S
M
T
W
T
F
S
30
77°
52°
31
70°
52°
1
72°
55°
2
76°
57°
3
74°
55°
4
75°
54°
5
75°
53°
6
87°
54°
7
92°
53°
8
91°
56°
9
92°
58°
10
92°
55°
11
92°
55°
12
88°
53°
13
88°
54°
14
89°
51°
15
87°
54°
16
83°
52°
17
88°
53°
18
86°
52°
19
82°
48°
20
83°
53°
21
83°
51°
22
87°
51°
23
82°
50°
24
80°
47°
25
79°
47°
26
80°
48°
27
79°
47°
28
80°
47°
29
81°
46°
30
80°
49°
1
79°
47°
2
80°
49°
3
86°
52°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Portola Valley
Portola Valley's September 2026 forecast shows daily high temperatures ranging from 72° to 92°, with overnight lows between 46° and 58°. The average high for September is 83° with an average low of 52°. 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 Portola Valley. See also: October | November | December.
