WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Sunday, 15-Mar-2026 04:00 pm
 
Tonight

Severe storm
Severe storm
Monday

Cloudy
Cloudy
Monday
night
Partly Cloudy
Partly Cloudy
Tuesday

Partly Cloudy
Partly Cloudy
Tuesday
night
Mix
Mix
Wednesday

Sunny
Sunny
Wednesday
night
Partly Cloudy
Partly Cloudy
Thursday

Partly Cloudy
Partly Cloudy
.25 in. <.1 in.
Low: 26° High: 28° Low: 11° High: 39° Low: 32° High: 64° Low: 39° High: 70°
WCh: 19° WCh: 5° WCh: -1°   WCh: 25°      
WNW
17-34
mph
WNW
17-34
mph
WNW
10-24
mph
NW→SW
7-22→4-22
mph
SE
8-23
mph
S→WSW
7-24
mph
WSW→SSW
3-18
mph
WSW→NW
4-21
mph
UV: 5
 Medium 
UV: 5
 Medium 

 

Tonight
 
Cloudy in the evening, becoming dense overcast after midnight. Patchy light fog in the evening. Rain likely in the evening, then a slight chance of a mix of rain and snow after midnight. Severe thunderstorms likely, with possible tornados. Windy and cold. Low 26°. Wind chill ranging from 19 to 57. Wind west-northwest around 17 mph, gusting to 34 mph. Chance of precipitation 70 percent. Precipitation (liquid equivalent) mostly around a quarter of an inch. No snow accumulation expected.
Monday
 
Dense overcast in the morning, becoming cloudy in the afternoon. Windy and very cold. High 28°, but temperatures falling in the afternoon. Wind chill ranging from 5 to 18. Wind west-northwest around 17 mph, gusting to 34 mph.
Monday night
 
Partly cloudy in the evening, becoming fair after midnight. Extremely cold. Low 11°. Wind chill ranging from -1 to 5. Wind west-northwest around 10 mph, gusting to 24 mph.
Tuesday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Cold. High 39°. Wind northwest around 7 mph, gusting to 22 mph, in the morning, becoming southwest around 4 mph, gusting to 22 mph, in the afternoon.
Tuesday night
 
Cloudy in the evening, becoming mostly cloudy to cloudy after midnight. A chance of a mix of sleet and snow. Low 32°. Wind chill ranging from 25 to 34. Wind southeast around 8 mph, gusting to 23 mph. Chance of precipitation 30 percent. Precipitation (liquid equivalent) mostly less than a tenth of an inch. No snow or ice (on ground) accumulation expected.
Wednesday
 
Sunny. Mild. High 64°. UV index up to 5. Wind south around 7 mph, gusting to 24 mph, in the morning, becoming west-southwest in the afternoon.
Wednesday night
 
Partly cloudy. Low 39°. Wind west-southwest around 3 mph, gusting to 18 mph, in the evening, becoming south-southwest after midnight.
Thursday
 
Partly cloudy in the morning, becoming sunny in the afternoon. Mild. High 70°. UV index up to 5. Wind west-southwest around 4 mph, gusting to 21 mph, in the morning, becoming northwest in the afternoon.
Thursday night
 
Clear. Low 39°. Wind northeast around 2 mph in the evening, becoming south-southwest after midnight.
Friday
 
Sunny. Unusually warm. High 75°. UV index up to 6. Wind south-southwest around 3 mph, gusting to 17 mph, in the morning, becoming 7 mph, gusting to 23 mph, in the afternoon.
Friday night
 
Fair. Low 43°. Wind south-southwest around 5 mph, gusting to 16 mph.
Saturday
 
Sunny. Unusually hot. High 82°. UV index up to 6. Wind west-northwest around 6 mph, gusting to 22 mph.
Saturday night
 
Clear. Low 44°. Wind south-southwest around 4 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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