WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Tuesday, 07-Jul-2026 04:00 pm
 
Tonight

Fog late
Fog late
Wednesday

Fog a.m.
Fog a.m.
Wednesday
night
Fog late
Fog late
Thursday

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

Thunder storm
Thunder storm
Friday
night
Thunder storm
Thunder storm
Saturday

Thunder storm
Thunder storm
<.1 in. .35 in. <.25 in. .35 in. <.1 in.
Low: 70° High: 90° Low: 71° High: 95° Low: 72° High: 89° Low: 75° High: 88°
  Heat: 96°   Heat: 103°   Heat: 96°   Heat: 95°
NNE
2-21
mph
W
2-21
mph
SSE
3-15
mph
SSW
5-23
mph
SW
5-18
mph
WSW
4-23
mph
NW→WSW
3-16
mph
NNE
4-22
mph
UV: 8
 Very High 
UV: 9
 Very High 
UV: 8
 Very High 
UV: 8
 Very High 

 

Tonight
 
Fair to partly cloudy in the evening, becoming fair after midnight. Patchy light fog after midnight. Low 70°. Wind north-northeast around 2 mph, gusting to 21 mph.
Wednesday
 
Mostly sunny in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. A chance of rain. High 90°. Heat index up to 96°. UV index up to 8. Wind west around 2 mph, gusting to 21 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Wednesday night
 
Mostly clear in the evening, becoming clear after midnight. Patchy light fog in the evening, then moderate fog after midnight. Low 71°. Wind south-southeast around 3 mph, gusting to 15 mph.
Thursday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Light to moderate fog in the morning. Hot. High 95°. Heat index up to 103°. UV index up to 9. Wind south-southwest around 5 mph, gusting to 23 mph.
Thursday night
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Moderate fog after midnight. A chance of rain in the evening, then rain likely after midnight. Scattered thunderstorms likely. Low 72°. Wind southwest around 5 mph, gusting to 18 mph. Chance of precipitation 70 percent. Precipitation mostly between a quarter and half an inch.
Friday
 
Mostly cloudy to cloudy in the morning, becoming mostly cloudy in the afternoon. Light to moderate fog in the morning. Rain likely. Scattered thunderstorms likely. High 89°. Heat index up to 96°. UV index up to 8. Wind west-southwest around 4 mph, gusting to 23 mph. Chance of precipitation 60 percent. Precipitation mostly less than a quarter of an inch.
Friday night
 
Mostly cloudy in the evening, becoming mostly cloudy to cloudy after midnight. Light to moderate fog. Rain likely in the evening, then a chance of rain after midnight. Scattered thunderstorms likely. Low 75°. Wind northwest around 3 mph, gusting to 16 mph, in the evening, becoming west-southwest after midnight. Chance of precipitation 80 percent. Precipitation mostly between a quarter and half an inch.
Saturday
 
Mostly cloudy to cloudy in the morning, becoming partly cloudy in the afternoon. Light to moderate fog in the morning. A chance of rain in the morning, then a slight chance of rain in the afternoon. Scattered thundershowers possible. High 88°. Heat index up to 95°. UV index up to 8. Wind north-northeast around 4 mph, gusting to 22 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch.
Saturday night
 
Partly to mostly cloudy in the evening, becoming mostly cloudy after midnight. Patchy light fog after midnight. A chance of rain. Low 74°. Wind northeast around 4 mph, gusting to 21 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Sunday
 
Mostly cloudy to cloudy in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. A chance of rain. High 87°. Heat index up to 94°. UV index up to 8. Wind east-northeast around 5 mph, gusting to 23 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Clear. Moderate fog after midnight. Low 71°. Wind east-northeast around 3 mph, gusting to 21 mph.
Monday
 
Sunny. Light to moderate fog in the morning. Hot. High 90°. Heat index up to 98°. UV index up to 9. Wind east-northeast around 5 mph, gusting to 23 mph.
Monday night
 
Clear. Patchy light fog after midnight. Low 70°. Wind east-northeast around 4 mph, gusting to 20 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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