S
M
T
W
T
F
S
29
57°
40°
30
57°
40°
1
55°
33°
2
42°
30°
3
45°
32°
4
53°
35°
5
53°
36°
6
43°
28°
7
40°
24°
8
39°
24°
9
39°
26°
10
44°
30°
11
46°
29°
12
50°
30°
13
46°
28°
14
41°
25°
15
42°
27°
16
42°
30°
17
43°
28°
18
41°
22°
19
39°
21°
20
38°
20°
21
36°
21°
22
37°
27°
23
42°
26°
24
39°
26°
25
38°
19°
26
38°
19°
27
37°
20°
28
37°
19°
29
36°
24°
30
37°
22°
31
37°
18°
1
38°
14°
2
36°
14°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
December Weather in O'Fallon
O'Fallon's December 2026 forecast shows daily high temperatures ranging from 36° to 57°, with overnight lows between 14° and 40°. The average high for December is 42° with an average low of 26°. 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 O'Fallon. See also: January | February | March.
