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

Fog late
Fog late
Wednesday

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

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

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

Thunder storm
Thunder storm
<.1 in. .1 in. <.25 in. <.25 in.
Low: 74° High: 94° Low: 75° High: 94° Low: 71° High: 87° Low: 67° High: 88°
  Heat: 102°   Heat: 105°       Heat: 92°
SW
6-23
mph
SW
9-27
mph
SSW
7-22
mph
S
7-27→12-28
mph
W
9-25→6-17
mph
WNW
5-24
mph
ENE→SSW
2-19
mph
SSW
6-24
mph
UV: 9
 Very High 
UV: 10
 Very High 
UV: 8
 Very High 
UV: 9
 Very High 

 

Tonight
 
Mostly clear. Light to moderate fog in the evening, then moderate fog after midnight. Low 74°. Wind southwest around 6 mph, gusting to 23 mph.
Wednesday
 
Partly cloudy. Light to moderate fog in the morning. A slight chance of rain in the afternoon. Scattered thunderstorms likely. Very hot. High 94°. Heat index up to 102°. UV index up to 9. Wind southwest around 9 mph, gusting to 27 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Wednesday night
 
Partly cloudy. Patchy light fog in the evening, then moderate fog after midnight. A chance of rain. Scattered thunderstorms likely. Low 75°. Wind south-southwest around 7 mph, gusting to 22 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Thursday
 
Mostly sunny. Moderate fog in the morning. Very hot. High 94°. Heat index up to 105°. UV index up to 10. Wind south around 7 mph, gusting to 27 mph, in the morning, becoming 12 mph, gusting to 28 mph, in the afternoon.
Thursday night
 
Partly to mostly cloudy in the evening, becoming partly cloudy after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thunderstorms likely. Low 71°. Wind west around 9 mph, gusting to 25 mph, in the evening, becoming 6 mph, gusting to 17 mph, after midnight. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Friday
 
Sunny. Patchy light fog in the morning. Hot. High 87°. UV index up to 8. Wind west-northwest around 5 mph, gusting to 24 mph.
Friday night
 
Clear in the evening, becoming mostly clear after midnight. Light to moderate fog after midnight. Low 67°. Wind east-northeast around 2 mph, gusting to 19 mph, in the evening, becoming south-southwest after midnight.
Saturday
 
Partly to mostly cloudy. Patchy light fog in the morning. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thundershowers possible. Hot. High 88°. Heat index up to 92°. UV index up to 9. Wind south-southwest around 6 mph, gusting to 24 mph. Chance of precipitation 40 percent. Precipitation mostly less than a quarter of an inch.
Saturday night
 
Mostly cloudy in the evening, becoming mostly cloudy to cloudy after midnight. Light to moderate fog in the evening, then moderate fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Thunderstorms very likely, some possibly severe. Low 72°. Wind south-southwest around 6 mph, gusting to 18 mph, in the evening, becoming west after midnight. Chance of precipitation 40 percent. Precipitation mostly less than a quarter of an inch.
Sunday
 
Mostly cloudy to cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Patchy light fog in the morning. A chance of rain. Scattered thunderstorms likely. High 83°. UV index up to 8. Wind north around 7 mph, gusting to 26 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Mostly cloudy in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Low 65°. Wind north-northeast around 4 mph, gusting to 23 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Monday
 
Mostly cloudy to cloudy in the morning, becoming dense overcast in the afternoon. Patchy light fog in the morning. A chance of rain. Scattered thundershowers possible. Relatively cool. High 72°. Wind west-northwest around 4 mph, gusting to 19 mph, in the morning, becoming 12 mph, gusting to 30 mph, in the afternoon. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Monday night
 
Partly cloudy in the evening, becoming clear after midnight. Relatively cool. Low 58°. Wind west-northwest around 11 mph, gusting to 29 mph, in the evening, becoming 6 mph, gusting to 21 mph, after midnight.

WXSIM forecast formatting script by Saratoga-Weather.org.

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