S
M
T
W
T
F
S
26
60°
37°
27
71°
37°
28
65°
53°
29
55°
45°
30
50°
41°
1
50°
36°
2
48°
35°
3
58°
34°
4
74°
46°
5
70°
48°
6
49°
42°
7
50°
40°
8
52°
42°
9
59°
46°
10
53°
40°
11
50°
39°
12
52°
38°
13
53°
38°
14
56°
40°
15
58°
46°
16
61°
44°
17
61°
46°
18
62°
46°
19
60°
47°
20
63°
46°
21
61°
42°
22
61°
42°
23
62°
45°
24
63°
45°
25
65°
49°
26
66°
50°
27
64°
47°
28
65°
44°
29
64°
44°
30
68°
51°
31
72°
54°
1
73°
52°
2
67°
48°
3
71°
52°
4
75°
56°
5
76°
56°
6
75°
55°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
May Weather in Ontario
Ontario's May 2026 forecast shows daily high temperatures ranging from 50° to 76°, with overnight lows between 38° and 56°. The average high for May is 63° with an average low of 46°. AccuWeather's monthly forecast extends further ahead than any other source, with day-by-day RealFeel® Temperatures giving a complete picture of how May weather will actually feel in Ontario. See also: June | July | August.
