S
M
T
W
T
F
S
30
89°
60°
31
80°
63°
1
81°
63°
2
87°
68°
3
89°
69°
4
89°
68°
5
88°
62°
6
87°
59°
7
80°
57°
8
79°
58°
9
80°
65°
10
82°
63°
11
79°
57°
12
78°
56°
13
77°
61°
14
79°
64°
15
81°
54°
16
84°
53°
17
74°
53°
18
74°
54°
19
75°
53°
20
73°
53°
21
73°
52°
22
74°
52°
23
74°
53°
24
77°
56°
25
78°
59°
26
80°
58°
27
81°
56°
28
73°
60°
29
78°
51°
30
80°
51°
1
72°
54°
2
71°
49°
3
69°
53°
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 69° to 89°, with overnight lows between 49° and 69°. The average high for September is 79° with an average low of 58°. 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.
