S
M
T
W
T
F
S
26
88°
67°
27
87°
72°
28
90°
70°
29
84°
68°
30
84°
70°
31
85°
68°
1
87°
72°
2
92°
72°
3
92°
71°
4
91°
70°
5
90°
71°
6
91°
72°
7
92°
71°
8
91°
72°
9
92°
70°
10
83°
66°
11
87°
69°
12
86°
70°
13
87°
69°
14
83°
63°
15
82°
62°
16
82°
62°
17
83°
63°
18
82°
64°
19
84°
67°
20
86°
69°
21
86°
68°
22
87°
68°
23
85°
67°
24
89°
62°
25
87°
64°
26
87°
66°
27
84°
67°
28
86°
62°
29
83°
61°
30
80°
61°
31
80°
64°
1
85°
62°
2
80°
56°
3
79°
55°
4
77°
56°
5
78°
57°
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 77° to 92°, with overnight lows between 55° and 72°. The average high for August is 86° with an average low of 66°. 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.
