WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Sunday, 19-Jul-2026 05:00 am
 
Today

Chance rain
Chance rain
Tonight

Chance rain
Chance rain
Monday

Chance rain
Hot!
Chance rain
Hot!
Monday
night
Fog late
Fog late
Tuesday

Fog a.m.
Hot!
Fog a.m.
Hot!
Tuesday
night
Fog late
Fog late
Wednesday

Fog a.m.
Fog a.m.
Wednesday
night
Partly Cloudy
Partly Cloudy
<.25 in. .1 in. .1 in. <.1 in.
High: 91° Low: 73° High: 91° Low: 75° High: 94° Low: 70° High: 87° Low: 65°
Heat: 99°   Heat: 100°   Heat: 103°      
NE
3-22
mph
NE
4-18
mph
ESE→W
3-20
mph
SSW
4
mph
NNW
6-23
mph
NNW
7-19
mph
NNE
7-25
mph
NE
5-24
mph
UV: 8
 Very High 
UV: 9
 Very High 
UV: 10
 Very High 
UV: 7
 High 

 

Today
 
Partly cloudy. A chance of rain. Hot. High 91°. Heat index up to 99°. UV index up to 8. Wind northeast around 3 mph, gusting to 22 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Tonight
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Light to moderate fog in the evening, then moderate fog after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Low 73°. Wind northeast around 4 mph, gusting to 18 mph. Chance of precipitation 40 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 chance of rain. High 91°. Heat index up to 100°. UV index up to 9. Wind east-southeast around 3 mph, gusting to 20 mph, in the morning, becoming west in the afternoon. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Monday night
 
Partly cloudy. Light to moderate fog in the evening, then moderate fog after midnight. A chance of rain. Low 75°. Wind south-southwest around 4 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Tuesday
 
Mostly sunny. Moderate fog in the morning. Hot. High 94°. Heat index up to 103°. UV index up to 10. Wind north-northwest around 6 mph, gusting to 23 mph.
Tuesday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Patchy light fog after midnight. Low 70°. Wind north-northwest around 7 mph, gusting to 19 mph.
Wednesday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. High 87°. UV index up to 7. Wind north-northeast around 7 mph, gusting to 25 mph.
Wednesday night
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Relatively cool. Low 65°. Wind northeast around 5 mph, gusting to 24 mph.
Thursday
 
Partly cloudy. High 89°. UV index up to 9. Wind east around 4 mph, gusting to 25 mph.
Thursday night
 
Mostly cloudy in the evening, becoming partly cloudy after midnight. Relatively cool. Low 66°. Wind east around 4 mph, gusting to 23 mph.
Friday
 
Partly to mostly cloudy in the morning, becoming mostly cloudy in the afternoon. A chance of rain. High 87°. UV index up to 7. Wind east around 5 mph, gusting to 24 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Friday night
 
Mostly cloudy in the evening, becoming cloudy after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Low 69°. Wind east around 8 mph, gusting to 22 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Saturday
 
Mostly cloudy to cloudy in the morning, becoming cloudy in the afternoon. High 82°. UV index up to 5. Wind east around 9 mph, gusting to 27 mph.
Saturday night
 
Mostly cloudy to cloudy in the evening, becoming fair after midnight. Relatively cool. Low 66°. Wind east around 5 mph, gusting to 24 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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