Eastern Arctic Outbreak Potential

[Nikolai]

FWIW: I could very easily be completely wrong on everything, so please don't take anything I say completely seriously (not that I need to tell anyone that, ).

Anyways!

I've been thinking that we'll have an arctic outbreak in the New Years time frame for several weeks now, as the zenith of the cold period we're currently in--though funny enough, the regimes won't be concurrent.

Our current pattern began, basically, when a massive -NAO setup over Greenland, progressively migrating westward. Remarkably, the -NAO will only end around Christmas time, briefly going neutral. As the AO has been concurrently negative for quite some time now, we have been significantly below average. Still we have been cold, not brutally cold--the -AO configuration has kept the true Siberian airmass blocked up--obviously--on the other side of the pole.

Shortly, we're about to see a relaxation of the -NAO, as well as the -AO. Normally, we would torch--but, fortunately for us, the relaxation will be temporary. Moreover, while the AO and NAO briefly jump to neutral, we see the models coming into agreement about a large +PNA ridge; the mechanism that could potentially deliver us our snow event around Christmas. With the fading of the Greenland block, it's clear the storm is very dependent on the good Pacific, and as modeling shows the Pacific is finally helping and not hurting. Besides this potential event, the +PNA also guarantees we stay below average during the brief neutral blip of the AO/NAO couplet--and here is where it gets interesting.

As mentioned, the coldest air is currently bottled up on the other side of the pole. Take the 0z EURO from tonight, for example:

Clearly, we've been on the relatively warm side of the Pole as of late, but even then--we've been seeing the most extreme December departures (so far) since 1989! Now here is where it gets interesting. As of 168 hours, there's a quasi-omega block over NAmerica. The funny thing is that the +PNA becomes so large, it lobes off and we end up with a block over NRN Canada, acting as a defacto west-based -NAO, which keeps us cold. The fact that the AO is neutral to positive at this point is, funny enough, a good thing. While we manage to hold onto our cold as the pattern shifts, the cold air trapped in Siberia can finally begin to migrate across the pole, as shown by the EURO one week from now;

By 240 hours, things are getting very interesting. The AO is sliding back to negative again, as a block develops over far Eastern Russia and a ridge begins to build over Scandinavia. This time though, the cold air mass has managed to shift over the Arctic and into Northern NAmerica, thanks to the airmass being freed by the now-fading +AO. Siberia begins to regenerate, but in the meantime, there's an arctic Siberian air mass, the kind of which we have not seen at all this winter, waiting on our doorstep.

More specifically, in addition to the global view, the region we care most about;

We see, on this map, continued cold temperatures on the East. Most importantly though, the Siberian airmass is just around the corner--a -20C airmass is coming into Minnesota, with the depth of the airmass over Nrn. Canada under -30C. Besides the cold, we see a +PNA popping on the West Coast again, and our old +PNA ridge that served as a quasi-NAO after lobing off is now a smaller ridge shifting east over Quebec. I think this is the particular feature and period that need to be most watched for an arctic outbreak. If this manages to evolve into another significant -NAO episode, which with the history of this year seems rather possible if not likely, the implications could include our first true arctic outbreak. If the PNA rises in tandem with a falling -NAO, with the fall in the -AO as well, the airmass over Nrn Canada could rather easily slide into the Northern tier during the New Years period. I'm not saying this is likely, merely possible--this year and winter have already featured historic blocking, and just as in 09-10, we could phase further episodes. La Ninas are also much more prone to arctic outbreaks, and not to hype (although this will certainly seem like hype), people have been throwing around 1917-18 and 1916-17 as analogs.

Just my thoughts, all input is appreciate & if people could provide ensemble forecasts it would be great as well.

[tombo82685]

great read...here are the gfs 500mb charts for hr 300 and 384, looks like you have some support with a good bit of the members

[ayuud]

06z gfs shows something similar to that

[mdsnowlover]

has the gfs gone from a lake cutter new years to a snofall in the first of the new year??

[Nikolai]

Obviously this is a 384 hour prog, but the point stands. The GFS is showing an increasingly cold signal towards the end of its period--and that's beyond how the highs stay in the 20s after Christmas. The signals for an arctic outbreak continue to grow for the period around New Years (likely just afterwards). Could the New Years event the GFS shows this run be the pattern changer that brings down our first truly frigid air of the season?

(side note: it's funny that the pattern change could potentially be to significantly colder as opposed to warmer. )

Also: actual 12z data... absolutely frigid!

http://wxweb.meteostar.com/sample/sample.shtml?text=Knyc