S
M
T
W
T
F
S
30
94°
64°
31
99°
66°
1
100°
73°
2
100°
73°
3
100°
73°
4
98°
72°
5
97°
70°
6
94°
67°
7
89°
68°
8
91°
64°
9
89°
67°
10
87°
63°
11
85°
58°
12
82°
59°
13
83°
60°
14
81°
57°
15
81°
61°
16
83°
62°
17
83°
62°
18
84°
61°
19
84°
62°
20
83°
62°
21
83°
61°
22
82°
61°
23
83°
60°
24
83°
60°
25
82°
59°
26
82°
58°
27
83°
59°
28
82°
59°
29
81°
58°
30
82°
58°
1
81°
57°
2
81°
58°
3
80°
57°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Collinsville
Collinsville's September 2026 forecast shows daily high temperatures ranging from 80° to 100°, with overnight lows between 57° and 73°. The average high for September is 86° with an average low of 62°. 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 Collinsville. See also: October | November | December.
