WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Saturday, 19-Sep-2026 04:00 pm
 
Tonight

Partly Cloudy
Partly Cloudy
Sunday

Partly Cloudy
Partly Cloudy
Sunday
night
Mostly Cloudy
Mostly Cloudy
Monday

Mostly Cloudy
Mostly Cloudy
Monday
night
Mostly Cloudy
Mostly Cloudy
Tuesday

Cloudy
Cloudy
Tuesday
night
Mostly Cloudy
Mostly Cloudy
Wednesday

Mostly Sunny
Mostly Sunny
<.1 in. <.1 in. <.1 in. <.1 in.
Low: 72° High: 90° Low: 68° High: 77° Low: 61° High: 70° Low: 54° High: 74°
  Heat: 94°            
SSE→SW
3-20
mph
W
5-24
mph
N
6-20
mph
N
6-23
mph
N
7-22
mph
NNE
7-25
mph
NNE
6-22
mph
NNE
7-25
mph
UV: 6
 High 
UV: 5
 Medium 
UV: 6
 High 

 

Tonight
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Warm. Low 72°. Wind south-southeast around 3 mph, gusting to 20 mph, in the evening, becoming southwest after midnight.
Sunday
 
Partly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Unusually hot. High 90°. Heat index up to 94°. UV index up to 6. Wind west around 5 mph, gusting to 24 mph.
Sunday night
 
Partly to mostly cloudy in the evening, becoming dense overcast after midnight. A chance of rain. Warm. Low 68°. Wind north around 6 mph, gusting to 20 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Monday
 
Cloudy in the morning, becoming mostly cloudy to cloudy in the afternoon. A chance of rain. High 77°. UV index up to 5. Wind north around 6 mph, gusting to 23 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 cloudy after midnight. A slight chance of rain. Low 61°. Wind north around 7 mph, gusting to 22 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Tuesday
 
Cloudy. A slight chance of rain. High 70°. Wind north-northeast around 7 mph, gusting to 25 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Tuesday night
 
Mostly cloudy in the evening, becoming partly to mostly cloudy after midnight. Low 54°. Wind north-northeast around 6 mph, gusting to 22 mph.
Wednesday
 
Sunny in the morning, becoming partly to mostly sunny in the afternoon. High 74°. UV index up to 6. Wind north-northeast around 7 mph, gusting to 25 mph.
Wednesday night
 
Fair to partly cloudy. Low 51°. Wind northeast around 5 mph, gusting to 22 mph.
Thursday
 
Partly cloudy in the morning, becoming partly to mostly sunny in the afternoon. High 75°. UV index up to 6. Wind northeast around 5 mph, gusting to 24 mph.
Thursday night
 
Mostly cloudy. Low 57°. Wind northeast around 5 mph, gusting to 19 mph.
Friday
 
Cloudy in the morning, becoming dense overcast in the afternoon. A chance of rain in the afternoon. High 70°. Wind east-northeast around 6 mph, gusting to 19 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Friday night
 
Dense overcast. A chance of rain in the evening, then a slight chance of rain after midnight. Low 58°. Wind east-northeast around 8 mph, gusting to 17 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.

WXSIM forecast formatting script by Saratoga-Weather.org.

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