WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Tuesday, 08-Sep-2026 04:00 pm
 
Tonight

Fog late
Fog late
Wednesday

Thunder storm
Hot!
Thunder storm
Hot!
Wednesday
night
Thunder storm
Thunder storm
Thursday

Thunder storm
Thunder storm
Thursday
night
Mostly Cloudy
Mostly Cloudy
Friday

Mostly Cloudy
Mostly Cloudy
Friday
night
Fog late
Fog late
Saturday

Fog a.m.
Fog a.m.
<.1 in. .5 in. <.25 in.
Low: 68° High: 95° Low: 72° High: 81° Low: 68° High: 84° Low: 67° High: 89°
  Heat: 101°           Heat: 95°
S
6-22
mph
SSW→W
7-23
mph
S→WNW
3
mph
WNW→NNE
3-20
mph
NNE→ENE
2-18
mph
ESE
4-21
mph
SE
4-16
mph
SW
4-22
mph
UV: 6
 High 
UV: 5
 Medium 
UV: 4
 Medium 
UV: 7
 High 

 

Tonight
 
Fair to partly cloudy in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Low 68°. Wind south around 6 mph, gusting to 22 mph.
Wednesday
 
Partly to mostly sunny in the morning, becoming partly to mostly cloudy in the afternoon. A chance of rain. Scattered thunderstorms likely, some possibly severe. Very hot. High 95°. Heat index up to 101°. UV index up to 6. Wind south-southwest around 7 mph, gusting to 23 mph, in the morning, becoming west in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Wednesday night
 
Mostly cloudy. Patchy light fog in the evening, then moderate fog after midnight. A chance of rain in the evening, then rain likely after midnight. Scattered thunderstorms likely. Warm. Low 72°. Wind south around 3 mph in the evening, becoming west-northwest after midnight. Chance of precipitation 70 percent. Precipitation mostly around half an inch.
Thursday
 
Mostly cloudy to cloudy. Light to 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 5. Wind west-northwest around 3 mph, gusting to 20 mph, in the morning, becoming north-northeast in the afternoon. Chance of precipitation 60 percent. Precipitation mostly less than a quarter of an inch.
Thursday night
 
Partly to mostly cloudy. Low 68°. Wind north-northeast around 2 mph, gusting to 18 mph, in the evening, becoming east-northeast after midnight.
Friday
 
Mostly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Warm. High 84°. UV index up to 4. Wind east-southeast around 4 mph, gusting to 21 mph.
Friday night
 
Clear. Patchy light fog in the evening, then light to moderate fog after midnight. Low 67°. Wind southeast around 4 mph, gusting to 16 mph.
Saturday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. Hot. High 89°. Heat index up to 95°. UV index up to 7. Wind southwest around 4 mph, gusting to 22 mph.
Saturday night
 
Partly to mostly cloudy in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Low 69°. Wind east-northeast around 2 mph in the evening, becoming south-southeast after midnight.
Sunday
 
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Patchy light fog in the morning. Hot. High 89°. Heat index up to 96°. UV index up to 5. Wind south-southeast around 4 mph, gusting to 20 mph.
Sunday night
 
Partly cloudy. Patchy light fog. Warm. Low 72°. Wind south-southeast around 5 mph, gusting to 15 mph.
Monday
 
Mostly cloudy in the morning, becoming mostly sunny in the afternoon. A chance of rain. Scattered thundershowers possible. Hot. High 90°. Heat index up to 98°. UV index up to 6. Wind south-southeast around 4 mph, gusting to 15 mph, in the morning, becoming 7 mph, gusting to 24 mph, in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Monday night
 
Fair to partly cloudy in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Warm. Low 72°. Wind south around 7 mph, gusting to 17 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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