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

Partly Cloudy
Partly Cloudy
Friday

Thunder storm
Thunder storm
Friday
night
Thunder storm
Thunder storm
Saturday

Thunder storm
Thunder storm
Saturday
night
Fog late
Fog late
Sunday

Thunder storm
Thunder storm
Sunday
night
Thunder storm
Thunder storm
Monday

Thunder storm
Thunder storm
<.1 in. <.1 in. <.1 in. .5 in. .35 in. 1.0 in.
Low: 65° High: 86° Low: 67° High: 83° Low: 70° High: 75° Low: 70° High: 75°
               
S
8-26
mph
S
9-27
mph
SSW
8-22
mph
SW
6-19
mph
SW
4-18
mph
SE
4-15→8-18
mph
SSE
7-16
mph
S
5
mph
UV: 6
 High 
UV: 6
 High 
UV: 4
 Medium 
UV: 4
 Medium 

 

Tonight
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Low 65°. Wind south around 8 mph, gusting to 26 mph.
Friday
 
Partly to mostly sunny in the morning, becoming partly to mostly cloudy in the afternoon. A slight chance of rain. Scattered thunderstorms likely, some possibly severe. High 86°. UV index up to 6. Wind south around 9 mph, gusting to 27 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Friday night
 
Mostly cloudy in the evening, becoming partly cloudy after midnight. Moderate fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Scattered thunderstorms likely. Low 67°. Wind south-southwest around 8 mph, gusting to 22 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Saturday
 
Mostly cloudy to cloudy in the morning, becoming mostly cloudy in the afternoon. Moderate fog in the morning. A chance of rain. Scattered thunderstorms likely, some possibly severe. High 83°. UV index up to 6. Wind southwest around 6 mph, gusting to 19 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Saturday night
 
Mostly cloudy in the evening, becoming mostly cloudy to cloudy after midnight. Light to moderate fog after midnight. Low 70°. Wind southwest around 4 mph, gusting to 18 mph.
Sunday
 
Dense overcast. Light to moderate fog in the morning, then patchy light fog in the afternoon. Rain very likely. Thunderstorms very likely, some possibly severe. High 75°. UV index up to 4. Wind southeast around 4 mph, gusting to 15 mph, in the morning, becoming 8 mph, gusting to 18 mph, in the afternoon. Chance of precipitation 80 percent. Precipitation mostly around half an inch.
Sunday night
 
Dense overcast in the evening, becoming mostly cloudy to cloudy after midnight. Patchy light fog in the evening, then moderate fog after midnight. Rain likely. Thunderstorms very likely, some possibly severe. Low 70°. Wind south-southeast around 7 mph, gusting to 16 mph. Chance of precipitation 70 percent. Precipitation mostly between a quarter and half an inch.
Monday
 
Moderate fog in the morning, then moderate to dense fog in the afternoon. A chance of rain in the morning, then rain likely in the afternoon. Scattered thunderstorms likely. High 75°. UV index up to 4. Wind south around 5 mph. Chance of precipitation 70 percent. Precipitation mostly around an inch.
Monday night
 
Moderate fog in the evening, then moderate to dense fog after midnight. A slight chance of rain. Scattered thundershowers possible. Low 69°. Wind south-southwest around 4 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Tuesday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Moderate fog in the morning. A slight chance of rain. Scattered thunderstorms likely, some possibly severe. Hot. High 90°. Heat index up to 98°. UV index up to 9. Wind south-southwest around 6 mph, gusting to 23 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Tuesday night
 
Partly to mostly cloudy in the evening, becoming fair to partly cloudy after midnight. Patchy light fog in the evening, then moderate fog after midnight. Low 74°. Wind south-southwest around 7 mph, gusting to 18 mph.
Wednesday
 
Sunny. Light to moderate fog in the morning. Very hot. High 93°. Heat index up to 105°. UV index up to 10. Wind southwest around 8 mph, gusting to 24 mph.
Wednesday night
 
Clear. Light to moderate fog in the evening, then moderate fog after midnight. Low 73°. Wind west-southwest around 4 mph, gusting to 17 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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