S
M
T
W
T
F
S
30
75°
40°
31
75°
41°
1
77°
39°
2
73°
44°
3
74°
44°
4
75°
41°
5
71°
37°
6
70°
36°
7
71°
38°
8
72°
39°
9
71°
38°
10
72°
37°
11
70°
37°
12
70°
36°
13
Hist. Avg.
75°
46°
14
Hist. Avg.
74°
45°
15
Hist. Avg.
74°
45°
16
Hist. Avg.
73°
45°
17
Hist. Avg.
73°
44°
18
Hist. Avg.
72°
44°
19
Hist. Avg.
72°
44°
20
Hist. Avg.
72°
43°
21
Hist. Avg.
71°
43°
22
Hist. Avg.
71°
43°
23
Hist. Avg.
70°
42°
24
Hist. Avg.
70°
42°
25
Hist. Avg.
69°
42°
26
Hist. Avg.
69°
42°
27
Hist. Avg.
68°
41°
28
Hist. Avg.
68°
41°
29
Hist. Avg.
67°
40°
30
Hist. Avg.
66°
40°
1
Hist. Avg.
66°
40°
2
Hist. Avg.
65°
39°
3
Hist. Avg.
65°
39°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
*Temporarily Unavailable
September Weather in Boulder
Boulder's September 2026 forecast shows daily high temperatures ranging from 70° to 77°, with overnight lows between 36° and 44°. The average high for September is 73° with an average low of 39°. 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.
