S
M
T
W
T
F
S
30
90°
71°
31
88°
67°
1
86°
61°
2
82°
60°
3
82°
61°
4
83°
62°
5
90°
61°
6
75°
64°
7
88°
70°
8
97°
74°
9
105°
77°
10
98°
79°
11
95°
69°
12
93°
66°
13
90°
64°
14
88°
63°
15
85°
62°
16
84°
63°
17
91°
65°
18
90°
65°
19
93°
67°
20
89°
65°
21
86°
64°
22
86°
63°
23
87°
64°
24
86°
59°
25
81°
58°
26
87°
60°
27
88°
61°
28
84°
57°
29
87°
59°
30
87°
62°
1
88°
62°
2
88°
61°
3
87°
62°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Ontario
Ontario's September 2026 forecast shows daily high temperatures ranging from 81° to 95°, with overnight lows between 57° and 69°. The average high for September is 88° with an average low of 63°. 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 Ontario. See also: October | November | December.
