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

[swfc]

As Steve said gfs 12 control looks pretty good ie ukmo. In fi looks a cleaner run with the low sliding south east. As usual there's a short wave forming to the north east

[Mucka]

2 minutes ago, swfc said:

As Steve said gfs 12 control looks pretty good ie ukmo. In fi looks a cleaner run with the low sliding south east. As usual there's a short wave forming to the north east

For me it is all about the small ridge in the Atlantic which prevents the phasing of the Atlantic trough with the low across the UK which allows it to push further East and fill unlike the GFS Op run.

Control/Operational

[swfc]

1 minute ago, Mucka said:

For me it is all about the small ridge in the Atlantic which prevents the phasing of the Atlantic trough with the low across the UK which allows it to push further East and fill unlike the GFS Op run.

Control/Operational

Yes mucka I agree. Was comparing ukmo to the control at 144 hrs. The sliding low and shortwave I mentioned are way out in fi

[GeordieX9v]

Brief spell of cold to very cold air then GFS?

[Scott Ingham]

6 hours ago, Tamara said:

That was the essence of the post and the numerous inane confused emoticons  were really not necessary.  The alleged techno-babble simply refers to processes that are  highly relevant all times of the year, and do not suddenly only have relevance in winter, which is an impression one can get from reading quite a few posts on this thread between November and March.  That is why I questioned the assertion that it is just a question of waiting for the MJO signal to propagate eastward again in the next cycle at some kind of linear amplitude and progression - because it is not as simple or true as that based on the known recurrence timelines of more active intra-seasonal activity.

The relocation of the tropical low frequency standing wave that has been underway of late from Africa and the Indian Ocean eastward to the Maritime Continent, as was attempted to mention yesterday, is depicted here

 

The importance of this is how much it re-configures the downstream pattern in terms of rossby wave re-alignment. In simple terms, this refers to the placement of the wavelength that amplification of the jet stream takes place c/o of torque processes which change the speed and direction of wind-flow and impact the jet stream.  Furthermore, how active, and how far east, the high frequency MJO (or 'mini ENSO cycle') further interferes during the winter with the walker cell circulation and impacts the tropospheric/.stratospheric pattern. With a w/QBO prevalent through the winter there will be particular reliance of tropical activity to propagate wave eddies poleward via the extra tropics and mountain torque processes to alter the tendency for the seasonal vortex to, otherwise, intensify under a w/QBO regime

Tropical forcing standing wave not progressing further east of the Maritimes (and absence of superimposed high frequency MJO forcing) will restrict convergence of wind-flow further upstream and hence the rossby wave feedback will tend to amplify the Pacific due to suppression of convection and enhanced easterly trade winds in this region. Due to the laws of conservation of angular momentum, there will be compensating extra westerly polar jet inertia heading downstream and restricting the amplification of the pattern here. In this way assisting organisation of the polar vortex gyre.

 

It is clear that the La Nina signal has not defied expectations and has consolidated over time

 

 

However the a-typical relationship that global wind-flows have taken to this Nina-ish base state is much closely aligned to a more Nino-like feedback. Global total angular momentum levels continue to track close to or even slightly above average

The impact of the intra-seasonal high frequency signal very much in play here. However, as per the gist of this and the other post, it will require the tropics to keep alight in order to sustain the present downstream amplification. Inactive MJO activity would lead to angular momentum collapsing and very much more closely matching the Nina-esque base state. This means a much more traditional and flatter pattern and greater influence of the Azores ridge and polar jet flowing around the northern perimeter of the ridge.

At present, there is uncertainty how this might develop in the coming few months. That is why there were very hedged suggestions yesterday - because if one wants to be neutral in assessment and has no particular vested interest in seeing a favoured solution play out, this seems to be (to me at least) an honest position.

 

Wonderful again.

To re-cap in layman's terms.

Look at the graph for total angular momentum. 

When its above that line were more likely to see ridges thrown up into higher latitudes.

When its below that line the pattern is more likely to be flatter 

La Nina in later winter tends to throw us below the angular momentum line.

Active MJO phases which can lead to mountain torque events and rossby waves throw us above the line and do two things. Create higher level blocking (in different positions dependant on the phase and if in the right phase 6/7 can throw waves up into the strat to bring it down.

We currently have a standing wave moving in to 6. Which is why we're above the angular momentum line and why we anticipate some strat damage but there's no certainty this will sustain further into winter.

If these don't sustain then the enso state takes over dropping angular momentum and creating a flatter pattern into deep winter. Late autumn and early winter is different it creates Atlantic ridges

 

[KTtom]

45 minutes ago, Tim Bland said:

A white Xmas for the south

Well we know thats not going to happen....its all south of the M4!

[MATTWOLVES 3]

I tell you what folks, the 12Z ens are anything but boring... There is plenty of excitement amongst a fair few of them... Certainly not a full on zonal express.. We just need to bring this into the more reliable now... I'm not your biggest fan GFS... but I do love it when ya tease me baby...

Edited December 9, 2020 by MATT☀️

[Daniel*]

22 minutes ago, CreweCold said:

Still there at day 11 on GEFS

Getting a bit twitchy this evening that the Arctic pattern may flatten before those heights are scrubbed...

We shouldn’t be expecting anything on ground if we get there till last week of December IMO the EPS has been incredibly persistent with Arctic heights, it first caught a whiff of it a while back so I’m impressed. We will not see +AO for a long time in my opinion.

 

Edited December 9, 2020 by Daniel*

[swfc]

12z control brings the greenland high and artic high togetherfi granted but go on then 

[Daniel*]

The day 8 mean is better than op more negatively tilted trough in Atlantic. Heights smidgen further east in Europe. 

Edited December 9, 2020 by Daniel*

[Optimus Prime]

1 hour ago, jules216 said:

Where is that hide the pain Harold expresion

Is Harold someone we're supposed to know? Like, Ronnie Pickering?

[Daniel*]

Day 5 on ECM stronger blocking in Arctic compared to 00z.

[jules216]

5 minutes ago, Optimus Prime said:

Is Harold someone we're supposed to know? Like, Ronnie Pickering?

its a face expresion that tries to put on Happy face despite pain inside.

[Zak M]

ECM vs UKMO @144

   

[Daniel*]

I think we could be onto something good here looks much better in next frame...

[lamppost watcher]

9 minutes ago, Optimus Prime said:

Is Harold someone we're supposed to know? Like, Ronnie Pickering?

 

[Day 10]

9 minutes ago, Zak M said:

ECM vs UKMO @144

   

NH View too, pretty close!

UKMO still looks slightly the better of the two though at this stage, no phasing of the two lows which would promote better heights around Southern Greenland.

Mind you EC 168 looking decent.

Edited December 9, 2020 by Day 10

[Skullzrulerz]

I'm not exactly keeping my hopes up regarding all this cold potential 

We need to get rid of the southern European high pressure especially!

[swfc]

Ec says maybe at 168 hrs

Edited December 9, 2020 by swfc

[mountain shadow]

Just now, Skullzrulerz said:

I'm not exactly keeping my hopes up regarding all this cold potential 

We need to get rid of the southern European high pressure especially!

The ECM at t+168 does!

This must deliver surely. 

[blizzard81]

The first chart is Monday's 192hr ecm chart for next Tuesday. The second is today's 12z 144hr chart for the same day. Massive improvement with the arctic high. 

[ICE COLD]

Oi oi whats going on here ECM 168 

[Captain Shortwave]

 

Will all the stars align to give us a proper north easterly. Given the positioning of heights, it is more likely that cold will come down from Scandinavia than any other direction. It does seem like we could be teased with some snowy nirvana perhaps for later in week 2.

Edited December 9, 2020 by Captain Shortwave

[bluearmy]

8 minutes ago, mountain shadow said:

The ECM at t+168 does!

This must deliver surely. 

does it  ?  looks pretty solid to me

the atlantic profile on gfs and ecm at day 7 look strangely similar 

the longer it takes to try to connect an atlantic ridge with the arctic ridge, the more chance that the Asian low heights will link up underneath via the neg AO and cut it off ..... that arctic high is tough to model !!

Edited December 9, 2020 by bluearmy

[swfc]

192 ec OK. Azores high needs to koff and let that low threw