S
M
T
W
T
F
S
30
71°
52°
31
79°
44°
1
85°
48°
2
82°
49°
3
77°
46°
4
76°
55°
5
74°
54°
6
75°
56°
7
67°
52°
8
63°
39°
9
75°
48°
10
82°
48°
11
62°
40°
12
56°
41°
13
49°
38°
14
62°
33°
15
68°
38°
16
67°
36°
17
68°
41°
18
71°
42°
19
75°
44°
20
76°
44°
21
70°
37°
22
64°
42°
23
62°
37°
24
67°
39°
25
73°
42°
26
72°
41°
27
67°
40°
28
60°
29°
29
56°
28°
30
56°
28°
1
58°
32°
2
58°
30°
3
63°
35°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Boulder
Boulder's September 2026 forecast shows daily high temperatures ranging from 49° to 82°, with overnight lows between 28° and 48°. The average high for September is 65° with an average low of 38°. 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 Boulder. See also: October | November | December.
