S
M
T
W
T
F
S
30
85°
55°
31
82°
66°
1
91°
68°
2
88°
70°
3
90°
69°
4
85°
64°
5
82°
59°
6
79°
58°
7
80°
58°
8
76°
56°
9
77°
57°
10
80°
58°
11
78°
57°
12
76°
56°
13
78°
54°
14
76°
54°
15
77°
59°
16
75°
58°
17
77°
52°
18
71°
49°
19
72°
50°
20
76°
57°
21
79°
58°
22
79°
58°
23
80°
57°
24
79°
55°
25
77°
54°
26
77°
54°
27
78°
55°
28
78°
55°
29
77°
52°
30
72°
48°
1
69°
47°
2
72°
52°
3
75°
53°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Lewistown
Lewistown's September 2026 forecast shows daily high temperatures ranging from 69° to 91°, with overnight lows between 47° and 70°. The average high for September is 78° with an average low of 56°. 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 Lewistown. See also: October | November | December.
