Blog posts have been few and far between lately, owing to personal circumstances, but hopefully the pace will improve in the near future. For now I think it's worth highlighting a particularly interesting aspect of this winter in Alaska: the remarkable juxtaposition of far above normal temperatures with a negative PDO phase.
And warm it certainly has been. While February climate data isn't all available yet, Fairbanks and McGrath both had their 3rd warmest winter (Dec-Feb) on record. Winter 2000-01 holds the record at both sites, and they differ on the 2nd warmest (1976-77 in Fairbanks, 2017-18 in McGrath), but both came in at #3 this winter. Here's the time series for Fairbanks:
We (or at least I) tend to think of 1976 as the great climate shift to multi-decadal warmth in Alaska, and that change certainly had a lot to do with the PDO phase shift at the time; here's a paper on that topic:
https://journals.ametsoc.org/view/journals/clim/18/22/jcli3532.1.xml
If we look at Fairbanks DJF temperatures since 1950 with the PDO phase indicated, we see the predominance of a positive PDO in the 1980s, and we also see that virtually all of the very warmest winters have occurred with a positive PDO phase - until this winter:
In terms of correlation, the PDO index has historically shown a moderately strong relationship with Fairbanks winter temperatures, and therefore again winter 2024-25 is a pretty significant outlier:
What seems to be happening is that the PDO-temperature correlation is diminishing over time; it was quite strong before 1990, much less significant in more recent decades, and now it seems this winter has lost the relationship altogether.
There are a few different hypotheses one could pursue on this. One might be that while the PDO ocean temperature index continue to oscillate (it's just a mathematical construct), the atmospheric circulation patterns that are occurring in tandem with those ocean anomalies have changed in such a way that the PDO now relates differently to Alaska climate. This winter, for instance, there was an atmospheric ridge over Alaska even though the anomalous warmth in the northwestern North Pacific (and consequent negative PDO) might have been expected to deliver a trough near Alaska.
Another perspective might be that high-latitude warming ("Arctic amplification" of global warming) has become so pronounced that a negative PDO can't be expected to produce historically cool temperatures; even a "cold" pattern is now warm by historical standards. I think there's some of this going on - broader Arctic temperature trends are partly responsible for this winter's warmth - but in fact the circulation pattern was favorable for warmth in Alaska this winter; it wasn't a "cold" pattern except in terms of the raw PDO index.
It's "interesting" to consider what might happen if all the signals line up on the side of warmth one of these years; it seems a strongly positive PDO index with a classically strong Aleutian low and rampant southerly flow could produce a winter far warmer than any observed in modern climate history. It may just be that this winter is actually quite "normal" in terms of the climate of the next few decades.
