WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Monday, 29-Jun-2026 04:00 pm
 
Tonight

Fog late
Fog late
Tuesday

Fog a.m.
Hot!
Fog a.m.
Hot!
Tuesday
night
Fog late
Fog late
Wednesday

Fog a.m.
Hot!
Fog a.m.
Hot!
Wednesday
night
Fog late
Fog late
Thursday

Thunder storm
Hot!
Thunder storm
Hot!
Thursday
night
Fog late
Fog late
Friday

Thunder storm
Hot!
Thunder storm
Hot!
<.1 in. <.1 in. <.1 in.
Low: 75° High: 97° Low: 73° High: 96° Low: 75° High: 95° Low: 75° High: 94°
  Heat: 105°   Heat: 106°   Heat: 107°   Heat: 105°
S
7-26
mph
S
7-25
mph
S
5-20
mph
S
6-24
mph
S
6-19
mph
S
5-23
mph
SSE
5-18
mph
SSW
5-20
mph
UV: 9
 Very High 
UV: 9
 Very High 
UV: 9
 Very High 
UV: 9
 Very High 

 

Tonight
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Light to moderate fog after midnight. Low 75°. Wind south around 7 mph, gusting to 26 mph.
Tuesday
 
Partly to mostly sunny in the morning, becoming sunny in the afternoon. Light to moderate fog in the morning. Very hot. High 97°. Heat index up to 105°. UV index up to 9. Wind south around 7 mph, gusting to 25 mph.
Tuesday night
 
Clear. Patchy light fog after midnight. Low 73°. Wind south around 5 mph, gusting to 20 mph.
Wednesday
 
Sunny. Patchy light fog in the morning. Very hot. High 96°. Heat index up to 106°. UV index up to 9. Wind south around 6 mph, gusting to 24 mph.
Wednesday night
 
Clear in the evening, becoming fair after midnight. Patchy light fog after midnight. Low 75°. Wind south around 6 mph, gusting to 19 mph.
Thursday
 
Partly to mostly cloudy in the morning, becoming partly cloudy in the afternoon. Patchy light fog in the morning. A slight chance of rain in the afternoon. Scattered thundershowers possible. Hot. High 95°. Heat index up to 107°. UV index up to 9. Wind south around 5 mph, gusting to 23 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Thursday 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 slight chance of rain. Low 75°. Wind south-southeast around 5 mph, gusting to 18 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Friday
 
Mostly sunny in the morning, becoming partly 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 thundershowers possible. Hot. High 94°. Heat index up to 105°. UV index up to 9. Wind south-southwest around 5 mph, gusting to 20 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Friday night
 
Partly cloudy in the evening, becoming fair to partly cloudy after midnight. Moderate fog. Low 75°. Wind south around 4 mph.
Saturday
 
Partly to mostly cloudy. Light to moderate fog in the morning. A chance of rain. Scattered thunderstorms likely. High 89°. Heat index up to 100°. UV index up to 8. Wind south around 3 mph, gusting to 17 mph. Chance of precipitation 50 percent. Precipitation mostly less than a quarter of an inch.
Saturday night
 
Partly cloudy in the evening, becoming fair after midnight. Light to moderate fog in the evening, then moderate fog after midnight. Low 74°. Wind south-southeast around 2 mph in the evening, becoming south-southwest after midnight.
Sunday
 
Mostly sunny in the morning, becoming partly to mostly sunny in the afternoon. Moderate fog in the morning. Hot. High 95°. Heat index up to 106°. UV index up to 9. Wind southwest around 4 mph, gusting to 21 mph, in the morning, becoming 7 mph, gusting to 24 mph, in the afternoon.
Sunday night
 
Mostly cloudy in the evening, becoming fair after midnight. Moderate fog in the evening, then moderate to dense fog after midnight. Rain likely in the evening, then a chance of rain after midnight. Thunderstorms very likely, some possibly severe. Low 75°. Wind east-northeast around 4 mph, gusting to 16 mph, in the evening, becoming south-southwest after midnight. Chance of precipitation 60 percent. Precipitation mostly between a quarter and half an inch.

WXSIM forecast formatting script by Saratoga-Weather.org.

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