S
M
T
W
T
F
S
30
82°
58°
31
84°
63°
1
87°
58°
2
90°
57°
3
92°
56°
4
89°
61°
5
91°
63°
6
91°
61°
7
92°
63°
8
88°
60°
9
87°
57°
10
83°
56°
11
82°
48°
12
84°
53°
13
86°
53°
14
86°
53°
15
85°
52°
16
85°
52°
17
86°
51°
18
85°
52°
19
84°
51°
20
84°
50°
21
83°
50°
22
84°
49°
23
83°
49°
24
83°
48°
25
82°
49°
26
81°
48°
27
80°
47°
28
80°
47°
29
79°
46°
30
78°
46°
1
77°
45°
2
76°
44°
3
77°
44°
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 76° to 92°, with overnight lows between 44° and 63°. The average high for September is 84° with an average low of 52°. 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.
