S
M
T
W
T
F
S
30
85°
67°
31
85°
66°
1
86°
65°
2
79°
59°
3
78°
60°
4
78°
61°
5
79°
59°
6
80°
63°
7
85°
65°
8
84°
65°
9
83°
64°
10
85°
65°
11
85°
64°
12
84°
65°
13
84°
65°
14
84°
58°
15
77°
56°
16
74°
54°
17
75°
55°
18
83°
60°
19
84°
61°
20
84°
61°
21
82°
56°
22
80°
51°
23
72°
54°
24
71°
58°
25
70°
57°
26
78°
57°
27
80°
58°
28
79°
58°
29
78°
57°
30
75°
57°
1
75°
55°
2
78°
50°
3
72°
46°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Herndon
Herndon's September 2026 forecast shows daily high temperatures ranging from 70° to 86°, with overnight lows between 46° and 67°. The average high for September is 80° with an average low of 59°. 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 Herndon. See also: October | November | December.
