S
M
T
W
T
F
S
30
98°
71°
31
99°
75°
1
99°
75°
2
100°
73°
3
97°
72°
4
99°
73°
5
100°
75°
6
100°
73°
7
97°
73°
8
100°
76°
9
99°
71°
10
79°
66°
11
88°
69°
12
89°
70°
13
96°
69°
14
97°
66°
15
82°
59°
16
81°
60°
17
80°
59°
18
77°
54°
19
73°
53°
20
76°
56°
21
79°
55°
22
84°
61°
23
85°
62°
24
85°
62°
25
84°
61°
26
82°
60°
27
82°
60°
28
83°
59°
29
82°
60°
30
79°
54°
1
74°
49°
2
68°
45°
3
67°
45°
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 67° to 100°, with overnight lows between 45° and 76°. The average high for September is 83° with an average low of 60°. 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.
