S
M
T
W
T
F
S
30
77°
51°
31
85°
46°
1
83°
50°
2
78°
56°
3
67°
47°
4
66°
44°
5
76°
42°
6
74°
46°
7
72°
46°
8
78°
42°
9
84°
42°
10
88°
51°
11
82°
45°
12
84°
50°
13
68°
42°
14
73°
41°
15
76°
44°
16
79°
45°
17
83°
48°
18
84°
52°
19
87°
55°
20
82°
55°
21
83°
52°
22
81°
50°
23
80°
50°
24
84°
51°
25
70°
45°
26
71°
50°
27
76°
43°
28
67°
38°
29
69°
46°
30
67°
40°
1
73°
48°
2
77°
47°
3
77°
47°
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 67° to 87°, with overnight lows between 38° and 55°. The average high for September is 77° with an average low of 47°. 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.
