Cold Exits Southeast

The unusual cold spell is largely over for much of Alaska now, as the core of the chilly air mass has finally migrated to southeast Alaska and western Canada; British Columbia and Alberta are now in the deep freeze.  In the past few days the harshest cold in Alaska has been in the southeastern interior, where Northway has reached -50°F for five days in a row; this is the most since January 2009.

The nearby famous cold spot of Chicken was colder, of course, and reached -62°F on Friday.  This is the coldest since 2013, but actually it's right on par for the typical coldest temperature of the winter; I was slightly surprised it wasn't a bit colder, given the -50°F or lower in many other spots.

Last week I mentioned the persistence of cold in Bethel, and their cold snap broke at last on Saturday, when Pacific air finally bumped the temperature back up towards the freezing mark (i.e. well above normal).  In the end Bethel endured 18 straight days without rising above 0°F, which is the most since 1989.  It's an impressive cold spell for a place that has borne the brunt of excessive winter warmth in recent years.

Here's a comparison of daily temperature anomalies over recent months in Bethel and Northway.  Since October 1, both sites are still running above the 1981-2010 normal (+0.6°F and +3.7°F respectively).  Click to enlarge:

One other note in this quick update: the PDO index has plummeted in recent days in response to the outbreak of cold air over the northeastern Pacific (and in fact a broader pattern shift extending all the way down towards Hawaii).  The PDO (Pacific Decadal Oscillation) is highly correlated with winter temperatures in much of Alaska, and the daily index hasn't been this low since late 2013.  Time will tell whether the regime shift has any staying power.

Update Jan 14: here are some long-range PDO index forecasts from the NMME and ECMWF seasonal models.  It's a fairly robust signal for a generally negative PDO regime by early summer, and this is closely related to the models' expectation for La Niña-like anomalies to develop in the equatorial Pacific.  Of course this doesn't mean the North Pacific will be cool as a whole - the opposite is more likely to be true.