WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Thursday, 02-Jul-2026 04:00 pm
 
Tonight

Thunder storm
Thunder storm
Friday

Thunder storm
Hot!
Thunder storm
Hot!
Friday
night
Thunder storm
Thunder storm
Saturday

Thunder storm
Hot!
Thunder storm
Hot!
Saturday
night
Thunder storm
Thunder storm
Sunday

Thunder storm
Thunder storm
Sunday
night
Fog late
Fog late
Monday

Fog a.m.
Fog a.m.
<.1 in. <.1 in. .1 in. <.25 in. .25 in. <.1 in.
Low: 75° High: 95° Low: 75° High: 94° Low: 75° High: 90° Low: 72° High: 88°
  Heat: 106°   Heat: 105°   Heat: 99°   Heat: 95°
SSW
4-22
mph
S
5-24
mph
SE→SW
4-19
mph
SW→W
5-23
mph
S→W
4
mph
WSW→NW
3-22
mph
N
3-19
mph
NNE
4-23
mph
UV: 8
 Very High 
UV: 10
 Very High 
UV: 10
 Very High 
UV: 8
 Very High 

 

Tonight
 
Partly to mostly cloudy in the evening, becoming fair after midnight. Patchy light fog in the evening, then moderate fog after midnight. A chance of rain. Scattered thunderstorms likely, some possibly severe. Low 75°. Wind south-southwest around 4 mph, gusting to 22 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Friday
 
Sunny in the morning, becoming partly to mostly cloudy in the afternoon. Moderate fog in the morning. A slight chance of rain in the morning, then a chance of rain in the afternoon. Scattered thunderstorms likely, some possibly severe. Hot. High 95°. Heat index up to 106°. UV index up to 8. Wind south around 5 mph, gusting to 24 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Friday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Moderate fog. A chance of rain in the evening, then a slight chance of rain after midnight. Scattered thunderstorms likely. Low 75°. Wind southeast around 4 mph, gusting to 19 mph, in the evening, becoming southwest after midnight. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch.
Saturday
 
Partly cloudy. Moderate fog in the morning. A slight chance of rain in the morning, then rain likely in the afternoon. Thunderstorms very likely, some possibly severe. Hot. High 94°. Heat index up to 105°. UV index up to 10. Wind southwest around 5 mph, gusting to 23 mph, in the morning, becoming west in the afternoon. Chance of precipitation 70 percent. Precipitation mostly less than a quarter of an inch.
Saturday night
 
Moderate fog. Rain likely in the evening, then a chance of rain after midnight. Scattered thunderstorms likely, some possibly severe. Low 75°. Wind south around 4 mph in the evening, becoming west after midnight. Chance of precipitation 80 percent. Precipitation mostly around a quarter of an inch.
Sunday
 
Partly to mostly cloudy in the morning, becoming partly cloudy in the afternoon. Moderate fog in the morning. A chance of rain. Scattered thunderstorms likely. High 90°. Heat index up to 99°. UV index up to 10. Wind west-southwest around 3 mph, gusting to 22 mph, in the morning, becoming northwest in the afternoon. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Fair in the evening, becoming fair to partly cloudy after midnight. Patchy light fog in the evening, then moderate fog after midnight. Low 72°. Wind north around 3 mph, gusting to 19 mph.
Monday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Moderate fog in the morning. High 88°. Heat index up to 95°. UV index up to 8. Wind north-northeast around 4 mph, gusting to 23 mph.
Monday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Patchy light fog after midnight. Low 70°. Wind north-northeast around 3 mph, gusting to 22 mph.
Tuesday
 
Partly cloudy. Patchy light fog in the morning. A chance of rain. High 86°. UV index up to 8. Wind north around 5 mph, gusting to 24 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Tuesday night
 
Clear in the evening, becoming fair to partly cloudy after midnight. Patchy light fog after midnight. Low 69°. Wind north around 2 mph, gusting to 21 mph, in the evening, becoming northeast after midnight.
Wednesday
 
Mostly sunny in the morning, becoming sunny in the afternoon. Patchy light fog in the morning. Hot. High 90°. Heat index up to 97°. UV index up to 10. Wind east-southeast around 4 mph, gusting to 23 mph.
Wednesday night
 
Partly cloudy in the evening, becoming partly to mostly cloudy after midnight. Light to moderate fog after midnight. A chance of rain after midnight. Scattered thunderstorms likely. Low 71°. Wind south-southeast around 8 mph, gusting to 21 mph. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch.

WXSIM forecast formatting script by Saratoga-Weather.org.

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