S
M
T
W
T
F
S
30
77°
58°
31
77°
57°
1
78°
55°
2
76°
56°
3
77°
55°
4
77°
56°
5
78°
58°
6
76°
55°
7
74°
55°
8
77°
60°
9
76°
53°
10
74°
52°
11
76°
56°
12
77°
59°
13
75°
51°
14
72°
59°
15
76°
60°
16
81°
61°
17
78°
57°
18
79°
49°
19
71°
48°
20
69°
48°
21
68°
49°
22
71°
56°
23
74°
55°
24
70°
52°
25
70°
46°
26
69°
47°
27
67°
46°
28
65°
47°
29
65°
45°
30
65°
43°
1
Hist. Avg.
69°
48°
2
Hist. Avg.
68°
47°
3
Hist. Avg.
68°
47°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Onalaska
Onalaska's September 2026 forecast shows daily high temperatures ranging from 65° to 81°, with overnight lows between 43° and 61°. The average high for September is 74° with an average low of 53°. 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 Onalaska. See also: October | November | December.
