S
M
T
W
T
F
S
26
81°
51°
27
83°
61°
28
66°
55°
29
64°
50°
30
67°
40°
1
64°
44°
2
61°
44°
3
78°
41°
4
79°
58°
5
70°
46°
6
63°
43°
7
68°
39°
8
77°
47°
9
81°
56°
10
70°
49°
11
78°
44°
12
83°
51°
13
75°
51°
14
75°
45°
15
84°
58°
16
77°
67°
17
92°
71°
18
81°
72°
19
79°
55°
20
68°
52°
21
73°
54°
22
80°
60°
23
81°
64°
24
83°
67°
25
80°
66°
26
82°
64°
27
84°
67°
28
83°
66°
29
81°
64°
30
80°
67°
31
85°
68°
1
85°
68°
2
84°
67°
3
78°
63°
4
77°
60°
5
80°
67°
6
86°
69°
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 68° to 92°, with overnight lows between 52° and 72°. The average high for May is 81° with an average low of 64°. 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.
