S
M
T
W
T
F
S
30
80°
58°
31
84°
60°
1
85°
60°
2
84°
59°
3
85°
60°
4
84°
59°
5
84°
56°
6
84°
56°
7
85°
58°
8
84°
59°
9
75°
58°
10
75°
51°
11
73°
53°
12
73°
49°
13
74°
50°
14
74°
57°
15
73°
48°
16
72°
50°
17
73°
54°
18
73°
57°
19
76°
58°
20
81°
53°
21
71°
46°
22
70°
48°
23
71°
51°
24
72°
55°
25
75°
58°
26
79°
58°
27
78°
57°
28
79°
56°
29
78°
46°
30
71°
51°
1
70°
53°
2
75°
47°
3
65°
44°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Lake Oswego
Lake Oswego's September 2026 forecast shows daily high temperatures ranging from 65° to 85°, with overnight lows between 44° and 60°. The average high for September is 77° 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 Lake Oswego. See also: October | November | December.
