Latest on La Nina

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A number of you have asked about La Nina and the upcoming winter.  It is always prudent to wait until mid-September before making the call, a call that in any case has considerable uncertainty.  The U.S. Climate Prediction Center has just upgraded the status from a La Nina Watch to a La Nina Advisory--they are basically committing to a forecast of a La Nina winter.  It is not unusual for two La Nina years to occur in a row, although the second one is generally weaker.

I don't have to tell you the implications of La Nina for the Northwest--AFTER January 1 it is generally associated with cooler/wetter conditions that produce more snowpack than normal in the mountains and a higher probability of lowland snow.   So local departments of transportation should stock up on road deicer!

So what are some of the signs of an upcoming La Nina?  First and foremost, colder than normal sea surface temperatures (SST) in the tropical Pacific.    Here are the SST anomalies (differences from normal) for the last year.  Take a particular look at the Nino 3.4 values.  The cold anomalies have increased.

We have also seen that cold anomalies have increased substantially BELOW the is the proof:
And the wind field (stronger trade winds) have not abated since the last La Nina.

Until recently, the NWS was undecided whether the coming winter would be a neutral (La Nada!) year (when tropical SSTs are near normal) or a La Nina year.   The trends now point to the latter, although there is still some uncertainty.   The latest computer predictions (see graphic below) are mixed between La Nina and Neutral, although the NWS coupled forecast model (which is a coupled ocean-atmosphere prediction system that is run out for months) is going for La Nina--and this model has been skillful lately.
One thing for does not look like an El Nino year! 

And here is the latest winter predictions from the Climatic Prediction Center:

Wetter and colder for us, warmer and drier for the SE.  Does this look familar?

So it might be a good winter to get that annual ski pass.  Probably lots of snowpack for next summer's water supply.  And local global warming skeptics will make the usual remarks.
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