Model Output Discussion - The Run In To Christmas

[frosty ground]

GFS (P) Still pretty cold and blocked.

People are taking details to literally rather th an looking at the pattern.

[No Balls Like Snow Balls]

I wouldn't say no to this bad boy scenario.

[IDO]

D10 on the P and everything moved east so cold but drier. A shift of several hundred miles west in that setup would be very snowy:

 

[John Badrick]

The half way house would be cold and snowy for all I would imagine though?

Is it the start of the down grades though???. Seen it many a time before, the excitement, then the down beat and disappointment. I've been a member on here for a couple of years now, but never seen charts upgrade to snowier solutions. They have always sniffed out cold solutions that look amazing, but by the time we get to D.0 they are always a major watered down version

[SnowBallz]

 

SnowBallz, on 11 Nov 2014 - 14:24, said:

 

 

Some interesting signals just beginning to appear into December - later on, I hasten to add. A cautious word though: this is well balanced against equally more probable synoptic, and therefore confidence is equally moderated. Near-term remains as stated last week: cyclonic incursions - seasonal, if you will. Apologies if my lack of enthusiasm/bravado for any near-term cold appeared to be 'sitting on the fence' - it wasn't; it was merely a view influenced by data which simply did not resonate to that tune at all.

Height anomalies are a frequent topic of discussion, by the way: organisation appears 2-3 weeks delayed, however stratospheric influence could further disrupt. Extrapolate beyond and hence tenuous plausibility for 'interesting signals'. Much to mull over.

SB

 

 

 

Just to add: without introducing any hyperbolic nonsense, the interesting signals alluded to remain (and, broadly speaking, have done since I first mentioned back around the time of this post)

 

Gritters: on your marks...

 

SB

[Weather of Mass Disruption]

WOMD - I think the main reason America can forecast slightly easier at slightly longer range is that they are not a little island sat under the path of a jet stream.  I think the UK is guaranteed to get colder post Xmas, but the variables are huge and the slightest change in the Atlantic can have huge effects on our little island.

 

Thanks Ali1977 

[Nick F]

I think one of the stumbling blocks to more amplification of the ridge over the far N Atlantic in across Greenland that we are seeing on the 06z GFS op and the 00z ECMWF is the flow upstream over N America not playing ball.

 

http://www.meteociel.fr/modeles/gfse_cartes.php?mode=0&ech=6&carte=1

 

Using the link above, if you hover over the time frames and work down toward t+150, you can see on the loop that a trough deepens over eastern US, this is what will help amplify a ridge downstream over the NW Atlantic. Problem is, the trough over eastern US does not hang around for long before a flatter 500mb flow develops from upstream - which doesn't allow a block to develop mid-Atlantic. Rather the ridge quickly flattens out.

 

More runs needed, but unless we see the flow more amplified upstream over N America to help slow the trough over the east, then I wouldn't get ready to go panicking buying and stocking up on esstentials just yet! Off topic, but dare I say it maybe the MetO are justified to remain cautious!

Edited December 18, 2014 by Nick F

[fergieweather]

Just to add: without introducing any hyperbolic nonsense, the interesting signals alluded to remain (and, broadly speaking, have done since I first mentioned back around the time of this post)

 

Gritters: on your marks...

 

SB

Lol. Quite...! Winter barely started.

[IDO]

^^^ Yes the interesting setup remains but the question has always been whether the amplification was going to develop into a block and have some longevity or was it going to be just transient amplification. It showed promise for a block for a few runs but the 06z suggests just a toppler at best on the Op & P. Obviously the 06z so the 12z will provide more conclusive evidence. But we are heading into the more certain output now so a flip today would unlikely be flopped.

 

 

P at D13 on 06z:  0z: 

[Weather of Mass Disruption]

Thanks to all that answered my question earlier - it has certainly helped to improve my understanding.   

[Gowon]

Is it the start of the down grades though???. Seen it many a time before, the excitement, then the down beat and disappointment. I've been a member on here for a couple of years now, but never seen charts upgrade to snowier solutions. They have always sniffed out cold solutions that look amazing, but by the time we get to D.0 they are always a major watered down version

 

So have I John and i'm not taking anything for granted yet.. we'll have to just wait and see how it unfolds.

[Summer Sun]

GFS P snow depth charts are not as widespread with the snow on this run

 

Christmas day 06z

 

 

18z

 

 

Boxing day 06z

 

 

18z

 

 

Saturday 27th 06z

 

 

18z

 

 

We had no 00z update at 0.25° so thats why I've had to use the 18z snow is still showing just not as widespread or as deep on this run. Only one run of course but until anything is showing in the reliable I remain cautious

 

 

[terrier]

Think we should await this evenings output and see if the 12z moves towards the 06z output. But it does seem like at the moment the European model is leading the way. And we have to remember this is the top model in the verification stats. So guess it's a waiting game again. Let's see where we are tonight. Still don't think this will be resolved until the weekend at the earliest. But the feeling I get is that both the gfs and gfsp will move towards the ECM outlook in the coming days.

[Midlands Ice Age]

I think that the difference between the GFS Parallel and the 'old', is that the P has the a much faster evolution.

You can see this from the charts already posted pre +150. As a result of the quicker evolution the P does not allow any intervening shortwaves to slow down the evolution.  It is quick and clean.

 

The GFS traditional model seems to be much slower, and it is now only slightly faster the the ECM.

 

However coldies, it may not be a bad thing.

 

Both the normal GFS and the ECM  look to be on path for a much longer cold shot via the midlevel block they show which is already showing signs of moving into the traditional Scandi high location in FI.(that is how 62 started).  Whereas the P  shows very wet and stormy conditions being spread throughout the NH  now being shown by the P for  the new year. 

 

It may well be that the atmosphere is not quite primed yet for the P solution. By the time the ECM  and GFS get there (2or 3days later) it may well be that  it is fully loaded.

 

MIA

[IDO]

Little change in the mean at D9 from the 0z:  

 

The difference is that the hi-res have moved towards the ensembles where as in the last few runs they have been the most amplified. So no changes if you have been looking at the mean for guidance. Interestingly the spread over the UK has reduced and now the uncertainty has moved across the continent:

 

 

 

The mean uppers on Christmas Day for London is now 0c (average). This morning it was -5c so quite a turn around: 

Edited December 18, 2014 by i'm dreaming of...

[johnholmes]

Whilst I agree with Ian that the met office shouldn't "scare" the public with warnings of snow etc I don't see why they can't just forecast the most likely scenario!? Their latest forecast (below) fof the period Boxing Day to new year bares no resemblance to any of the models / means we can see! Can Ian update us as to whether this fits in with models he can see ie MOGREPS ?

"Showers will likely ease during Boxing Day. Thereafter, it is thought it will be generally windy throughout with further spells of wet and mild weather, interspersed with colder, showery conditions. "

 

so what is wrong with that outlook?

To me it seems reasonable UNTIL any more definitie signals show consistently?

[Tamara]

<the type of alluring GFS output we are currently seeing in FI may become more and more plausible sooner rather than later

.
<all bets are off as stated in the extended period.

<we could do with treading water in GWO phase spacing 1/2 right into the first week or so of the New Year so that the indicated amplification potential is maximised whilst negative frictional torque longevity sustains the strength of the Azores High. ..

<could it be that the amplification signal being picked up in the last week of this month leads us to simultaneous timing of vortex demise and flip in the NAO from the persistently + signal we have been seeing... early in January?

<There are dominoes to fall that need a little luck (for coldest outcomes) to get to that Havana - but the retrogressed Pacific pattern and quieter Atlantic profile represents very promising progress at mid month on the basis that further vortex assassination has re-commenced in good time after that annoying blip. Hopefully the troposphere/stratosphere relationship (allied with the atmosphere calling in a favour for us) will do the rest....

Edited by Tamara תָּ 16 December 2014 - 19:05
...........................................................................................................

All bets are off indeed and rapid changes in modelling in conjuction with the pattern change have kicked off in the earlier timeframes of expected developments. Look out for some lively atmospheric ying and yang commencing from the festive period and taking us right into the New Year

Whatever the outcome, some utterly compelling MOD days ahead of us that is certain

Negative AAM and GWO phases 1/2 have duly supplied the long awaited amplification signal in the Atlantic. Recent negative mountain and frictional torques as discussed in previous post(s) will reinforce sending the GWO into high amplitude phase 3/4 as now forecasted and imply a strong Mountain torque (MT) as snowking mentions this morning

 

 

 

There is a phase synergy at this stage with the MJO indicated to also emerge in Phase 3

 

.

 

Composites for GWO phase 3 and MJO phase 3 teleconnect to an upper ridge in the Mid Atlantic and positive height anomalies towards Greenland with a deep upper trough over Scandinavia

The trend right across the models fully supports this

 

The implied MT strongly underpins the signposting of robust wave 2 activity as discussed on the stratosphere thread and it is on this basis that we can continue to reason that the vortex might be receiving its last rites in the early part of the New Year....

 

On this proposed basis though, the poleward westerly momentum flux associated with Phase 3 heading into 4 that might ordinarily threaten greater flow through the northern arm and break down the amplification, will instead be meeting an increasingly hostile reversing polarity zonal wind environment as the tropospheric spoke into the stratosphere stuns the already weak vorticity spinning wheel in its tracks.

So, a sharp decline in momentum is likely to ensue as these attempts at westerly additions are rapidly removed from the atmosphere. Against the background of low AAM, this supports latest GWO forecasts (as above) for a return to high amplitude phase 1-2

Fast orbit Phases 1/2 towards 3/4 before rebound into Phase 2 suggests and supports high impact weather events. With the stakes upping all the time, i.e that the nadire of the polar vortex is approaching (SSW?) the implications for the Northern Hemisphere are especially greater in terms of high impact weather

On this basis, no surprise that the METO have an eye out during the whole festive period for snow and also rapid low development along the PFJ gradient and on the left advancing axis (atlantic) gyre of the Scandinavian/UK troughing. A lot of polar air spilling south and meeting air of sub tropical nature.

Should stratospheric detonation occur in tandem with the atmosphere in this ying and yang state, then as snowking rightly hints, this will have even better omens..... with renewed and ever more vigorous blocking signals (at return to Phase 2) enhancing and further sustaining (next time around) upper Greenland heights rather than amplified Atlantic ridging.

 

Dare one suggest such a HLB scenario could then lead to backing the beast westwards through January??

 

*Before she gets too carried away (and gets bodily carted away!) *  ......A lot to happen before we get here and we should exercise large caution with such a chaotic programme unfolding.

 

We must exercise such care in expectations because the sheer complexity of upcoming events will almost certainly contain possible pitfalls - but it should not be a surprise to see such spectacular charts as we have been seeing in the GFS (P)

 

Edit: A long way off anyway within this context, but ECM extended ensemble hints of trying to sink the atlantic ridge will be tied into any future (temporary) 3/4 GWO phasing. This is greatly uncertain at this juncture bearing in mind future stratospheric trends - as discussed above

Edited December 18, 2014 by Tamara תָּמָר

[Snowman.]

Uncertainty has increased drastically for -EPO ridge.

 

 

 

FI has drawn closer so we should stick to the 5-7 day rule.

[Snowman.]

IF anything the ensembles are now even more keen on increasing heights in the greenland locale and the -EPO ridge is stronger.

 

6z 

0z

Edited December 18, 2014 by SN0WM4N

[Joe Levy]

IF anything the ensembles are now even more keen on increasing heights in the greenland locale.

 

6z 0z

It's definitely too early to call this one. I concur, if people look at the ensembles blocking is even more prevalent now (scroll forward to between 192 and 240 hours which is where all this takes place) http://www.meteociel.fr/modeles/gefs_cartes.php

[IDO]

Still some cold and snowy charts at D10 on the GEFS. In fact the mix here is similar to the 0z with the exception the wintry ones are in the ensembles rather than the hi-res runs:

 

 My 2 favs:  

Edited December 18, 2014 by i'm dreaming of...

[IDO]

With regard to this morning's ECM D10 chart where I said it was another outlier, it continues to not disappoint:

 

 

London temps about 7c above the mean!!

[chionomaniac]

With regard to this morning's ECM D10 chart where I said it was another outlier, it continues to not disappoint:

 

ensemble-tt6-london (9).gif

 

London temps about 7c above the mean!!

Which means that the majority of ensemble members will have that depression crossing as a channel low...........hmmm

 

or to edit looking again - keep the ridge in place

Edited December 18, 2014 by chionomaniac

[weirpig]

Which means that the majority of ensemble members will have that depression crossing as a channel low...........hmmm

 

or to edit looking again - keep the ridge in place

Yep either way  good news in respect to the ensembles  lets hope the 12z op  moves more towards these 

[snowy weather]

Which means that the majority of ensemble members will have that depression crossing as a channel low...........hmmm

 

or to edit looking again - keep the ridge in place

what is a channel low please?

Thanks