S
M
T
W
T
F
S
30
92°
71°
31
93°
70°
1
93°
71°
2
92°
68°
3
91°
66°
4
88°
68°
5
90°
68°
6
91°
67°
7
90°
68°
8
89°
67°
9
90°
69°
10
90°
68°
11
89°
67°
12
84°
66°
13
83°
66°
14
83°
65°
15
84°
66°
16
83°
66°
17
83°
65°
18
82°
61°
19
82°
58°
20
80°
57°
21
79°
58°
22
81°
60°
23
83°
63°
24
84°
64°
25
85°
63°
26
84°
60°
27
83°
62°
28
78°
59°
29
79°
56°
30
82°
60°
1
85°
61°
2
Hist. Avg.
79°
55°
3
Hist. Avg.
78°
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 78° to 93°, with overnight lows between 56° and 71°. The average high for September is 86° with an average low of 64°. 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.
