Model Output Discussions 06z 04/11/16

[Frosty.]

And closer..

Edited November 21, 2016 by Frosty.

[Kieran]

Beautiful chart at +300 hours...

 

Edited November 21, 2016 by Kieran

[Zakos]

Best chart ive seen in the reliable (sort of) timeframe, only 180 hours out and it strongly hints towards retrogression.

Divergence in the output beyond day 10 is ridiculous.

 

[feb1991blizzard]

Heavy snow steadily moving down the country.

[booferking]

2 minutes ago, Kieran said:

Beautiful chart at +300 hours...

 

That chart is a belter hope we are on the right track now. SNOW FOR ALL

Edited November 21, 2016 by booferking

[Banbury]

Nice

[nick sussex]

Good consistency between GFS outputs! lol Whats going on! After some very underwhelming morning outputs the GFS pulls back from the mediocre precipice and goes onto a different solution.

The UKMO at T144hrs is similar upstream but whether it would go onto develop the same later evolution is hard to say. It's quite an unusual evolution from the GFS.

 

[Cheshire Freeze]

2 minutes ago, Zakos said:

Best chart ive seen in the reliable (sort of) timeframe, only 180 hours out and it strongly hints towards retrogression.

Divergence in the output beyond day 10 is ridiculous.

 

Divergence will be stark in this pattern because you either get sufficient WAA and a stronger block that sustains or you don't. It's as simple as that. Knife edge stuff but the direction of travel today has been good with that low exiting stateside being held back more and more each run.

Edited November 21, 2016 by CreweCold

[Banbury]

1 minute ago, feb1991blizzard said:

Heavy snow steadily moving down the country.

Miles away but worth the comment , get it to 24h and we can discuss the kinks in the isobars

[warrenb]

I think the difference was the slight trough disruption at around 144 on the GFS, UKMO has it slightly earlier with more of an undercut, hence the heights are further north.

[Frosty.]

Looking good chaps

Edited November 21, 2016 by Frosty.

[Tamara]

On ‎14‎/‎11‎/‎2016 at 16:13, Tamara said:

 

 But, notwithstanding any start of winter cold potential, a follow-up is required to sustain the process of keeping adding an meridional aspect to NWP patterns.

As the forcing fades in completion of the latest tropical convection cycle, then accordingly the westerly wind additions that occurred in tandem with it, also fade and the weak ocean easterly wind (Nina) default re-emerges.  

With the ocean/atmosphere balance so highly stretched like elastic in opposite directions, the only way for angular momentum at present to head, is downwards. Frictional torque has already fallen to -ve 2SD - in contrast to AAM (as above) peaking at almost +2SD.

Frictional torque will lead mountain torque and AAM tendency downwards from the latest peak. The GWO has already responded to this with an orbit through to Phase 8  (which will show on the soon to be updated WDT futures plots)

The question is where the floor limit lies.  In this respect, as much discussed in recent technical discussions, return of tropical forcing to the Maritimes restores the trend to being the friend and the next upturn in angular momentum and sets the -AO profile right back on course. 

 Logic would suggest that the atmospheric floor has higher limits since early autumn, but much depends if the atmosphere/ocean couples up to any greater extent in the upcoming lull in the tropics and in line with the cooling Pacific profile following the MJO passage. It continues to be my opinion to hope that it doesn't. if we want any early cold to rinse and repeat.

Amplification is the key word - and that amplification comes with a higher angular momentum state that in contrast to last winters super Nino, has much gentler forcing in tandem with a feeble vortex that suggests high latitude blocks are wholly capable with the assistance of the poleward Rossby waves that are created under these conditions.

Scepticism has reigned supreme so far from me about the development of La Nina. - but the coming weeks will tell a lot more about that and how much the atmospheric profile can take advantage of an early season vortex that is there for the taking and poised to provide some very interesting wintry potential to begin 16/17 proceedings.

This in turn, at least as far as I am concerned, will start to answer questions about how long lasting and how potent any early cold air advection may be, and whether or not it is the first of others to follow, 

In that sense any signal from the long range seasonal big gun models of recurrent blocking would potentially offer encouragement.

But I will have to be forgiven, just for now, for continuing to ponder about exciting beginnings to further exciting things -  or flattering to deceive beyond an initial promising start. Been here with the T-shirt many times to get carried away, however things may appear.

 Here is to the next tropical cycle doing what it says on the tin on re-arrival in the Maritimes.

 

The uncertainties expressed above, which sounded a more cautious note than many of late, has grown further in my own mind - at least in context of the highlighted extracts from the previous post.

This is very much now whether the default position of October in terms of the developed feedbacks that have generated the vortex weaknesses we have seen - will rinse and repeat at the start of winter to increase the chances of seasonal cold potential this side of the North Pole.

Or, whether the latest (signposted as above) switch to more coupled ocean/atmosphere Nina wind-flows changes expectations, and ups a longer game watch over the popularist front loaded winter thinking. We are not there yet, but this thinking has not gone away - quite the reverse in fact.

My stuck record I know, but the problem with a Nina tendency to the atmospheric circulation is that wave fluxes tend to directed towards the equator with the result that torque tendencies are pushed negative and synoptically this has the effect of easterly wind momentum in the sub tropics boosting strength to a string of circum-global mid latitude high pressure cells encompassing both the Pacific and the Atlantic.

The obvious manifestation of this in our vicinity is the dominance of Azores high pressure. With relative angular momentum supressed, southward directed flux increases easterly momentum over the sub tropics but is compensated with increased westerly momentum to higher latitudes. In this way, fuel is provided to the stratospheric vortex - and it is no surprise to see latest modelling both in the stratosphere and longer term NWP modelling showing hints of this.

BUT...

Of course, its never that simple and between now and mid December a series of complex factors are going to unravel that will determine whether the colder winter progress default is resumed, or whether the vortex gets out of jail with amplification sustained the Pacific side - whilst a more +AO profile emerges this side.

So, to try and link some of the above discussion into a forward programme of thinking regarding present developments leading into possible evolutions :

1) Much of the advertised fall in global torques has occurred due to a large -ve Asian mountain torque - which is a Pacific upstream pattern changer as the Jetstream there decelerates from the high velocity flow through October and the early part of November.

.  

This switches jet flow downstream in the Atlantic.

The Global Wind Oscillation, as predicted in the previous update, has swiftly orbited back to Phase 8

As a consequence of the above, relative angular momentum tendency has witnessed a highly sizeable correction from its substantive (Nino-like) disconnect..  Total angular momentum fallen back from nearly +2SD +ve revised back to slightly -ve to much more closely reflect  very weak Nina ENSO SST base state coupling

Bearing in mind the tightly tensioned stretched elastic analogy supplied in the previous post, when atmospheric flux is snapped one way, and then the other through sudden sharp global wind-flow changes - this as a consequence creates quite abrupt an shake-ups to NWP performance

 But If this ying-yang process is further combined with the uncertain behaviour of a seasonal vortex that has been strongly supressed from its 'traditional' life cycle patterns then its no surprise to see not just model vicissitude and forecasting problems which explain the volatility and erratic (lack of) continuity from NWP to dedicated net weather followers of the MOD. - but also high impact weather phenomena occur along abruptly created steepened gradients where jet stream angles are carved out. Effects commonly felt downstream (read UK and NW Europe) This being experienced, especially, where anomalous warmth is suddenly replaced by arctic cold (or vice versa) and which happens very often over the large continental landmasses of the US states when the Pacific undergoes changes in teleconnection mode.

Now as far as the stratosphere is concerned, as long as poleward flux via the troposphere is restored, then any uptick in zonal winds higher up need not be a problem at all. Poleward rossby wave bombardment is the perfect antidote to top downwards downwelling of +ve zonal winds in terms of helping to preserve the early weakness throughout the stratosphere on the one hand, but also sustain the 'bottom upwards pressure' on the other. 

In this way, downwelling is prevented/delayed until perhaps a more large scale stratospheric forcing comes along (e.g accumulated SIA Eurasian snowcover -AO feedback processes) by the middle of the winter to trigger larger scale hemispheric bleeding southwards of cold air advection to mid latitudes.

In tandem with pre-conditioned stratospheric instability, this is where a recycling +ve angular momentum state has importance in terms of reversing short term southward directed flux - thereby resuming the poleward directed wave assaults that help carve out the higher latitude ridges our side of the pole where the vortex 'warms out' the most.. Wave breaking happening only on the Pacific side of the pole, aka an Aleutian ridge is no good to us if the vortex is consolidated centrally over the pole and Greenland. This simply means a cold US and a gradient steepened Atlantic, of which everyone is fully aware of the totally unwanted implications downstream to us.

2) However, we are seeing indications already that a reverse courtesy of the extra tropics to any potential future rot may in the pipeline in the next two weeks as torques reverse once more. Frictional torque leading the way sharply upwards already

This implies that a strong compensating +mountain torque will occur over Asia within the next fortnight, with angular momentum tendency bouncing back, helping contribute to resuming the 'favourable' ENSO disconnect - and the pattern over the Pacific reverting to the low pressure profile of previously (Aleutian Low). This also means that taking into account the lagged stratospheric effects from this next MT, we will see pressure re-exerted on the vortex so that the amplified profile in the Atlantic has chance to return with possible avenues to cold air advection supply from wind vectors between NW and NE. 

3) So, that is how the extra tropics may assist us stratospherically/tropospherically.  What of tropical forcing? Although there is still some uncertainty of this, expectations remains of tropical convective forcing returning to Indonesia/Maritimes and resuming the default amplification setter to UK/NW Europe - as propagating westerly winds pushed ahead of thunderstorm cloudiness zones scrub easterlies from the sub tropics and more importantly then tend to head poleward to reduce the westerly wind flows at higher latitude. This obviously translates to further vortex instability. Hence why an upper tightening of the vortex need not be a problem to those seeking greater cold potential

Finally, to the seasonal ENSO chestnut

4) Taking into account the present expectations/hopes reasoned and expressed in both 2) and 3) the view remains that the life-span of this weak Nina, to what llimited capacity it is, expected to be short-lived. This leads the prospect of developments under both captions 2) and 3) being capitalised on further through a programme of further sustained tropical and extra tropical induced amplification fluxes to the atmospheric circulation as the ENSO SST slightly cooler than average profile begins to relax even further and warm out completely.

This will only encourage an atmosphere that has already wanted to embrace a starkly decoupled state this autumn. - with angular momentum cycles steadily upgrading higher upwards and more and more westerly momentum added to quell easterly trades ( propagating to higher latitudes as net easterlies) is created. Net effect is to help prevent downwelling of the early season faster upper vortex through created supplies of tropopause disturbances in the shorter/medium term, and even perpetuating the SIA Eurasian feedback conditions for a traditional New Year major stratospheric event.

In that sense, focus is not necessarily on the shorter term stratospheric disturbances and associated consternation over 'will it/wont it' reverse - but the momentum that might be created over short term forcing that lends itself towards the end of year/New Year evolution of macro factors such as the ENSO status amendments - neutral (but with a Nino powder puff atmospheric signal application), SIA and weak solar activity

This longer term scenario is not currently supported in terms of the late autumn expressed consensus front loading to the winter by seasonal modelling authorities, but to my mind the uncertainties of the coming weeks as described here (and mooted from previous harboured) suspicions) have only grown further as we have been heading through this month

@chrisbell-nottheweatherman     I'm tentatively thinking that way - although that obviously doesn't preclude more immediate prospects for the start of winter either. Uncertainties abound as stated though. As ever, time will tell more

Edited November 21, 2016 by Tamara

[Zakos]

Just now, CreweCold said:

Divergence will be stark in this pattern because you either get sufficient WAA and a stronger block that sustains or you don't. It's as simple as that. Knife edge stuff but the direction of travel today has been good with that low exiting stateside being held back more on more each run.

yes agreed, it all rests on this WAA event , otherwise back to square one it seems.

and yes it's definitely been good viewing today, nice to see these lovely charts creeping closer to the reliable rather than the opposite for a change! 

[Ali1977]

Just now, Frosty. said:

Looking good chaps

It would be great if the ECM followed this solution, unfortunately still along way out but atleast it's cheered up the forum again.  

[Kieran]

BRRRR....

 

[Frosty.]

5 minutes ago, Ali1977 said:

It would be great if the ECM followed this solution, unfortunately still along way out but atleast it's cheered up the forum again.  

Agreed, now that was an exciting low res on the Gfs 12z, I would take that in early December.

Edited November 21, 2016 by Frosty.

[warrenb]

GFS control going the other way.

[K9]

All good stuff...but so far out into fantasy land it's not even worth getting myself worked up about...and this is from a die hard 'Coldie'...!!!....why do we do this to ourselves !!!

[Frosty.]

4 minutes ago, K9 said:

why do we do this to ourselves !!!

The thrill of the chase, it's a long way out but the seasonal long range models must be looking good, judging by the latest MO update. I expect we will be seeing plenty of runs like that, slowly creeping closer range.

Edited November 21, 2016 by Frosty.

[Banbury]

5 minutes ago, warrenb said:

GFS control going the other way.

Hmmmm bit early yet Warren, could still get a decent block at Greenland

[chrisbell-nottheweatherman]

20 minutes ago, Tamara said:

This longer term scenario is not currently supported in terms of the late autumn expressed consensus front loading to the winter by seasonal modelling authorities, but to my mind the uncertainties of the coming weeks as described here (and mooted from previous harboured) suspicions) have only grown further as we have been heading through this month

I don't mind admitting that I lack the technical understanding to follow the details of your post, Tamara, but the above quote suggests that you, like the WSI in their latest winter forecast (see https://business.weather.com/news/european-seasonal-forecast-unusual-early-season-cold-a-sign-of-further-wintry-conditions), doubt that the forecast of a front-loaded winter is necessarily going to verify?

Edited November 21, 2016 by chrisbell-nottheweatherman
Correcting typo.

[Cheshire Freeze]

The mean is now on board with the extra WAA at day 8..

Also digs the LP to S of Greenland further SE.

Encouraging at least- there will be some decent perturbations in this lot.

Edited November 21, 2016 by CreweCold

[northwestsnow]

3 minutes ago, CreweCold said:

The mean is now on board with the extra WAA at day 8..

Also digs the LP to S of Greenland further SE.

Encouraging at least- there will be some decent perturbations in this lot.

Absolutely, good news Crewe- im positively exhausted already its only mid November ! ;D

Edited November 21, 2016 by northwestsnow

[feb1991blizzard]

1 minute ago, CreweCold said:

The mean is now on board with the extra WAA at day 8..

Also digs the LP to S of Greenland further SE.

Encouraging at least.

Yes, theres going to be some belters in there.

[Cheshire Freeze]

The control makes it....