WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Saturday, 15-Aug-2026 05:00 am
 
Today

Chance rain
Hot!
Chance rain
Hot!
Tonight

Chance rain
Chance rain
Sunday

Thunder storm
Hot!
Thunder storm
Hot!
Sunday
night
Thunder storm
Thunder storm
Monday

Fog a.m.
Fog a.m.
Monday
night
Fog late
Fog late
Tuesday

Fog a.m.
Fog a.m.
Tuesday
night
Partly Cloudy
Partly Cloudy
.1 in. .1 in. <.1 in. .1 in. <.1 in.
High: 97° Low: 78° High: 97° Low: 73° High: 86° Low: 68° High: 90° Low: 72°
Heat: 110°   Heat: 111°       Heat: 96°  
SSW
5-24
mph
SW
3-15
mph
SW
5-23
mph
NNW
5-18
mph
NNW
5-23
mph
NE
2-20
mph
SSE
3-21
mph
ESE
4-15
mph
UV: 7
 High 
UV: 8
 Very High 
UV: 8
 Very High 
UV: 8
 Very High 

 

Today
 
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. A chance of rain. Very hot. High 97°. Heat index up to 110°. UV index up to 7. Wind south-southwest around 5 mph, gusting to 24 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Tonight
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. A chance of rain. Warm. Low 78°. Wind southwest around 3 mph, gusting to 15 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Sunday
 
Partly cloudy. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thundershowers possible. Very hot. High 97°. Heat index up to 111°. UV index up to 8. Wind southwest around 5 mph, gusting to 23 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Mostly cloudy in the evening, becoming fair to partly cloudy after midnight. Patchy light fog in the evening, then moderate fog after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thundershowers possible. Low 73°. Wind north-northwest around 5 mph, gusting to 18 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Monday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Moderate fog in the morning. A slight chance of rain. High 86°. UV index up to 8. Wind north-northwest around 5 mph, gusting to 23 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Monday night
 
Partly cloudy. Patchy light fog after midnight. Low 68°. Wind northeast around 2 mph, gusting to 20 mph.
Tuesday
 
Partly to mostly sunny in the morning, becoming sunny in the afternoon. Patchy light fog in the morning. Hot. High 90°. Heat index up to 96°. UV index up to 8. Wind south-southeast around 3 mph, gusting to 21 mph.
Tuesday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Low 72°. Wind east-southeast around 4 mph, gusting to 15 mph.
Wednesday
 
Partly cloudy. Hot. High 91°. Heat index up to 95°. UV index up to 8. Wind north around 5 mph, gusting to 24 mph.
Wednesday night
 
Mostly cloudy to cloudy in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Precipitation showery or intermittent. Low 68°. Wind northeast around 4 mph, gusting to 18 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Thursday
 
Mostly cloudy to cloudy in the morning, becoming mostly cloudy in the afternoon. Patchy light fog in the morning. A slight chance of rain in the morning, then a chance of rain in the afternoon. High 82°. UV index up to 6. Wind east around 4 mph, gusting to 21 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Thursday night
 
Mostly cloudy to cloudy in the evening, becoming partly cloudy after midnight. Light to moderate fog after midnight. A chance of rain. Precipitation showery or intermittent. Low 69°. Wind east around 4 mph, gusting to 19 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Friday
 
Mostly cloudy to cloudy in the morning, becoming mostly cloudy in the afternoon. Patchy light fog in the morning. A slight chance of rain. Precipitation showery or intermittent. High 82°. UV index up to 5. Wind east around 5 mph, gusting to 23 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Friday night
 
Fair to partly cloudy in the evening, becoming clear after midnight. Moderate fog after midnight. Low 65°. Wind northeast around 4 mph, gusting to 22 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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