S
M
T
W
T
F
S
29
50°
19°
30
53°
18°
1
46°
17°
2
47°
19°
3
46°
19°
4
47°
18°
5
52°
15°
6
51°
9°
7
41°
11°
8
39°
13°
9
43°
11°
10
43°
11°
11
40°
12°
12
39°
17°
13
41°
9°
14
41°
6°
15
38°
8°
16
38°
8°
17
42°
12°
18
41°
11°
19
45°
15°
20
44°
13°
21
43°
7°
22
39°
8°
23
38°
6°
24
38°
8°
25
39°
10°
26
41°
7°
27
38°
8°
28
38°
4°
29
37°
4°
30
37°
8°
31
39°
6°
1
37°
8°
2
38°
9°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
December Weather in Longmont
Longmont's December 2026 forecast shows daily high temperatures ranging from 37° to 53°, with overnight lows between 4° and 19°. The average high for December is 42° with an average low of 11°. AccuWeather's monthly forecast extends further ahead than any other source, with day-by-day RealFeel® Temperatures giving a complete picture of how December weather will actually feel in Longmont. See also: January | February | March.
