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

Thunder storm
Thunder storm
Sunday

Thunder storm
Thunder storm
Sunday
night
Thunder storm
Thunder storm
Monday

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

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

Fog a.m.
Fog a.m.
<.25 in. <.1 in. <.1 in.
Low: 73° High: 89° Low: 70° High: 89° Low: 68° High: 90° Low: 67° High: 93°
  Heat: 96°   Heat: 94°   Heat: 94°   Heat: 98°
WNW
3-18
mph
NNW
3-21
mph
NNW
4-18
mph
NNE
6-25
mph
NNE
4-21
mph
NNE
3-23
mph
NE→SSW
2-19
mph
SW
3-22
mph
UV: 7
 High 
UV: 9
 Very High 
UV: 9
 Very High 
UV: 9
 Very High 

 

Tonight
 
Partly cloudy. Light to moderate fog in the evening, then moderate fog after midnight. Rain likely. Scattered thunderstorms likely. Low 73°. Wind west-northwest around 3 mph, gusting to 18 mph. Chance of precipitation 60 percent. Precipitation mostly less than a quarter of an inch.
Sunday
 
Partly cloudy in the morning, becoming partly to mostly 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. Thunderstorms very likely, some possibly severe. High 89°. Heat index up to 96°. UV index up to 7. Wind north-northwest around 3 mph, gusting to 21 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Fair to partly cloudy in the evening, becoming fair after midnight. Light to moderate fog in the evening, then moderate fog after midnight. A slight chance of rain. Scattered thunderstorms likely. Low 70°. Wind north-northwest around 4 mph, gusting to 18 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Monday
 
Partly to mostly sunny. Light to moderate fog in the morning. High 89°. Heat index up to 94°. UV index up to 9. Wind north-northeast around 6 mph, gusting to 25 mph.
Monday night
 
Mostly clear. Patchy light fog after midnight. Low 68°. Wind north-northeast around 4 mph, gusting to 21 mph.
Tuesday
 
Partly to mostly sunny in the morning, becoming sunny in the afternoon. Patchy light fog in the morning. Hot. High 90°. Heat index up to 94°. UV index up to 9. Wind north-northeast around 3 mph, gusting to 23 mph.
Tuesday night
 
Clear in the evening, becoming fair after midnight. Patchy light fog after midnight. Relatively cool. Low 67°. Wind northeast around 2 mph, gusting to 19 mph, in the evening, becoming south-southwest after midnight.
Wednesday
 
Mostly sunny. Patchy light fog in the morning. Hot. High 93°. Heat index up to 98°. UV index up to 9. Wind southwest around 3 mph, gusting to 22 mph.
Wednesday night
 
Clear in the evening, becoming mostly clear after midnight. Low 69°. Wind south around 5 mph, gusting to 18 mph.
Thursday
 
Partly cloudy. A chance of rain. Scattered thundershowers possible. Hot. High 91°. Heat index up to 100°. UV index up to 8. Wind southwest around 5 mph, gusting to 23 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Thursday night
 
Partly to mostly cloudy in the evening, becoming mostly cloudy after midnight. Patchy light fog. Rain likely. Scattered thunderstorms likely. Low 74°. Wind west-southwest around 3 mph, gusting to 18 mph. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch.
Friday
 
Mostly cloudy in the morning, becoming partly to mostly sunny in the afternoon. Patchy light fog in the morning. A slight chance of rain. Precipitation showery or intermittent. Hot. High 94°. Heat index up to 103°. UV index up to 10. Wind west-southwest around 8 mph, gusting to 24 mph, in the morning, becoming 12 mph, gusting to 29 mph, in the afternoon. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Friday night
 
Partly to mostly cloudy. Low 71°. Wind west-northwest around 7 mph, gusting to 25 mph, in the evening, becoming 4 mph after midnight.

WXSIM forecast formatting script by Saratoga-Weather.org.

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