S
M
T
W
T
F
S
29
57°
24°
30
53°
22°
1
42°
24°
2
43°
24°
3
48°
30°
4
49°
36°
5
49°
39°
6
55°
34°
7
57°
33°
8
48°
33°
9
46°
31°
10
46°
22°
11
44°
20°
12
38°
23°
13
39°
20°
14
37°
19°
15
38°
20°
16
38°
18°
17
39°
19°
18
36°
25°
19
44°
28°
20
46°
33°
21
47°
32°
22
49°
27°
23
45°
20°
24
38°
17°
25
35°
20°
26
36°
24°
27
42°
24°
28
46°
20°
29
45°
20°
30
37°
21°
31
39°
25°
1
42°
25°
2
46°
24°
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 35° to 57°, with overnight lows between 17° and 39°. The average high for December is 44° 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 O'Fallon. See also: January | February | March.
