S
M
T
W
T
F
S
30
78°
52°
31
79°
44°
1
71°
53°
2
83°
51°
3
83°
56°
4
86°
51°
5
86°
57°
6
85°
59°
7
80°
57°
8
75°
46°
9
71°
44°
10
80°
43°
11
80°
49°
12
62°
44°
13
69°
56°
14
74°
43°
15
65°
46°
16
73°
51°
17
71°
55°
18
70°
46°
19
70°
45°
20
74°
47°
21
73°
46°
22
73°
50°
23
79°
50°
24
79°
49°
25
75°
46°
26
68°
38°
27
74°
47°
28
58°
44°
29
67°
36°
30
63°
44°
1
71°
38°
2
66°
43°
3
72°
40°
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 58° to 79°, with overnight lows between 36° and 56°. The average high for September is 71° with an average low of 46°. 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.
