S
M
T
W
T
F
S
30
82°
66°
31
85°
70°
1
91°
75°
2
93°
73°
3
93°
72°
4
84°
69°
5
80°
65°
6
77°
58°
7
78°
55°
8
85°
58°
9
88°
66°
10
81°
62°
11
79°
56°
12
78°
63°
13
82°
57°
14
71°
49°
15
87°
56°
16
84°
69°
17
81°
63°
18
76°
58°
19
76°
66°
20
73°
58°
21
68°
58°
22
68°
57°
23
72°
55°
24
71°
54°
25
73°
52°
26
71°
48°
27
74°
54°
28
74°
54°
29
73°
52°
30
72°
49°
1
74°
55°
2
68°
54°
3
65°
55°
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 65° to 81°, with overnight lows between 48° and 66°. The average high for September is 72° 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.
