S
M
T
W
T
F
S
30
81°
54°
31
83°
55°
1
81°
52°
2
81°
54°
3
82°
55°
4
77°
50°
5
78°
52°
6
77°
51°
7
85°
54°
8
82°
53°
9
73°
50°
10
76°
50°
11
76°
51°
12
80°
53°
13
81°
50°
14
80°
54°
15
76°
54°
16
72°
52°
17
73°
49°
18
77°
52°
19
74°
48°
20
70°
48°
21
80°
52°
22
72°
47°
23
71°
46°
24
73°
47°
25
68°
41°
26
69°
42°
27
72°
44°
28
75°
45°
29
74°
37°
30
68°
36°
1
64°
38°
2
66°
40°
3
70°
36°
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 85°, with overnight lows between 36° and 55°. The average high for September is 75° with an average low of 48°. 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.
