S
M
T
W
T
F
S
30
90°
64°
31
90°
63°
1
86°
60°
2
79°
56°
3
81°
60°
4
89°
62°
5
89°
61°
6
77°
50°
7
76°
50°
8
78°
52°
9
84°
56°
10
87°
57°
11
87°
60°
12
86°
59°
13
85°
60°
14
80°
48°
15
74°
51°
16
76°
52°
17
78°
58°
18
73°
54°
19
72°
53°
20
76°
51°
21
77°
58°
22
81°
53°
23
80°
46°
24
70°
46°
25
71°
47°
26
69°
43°
27
68°
42°
28
67°
40°
29
68°
42°
30
68°
49°
1
70°
45°
2
74°
47°
3
70°
42°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Boise
Boise's September 2026 forecast shows daily high temperatures ranging from 67° to 90°, with overnight lows between 40° and 64°. The average high for September is 78° 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 Boise. See also: October | November | December.
