S
M
T
W
T
F
S
26
92°
72°
27
92°
72°
28
93°
71°
29
93°
72°
30
92°
71°
31
92°
70°
1
91°
72°
2
94°
71°
3
88°
68°
4
92°
71°
5
93°
72°
6
93°
71°
7
92°
70°
8
88°
66°
9
92°
69°
10
87°
65°
11
89°
69°
12
91°
70°
13
92°
69°
14
93°
70°
15
92°
69°
16
93°
69°
17
93°
63°
18
90°
61°
19
84°
60°
20
84°
60°
21
85°
61°
22
84°
61°
23
84°
62°
24
85°
61°
25
85°
61°
26
87°
65°
27
89°
59°
28
84°
59°
29
84°
60°
30
88°
61°
31
87°
62°
1
89°
59°
2
83°
58°
3
82°
64°
4
86°
65°
5
85°
64°
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 82° to 94°, with overnight lows between 58° and 72°. The average high for August is 89° 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.
