Model Output Discussion 29th December - Into mid-Winter.

[mulzy]

The extended eps is again broadly similar to the last few runs though higher heights over Europe is pushing the jet a little bit further to the north meaning that the 850's are anomalously warm right through to day 15.  From what the NWP is showing, it's a long way to cold.  However, we all know things can change quickly but for the sake of your sanity reign in expectations for the rest of this month and early February.

[nick sussex]

Re Singularitys post this MJO update from NCEP is interesting, they're suspicious of the GFS weakening of the signal. Additionally it could be that the correct MJO signal has already quickly gone through phase 8, the original outputs picked that up but the ECM is now seeing more phase 1.

The ECM changes between outputs suggests the MJO could be causing this jumpiness.

 While the RMM index indicates weakness of the MJO at present, Hovmöller analyses depict the eastward propagation since late 2016 of an intraseasonal signal presently over the Western Hemisphere.  The CPC velocity potential MJO index appears to have done a better job tracking this signal. 
 The low frequency background state continues to influence the tropics and subtropics, with suppressed convection in the Central Pacific and enhanced convection for the Maritime Continent. The subseasonal signal appears to be destructively interfering with the convective signal over the Maritime Continent in recent days. 
 Dynamical model forecasts of the RMM index support an emerging MJO signal in the Western Hemisphere during Week-1 that continues into the Indian Ocean during Week-2.  Uncertainty is high late in Week-2 where ensemble mean forecasts support weakening of the MJO, although this could be tied to inconsistent simulated phase speeds cancelling out with one another.
 

Further on:

The GEFS forecast depicts an emerging MJO signal over the Western Hemisphere in the next few days.  This signal is forecast to continue into the Indian Ocean during Week-2 before the ensemble mean supports a weakening signal around the 25th of January. 
Caution should be exercised with the weakening forecast late in Week-2 as differences in the model forecast phase speeds of the intraseasonal envelope could be destructively interfering. 
Continued eastward propagation is consistent among ensemble members.

The ECM monthly could also be wide of the mark because it also wants to weaken the signal quickly into the COD.

Whether we get to anything interesting is still open to debate but its unlikely the MJO won't have some impact on the NH pattern. The ECM op output looks like a response to phase 1.

[Seasonality]

1 minute ago, Nicholas B said:

Nope I believe it is what the chart shows for the majority of the uk, yes high pressure is in control of the vast of Europe but we are talking about the UK. we will have to agree to disagree. High pressure is clearly in control as we speak and it is grey and drizzly in my location so I understand what you say, but if you watched the BBC forecast for the day shown (if it turned out that way) they would not be saying high pressure in control. We will have to agree to disagree  

Ok, I happily agree to leave you to your subjective perception rather than an objectively veracious view.

[chris55]

Any chance of a ridge being thrown up ahead of the Atlantic low around 144 on ECM? Very unlikely and the 00z flattens things at 168,  but with little forcing coming out of Newfoundland its a wildcard option.

[TEITS]

33 minutes ago, Seasonality said:

Just to emphasise the differences between the two most recent ECM runs.

Nicely illustrates the uncertainty as we enter the last week of Jan. This is another reason why I take GEFS means at D10 and monthly ECM forecasts with a huge dose of salt.

I would be eager to hear GPs latest thoughts on how we may progress forward.

[Troubleatmill]

35 minutes ago, Seasonality said:

Ok, I happily agree to leave you to your subjective perception rather than an objectively veracious view.

OK mate, and I will leave you to yours

 

[TEITS]

4 minutes ago, Nicholas B said:

OK mate, and I will leave you to yours

 

High pressure is controlling our weather on the ECM charts. Only after +240 does low pressure start influencing our weather. The only exception is the far N of Scotland at +216.

[Singularity]

Some excellent information there @nick sussex, thanks for that 

It has to be said, interference or no, the current ECM ensembles paint a very interesting picture going forward i.e. into the first half of February. Having the MJO propagating steadily into and then likely across at least part of the Pacific while the stratospheric vortex undergoes significant weakening (or, who knows, even a SSW), well that would be a mighty combination.

The spread is balanced around the COD though, so no assumptions can be made here - but the words of NCEP are encouraging 

[Troubleatmill]

22 minutes ago, TEITS said:

High pressure is controlling our weather on the ECM charts. Only after +240 does low pressure start influencing our weather. The only exception is the far N of Scotland at +216.

With High pressure close by to the South East and Low pressure close by to the Northwest, how can one be in control? The 1013mb line at t216 is over northern England which is central UK, 1013mb is the standard pressure for the UK as stated by the Met (neither high nor low). If at t240 low pressure starts to become dominant then that should say something to us? Anyhow i'm out numbered here by you guys so guess I must be wrong, in which case I will eat humble pie!  

[snowray]

Can we please get back to the models guys.

 

Seems to me that HP is in control for the next week or so, and if anything holding on a bit longer on the 06z. Pretty cold charts on the whole, some frosts and a few grains of the white stuff on higher ground. 

[snowray]

Pity really, uppers could have been a bit colder on this sort of a continental flow. 

[snowray]

Nice chart at T192, now LP starting to dominate, Euro slug being shifted at last, and is that a bit of yellow and green there that I can see up towards Greenland? 

[bluearmy]

5 minutes ago, snowray said:

Nice chart at T192, now LP starting to dominate, Euro slug being shifted at last, and is that a bit of yellow and green there that I can see up towards Greenland? 

I think you are on a wasted journey expecting a height rise into Greenland within the next 10/12 days.

of course the extended modelling may flip completely but I doubt it would to that extent

[swfc]

finding any positives on the gfs 6z is a big ask imo and things just look to drift on towards the latter part of jan.ssw- mjo nothing seems to bring any other outcome other than whats past since late november.todays ecm does show some promise i guess but i sound like a broken record.i wonder if a "backloaded" winter is the next way forward

 

Edited January 17, 2017 by swfc

[snowray]

Just trying to be a bit more optimistic thats all...There is some scope there for a toppler I think though, around D10.

[Man With Beard]

2 minutes ago, snowray said:

Just trying to be a bit more optimistic thats all...There is some scope there for a toppler I think though, around D10.

Maybe not headed for a Greenland High but I think there is room for optimism all the same. The pattern does seem to want to head east - if the models are under-doing the signal for progression, we might get a tasty low from the Greenland area - the latest GFS a case in point:

from   to 

maybe a long way off but not  inconsistent with some other output

[snowray]

Not bad chart there for Northern half of the UK, could be very snowy. Long way off I know.

[Snowmaiden]

Oh my word the 00z and 06z GFS bring new levels of awfulness to the medium term for cold lovers. Long and screaming SWerlies running up one of those horrible 'escalator' high pressure systems. And there is no cold of note pooling to make any change to the pattern worthwhile from that cold perspective. Hard to find anything enjoyable for anyone who isn't a fan of windy winter weather.

having said that of course, it will be immense fun on the hills and mountains of Scotland, where such conditions bring white gold to theadventurous.

[nick sussex]

The GFS 06hrs run moves towards the ECM solution in the early stages, whether this is a one hit wonder from the ECM and its new evolution we'll see this evening but the trend to amplify troughing over the central USA downstream causes the jet to angle more se'wards by T240hrs.

If this trend doesn't hit the buffers I fear we may soon start to be chasing another east/ne flow!

 

 

[Snowmaiden]

When the 06z does finally move it succeeds in bringing Atlantic sleet above a couple hundred metres to Donegal and western Ireland and maybe a flake or two for elevated Ulstermen. What a dreary and depressing set of runs. and no sign of any stratospheric warming, sudden or otherwise on display. 

[Bobd29]

24 minutes ago, nick sussex said:

The GFS 06hrs run moves towards the ECM solution in the early stages, whether this is a one hit wonder from the ECM and its new evolution we'll see this evening but the trend to amplify troughing over the central USA downstream causes the jet to angle more se'wards by T240hrs.

If this trend doesn't hit the buffers I fear we may soon start to be chasing another east/ne flow!

 

 

Perish the thought Nick, cannot go down that road again this winter

[Seasonality]

Just an observation, but the 06z extends sub zero surface temperatures over central, eastern and south eastern Europe, as did the 00z ECM, albeit in a different form. Changes afoot or one run blip? More interesting model watching, that is for sure.

[stodge]

Morning All

Into the second half of winter we go.

The current "problem" is the HP over Canada is drawing cold N'ly air down into the Atlantic encouraging cyclogenesis and firing up the northern arm of the jet.

Further down the line into FI (and I do wonder if this is the initial response to the warming on the Eurasian side), the PV energy gets bounced back over to the North American side and we get the PV shunting cold air south and encouraging cyclogenesis etc,

So we first have an unfavourable tropospheric scenario followed by an unfavourable stratospheric scenario. That said, the GFS in FI is giving the PV a real hammering at 10 HPA so IF the "warming" happens (whether an actual SSW with reversal or not), we will have a much weaker PV in February than last year when all we got was a much earlier final warming. The hints at blocking in February support the scenario of a weakened PV but I'm not expecting a Greenland HP - I think Scandinavia will be the more likely option.

As we've seen, the standard response to a period of "disruption" is a 10-14 day reset of Atlantic domination. We're probably looking at that now in all honesty from the weekend and next week could be very mild in the south. That said, we're not really seeing the Atlantic in full fury as past winters - the "interest" is the modelling of secondary features which "could" be nasty in terms of wind and heavy rain (and plenty of potential for snow to altitude).

It's worth pointing out once again that even with two weeks "gone", there's a full third of winter left and as past winters have shown, March is more than capable of delivering lowland snow and cold (perhaps not on the scale of the exceptional 2013 experience though there was an SSW at that time).

[Troubleatmill]

41 minutes ago, Seasonality said:

Just an observation, but the 06z extends sub zero surface temperatures over central, eastern and south eastern Europe, as did the 00z ECM, albeit in a different form. Changes afoot or one run blip? More interesting model watching, that is for sure.

Certainly some decent surface cold in the areas you mention, O6Z for the UK is not great though with the current HP sinking SE with the only chance of anything cold in the UK being some brief PM incursions, lets hope the ensembles show a glimmer of something we are looking for toward the back end.

EDIT out to t240 the ensembles have to be the worst for cold possibilities I have seen for the UK this winter . As Blue army said, I think we are going to have to take the medicine before anything.   

  

Edited January 17, 2017 by Nicholas B

[Tamara]

As suggested on some previous occasions, we should view any suggested tropical forcing (MJO) affects on NWP as only part of the total budget global wind-flow that determines upstream (and consequent downstream) jet and pattern evolution. The total budget, which compromises tropical and extra tropical forcing is shown as an accumulated wind-flow budget within the spectrum of the Global Wind Oscillation.

So whilst its certainly true that greater amplitude of tropical forcing is the engine room for increasing meridional NWP consequences the further this progresses eastward, - a more accurate and reliable picture can be gained by looking at net total atmospheric angular momentum fluxes as represented and viewed through GWO Phase space orbit, than trying to manage expectations of NWP through the MJO phase spaces and composites in isolation.

The MJO global AAM component of the wind-flow signal is forced principally by a frictional torque (a sudden change in longitudinal pressure) and to a lesser degree by the consequent mountain torque that follows it. The Mountain torque being the extra tropical component to AAM.

As tropical forcing engages changes in momentum transport in the tropics, and which can propagate poleward, it is the mountains which act as additional sources of momentum transport in the mid and higher latitudes - as possible by the ensuing mountain torque events. The latter also have consequences for changing and disrupting stratospheric polar vortex temperature profiles of course  - on a further wavelength anticipated timeline

So to summarise the above catalysts, MJO tropical convection initiates the wave train, but it is the poleward extension of the meridional (amplifying) momentum transport that triggers the response of the mountain torque in the extra tropics and causes sudden switches in regional hemispheric jet stream and synoptic patterns.

There is a decay (wavelength) response time of about 6 days from when the acting frictional torque returns AAM to the earth, as extracted by the Mountain torque.   This is why it is so useful to very regularly monitor frictional torque changes ("the starting pistol") to gauge the follow-on extra tropical (mountain torque) response and then be able to gauge the NWP response that follows on from the domino effect.

To try to put the above into some context of real-time NWP:

Following on from the small amplification of late December which, on its own torque timeline to the extra tropics, resulted downstream in our window of wintry weather to end last week, we see frictional torque on a downward trend - as tropical convection prepares to return to the Indian Ocean, adding easterly momentum to the atmosphere and putting initial pressure on atmospheric angular momentum tendency.

Calculated tendency is holding up total atmospheric angular momentum close to average parity, as the residual positive mountain torque provides support.

The Global Wind Oscillation, the representation of all these total on-going atmospheric circulations is already anticipating the increasing negative tendency.  The dampening frictional torque in due course will induce negative global mountain torque response. These dual actions are therefore depicted with some credible accuracy by GEFS forecasts as an imminent Phase 8/1 orbit

 

Decreasing atmospheric angular momentum removes westerly wind momentum from the atmosphere and serves to build anomalous ridges from the sub tropics to mid latitudes starting in the Pacific.  The return of the US west coast ridge in extended NWP is a signal of this rising pressure in the Pacific.

With the polar vortex modelled to return to Greenland and Canada, a La Nina-type atmospheric phase with the tropical signal based in the Indian Ocean and supporting the mid latitude Pacific >.Atlantic pattern, its no surprise to see the current settled phase morph into an unsettled zonal passage of weather.

The uncertainties remain about the amplitude and speed of the tropical signal - and as others have correctly said, this will determine the route of NWP beyond the expected spell of westerlies. 

A high amplitude eastward tropical response would spike frictional torque significantly and set the ball rolling for extra tropical mountain torque and substantive amplified consequence downstream. The key extra tropical amplification signal potentially further exciting the on-going modelled stratospheric warming signal in the furthest extended period approaching months end and more especially into February. 

It will ultimately though, be the total global torque strength that will both aid and abet the eventual vortex warming signal (of which we cannot wholly rely on at distance) However a strong +ve MT response could be the thing that helps nudge zonal winds over the polar field to sufficient deceleration to allow much better chances of blocking to our N and NE next time around.

So, some attempted further back-up reasoning behind the GSDM to illustrate why it is such a forward tool in evaluating NWP and not the stuff of soothsayers.

In tandem with monitoring stratospheric forecasts, it will therefore be the other place to look for the next "starting pistol" to maintain hopes of winter providing a main course follow-up to the mid January modest "amouse-bouche"

@TEITS I clearly cannot speak for other members and their interpreted comments based on a same data source. I can only be expected to speak for my own posts which are intended to objectively state the possibilities and try not to over gild any "good news"  Not saying here, there has been any attempt elsewhere to do this

Anyway, the atmosphere is constantly in flux and you simply cannot take the context of a post made a few days back by someone else, and then apply exactly the same context of thinking once more! All this said, the message wrt the tropical forcing in the Indian Ocean and the time and amplitude spent there determining the longer term outlook is still precisely the same, so not sure what differences of any significance there are to highlight anyway

I wouldn't worry, there is an on-going effort to disagree with and try and find this analysis wrong by finding a path to cold before the end of January, so for purposes of this thread, using these tools only have any meaningful emphasis if they appear to support a cold outcome and/or their validity and purpose is also dependant on who it actually is who is interpreting them

@Interitus   The December trends between AAM and AO match so well because both the strength of the w/QBO and the effects of engaging a La Nina signal with lowering AAM (through interference from tropical signal in I/O creating southward/equatorial momentum flux transport. ) both contributed to increasing polar westerlies, depressing heights across the arctic, providing extra energy to the northern branch of the Jetstream.

Pretty much the theme of summary posts on here since the late autumn, and despite the much more alluring promises of extended NWP suites.....

Edited January 17, 2017 by Tamara