S
M
T
W
T
F
S
30
99°
73°
31
99°
72°
1
97°
74°
2
97°
71°
3
81°
75°
4
92°
74°
5
92°
73°
6
97°
73°
7
95°
74°
8
96°
75°
9
96°
74°
10
94°
73°
11
100°
72°
12
99°
74°
13
95°
72°
14
93°
71°
15
91°
70°
16
90°
67°
17
94°
72°
18
87°
68°
19
91°
71°
20
93°
71°
21
93°
70°
22
92°
70°
23
92°
69°
24
91°
70°
25
92°
69°
26
92°
67°
27
84°
60°
28
83°
61°
29
82°
60°
30
87°
63°
1
90°
66°
2
90°
61°
3
81°
57°
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 81° to 100°, with overnight lows between 57° and 75°. The average high for September is 91° with an average low of 69°. 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.
