S
M
T
W
T
F
S
30
71°
41°
31
71°
40°
1
70°
39°
2
70°
39°
3
69°
38°
4
65°
38°
5
65°
39°
6
66°
38°
7
65°
38°
8
59°
37°
9
62°
37°
10
60°
36°
11
66°
37°
12
66°
37°
13
60°
36°
14
60°
35°
15
62°
38°
16
62°
36°
17
63°
35°
18
57°
36°
19
58°
37°
20
63°
34°
21
63°
31°
22
58°
30°
23
55°
30°
24
56°
29°
25
57°
32°
26
63°
33°
27
59°
31°
28
56°
33°
29
62°
28°
30
59°
30°
1
60°
32°
2
61°
34°
3
60°
32°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Keystone
Keystone's September 2026 forecast shows daily high temperatures ranging from 55° to 71°, with overnight lows between 28° and 41°. The average high for September is 62° with an average low of 35°. 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 Keystone. See also: October | November | December.
