S
M
T
W
T
F
S
30
97°
76°
31
96°
77°
1
98°
76°
2
97°
77°
3
98°
77°
4
98°
76°
5
97°
77°
6
98°
77°
7
98°
76°
8
96°
76°
9
97°
77°
10
97°
75°
11
96°
74°
12
96°
75°
13
95°
75°
14
96°
74°
15
96°
74°
16
94°
73°
17
94°
74°
18
93°
74°
19
94°
73°
20
94°
73°
21
93°
72°
22
94°
73°
23
93°
73°
24
93°
72°
25
92°
71°
26
92°
72°
27
94°
71°
28
93°
72°
29
92°
71°
30
92°
72°
1
91°
70°
2
93°
71°
3
93°
70°
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 91° to 98°, with overnight lows between 70° and 77°. The average high for September is 95° with an average low of 74°. 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.
