Fears of a Double Dip

Nothing terrifies Northwesteners more.  

Many of us have suffered greatly because of it. 

Folks are depressed over its effects.  

Supposed experts are not sure which way it will go. 

And the media can't seem to get enough of it, with headlines and articles describing its unpleasant effects all the time.

The nation's financial mess?   Political paralysis in Washington D.C.?

No.....

 I am talking about the threat of...dare I say it?...the return of La Nina next winter.  Or to use a technical term:  a double-dip La Nina.

I know, we suffered from La Nina last winter and this spring, and the forecasts were for an escape to a neutral year.  But the atmosphere is not following the script and the Climate Prediction Center has just put out a La Nina WATCH, which means it is not certain but possible.


So here is the situation.  Last winter we were in a fairly strong La Nina, one that weakened during the spring.   A primary measure of La Ninas (and El Ninos) are the anomalies (differences from climatology) of the sea surface temperatures (SST) in the tropical Pacific. The most well-known index is the SST anomaly in the Nino 3.4 region (see below).  The anomaly weakened to near zero by May, went slightly positive, and now is slightly negative.   Call it Neutral.

The trouble is that although the ocean say neutral the atmosphere has been holding to a La Nina-like configuration...including the troughing and cool weather along the West Coast.  And subsurface temperature sensors in the Pacific indicate cooling.  Ominous. 

The NOAA Climate Prediction Center has a number of models available that simulate the tropical sea surface temperatures.  As shown below, they are all over the place..some near zero, some indicating warming, but an equal number going for cooling.  Looks like a coin flip.

Even more worrisome, the NOAA Coupled Climate Model, their main simulation model for the atmosphere and ocean, is now turning more towards the La Nina (negative) side (see below)

 A look at the history of El Ninos/La Ninas (the ENSO Index) over the past 60 years shows that double dips do occur...such as in 2008/9 and during the mid 70s. (La Ninas correspond to the blue negative excursions).   In fact, double dips are not rare.

So the bottom line:  a double dip, with La Nina coming back is a real possibility, but no sure thing.  By late September, we should have a much better idea, but believe me, we have gotten this wrong plenty of times in the past.

So if I was Mayor McGinn I would kick the tires of those snowplows and be ready to order some more salt if needed.  My group is rushing to complete a powerful new aid for the City, a web-based application called SNOWWATCH. You will not believe what it is capable of!  With the new coastal radar in place, expect better snow forecasts if it does occur.  And KING TV's snowmaven Jim Forman should get his famous parka cleaned--he might need it.