S
M
T
W
T
F
S
26
67°
31°
27
73°
35°
28
65°
32°
29
53°
36°
30
48°
43°
1
60°
33°
2
48°
30°
3
47°
40°
4
62°
32°
5
68°
41°
6
60°
50°
7
63°
41°
8
56°
33°
9
60°
30°
10
63°
49°
11
62°
39°
12
57°
32°
13
57°
33°
14
65°
47°
15
66°
52°
16
77°
46°
17
78°
52°
18
64°
46°
19
89°
46°
20
87°
59°
21
63°
45°
22
68°
33°
23
68°
36°
24
62°
43°
25
62°
46°
26
79°
57°
27
75°
47°
28
61°
43°
29
61°
44°
30
59°
40°
31
62°
42°
1
63°
43°
2
68°
43°
3
76°
52°
4
75°
51°
5
75°
53°
6
73°
47°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
May Weather in Alton
Alton's May 2026 forecast shows daily high temperatures ranging from 59° to 79°, with overnight lows between 40° and 57°. The average high for May is 68° with an average low of 47°. AccuWeather's monthly forecast extends further ahead than any other source, with day-by-day RealFeel® Temperatures giving a complete picture of how May weather will actually feel in Alton. See also: June | July | August.
