WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Sunday, 24-May-2026 05:00 am
 
Today

Mostly Cloudy
Mostly Cloudy
Tonight

Fog late
Fog late
Monday

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

Thunder storm
Thunder storm
Tuesday
night
Thunder storm
Thunder storm
Wednesday

Thunder storm
Thunder storm
Wednesday
night
Thunder storm
Thunder storm
<.1 in. <.1 in. <.25 in. .5 in. <.1 in.
High: 81° Low: 58° High: 82° Low: 60° High: 77° Low: 66° High: 77° Low: 65°
               
N
4-23
mph
NNE→E
2-21
mph
E
4-24
mph
ESE
4-19
mph
ESE
5-22
mph
ESE
3-17
mph
ESE
2-15
mph
ENE
3
mph
UV: 8
 Very High 
UV: 8
 Very High 
UV: 5
 Medium 
UV: 7
 High 

 

Today
 
Partly to mostly cloudy in the morning, becoming mostly sunny in the afternoon. A slight chance of rain. High 81°. UV index up to 8. Wind north around 4 mph, gusting to 23 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Tonight
 
Clear. Patchy light fog after midnight. Low 58°. Wind north-northeast around 2 mph, gusting to 21 mph, in the evening, becoming east after midnight.
Monday
 
Sunny. Patchy light fog in the morning. High 82°. UV index up to 8. Wind east around 4 mph, gusting to 24 mph.
Monday night
 
Clear in the evening, becoming fair to partly cloudy after midnight. Patchy light fog after midnight. Low 60°. Wind east-southeast around 4 mph, gusting to 19 mph.
Tuesday
 
Mostly cloudy to cloudy. Patchy light fog in the morning. A chance of rain. Scattered thundershowers possible. High 77°. UV index up to 5. Wind east-southeast around 5 mph, gusting to 22 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Tuesday night
 
Cloudy in the evening, becoming dense overcast after midnight. Patchy light fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Scattered thundershowers possible. Low 66°. Wind east-southeast around 3 mph, gusting to 17 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Wednesday
 
Mostly cloudy in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning, then light to moderate fog in the afternoon. A chance of rain in the morning, then rain likely in the afternoon. Scattered thundershowers possible. High 77°. UV index up to 7. Wind east-southeast around 2 mph, gusting to 15 mph. Chance of precipitation 70 percent. Precipitation mostly around half an inch.
Wednesday night
 
Mostly cloudy. Patchy light fog in the evening, then light to moderate fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Scattered thundershowers possible. Low 65°. Wind east-northeast around 3 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Thursday
 
Cloudy in the morning, becoming mostly cloudy in the afternoon. Patchy light fog in the morning. A chance of rain. Precipitation showery or intermittent. High 78°. UV index up to 7. Wind east-northeast around 6 mph, gusting to 21 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Thursday night
 
Mostly cloudy in the evening, becoming cloudy after midnight. Low 64°. Wind east-northeast around 5 mph, gusting to 17 mph.
Friday
 
Dense overcast. A chance of rain. Precipitation showery or intermittent. High 76°. UV index up to 5. Wind east around 7 mph, gusting to 21 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Friday night
 
Cloudy. A slight chance of rain. Precipitation showery or intermittent. Low 66°. Wind east around 6 mph, gusting to 18 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Saturday
 
Mostly cloudy to cloudy in the morning, becoming mostly cloudy in the afternoon. High 81°. UV index up to 7. Wind east around 8 mph, gusting to 26 mph.
Saturday night
 
Mostly cloudy to cloudy in the evening, becoming partly to mostly cloudy after midnight. Low 63°. Wind east around 7 mph, gusting to 24 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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