WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Wednesday, 10-Jun-2026 05:00 am
 
Today

Thunder storm
Hot!
Thunder storm
Hot!
Tonight

Thunder storm
Thunder storm
Thursday

Thunder storm
Hot!
Thunder storm
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
Saturday
night
Thunder storm
Thunder storm
<.1 in. <.1 in. <.1 in. .25 in. <.1 in. .1 in.
High: 98° Low: 79° High: 98° Low: 73° High: 87° Low: 68° High: 87° Low: 72°
Heat: 109°   Heat: 113°   Heat: 92°   Heat: 93°  
SSW
9-30
mph
SSW
7-24
mph
SSW
8-29→12-30
mph
W
9-24→5-19
mph
WNW
5-25
mph
E→SE
3-20
mph
SSW
7-25
mph
SSW→W
5-19
mph
UV: 8
 Very High 
UV: 10
 Very High 
UV: 9
 Very High 
UV: 6
 High 

 

Today
 
Partly cloudy. A chance of rain in the afternoon. Scattered thunderstorms likely, some possibly severe. Very hot. High 98°. Heat index up to 109°. UV index up to 8. Wind south-southwest around 9 mph, gusting to 30 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Tonight
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thunderstorms likely, some possibly severe. Warm. Low 79°. Wind south-southwest around 7 mph, gusting to 24 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Thursday
 
Mostly sunny in the morning, becoming partly to mostly sunny in the afternoon. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thundershowers possible. Very hot. High 98°. Heat index up to 113°. UV index up to 10. Wind south-southwest around 8 mph, gusting to 29 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.
Thursday night
 
Partly to mostly cloudy in the evening, becoming fair after midnight. Light to moderate fog in the evening, then moderate to dense fog after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thunderstorms likely. Low 73°. Wind west around 9 mph, gusting to 24 mph, in the evening, becoming 5 mph, gusting to 19 mph, after midnight. Chance of precipitation 60 percent. Precipitation mostly around a quarter of an inch.
Friday
 
Sunny. Moderate fog in the morning. High 87°. Heat index up to 92°. UV index up to 9. Wind west-northwest around 5 mph, gusting to 25 mph.
Friday night
 
Clear in the evening, becoming mostly clear after midnight. Moderate fog after midnight. Low 68°. Wind east around 3 mph, gusting to 20 mph, in the evening, becoming southeast after midnight.
Saturday
 
Mostly cloudy. Light to moderate fog in the morning. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thunderstorms likely. High 87°. Heat index up to 93°. UV index up to 6. Wind south-southwest around 7 mph, gusting to 25 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Saturday night
 
Partly to mostly cloudy in the evening, becoming cloudy after midnight. Patchy light fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Scattered thunderstorms likely. Low 72°. Wind south-southwest around 5 mph, gusting to 19 mph, in the evening, becoming west after midnight. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Sunday
 
Mostly cloudy to cloudy in the morning, becoming partly cloudy in the afternoon. Light to moderate fog in the morning. A chance of rain. Scattered thundershowers possible. High 85°. UV index up to 8. Wind north around 8 mph, gusting to 28 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Sunday night
 
Partly cloudy in the evening, becoming mostly cloudy after midnight. Low 65°. Wind northeast around 5 mph, gusting to 26 mph.
Monday
 
Cloudy in the morning, becoming dense overcast 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. Cool. High 70°. UV index up to 4. Wind northeast around 6 mph, gusting to 24 mph. Chance of precipitation 70 percent. Precipitation mostly around half an inch.
Monday night
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Patchy light fog after midnight. Relatively cool. Low 61°. Wind north around 5 mph, gusting to 23 mph.
Tuesday
 
Mostly cloudy to cloudy in the morning, becoming partly cloudy in the afternoon. A slight chance of rain in the morning, then a chance of rain in the afternoon. Precipitation showery or intermittent. High 78°. UV index up to 10. Wind west-northwest around 4 mph, gusting to 24 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Tuesday night
 
Mostly clear in the evening, becoming clear after midnight. Light to moderate fog after midnight. Relatively cool. Low 61°. Wind west-southwest around 4 mph, gusting to 18 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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