S
M
T
W
T
F
S
30
74°
56°
31
75°
61°
1
74°
63°
2
79°
55°
3
74°
52°
4
72°
53°
5
70°
52°
6
71°
56°
7
76°
57°
8
78°
61°
9
79°
60°
10
78°
53°
11
72°
59°
12
72°
56°
13
73°
51°
14
70°
51°
15
69°
50°
16
68°
49°
17
70°
57°
18
73°
47°
19
68°
51°
20
68°
48°
21
70°
50°
22
68°
56°
23
73°
57°
24
75°
56°
25
70°
56°
26
73°
55°
27
73°
56°
28
74°
53°
29
72°
54°
30
71°
55°
1
73°
52°
2
73°
45°
3
70°
42°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Round Lake
Round Lake's September 2026 forecast shows daily high temperatures ranging from 68° to 79°, with overnight lows between 42° and 63°. The average high for September is 73° with an average low of 54°. 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 Round Lake. See also: October | November | December.
