WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com
Updated: Friday, 18-Sep-2026 05:00 am
 
Today

Sunny
Hot!
Sunny
Hot!
Tonight

Partly Cloudy
Partly Cloudy
Saturday

Partly Cloudy
Hot!
Partly Cloudy
Hot!
Saturday
night
Partly Cloudy
Partly Cloudy
Sunday

Chance rain
Chance rain
Sunday
night
Rain likely
Rain likely
Monday

Chance rain
Chance rain
Monday
night
Chance rain
Chance rain
.1 in. .35 in. .1 in. <.1 in.
High: 97° Low: 72° High: 95° Low: 71° High: 89° Low: 70° High: 75° Low: 61°
Heat: 103°   Heat: 101°   Heat: 93°      
ENE→S
2-23
mph
SSE
4
mph
SW
6-24
mph
S→SW
2
mph
NW→W
3-21
mph
NE→NW
2
mph
NW
3-17→8-23
mph
N
7-22
mph
UV: 7
 High 
UV: 6
 High 
UV: 5
 Medium 

 

Today
 
Sunny. Extremely hot. High 97°. Heat index up to 103°. UV index up to 7. Wind east-northeast around 2 mph, gusting to 23 mph, in the morning, becoming south in the afternoon.
Tonight
 
Fair in the evening, becoming fair to partly cloudy after midnight. Warm. Low 72°. Wind south-southeast around 4 mph.
Saturday
 
Partly to mostly cloudy in the morning, becoming partly cloudy in the afternoon. Very hot. High 95°. Heat index up to 101°. UV index up to 6. Wind southwest around 6 mph, gusting to 24 mph.
Saturday night
 
Partly cloudy. Warm. Low 71°. Wind south around 2 mph in the evening, becoming southwest after midnight.
Sunday
 
Partly cloudy in the morning, becoming mostly cloudy in the afternoon. A chance of rain in the afternoon. Unusually hot. High 89°. Heat index up to 93°. UV index up to 5. Wind northwest around 3 mph, gusting to 21 mph, in the morning, becoming west in the afternoon. Chance of precipitation 40 percent. Precipitation mostly around a tenth of an inch.
Sunday night
 
Partly to mostly cloudy in the evening, becoming cloudy after midnight. Moderate fog in the evening, then patchy light fog after midnight. Rain likely. Warm. Low 70°. Wind northeast around 2 mph in the evening, becoming northwest after midnight. Chance of precipitation 60 percent. Precipitation mostly between a quarter and half an inch.
Monday
 
Cloudy in the morning, becoming mostly cloudy to cloudy in the afternoon. Patchy light fog in the morning. A chance of rain. High 75°. Wind northwest around 3 mph, gusting to 17 mph, in the morning, becoming 8 mph, gusting to 23 mph, in the afternoon. Chance of precipitation 50 percent. Precipitation mostly around a tenth of an inch.
Monday night
 
Mostly cloudy in the evening, becoming cloudy after midnight. Patchy light fog after midnight. A chance of rain. Low 61°. Wind north around 7 mph, gusting to 22 mph. Chance of precipitation 40 percent. Precipitation mostly less than a tenth of an inch.
Tuesday
 
Cloudy. A slight chance of rain. High 69°. Wind north-northeast around 8 mph, gusting to 26 mph. Chance of precipitation 20 percent. Precipitation mostly less than a tenth of an inch.
Tuesday night
 
Mostly cloudy to cloudy in the evening, becoming mostly cloudy after midnight. Low 56°. Wind north-northeast around 7 mph, gusting to 24 mph.
Wednesday
 
Partly to mostly cloudy. High 73°. UV index up to 5. Wind north-northeast around 8 mph, gusting to 26 mph.
Wednesday night
 
Mostly cloudy in the evening, becoming mostly cloudy to cloudy after midnight. Low 57°. Wind north-northeast around 6 mph, gusting to 22 mph.
Thursday
 
Mostly cloudy in the morning, becoming partly to mostly cloudy in the afternoon. High 74°. UV index up to 5. Wind northeast around 6 mph, gusting to 25 mph.
Thursday night
 
Partly to mostly cloudy in the evening, becoming mostly cloudy after midnight. Low 56°. Wind northeast around 5 mph, gusting to 21 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