting to 16 mph, in the evening, becoming southeast after midnight.
Thursday
 
Partly to mostly cloudy in the morning, becoming mostly cloudy in the afternoon. Patchy light fog in the morning. Hot. High 92°. UV index up to 8. Wind east-southeast around 5 mph, gusting to 24 mph.
Thursday night
 
Partly cloudy in the evening, becoming clear after midnight. Relatively cool. Low 66°. Wind east around 4 mph, gusting to 22 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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