S
M
T
W
T
F
S
30
95°
65°
31
97°
64°
1
99°
71°
2
99°
73°
3
99°
74°
4
100°
72°
5
102°
73°
6
90°
74°
7
89°
62°
8
93°
59°
9
94°
69°
10
80°
68°
11
84°
66°
12
92°
65°
13
86°
66°
14
88°
61°
15
97°
76°
16
94°
73°
17
97°
71°
18
97°
71°
19
96°
69°
20
92°
67°
21
72°
67°
22
71°
62°
23
71°
54°
24
68°
54°
25
75°
53°
26
72°
58°
27
75°
60°
28
80°
52°
29
83°
49°
30
91°
64°
1
89°
67°
2
75°
49°
3
74°
46°
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.
