S
M
T
W
T
F
S
30
76°
45°
31
80°
47°
1
80°
47°
2
79°
48°
3
82°
45°
4
80°
42°
5
76°
42°
6
75°
41°
7
74°
40°
8
75°
41°
9
76°
41°
10
75°
39°
11
77°
44°
12
76°
44°
13
73°
44°
14
71°
38°
15
70°
37°
16
Hist. Avg.
70°
36°
17
Hist. Avg.
70°
35°
18
Hist. Avg.
69°
35°
19
Hist. Avg.
69°
34°
20
Hist. Avg.
69°
34°
21
Hist. Avg.
68°
34°
22
Hist. Avg.
68°
34°
23
Hist. Avg.
67°
33°
24
Hist. Avg.
67°
33°
25
Hist. Avg.
67°
32°
26
Hist. Avg.
66°
32°
27
Hist. Avg.
66°
32°
28
Hist. Avg.
65°
31°
29
Hist. Avg.
65°
31°
30
Hist. Avg.
64°
31°
1
Hist. Avg.
64°
30°
2
Hist. Avg.
64°
30°
3
Hist. Avg.
63°
30°
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 70° to 82°, with overnight lows between 37° and 48°. The average high for September is 76° with an average low of 43°. 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.
