Extended Cold

My posts this month are taking on a particular theme - cold - as the ongoing cold spell is starting to make this winter feel like an "old fashioned" La Niña winter for eastern and southeastern parts of the state.  (See this post for comments on cold spells in La Niña versus El Niño winters.)

The cold has been most intense for the southeastern interior, where Northway is having its coldest December to-date since 1980, and that's with the first 4 days of the month being very warm.  The contrast with the very persistently and unusually warm autumn is striking:

Remarkably, Northway saw -50°F on 4 consecutive days from the 8th through the 11th, and 1980 was also the last time that happened before the middle of the month.  The only other Decembers this century with -50°F in Northway at any time in the month were 2012 and 2022.

The state's lowest measurement this month came from Chicken, of course: -56°F on the 9th.  With data back to 1997, that's the second earliest date for such cold; the earliest was December 1, 2012.  So far this month, the average temperature in Chicken is below -32°F, and that's on track for the coldest calendar month on record (again, during the short period of record).  There have only been three Januarys with an average temperature below -30°F in Chicken: 2004, 2012, and 2020.

It's really only the far eastern interior that has been extremely cold, as the core of the cold air has been in northwestern Canada, transported southward on the east side of a very strong ridge over the Bering Sea.  The two following figures show the average 850mb temperature departure from normal and the average 500mb height since December 5, when it turned cold:

It's interesting to note that the persistence of this pattern - and it shows no real signs of stopping - was successfully anticipated by long-range forecast models.  My post on December 6 highlighted this, and the latest forecast update shows much the same signal (above-normal 500mb heights near the Date Line) for several more weeks (refer to the bottom of the post for an explanation of this graphic):

If the model (in this case the ECMWF subseasonal model) is correct, the cold will shift westward slightly in the coming weeks, implying that Fairbanks may not have seen the worst of it yet.  But of course the model could well be wrong.

Note on interpreting these figures: the format takes a bit of getting used to.  The idea is to show the progression of anomalies (departures from normal) from top to bottom in time, with longitude varying from left to right; refer to the map cutout at the bottom for a visual reference of longitude.  The values on the chart are averages from 50-80°N.  The top part of the figure (labeled as "ANALYSIS" on the right) is the progression that has already happened, in this case the 30 days prior to December 18.  The lower part of the figure (labeled as "FORECAST" on the right) is the predicted progression from the ECMWF 46-day model, extending out to February 1st in this case.

The last figure shows temperature anomalies and indicates that below-normal temperatures are expected to persist well into January over Alaska and western Canada, and there's a hint of westward progression in the core of the cold.  The previous figure shows 500mb height anomalies (i.e. pressure in the middle atmosphere), and the persistent orange shading near 180°W is the Bering Sea ridge.