S
M
T
W
T
F
S
30
81°
63°
31
75°
64°
1
75°
63°
2
78°
59°
3
75°
54°
4
74°
55°
5
74°
58°
6
75°
59°
7
80°
62°
8
82°
61°
9
78°
59°
10
78°
61°
11
73°
51°
12
72°
52°
13
71°
51°
14
73°
49°
15
72°
51°
16
73°
49°
17
71°
50°
18
71°
48°
19
72°
47°
20
68°
46°
21
69°
47°
22
70°
47°
23
70°
49°
24
74°
53°
25
77°
56°
26
77°
56°
27
69°
54°
28
76°
52°
29
69°
45°
30
68°
50°
1
67°
55°
2
75°
42°
3
76°
42°
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 67° to 82°, with overnight lows between 42° and 64°. The average high for September is 74° with an average low of 53°. 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.
