December was an unusual month in terms of the circulation pattern over the North Pacific and Alaska: a strong mid-atmosphere trough was dominant across the North Pacific from Japan to the waters south of Alaska, but to the north a very broad ridge prevailed from Siberia to central Canada.
This pattern reflects a strongly positive phase of the Pacific-North American (PNA) pattern (see here for explanation), and this is reliably and strongly associated with unusual warmth in Alaska at this time of year. Hence temperatures were well above normal nearly everywhere, and it was a top-10 warm December for the state as a whole.
The NCEI data shows the Northwest Gulf division with its warmest December on record, but Kodiak airport actually came in at 6th warmest, with December 2014 still holding the record.
The December pattern was substantially inverse of what is typical for La Niña; here's the average 500mb height anomaly for 10 Decembers with strong La Niña:
But of course, La Niña is not particularly strong this winter; it only recently gained enough amplitude to be officially classified as such by NOAA:
December precipitation was a mixed bag. The major anomaly was the wet pattern for much of the Gulf coast, and especially the lower Alaska Peninsula to Kodiak Island and the southern Kenai Peninsula. Kodiak reported its 2nd wettest December on record. Southeast was fairly wet too, a big change from autumn.
As for wind, ERA5 data shows a return to above-normal wind for western Alaska as well as the northern interior.
Here's the situation in terms of sea surface temperatures: still very warm from Japan to the region south of Aleutians, although the persistent trough produced a lot of cooling near and south of 40°N (and warming closer to Alaska):
Looking back at annual-average data for 2024, temperatures were modestly warmer than normal, as a result of 8 months above the 30-year normal and 4 months below (January, May, July, August). December was the most anomalously warm month, although June was very unusual too.
According to NCEI, the statewide annual mean temperature was 28.9°F, which marks the 5th consecutive year below 29°F after the run of very warm years from 2014-2019. It seems likely that this reprieve is related to the persistence of La Niña and the negative PDO phase in recent years; this winter is the 4th La Niña winter out of the last 5 years (although last winter was a strong El Niño).
2024 annual precipitation and annual-mean wind speed were more anomalous than the year's average temperature; ERA5 data shows much of western and northern Alaska with much above normal precipitation and wind speed. NCEI data shows drier conditions in southwestern and south-central Alaska, but I'm not sure how accurate that is; Anchorage certainly had a wet year. Both data sources show a notably dry year in the southern Alaska Panhandle.
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