S
M
T
W
T
F
S
30
80°
61°
31
77°
54°
1
74°
54°
2
74°
55°
3
75°
54°
4
75°
55°
5
74°
55°
6
72°
56°
7
71°
57°
8
73°
57°
9
73°
53°
10
72°
53°
11
72°
52°
12
70°
52°
13
71°
53°
14
70°
52°
15
71°
55°
16
71°
51°
17
70°
50°
18
71°
54°
19
70°
57°
20
69°
54°
21
72°
54°
22
Hist. Avg.
75°
48°
23
Hist. Avg.
74°
48°
24
Hist. Avg.
74°
48°
25
Hist. Avg.
74°
47°
26
Hist. Avg.
73°
47°
27
Hist. Avg.
73°
46°
28
Hist. Avg.
72°
46°
29
Hist. Avg.
72°
46°
30
Hist. Avg.
72°
45°
1
Hist. Avg.
71°
45°
2
Hist. Avg.
71°
44°
3
Hist. Avg.
70°
44°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
*Temporarily Unavailable
September Weather in Alton
Alton's September 2026 forecast shows daily high temperatures ranging from 69° to 80°, with overnight lows between 50° and 61°. The average high for September is 72° with an average low of 54°. 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.
