Model discussion highlights

[Midlands Ice Age]

1 hour ago, Derecho said:

Without working on the ECM, GFS or UKMO models, I don't know how you can prove this without any evidence?

If you were just letting Machine learning algorithms take over the models without an understanding of how the output is created, then yes I'd agree... but every piece of software is different.

Derecho...

30 years of modelling, programming , analysis, technology design and implementation has left its scars on me. 

Twenty years ago we needed more machine power.

Now, unless we sort out the assumptions  and get them analysed correctly into mathematics  we will only magnify the errors as we push ever deeper into being able to look at ever more local detail.

Tamara is showing where some of the current assumptions are wrong, or at least give a totally different view. .

People on here showed how the stratosphere could affect things greatly. (10 years ago) This was incorporated into the models (though I believe is now possibly over responsive (see below)).

The only people to gain by increasing the computing power right now are 1) computer salesmen, and 2) system design specialists who have no further ideas as to how to improve the current models.

Incorrect assumptions ALWAYS increase volatility in output. Increased  computing power will only serve to show up any design errors.

I appreciate that increasing the spread by the changing the input criteria, is one method of reducing any errors. But the initial 'errors' are still present, and will only serve to produce more chaos.

I am talking about from where the models are standing today (which is much better than they were 5-10 years ago).  Spending hundreds of millions on more computing power right now will not give the same rewards as ensuring some of the 'unknowns' are fully researched and included  as regards the accuracy of the models..

1)     Extra notes.... Take today and this graphic taken from the above (to be saved)....

  

The whole of even  the western hemisphere has been impacted by the the slope and shape of the high forecast to develop  over  the Bering Ocean.  Changing its inclination or intensity will dramatically change the forecast for the whole Northern Hemisphere via mechanisms previously discussed on here. Both the ECM and GFS have shown this happening over the last week. Both had to withdraw from their positions . Something is not 'spot on'.

Will they this time? Can you tell me? I assume that this situations has come about as to their incorrectly handling the totality of the 'telecomms' signals. 

2) As to whether the models are accurate from a scientific pov.    I cannot make any comments  (you are correct).  However they have now released documentation on the 'CC' models, which were based upon forecast models  (I  am told),  and for the previous release of them there were still around 25 assumptions which were not yet proven. If they were missing in the 'CC' models then I assume they were not in the forecast models.  - In the CC models they substituted parameters. 

Sorry to mention the XX word banned on here  - MODS.

So IMO opinion,   (FWIW)  there is still quite a way to go before we can say that all the assumptions (and therefore the absolutely correct science) built into the models, means that models are correct.

Until that happens  putting in more computing power will increase chaos (not decrease). that is what my 30 odd years of experience has taught me.

MIA

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008583

[bluearmy]

the day 15 eps mean and spreads scream Greenland tpv very loudly and upper ridge into Iberia 

= flat zonal 

now the extended ens have been promising a return to a ne Canadian vortex for some time - it’s taken longer to get there than first modelled but it’s now looking v likely indeed

the only caveat I have is that the trop continues to lead the dance and we know how unpredictable trop modelling is as week 2 progresses. there may be feedback issues that are consolidating a strengthening which may not verify in that fashion.  Having said that, it was noted about a week ago that the modelling wanted to stretch the spv from Barents to e Canada, split it, then return the Canadian segment back to svaalbard. We know from experience that this east - west - east movement of a coupled  spv/tpv will usually fire up the northern arm.  It looks like the split that enables the n Atlantic height rise will also be responsible for the fired up jet as the two segments are rejoined on our side of the NH.  in addition, the split Canadian segment dropping into n America doesn’t help as it increases the temp differential which leads to an even stronger jet. and the displaced nature of the spv our side means that this movement is at a southerly latitude which means the jet is aimed at us.  

as nick alluded earlier, there are sniffs of disruption which could force that jet into Iberia but that’s not what the nwp is showing 

I do have nagging doubts on this but it’s rare that the modelling for week 2 is wrong when there is so much agreement across the nwp  

there currently aren’t enough rogue ens members to justify any doubts  (actually the 06z gefs have a few so maybe need to see what happens on the 12z eps) 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008588

[February1978]

41 minutes ago, Midlands Ice Age said:

Derecho...

30 years of modelling, programming , analysis, technology design and implementation has left its scars on me. 

Twenty years ago we needed more machine power.

Now, unless we sort out the assumptions  and get them analysed correctly into mathematics  we will only magnify the errors as we push ever deeper into being able to look at ever more local detail.

Tamara is showing where some of the current assumptions are wrong, or at least give a totally different view. .

People on here showed how the stratosphere could affect things greatly. (10 years ago) This was incorporated into the models (though I believe is now possibly over responsive (see below)).

The only people to gain by increasing the computing power right now are 1) computer salesmen, and 2) system design specialists who have no further ideas as to how to improve the current models.

Incorrect assumptions ALWAYS increase volatility in output. Increased  computing power will only serve to show up any design errors.

I appreciate that increasing the spread by the changing the input criteria, is one method of reducing any errors. But the initial 'errors' are still present, and will only serve to produce more chaos.

I am talking about from where the models are standing today (which is much better than they were 5-10 years ago).  Spending hundreds of millions on more computing power right now will not give the same rewards as ensuring some of the 'unknowns' are fully researched and included  as regards the accuracy of the models..

1)     Extra notes.... Take today and this graphic taken from the above (to be saved)....

  

The whole of even  the western hemisphere has been impacted by the the slope and shape of the high forecast to develop  over  the Bering Ocean.  Changing its inclination or intensity will dramatically change the forecast for the whole Northern Hemisphere via mechanisms previously discussed on here. Both the ECM and GFS have shown this happening over the last week. Both had to withdraw from their positions . Something is not 'spot on'.

Will they this time? Can you tell me? I assume that this situations has come about as to their incorrectly handling the totality of the 'telecomms' signals. 

2) As to whether the models are accurate from a scientific pov.    I cannot make any comments  (you are correct).  However they have now released documentation on the 'CC' models, which were based upon forecast models  (I  am told),  and for the previous release of them there were still around 25 assumptions which were not yet proven. If they were missing in the 'CC' models then I assume they were not in the forecast models.  - In the CC models they substituted parameters. 

Sorry to mention the XX word banned on here  - MODS.

So IMO opinion,   (FWIW)  there is still quite a way to go before we can say that all the assumptions (and therefore the absolutely correct science) built into the models, means that models are correct.

Until that happens  putting in more computing power will increase chaos (not decrease). that is what my 30 odd years of experience has taught me.

MIA

As someone also in a similar scientific software business, I agree with the sentiment of this.

Initial conditions are a big thing in my opinion. In an inherently chaotic system, if you don't get the initial state correct you won't get an accurate answer. Rubbish in ---> rubbish out. 

Areas lacking data are at altitude, over the oceans and near the poles where there are no humans to record and report data, so satellite and aircraft data are used I believe.

Then you have the solution method which always has a truncation error and probably has efficiencies to make sure it is a) robust and b) quick enough to reach a solution. Developers make compromises/assumptions which always have impacts in due course. For example, mountainous areas will be a problem - how do you model the boundaries there? You can't directly model each feature (mountain), it's too small a part of the domain, but they are important for (eg) torque as discussed at length by others previously – how do we know we are accurate enough?

All numerical models have inherent assumptions and weaknesses, much of the skill of those using them is to understand where those limitations are. It has been really fascinating to see the experts here comment on the output, what they trust and what they don't. We're in one of those spells where they are not convinced by the outputs they are seeing and giving their opinions, much respect for them sharing their knowledge from me – thanks!

Apologies if this is slightly off piste, but it is relatively quiet….

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008639

[Tamara]

The extended period continues to look very problematic in respect of NWP to me.

The MJO passing through the Indian Ocean has bumped up easterly inertia/trade winds and creating problems in the modelling with Pacific ridging and with the models gunning for booting up the polar jet downstream as a consequence. This at the same time providing insight into the modelling of the lobes of the polar vortex and the spectre of them fusing together.

However, westerly wind inertia remains above average across the extra tropics and this presents a question mark about the Pacific amplification and downstream polar jet being over modelled. But most especially based on the passage of tropical convection quickly set to navigate through Phases 4 & 5 imminently during the period in question when the northern arm is being programmed to flatten the pattern. As the MJO hits the borders of Phase 5 the next starting pistol is renewed to ladder up angular momentum tendency. Putting all this together,  a very squeezed timeframe for this sequence of polar jet modelling is only available in my book to complete, let alone sustain itself if it does.

The suspicion I continue to have is that these poleward eddies that the models propose to increase polar jet momentum, will get sheared off and this whilst this still leaves a flat jet stream coming from upstream, the shearing off process will cut off the supply to the polar jet in mid stream and force it to backtrack into the sub tropical jet. Much the theme of discussion of late. 

That process, leaving some of the residual ridging between Greenland & Iceland intact and/or re-programming re-emergence of wedge type ridging and subsequent disruption of Canadian lobe energy in mid Atlantic. This leaves southerly jet kayaks to resume progress and changes the extended ensemble means that propose a flat westerly pattern across NW Europe & inflating Azores High.

It will be very interesting (as I see it) to watch and monitor if this does actually transpire.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008660

[Catacol]

1 hour ago, mountain shadow said:

No one is arguing that synoptically things looks great with rare Arctic air making an appearance and bitter cold is a certainty.

What is currently frustrating is the lack of snow falling for 75% of the population. 

Things could change of course.

Sorry MS - I've got to come back on this. The chart I posted has a moisture-laden (given its origins) system in the bay of biscay approaching on a ENE vector and a cold to very cold (-8 850s over most of the UK) trough in place that has come from Scandy to the NE. If anyone on here is frustrated at this 120h context then either they grew up in Finland, haven't been on this forum long enough to understand the usual bounds of our winter weather or are just not interpreting the pattern effectively. Maybe a combination of all 3.

Deep breath. These synoptics are rare. There is no way we can have a handle on precipitation amounts at this range. If a system was forecast to hit direct from the W or SW then it becomes a snow to rain event....so we NEED it to deflect and run to the south even though it narrows the band of snowfall and involves fewer people. We would love a strong flow off the north sea for streamers, but again there is no way at this range that we can be sure quite what will occur there, and in that NE flow it is quite possible for features to become embedded that - once again - we have no chance of spotting at 120h.

If what is on offer next week is not good enough then it virtually never will be. The 7 Feb 1991 style of synoptic is SO rare that, at the age of 53, I reckon I've seen no more than half a dozen of those in my lifetime and in the last 27 years only two - 2010 and 2018. Before that 1996 which locally around me was spectacular. Do we really need to go down the track of waiting for events that happen twice in 27 years to start feeling good about them?

The answer has to be no. Next week is looking great. Is it looking 1991 great? No. But great nonetheless and some are going to end up very happy indeed. And bear in mind that this is just the start of a drawn out spell of cool/cold/very cold weather which I am pretty certain is going to feature more than a single bite at the cherry. The 1991 redux isn't off the table.

Rant over. I hope the majority of folk on here are enjoying what is unfurling. Short range surprises will happen, next week will be properly cold and the long term prognosis is good. The models today are suddenly seeing ridges popping up in a flow that was modelled pretty flat into week 2 yesterday. Watch that trend develop. The only thing frustrating me at the moment is the wait for the MJO to get through the maritimes and for frictional torque to start climbing again. As of 9th Jan still waiting...should be soon now. But otherwise - all good!!!

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008658

[Catacol]

1 hour ago, Cambrian said:

The models are struggling big time. The Scandinavian trough is still very much in attendance and looking at that, a reasonable observation would be that it only needs just a little more amplification in the Atlantic heights to altogether prevent any phasing of the troughs associated with two lobes of the PV and keep us very much under the influence of the cold trough to the northeast. 

This analysis nails it. It will be a very close run thing, and some average temps thrown into the mix in week 2 is an inevitability I think - but cold air will also be present and close by. These are the sorts of scenarios that, in theory, produce the snowiest conditions for the UK. It would be counter intuitive - but entirely possible - that the very cold week next week produces less of a snow impact than the milder one that follows. And then all eyes on the expected impacts of spiking AAM and MJO orbit as we hit February and that lovely Glosea chart.

As for next week - well: there is a huge amount to be worked out. We are not close to knowing what might be embedded in the flow come Mon/Tues/Weds/Thurs nor what may or may not encroach from the SW. This is where the luck comes in - macro scale has done its job and it is time for the micro to sort itself out over a 5-6 day period. Once this warm ridge gets shunted to Greenland then the fun begins...  Let's hope for a fair slice of that required luck because snow hunters on this island, in the best synoptics and large scale pattern in 6 years, deserve a bit!

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008507

[Met4Cast]

48 minutes ago, Tamara said:

The extended period continues to look very problematic in respect of NWP to me.

The MJO passing through the Indian Ocean has bumped up easterly inertia/trade winds and creating problems in the modelling with Pacific ridging and with the models gunning for booting up the polar jet downstream as a consequence. This at the same time providing insight into the modelling of the lobes of the polar vortex and the spectre of them fusing together.

However, westerly wind inertia remains above average across the extra tropics and this presents a question mark about the Pacific amplification and downstream polar jet being over modelled. But most especially based on the passage of tropical convection quickly set to navigate through Phases 4 & 5 imminently during the period in question when the northern arm is being programmed to flatten the pattern. As the MJO hits the borders of Phase 5 the next starting pistol is renewed to ladder up angular momentum tendency. Putting all this together,  a very squeezed timeframe for this sequence of polar jet modelling is only available in my book to complete, let alone sustain itself if it does.

The suspicion I continue to have is that these poleward eddies that the models propose to increase polar jet momentum, will get sheared off and this whilst this still leaves a flat jet stream coming from upstream, the shearing off process will cut off the supply to the polar jet in mid stream and force it to backtrack into the sub tropical jet. Much the theme of discussion of late. 

That process, leaving some of the residual ridging between Greenland & Iceland intact and/or re-programming re-emergence of wedge type ridging and subsequent disruption of Canadian lobe energy in mid Atlantic. This leaves southerly jet kayaks to resume progress and changes the extended ensemble means that propose a flat westerly pattern across NW Europe & inflating Azores High.

It will be very interesting (as I see it) to watch and monitor if this does actually transpire.

Sounds like what you’re expecting is something similar to the 00z GEM, i.e a more active jet into the Atlantic meeting residual wedges of high pressure to the north causing the jet & subsequent low pressure systems to disrupt SEwards. 

What you advertise is appearing within model outputs albeit as a lower probability outcome currently within the modelling. 

I’m not sure models will be handling this particularly well at extended ranges, resolving split flows & disrupting energy is something modelling always struggles to handle so what initially looks like a flat, zonal-esq pattern often corrects as the lead time shortens. 

No doubt that less cold air will push in as blocking wanes, but that doesn’t necessarily mean a mild zonal onslaught is on the way. 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008741

[Cambrian]

6z ICON is neat for showing the temperature changes over the weekend, during the next 72h, hour by hour, reflected in freezing levels and the rain / snow boundaries

 

Get the cold in…  

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008662

[Eagle Eye]

This post is going to explain the Stratospheric and Tropospheric circulation and link it with this current case study. 

This is a case study for my EPQ so any EPQ checker here, this is directly copied as I'm working on my EPQ not copied from here.

During the winter months (more specifically, starting late November and going into late January) the Arctic is plunged into night throughout the whole day. Leading to large temperature differences between the mid-latitudes and the poles and so the jet stream is fired up into a polar-night jet that circulates around the Arctic. The jet still stays strong, especially in the stratosphere, through till early March.  

The strongest part of the polar-night jet is in the stratosphere and that’s important for top-down interactions with zonal anomalies. A stronger than average stratospheric vortex can push westerly wind anomalies further down into the troposphere. Similarly for the opposite but the processes that forces this is what we will be discussing in this research along with the extent we can attribute the stratospheric setup to the surface impacts by looking at what causes these connections and how strong they were in the January 2024 situation. 

The variability in the polar-night jet is importantly influenced by temperature anomalies, with diffusion of anomalous temperatures into the vortex, able to weaken the jet stream over the pole. The zonal jet for the pole (zonal jets being the different jets at different latitudes. The polar zonal jet is from 60-900 latitudes, the subtropical jet is from 30-600 and the equatorial jet is from 0-300 ,both north and south of the equator.) can be displaced or split under certain stratospheric polar warming conditions. Though the polar-night jet oscillation (PJO) is a low frequency intra-seasonal variable compared to a more varied tropospheric polar vortex, it is still influential, especially in certain circumstances. 

 

Stratospheric warmings can sometimes be strong enough to reverse the zonal wind and that is called a major warming when it does. That wind reversal pushes down into the troposphere through wave breaking. That wave breaking can cause reactions in both the tropospheric polar zonal jet but also the momentum budget and general patterning conditions.

A major warming is linked with a negative (-VE) NAM (northern annular mode) or also known as the AO (Arctic oscillation) pattern where +VE (positive) pressure anomalies migrate poleward and –VE pressure anomalies filter down towards the subtropical latitudes. That is a perfect –VE NAM pattern though which doesn’t tend to happen, if at all, in the atmosphere due to the imperfect nature of the atmosphere. You can get lots of varied patterns associated with a –VE NAM pattern with the distribution of zonal winds and energy. The NAM is essentially just a representation of the atmospheric response to momentum being input, taken away or moved around the atmosphere. For what it’s worth, a perfect +VE NAM pattern also rarely, if ever, happens with an entirely zonal jet (both subtropical and polar) with the momentum budget always affecting the distribution of the jet. Given the SSW (sudden stratospheric warming) we’re studying, this isn’t necessary but a vortex intensification event has the opposite effect of an SSW. Neither setup shown on the AO images are perfect either, they’re just two strong events of both.

The zonal response to a major SSW (assuming it can break down to the troposphere) is to weaken the zonal winds at higher latitudes through eastern enhancement propagating towards the surface and weakening the higher-latitude jets. This response is to increase amplification of the Rossby waves transversing the mid-latitudes and so the mid-latitude highs propagate poleward which pushes the Arctic air down towards the subtropical area, hence the –VE NAM response. 

 

Atmospheric Rossby waves are transverse waves like every other one, they’re just the connected high-pressure and low-pressure relationship. They’re also important for distribution of energy in the atmosphere, the poleward and equatorward movement of Rossby waves impart eastward zonal wind forcing where they propagate. Hence poleward waves are an important process for filtering cold air down from the Arctic towards where the subtropical jet propagated from. That’s what’s important for determining the tropospheric impact as that conditioning of the zonal jet can be more troposphere driven with the momentum budget and wave response.

The ability of major warming PJO to affect surface conditions is well documented but minor warming’s effect on surface conditions is more event based. It depends on the tropospheric setup prior to the stratospheric warming and whether the troposphere to stratosphere (T-S) connections remain.

Troposphere-Stratosphere connections 

The T-S connection is extremely important for the stratospheric variation with the transfer of heat flux through eddies forced by instability and in tropospheric Rossby waves, where they can ride along the waves transferring heat to geostrophically balance the atmosphere. Hence the eddy heat flux (EHF) acts for poleward heat amplification and carries equatorward cold suppression. EHF transfers heat vertically due to Rossby wave driving through zonal flow between atmospheric levels. This can be seen with an eddy-driven jet (EDJ) in the subtropics during times of large Rossby heat transfer. This EDJ migrates poleward with the poleward transfer of Rossby waves and thus EHF, which affects the balance in temperature between different levels of the atmosphere at the poles. 

 

The vertical temperature gradient diffuses the EHF upwards into the Stratosphere, transferring the Rossby wave. Assuming +VE heat transfer Stratospherically, the –VE zonal link with heat and zonal wind also transfers. However, Rossby waves cannot penetrate easterly zonal wind and so wave-breaking occurs, which is how easterly winds down-well after a major SSW. The stronger the temperature gradient where the transfer of EHF occurs, the stronger the diffusion occurs and therefore, the stronger the easterly zonal mean is imparted onto the zonal wind. A strong imparting of a Rossby wave poleward in the Stratosphere that completely reverses the zonal wind easterly is called a major SSW, whereas one that doesn’t fully reverse the zonal wind to easterly is a minor SSW.

Stratosphere-Troposphere connection 

 

The connection between the stratosphere and troposphere is mostly done through wave breaking or wave reflection. There are certain setups favouring each of these, both are to do with the aforementioned Rossby wave driving. The –VE NAM imprint that can imprint on the stratosphere comes from a stretched polar vortex. However, compared to wave-breaking major SSW events, the zonal wind appears to be less of a factor. Only 1 in 5 wave reflection events (roughly) tend to be major SSW induced. However, it is harder to get a wave reflection event to occur during weakened vortex events. It’s almost exclusively stronger vortex events that are reflective when the reflection occurs in the lower-mid stratosphere, which is more frequent. Though in the upper stratosphere, reflectivity increases with a weaker vortex. Stronger reflection event past 10hPa become increasingly –VE zonal wind based.

The onset of deceleration of zonal winds forms the reflective surfaces that forces the Rossby wave reflection and the heat diffusion vertically is distributed back surface-ward and are a strong force back towards the pre-conditioned state that the waves were forced from . The EHF re-follows the Rossby wave hence the stratosphere superimposes on the tropospheric state through both wave interactions but also the initial heat that’s imposed onto the wave state. However, that assumes that the Rossby wave hasn’t been forced to become barotropic in the stratosphere as a slow-moving wave packet would do, that disconnects from the quasi-stationary wave as it propagates meridionally, losing its initial base state. Then the wave and EHF connection dissipates as the heat flux is transferred at the same time as the baroclinic to barotropic link occurs. If the reflection can occur quickly enough for the wave to be quasi-base state, then the EHF should follow the wave back down.

The strength of reflection is important for how much EHF is transferred back tropospheric-ward over the state that the Rossby wave packet imposes on. High reflection will clearly have a stronger impact upon returning to the –VE NAM base state that the wave driving likely was forced up with given the T-S links. It can influence the mean state of momentum transfer in the troposphere, important for the momentum budget distribution to tend to return to that initial driving state, especially with a stronger reflective response to induce that surface response. The wind shear response in the troposphere, important to show zonal flow against wave flow (horizontal against vertical zonal distribution. So, the zonal state forcing low pressures to form in the Atlantic when looking at influencing Europe’s weather, compared to the natural Rossby wave packet shear) and it’s in reaction to stratospheric influence. The westerly flow from the lower-mid stratosphere reflects and strengthens the polar vortex state, hence the shear showing both zonal and wave influence from the stratosphere. The wave energy can easily show itself based off the shear then because the difference in the western backing of the top of the wave between the heights showing the wave strength will also show up on shear. So the energy-shear link with Rossby waves for vortex disruption strength and linking it between zonal mean in the stratosphere imposing downwards is going to be important for understanding the case specific forcing.

Case specific 

 

The reflective strength of the wave if it weren’t an upper stratospheric reflection of the –VE NAM state would be low, however, the upper stratospheric reflection means that we know that the reflection did at least have some strength. Given the weak zonal flow from the Rossby wave nearly reversing the upper stratospheric state, the thermal gradient would’ve been enough to force a large temperature flux to force that minor SSW which was a stretch and displacement of the vortex state. That stretch pre-displacement was what forced a reflective surface for the wave packet to reflect down off. 

 

The PJO occurs during a baroclinic wave setup, so the minor SSW is a clear showing that the wave hadn’t transferred to a barotropic wave yet and so the EHF was still wave-trapped remaining quasi-stationary and the pre-setup tropospheric state is still being reflected in the wave packet as it hasn’t changed its v distributed setup. Meaning that a perfect reflection would re-force the troposphere back to the forced state. However, as always, it won’t be perfect, so the response must interact with the setup it forced onto. 

 

Hence the strong –VE NAM response in the upper stratosphere shown will be watered back down as it approaches the surface, similar to the –VE NAM state that forced it. This is also likely due to the low wavenumber impact being stronger on the upper part of the atmosphere than the surface with a larger wavenumber at the surface being more normal so the deviation from average at the surface of the mostly wave-1 driven change, is translated to less at the surface than the stratosphere.

The imprint of the reflection onto the troposphere can be seen by the linking on the time series, yet the surface driving of that through AAM wouldn’t be seen so it must be a balance between the two. This is especially given the built-up momentum pooled over the north Atlantic that could easily have been the main forcer of linear change in the evolution. So, the linear time scale of this is very important in determining the main force for change in the tropospheric state towards that weak –VE NAM. Normally, you’d say that the AAM and reflection destructively interacted to weaken the AAM signal towards just below average. However, this time, the Greenland high response being so high works linearly with the +VE AAM lag over the north Atlantic and the downwelling of EHF to re-imprint its own wave response. 

 

So, it is very possible that these waves constructively interacted to force such a strong Greenland high but then it becomes an almost impossible working out of surface drive against zonal wind drive. The stratosphere’s impact upon momentum though suggests that when looking at just the tropospheric response, the stratosphere would’ve influenced the momentum distribution throughout the northern hemisphere. This weakens the MJO influence because of the momentum being influenced more by the +VE EAMT event and stratospheric reflection.

Therefore, we can work out through the Greenland high’s linear scaling, that the AAM and reflected wave constructively interacted to force the Greenland high. However, it is hard to link the AAM to the forcing of the Greenland high without assuming the stratosphere pooled momentum to force the wave. 

 

On the other hand, it is also hard to argue the other way with both working together assuming an in-phase wave evolution for a quite strong Greenland high to be forced despite only moderate strength of background signals with an out of phase MJO destructively interacting with the wave creation. 

 

The distribution of momentum being modulated by the stratospheric reflection however takes more of a precedence here because the +VE AAM event was relatively weak compared to the reflection taking place during a very weak zonal state. So, you could still make the argument that the stratospheric state is stronger of a force here because of how it projects onto the troposphere directly including previous events but because of the rising AAM, it’s hard to confirm it.

Except using the zonal state, the zonal evolution clearly shows the surface development of poleward –VE anomalies pre-reflection reaching surface. The reflection forced onto the surface pattern and may have directed the pattern and strengthened the –VE zonal state at the surface but the AAM drove the initial wave.

Initial wave driving was through momentum forcing but the stratosphere reflected the state it was initially forced from, hence the Greenland high was stratospherically influenced more than surface from the initial wave state of a UK-Iceland high. The stratosphere would have been what forced our potential prolonged cold episode then through anticyclonic wave breaking (polewards) and helped increase the strength of Arctic forcing projecting onto the –VE NAM state.

This isn't done for anything specific but to show what forced this for future setup preferences. Especially in westerly lower Strat states w/high AAM as it can suggest a reflective tropospheric state is possible further down the line. Also, potentially suggests more Strat influence down the line w/the -VE NAM re-reflecting into the lower Strat from the AWB driving. AWB driving forced a minor SSW last year, however, the weak zonal mean zonal wind state after the minor SSW suggests to me that the wave should chip away at the lower Strat and could well split the lower Strat which re-works it's way back down for early February combing w/another rising AAM episode. So this is a long way of saying that we also need to keep an eye out for February because of the initial wave reflection we look to be getting at least 2 surface responses and given the driving AAM episode, I wouldn't be surprised if we got a 3rd reflective/wave-breaking and this ended up being a typical tripole major SSW reaction through multiple wave eflections forcing a weak SSWE from an initial minor SSW in the upper Strat. Potentially another setup from Strat-Trop connections to keep in case of a similar event.

Away from the Stratosphere. 

We have now got a good consistent signal strong enough on the mean to show that we should be moving towards a retrogression towards Alaska w/the rising AAM and potentially another later mirroring of the wave reflection initially suppressed. Leading to the boxing in of a SW'ern USA low that forms as it works w/the retreating Greenland high. 

However, as the momentum budget redistributes likely due to either the re-reflection of the NAM state w/out a major SSW forced or if a major SSW is forced then it's through wavebreaking that the same reflection occurs. So the jets seperate and look to be slowly seperating well before the last few frames of the mean run. So we get another seperate jet situation w/favourably kinematics for the high just south of the Caribbean to be forced up again eventually as the momentum forces itself from jet to poleward forcing and so a mid-Atlantic block and/or a Greenland high is very possible. So going into February, we have multiple suggestions including the S2S models suggesting that there's a lot of support for a blocked pattern.  

The CFS weekly is showing the southern disconnected jet and the slow southern descent of - VE zonal wind anomalies into the 2nd week of February ish, hence the Greenland high support increases. 

The zonal component reflecting its state from Strat to Trop is a supported statement by the latest update w/a clear vertical suppression of the - VE zonal mean zonal winds through wavebreaking or reflection. Hard to tell here but if we can get wavebreaking from a major SSW it'd probably be better for total NAM circulation so easier for the prolonging of blocking w/less north American influence. 

Going into February and what I've said before is still represented by the low pass composite though it's still struggling to come up w/the north Pacific high w/Pacific trough (it still has the Pacific trough) bit maybe the signal for that wanes into February. However, the analog suggests that the atmospheric representation should be one similar to that of a La Nina probably phase 6/7 esque response rather than ENSO (most likely the Pacific trough signal supports an analog similar to this) which is perhaps a bit more transient than were it to be a La Nina signal and again, that Pacific trough is probably the signal for that. However, if we can get rid of that then we are really getting a good signal going through February. 

Thats all for now, might also look back at how the teleconnections did from late December to the current expected response. Given the 15/16 days lead time ish of the north Pacific ridge over the trough, I think both the mean and the teleconnections actually did well. I'm not great at current forecasts away from convection and sometimes using PV lobes to forecast small-scal precipitation but I tend to try to avoid it as people can tell. 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008797

[Derecho]

13 minutes ago, Midlands Ice Age said:

Whilst I understand what you are saying....

If you can get down to the physics (maybe chemistry) then that also ought to be possible.

Summary - we are no where near there yet from a 'software' point of view.

I have spent much time looking at 'the weather' since retiring (It has always been a big interest), and some of the characteristics closely resemble  share dealing systems, with apparently 'outside'  influence having a large impact. Is this the same as a random 'butterfly' effect in our hobby/ pasttime?.

Also, I did spend sometime working on share-dealing and trading systems, which I put to use when I retired. (more good,  though some bad), and/but they do also follow  'weekly' trends, which need to be built in the standard share models.

Anyway probably enough on this sort of topic before the afternoon fun and games begin.

MIA

It's an interesting take on the models MIA and the questions from me weren't necessary a criticism, more a position of intrigue.

There are two main aspects to the model uncertainty argument:

1) The assumptions aren't fully correct - This is why weather modelling is so difficult (chaos). It makes up the majority of the errors in longer range forecasting as you say.
2) Lack of data coverage: - Bodes into the "junk in, junk out" argument as well. Without a full understanding of the surface state the weather model is already wrong.

Just out of interest here is the uncertainty at T0 on the GFS and EC

Both the key areas of uncertainty at T0 are with regards to the Azores low and over Greenland.

You can see from the two plots how much quickly the uncertainty increases first around areas where the understanding of the initial surface state isn't as good.

So I believe that if we had a correct surface state the 'butterfly effect' would kick in later.  More data would result in less error but there is a limit into how much we can improve due to incorrect assumptions. 

How much can we learn about these assumptions if we have more data though?

Interesting topic.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008804

[Tamara]

52 minutes ago, Met4Cast said:

No doubt that less cold air will push in as blocking wanes, but that doesn’t necessarily mean a mild zonal onslaught is on the way. 

For quite some time, in anticipation of the blocked pattern and sub tropical jet, I have used the word "attrition" in respect of the eventual attempted breakdown.

I am always open to evidence that changes the picture to reflect the extended modelling but it is equally my natural instinct to question anything that gets taken at face value. This second half of January has too many aspects that at present make me question the degree (at least the degree of latitude) that the Atlantic returns.

Thereafter there seems no evidence on the other hand to question a reload of blocking (caveat being how much this does actually break down fully in the first place).

Everything points to AAM soaring regardless heading into, or just before, the last week of January to early February and with the GWO likely at high amplitude in the Nino attractor phases under stratospheric diminution, the representation of height rises in a spectrum between Greenland, Iceland & Scandinavia, alongside a fully brooked sub tropical jet - and so therefore good vindication of the latter winter seasonal modelling.

This is one modelling outlet that does make complete sense at this time. Sometimes its the case that the conclusion point is clearer than the path towards it. Which does sound rather odd, but there we are!....

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008841

[Tamara]

40 minutes ago, CoventryWeather said:

I'm still not convinced on this mild blip. 

I feel the UKMO is closest to the mark. Not biased or anything, but the evolution looks better, the GFS is really messy last few runs.. moved a bit closer to the UKMO which has remained consistent. 

Also was the UKMO the first to pick up the slight extension to the cold spell? It seems to be handling the block and wedges a tad better than others..

As detailed fully earlier, it is easy to see why the models are looking to re-energise the polar jet. What still remains a question is how much flat west to east energy actually verifies beyond the meridian over a week away and how much instead is broken off. A lot of rationale has been given about the question mark over how sustained polar jet energy might be earlier today.

 The area between the UK and Iceland holds a key to a residual ridge and cold pooling that may well prove more resistant than modelling suggests 8 and more days away. Conceivably there is a route towards Scandinavia into the last week of the month and the start of a road back to late January blocking.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5009046

[Met4Cast]

12 minutes ago, mountain shadow said:

So, despite favourable EAMTs, MTs, GWO orbits, MJOs and a weak PV, the long awaited cold spell is now a cold snap with snow pretty much only in Scotland and favourable high ground in the North West.

Here's hoping February delivers.

Because of a single run? I think we need a little perspective here. 

We currently have below average/cold conditions across the UK and by the end of next week we would have had (apart from a couple of days) 2 weeks of colder, blocked conditions. Many southern areas saw snow (albeit not a lot) last Monday. 

We go into next week with much colder air moving south across the UK with increasing snow risks. 

Background forcing has done it’s job, the broadscale pattern is as advertised & expected, high latitude blocking is becoming established. 

The UK is a small island though so despite everything being favourable, blocking & cold conditions in place snow can still be elusive, but I don’t think it will be. 

Next week looks very unstable and open to small-scale features developing and bringing widespread snow risks, these may not be picked up until 12hrs before they arrive.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5009289

[lorenzo]

At pains of wishing all our lives away and a cold spell right on our doorstep am fascinated right now between 

1 Something like this from 06z GFS - which in isolation - you stopped any of us and said - What kind of winter was this? Would most probably say - Vortex in control Strat-Trop connected, ridging into Europe - the worst of Winters.. etc.

2 Vs - Right now we have an imminent cold spell, granted it has been a long, long , model weary countdown, but the anomalies and progression are probably the *best advertised since 2010 ( Note not same synoptic). And, that we are now into the realms of shorter range modelling tools.

Then, we have the contrast of such a long lead to eventuality, coupled with the last 10 days of Jan being a period where the regimes shift, yet, everything points back to re-load ( seasonals / MJO / AAM / Strat), Nino-expected, QBOe, it really is a winter where everyone on here has been on a roller-coaster.

The point being - it's a new roller coaster, it is not one we have entertained - the Canadian warming perhaps heralded that given it's strength back during Nov, significantly beyond the envelope and very rare in terms of historic dynamics. That's on top of everything else mentioned.

And now, a cold spell and it will be cold - brutally so in some places and noteworthy - is it a stick on for the cold counter part snow - no, and it never would be - this was always the way in any of these winters we herald, there was not wall to wall snow EveryWhere All At Once. And to tonights 12z another variation - EC slamming Scotland with snow has now dipped 300 miles south - we are in a Nowcast scenario.

Do we have tentative beginnings of Scandi things ahead... January and now may be the appetiser - the real deal may be Feb.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5009276

[bluearmy]

Well I said I’d wait for the 12z eps to check out rogue runs and on a hemispheric level they have delivered 

whilst the low spread persists around low heights over Greenland, the remainder of the polar profile looks very broken vortex with plenty of amplification and high level blocking. . Of course that Greenland vortex is a problem for us but it doesnt necessarily persist there into week 3 and the mean vortex is actually west of Greenland so that’s already a positive. 

whilst the breakdown days 8/10 is a poor end to the weeks chase, I made my peace with that a couple of days ago 

the next chase comes into view - maybe a height rise east of the meridian which then retrogresses 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5009483

[WYorksWeather]

Been a while since I've got chance to post, so I'm going to divide my thoughts into three bits. Firstly, we have an analysis of any snow risk, then a look at the medium range modelling, then my general thoughts on where we go from here.

Short range

Arpege

Of course, forecasting snow is never easy, but what we can do is see what some of the higher resolution models are showing for the next few days.

The 12z Arpege reaches to Tuesday evening, and shows relatively little activity until Monday, and on Tuesday temperatures are higher, and conditions are likely less conducive to snowfall.

The period of interest is shown here.

 

Looks like some chances of snow for Scotland, but there is also some just grazing eastern coasts. It wouldn't take much to get a bit of a covering into some English coastal areas. The band of snow is moving slightly east of south, maybe SSE, so any slight variation in the track could bring more eastern areas into play, and of course a shift the other way could see all of the snow just remain in the North Sea. The right chart shows temperatures, and conditions are highly conducive to snow accumulations.

UKV

For Monday's time of interest, the 15z UKV shows the following.

   

Possibly more widespread snow in Scotland. However, the bands of snow seem to have slightly more of a south-eastern track, and therefore there seems to be a lower risk of much in the way of snow showers for England. The difference in track does, however, bring Wales and parts of the SW into play for a slight covering. Worth pointing out that conditions if anything even more conducive to snow than the UKV, it looks seriously cold on Monday morning. Surface temperatures sub-zero for most of the UK, 850s near -10C, dew points around -5C.

I would also note that as a slight warm sector (in relative terms!) moves in from the west, UKV is suggesting another chance for some of us on Tuesday, possibly down into northern or even central England.

In short, I don't think the evidence supports that this will be an entirely dry high. Widespread snow is probably a no, especially in the south, but I do think some areas will get some snow out of this. Forecasting exactly where is almost impossible even at only three or four days out, so treat this as just showing the possibilities.

Medium range

So, now on to the ensembles. Again, the advantage of being away from the models for a couple of days is that I have charts saved from a while ago, so I can compare and see how things have changed over the past couple of days. Here is what the GFS was showing for York and London on the 12z on Wednesday.

 

And here is what it is showing today.

So, here is my thoughts. Firstly, we can see that modelling is firming up on pretty deep cold for early next week. Probably some exceptionally cold temperatures in exposed locations. Sub-zero daily means will be expected in most areas, and possibly ice days further north. The mean projects that 850hPa temperatures will drop away to around -10C, briefly rise to around -5C on Monday and Tuesday, then drop back to around -7C. In short, looking out to around Friday, it constitutes a significant upgrade of the cold.

However, looking further ahead, it has to be said that there is a stronger signal for a breakdown of the cold spell beginning around the 20th, with a return to average or above average temperatures by the 24th. It must be said that we're still too far from the time in question to be confident in the exact timescale, but the trend is much clearer than it was a couple of days ago, when there were more model runs staying cold.

General thoughts

I'm going to be extremely boring and take the middle ground on this. It has to be said that the initial spell of cold we've had this week has been a bit of a damp squib away from the south, where some areas have seen rare snowfalls and colder temperatures, so it probably feels more notable. At my location only a couple of nights have even seen overnight frosts.

That will change next week, and it does look cold until next weekend, likely very cold. After that, though, there is a stronger signal for a return to average, or above average conditions.

I'm still expecting my prediction that the CET for the first half of January will finish below average on 1961-1990 is favoured on the balance of probabilities, but I'll admit I'm feeling a bit nervous about it, and it won't be anything spectacular, most likely in the 3s or 4s. It is very early to say this, but a mild last third of the month is favoured at this stage, though by no means guaranteed. This would naturally be a disappointment to many on here.

All I would say if this does play out in an unwanted fashion from a cold fans' point of view, let's not disrespect the knowledge that is imparted by many of the posters on here who discuss the teleconnections - it is a matter of probability. Background signals currently indicate a strongly increased chance of cold, but that does not guarantee cold for the UK, and does not guarantee snow if we get cold. It's important to remember that.

To illustrate, getting a good winter cold spell with some snow in the UK is probably like rolling a die and getting a six. Getting something really memorable, with very large accumulations that stick around for weeks, is probably like rolling double six. Good background conditions are like being allowed a couple of additional attempts at those rolls. They don't guarantee you anything.

I may drop back in for the 12z ECM ensembles later.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5009388

[Midlands Ice Age]

50 minutes ago, MKN said:

Hopefully this week has acted as a learning curve to alot of a I assume fairly new followers of the various model outputs. In the UK away from Scotland, charts showing cold and snow at 120-200 odd hours away are just pure fantasy. Unless the charts which are showing cold and snow are within +48 to +72 they are far from reliable. It's one area that even after all the years of model development they simply are not that good at getting right. I Mentioned the same at the start of the week incase people assume I'm just saying it now. Anyway fingers crossed for one or two surprises and if not this week there's still a good 6 weeks left for another chance to come along.

This post is a pretty accurate summary of where we sit today with the models.

Also the last couple of hours are basically  bemoaning that the Greenland high has not survived and that this caused the collapse of our bitter weather beyond next week.

As mentioned last week in relation to 850's and surface temps  (CET) I have  'a quickfire' database ready made for a bit of analysis, (that I produced in 2018), which contains my overall 'reason' for the cold outbreak. (I was looking at the 2018 outbreak in relation to cold winters past.

Well guys  ...

It seems as though from the records that I produced from my reanalysis going back to 1870 that in the spells reviewed (about 100), that the Greenland high was the major contributor in only 3 of them. The most notable was clearly 2010 and then the previous really biggy was 125 years previous. Certainly they have been around, but only helping the atmospheric conditions to serve up as easterlies/highs over Europe which are nearly 50%,    and northerlies around 40%.   (These may have been helped by the Greenland high, but in the main followed a deep depression in the Eastern Atlantic somewhere, and hence were cyclonically initiated in my view).

So , could it be that us expecting the Greenland high to pump bitter cold  each year is the  unrealistic diagnostic??. 

I realise that the 'models' have been leading us up this path... So are they also over-estimating the strength of this blocking?

It is very apparent to me that what has caused the breakdown of the high  (if it happens), is the formation of a huge 'Pacific' high which is forcing the very cold airmass down into the Central USA. This cold outbreak then has sufficient momentum to push into the Atlantic, and it seems to have been happening regularly over the last 10 years (IMO), but I have no data to prove my suspicions.     As KW is showing NA does seem to have missed a lot of the global warming in winter, and new records might well be set again this week - so I understand from USA forecasts.

If this is true then one has to ask why the Pacific high seems to have so much energy these days... is it cyclic or the result of a warming world, or has it always been so?   There are papers out there about the regularity of the pacific high in relation to the last 1 -  2000 years. It could be a useful read.  

Finally mods - if you think that reviewing the situation is not on for this thread I understand, but whilst it is quiet I thought it would be OK.

But it could be that it might just  lower some people's expectations,  and will hit the sales of Prosac (sorry Nick).

Greenland highs are very difficult to sustain. I would love this to be another case of a recorded hit for a 'Greenie' but somehow I feel the odds are against it.  

MIA

 

 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5010085

[johnholmes]

Not got time to post the full set of charts I use but they are along similar lines to yesterday. So deepish cold to start next week before the upper flow on NOAA and ECMWF turns more westerly cutting off the deep cold. Also borne out by UK met at 144h. Just where snow will fall and settle still seems uncertain but the low shown on Met Fx charts is the system that is the cause so watch how UK Met deal with it over the next 3-4 days and their forecasts/warnings for where snow is most likely. Certainly looks to become less cold/milder into next weekend I feel.

ps obviously coastal areas from Monday into perhaps Wednesday are likely to see coastal snow showers, with a small risk of these being more extensive on any troughs that form, little advance warning of these, say 6-12 hours at most.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5010067

[Chesil View]

Probably my longest ever post coming up. But a few things I feel need to be said

.Some quite understandable disappointment abounds that a nationwide freeze up and snow for everyone has not materialised in the models.

But some points to bear in mind going forwards especially for our newer members.

Even our harshest legendary winters waxed and waned within their admittedly cold envelopes especially here in the south. 

People saying oh the background signals haven't worked. But yes they have and will continue to do so.

The background signals at no time said another 47 or 63 was on the way. They suggested that the atmospheric circulation in our part of the world would show a propensity for blocked scenarios particularly the longer winter went on and come Friday we will have been in blocked scenario for a fortnight.

The background signal did not say the situation would remain intact everyday for January and February. Except in very very exceptional circumstances the atmosphere is naturally too dynamic for that to happen especially in northwest Europe on the wrong side of a comparatively warm ocean.

What the background signals do suggest especially El nino/Easterly Qbo is that as per Tamara's excellent posts that further blocking opportunities will arise through Feb and March.

There will be those who say oh god no not March but if you really do like cold and snow. It would be churlish in the extreme to turn your nose up at snow that comes then. The beast from the east gave me March ice days and an aggregate total of 35cm of snow at my  location within 5 miles of the south coast  in the first half of march 2018. Do you think I turned my nose up at it because it didn't come in Jan or Feb. Of course I bloody didn't. I enjoyed it for what it was. Sensational.

50 years of winter watching in southern England teaches you to be philosophical to live in thd now when the rare events arise.

What last week and the coming are is simply round 1 of the contest between a propensity for more blocking than usual as per the background signals and  our normal westerly winter regime.

There are more rounds/battles to come over the next 8 to 10 weeks

Yes the charts medium to extended outlook don't look great but I would suggest to anyone who thinks that's it for winter go to the archive charts on wetterzentrale where you will find Bartletts and Greeland PV's just days before the winters of 1947 and 1963 started to understand how quickly things can change when the background signals suggest a higher than normal propensity for blocking in our corner of the atmosphere.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5010195

[Tamara]

14 hours ago, Eagle Eye said:

Despite a potential major warming and split (sort of) , the increasing barotropic wave disconnects between wave heat and the wave itself pushing it polewards. This is usual, however...

1) The reversal is unlikely to be strong

2) We are relying on wavebreaking

3) This rules out a reflection unless it occurs before the SSW. This does not rule out future reflections though. 

Further on point 2

Longevity of wavebreaking appears to be short and overriden by other factors. Nor does it push equatorward, so it's just a downwelling of - VE zonal mean anomalies for a few days, a failed major SSW proper response if it happens. 2nd in the last 2 major SSW's (pretty sure that one that was in I think 2021 didn't connect with the troposphere). It's possible wavebreaking could still make it down but it appears unlikely. 

This is a very good post from yesterday evening that appears to have been missed in the UK "it won't snow in my garden" cacophony. It looks like precise timing of movement of SPV lobes between Canada and Siberia scuppers the notion that the polar jet return was being overplayed following initial amplification that is now in progress.

My niggle of the last few days has been about what should be immense wavebreaking pressure from the MJO progression through Phases 4 and 5 and then continued rossby wave driving on into the Pacific at the high amplitude expected - all being instrumental on diminution within the SPV in such a way as fracture the polar jet more sustainably around the time that this passage of tropical forcing is happening (circa up to 23rd Jan).  Which is coincidentally very close to the period the amplified pattern flattens out.

In that sense, whilst a cyclonic period made sense from upstream, following the ongoing current amplification response, the degree of polar jet return to follow didn't. 

One of those broken clock situations where taking NWP at face value at more extended time periods does turn out to be correct.

Notwithstanding the override of the SPV lobe movements, I am still suspicious of any over muted response to the colossal momentum drive from the MJO induced tropics to extra tropics passage to the Pacific (and associated tangible effects of surging angular momentum) on any sustainable basis heading to late month and beyond.

 

 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5010215

[bluearmy]

The gfs op is generally inconsistent back end of its runs in the upper strat but the last few runs has it taking the spv to Barents /novaya zemlaya with the axis heading back towards the meridian. 
 

I would expect that could indicate that by the back end of jan we would see another set up similar to what we have this week 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5010574

[bluearmy]

Would be a good time for the strat to take the lead …..

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5010641

[Singularity]

Based on the high AAM state limiting the strength of westerlies, I’d not be surprised to see the shift to a more settled outcome next weekend into the week after be repeated again tomorrow such that UKM & ECM keep wet weather north of most or all of the UK, perhaps even with the south holding onto light winds.

Regardless, the high across W or NW Europe should tend to migrate further N or NNE during the final third of Jan as the new high AAM cycle plays out in tandem with an active MJO setting out across the Pacific.

In Feb the response to a Pacfic-crossing MJO becomes most strongly in favour of HLB out of the winter months. No surprise that the seasonal models have been so keen on a HLB dominated month.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5010756

[Tamara]

19 minutes ago, Singularity said:

Based on the high AAM state limiting the strength of westerlies, I’d not be surprised to see the shift to a more settled outcome next weekend into the week after be repeated again tomorrow such that UKM & ECM keep wet weather north of most or all of the UK, perhaps even with the south holding onto light winds.

Regardless, the high across W or NW Europe should tend to migrate further N or NNE during the final third of Jan as the new high AAM cycle plays out in tandem with an active MJO setting out across the Pacific.

In Feb the response to a Pacfic-crossing MJO becomes most strongly in favour of HLB out of the winter months. No surprise that the seasonal models have been so keen on a HLB dominated month.

Hi James

Agreed The starting pistol for AAM tendency to jump sharply upwards,  as I stated yesterday, is from MJO Phase 5/6. Taking into account the very high amplitude of this intraseasonal wave, NWP is likely to come to a screeching halt with attempts at a low pressure conveyor into NW Europe and as you say, the downstream European ridge start to migrate NNE.

Your comment about Feb holds very true about Pacific feedbacks. Significant inflection of +ve MT torque within the extra tropics and likely very strong rossby wave action on the polar vortex. Peak winter wavelengths would support the most extensive blocking regime of the season.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5010799

[Eagle Eye]

Still a while away from the next?Sharp AAM rising event w/tangible results. Not in the GFS 5 day forecast yet. 

Double rise to a significant AAM rise by early February which is what Tamara was talking about w/MJO phase 5/6. That would result in tangible results by mid month. CFS has been insistent on this for the last 3 runs. General support is for a high rise GLAAM response which should be enough to re-invigorate momentum distribution in the Northern Hemisphere to displace the zonal pattern if it did happen. Winter is far from over. It's not all doom and gloom. This would be the strongest rise in a while with it moving towards a 2 S.D rise where GLAAM has spent most of my time in this forum very close to the COD. GLAAM forecasts are rarely that accurate but gloom posters are trying to invoke a response if they're saying Winter is over in January. Im not even going to bother deep diving into the potential responses when looking at the MJO propagation, clearly it's not worth it. Just kidding of course I will. 

MJO Nino Phase 6-7 response to have high latitudal blocking and combined with tropical forcing, there should be a constructive interaction signal. Wouldn't get overly confident of x+y = x again, the GLAAM will intefer with the RWT signal either favourably or unfavourably depending on the strength of the GLAAM input into the total distribution. However, a high rise GLAAM + MJO + weak vortex suggests either a wave reflection of the 6-7 state or a total Strat buster and double major SSW technically possible given the Arctic and lower Strat vortex basing of the current one meaning that it should recover well despite the slowest recovery occurring in the lower Strat, it just doesn't really do much damage the major warming though it may cut off momentum feed vertically for a bit post SSWE (appearing likely). Either way, February or maybe March if delays occur are looking good. 

Easy to lose momentum and MJO strength and the vortex can recover properly but for now general synoptics are favouring that high tropical forcing. The ENSO support for active MJO phases should probably get some work done soon otherwise we'll have been really unlucky. 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5010810