S
M
T
W
T
F
S
30
82°
61°
31
83°
64°
1
87°
64°
2
88°
65°
3
88°
65°
4
87°
59°
5
82°
58°
6
82°
58°
7
83°
59°
8
84°
64°
9
83°
62°
10
81°
63°
11
86°
62°
12
87°
63°
13
87°
62°
14
86°
63°
15
86°
62°
16
85°
62°
17
85°
61°
18
84°
57°
19
84°
58°
20
82°
52°
21
77°
54°
22
77°
57°
23
79°
57°
24
82°
52°
25
77°
51°
26
77°
57°
27
76°
54°
28
75°
53°
29
80°
55°
30
80°
56°
1
81°
54°
2
80°
54°
3
75°
55°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Alton
Alton's September 2026 forecast shows daily high temperatures ranging from 75° to 88°, with overnight lows between 51° and 65°. The average high for September is 82° with an average low of 59°. 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 Alton. See also: October | November | December.
