S
M
T
W
T
F
S
30
94°
64°
31
99°
66°
1
100°
71°
2
100°
74°
3
100°
74°
4
100°
74°
5
103°
74°
6
92°
71°
7
89°
64°
8
94°
60°
9
95°
70°
10
82°
70°
11
87°
68°
12
93°
67°
13
89°
66°
14
87°
61°
15
98°
67°
16
96°
74°
17
98°
73°
18
98°
72°
19
96°
71°
20
94°
69°
21
77°
67°
22
73°
60°
23
71°
58°
24
74°
60°
25
77°
58°
26
74°
58°
27
75°
58°
28
82°
55°
29
86°
50°
30
95°
64°
1
93°
71°
2
74°
56°
3
78°
50°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in O'Fallon
O'Fallon's September 2026 forecast shows daily high temperatures ranging from ° to °, with overnight lows between ° and °. The average high for September is ° with an average low of °. AccuWeather's monthly forecast extends further ahead than any other source, with day-by-day RealFeel® Temperatures giving a complete picture of how September weather will actually feel in O'Fallon. See also: October | November | December.
