S
M
T
W
T
F
S
30
82°
69°
31
78°
71°
1
80°
68°
2
74°
67°
3
88°
69°
4
86°
75°
5
80°
70°
6
74°
59°
7
79°
63°
8
82°
68°
9
85°
73°
10
84°
65°
11
80°
61°
12
77°
65°
13
81°
67°
14
83°
65°
15
80°
65°
16
76°
60°
17
73°
63°
18
75°
60°
19
74°
61°
20
79°
62°
21
76°
63°
22
70°
63°
23
71°
62°
24
71°
62°
25
72°
59°
26
76°
58°
27
71°
55°
28
71°
58°
29
76°
61°
30
77°
61°
1
76°
60°
2
75°
61°
3
74°
57°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Mount Vernon
Mount Vernon's September 2026 forecast shows daily high temperatures ranging from 70° to 85°, with overnight lows between 55° and 73°. The average high for September is 76° with an average low of 62°. 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 Mount Vernon. See also: October | November | December.
