S
M
T
W
T
F
S
29
36°
8°
30
29°
6°
1
28°
7°
2
31°
18°
3
37°
18°
4
32°
13°
5
28°
14°
6
28°
5°
7
26°
4°
8
29°
11°
9
36°
13°
10
36°
12°
11
38°
13°
12
38°
15°
13
37°
15°
14
33°
16°
15
31°
15°
16
34°
5°
17
31°
11°
18
28°
13°
19
29°
15°
20
32°
15°
21
32°
4°
22
31°
10°
23
30°
8°
24
31°
8°
25
29°
18°
26
33°
12°
27
37°
-2°
28
32°
9°
29
24°
2°
30
29°
2°
31
23°
8°
1
30°
16°
2
34°
6°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
December Weather in Johnstown
Johnstown's December 2026 forecast shows daily high temperatures ranging from 23° to 38°, with overnight lows between -2° and 18°. The average high for December is 31° with an average low of 10°. 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 Johnstown. See also: January | February | March.
