S
M
T
W
T
F
S
30
77°
58°
31
80°
57°
1
82°
60°
2
81°
63°
3
84°
63°
4
82°
54°
5
81°
59°
6
81°
62°
7
78°
60°
8
83°
61°
9
85°
61°
10
85°
60°
11
84°
61°
12
84°
61°
13
83°
60°
14
82°
60°
15
81°
59°
16
79°
60°
17
77°
56°
18
79°
52°
19
76°
49°
20
72°
48°
21
71°
51°
22
74°
47°
23
70°
48°
24
70°
55°
25
69°
55°
26
75°
54°
27
70°
56°
28
70°
56°
29
75°
55°
30
72°
44°
1
72°
42°
2
65°
41°
3
64°
40°
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 64° to 85°, with overnight lows between 40° and 63°. The average high for September is 77° with an average low of 55°. 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.
