WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Saturday, 06-Jun-2026 04:00 pm
 
Tonight

Fog late
Fog late
Sunday

Thunder storm
Thunder storm
Sunday
night
Thunder storm
Thunder storm
Monday

Thunder storm
Thunder storm
Monday
night
Thunder storm
Thunder storm
Tuesday

Fog a.m.
Hot!
Fog a.m.
Hot!
Tuesday
night
Fog late
Fog late
Wednesday

Fog a.m.
Hot!
Fog a.m.
Hot!
<.1 in. .35 in. <.25 in. <.25 in.
Low: 74° High: 86° Low: 73° High: 85° Low: 74° High: 91° Low: 75° High: 93°
      Heat: 92°   Heat: 101°   Heat: 103°
SSW
4-22
mph
SSE
5-20→9-26
mph
S
6-21
mph
SSE→SSW
7-22
mph
SSW
4-18
mph
SSW
7-25
mph
SSW
6-21
mph
SSW
9-26
mph
UV: 8
 Very High 
UV: 7
 High 
UV: 10
 Very High 
UV: 8
 Very High 

 

Tonight
 
Cloudy. Patchy light fog after midnight. Low 74°. Wind south-southwest around 4 mph, gusting to 22 mph.
Sunday
 
Partly to mostly cloudy in the morning, becoming mostly cloudy in the afternoon. Light to moderate fog in the morning. A slight chance of rain. Scattered thunderstorms likely. High 86°. UV index up to 8. Wind south-southeast around 5 mph, gusting to 20 mph, in the morning, becoming 9 mph, gusting to 26 mph, in the afternoon. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Cloudy. Light to moderate fog in the evening, then moderate fog after midnight. Rain likely. Thunderstorms very likely, some possibly severe. Low 73°. Wind south around 6 mph, gusting to 21 mph. Chance of precipitation 60 percent. Precipitation mostly between a quarter and half an inch.
Monday
 
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Moderate fog in the morning. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thunderstorms likely, some possibly severe. High 85°. Heat index up to 92°. UV index up to 7. Wind south-southeast around 7 mph, gusting to 22 mph, in the morning, becoming south-southwest in the afternoon. Chance of precipitation 40 percent. Precipitation mostly less than a quarter of an inch.
Monday night
 
Partly to 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 chance of rain. Thunderstorms very likely, some possibly severe. Low 74°. Wind south-southwest around 4 mph, gusting to 18 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Tuesday
 
Sunny. Moderate fog in the morning. Hot. High 91°. Heat index up to 101°. UV index up to 10. Wind south-southwest around 7 mph, gusting to 25 mph.
Tuesday night
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Patchy light fog in the evening, then moderate fog after midnight. Low 75°. Wind south-southwest around 6 mph, gusting to 21 mph.
Wednesday
 
Sunny in the morning, becoming partly cloudy in the afternoon. Moderate fog in the morning. Hot. High 93°. Heat index up to 103°. UV index up to 8. Wind south-southwest around 9 mph, gusting to 26 mph.
Wednesday night
 
Mostly clear in the evening, becoming mostly cloudy after midnight. Patchy light fog after midnight. Warm. Low 75°. Wind south-southwest around 8 mph, gusting to 22 mph.
Thursday
 
Partly to mostly cloudy in the morning, becoming partly to mostly sunny in the afternoon. Very hot. High 93°. Heat index up to 103°. UV index up to 10. Wind south-southwest around 9 mph, gusting to 27 mph.
Thursday night
 
Fair to partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. A slight chance of rain. Scattered thunderstorms likely. Low 72°. Wind south-southwest around 6 mph, gusting to 22 mph, in the evening, becoming west-northwest after midnight. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Friday
 
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 thunderstorms likely. High 83°. UV index up to 8. Wind northwest around 8 mph, gusting to 26 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Friday night
 
Partly to mostly cloudy. Patchy light fog after midnight. Low 66°. Wind north around 6 mph, gusting to 24 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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