WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Sunday, 13-Sep-2026 04:00 pm
 
Tonight

Fog late
Fog late
Monday

Fog a.m.
Fog a.m.
Monday
night
Partly Cloudy
Partly Cloudy
Tuesday

Thunder storm
Thunder storm
Tuesday
night
Thunder storm
Thunder storm
Wednesday

Thunder storm
Thunder storm
Wednesday
night
Thunder storm
Thunder storm
Thursday

Thunder storm
Thunder storm
.1 in. <.25 in. <.1 in. <.1 in. <.1 in.
Low: 59° High: 86° Low: 62° High: 90° Low: 66° High: 91° Low: 69° High: 93°
          Heat: 96°   Heat: 99°
NE
5-21
mph
ESE
8-26
mph
SE
8-21
mph
SSW→WSW
6-19
mph
ENE
2
mph
ENE→S
3-18
mph
S
4
mph
SW→WNW
4-20
mph
UV: 7
 High 
UV: 5
 Medium 
UV: 6
 High 
UV: 6
 High 

 

Tonight
 
Partly cloudy in the evening, becoming fair after midnight. Patchy light fog after midnight. Low 59°. Wind northeast around 5 mph, gusting to 21 mph.
Monday
 
Partly to mostly sunny in the morning, becoming mostly sunny in the afternoon. Patchy light fog in the morning. Hot. High 86°. UV index up to 7. Wind east-southeast around 8 mph, gusting to 26 mph.
Monday night
 
Partly cloudy in the evening, becoming mostly clear after midnight. Low 62°. Wind southeast around 8 mph, gusting to 21 mph.
Tuesday
 
Mostly sunny in the morning, becoming partly to mostly cloudy in the afternoon. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thunderstorms likely. Unusually hot. High 90°. UV index up to 5. Wind south-southwest around 6 mph, gusting to 19 mph, in the morning, becoming west-southwest in the afternoon. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Tuesday night
 
Partly cloudy. 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 thundershowers possible. Low 66°. Wind east-northeast around 2 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Wednesday
 
Partly to mostly sunny. Light to moderate fog in the morning. A slight chance of rain. Scattered thundershowers possible. Very hot. High 91°. Heat index up to 96°. UV index up to 6. Wind east-northeast around 3 mph, gusting to 18 mph, in the morning, becoming south in the afternoon. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Wednesday night
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Light to moderate fog. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thundershowers possible. Low 69°. Wind south around 4 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Thursday
 
Partly cloudy. A chance of rain. Scattered thundershowers possible. Very hot. High 93°. Heat index up to 99°. UV index up to 6. Wind southwest around 4 mph, gusting to 20 mph, in the morning, becoming west-northwest in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Thursday night
 
Partly cloudy. Light to moderate fog after midnight. A slight chance of rain. Scattered thundershowers possible. Low 67°. Wind northeast around 2 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Friday
 
Mostly sunny in the morning, becoming sunny in the afternoon. Light to moderate fog in the morning. Unusually hot. High 89°. Heat index up to 94°. UV index up to 7. Wind east around 3 mph.
Friday night
 
Partly cloudy in the evening, becoming fair after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. A slight chance of rain. Scattered thundershowers possible. Low 67°. Wind east around 4 mph in the evening, becoming southeast after midnight. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Saturday
 
Mostly sunny in the morning, becoming partly to mostly sunny in the afternoon. Patchy light fog in the morning. Very hot. High 94°. Heat index up to 99°. UV index up to 5. Wind southwest around 8 mph, gusting to 23 mph.
Saturday night
 
Partly cloudy. A slight chance of rain. Scattered thundershowers possible. Low 66°. Wind northwest around 4 mph in the evening, becoming north-northeast after midnight. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.

WXSIM forecast formatting script by Saratoga-Weather.org.

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