WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Saturday, 22-Aug-2026 05:00 am
 
Today

Mostly Sunny
Mostly Sunny
Tonight

Fog late
Fog late
Sunday

Chance rain
Chance rain
Sunday
night
Fog late
Fog late
Monday

Fog a.m.
Fog a.m.
Monday
night
Thunder storm
Thunder storm
Tuesday

Thunder storm
Thunder storm
Tuesday
night
Fog late
Fog late
<.1 in. <.1 in. .5 in. .1 in.
High: 87° Low: 65° High: 83° Low: 66° High: 85° Low: 67° High: 82° Low: 67°
               
NNW
6-25
mph
NNW
3-19
mph
NNW
3-21
mph
SSE→ESE
2
mph
ESE
5-22
mph
ESE
6-20
mph
ESE
4-17
mph
ESE→WNW
2-16
mph
UV: 7
 High 
UV: 7
 High 
UV: 7
 High 
UV: 5
 Medium 

 

Today
 
Mostly sunny. Hot. High 87°. UV index up to 7. Wind north-northwest around 6 mph, gusting to 25 mph.
Tonight
 
Fair in the evening, becoming fair to partly cloudy after midnight. Patchy light fog after midnight. Low 65°. Wind north-northwest around 3 mph, gusting to 19 mph.
Sunday
 
Partly cloudy. Patchy light fog in the morning. A chance of rain. High 83°. UV index up to 7. Wind north-northwest around 3 mph, gusting to 21 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Partly cloudy in the evening, becoming clear after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. A chance of rain. Low 66°. Wind south-southeast around 2 mph in the evening, becoming east-southeast after midnight. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Monday
 
Mostly sunny in the morning, becoming partly cloudy in the afternoon. Light to moderate fog in the morning. High 85°. UV index up to 7. Wind east-southeast around 5 mph, gusting to 22 mph.
Monday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Moderate fog after midnight. Rain likely after midnight. Scattered thundershowers possible. Low 67°. Wind east-southeast around 6 mph, gusting to 20 mph. Chance of precipitation 60 percent. Precipitation mostly around half an inch.
Tuesday
 
Mostly cloudy. Light to moderate fog in the morning. A chance of rain in the morning, then a slight chance of rain in the afternoon. Scattered thundershowers possible. High 82°. UV index up to 5. Wind east-southeast around 4 mph, gusting to 17 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Tuesday night
 
Fair. Light to moderate fog after midnight. Low 67°. Wind east-southeast around 2 mph, gusting to 16 mph, in the evening, becoming west-northwest after midnight.
Wednesday
 
Partly cloudy in the morning, becoming mostly cloudy in the afternoon. Patchy light fog in the morning. High 85°. UV index up to 6. Wind southwest around 3 mph, gusting to 19 mph, in the morning, becoming west-northwest in the afternoon.
Wednesday night
 
Fair in the evening, becoming mostly clear after midnight. Light to moderate fog after midnight. Low 67°. Wind south around 2 mph in the evening, becoming west-northwest after midnight.
Thursday
 
Sunny. Light to moderate fog in the morning. High 85°. UV index up to 7. Wind northwest around 6 mph, gusting to 22 mph.
Thursday night
 
Clear. Patchy light fog after midnight. Low 64°. Wind north-northeast around 5 mph, gusting to 17 mph, in the evening, becoming near calm after midnight.
Friday
 
Sunny in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. High 83°. UV index up to 7. Wind east-northeast around 2 mph, gusting to 20 mph.
Friday night
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. Low 66°. Wind east-southeast around 4 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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