S
M
T
W
T
F
S
30
80°
67°
31
83°
67°
1
86°
66°
2
82°
63°
3
82°
64°
4
83°
65°
5
84°
62°
6
82°
59°
7
80°
64°
8
85°
64°
9
86°
65°
10
86°
64°
11
86°
65°
12
89°
54°
13
87°
53°
14
84°
61°
15
86°
57°
16
83°
52°
17
73°
50°
18
75°
56°
19
84°
51°
20
76°
56°
21
77°
54°
22
81°
47°
23
76°
47°
24
78°
48°
25
79°
52°
26
80°
53°
27
82°
49°
28
77°
53°
29
76°
50°
30
81°
58°
1
81°
42°
2
84°
40°
3
75°
44°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Ottawa
Ottawa's September 2026 forecast shows daily high temperatures ranging from 73° to 89°, with overnight lows between 40° and 67°. The average high for September is 81° with an average low of 56°. 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 Ottawa. See also: October | November | December.
