It appears that the temperature spiked to 47F at 1119am at the Fairbanks Airport right as the front came through, mixing out the weak inversion that was present. If this is correct, this is the highest temperature of record in December EXCEPT for the five days from December 4-8 1934, when the temperature got to 50F or higher each day. More on this to follow.
Here's the plot of temperatures from the 3am and 3pm RAOBs from Fairbanks.
That's a lot of cooling!