S
M
T
W
T
F
S
30
81°
68°
31
87°
70°
1
93°
70°
2
93°
71°
3
88°
70°
4
87°
69°
5
86°
68°
6
82°
62°
7
78°
61°
8
79°
62°
9
82°
60°
10
76°
56°
11
74°
55°
12
75°
54°
13
74°
57°
14
77°
54°
15
79°
59°
16
80°
60°
17
79°
59°
18
78°
59°
19
79°
60°
20
80°
60°
21
80°
59°
22
79°
59°
23
79°
58°
24
78°
58°
25
79°
57°
26
79°
58°
27
78°
57°
28
77°
57°
29
76°
56°
30
76°
55°
1
75°
55°
2
76°
54°
3
76°
54°
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 74° to 93°, with overnight lows between 54° and 71°. 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 St. Charles. See also: October | November | December.
