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
92°
73°
12
93°
66°
13
90°
63°
14
88°
63°
15
85°
62°
16
87°
61°
17
88°
63°
18
90°
65°
19
93°
64°
20
89°
65°
21
86°
64°
22
86°
63°
23
87°
62°
24
86°
64°
25
86°
58°
26
87°
60°
27
88°
61°
28
83°
56°
29
85°
59°
30
82°
59°
1
80°
58°
2
79°
58°
3
79°
57°
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 79° to 93°, with overnight lows between 56° and 66°. The average high for September is 86° with an average low of 61°. 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.
