S
M
T
W
T
F
S
30
82°
66°
31
84°
63°
1
88°
61°
2
90°
61°
3
91°
59°
4
95°
59°
5
95°
63°
6
90°
63°
7
90°
63°
8
86°
63°
9
82°
55°
10
90°
54°
11
90°
55°
12
83°
61°
13
91°
64°
14
84°
55°
15
67°
52°
16
76°
57°
17
74°
58°
18
75°
55°
19
77°
54°
20
79°
56°
21
78°
55°
22
75°
52°
23
71°
53°
24
76°
45°
25
75°
46°
26
74°
47°
27
78°
50°
28
77°
49°
29
67°
47°
30
74°
43°
1
71°
45°
2
77°
47°
3
76°
47°
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 67° to 91°, with overnight lows between 43° and 64°. The average high for September is 77° with an average low of 52°. 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.
