WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Thursday, 16-Jul-2026 05:00 am
 
Today

Chance rain
Chance rain
Tonight

Chance rain
Chance rain
Friday

Chance rain
Chance rain
Friday
night
Fog late
Fog late
Saturday

Fog a.m.
Hot!
Fog a.m.
Hot!
Saturday
night
Fog late
Fog late
Sunday

Fog a.m.
Hot!
Fog a.m.
Hot!
Sunday
night
Fog late
Fog late
.1 in. <.25 in. .1 in. <.1 in. <.1 in. <.1 in.
High: 91° Low: 74° High: 90° Low: 75° High: 92° Low: 75° High: 94° Low: 74°
Heat: 97°   Heat: 99°   Heat: 103°   Heat: 105°  
NW→ESE
2-20
mph
SW
2
mph
WSW
5-24
mph
WSW
5-19
mph
WSW
8-25
mph
W
5-21
mph
W
3-20
mph
E→S
2-16
mph
UV: 9
 Very High 
UV: 8
 Very High 
UV: 9
 Very High 
UV: 10
 Very High 

 

Today
 
Partly to mostly sunny 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. Hot. High 91°. Heat index up to 97°. UV index up to 9. Wind northwest around 2 mph, gusting to 20 mph, in the morning, becoming east-southeast in the afternoon. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Tonight
 
Partly to mostly cloudy. Light to moderate fog. A chance of rain in the evening, then a slight chance of rain after midnight. Low 74°. Wind southwest around 2 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Friday
 
Partly cloudy. Light to moderate fog in the morning. A chance of rain. High 90°. Heat index up to 99°. UV index up to 8. Wind west-southwest around 5 mph, gusting to 24 mph. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Friday night
 
Partly cloudy in the evening, becoming mostly clear after midnight. Light to moderate fog in the evening, then moderate to dense fog after midnight. A chance of rain. Low 75°. Wind west-southwest around 5 mph, gusting to 19 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Saturday
 
Mostly sunny in the morning, becoming partly to mostly sunny in the afternoon. Moderate fog in the morning. Hot. High 92°. Heat index up to 103°. UV index up to 9. Wind west-southwest around 8 mph, gusting to 25 mph.
Saturday night
 
Fair to partly cloudy. Moderate fog after midnight. A chance of rain. Low 75°. Wind west around 5 mph, gusting to 21 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Sunday
 
Mostly sunny in the morning, becoming partly to mostly sunny in the afternoon. Light to moderate fog in the morning. Hot. High 94°. Heat index up to 105°. UV index up to 10. Wind west around 3 mph, gusting to 20 mph.
Sunday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Light to moderate fog after midnight. A slight chance of rain after midnight. Low 74°. Wind east around 2 mph, gusting to 16 mph, in the evening, becoming south after midnight. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Monday
 
Partly cloudy in the morning, becoming mostly cloudy in the afternoon. Patchy light fog in the morning. A slight chance of rain. Precipitation showery or intermittent. Hot. High 94°. Heat index up to 104°. UV index up to 7. Wind southwest around 4 mph, gusting to 19 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Monday night
 
Fair in the evening, becoming partly cloudy after midnight. Moderate fog after midnight. A slight chance of rain. Precipitation showery or intermittent. Low 76°. Wind southwest around 4 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Tuesday
 
Partly cloudy. A chance of rain. Precipitation showery or intermittent. Very hot. High 99°. Heat index up to 110°. UV index up to 9. Wind west around 7 mph, gusting to 25 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Tuesday night
 
Partly to mostly cloudy in the evening, becoming mostly cloudy after midnight. Light to moderate fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Precipitation showery or intermittent. Low 71°. Wind northeast around 7 mph, gusting to 22 mph. Chance of precipitation 50 percent. Precipitation mostly around a quarter of an inch.
Wednesday
 
Dense overcast. Light to moderate fog in the morning, then patchy light fog in the afternoon. Rain likely in the morning, then a chance of rain in the afternoon. Relatively cool. High 78°. UV index up to 5. Wind east-southeast around 6 mph, gusting to 23 mph. Chance of precipitation 80 percent. Precipitation mostly around an inch.
Wednesday night
 
Cloudy in the evening, becoming mostly clear after midnight. Patchy light fog after midnight. Low 69°. Wind east-southeast around 5 mph, gusting to 22 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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