WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Saturday, 27-Jun-2026 04:00 pm
 
Tonight

Rain likely
Rain likely
Sunday

Fog a.m.
Hot!
Fog a.m.
Hot!
Sunday
night
Fog late
Fog late
Monday

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

Fog a.m.
Hot!
Fog a.m.
Hot!
Tuesday
night
Fog late
Fog late
Wednesday

Fog a.m.
Hot!
Fog a.m.
Hot!
.1 in.
Low: 74° High: 94° Low: 74° High: 96° Low: 74° High: 95° Low: 73° High: 97°
  Heat: 105°   Heat: 106°   Heat: 106°   Heat: 107°
S
3-19
mph
SSE
6-25→9-26
mph
SSE
7-23
mph
S
9-27
mph
SSW
7-23
mph
SSW
8-26
mph
SSW
5-19
mph
SSW
6-25
mph
UV: 9
 Very High 
UV: 10
 Very High 
UV: 9
 Very High 
UV: 10
 Very High 

 

Tonight
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Patchy light fog in the evening, then moderate fog after midnight. Rain likely. Low 74°. Wind south around 3 mph, gusting to 19 mph. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch.
Sunday
 
Sunny. Light to moderate fog in the morning. Hot. High 94°. Heat index up to 105°. UV index up to 9. Wind south-southeast around 6 mph, gusting to 25 mph, in the morning, becoming 9 mph, gusting to 26 mph, in the afternoon.
Sunday night
 
Mostly clear in the evening, becoming partly cloudy after midnight. Patchy light fog after midnight. Low 74°. Wind south-southeast around 7 mph, gusting to 23 mph.
Monday
 
Partly cloudy in the morning, becoming sunny in the afternoon. Patchy light fog in the morning. Very hot. High 96°. Heat index up to 106°. UV index up to 10. Wind south around 9 mph, gusting to 27 mph.
Monday night
 
Clear in the evening, becoming fair after midnight. Light to moderate fog after midnight. Low 74°. Wind south-southwest around 7 mph, gusting to 23 mph.
Tuesday
 
Sunny. Light to moderate fog in the morning. Very hot. High 95°. Heat index up to 106°. UV index up to 9. Wind south-southwest around 8 mph, gusting to 26 mph.
Tuesday night
 
Clear. Light to moderate fog after midnight. Low 73°. Wind south-southwest around 5 mph, gusting to 19 mph.
Wednesday
 
Sunny in the morning, becoming partly to mostly sunny in the afternoon. Patchy light fog in the morning. Very hot. High 97°. Heat index up to 107°. UV index up to 10. Wind south-southwest around 6 mph, gusting to 25 mph.
Wednesday night
 
Fair to partly cloudy. Patchy light fog after midnight. Low 74°. Wind south-southwest around 5 mph, gusting to 19 mph.
Thursday
 
Sunny 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 thundershowers possible. Hot. High 96°. Heat index up to 106°. UV index up to 9. Wind south-southwest around 5 mph, gusting to 23 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Thursday night
 
Partly to mostly cloudy in the evening, becoming partly cloudy after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. A chance of rain. Scattered thundershowers possible. Low 74°. Wind south around 4 mph, gusting to 18 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Friday
 
Sunny in the morning, becoming partly to mostly cloudy in the afternoon. Light to moderate fog in the morning. Hot. High 96°. Heat index up to 106°. UV index up to 9. Wind south around 5 mph, gusting to 24 mph.
Friday night
 
Partly cloudy. Patchy light fog after midnight. A chance of rain. Scattered thunderstorms likely. Low 74°. Wind west-southwest around 2 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.

WXSIM forecast formatting script by Saratoga-Weather.org.

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