WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Tuesday, 16-Jun-2026 04:00 pm
 
Tonight

Fog late
Fog late
Wednesday

Thunder storm
Thunder storm
Wednesday
night
Thunder storm
Thunder storm
Thursday

Fog a.m.
Fog a.m.
Thursday
night
Fog late
Fog late
Friday

Fog a.m.
Fog a.m.
Friday
night
Fog late
Fog late
Saturday

Thunder storm
Thunder storm
<.1 in. <.1 in. <.1 in. <.1 in.
Low: 64° High: 89° Low: 69° High: 85° Low: 65° High: 85° Low: 64° High: 89°
  Heat: 92°            
W→S
5-24
mph
SSW
8-24→16-31
mph
WSW
13-27→9-16
mph
NW
6-26
mph
WNW
3-22
mph
NNW
3-22
mph
SSE
4-17
mph
SSE
3-21
mph
UV: 8
 Very High 
UV: 8
 Very High 
UV: 9
 Very High 
UV: 7
 High 

 

Tonight
 
Fair in the evening, becoming fair to partly cloudy after midnight. Light to moderate fog after midnight. Relatively cool. Low 64°. Wind west around 5 mph, gusting to 24 mph, in the evening, becoming south after midnight.
Wednesday
 
Partly cloudy. Patchy light fog in the morning. A chance of rain. Scattered thundershowers possible. Breezy and hot. High 89°. Heat index up to 92°. UV index up to 8. Wind south-southwest around 8 mph, gusting to 24 mph, in the morning, becoming 16 mph, gusting to 31 mph, in the afternoon. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Wednesday 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 chance of rain in the evening, then a slight chance of rain after midnight. Scattered thunderstorms likely. Breezy. Low 69°. Wind west-southwest around 13 mph, gusting to 27 mph, in the evening, becoming 9 mph, gusting to 16 mph, after midnight. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Thursday
 
Partly to mostly cloudy. Patchy light fog in the morning. A chance of rain. High 85°. UV index up to 8. Wind northwest around 6 mph, gusting to 26 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Thursday night
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Patchy light fog after midnight. Low 65°. Wind west-northwest around 3 mph, gusting to 22 mph.
Friday
 
Partly cloudy in the morning, becoming sunny in the afternoon. Patchy light fog in the morning. High 85°. UV index up to 9. Wind north-northwest around 3 mph, gusting to 22 mph.
Friday night
 
Clear in the evening, becoming mostly clear after midnight. Light to moderate fog after midnight. Relatively cool. Low 64°. Wind south-southeast around 4 mph, gusting to 17 mph.
Saturday
 
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 afternoon. Scattered thundershowers possible. Hot. High 89°. UV index up to 7. Wind south-southeast around 3 mph, gusting to 21 mph. Chance of precipitation 20 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 in the evening, then light to moderate fog after midnight. A chance of rain in the evening, then rain likely after midnight. Scattered thundershowers possible. Low 69°. Wind south-southeast around 5 mph. Chance of precipitation 80 percent. Precipitation mostly around half an inch.
Sunday
 
Cloudy in the morning, becoming mostly cloudy in the afternoon. Light to moderate fog in the morning, then patchy light fog in the afternoon. Rain likely in the morning, then a chance of rain in the afternoon. Scattered thunderstorms likely. High 84°. UV index up to 6. Wind south-southwest around 7 mph, gusting to 18 mph, in the morning, becoming 10 mph, gusting to 24 mph, in the afternoon. Chance of precipitation 90 percent. Precipitation mostly between half an inch and one inch.
Sunday night
 
Cloudy. Light to moderate fog. Rain likely in the evening, then a chance of rain after midnight. Scattered thunderstorms likely. Low 71°. Wind west-southwest around 8 mph, gusting to 21 mph. Chance of precipitation 70 percent. Precipitation mostly around a quarter of an inch.
Monday
 
Mostly cloudy to cloudy in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. High 82°. UV index up to 10. Wind northeast around 9 mph, gusting to 28 mph, in the morning, becoming east in the afternoon.
Monday night
 
Mostly cloudy. Low 69°. Wind east around 5 mph, gusting to 25 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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