Tuesday, December 13, 2022

Anchorage Snow

Rick Thoman has a Substack post up about the snow onslaught in the Anchorage area: there have been two big storms in a week, producing nearly 30" of snow at the airport, and more in some spots.  Rick shows that the 7-day snow total is about a once-in-20-year event.


Seasonal snowfall totals in Anchorage have a modest (inverse) correlation with the Pacific Decadal Oscillation (PDO), a well-known pattern of sea surface temperature variations in the North Pacific.  Here's a scatter plot using data since 1953:


If we look at a map of sea temperature anomalies in the top 8 snowfall seasons, we see the negative PDO pattern, consisting of a horseshoe-shaped area of cool (for the negative phase) along the west coast of North America, along with unusual warmth in the central North Pacific.

The correlation between Anchorage snowfall and the PDO index has actually strengthened somewhat over time, with recent decades seeing extremes of both positive PDO/low snow (e.g. 2014-2016) and negative PDO/high snow (e.g. 2011/12).

The PDO has been negative for more than 2 years now, so last winter's relatively high snowfall and the current "snowpocalypse" fit the historical pattern nicely.

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