WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Friday, 07-Aug-2026 04:00 pm
 
Tonight

Fog late
Fog late
Saturday

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

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

Fog a.m.
Hot!
Fog a.m.
Hot!
Monday
night
Partly Cloudy
Partly Cloudy
Tuesday

Mostly Sunny
Hot!
Mostly Sunny
Hot!
<.1 in. <.1 in. <.1 in. <.1 in.
Low: 73° High: 89° Low: 73° High: 92° Low: 74° High: 95° Low: 75° High: 97°
  Heat: 96°   Heat: 101°   Heat: 106°   Heat: 107°
SW
5-21
mph
W→ENE
3-21
mph
E→S
3-16
mph
SSW
6-23
mph
SSW
6-18
mph
SSW
8-26
mph
SSW→SE
7-19
mph
SSW
6-24
mph
UV: 8
 Very High 
UV: 8
 Very High 
UV: 8
 Very High 
UV: 8
 Very High 

 

Tonight
 
Fair to partly cloudy in the evening, becoming fair after midnight. Light to moderate fog in the evening, then moderate to dense fog after midnight. A chance of rain in the evening, then a slight chance of rain after midnight. Low 73°. Wind southwest around 5 mph, gusting to 21 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Saturday
 
Partly to mostly sunny in the morning, becoming mostly sunny in the afternoon. Moderate to dense fog in the morning. A chance of rain. Hot. High 89°. Heat index up to 96°. UV index up to 8. Wind west around 3 mph, gusting to 21 mph, in the morning, becoming east-northeast in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Saturday night
 
Fair in the evening, becoming fair to partly cloudy after midnight. Moderate fog after midnight. A slight chance of rain after midnight. Low 73°. Wind east around 3 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.
Sunday
 
Mostly sunny in the morning, becoming sunny in the afternoon. Moderate fog in the morning. A chance of rain. Hot. High 92°. Heat index up to 101°. UV index up to 8. Wind south-southwest around 6 mph, gusting to 23 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Clear. Light to moderate fog after midnight. Low 74°. Wind south-southwest around 6 mph, gusting to 18 mph.
Monday
 
Mostly sunny in the morning, becoming sunny in the afternoon. Light to moderate fog in the morning. Very hot. High 95°. Heat index up to 106°. UV index up to 8. Wind south-southwest around 8 mph, gusting to 26 mph.
Monday night
 
Fair to partly cloudy in the evening, becoming fair after midnight. Low 75°. Wind south-southwest around 7 mph, gusting to 19 mph, in the evening, becoming southeast after midnight.
Tuesday
 
Mostly sunny in the morning, becoming partly to mostly sunny in the afternoon. Very hot. High 97°. Heat index up to 107°. UV index up to 8. Wind south-southwest around 6 mph, gusting to 24 mph.
Tuesday night
 
Partly cloudy. Patchy light fog after midnight. A chance of rain after midnight. Precipitation showery or intermittent. Low 74°. Wind south-southwest around 4 mph, gusting to 17 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Wednesday
 
Partly cloudy in the morning, becoming mostly sunny in the afternoon. Moderate fog in the morning. A chance of rain in the morning, then a slight chance of rain in the afternoon. Scattered thundershowers possible. Very hot. High 97°. Heat index up to 108°. UV index up to 8. Wind southwest around 5 mph, gusting to 21 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch.
Wednesday night
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Patchy light fog after midnight. Rain likely. Scattered thunderstorms likely. Low 75°. Wind south-southwest around 2 mph, gusting to 17 mph. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch.
Thursday
 
Mostly cloudy to cloudy in the morning, becoming partly to mostly cloudy in the afternoon. Light to moderate fog in the morning. A chance of rain. Scattered thundershowers possible. Hot. High 93°. Heat index up to 104°. UV index up to 6. Wind south-southwest around 3 mph, gusting to 18 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Thursday night
 
Fair to partly cloudy. Light to moderate fog after midnight. Low 72°. Wind east-northeast around 7 mph, gusting to 20 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

Powered by Davis Vantage Pro2  and   CumulusMX   v 4.6.4 (b4128)   MXUI Template v 2.2.6 by  Silver Acorn     Valid HTML5 USA Weather Finder Badge