S
M
T
W
T
F
S
30
92°
71°
31
92°
71°
1
91°
70°
2
92°
70°
3
92°
68°
4
86°
66°
5
86°
67°
6
87°
64°
7
90°
65°
8
91°
68°
9
90°
69°
10
90°
69°
11
91°
68°
12
90°
69°
13
89°
69°
14
89°
63°
15
90°
67°
16
89°
67°
17
90°
66°
18
84°
61°
19
89°
60°
20
81°
64°
21
82°
61°
22
83°
60°
23
83°
61°
24
87°
61°
25
87°
63°
26
81°
59°
27
82°
59°
28
84°
62°
29
80°
62°
30
85°
61°
1
82°
61°
2
82°
60°
3
83°
61°
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 80° to 92°, with overnight lows between 59° and 71°. The average high for September is 87° with an average low of 65°. 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.
