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

Cloudy
Cloudy
Tonight

Mostly Cloudy
Mostly Cloudy
Saturday

Partly Cloudy
Partly Cloudy
Saturday
night
Thunder storm
Thunder storm
Sunday

Thunder storm
Thunder storm
Sunday
night
Fog late
Fog late
Monday

Thunder storm
Thunder storm
Monday
night
Thunder storm
Thunder storm
.1 in. <.1 in. <.1 in. <.1 in.
High: 77° Low: 61° High: 80° Low: 63° High: 78° Low: 63° High: 81° Low: 67°
               
E
5-26
mph
NE→NNW
3-23
mph
NNW→WSW
3-22
mph
W
3-19
mph
WNW
3-19
mph
E
2-18
mph
ESE
4-21
mph
ESE
3-16
mph
UV: 7
 High 
UV: 6
 High 
UV: 5
 Medium 
UV: 6
 High 

 

Today
 
Cloudy. High 77°. UV index up to 7. Wind east around 5 mph, gusting to 26 mph.
Tonight
 
Partly to mostly cloudy in the evening, becoming mostly cloudy to cloudy after midnight. Low 61°. Wind northeast around 3 mph, gusting to 23 mph, in the evening, becoming north-northwest after midnight.
Saturday
 
Partly cloudy in the morning, becoming mostly cloudy to cloudy in the afternoon. High 80°. UV index up to 6. Wind north-northwest around 3 mph, gusting to 22 mph, in the morning, becoming west-southwest in the afternoon.
Saturday night
 
Mostly cloudy to cloudy in the evening, becoming mostly cloudy after midnight. Light to moderate fog after midnight. A chance of rain. Scattered thunderstorms likely. Low 63°. Wind west around 3 mph, gusting to 19 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Sunday
 
Mostly cloudy to cloudy in the morning, becoming mostly cloudy in the afternoon. Patchy light fog in the morning. A slight chance of rain. Scattered thunderstorms likely, some possibly severe. High 78°. UV index up to 5. Wind west-northwest around 3 mph, gusting to 19 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. Low 63°. Wind east around 2 mph, gusting to 18 mph.
Monday
 
Mostly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Patchy light fog in the morning. A slight chance of rain. Scattered thundershowers possible. High 81°. UV index up to 6. Wind east-southeast around 4 mph, gusting to 21 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Monday night
 
Mostly cloudy to cloudy. Patchy light fog after midnight. A slight chance of rain in the evening. Scattered thunderstorms likely. Low 67°. Wind east-southeast around 3 mph, gusting to 16 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Tuesday
 
Mostly cloudy to cloudy in the morning, becoming cloudy in the afternoon. Patchy light fog in the morning. A slight chance of rain in the morning, then a chance of rain in the afternoon. Thunderstorms very likely, some possibly severe. High 78°. UV index up to 5. Wind east around 6 mph, gusting to 23 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Tuesday night
 
Dense overcast. Patchy light fog in the evening, then light to moderate fog after midnight. Rain likely. Thunderstorms very likely, some possibly severe. Low 68°. Wind east around 6 mph, gusting to 20 mph. Chance of precipitation 70 percent. Precipitation mostly around a quarter of an inch.
Wednesday
 
Cloudy. Light to moderate fog. A chance of rain in the morning, then rain likely in the afternoon. Thunderstorms very likely, some possibly severe. High 72°. Wind east around 6 mph, gusting to 17 mph. Chance of precipitation 80 percent. Precipitation mostly around half an inch.
Wednesday night
 
Mostly cloudy in the evening, becoming cloudy after midnight. Moderate fog in the evening, then light to moderate fog after midnight. Rain likely. Scattered thunderstorms likely. Low 67°. Wind east-southeast around 7 mph, gusting to 16 mph. Chance of precipitation 60 percent. Precipitation mostly less than a quarter of an inch.
Thursday
 
Cloudy in the morning, becoming mostly cloudy in the afternoon. Light to moderate fog in the morning, then patchy light fog in the afternoon. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thunderstorms likely. High 78°. UV index up to 7. Wind east-southeast around 8 mph, gusting to 20 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Thursday night
 
Dense overcast in the evening, becoming cloudy after midnight. Patchy light fog. A chance of rain. Thunderstorms very likely, some possibly severe. Low 70°. Wind east-southeast around 7 mph, gusting to 19 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.

WXSIM forecast formatting script by Saratoga-Weather.org.

Powered by Davis Vantage Pro2  and   CumulusMX   v 4.6.4 (b4128)   MXUI Template v 2.2.6 by  Silver Acorn     Valid HTML5 USA Weather Finder Badge