Saturday, October 25, 2014

Gulf of Alaska Waters Continue Cooling; Winter Implications Changing

As I had noted in my Long Range Discussion post last week, the Gulf of Alaska had begun a cooling trend as stormy conditions overtook the basin. Since then, waters have continued cooling to the point where much of the basin is now below normal.

ESRL
The image above shows sea surface temperature anomalies over the North Pacific basin on October 1st. On that day, we saw well above normal SSTAs across the Bering Sea, with more variable conditions to the southwest. The waters east of Japan were predominantly cool, in contrast to the very warm Gulf of Alaska and waters off the coast of California, Oregon, Washington state, British Columbia, etc.

I've seen many forecasters across the Internet push for a cold winter due to the waters being very warm in the Gulf of Alaska, myself included. It's not a bad path to choose- after all, it's that same swath of warm waters last winter that allowed for such brutally cold weather to enter North America. With those waters present again leading into fall, if they stay put, it's quite plausible that we might see another cold winter for some of the same reasons as last winter.

Those warm waters are gone.

ESRL
The graphic above shows sea surface temperature anomalies for the same area as the image on October 1st, but this graphic is now valid on October 22nd, just a few days ago. The changes in only a three-week period are astounding. The Bering Sea has cooled off dramatically, now predominantly below-normal instead of the nearly-3-degrees-above-normal anomalies in place on the 1st. The waters to the east of Japan are still below normal, but that swath of below-normal anomalies now extends far to the east, and has decimated the warmth in the Gulf of Alaska.

I had said that this would be a possibility with all of the storm activity in the Pacific, but many believed I was losing my mind...

So, we've lost the factor that provided such a cold winter for us last year. Now what?
The alignment of sea surface temperatures leads us to believe we are now entrenched in a positive-PDO pattern. If you look closely, you might be able to make out a semi-circle of warmth along the west coast of North America encircling the cool waters further west. This horseshoe-like alignment is a textbook example of a positive PDO, as the graphic below shows.

NCSU
The phase-definition chart, my personal label to the graph that tells us which phase the PDO is in, also confirms the positive PDO orientation.

NOAA
So, we've lost the big pool of warm water anomalies in the Gulf of Alaska, and as of right now, we're neck-deep in a positive PDO event.
Sounds like a real downer for cold weather fans, right?
Not exactly.

ESRL
The image above shows correlations with the Pacific Decadal Oscillation (PDO) and surface temperatures during a December-January-February period. What this chart is saying, is whenever the PDO is positive, temperatures in the West US will be warm (due to the positive correlation), and temperatures in the East US will be cold (due to the negative correlation). Similarly, when the PDO is negative, temperatures in the West US (East US) will be cold (warm), due to the positive (negative) correlation. So long as the PDO remains positive this winter, the risk of a cold winter would still be maintained for most of the Central and all of the East US. It remains to be seen if the cold waters will keep pushing east and erase the positive PDO completely, but as of right now, this would be a beneficial development for both cold weather fans in the East US, and warm weather fans in the West US.

Interestingly enough, positive PDO winters tend to bring wetter than normal winters to the Northern Plains...

Andrew 

11 comments:

Anonymous said...

wait...'warm weather fans in the west?' andrew? we need rain and snow...not more 'warm.' especially california.

BearCub said...

Phew Andrew, you scared me with the first half of your forecast! I thought the cold in the East US was gone. May be a 1977 year here in the East-fine with me. Could be a later start to to Winter if it is, but big snows and cold after December.

Andrew said...

Anonymous at 2:29: That's fine that you aren't a warm weather fan. Bear in mind California does not make up the entire West ;)

Anonymous said...

Check out Joes weather Bell forcast.

Anonymous said...

Do you think the water might warm back up again later this fall. Also is the east in for a lot of snow this year?

Anonymous said...

And folks, this is why you should not try to forecast 5+ months ahead of time. Why don't they just wait until winter starts? Not like you can prepare months ahead of time anyway.

Anonymous said...

There are many more factors that influence our weather other than the waters in the Gulf of Alaska. Even though a warm Gulf of Alaska would play a significant role in bringing the cold air into the eastern United States, it is not the ONLY thing that allows the cold air to flow into the central & east US. So much goes on in the atmosphere and many of these signals change in a blink of an eye. In no way are we out of the woods from a cold winter. I'm not ready to give up hope on a cold winter when it's not even Halloween yet :)

Anonymous said...

I use to rely on your weather, but you change it from post to post. No you wont post this because you see it as being negative. Changed over to weather Bell. Joe B.

Andrew said...

Anonymous at 10:56: There's always that possibility of the waters warming back up, though right now, trends don't favor it. As for a snowy east, it'll come down to how strong blocking will be in Greenland.

Anonymous at 11:38: Huh? My forecast remains unchanged; this post is pointing out something that's happening with a relation to winter, not overhauling my forecast...

Anonymous at 5:50: Correct; you shouldn't be giving up on a cold winter, as it's still quite likely, hence my forecast of a cold central & east US.

Anonymous at 2:58: I would explain your misinterpretation, but I have a feeling you aren't here for an explanation at all...
In the spirit of providing something to counter your accusation, nowhere in my post did I say, nor have I ever said, that my forecast is being changed. My official forecast still stands; if that changes, you'' hear about it far in advance.

Anonymous said...

Cold...yes in the east...Just not much cross polar flow. The cold events may not be so prolonged because of the stronger subtropical jet due to El Nino. The wave length will probably open more frequently across the CONUS as cold air gets flushed eastward more often...

Watch out for the negative phase of the TNH pattern....

Frank-o said...

I for one would love to see "ANONYMOUS" posting "BANNED"... I use my "REAL" name and I am not hiding behind a key board.....Come-on folks........Stop hiding..Man up.........or woman up...Frank-o