S
M
T
W
T
F
S
26
98°
75°
27
98°
75°
28
91°
76°
29
87°
68°
30
87°
63°
31
80°
70°
1
78°
67°
2
83°
65°
3
86°
62°
4
89°
63°
5
88°
67°
6
76°
68°
7
90°
68°
8
90°
66°
9
93°
72°
10
92°
75°
11
95°
75°
12
94°
73°
13
95°
75°
14
98°
75°
15
97°
72°
16
98°
75°
17
90°
67°
18
86°
66°
19
92°
69°
20
93°
68°
21
91°
69°
22
92°
68°
23
87°
65°
24
83°
65°
25
87°
64°
26
89°
69°
27
89°
69°
28
81°
61°
29
86°
63°
30
88°
67°
31
89°
67°
1
90°
68°
2
90°
68°
3
89°
67°
4
88°
66°
5
87°
66°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
August Weather in O'Fallon
O'Fallon's August 2026 forecast shows daily high temperatures ranging from 81° to 98°, with overnight lows between 61° and 75°. The average high for August is 90° with an average low of 68°. AccuWeather's monthly forecast extends further ahead than any other source, with day-by-day RealFeel® Temperatures giving a complete picture of how August weather will actually feel in O'Fallon. See also: September | October | November.
