S
M
T
W
T
F
S
30
95°
69°
31
97°
70°
1
97°
74°
2
96°
71°
3
96°
72°
4
95°
73°
5
96°
73°
6
95°
72°
7
96°
72°
8
95°
73°
9
92°
72°
10
94°
72°
11
93°
71°
12
95°
72°
13
95°
72°
14
94°
70°
15
93°
64°
16
85°
62°
17
84°
69°
18
89°
69°
19
85°
66°
20
84°
65°
21
83°
63°
22
84°
67°
23
87°
67°
24
88°
66°
25
90°
67°
26
90°
66°
27
89°
65°
28
88°
64°
29
87°
63°
30
86°
63°
1
87°
62°
2
87°
64°
3
79°
57°
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 97°, with overnight lows between 57° and 74°. The average high for September 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 September weather will actually feel in Lake Forest. See also: October | November | December.
