WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Monday, 11-May-2026 04:00 pm
 
Tonight

Clear
Clear
Tuesday

Sunny
Sunny
Tuesday
night
Fog late
Fog late
Wednesday

Sunny
Sunny
Wednesday
night
Clear
Clear
Thursday

Mostly Sunny
Mostly Sunny
Thursday
night
Partly Cloudy
Partly Cloudy
Friday

Chance rain
Chance rain
<.1 in. <.25 in.
Low: 51° High: 81° Low: 58° High: 75° Low: 51° High: 75° Low: 53° High: 75°
               
S
3-23
mph
SW
6-24→10-28
mph
W
8-22
mph
NW
9-29
mph
NNW→NE
4-24
mph
ESE
5-25
mph
ESE
8-24
mph
S
12-27
mph
UV: 8
 Very High 
UV: 7
 High 
UV: 8
 Very High 
UV: 5
 Medium 

 

Tonight
 
Clear. Cool. Low 51°. Wind south around 3 mph, gusting to 23 mph.
Tuesday
 
Sunny. Warm. High 81°. UV index up to 8. Wind southwest around 6 mph, gusting to 24 mph, in the morning, becoming 10 mph, gusting to 28 mph, in the afternoon.
Tuesday night
 
Partly to mostly cloudy in the evening, becoming clear after midnight. Patchy light fog after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Low 58°. Wind west around 8 mph, gusting to 22 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Wednesday
 
Sunny. High 75°. UV index up to 7. Wind northwest around 9 mph, gusting to 29 mph.
Wednesday night
 
Clear. Cool. Low 51°. Wind north-northwest around 4 mph, gusting to 24 mph, in the evening, becoming northeast after midnight.
Thursday
 
Sunny in the morning, becoming partly to mostly sunny in the afternoon. High 75°. UV index up to 8. Wind east-southeast around 5 mph, gusting to 25 mph.
Thursday night
 
Partly cloudy. Cool. Low 53°. Wind east-southeast around 8 mph, gusting to 24 mph.
Friday
 
Mostly cloudy in the morning, becoming mostly cloudy to cloudy in the afternoon. A chance of rain. Breezy. High 75°. UV index up to 5. Wind south around 12 mph, gusting to 27 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Friday night
 
Mostly cloudy in the evening, becoming fair after midnight. Moderate fog. A chance of rain in the evening, then a slight chance of rain after midnight. Precipitation showery or intermittent. Low 60°. Wind south-southwest around 5 mph, gusting to 18 mph, in the evening, becoming west after midnight. Chance of precipitation 60 percent. Precipitation mostly around a quarter of an inch.
Saturday
 
Sunny. Light to moderate fog in the morning. Warm. High 84°. UV index up to 8. Wind west around 5 mph, gusting to 21 mph.
Saturday night
 
Fair in the evening, becoming partly to mostly cloudy after midnight. Moderate fog after midnight. Low 60°. Wind southeast around 5 mph.
Sunday
 
Sunny in the morning, becoming partly cloudy in the afternoon. Light to moderate fog in the morning. Unusually hot. High 90°. UV index up to 9. Wind south around 9 mph, gusting to 27 mph.
Sunday night
 
Clear in the evening, becoming fair after midnight. Low 64°. Wind south around 9 mph, gusting to 23 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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