S
M
T
W
T
F
S
30
89°
63°
31
86°
62°
1
91°
60°
2
90°
61°
3
86°
61°
4
89°
62°
5
88°
61°
6
89°
58°
7
88°
57°
8
87°
56°
9
89°
57°
10
89°
58°
11
88°
57°
12
82°
56°
13
87°
56°
14
88°
55°
15
87°
56°
16
87°
55°
17
79°
48°
18
71°
46°
19
74°
45°
20
80°
50°
21
76°
50°
22
83°
49°
23
79°
50°
24
78°
51°
25
74°
51°
26
70°
50°
27
77°
51°
28
75°
48°
29
75°
49°
30
79°
49°
1
78°
48°
2
79°
49°
3
79°
48°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Thornton
Thornton's September 2026 forecast shows daily high temperatures ranging from 70° to 91°, with overnight lows between 45° and 63°. The average high for September is 82° with an average low of 54°. 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 Thornton. See also: October | November | December.
