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
91°
59°
12
79°
55°
13
97°
54°
14
88°
66°
15
73°
55°
16
77°
52°
17
73°
63°
18
84°
59°
19
79°
57°
20
75°
54°
21
77°
52°
22
82°
50°
23
73°
59°
24
77°
59°
25
72°
54°
26
88°
57°
27
81°
57°
28
70°
54°
29
66°
53°
30
69°
48°
1
64°
48°
2
76°
53°
3
73°
44°
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 64° to 88°, with overnight lows between 44° and 57°. The average high for September is 73° 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.
