S
M
T
W
T
F
S
30
83°
57°
31
79°
52°
1
81°
56°
2
81°
54°
3
85°
54°
4
84°
56°
5
77°
56°
6
78°
55°
7
86°
51°
8
86°
50°
9
80°
48°
10
78°
50°
11
77°
51°
12
78°
50°
13
83°
48°
14
75°
48°
15
75°
44°
16
76°
44°
17
75°
52°
18
80°
52°
19
82°
51°
20
82°
52°
21
83°
53°
22
83°
54°
23
84°
52°
24
82°
52°
25
81°
49°
26
80°
48°
27
70°
49°
28
73°
50°
29
76°
48°
30
70°
47°
1
76°
41°
2
66°
43°
3
72°
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 66° to 86°, with overnight lows between 41° and 57°. The average high for September is 79° with an average low of 50°. 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.
