WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Thursday, 16-Jul-2026 04:00 pm
 
Tonight

Rain likely
Rain likely
Friday

Rain likely
Rain likely
Friday
night
Chance rain
Chance rain
Saturday

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

Thunder storm
Hot!
Thunder storm
Hot!
Sunday
night
Thunder storm
Thunder storm
Monday

Thunder storm
Hot!
Thunder storm
Hot!
.1 in. .1 in. <.1 in. <.1 in. <.1 in. <.1 in. <.1 in. <.1 in.
Low: 73° High: 89° Low: 75° High: 91° Low: 76° High: 91° Low: 75° High: 93°
  Heat: 96°   Heat: 102°   Heat: 101°   Heat: 105°
SW
2-17
mph
WSW
4-17→7-23
mph
WSW
5-19
mph
W
7-24
mph
W
5-20
mph
N
3-20
mph
E
2-15
mph
SSE→SW
3-19
mph
UV: 9
 Very High 
UV: 9
 Very High 
UV: 8
 Very High 
UV: 9
 Very High 

 

Tonight
 
Partly cloudy. Patchy light fog in the evening, then moderate fog after midnight. Rain likely. Precipitation showery or intermittent. Low 73°. Wind southwest around 2 mph, gusting to 17 mph. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch.
Friday
 
Partly to mostly sunny. Moderate fog in the morning. Rain likely. Precipitation showery or intermittent. High 89°. Heat index up to 96°. UV index up to 9. Wind west-southwest around 4 mph, gusting to 17 mph, in the morning, becoming 7 mph, gusting to 23 mph, in the afternoon. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch.
Friday night
 
Fair. Light to moderate fog in the evening, then moderate fog after midnight. A chance of rain. Low 75°. Wind west-southwest around 5 mph, gusting to 19 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch.
Saturday
 
Partly to mostly sunny. Moderate fog in the morning. A chance of rain. Scattered thundershowers possible. Hot. High 91°. Heat index up to 102°. UV index up to 9. Wind west around 7 mph, gusting to 24 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch.
Saturday night
 
Fair to partly cloudy in the evening, becoming mostly cloudy after midnight. Patchy light fog after midnight. A chance of rain. Scattered thundershowers possible. Low 76°. Wind west around 5 mph, gusting to 20 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Sunday
 
Partly to mostly sunny in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. Rain likely. Scattered thundershowers possible. Hot. High 91°. Heat index up to 101°. UV index up to 8. Wind north around 3 mph, gusting to 20 mph. Chance of precipitation 60 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Fair to partly cloudy in the evening, becoming partly cloudy after midnight. Patchy light fog in the evening, then moderate fog after midnight. A chance of rain. Scattered thundershowers possible. Low 75°. Wind east around 2 mph, gusting to 15 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch.
Monday
 
Partly cloudy in the morning, becoming partly to mostly sunny in the afternoon. Moderate fog in the morning. A chance of rain. Scattered thundershowers possible. Hot. High 93°. Heat index up to 105°. UV index up to 9. Wind south-southeast around 3 mph, gusting to 19 mph, in the morning, becoming southwest in the afternoon. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch.
Monday night
 
Fair in the evening, becoming partly cloudy after midnight. Light to moderate fog after midnight. Low 76°. Wind southwest around 4 mph, gusting to 15 mph.
Tuesday
 
Sunny in the morning, becoming partly to mostly sunny in the afternoon. Light to moderate fog in the morning. Hot. High 96°. Heat index up to 108°. UV index up to 9. Wind southwest around 8 mph, gusting to 24 mph, in the morning, becoming northwest in the afternoon.
Tuesday night
 
Mostly clear in the evening, becoming clear after midnight. Light to moderate fog after midnight. Relatively cool. Low 67°. Wind north around 7 mph, gusting to 19 mph.
Wednesday
 
Sunny. Light to moderate fog in the morning. High 81°. UV index up to 9. Wind northeast around 8 mph, gusting to 29 mph.
Wednesday night
 
Mostly cloudy to cloudy in the evening, becoming partly cloudy after midnight. Relatively cool. Low 65°. Wind northeast around 4 mph, gusting to 24 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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