WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Monday, 09-Mar-2026 04:00 pm
 
Tonight

Fog late
Fog late
Tuesday

Thunder storm
Thunder storm
Tuesday
night
Thunder storm
Thunder storm
Wednesday

Rain likely
Rain likely
Wednesday
night
Fog late
Fog late
Thursday

Fog a.m.
Fog a.m.
Thursday
night
Partly Cloudy
Partly Cloudy
Friday

Partly Cloudy
Partly Cloudy
<.1 in. .1 in. .5 in.
Low: 57° High: 77° Low: 60° High: 62° Low: 36° High: 57° Low: 43° High: 64°
               
SSW
9-28
mph
SSW
7-21→12-25
mph
SSW
11-22
mph
WNW
12-31
mph
NW
10-29→6-21
mph
SW
2-21→7-23
mph
SSW
9-20→16-23
mph
WSW→WNW
10-26
mph
UV: 4
 Medium 

 

Tonight
 
Fair to partly cloudy. Patchy light fog in the evening, then moderate fog after midnight. Mild. Low 57°. Wind south-southwest around 9 mph, gusting to 28 mph.
Tuesday
 
Partly to mostly sunny in the morning, becoming mostly cloudy in the afternoon. Moderate fog in the morning. A slight chance of rain. Scattered thunderstorms likely. Unusually warm. High 77°. Wind south-southwest around 7 mph, gusting to 21 mph, in the morning, becoming 12 mph, gusting to 25 mph, in the afternoon. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Tuesday night
 
Mostly cloudy to cloudy in the evening, becoming dense overcast after midnight. Patchy light fog after midnight. A slight chance of rain in the evening, then a chance of rain after midnight. Scattered thundershowers possible. Unusually mild. Low 60°. Wind south-southwest around 11 mph, gusting to 22 mph. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Wednesday
 
Dense overcast in the morning, becoming mostly cloudy in the afternoon. Patchy light fog. Rain likely in the morning, then a chance of rain in the afternoon. Precipitation showery or intermittent. Breezy and mild. High 62°, but temperatures falling in the afternoon. Wind west-northwest around 12 mph, gusting to 31 mph. Chance of precipitation 70 percent. Precipitation mostly around half an inch.
Wednesday night
 
Fair in the evening, becoming clear after midnight. Patchy light fog after midnight. Low 36°. Wind northwest around 10 mph, gusting to 29 mph, in the evening, becoming 6 mph, gusting to 21 mph, after midnight.
Thursday
 
Sunny. Patchy light fog in the morning. High 57°. Wind southwest around 2 mph, gusting to 21 mph, in the morning, becoming 7 mph, gusting to 23 mph, in the afternoon.
Thursday night
 
Partly cloudy. Breezy. Low 43°. Wind south-southwest around 9 mph, gusting to 20 mph, in the evening, becoming 16 mph, gusting to 23 mph, after midnight.
Friday
 
Partly cloudy. Mild. High 64°. UV index up to 4. Wind west-southwest around 10 mph, gusting to 26 mph, in the morning, becoming west-northwest in the afternoon.
Friday night
 
Partly cloudy in the evening, becoming clear after midnight. Low 35°. Wind north around 5 mph, gusting to 22 mph, in the evening, becoming east after midnight.
Saturday
 
Sunny. Mild. High 67°. UV index up to 5. Wind east around 8 mph, gusting to 21 mph, in the morning, becoming southeast around 11 mph, gusting to 28 mph, in the afternoon.
Saturday night
 
Clear in the evening, becoming partly cloudy after midnight. Low 47°. Wind south-southeast around 10 mph, gusting to 22 mph.
Sunday
 
Mostly cloudy to cloudy in the morning, becoming dense overcast in the afternoon. A chance of rain. Breezy. High 54°, but temperatures falling in the afternoon. Wind west-southwest around 12 mph, gusting to 26 mph, in the morning, becoming north-northwest around 16 mph, gusting to 33 mph, in the afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Sunday night
 
Mostly cloudy in the evening, becoming clear after midnight. Breezy and cold. Low 27°. Wind chill ranging from 19 to 36. Wind north-northwest around 14 mph, gusting to 31 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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