S
M
T
W
T
F
S
26
80°
53°
27
83°
62°
28
66°
54°
29
67°
48°
30
66°
41°
1
64°
43°
2
62°
44°
3
75°
42°
4
78°
57°
5
69°
47°
6
64°
44°
7
68°
40°
8
78°
49°
9
82°
56°
10
71°
53°
11
77°
45°
12
82°
51°
13
74°
46°
14
73°
55°
15
81°
65°
16
78°
63°
17
88°
69°
18
82°
66°
19
75°
57°
20
72°
57°
21
77°
58°
22
75°
55°
23
75°
56°
24
77°
58°
25
83°
62°
26
81°
59°
27
81°
64°
28
84°
63°
29
85°
61°
30
77°
59°
31
77°
58°
1
78°
56°
2
78°
57°
3
79°
60°
4
82°
65°
5
86°
66°
6
87°
67°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
May Weather in O'Fallon
O'Fallon's May 2026 forecast shows daily high temperatures ranging from 72° to 88°, with overnight lows between 46° and 69°. The average high for May is 79° with an average low of 60°. 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 O'Fallon. See also: June | July | August.
