S
M
T
W
T
F
S
30
96°
72°
31
99°
73°
1
100°
79°
2
100°
82°
3
99°
82°
4
100°
81°
5
101°
81°
6
90°
73°
7
87°
65°
8
93°
65°
9
93°
72°
10
80°
71°
11
83°
69°
12
92°
71°
13
86°
66°
14
88°
63°
15
98°
76°
16
94°
75°
17
99°
79°
18
98°
75°
19
97°
79°
20
92°
70°
21
73°
66°
22
72°
61°
23
70°
56°
24
70°
60°
25
72°
59°
26
69°
59°
27
74°
60°
28
80°
58°
29
84°
55°
30
92°
71°
1
90°
71°
2
69°
49°
3
73°
50°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in St. Charles
St. Charles's September 2026 forecast shows daily high temperatures ranging from 69° to 73°, with overnight lows between 49° and 50°. The average high for September is 71° with an average low of 50°. 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 St. Charles. See also: October | November | December.
