S
M
T
W
T
F
S
30
82°
51°
31
86°
54°
1
87°
52°
2
85°
50°
3
82°
50°
4
80°
47°
5
79°
47°
6
80°
50°
7
85°
50°
8
86°
52°
9
81°
50°
10
84°
51°
11
85°
47°
12
85°
48°
13
81°
44°
14
78°
43°
15
79°
44°
16
78°
46°
17
79°
47°
18
83°
49°
19
81°
40°
20
75°
44°
21
77°
45°
22
81°
48°
23
Hist. Avg.
78°
43°
24
Hist. Avg.
77°
42°
25
Hist. Avg.
76°
42°
26
Hist. Avg.
76°
41°
27
Hist. Avg.
76°
41°
28
Hist. Avg.
75°
40°
29
Hist. Avg.
74°
40°
30
Hist. Avg.
74°
39°
1
Hist. Avg.
73°
39°
2
Hist. Avg.
73°
38°
3
Hist. Avg.
72°
38°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
*Temporarily Unavailable
September Weather in Longmont
Longmont's September 2026 forecast shows daily high temperatures ranging from 75° to 87°, with overnight lows between 40° and 54°. The average high for September is 82° with an average low of 48°. 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.
