WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Wednesday, 01-Jul-2026 05:00 am
 
Today

Sunny
Hot!
Sunny
Hot!
Tonight

Partly Cloudy
Partly Cloudy
Thursday

Thunder storm
Hot!
Thunder storm
Hot!
Thursday
night
Thunder storm
Thunder storm
Friday

Fog a.m.
Hot!
Fog a.m.
Hot!
Friday
night
Thunder storm
Thunder storm
Saturday

Thunder storm
Hot!
Thunder storm
Hot!
Saturday
night
Thunder storm
Thunder storm
.1 in. .1 in. <.1 in. <.1 in. <.1 in.
High: 100° Low: 75° High: 99° Low: 77° High: 95° Low: 76° High: 93° Low: 76°
Heat: 108°   Heat: 109°   Heat: 107°   Heat: 104°  
SSW
6-27
mph
SSW
5-22
mph
SSW
5-25
mph
SSE
4
mph
SSE
5-23
mph
S
4-16
mph
SE→SSW
5-23
mph
SSE→W
4-17
mph
UV: 11
 Extreme 
UV: 10
 Very High 
UV: 7
 High 
UV: 9
 Very High 

 

Today
 
Sunny. Very hot. High 100°. Heat index up to 108°. UV index up to 11. Wind south-southwest around 6 mph, gusting to 27 mph.
Tonight
 
Mostly clear in the evening, becoming fair to partly cloudy after midnight. Low 75°. Wind south-southwest around 5 mph, gusting to 22 mph.
Thursday
 
Sunny in the morning, becoming partly cloudy in the afternoon. A chance of rain in the afternoon. Thunderstorms very likely, some possibly severe. Very hot. High 99°. Heat index up to 109°. UV index up to 10. Wind south-southwest around 5 mph, gusting to 25 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Thursday night
 
Partly to mostly cloudy in the evening, becoming partly cloudy after midnight. Moderate fog. A chance of rain. Scattered thundershowers possible. Low 77°. Wind south-southeast around 4 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Friday
 
Partly to mostly sunny in the morning, becoming partly to mostly cloudy in the afternoon. Moderate fog in the morning. Hot. High 95°. Heat index up to 107°. UV index up to 7. Wind south-southeast around 5 mph, gusting to 23 mph.
Friday night
 
Partly to mostly cloudy. Patchy light fog after midnight. A chance of rain. Scattered thunderstorms likely, some possibly severe. Low 76°. Wind south around 4 mph, gusting to 16 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Saturday
 
Partly to mostly cloudy in the morning, becoming partly 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. Scattered thunderstorms likely, some possibly severe. Hot. High 93°. Heat index up to 104°. UV index up to 9. Wind southeast around 5 mph, gusting to 23 mph, in the morning, becoming south-southwest in the afternoon. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Saturday night
 
Partly to mostly cloudy in the evening, becoming fair to partly cloudy after midnight. Patchy light fog in the evening, then moderate fog after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Thunderstorms very likely, some possibly severe. Low 76°. Wind south-southeast around 4 mph, gusting to 17 mph, in the evening, becoming west after midnight. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Sunday
 
Partly cloudy in the morning, becoming partly to mostly sunny in the afternoon. Moderate fog in the morning. Hot. High 94°. Heat index up to 105°. UV index up to 9. Wind west around 4 mph, gusting to 22 mph, in the morning, becoming north-northwest in the afternoon.
Sunday night
 
Partly to mostly cloudy in the evening, becoming mostly cloudy after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. A chance of rain. Thunderstorms very likely, some possibly severe. Low 75°. Wind east-northeast around 4 mph, gusting to 17 mph, in the evening, becoming southwest near calm after midnight. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Monday
 
Partly to mostly cloudy in the morning, becoming partly cloudy in the afternoon. Light to moderate fog in the morning. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thunderstorms likely, some possibly severe. Hot. High 92°. Heat index up to 102°. UV index up to 9. Wind east around 2 mph, gusting to 21 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Monday night
 
Mostly cloudy to cloudy in the evening, becoming partly to mostly 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. Thunderstorms very likely, some possibly severe. Low 76°. Wind south-southeast around 4 mph in the evening, becoming southwest after midnight. Chance of precipitation 60 percent. Precipitation mostly less than a quarter of an inch.
Tuesday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Moderate fog in the morning. A chance of rain. Scattered thunderstorms likely. Hot. High 91°. Heat index up to 102°. UV index up to 8. Wind west around 4 mph, gusting to 22 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Tuesday night
 
Fair to partly cloudy in the evening, becoming clear after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. Low 74°. Wind north-northwest around 2 mph, gusting to 18 mph, in the evening, becoming east after midnight.

WXSIM forecast formatting script by Saratoga-Weather.org.

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