WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Monday, 14-Sep-2026 05:00 am
 
Today

Partly Cloudy
Partly Cloudy
Tonight

Partly Cloudy
Partly Cloudy
Tuesday

Thunder storm
Thunder storm
Tuesday
night
Thunder storm
Thunder storm
Wednesday

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

Mostly Cloudy
Hot!
Mostly Cloudy
Hot!
Thursday
night
Fog late
Fog late
<.1 in. <.1 in. <.1 in. <.1 in.
High: 85° Low: 63° High: 97° Low: 68° High: 93° Low: 70° High: 93° Low: 68°
        Heat: 100°   Heat: 101°  
ESE
8-27
mph
SE
8-21
mph
S→WSW
6-23
mph
SE
2
mph
SE→SSW
3-20
mph
S
3
mph
WSW→WNW
4-19
mph
N
2
mph
UV: 6
 High 
UV: 7
 High 
UV: 6
 High 
UV: 5
 Medium 

 

Today
 
Mostly sunny in the morning, becoming partly cloudy in the afternoon. Hot. High 85°. UV index up to 6. Wind east-southeast around 8 mph, gusting to 27 mph.
Tonight
 
Clear in the evening, becoming fair to partly cloudy after midnight. Low 63°. Wind southeast around 8 mph, gusting to 21 mph.
Tuesday
 
Sunny in the morning, becoming partly cloudy in the afternoon. A chance of rain in the afternoon. Scattered thunderstorms likely. Extremely hot. High 97°. UV index up to 7. Wind south around 6 mph, gusting to 23 mph, in the morning, becoming west-southwest in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Tuesday night
 
Partly to mostly cloudy in the evening, becoming partly cloudy after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thundershowers possible. Low 68°. Wind southeast around 2 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Wednesday
 
Partly cloudy in the morning, becoming partly to mostly sunny in the afternoon. A chance of rain. Scattered thundershowers possible. Very hot. High 93°. Heat index up to 100°. UV index up to 6. Wind southeast around 3 mph, gusting to 20 mph, in the morning, becoming south-southwest in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Wednesday night
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Patchy light fog after midnight. A slight chance of rain. Scattered thunderstorms likely. Warm. Low 70°. Wind south around 3 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Thursday
 
Mostly sunny in the morning, becoming partly to mostly cloudy in the afternoon. Very hot. High 93°. Heat index up to 101°. UV index up to 5. Wind west-southwest around 4 mph, gusting to 19 mph, in the morning, becoming west-northwest in the afternoon.
Thursday night
 
Partly cloudy. Patchy light fog after midnight. Low 68°. Wind north around 2 mph.
Friday
 
Mostly sunny. Patchy light fog in the morning. Very hot. High 92°. Heat index up to 98°. UV index up to 7. Wind east-northeast around 3 mph, gusting to 17 mph, in the morning, becoming southeast in the afternoon.
Friday night
 
Partly cloudy in the evening, becoming mostly clear after midnight. Light to moderate fog after midnight. A slight chance of rain. Scattered thundershowers possible. Low 68°. Wind southeast around 4 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Saturday
 
Sunny. Patchy light fog in the morning. Very hot. High 96°. Heat index up to 101°. UV index up to 7. Wind south-southwest around 6 mph, gusting to 21 mph.
Saturday night
 
Partly cloudy in the evening, becoming fair after midnight. Light to moderate fog. A chance of rain. Scattered thundershowers possible. Warm. Low 69°. Wind south around 3 mph. Chance of precipitation 50 percent. Precipitation mostly around a quarter of an inch.
Sunday
 
Sunny in the morning, becoming partly to mostly sunny in the afternoon. Patchy light fog in the morning. Very hot. High 92°. Heat index up to 98°. UV index up to 6. Wind southwest around 7 mph, gusting to 24 mph.
Sunday night
 
Partly to mostly cloudy. Moderate fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Scattered thundershowers possible. Low 69°. Wind west around 3 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.

WXSIM forecast formatting script by Saratoga-Weather.org.

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