S
M
T
W
T
F
S
30
82°
58°
31
84°
58°
1
88°
57°
2
90°
50°
3
91°
52°
4
93°
49°
5
94°
55°
6
90°
58°
7
90°
59°
8
87°
56°
9
80°
49°
10
90°
46°
11
91°
48°
12
76°
51°
13
95°
48°
14
87°
62°
15
74°
55°
16
80°
48°
17
77°
60°
18
84°
55°
19
79°
49°
20
75°
47°
21
76°
46°
22
83°
45°
23
74°
57°
24
76°
56°
25
71°
50°
26
86°
43°
27
86°
54°
28
72°
51°
29
75°
53°
30
68°
53°
1
74°
46°
2
83°
41°
3
85°
42°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Longmont
Longmont's September 2026 forecast shows daily high temperatures ranging from ° to °, with overnight lows between ° and °. The average high for September is ° with an average low of °. 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 Longmont. See also: October | November | December.
