Friday, September 25, 2015

Negative NAO this Winter?

I am always researching variables as they relate to winter. As most of us know having a negative North Atlantic Oscillation (NAO) during winter is key for big winter storms. In fact this pattern can even save an otherwise warm and mild winter due to other external factors.

As a refresher this image below represents a -NAO pattern..



Below I took five of the largest negative NAO winters (good for cold and snow) and subtracted five of the most positive NAO winters in terms of sea surface temperature anomalies.

The result is below..



 Few key areas in the Atlantic. Notice the largest -NAO winters had warm water in the Caribbean, colder water to the North and then warmer water in the Arctic near Greenland. This is actually called the Atlantic Tri Pole and is a good precursor to a negative NAO winter (always other factors too at play). 

Here are current model projection ocean temps for this winter..


Comparing the two, notice the Atlantic does not look as favorable for a Negative NAO. We would need warmer water near Greenland and that cold pool to drift a little more south. 

However, look out in the pacific in the El Nino region. Notice in the top -NAO winters (first image) we had the warm waters more west and in the model projection they are more west as well. That is a favorable sign for a -NAO. What will the final verdict be? Too early for me to say, just showing you guys my observations as of now. 

Find out more in my Winter 2016 Outlook coming in October!

3 comments:

  1. Willy, pretty cool. But your neg NAO historical set-up also has cool water along the Peruvian coast with a cold water blob west of Chile. The early 2016 projection shows mostly warm water in those areas. Gonna be a lot more warm air rising up from the Equator than in a typical neg NAO (el Nino effects, even with a western bias). At some point that all has to hit cold air and make snow (and perhaps spectacular snow), but at what latitude? Also, not all that much hot water in the Gulf of Alaska, with a cool zone just to the south. So, do we still get an RR Ridge over the west coast, and the northern jet dipping into Pennsylvania once again? Or back to more zonal flows? Again, too soon, just a few rough observations from the gallery. In a few weeks you will have some snow reports from Siberia, more Nino development, and hopefully the picture will start to focus a bit. I'll stay tuned!
    Jim G

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    1. Yup, I think the biggest development here is the nino that might not peak as high as expected and start to crash below 2 by DJF. With signs of a westward shift in NINO with its potential weaker outcome (check out PDF corrected CFSv2 projections of Nino 3.4) I am getting more excited than say I was a month ago. In terms of the NAO I agree with you, the pacific will likely play a bigger role. Regardless, I would feel more comfortable if we get that Atlantic cool pool a little further south. I am looking at a blend of analogs right now but I think when I make this winter forecast in Mid October I am going to be able to take a pretty strong stance on winter. Will I be right? I guess we can talk about that in March haha.

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    2. Also, in terms of the GOA situation. The warm water will help enhance things but I think this year the El Nino will be a variable you weight 65% at least so compared to last year it will not dominate the pattern. In my opinion, I think that westward shift in SSTA's is so key here. And we just need to keep that warm water exactly as it is off pacific coast. If it gets to skinny I wouldn't feel too comfortable.

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