S
M
T
W
T
F
S
26
90°
71°
27
91°
71°
28
92°
72°
29
92°
72°
30
91°
71°
31
91°
71°
1
90°
72°
2
93°
71°
3
90°
70°
4
91°
71°
5
92°
72°
6
92°
71°
7
91°
70°
8
88°
68°
9
91°
69°
10
86°
66°
11
87°
69°
12
89°
69°
13
90°
70°
14
91°
71°
15
92°
70°
16
92°
70°
17
91°
62°
18
89°
61°
19
82°
60°
20
82°
59°
21
83°
60°
22
82°
61°
23
82°
62°
24
83°
61°
25
84°
61°
26
86°
66°
27
87°
59°
28
82°
59°
29
82°
60°
30
86°
62°
31
86°
63°
1
88°
59°
2
81°
58°
3
80°
65°
4
84°
66°
5
82°
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 80° to 93°, with overnight lows between 58° and 72°. The average high for August is 87° 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.
