WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Monday, 20-Jul-2026 05:00 am
 
Today

Chance rain
Chance rain
Tonight

Thunder storm
Thunder storm
Tuesday

Thunder storm
Thunder storm
Tuesday
night
Fog late
Fog late
Wednesday

Fog a.m.
Fog a.m.
Wednesday
night
Partly Cloudy
Partly Cloudy
Thursday

Partly Cloudy
Partly Cloudy
Thursday
night
Partly Cloudy
Partly Cloudy
.1 in. .1 in. .1 in. <.1 in.
High: 92° Low: 74° High: 90° Low: 70° High: 85° Low: 63° High: 84° Low: 63°
Heat: 98°   Heat: 98°          
ESE→SSE
3-21
mph
SSE→SW
4
mph
W→NNW
7-22
mph
NNW
6-19
mph
N
7-26
mph
NE
5-25
mph
NE
5-25
mph
NE
3-23
mph
UV: 9
 Very High 
UV: 10
 Very High 
UV: 9
 Very High 
UV: 8
 Very High 

 

Today
 
Partly to mostly sunny. A chance of rain. Hot. High 92°. Heat index up to 98°. UV index up to 9. Wind east-southeast around 3 mph, gusting to 21 mph, in the morning, becoming south-southeast in the afternoon. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Tonight
 
Partly cloudy. Moderate fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Scattered thundershowers possible. Low 74°. Wind south-southeast around 4 mph in the evening, becoming southwest after midnight. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Tuesday
 
Partly cloudy in the morning, becoming partly to mostly sunny in the afternoon. Patchy light fog in the morning. A chance of rain in the morning, then a slight chance of rain in the afternoon. Scattered thunderstorms likely. High 90°. Heat index up to 98°. UV index up to 10. Wind west around 7 mph, gusting to 22 mph, in the morning, becoming north-northwest in the afternoon. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Tuesday night
 
Fair in the evening, becoming mostly clear after midnight. Light to moderate fog after midnight. Low 70°. Wind north-northwest around 6 mph, gusting to 19 mph.
Wednesday
 
Sunny in the morning, becoming partly cloudy in the afternoon. Light to moderate fog in the morning. High 85°. UV index up to 9. Wind north around 7 mph, gusting to 26 mph.
Wednesday night
 
Partly cloudy in the evening, becoming fair after midnight. Relatively cool. Low 63°. Wind northeast around 5 mph, gusting to 25 mph.
Thursday
 
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. High 84°. UV index up to 8. Wind northeast around 5 mph, gusting to 25 mph.
Thursday night
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. A slight chance of rain. Relatively cool. Low 63°. Wind northeast around 3 mph, gusting to 23 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Friday
 
Mostly cloudy to cloudy in the morning, becoming cloudy in the afternoon. Patchy light fog in the afternoon. A chance of rain in the morning, then rain likely in the afternoon. Relatively cool. High 77°. UV index up to 5. Wind east-southeast around 3 mph, gusting to 19 mph, in the morning, becoming northeast in the afternoon. Chance of precipitation 70 percent. Precipitation mostly around half an inch.
Friday night
 
Mostly cloudy to cloudy in the evening, becoming mostly cloudy after midnight. Patchy light fog. A chance of rain. Relatively cool. Low 68°. Wind east around 4 mph in the evening, becoming south-southeast after midnight. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Saturday
 
Mostly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. High 88°. Heat index up to 93°. UV index up to 7. Wind south-southeast around 5 mph, gusting to 25 mph.
Saturday night
 
Mostly cloudy in the evening, becoming partly cloudy after midnight. Moderate fog after midnight. Low 70°. Wind east-southeast around 4 mph, gusting to 21 mph.
Sunday
 
Sunny. Moderate fog in the morning. Hot. High 92°. Heat index up to 100°. UV index up to 9. Wind south-southeast around 4 mph, gusting to 22 mph.
Sunday night
 
Clear in the evening, becoming partly cloudy after midnight. Patchy light fog after midnight. Low 73°. Wind southeast around 5 mph, gusting to 15 mph, in the evening, becoming south after midnight.

WXSIM forecast formatting script by Saratoga-Weather.org.

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