WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Saturday, 20-Jun-2026 04:00 pm
 
Tonight

Partly Cloudy
Partly Cloudy
Sunday

Thunder storm
Thunder storm
Sunday
night
Thunder storm
Thunder storm
Monday

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

Mostly Cloudy
Mostly Cloudy
Tuesday
night
Partly Cloudy
Partly Cloudy
Wednesday

Thunder storm
Thunder storm
.35 in. .1 in. <.1 in. .25 in.
Low: 67° High: 79° Low: 67° High: 77° Low: 62° High: 82° Low: 59° High: 76°
               
NE→ESE
5-21
mph
SE→SSW
9-22
mph
NW
8-20
mph
NNE
7-25
mph
NNE→ENE
4-22
mph
ENE
5-23
mph
ENE
4-22
mph
SSE
3
mph
UV: 6
 High 
UV: 6
 High 
UV: 7
 High 
UV: 4
 Medium 

 

Tonight
 
Fair to partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Low 67°. Wind northeast around 5 mph, gusting to 21 mph, in the evening, becoming east-southeast after midnight.
Sunday
 
Cloudy in the morning, becoming mostly cloudy to cloudy in the afternoon. A chance of rain in the morning, then rain likely in the afternoon. Scattered thundershowers possible. High 79°. UV index up to 6. Wind southeast around 9 mph, gusting to 22 mph, in the morning, becoming south-southwest in the afternoon. Chance of precipitation 70 percent. Precipitation mostly between a quarter and half an inch.
Sunday night
 
Mostly cloudy. Patchy light fog. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thundershowers possible. Low 67°. Wind northwest around 8 mph, gusting to 20 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Monday
 
Mostly cloudy in the morning, becoming mostly cloudy to cloudy in the afternoon. Patchy light fog in the morning. A chance of rain. High 77°. UV index up to 6. Wind north-northeast around 7 mph, gusting to 25 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Monday night
 
Mostly cloudy to cloudy in the evening, becoming mostly cloudy after midnight. Relatively cool. Low 62°. Wind north-northeast around 4 mph, gusting to 22 mph, in the evening, becoming east-northeast after midnight.
Tuesday
 
Partly to mostly cloudy in the morning, becoming partly to mostly sunny in the afternoon. High 82°. UV index up to 7. Wind east-northeast around 5 mph, gusting to 23 mph.
Tuesday night
 
Mostly clear in the evening, becoming fair to partly cloudy after midnight. Relatively cool. Low 59°. Wind east-northeast around 4 mph, gusting to 22 mph.
Wednesday
 
Mostly cloudy to cloudy in the morning, becoming cloudy in the afternoon. Rain likely. Scattered thundershowers possible. High 76°. UV index up to 4. Wind south-southeast around 3 mph. Chance of precipitation 60 percent. Precipitation mostly around a quarter of an inch.
Wednesday night
 
Partly to mostly cloudy in the evening, becoming mostly cloudy after midnight. Patchy light fog after midnight. A chance of rain. Scattered thundershowers possible. Relatively cool. Low 65°. Wind southeast around 2 mph in the evening, becoming west-northwest after midnight. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Thursday
 
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Patchy light fog in the morning. A chance of rain. Precipitation showery or intermittent. High 82°. UV index up to 6. Wind north-northwest around 4 mph, gusting to 21 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Thursday night
 
Mostly clear in the evening, becoming clear after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. Relatively cool. Low 63°. Wind north-northeast around 2 mph, gusting to 15 mph.
Friday
 
Mostly sunny in the morning, becoming mostly cloudy to cloudy in the afternoon. Patchy light fog in the morning. A slight chance of rain in the afternoon. Scattered thundershowers possible. High 84°. UV index up to 7. Wind east-northeast around 6 mph, gusting to 23 mph, in the morning, becoming east-southeast in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Friday night
 
Cloudy in the evening, becoming mostly cloudy after midnight. Light to moderate fog in the evening, then moderate fog after midnight. Rain likely in the evening, then a chance of rain after midnight. Scattered thundershowers possible. Low 70°. Wind southeast around 6 mph, gusting to 18 mph, in the evening, becoming south after midnight. Chance of precipitation 80 percent. Precipitation mostly around half an inch.

WXSIM forecast formatting script by Saratoga-Weather.org.

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