S
M
T
W
T
F
S
30
90°
71°
31
84°
66°
1
84°
61°
2
83°
61°
3
82°
61°
4
82°
63°
5
85°
70°
6
86°
69°
7
93°
68°
8
88°
65°
9
87°
63°
10
86°
63°
11
91°
66°
12
90°
65°
13
89°
64°
14
88°
61°
15
91°
66°
16
90°
65°
17
90°
64°
18
87°
61°
19
83°
60°
20
85°
61°
21
88°
62°
22
88°
63°
23
87°
63°
24
84°
60°
25
80°
56°
26
80°
57°
27
79°
56°
28
80°
56°
29
82°
58°
30
82°
60°
1
81°
58°
2
84°
59°
3
87°
63°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Lake Forest
Lake Forest's September 2026 forecast shows daily high temperatures ranging from 79° to 93°, with overnight lows between 56° and 70°. The average high for September is 86° with an average low of 62°. AccuWeather's monthly forecast extends further ahead than any other source, with day-by-day RealFeel® Temperatures giving a complete picture of how September weather will actually feel in Lake Forest. See also: October | November | December.
