WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Tuesday, 23-Jun-2026 04:00 pm
 
Tonight

Partly Cloudy
Partly Cloudy
Wednesday

Thunder storm
Thunder storm
Wednesday
night
Fog late
Fog late
Thursday

Thunder storm
Thunder storm
Thursday
night
Thunder storm
Thunder storm
Friday

Thunder storm
Thunder storm
Friday
night
Thunder storm
Thunder storm
Saturday

Thunder storm
Thunder storm
.1 in. .5 in. .75 in. 1.5 in. 1.5 in. .1 in.
Low: 65° High: 84° Low: 66° High: 86° Low: 69° High: 72° Low: 68° High: 86°
              Heat: 92°
E→SSE
4-23
mph
SSE→SW
5-23→8-27
mph
W
4-24
mph
W
4-23
mph
E→SSE
3
mph
ESE
4
mph
NNE→SSW
3
mph
SSW
4-20
mph
UV: 7
 High 
UV: 7
 High 
UV: 4
 Medium 
UV: 7
 High 

 

Tonight
 
Partly cloudy in the evening, becoming mostly cloudy after midnight. Relatively cool. Low 65°. Wind east around 4 mph, gusting to 23 mph, in the evening, becoming south-southeast after midnight.
Wednesday
 
Mostly cloudy in the morning, becoming partly cloudy in the afternoon. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thundershowers possible. High 84°. UV index up to 7. Wind south-southeast around 5 mph, gusting to 23 mph, in the morning, becoming southwest around 8 mph, gusting to 27 mph, in the afternoon. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Wednesday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Patchy light fog in the evening, then moderate fog after midnight. Low 66°. Wind west around 4 mph, gusting to 24 mph.
Thursday
 
Partly to mostly cloudy in the morning, becoming mostly cloudy to cloudy in the afternoon. Patchy light fog in the morning, then light to moderate fog in the afternoon. A slight chance of rain in the morning, then rain likely in the afternoon. Scattered thunderstorms likely. High 86°. UV index up to 7. Wind west around 4 mph, gusting to 23 mph. Chance of precipitation 70 percent. Precipitation mostly around half an inch.
Thursday night
 
Cloudy in the evening, becoming dense overcast after midnight. Light to moderate fog in the evening, then patchy light fog after midnight. Rain very likely. Scattered thundershowers possible. Low 69°. Wind east around 3 mph in the evening, becoming south-southeast after midnight. Chance of precipitation 80 percent. Precipitation mostly between half an inch and one inch.
Friday
 
Dense overcast in the morning, becoming cloudy in the afternoon. Light to moderate fog in the morning, then moderate fog in the afternoon. Rain very likely. Scattered thundershowers possible. Relatively cool. High 72°. UV index up to 4. Wind east-southeast around 4 mph. Chance of precipitation 80 percent. Precipitation mostly between 1 and 2 inches.
Friday night
 
Cloudy in the evening, becoming mostly cloudy to cloudy after midnight. Moderate fog. Rain likely. Scattered thunderstorms likely. Low 68°. Wind north-northeast around 3 mph in the evening, becoming south-southwest after midnight. Chance of precipitation 80 percent. Precipitation mostly between 1 and 2 inches.
Saturday
 
Partly to mostly cloudy. Moderate fog in the morning. A chance of rain. Scattered thunderstorms likely. High 86°. Heat index up to 92°. UV index up to 7. Wind south-southwest around 4 mph, gusting to 20 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Saturday night
 
Partly cloudy. Moderate fog. Rain likely. Scattered thunderstorms likely. Low 73°. Wind south-southeast around 4 mph in the evening, becoming southwest after midnight. Chance of precipitation 70 percent. Precipitation mostly around half an inch.
Sunday
 
Partly to mostly sunny in the morning, becoming mostly sunny in the afternoon. Moderate to dense fog in the morning. Hot. High 90°. Heat index up to 101°. UV index up to 9. Wind south-southeast around 6 mph, gusting to 21 mph.
Sunday night
 
Clear. Light to moderate fog in the evening, then moderate to dense fog after midnight. Low 74°. Wind south around 5 mph, gusting to 17 mph.
Monday
 
Sunny. Moderate fog in the morning. Hot. High 93°. Heat index up to 105°. UV index up to 10. Wind south around 5 mph, gusting to 18 mph, in the morning, becoming southwest in the afternoon.
Monday night
 
Mostly clear in the evening, becoming mostly cloudy to cloudy after midnight. Patchy light fog. Low 76°. Wind southeast around 2 mph in the evening, becoming south-southwest after midnight.

WXSIM forecast formatting script by Saratoga-Weather.org.

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