Emerging threat for eastern N/A cyclogenesis, D7-14

[Typhoon Tip]

Hello folks,

Today is the official Meteorological beginning of the 2012-2013? winter season (? = provided we survive December 21 2012 nyuk nyuk) so perhaps it is fitting that we have something more than nuanced overrunning attributed light snow, flurries and freezing drizzle.

First it gets warm, then it gets cold. BOOM

Primer on the Archambault study:

Statistical and synoptic-dynamic relationships between major cool-season Northeast precipitation events and North Atlantic Oscillation and Pacific–North American regime transitions.

http://www.atmos.alb..._et_al_2010.pdf

and here:

http://www.atmos.alb..._et_al_2008.pdf

I suggest any newbies to weather enthusiasm, or those setting upon the arduous journey of being educated in Meteorology, might want to read these papers - its up to you.

In short, when the PNA is rising, and the NAO is falling, either together or independently during DJF, the study shows statistical correlation to significant precipitation events. It is important to note, that does not specify between rain vs snow. I would also mention from a personal perspective on the science, though it is wonderful to see it mathematically demonstrated through the use of statistics, the result is quite intuitively satisfying. The reason being, if a given area is in a given mode that is persisting a temperature and moisture layout, and than that region is perturbed by an encroaching force substantial enough to change the layout, storminess should result. This is because you cannot have storms without advection, and any such perturbational force sufficient to change the regions layout must by definition encounter advection. It is hugely useful, however, to point that out scientifically using statistics, because it adds some concrete evidence to back any prediction that is using/based upon recognizing large scale phase changes.

Regarding our "threat" - it may be too early to call it that, but, sufficed it is to say there is an emerging signal that is fairly consistent with the Archambault study for the time period roughly between day 7 and day 14. Here are the CDC and CPC teleconnector (if anyone has access to the ECM ens -derived indices, by all means...).

CDC:

In the annotation above we clearly see a discerned rise in both the ESRL/PSD and NCEP channels with regard to the PNA. Considering that the atmosphere has been characterized spanning the last 10 days to 2 weeks, as being steady-state -PNA ( -.5 to -1.0 SD), and here we see an average rise exceeding 2 standard deviations, argues fairly strongly for a mass field break down and a reconstruction along a newer paradigm - most likely one that features a different sort of relay from the eastern Pacific into western North America, and subsequently transmitting a signal downstream to the eastern portions of the North American middle latitudes. It is noted that the signal is less elaborated in the NAO, particularly from the ESRL' channel; however, given the well established periodicity with the NAO stemming back several months, if that trend could serve as any guide at all, it is likely to me that the NCEP channel is more plausible given to that expectation.

CPC:

We also see from teh CPC, a unanimously agreed upon rise in the PNA. There is some disagreement among the members as to the magnitude, but the 50,000 foot perspective on this output above is that every member is rising - that's the impetus. And every member goes from negative phase space to positive phase space. The bulk of the members, near +1SD from a beginning of nearly -1SD. Again, given to the fact that the recent 10 days to 2 weeks has verified in the given characteristic flow, the assertion from these products that the index should rise 2 complete SD values, strongly suggests that there is going to be a mass field change by D10 - it should be well underway.

Adding in the Archambault science brings this logic circular, and the closed implication is that there should be an enhanced precipitation threat during the time frame in question. Again, it is important to remember, that speaking in terms of p-type is not what the science discusses. However, it is certainly useful in the winter for determine intervals of increased cyclogenesis potential.

That said, the atmosphere over N/A is going into a cold phase toward mid month. This was led by a recent -EPO reign, which is indeed weakening, however, cold loading into the northern continental area has already taken place; this air mass is thus made available to the middle latitudes from the NP to NE regions, given to an flow tendency turning NW of west and central Canada. The rise in the PNA certainly also argues for that result.

Operationally, we see both the GGEM and the ECMWF forecast models occasionally deterministic solutions for an important coastal storm.

Normally, we do not carry much confidence in any given D10 solution, from any model. However, there are times when the consideration for the bigger picture and how the environmental variable et al play in, we might establish somewhat better confidence than the normal. This is one of those times. As to these particular solutions, I am not altogether impressed by the Euro's handling of the PNA in the operational version. However, the 00z ensembles, from what I have seen through D10, suggest the operational version may be too low with heights over the Gulf of Alaska by D7+, and therefore, some correction toward higher heights rolling into W. N/A by then, plausibly feeding into a deeper solution E of ~100 W is all on the table at this time. I like the idea that the operational models have something at all more than the details for obvious reasons.

I'd put the possibility for an important event at 40/60 ... maybe 50/50, which for this type of time lead would have to be considered high. If all CDC channels were more amped up with the teleconnector oscillation, and CPC also more robust, that could vary those odds. It's not science to say so, per se, but more conceptual - though backed using the science.

[CoastalWx]

Nice disco John. There does seem to be a signal for something at this time. I really hope the PNA can jump + like that.

[Typhoon Tip]

Nice disco John. There does seem to be a signal for something at this time. I really hope the PNA can jump + like that.

Yeah, that's the big question, will the PNA succeed in doing so - if we wake up tomorrow and things are unraveled...well, heh. yeah.

I don't think so though. The PNA rise has some merit from the periodicity argument in its own rite. The PNA should rise by now without any obvious environmental factors/variable keeping it negative - which if there are any, it is not abundantly clear what they would be.

But ... we have discussed in more upper level terms in other threads why the wave spacing should change from the WPO domain clear around the hemisphere. For one, the WPO is rising over the next 10 days to two weeks. Though the PNA correlation there is weak, it does get strong as the cold season gets going, and the correlation is positive. There are some clues out there that suggest paradigm shift.

How long it last and or if it will determine the anomaly distribution for the rest of Dec, who the h knows, but at least for the next 2 weeks ... I'd suggest folks just allow the warm up over the next 3 days and have fun with it, because from where I'm sitting ...it doesn't look to last.

By the way, if all this were not enough the MJO has recently popped out of the COD in Phase 2, which for Dec is colder eastern signal.

[Baroclinic Zone]

Bump so that we can keep discussion in here regarding this potential

[Damage In Tolland]

We may have to entertain the threat of a damaging interior icestorm as well . Tippy can address.

[Baroclinic Zone]

All possibilities are on the table in this timeframe

[Typhoon Tip]

We may have to entertain the threat of a damaging interior icestorm as well . Tippy can address.

Well I wouldn't venture to guess on any impacts but you're right, there are some suggestion in the runs for something more of that type of event, too - we are still in monitoring an onset PNA mode with this, and anticipating some activity in that D7-14 time frame.

[Typhoon Tip]

Update on the progress of this ...

There is no progress -

Fascinatingly, the PNA progs at both agencies have completely abandoned the previous multiple cycle insistance that it will rise +2 SD over 10 days, now having the CDC side actually lower the PNA.

I don't think I've ever seen that kind of incredible hemispheric-scaled mishandling of the mass-fields - although there was one day prior to the light overrunning event that did the same thing, this is is just more astounding. It will be interesting to see if the CEFs members combine to fluctuate back toward a PNA rise, or if this is for real.

Sufficed it is to say, without the PNA rise, the H.A. idea is gonzo.

Having said all this, there is still still a weakly descending NAO at CDC, and perhaps a more robust descent at CPC by a little - that "might" argue for placing a bomb on a track through Lake Superior as less likely; but the falling NAO signal also seems to be weakening now across these last 3 days.

It's interesting as a Meteorologist to see teleconnector stochastic nature of this extremeness - all domains are doing this, too. When we say "the PNA teleconnector", we are talking a truly mammoth domain space of atmosphere mass - to have it fluctuate this wildly across just 2 days of 21 member modeling is pretty fantastic. Wow.

By the way, the 06z at least had a 3-day ice storm. The funny thing is, the far east Pacific does actually ridge out to some degree, albeit 3-5 days. So whether the whole of the PNA domain actually enters a positive modelity or not, if that local segment of the field does differentiate that way, there probably would still need to be some kind of cyclogenic response down stream over middle latitudes of N/A.

[Typhoon Tip]

Giving this a bump because the 12z operational Euro is actually signaling strong +PNAP pattern emerging upon this D7.5 juggernaut coastal low - whether the guidance clusters have failed the PNA preceding, that +PNAP appears +PNA related, and overall the Archembault scenario is afoot.