WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Sunday, 31-May-2026 04:00 pm
 
Tonight

Thunder storm
Thunder storm
Monday

Thunder storm
Thunder storm
Monday
night
Fog late
Fog late
Tuesday

Fog a.m.
Fog a.m.
Tuesday
night
Mostly Clear
Mostly Clear
Wednesday

Partly Cloudy
Partly Cloudy
Wednesday
night
Partly Cloudy
Partly Cloudy
Thursday

Partly Cloudy
Partly Cloudy
<.25 in. .1 in.
Low: 65° High: 81° Low: 62° High: 81° Low: 57° High: 81° Low: 58° High: 86°
               
E→SSW
5-20
mph
NE
5-22
mph
NE
5-20
mph
NE
8-26
mph
ENE
5-23
mph
E
6-25
mph
E→SSE
4-21
mph
SSE
6-25
mph
UV: 6
 High 
UV: 8
 Very High 
UV: 7
 High 
UV: 8
 Very High 

 

Tonight
 
Partly to mostly cloudy in the evening, becoming partly cloudy after midnight. Patchy light fog in the evening, then moderate to dense fog after midnight. A chance of rain. Thunderstorms very likely, some possibly severe. Low 65°. Wind east around 5 mph, gusting to 20 mph, in the evening, becoming south-southwest after midnight. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Monday
 
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Moderate fog in the morning. A chance of rain in the morning, then a slight chance of rain in the afternoon. Scattered thunderstorms likely. High 81°. UV index up to 6. Wind northeast around 5 mph, gusting to 22 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Monday night
 
Fair in the evening, becoming partly cloudy after midnight. Patchy light fog after midnight. Low 62°. Wind northeast around 5 mph, gusting to 20 mph.
Tuesday
 
Partly to mostly sunny. Patchy light fog in the morning. High 81°. UV index up to 8. Wind northeast around 8 mph, gusting to 26 mph.
Tuesday night
 
Mostly clear in the evening, becoming clear after midnight. Relatively cool. Low 57°. Wind east-northeast around 5 mph, gusting to 23 mph.
Wednesday
 
Partly cloudy. High 81°. UV index up to 7. Wind east around 6 mph, gusting to 25 mph.
Wednesday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Relatively cool. Low 58°. Wind east around 4 mph, gusting to 21 mph, in the evening, becoming south-southeast after midnight.
Thursday
 
Partly to mostly cloudy in the morning, becoming partly cloudy in the afternoon. Hot. High 86°. UV index up to 8. Wind south-southeast around 6 mph, gusting to 25 mph.
Thursday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Low 61°. Wind south-southeast around 7 mph, gusting to 22 mph.
Friday
 
Partly cloudy in the morning, becoming cloudy in the afternoon. A chance of rain in the afternoon. Scattered thunderstorms likely. Hot. High 88°. UV index up to 7. Wind south-southeast around 6 mph, gusting to 26 mph, in the morning, becoming south-southwest in the afternoon. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Friday night
 
Mostly cloudy to cloudy in the evening, becoming cloudy after midnight. A chance of rain. Scattered thundershowers possible. Low 68°. Wind southeast around 5 mph in the evening, becoming south-southwest after midnight. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Saturday
 
Mostly cloudy in the morning, becoming cloudy in the afternoon. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thunderstorms likely. Hot. High 86°. UV index up to 6. Wind south-southwest around 4 mph, gusting to 19 mph, in the morning, becoming east in the afternoon. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Saturday night
 
Partly to mostly cloudy in the evening, becoming mostly cloudy to cloudy after midnight. 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 thunderstorms likely. Low 68°. Wind southeast around 5 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.

WXSIM forecast formatting script by Saratoga-Weather.org.

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