S
M
T
W
T
F
S
30
73°
46°
31
65°
43°
1
67°
44°
2
72°
40°
3
73°
33°
4
74°
47°
5
75°
42°
6
57°
37°
7
70°
41°
8
82°
59°
9
85°
61°
10
86°
65°
11
83°
61°
12
83°
58°
13
78°
56°
14
72°
58°
15
75°
58°
16
70°
57°
17
70°
57°
18
73°
55°
19
74°
55°
20
73°
54°
21
72°
50°
22
66°
52°
23
66°
49°
24
65°
48°
25
65°
50°
26
66°
52°
27
64°
51°
28
64°
46°
29
65°
42°
30
60°
40°
1
60°
41°
2
61°
43°
3
62°
46°
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 60° to 86°, with overnight lows between 40° and 65°. The average high for September is 71° 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.
