S
M
T
W
T
F
S
30
88°
69°
31
92°
69°
1
94°
72°
2
96°
71°
3
96°
73°
4
98°
74°
5
96°
67°
6
82°
63°
7
82°
60°
8
87°
61°
9
86°
67°
10
77°
57°
11
83°
62°
12
84°
65°
13
85°
68°
14
90°
68°
15
85°
58°
16
76°
59°
17
77°
55°
18
78°
56°
19
70°
48°
20
69°
50°
21
72°
49°
22
75°
50°
23
73°
56°
24
79°
55°
25
77°
55°
26
79°
55°
27
79°
54°
28
78°
55°
29
78°
55°
30
77°
53°
1
77°
49°
2
72°
53°
3
77°
54°
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 69° to 90°, with overnight lows between 48° and 68°. The average high for September is 78° with an average low of 56°. 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.
