S
M
T
W
T
F
S
30
80°
57°
31
79°
58°
1
78°
63°
2
77°
64°
3
85°
63°
4
86°
64°
5
85°
59°
6
80°
55°
7
78°
60°
8
81°
55°
9
77°
53°
10
76°
54°
11
76°
54°
12
79°
53°
13
78°
60°
14
82°
54°
15
74°
52°
16
72°
57°
17
73°
55°
18
74°
58°
19
78°
50°
20
74°
52°
21
76°
50°
22
79°
50°
23
74°
49°
24
75°
49°
25
75°
54°
26
76°
55°
27
74°
56°
28
77°
55°
29
78°
47°
30
70°
50°
1
72°
55°
2
76°
53°
3
75°
47°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Williamsport
Williamsport's September 2026 forecast shows daily high temperatures ranging from 70° to 86°, with overnight lows between 47° and 64°. The average high for September is 77° 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 Williamsport. See also: October | November | December.
