Model Output Discussion - Colder spell ending, what's to follow?

[Griff]

2 minutes ago, Mike Poole said:

Pub run T180:

Pick the bones out of that!  Going to be a classic!  

Always knew the gem was a trend setter

[Ravelin]

Even if the actual pressure charts don't look obviously exciting, just look at the pressure anomolies... 

[northwestsnow]

NH view is eye candy...

Atlantic sector is eye sore...

 

[chionomaniac]

.?Nice chart this. PV has left area in red and arctic high linking up in orange. 

 

In these cases only a slight shift in modelling brings a large difference in surface conditions for the uk

Edit again. I haven’t looked once at the UK when looking at this run tonight. What is happening everywhere else is far more important and fascinating too

Edited December 8, 2020 by chionomaniac

[blizzard81]

18 minutes ago, chionomaniac said:

Pub run very close to being great no matter what happens next on it. It is up to day 6 that we need to take notice of

Hmmm! But the GFS still has the daughter vortex towards the southern tip of Greenland. 

[northwestsnow]

We just cannot seem to get any Atlantic amplification ....

Despite a fabulous NH profile.

 

[georgiedre]

9 minutes ago, chionomaniac said:

Nice chart this. PV has left area in red and arctic high linking up in orange. 

It will probably be back nxt run lol 

[Catacol]

Oooo yummy. Dont care what comes after - this is a cracking chart at 240h for what might follow. But it's gfs18z. No sense getting too excited about such things....yet.

Edited December 8, 2020 by Catacol

[chionomaniac]

1 minute ago, blizzard81 said:

Hmmm! But the GFS still has the daughter vortex towards the southern tip of Greenland. 

Hence very close. With the latest GFS shift west it won’t take much to produce something epic. With a small shift of energy from the eastern seaboard low towards the north rather than west then the floodgates open. This is as close in the build up as watching an easterly just miss us

[feb1991blizzard]

10 minutes ago, chionomaniac said:

Nice chart this. PV has left area in red and arctic high linking up in orange. 

 

 

In these cases only a slight shift in modelling brings a large difference in surface conditions for the uk

Its one of those synoptics where this kind of chart could easily develop out of nowhere, however, you would think there would be more advertisement in the ensembles if it was going to happen anytime  soon.

[Griff]

1 minute ago, Catacol said:

Oooo yummy. Dont care what comes after - this is a cracking chart at 240h for what might follow. But it's gfs18z. No sense getting to excited about such things....yet.

If nothing else it has a pleasing symmetry... 

But as @northwestsnow said it's a shame there's no pay off, but I guess it's steps in the right direction.

Looking at the accompanying weather it's going to be a bit miserable. 

[Mike Poole]

GFS 18z T264:

This run has now gone totally off the rails with lows and shortwaves all over the place in the Atlantic.  But the bigger picture is interesting, the vortex seems to be in 4 or 5 pieces and none of them over Greenland!!  

[Mike Poole]

2 minutes ago, feb1991blizzard said:

Its one of those synoptics where this kind of chart could easily develop out of nowhere, however, you would think there would be more advertisement in the ensembles if it was going to happen anytime  soon.

Wow, I didn’t think such things were even possible, Feb!  

[Zak M]

Oh wow, that GFS run looks really g-   Oh, hold on, it’s the pub run.

The NH view of the PV is amazing though! Looks to be in a very good position for cold weather in a couple of weeks time...

A good pub run tonight. In other news, the grass is green.

Edited December 8, 2020 by Zak M

[Johnp]

7 minutes ago, feb1991blizzard said:

Its one of those synoptics where this kind of chart could easily develop out of nowhere, however, you would think there would be more advertisement in the ensembles if it was going to happen anytime  soon.

Looks like it could happen on this run by the end.

[blizzard81]

5 minutes ago, chionomaniac said:

Hence very close. With the latest GFS shift west it won’t take much to produce something epic. With a small shift of energy from the eastern seaboard low towards the north rather than west then the floodgates open. This is as close in the build up as watching an easterly just miss us

But the low in question (I refer to as the spin off lobe) spins off the main pv lobe over northern Canada, not a cyclogenesis low off the eastern seaboard. This is a recurring theme on the GFS runs. 

[feb1991blizzard]

1 minute ago, Johnp said:

Looks like it could happen on this run by the end.

Yes, the giveaway on these type of synoptics is where cold from the NE is edging ever closer without a huge amount of amplification, you just know that the slightest decent ridge will just blast the floodgates open.

[BLAST FROM THE PAST]

As I’ve said, Atlantic interaction is necessary going forward, but angle of attack and disruption is key....don’t worry about Atlantic affecting the Uk

 

BFTP

[georgiedre]

14 minutes ago, Tamara said:

This analysis is geared towards fitting a bias preference into a diagnostic framework which doesn't exist to support singular ice sculptured solutions.

No theory (in the true sense of the word) has been turned on its head in respect of La Nina. What has happened, as has occurred in some previous late autumns and early winter, is that a relatively active intra-seasonal high frequency tropical signal has created a rossby wave feedback that has resulted in a higher amplified downstream tropospheric pattern than would be seen in a more typical -ve frictional/mountain torque regime that represents a La Nina feedback. However, that doesn't on its own mean anything for the weeks and months to come - especially when pivotal wavelength changes will couple the NAO and AO much more closely, one way or the other, as deeper winter arrives in a few weeks

Intrinsic coupling of the Annular Mode heading into deeper winter requires more exacting forcing than seen so far - and, with a w/QBO likely to influence, once again, the most important layers of atmosphere through the winter the chances increase that a more organised westerly gyre takes over once present intra-seasonal factors diminish and the tropics cease propagating rossby wave eddies poleward to sustain the imbalance between the pole and the mid latitude. .

So, in this way, the tropospheric/stratospheric relationship can quickly can become much more stable (i.e through a much more stable GSDM relationship to the oceanic base state) This comes about by less eastward propagation of tropical forcing and greater additions of easterly wind inertia to re-configure the upstream pattern and send greater polar jet energy further downstream. This, in the absence of a top-down forcing to loop that polar jet, rather than across the mid latitudes, instead around the arctic and sustain and/or intensify an unstable profile across the polar field.

At present, while there is indication that the African/Indian Ocean low frequency standing wave present for quite some time through the summer and into the autumn is relocating/propagating east towards the Maritimes, much more evidence is required to see whether a more specific tropical convergence can set up even further east into the western/central Pacific. This, essentially, leading to a more east based La Nina pattern. Much as happened for example  in 2017/18. This cycle meant that a more unstable GSDM profile persisted into the New Year and which ultimately led to the SSW in February 2018. At present, there is no clear indication, either way, what is going to happen - and angular momentum trends during the remainder of December will be pivotal in this respect.

From my point of view at 39N, where I will be residing in the next couple of weeks, it is immaterial in terms of any high impact cold weather repercussions this winter - but for those looking for winter wonderlands at latitudes further north - its always worth being aware that there is never any x+y= equation when it comes to fitting given diagnostic parameters to weather patterns

It is necessary to look at periodicity of high frequency tropical signals (the recurrence timeline) and not assume that the tropical cycle behaves like a time-clock which replicates the same on its subsequent 'mini ENSO cycle' within the next circa 30 days.  These periodicity timelines extend up to circa 60 to 90 day  lengths. Unlike a winter such as 2017/18 the likely persistence of a westerly QBO gyre at the most important levels of the atmosphere means that the tropospheric/stratospheric relationship is going to be also be dependant on solar assistance to de-couple ( ramifications for Brewer Dobson Circulation transport between the tropical and polar stratosphere). Equally, in tandem with US and Asian torque mechanisms getting in on the act to trigger poleward momentum transport  - but then as the complexities of even the last two winters have shown where contravailing forces have mitigated the propagation of these poleward eddies, staring at stratospheric forecasts at *insert time-period* does not not inextricably make it snow even if they move forward in time.

What does this mean in normal meteorological terms for us no brainers hahaha it sounds really complicated and even the best of us are struggling with all the changes this winter 

[snowlessayr]

The end of this run looks like putting us into the freezer, major caveat being it is the pub run and could easily be back on the alcohol again since the lockdown is over for you guys in England. very interesting  NH pattern again though which is more important at this point as we all know the GFS can come up with some ridiculous solutions at times 

[Scott Ingham]

15 minutes ago, Tamara said:

This analysis is geared towards fitting a bias preference into a diagnostic framework which doesn't exist to support singular ice sculptured solutions.

No theory (in the true sense of the word) has been turned on its head in respect of La Nina. What has happened, as has occurred in some previous late autumns and early winter, is that a relatively active intra-seasonal high frequency tropical signal has created a rossby wave feedback that has resulted in a higher amplified downstream tropospheric pattern than would be seen in a more typical -ve frictional/mountain torque regime that represents a La Nina feedback. However, that doesn't on its own mean anything for the weeks and months to come - especially when pivotal wavelength changes will couple the NAO and AO much more closely, one way or the other, as deeper winter arrives in a few weeks

Intrinsic coupling of the Annular Mode heading into deeper winter requires more exacting forcing than seen so far - and, with a w/QBO likely to influence, once again, the most important layers of atmosphere through the winter the chances increase that a more organised westerly gyre takes over once present intra-seasonal factors diminish and the tropics cease propagating rossby wave eddies poleward to sustain the imbalance between the pole and the mid latitude. .

So, in this way, the tropospheric/stratospheric relationship can quickly can become much more stable (i.e through a much more stable GSDM relationship to the oceanic base state) This comes about by less eastward propagation of tropical forcing and greater additions of easterly wind inertia to re-configure the upstream pattern and send greater polar jet energy further downstream. This, in the absence of a top-down forcing to loop that polar jet, rather than across the mid latitudes, instead around the arctic and sustain and/or intensify an unstable profile across the polar field.

At present, while there is indication that the African/Indian Ocean low frequency standing wave present for quite some time through the summer and into the autumn is relocating/propagating east towards the Maritimes, much more evidence is required to see whether a more specific tropical convergence can set up even further east into the western/central Pacific. This, essentially, leading to a more east based La Nina pattern. Much as happened for example  in 2017/18. This cycle meant that a more unstable GSDM profile persisted into the New Year and which ultimately led to the SSW in February 2018. At present, there is no clear indication, either way, what is going to happen - and angular momentum trends during the remainder of December will be pivotal in this respect.

From my point of view at 39N, where I will be residing in the next couple of weeks, it is immaterial in terms of any high impact cold weather repercussions this winter - but for those looking for winter wonderlands at latitudes further north - its always worth being aware that there is never any x+y= equation when it comes to fitting given diagnostic parameters to weather patterns

It is necessary to look at periodicity of high frequency tropical signals (the recurrence timeline) and not assume that the tropical cycle behaves like a time-clock which replicates the same on its subsequent 'mini ENSO cycle' within the next circa 30 days.  These periodicity timelines extend up to circa 60 to 90 day  lengths. Unlike a winter such as 2017/18 the likely persistence of a westerly QBO gyre at the most important levels of the atmosphere means that the tropospheric/stratospheric relationship is going to be also be dependant on solar assistance to de-couple ( ramifications for Brewer Dobson Circulation transport between the tropical and polar stratosphere). Equally, in tandem with US and Asian torque mechanisms getting in on the act to trigger poleward momentum transport  - but then as the complexities of even the last two winters have shown where contravailing forces have mitigated the propagation of these poleward eddies, staring at stratospheric forecasts at *insert time-period* does not not inextricably make it snow even if they move forward in time.

Spectacular post. Really highlights the complexities and countless layers and variables that go into the weather on the ground. But its why we love this hobby so much

[bluearmy]

This op run is seriously tooth pulling !

[Mike Poole]

3 minutes ago, georgiedre said:

What does this mean in normal meteorological terms for us no brainers hahaha it sounds really complicated and even the best of us are struggling with all the changes this winter 

I think it means coldies are in with a shout!  But also highlights the uncertainties that any kind of medium to long range predictions are frought with.  So watch the drama unfold right here... or

[mountain shadow]

Just now, bluearmy said:

This op run is seriously tooth pulling !

It's the slowest Eastward movement of low pressure I've ever seen, but at least will give Santa a following wind!

[chionomaniac]

8 minutes ago, Tamara said:

This analysis is geared towards fitting a bias preference into a diagnostic framework which doesn't exist to support singular ice sculptured solutions.

No theory (in the true sense of the word) has been turned on its head in respect of La Nina. What has happened, as has occurred in some previous late autumns and early winter, is that a relatively active intra-seasonal high frequency tropical signal has created a rossby wave feedback that has resulted in a higher amplified downstream tropospheric pattern than would be seen in a more typical -ve frictional/mountain torque regime that represents a La Nina feedback. However, that doesn't on its own mean anything for the weeks and months to come - especially when pivotal wavelength changes will couple the NAO and AO much more closely, one way or the other, as deeper winter arrives in a few weeks

Intrinsic coupling of the Annular Mode heading into deeper winter requires more exacting forcing than seen so far - and, with a w/QBO likely to influence, once again, the most important layers of atmosphere through the winter the chances increase that a more organised westerly gyre takes over once present intra-seasonal factors diminish and the tropics cease propagating rossby wave eddies poleward to sustain the imbalance between the pole and the mid latitude. .

So, in this way, the tropospheric/stratospheric relationship can quickly can become much more stable (i.e through a much more stable GSDM relationship to the oceanic base state) This comes about by less eastward propagation of tropical forcing and greater additions of easterly wind inertia to re-configure the upstream pattern and send greater polar jet energy further downstream. This, in the absence of a top-down forcing to loop that polar jet, rather than across the mid latitudes, instead around the arctic and sustain and/or intensify an unstable profile across the polar field.

At present, while there is indication that the African/Indian Ocean low frequency standing wave present for quite some time through the summer and into the autumn is relocating/propagating east towards the Maritimes, much more evidence is required to see whether a more specific tropical convergence can set up even further east into the western/central Pacific. This, essentially, leading to a more east based La Nina pattern. Much as happened for example  in 2017/18. This cycle meant that a more unstable GSDM profile persisted into the New Year and which ultimately led to the SSW in February 2018. At present, there is no clear indication, either way, what is going to happen - and angular momentum trends during the remainder of December will be pivotal in this respect.

From my point of view at 39N, where I will be residing in the next couple of weeks, it is immaterial in terms of any high impact cold weather repercussions this winter - but for those looking for winter wonderlands at latitudes further north - its always worth being aware that there is never any x+y= equation when it comes to fitting given diagnostic parameters to weather patterns

It is necessary to look at periodicity of high frequency tropical signals (the recurrence timeline) and not assume that the tropical cycle behaves like a time-clock which replicates the same on its subsequent 'mini ENSO cycle' within the next circa 30 days.  These periodicity timelines extend up to circa 60 to 90 day  lengths. Unlike a winter such as 2017/18 the likely persistence of a westerly QBO gyre at the most important levels of the atmosphere means that the tropospheric/stratospheric relationship is going to be also be dependant on solar assistance to de-couple ( ramifications for Brewer Dobson Circulation transport between the tropical and polar stratosphere). Equally, in tandem with US and Asian torque mechanisms getting in on the act to trigger poleward momentum transport  - but then as the complexities of even the last two winters have shown where contravailing forces have mitigated the propagation of these poleward eddies, staring at stratospheric forecasts at *insert time-period* does not not inextricably make it snow even if they move forward in time.

I think that this first premise is unfair. Maybe it is because so far the atmosphere has not responded in a typical La Niña way. As for the tropics, it does look like eastward propagation may occur regarding MJO progression and the strat is already being affected by wave activity - how long or strong this is may depend on the tropical influences and subsequent mid latitude wave responses to this. 

As ever, Tamara it would be wonderful if you could temper your posts for the masses and not for the few, in order that the majority of the posters hear can benefit from your wisdom, without having to resort to guesswork as to what you may mean. Most here just want to know whether a cold spell is likely or not and I suspect many are none the wiser after reading your post. As am I. Kindest regards.