Here are the high temperatures observed that day; click to enlarge (apologies for the split image).
It's remarkable to see that the temperature reached 32°F or higher at valley level nearly everywhere to the west and north of the Alaska Range, except in the eastern interior and the Brooks Range.
I looked at the history of the following 8 observing sites for dates when 32°F was reached at all of the locations, and this is the first time on record for December. Here are Monday's high temperatures at the 8 sites, which all have data back to at least the early 1950s.
King Salmon 37°F
There have been a few early November dates when all 8 sites reached 32°F (including last year), but the only other date in deep winter that achieved this feat was February 4, 1982; it has not been observed before in December or January. However, if we take out Utqiaġvik, then it's not as uncommon, particularly in recent years: 2015, 2016, and 2017 all saw similar widespread warmth in December, but not extending all the way to the Arctic Ocean.
And a quick note on current weather: the thaw has lasted about a week now in the Bristol Bay region, which is an astonishing turnaround from November's extreme cold. This morning the warmth is spreading inland again, and it's raining and +34°F at Aniak. Contrast that with -34°F at Fort Yukon.