WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Friday, 07-Aug-2026 05:00 am
 
Today

Chance rain
Chance rain
Tonight

Thunder storm
Thunder storm
Saturday

Fog a.m.
Fog a.m.
Saturday
night
Fog late
Fog late
Sunday

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

Fog a.m.
Hot!
Fog a.m.
Hot!
Monday
night
Partly Cloudy
Partly Cloudy
.1 in. <.1 in. <.1 in.
High: 87° Low: 70° High: 88° Low: 70° High: 91° Low: 71° High: 92° Low: 73°
    Heat: 93°   Heat: 99°   Heat: 101°  
SW→W
4-21
mph
WSW
5
mph
WNW→ENE
4-20
mph
SE
3
mph
SSE→SSW
7-22
mph
SSW
7-15
mph
SSW
8-25
mph
SSW
6-18
mph
UV: 7
 High 
UV: 8
 Very High 
UV: 8
 Very High 
UV: 8
 Very High 

 

Today
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. A chance of rain. High 87°. UV index up to 7. Wind southwest around 4 mph, gusting to 21 mph, in the morning, becoming west in the afternoon. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Tonight
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Moderate fog after midnight. A chance of rain. Scattered thundershowers possible. Low 70°. Wind west-southwest around 5 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Saturday
 
Partly to mostly sunny. Light to moderate fog in the morning. A chance of rain. High 88°. Heat index up to 93°. UV index up to 8. Wind west-northwest around 4 mph, gusting to 20 mph, in the morning, becoming east-northeast in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Saturday night
 
Fair. Patchy light fog after midnight. Low 70°. Wind southeast around 3 mph.
Sunday
 
Sunny. Light to moderate fog in the morning. Hot. High 91°. Heat index up to 99°. UV index up to 8. Wind south-southeast around 7 mph, gusting to 22 mph, in the morning, becoming south-southwest in the afternoon.
Sunday night
 
Mostly clear in the evening, becoming clear after midnight. Patchy light fog after midnight. Low 71°. Wind south-southwest around 7 mph, gusting to 15 mph.
Monday
 
Mostly sunny in the morning, becoming sunny in the afternoon. Patchy light fog in the morning. Hot. High 92°. Heat index up to 101°. UV index up to 8. Wind south-southwest around 8 mph, gusting to 25 mph.
Monday night
 
Fair to partly cloudy in the evening, becoming mostly clear after midnight. Low 73°. Wind south-southwest around 6 mph, gusting to 18 mph.
Tuesday
 
Mostly sunny. Very hot. High 96°. Heat index up to 104°. UV index up to 8. Wind southwest around 7 mph, gusting to 24 mph.
Tuesday night
 
Mostly clear. Patchy light fog after midnight. Low 73°. Wind south-southwest around 5 mph, gusting to 17 mph.
Wednesday
 
Partly cloudy. A slight chance of rain. Scattered thunderstorms likely. Hot. High 95°. Heat index up to 102°. UV index up to 8. Wind west-southwest around 6 mph, gusting to 23 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Wednesday night
 
Mostly cloudy in the evening, becoming fair to partly cloudy after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thunderstorms likely. Low 71°. Wind northwest around 5 mph, gusting to 20 mph, in the evening, becoming north-northeast after midnight. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Thursday
 
Partly to mostly cloudy in the morning, becoming mostly cloudy to cloudy in the afternoon. Patchy light fog in the morning. High 87°. UV index up to 7. Wind northeast around 3 mph, gusting to 21 mph, in the morning, becoming east-southeast in the afternoon.
Thursday night
 
Partly cloudy in the evening, becoming clear after midnight. Patchy light fog after midnight. Low 68°. Wind southeast around 3 mph, gusting to 19 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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