S
M
T
W
T
F
S
30
78°
56°
31
76°
55°
1
75°
58°
2
77°
58°
3
76°
55°
4
77°
55°
5
76°
58°
6
77°
60°
7
75°
54°
8
76°
53°
9
73°
59°
10
77°
52°
11
74°
51°
12
74°
51°
13
75°
53°
14
75°
57°
15
80°
58°
16
80°
58°
17
79°
57°
18
80°
56°
19
79°
48°
20
71°
49°
21
70°
54°
22
71°
55°
23
75°
55°
24
76°
56°
25
77°
48°
26
76°
45°
27
73°
47°
28
68°
46°
29
68°
46°
30
67°
45°
1
Hist. Avg.
71°
48°
2
Hist. Avg.
70°
48°
3
Hist. Avg.
70°
48°
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 67° to 80°, with overnight lows between 45° and 60°. The average high for September is 75° with an average low of 53°. 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.
