S
M
T
W
T
F
S
30
79°
56°
31
78°
55°
1
77°
56°
2
79°
59°
3
78°
56°
4
79°
55°
5
79°
55°
6
78°
57°
7
76°
53°
8
77°
52°
9
75°
59°
10
77°
52°
11
76°
51°
12
75°
51°
13
75°
56°
14
78°
57°
15
81°
57°
16
81°
56°
17
80°
57°
18
81°
56°
19
80°
49°
20
76°
48°
21
71°
52°
22
72°
54°
23
76°
54°
24
77°
55°
25
78°
48°
26
77°
45°
27
74°
47°
28
69°
46°
29
69°
46°
30
68°
49°
1
69°
46°
2
68°
42°
3
Hist. Avg.
72°
48°
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 68° to 81°, with overnight lows between 42° and 59°. The average high for September is 76° 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 Williamsport. See also: October | November | December.
