WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Thursday, 09-Jul-2026 04:00 pm
 
Tonight

Thunder storm
Thunder storm
Friday

Thunder storm
Thunder storm
Friday
night
Thunder storm
Thunder storm
Saturday

Thunder storm
Thunder storm
Saturday
night
Fog late
Fog late
Sunday

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

Fog a.m.
Fog a.m.
<.25 in. .1 in. .25 in. <.25 in.
Low: 70° High: 88° Low: 72° High: 85° Low: 70° High: 89° Low: 68° High: 89°
  Heat: 95°   Heat: 92°   Heat: 95°   Heat: 95°
S
4
mph
W→S
3-20
mph
NE→NNW
2-16
mph
NE
3-18→6-24
mph
NE
5-20
mph
NE
6-24
mph
NE
4-23
mph
ENE
5-24
mph
UV: 7
 High 
UV: 8
 Very High 
UV: 9
 Very High 
UV: 9
 Very High 

 

Tonight
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. Rain likely. Scattered thunderstorms likely. Low 70°. Wind south around 4 mph. Chance of precipitation 70 percent. Precipitation mostly less than a quarter of an inch.
Friday
 
Mostly cloudy. Patchy light fog in the morning. Rain likely. Scattered thunderstorms likely. High 88°. Heat index up to 95°. UV index up to 7. Wind west around 3 mph, gusting to 20 mph, in the morning, becoming south in the afternoon. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch.
Friday night
 
Mostly cloudy. Light to moderate fog. Rain likely in the evening, then a chance of rain after midnight. Scattered thunderstorms likely. Low 72°. Wind northeast around 2 mph, gusting to 16 mph, in the evening, becoming north-northwest after midnight. Chance of precipitation 80 percent. Precipitation mostly around a quarter of an inch.
Saturday
 
Partly to mostly cloudy in the morning, becoming partly to mostly sunny in the afternoon. Light to moderate fog in the morning. Rain likely. Scattered thunderstorms likely. High 85°. Heat index up to 92°. UV index up to 8. Wind northeast around 3 mph, gusting to 18 mph, in the morning, becoming 6 mph, gusting to 24 mph, in the afternoon. Chance of precipitation 60 percent. Precipitation mostly less than a quarter of an inch.
Saturday night
 
Clear. Patchy light fog in the evening, then light to moderate fog after midnight. Low 70°. Wind northeast around 5 mph, gusting to 20 mph.
Sunday
 
Sunny. Light to moderate fog in the morning. High 89°. Heat index up to 95°. UV index up to 9. Wind northeast around 6 mph, gusting to 24 mph.
Sunday night
 
Clear. Patchy light fog after midnight. Low 68°. Wind northeast around 4 mph, gusting to 23 mph.
Monday
 
Sunny. Patchy light fog in the morning. High 89°. Heat index up to 95°. UV index up to 9. Wind east-northeast around 5 mph, gusting to 24 mph.
Monday night
 
Clear. Patchy light fog after midnight. Low 68°. Wind east-northeast around 3 mph, gusting to 20 mph.
Tuesday
 
Sunny in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. Hot. High 91°. Heat index up to 97°. UV index up to 8. Wind northeast around 4 mph, gusting to 22 mph.
Tuesday night
 
Mostly clear in the evening, becoming clear after midnight. Patchy light fog after midnight. Low 68°. Wind east-northeast around 3 mph, gusting to 17 mph, in the evening, becoming south after midnight.
Wednesday
 
Mostly sunny in the morning, becoming sunny in the afternoon. Patchy light fog in the morning. Hot. High 91°. Heat index up to 97°. UV index up to 9. Wind north around 3 mph, gusting to 22 mph.
Wednesday night
 
Clear. Patchy light fog after midnight. Low 68°. Wind east-northeast around 1 mph, gusting to 16 mph, in the evening, becoming south-southwest after midnight.

WXSIM forecast formatting script by Saratoga-Weather.org.

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