S
M
T
W
T
F
S
30
93°
64°
31
98°
63°
1
99°
70°
2
99°
74°
3
99°
74°
4
100°
72°
5
96°
71°
6
93°
69°
7
91°
70°
8
92°
70°
9
94°
71°
10
92°
67°
11
85°
64°
12
85°
62°
13
86°
63°
14
83°
62°
15
81°
59°
16
83°
64°
17
83°
63°
18
78°
60°
19
79°
63°
20
82°
62°
21
81°
63°
22
79°
62°
23
80°
58°
24
80°
60°
25
81°
61°
26
79°
55°
27
71°
49°
28
70°
48°
29
68°
49°
30
72°
49°
1
69°
52°
2
73°
56°
3
67°
54°
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 67° to 100°, with overnight lows between 48° and 74°. The average high for September is 83° with an average low of 62°. 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.
