Friday, September 9, 2011

Latest on La Nina

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 surface...here 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 sure...it 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.

8 comments:

Unknown said...

Just a quick observation Cliff-

The 2008 "almost" La Nina December Snows and the 1996 huge Late December snow/Ice storm were both the second dip after a stronger La Nina. Pretty interesting even though La Nina doesn't get going strongly until later in the winter.

If we get blasted this December, that would be a pretty interesting coincidence.

smokejumper said...

I'm a weather nerd who likes to study WA climate almanac. See if there are any connections to one year to another, etc. I've come to the conclusion there is none, lol.

But this hot dry spell sparked an interest and crunched some simple figures. Since 1949 at SeaTac, I took our wettest Novembers.. One S.D. above average (essentially 9+ inches), and the average Sept. rainfall on those years averaged 1.04. Substantially below average.

If you take wet Septembers (1 S.D. above average), November rainfall averaged 4.83 inches (below average).

While this means nothing, one could actually have a better arguement that nice Septembers bring worse late fall weather.

codetalker said...

According to Joe Bastardi Chief Long Range Forecaster for AccuWeather.com studies over the past 100 years or so show that after the first winter following the onset of a La Niña, the next several winters thereafter tend to be colder than normal in the U.S.

He says the first winter during a La Niña tends to be warm. The next winter that follows is usually less warm, and the winter after that is usually cold.

http://www.accuweather.com/blogs/news/story/45220/bastardi-three-of-next-five-wi.asp

Anonymous said...

I'm inclined to agree with codetalker and Unknown. Strength of the Nina doesn't seem to matter when it comes to lowland snow in Seattle. My own unofficial research has shown that the second dip in a La Nina pattern usually brings a snowier winter than the first.

Of course, I would not want to overhype the situation after last winter, which didn't really go according to plan. We didn't see La Nina conditions set in until about the third week of February. If we didn't have that delay, I think last winter would have been unreal.

lhsouthern said...

after this span of hot weather I am HAPPY its going to be a la nina winter.

windlover said...

Just read the article by Joe Bastardi that was suggested by "codetalker"....Hmmmmm...then maybe this year we will have a real winter? And maybe next year will lean more towards nuetral and be windier and snowier? That would be so cool!

Doug said...

I feel very sorry for Texas; they really need to lose the La Nina picture.

BTW, how does one figure out when ex-Accuweather staffer Joe Bastardi is right and when he's wrong? Any clues on that?

Sysiphus said...

Bastardi is more an entertainer than a weatherman. And, even if he were a good weatherman (which I do not concede), that does not make him a climate expert. Where would Accuweather and The Weather Channel be without NWS data and forecasts, and models provided by public universities and governments?