S
M
T
W
T
F
S
30
81°
62°
31
76°
63°
1
78°
63°
2
82°
59°
3
81°
53°
4
73°
54°
5
73°
62°
6
79°
57°
7
78°
53°
8
72°
56°
9
71°
57°
10
72°
60°
11
75°
59°
12
80°
61°
13
79°
60°
14
79°
55°
15
78°
52°
16
70°
54°
17
70°
50°
18
71°
49°
19
69°
46°
20
67°
46°
21
66°
48°
22
67°
55°
23
68°
48°
24
70°
54°
25
73°
55°
26
69°
55°
27
75°
56°
28
74°
52°
29
73°
50°
30
66°
50°
1
67°
51°
2
72°
52°
3
70°
53°
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 66° to 82°, with overnight lows between 46° and 63°. The average high for September is 73° with an average low of 55°. 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.
