S
M
T
W
T
F
S
30
66°
63°
31
73°
66°
1
83°
65°
2
82°
58°
3
78°
57°
4
75°
51°
5
75°
51°
6
76°
54°
7
77°
53°
8
77°
55°
9
71°
52°
10
72°
51°
11
74°
47°
12
74°
51°
13
75°
53°
14
70°
50°
15
70°
52°
16
74°
51°
17
73°
48°
18
66°
46°
19
70°
50°
20
73°
52°
21
73°
52°
22
74°
51°
23
74°
50°
24
72°
49°
25
72°
49°
26
71°
50°
27
72°
49°
28
72°
48°
29
70°
46°
30
65°
45°
1
65°
46°
2
69°
48°
3
69°
46°
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 65° to 83°, with overnight lows between 45° and 66°. The average high for September is 73° with an average low of 52°. 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.
