S
M
T
W
T
F
S
30
78°
60°
31
80°
58°
1
74°
53°
2
69°
48°
3
71°
57°
4
80°
59°
5
80°
59°
6
79°
58°
7
78°
58°
8
76°
57°
9
73°
56°
10
75°
56°
11
71°
45°
12
74°
50°
13
72°
48°
14
75°
46°
15
69°
42°
16
64°
39°
17
62°
39°
18
62°
40°
19
63°
45°
20
65°
50°
21
72°
52°
22
73°
52°
23
74°
53°
24
75°
51°
25
74°
49°
26
73°
39°
27
65°
47°
28
61°
44°
29
68°
47°
30
62°
42°
1
70°
35°
2
55°
31°
3
52°
38°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Thief River Falls
Thief River Falls's September 2026 forecast shows daily high temperatures ranging from 52° to 80°, with overnight lows between 31° and 60°. The average high for September is 70° with an average low of 49°. 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 Thief River Falls. See also: October | November | December.
