S
M
T
W
T
F
S
29
43°
28°
30
44°
25°
1
41°
25°
2
39°
26°
3
41°
24°
4
39°
26°
5
39°
29°
6
43°
35°
7
47°
38°
8
54°
33°
9
55°
30°
10
43°
27°
11
42°
29°
12
42°
27°
13
41°
27°
14
40°
23°
15
40°
21°
16
38°
22°
17
36°
20°
18
37°
20°
19
36°
19°
20
37°
33°
21
43°
27°
22
46°
24°
23
40°
31°
24
42°
32°
25
49°
29°
26
45°
23°
27
41°
25°
28
42°
19°
29
41°
21°
30
33°
14°
31
47°
15°
1
32°
18°
2
34°
18°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
December Weather in Fullerton
Fullerton's December 2026 forecast shows daily high temperatures ranging from 32° to 55°, with overnight lows between 14° and 38°. The average high for December is 41° with an average low of 25°. 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 Fullerton. See also: January | February | March.
