Model discussion highlights

[WYorksWeather]

2 minutes ago, Relativistic said:

You would think so. The Hadley cell's got to be bigger than it was 30 years ago.

Sources suggest that the rate of expansion has been around 0.1 degrees to 0.5 degrees of latitude northward per decade. Using the rough 60 miles per degree, then we can say that the Hadley cell is somewhere between 18 and 90 miles further north on average than it was 30 years ago. However, it has also strengthened, so the impact is probably larger than that suggests. IPCC says it is likely that the Hadley Cell has widened since the 1980s, but has only moderate confidence in the extent.

Here's the accompanying chart from AR6:

And the full explanation / discussion is on pages 49 to 51 of the PDF here:

https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter02.pdf

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4981759

[Catacol]

23 minutes ago, Don said:

I've been thinking (and I'm sure others have too) that had this winter occurred 20 or 30 years ago, it would likely have been a straight forward cold season, with the pesky Iberian heights being less of an issue?

Hard to be certain…but one of the artefacts of CC is the northerly shunt of the sub tropical high pressure belt. When we combine this with a generally stronger stratospheric polar vortex (another consequence of CC caused by a cooling stratosphere) we have a more difficult envelope for high latitude ridges in winter. Pressure from the north in terms of the vortex and from the south in terms of a more obvious and intrusive Azores/Euro High suggests to me that we get less cold blocking and tropospheric forcing from the pacific is less reliable and dominant in shaping patterns. This is why I continue to think that we need the removal of one of these factors in order to achieve cold…and there is little sign of the Hadley Cell retreating….so that leaves the vortex. I have a totally unevidenced sense that CC might provide more frequent setups for SSWs to occur though we will need a much longer tale of the tape to be sure. So…in winters without a SSW we are really up against it to see a properly cold spell but when we get a SSW we are in the game…though admittedly an SSW is not a guarantee of anything and the 2018 style setup is unlikely to become common.

Our grandchildren may reflect on a U.K. context which sees properly cold spells in winter becoming a 1 in 10 year event. Sadly I’m not sure the direction of travel suggests anything other than this. I grew up in the 80s when cold spells were common. Those days - until something significant changes in the climate - are gone for now.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4981762

[Cambrian]

This comes up a lot in the winter and draws excellent discussion, but the reflections surrounding the Hadley Cell often occur as a reaction to a specific phase of “Hadleyesque” heights, an oscillating signature of which the waxing phase has to be progressed through, before we often quite swiftly get to a pattern where the last thing anyone is thinking about is anything close to what concerned George Hadley in 1735. 

If we take the 18z GEFS at day 5, and compare it with the classic Hadley signature, Azores and eastern Med heights, we have a culprit. Shoot the Hadley. 

 

But look at the north-south alignment of the Greenland and Atlantic lows, and the forcing heights through eastern Canada, ready to progress that wall of low heights east into Europe.

By day 10, the trough moves east and south, a cold trough with low heights through the Norwegian Sea, UK, Ireland and North Sea down through the continent to Algeria.

Irony is of course that the telltale elements are still there, Azores and eastern Med heights, just we’re not thinking about them any more because they have waned and because we’re on the cold side of a sumptuous looking trough that could well bed down as a Euro-low by day 14, a notion reinforced by a look at tonight’s EC46, and the NAO- signal for the first week of January. 

 

Are we thinking Hadley and its associated roaring NAO+?

Yeah, exactly, not at all, more Hadbeenley than Hadley, and as is so often the case after a milder Christmas, the winter resumes. 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4981775

[Uncertainty]

A significant phase of amplification is emerging in the eps/GEFS around day 14-15.

I expect this is linked more to tropical activity than the strat at this stage.

The mjo is now forecast to move quite strongly into phase 1.

The phase 1 January Nino composite (and I am in no way suggesting a linear relationship between phases and anomalies) is indicative of a strong N U.K. high. The unusually strong amp and the fact it is happening very soon give a bit more credence to the composite imho

 

Given the lag, the GEFS and eps are not to be dismissed, the eps is almost identical to last night’s run.

 

 

This is when the real internet begins…

 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4981853

[Eagle Eye]

Whilst it is in a far distant time frame, we're currently seeing the start of a split potential to arise not just from a best guess based off the factors as they have been for a few weeks now but the model runs. They're not quite at split strength and haven't reversed it yet. However, this is the most significant run we've seen yet. With the development of the +VE heights of Greenland and the Siberian heights sliding into Kamchatka really tightening into the vortex. Also, that displacement if it were just that would be potentially good for us. The vortex stays quite strong after the mid run re-strengthening but it starts to lose its shape and the last frame I've attached of the anomalies really show how tight it gets stretched on the run. This has quickly changed into a weak Wave-2 event and mainly Wave-1 initiated, with a Wave-2 developing right towards the end from the Siberian eddies. The refraction caused by the large temperature gradient diffuses the temperature towards the north Pole.  

The diffused temperature goes stronger towards the poles with a higher temperature gradient. Essentially forcing a stronger zonal wind pre-SSW. This forms a polar-night jet and a stronger Rossby wave in the Strat. The bigger the temperature gradient, the stronger the zonal winds and the more Waves, the better. That is the exact reason it's better. It causes a stronger Rossby wave and so to reach thermal equilibrium, the atmosphere tries to balance itself out. So the warm air pushes towards the cold air replacing it and typically displacing it typically if its a Wave-1 leading to a large decrease in zonal winds and sometimes but not always a reversal. Sometimes it can force a splitting but I don't feel like this is one of those times yet . So it's good that we get the Wave-2 development. With Wave-2, the temperature gradient is strong enough on both sides that if the warm air rushing into the Arctic on both sides, they can connect up and quite often lead to a major reversal. However, at silly run time still, it's ages away.  

As the Rossby wave develops, it's an easterly wave that decelerates the vortex and that and the temperature movement act to completely reverse the polar vortex. So, I'd argue that we need the polar-night jet to form to really force a split here and it gives the time for the Siberian-north Pacific wave to properly form and stops a really messy and complex evolution to occur. The variability in the polar vortex to react opposingly to initial changes if they occur quickly is what forces a SSW. This is a different evolution to the polar-night jet forming over the space of a month as this is it being forced to strengthen.  

What I mean by that is that the atmosphere kind of doesn't want to form the polar-night jet and it's reactionary. So to balance it out, it changes the temperature around to form a dynamic equilibrium. As my Geography teacher would put it (obviously not talking about the polar-night jet, something else), "it's over-compensating" and the atmosphere and the earth does that a lot. Just a natural reaction of physics. So, the imperfect world can benefit us, sort of the same reason we get thunderstorms as well.  

The day-night temperature gradient (polar-night jet) is what forces the zonal jet formation during Winter along with the mid-latitude to Arctic difference. However, the unnatural oscillating jet disturbed by Rossby waves completely switches up. The amplification of temperature anomalies and movement talked about before forcing the reversal and downwards forcing of the reversal through wave breaking, which completely switches up the surface pattern pretty much. I would argue that the quicker it takes, the more it switches it up due to the less movement of the pattern which is essentially a reversed tropospheric Rossby wave pattern from rotation occurs. So a quicker amplification of Rossby waves, the better for us, especially this Winter.  

The recovery is not necessarily as quick as you would think it would be if the MJO quickly re-transfers back. The radiative heating transfer can take months to properly recover, quicker at the surface though, in the Stratosphere and that implies a less zonal potential from downwelling the rest of the Winter. So, the earlier the better. The lower Stratosphere takes the longest to recover and so we kind of lose the connection assuming a major SSW were to happen.  

If a PJO were to occur, it's our best scenario for this Winter. Now, in my opinion, we are at a potentially god scenario. They are typical with long-periods of wave activity going into the Stratosphere. Essentially, what we've been having since November ish with pulsed wave activity though not as strong as it has been in times before. I also suspect that's why 2018 was such an impactful SSW, as it was a PJO scenario.  

The anticyclonic wave developing over the north Pacific connecting up with the main vortex is a very good sign in my opinion and the +VE wave driving just to the south over Greenland to Europe could also be good in the future. This temperature gradient will be really good signs for a split if the southern wave could become an anticyclonic wave connecting up with the main vortex. The clear polar-night jet formation is another good sign. However, right at the end of the run, it’s still not a particularly high possibility. However, assuming an eddy forced trop-jet connecting up with the Strat polar-night jet then we will have a good situation.  The significant polar-night jet occurring on one of these runs is in my mind that we're at least in with a chance of a major SSW and given how the ground is evolving, this is our best chance for a while.

Looking at the specific setup into the future. The current runs have that meridional jet fired up by the eddy flux pushing towards the higher latitudes in the Arctic. This is a stronger flux into the mid-upper Strat (not quite at the Stratopause level yet and sometimes, top down is a more viable option but we'll have to wait and wait for this one. Often I find that SSW's are delayed and we aren't by any means guaranteed a SSW. I will often assume we are in this post just because I'm trying to analyse the setup deeper into the future. This is a cautious attempt to look at the best case setup.

The different levels of reversals at the equator and showing up mid-latitude in the mid-upper Stratosphere are more than what happened last time. The setup with the polar-night jet and strong deep-rooted flux + mid-upper meridional anticyclonic wave that I've been talking about is good for Rossby wave refraction. Again, it's still way way into the future. We've seen this before on the models.

This can easily be undone and messed up and I talked about that possibility earlier. If the polar-night jet doesn't get rooted out by a strong enough thermal gradient (e.g. we don't see a strong +VE anticyclonic wave or the polar-night jet is being overblown on the models or both then we end up in kind of a bad situation. However, if you don't play the game you can't win) then we get a Stratospheric downwelling of westerly winds and forcing a large +VE NAM response. I suspect that'll leave the convective forcing at a low for a while. That's an unfortunate possibility of what happens. The suppressed and active convective phase is dominated by zonal wind deviations. The tropical forcing from the GWO becomes an extension of the +VE TNH phase (/turning into a +VE TNH pattern) being stuck in a low AAM phasing situation and the evolution of the atmosphere becomes increasingly barotropic from the top down and the vortex spins up again. This feels like it could become a +VE EPO situation and the expansion of the Hadley cell would be pretty much entirely expected in this situation.

The thermal gradient if it becomes big enough to replace the energy in the Arctic, it will become increasingly baroclinic and that forces, the anomalous polar-jet displacement and the reactionary atmospheric wave response which flips the reversal and positives on the graph. This would likely result in the AAM response to be increasing the AMB through rising frictional torque I would suspect. This is as with a net easterly wind, the rotary force on the earth slows down, transferring angular momentum out of the earth and into the atmosphere. The frictional torque response will lead to the synoptic SLP pattern having to balance out the atmosphere by decreasing mountain torque and retracting the north Pacific jet. Now depending on the exact scenario, the separation of two jets and the increase of tropical forcing into a rising Rossby wave over the Atlantic is the generic scenario that'll likely be slightly altered closer to time if a major SSW were to happen.

Wave-2 is clearly on the rise right towards the end of the run compared to Wave-2 which is another good sign assuming it keeps rising. Then with the shrunken vortex, a split would be very likely. So, taking the 12Z at face value and it's very good. With the strong Wave-1 lasting right up till the Siberian wave properly develops with the Uralian omega block rapidly expanding in the Troposphere. We saw a similar evolution with the one earlier this year, however, we didn't have such a good Greenland-Svalbard signal. If that forms a dipole then we've technically got a tripole but that's just a bit of fun my mind had as that's a typical dipole that sets up. Again though, good signs are good signs on the models and we've been moving towards them for a while.

Looking at the Wave-2 strength towards the end of the run as it's being transferred into the Strat and it really does look like a pretty perfect planetary wave setup. The energy transferred from the Rossby waves into the Strat is a clear opposite of the tropopause so a slightly deeper rooted trough than I initially thought a few days ago, which may mean a higher reach for the eddy flux but it's not a particularly big matter, I just noticed it.

The Strat centre of the waves are very interesting as well. A south Greenland centre is a pretty good setup and I'm pretty sure I've seen this pop up on a few case studies I've seen before. Then a slightly displaced Uralian wave with a wider Rossby wave meaning that it's more over the Kamchatka area but nonetheless, it's the best I've seen in years. However, at this range it is still a wait and see.

Not everything with a SSW is black and white, there aren't exact setups just guidelines. If a split occurs, most of the time it should favour us, as we're at a higher latitude than we tend to think. Also, a split here, in this evolution, with a few days of planetary wave rotation, is more having the strong zonal winds retraction towards north America and Russia. So it's a fairly good sign of the forecast being favourable towards a systematic reversal and a typical major SSW evolution if things went right enough. I couldn't tell you if the numbers and temperature gradients are enough to force a reversal here and I don't want to because it's one run and even though, I've written a lot here, it's mostly just been about the possibilities I see occurring.

At this range the range of possibilities is rather large and so this specific run focusing on a fairly split focused set of circumstances is neither good or bad or maybe both. Who knows?

Oddly good thing about weather forecasting, you can still make your own conclusions once you're beyond about 30 seconds ha ha.

The baroclinic tilting with height of the vortex and it shrinking (apart from the top of the Strat)  is a good sign but just that for now. The tilting isn't particularly strong  away from the tropopause here but it's been shifted away from the initial vortex.

Right at the end of the run, we see the meridional temp increasing quite strongly & the temperature gradient pre-that could well be a driving force force for Rossby wave refraction towards the polar vortex. That - VE noodle pushing down really helps force a potential split.

The EQBO setup is a fairly typical one with a late stage EQBO, westerly trying to form in the far upper Strat. The downwelling properly could still take a few months, however, right now it's now in the crucial part of the late stage phase. Where we've got weak WQBO at the surface with a slowly downforcing -VE winds and colder forcing into the mid Strat. If this aligns well enough in January with +VE temps and easterlies mixing with the potential SSW, then we've got a near perfect scenario in my mind.

Looking down at the surface and despite the -VE TNH, the extension of the Pacific jet appears to reach the Atlantic and force the building of a ridge and until the +VE NAM changes, which to be fair it is forecasted to sort of do, then we're still in a bad situation. The +VE EAMT hasn't faired well for us with the extension of the Pacific jet coupling with the Atlantic jet and the pattern flip in north America essentially being meaningless.

The frictional torque response should occur late December and that might change the pattern setup, with the -VE frictional torque acting to balance the zonal winds into January and replace the +VE north Pacific basic non-wave setup w/a clear Rossby wave setup an a flip to -VE near the north Pacific leading to more backing of the Alaskan ridge. If this reaction occurs well enough, then that's part 1 of our SSW journey done with, pretty much a renewed pulse of our Greenland wave (it would be alternated to over Greenland) and if our Ural wave can materialise as well, that's 1/2 of the job done. The fact that it's on the ensembles is a good sign though. Another potentially good sign is the slightly blocking on the ensembles an this makes some sense given the eastern north American wave is allowed to exit and the north Atlantic ridge becomes flipped and we go into a neutral of -VE NAM scenario. We'll see though.

The MJO is currently wandering really in the middle of nowhere, or rather were we don't really want it. Most of the convective envelope stalled over Africa for quite a while on the forecasts. A good thing potentially if a SSW were to happen, as it could force the MJO to push quickly towards a strong 5-7 phasing. Without it, we're kind of lost for January without any torque breaks. I want snow on my birthday as I'm being a bit selfish but hopefully the setup favours me ha ha. That's enough for now, I'm tired. 

 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4982285

[TillyS]

50 minutes ago, Harsh Climate said:

Just as I thought, close to being a mild outlier.

For me the models are collectively looking very nice now, I see nothing other than blocked and cold/snowy weather the further we go into January. Just patience is needed now as the models get to grips with this big upcoming pattern change. I expect to start seeing some stellar runs over the coming days. Maybe the odd snow surprise for more northern parts of the UK over the coming 7-10 days to wet the appetite,but main course coming mid January onwards and should be difficult to shift..

Just a couple of minor points of correction to make here.

First, Luke was referring to the 0z not the 18z, which is where your ensemble chart is from. The 0z ensembles are here:

Second, an outlier isn’t something which is on the milder or colder end of the spectrum, it’s an operational which lies partly or in whole outside of the other members entirely. Neither the 18z nor the 0z are close to ‘outliers’ as such. They each vary at times from milder to colder, as you’d expect.

Moving on, the only blocking that is persisting for the time being on the models is the Iberian High. Here’s the ECM at T240:

 

For as long as that is there and there’s no consistent northerly blocking there really isn’t a clear path to prolonged UK cold. The best we can aspire to with this kind of set up are northerly incursions, which as you say may bring some snow surprises especially to the northern high ground. One of those might then lead to retrogression of the high into mid-Atlantic but this isn’t really evidenced in the models as yet. There’s also sadly no firm evidence for a big pattern change as yet. We can but hope.

 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4982304

[Cambrian]

Changeable with fluctuating temperatures during Christmas week on the 0z ECM operational run. The mildest period is tomorrow, Christmas Eve, good for travelling, the UK and Ireland in the warm sector of a low pressure system between Scotland and Iceland. 

 

This moves east to merge with the trough over Scandinavia by day 4, trying to bring down a northerly on its western flank, but this is held off by low pressure heading in on a much more southerly track from the Atlantic.   A seesaw in the T850s for a few days thereafter.

 

This low pressure is the main feature of the coming week, passing through the UK and Ireland to the North Sea by day 6.

 

It gets interesting by then, as temperatures have dropped off considerably. The North Atlantic is prone to wedges throughout this period and as a result, the following low pressure is being disrupted and is sliding southeastward to merge with the base of the North Sea low at day 7. The T850s at day 8, New Year’s Eve, show the extent of the cold air in the mix and a long way south too.

 

Mild to begin with, but overall changeable, cyclonic at times and increasingly cold. All in all, a quite seasonal end to the year, with plenty of interest in the models.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4982346

[bluearmy]

I was thinking that I couldn’t really draw a better mean anomoly for early week 3 than the gefs shows. The gem and eps not so far away . A tweak here and there.  The individual members are pretty chaotic though so tough to analyse where we’ll end up 

and then I came in here !

 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4982352

[Kasim Awan]

Not sure why we are suddenly taking day 10 runs from the ECM as decisive. The ECM had us all in a very cold northerly today 10 days ago.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4982592

[Derecho]

Evening all. Hope all is well. Haven't posted much recently given the dud charts at short range. The EC ens mean isn't really shaking off the Iberian heights for good.

Perhaps there is a brief relaxation around T168 on the OP but the Azores high is keen to ridge east again.

So still a poor outlook to be honest. The SSW event is understandably the main area of interest at the moment, we seem to be hitting a wall of predictability around the New Year so hopefully this time next week we will have a good idea if the reversal takes place around Jan 6th.

On further note, the MJO is now going into strong phase 1 and maybe into a strong phase 2. These are cold composites for an El Nino January but as I mentioned in an earlier post they are quite different so not sure how reliable they are. Only convincing signal I get from these is a mild Canada.

Which funnily enough is what the anomaly charts currently show.

The upcoming period should be a useful test of whether the MJO anomaly composites for phase 1 in January are any good. However I'm unconvinced of any potential blocking until the 2nd week of January.... maybe a bit earlier if the MJO shows its worth after all.

Even though the weather gods were not feeling festive this Christmas, they at least greeted me with another great sunset this evening.

Will probably post shortly after Christmas if any model output in the somewhat reliable period is of any interest. Merry Christmas all.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4982709

[Mike Poole]

2 hours ago, KTtom said:

So, if im reading these correctly a 10 to 20 pascal possitive anomoly over Greenland / Iceland area. Does this equate to high pressure, which im sure most instantly think when looking at those charts, or just not quite as low as normal? Quite a difference between the 2.

It is the average of 100 runs on the 46 dayer.  So it could be high pressure on just a few runs, or it could be not quite as low as normal pressure on all the runs.  The end of January chart needs to be viewed with an eye to what will have happened in the strat by then, but the earlier chart on which I think you were commenting - a very similar anomaly is shown on the GFS 0z at T384 (this is heights not surface pressure, but it is showing the same feature):

But in this case, we can look at the individual realisations and see what this anomaly is comprised of, from the postage stamps, here looking at the actual pressure/heights:

And here looking at the height anomalies for the individual runs:

So it is clear from these that the mean anomaly is caused by a few runs with strong high heights in the region, some runs show a ‘black hole’ (off the scale) individual anomaly.  So it is a signal for high pressure in the region, the question is will this signal grow as the clock ticks down to zero?

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4982813

[bluearmy]

3 hours ago, KTtom said:

So, if im reading these correctly a 10 to 20 pascal possitive anomoly over Greenland / Iceland area. Does this equate to high pressure, which im sure most instantly think when looking at those charts, or just not quite as low as normal? Quite a difference between the 2.

Back to the more reliable timeframe and UKMO sticking with the UK limpet low idea to see in the new year..

 

59 minutes ago, Mike Poole said:

It is the average of 100 runs on the 46 dayer.  So it could be high pressure on just a few runs, or it could be not quite as low as normal pressure on all the runs.  The end of January chart needs to be viewed with an eye to what will have happened in the strat by then, but the earlier chart on which I think you were commenting - a very similar anomaly is shown on the GFS 0z at T384 (this is heights not surface pressure, but it is showing the same feature):

But in this case, we can look at the individual realisations and see what this anomaly is comprised of, from the postage stamps, here looking at the actual pressure/heights:

And here looking at the height anomalies for the individual runs:

So it is clear from these that the mean anomaly is caused by a few runs with strong high heights in the region, some runs show a ‘black hole’ (off the scale) individual anomaly.  So it is a signal for high pressure in the region, the question is will this signal grow as the clock ticks down to zero?

Mike gives a good indication of how mean anoms work. And it says to look at heights rather than just slp. Infact I would always look at heights before slp on ens mean output post 10 days.  Then check the 552 dam contour. It’s a fair indicator of how cold the air is likely to be. unless there is very strong indication that there is a big high and continental feed where heights above 552 can deliver cold conditions it’s a good pointer.  A good ridge/trough pattern can be revealed as likely not cold without that 552 dam line south of the U.K.  the further the better 

Anyway - back to the ec46 thru jan 

heights and slp anoms 

8/15 Jan shows solid upper ridge just to our west with a mean surface high probably centred between Iceland and Ireland 

beyond mid month it’s a tough call. Given that the mean weakish  vortex is shown just nw of greeny, I doubt we’d see a stonking greeny ridge (but at this range that could easily evolve that way). More likely an griceland feature. Whilst the mean upper flow shows a euro trough, it’s unlikely to show a mean 7 day ridge beyond week 2 in the Atlantic sector. That would be a v strong indication- watch this space btw if a split ssw gains mean ens support over the next few days. 

there should be a concern that an ssw split could evolve in a poor position re the upstream segment and that would  certainly change the ec46 January outlook beyond mid month.  We do look to be in a very good position re January cold but as we’ve learned over the years, never underestimate this country’s ability to pluck failure from the jaws of victory ref wintry weather! 
 

       

 

      
 

EDIT

I also should have pointed out that we know the nwp doesn’t do post ssw period very well (especially if we get a quick downwelling). This is the first time we will have seen the eps running at such a high resolution with an impending reversal.
The ec46 will likely not be handling the January period as well as it would without the reversal. It may be that what we currently see being churned out with reasonable consistency might be quite different once we get flow reversed high up. A gentle reversal below -10 m/s  may well not resonate too much but the speed of the slowdown as currently modelled going and then going beyond -10m/s will likely increase the chaos to levels at which the model cannot be  expected to cops with. 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4982843

[bluearmy]

Just saying it again because some of you don’t seem to have realised, the ec control is indeed effectively the ec op running out to day 15. BUT, because all the 50 eps members are at the same resolution, it is of no more value than any of the ens members beyond day 8/9. 
 

whilst no op should have any credence beyond day 8 because of the chaos that exists in the atmosphere, I get why some folk like to use the gfs op for trends at that range and beyond as it is higher resolution than the gefs members.  But in the ec suite, with all the members at 9km and using the same algorithms as the op and control, the control is just another member.  No one would pick out run no 37 and say ‘oh look, member 37 has a huge scandi high and associated bfte at day 13’ as being anything noteworthy amongst 50 runs.  so please let’s not use the control as an indicator of anything apart from seeing where the op (effectively another ens member post day 7/8) may have gone beyond day 10. And as someone used to say - that’s JFF 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4982847

[Catacol]

Merry Xmas everyone!

Trop split quickly followed by Strat split

Roll on The New Year….

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4983518

[Catacol]

Well - here we go. Time to forget the Xmas chase entirely and focus on the path into January that always looked a more likely landing zone for extended cold given the ENSO signature.

And the signals are lining up. First of all we have the expected firing up of mountain torque, sending the pacific jet into overdrive and prompting eddy patterns in the atlantic

Don’t underestimate the likely impact on the vortex as well further down the line of such a massive spike off the Tibetan plateau. GLAAM now very strongly positive

…and this now means we are firmly in coupled Nino territory. GWO orbit consequently climbing fast, and this means high lat blocking and probably split flow potential too

Supportive of this very positive overall picture is the MJO which has not fallen into COD territory as EC and GFS had it doing - instead we have a decent amplitude phase through 8/1 until we get to the end of the calendar year and the wave resets in the IO.

All of this means we have an extremely positive envelope for blocking potential to work within as we move through New Year and into the first week of January. NWP beginning to play catch up.

And running parallel to this, the vortex looks set to be shredded. Strong poleward heat flux in week 1 of 2024 likely to provide a killer blow

A savage warm air assault on the vortex illustrated here - mostly wave 1 but with some wave 2 impacts also.

Currently the likely angle of this split (which is what we look to be heading towards) puts the U.K. in a good place for further impacts with one vortex shard breaking towards Scrussia and the other into Canada, allowing further blocking potential over Griceland - just in case the very positive tropospheric drivers aren’t enough!

Beyond this? Best to wait and see. All I will say at this early stage is that a 2018 style event is possible which, given we are 6 weeks earlier in winter, would be brutal. But there is still much to unravel yet and best not expecting the kind of downwelling response we got 6 years ago quite yet. Need to see how blocking emerges, how the vortex actually splits - if it splits.

This is going to make for some fabulous watching. NWP is going to upgrade steadily.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4983959

[MATTWOLVES 3]

Firstly I would like to point out that if a major ssw occurs then it has the dynamics to alter literally everything in the atmosphere! Infact scientists are now only realising how it influences even greater and more widespread areas than once previously thought. We are not just talking of a reversal of the mean Wstly winds here it can literally kick the entire NH profile right up the backside and even influence parts of the Southern Hemisphere! So to think it wouldn't be able to budge Iberian Heights is a tad premature.

I feel we are now seeing evidence from the ens that a pattern shake up is getting very close. The met also have to be feeling pretty confident to be mentioning prolonged cold spells at this range...if it was much less likely then I'm pretty sure they wouldn't even be flagging it up at this stage.

There's something a stirring in the air and I feel more and more confident a gr8 change is coming.

So I suggest you sit back and contemplate said events while you butcher your turkey dinner and wolf down the mince pies...to be washed down by a gallon of wine or single malt...what ever takes your fancy.

But let's be honest here...how often at this time of the year are we seeing something very exciting weather wise in the making.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4983637

[TEITS]

My view on the models is this.

Whilst we all know the rollercoaster ride of following potential cold spells in the output. However it is the thrill of the chase that can be just as exciting as the actual weather it brings. I'm sure storm chasers will say the same thing despite often being a bust. In recent years the most disappointing aspect of our winters is the lack of cold spells to even chase. That certainly cannot be said for the position we are currently in.

The GEFS mean SLP for Iceland, Scandi has certainly changed with both showing an increase to 1020mb.

Based on the output if the blocking does occur then it is much more likely that our cold spell initially originates from blocking over Greenland/Iceland with a corresponding N/NE,ly flow.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4983998

[Cambrian]

A very interesting period underway with the NWP models, that are in the process of very actively modifying the near-reliable as well as the longer ranges. 

There’s quite a stark difference between yesterday’s 0z EPS for day 7 and today’s day 6.

 

The upper trough heading south from Scandinavia into Italy and the stronger heights to the northwest of Iberia have both been moved northwest to the order of a thousand miles or so, bringing the trough through the UK and Ireland, at the western end of what is now actually a deeper trough running through the Baltic Sea. 

This has the effect down the line of setting up low European heights by day 10 (right), compared here with yesterday’s day 11 (left).

 

There is a polar high anomaly too, bringing cold air westward through the Siberian Arctic towards Northern Europe.

 

It’s this combination of developments that ultimately digs out the Iberian heights and makes the difference between the continuation of average to slightly above temperatures across the continent and the beginning of a European cold spell. 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4984089

[lorenzo]

While on average the “downward impact” of SSWs is robust, not all SSWs appear to couple down to the surface. Most studies agree that about two thirds (Charlton-Perez et al., 2018; Domeisen, 2019; White et al., 2019) of SSW events are characterized as having a visible downward impact (e.g., persistent negative phase of the NAM or NAO in the lower troposphere and/or the lower stratosphere, (e.g., Domeisen, 2019; Karpechko et al., 2017). One factor affecting the appearance of downward impact is the tropospheric NAM index prior to and at the time of the SSW. If the NAM is already negative, there will be a vertical connection to the negative stratospheric NAM. On the other hand, if the tropospheric NAM is strongly positive prior to the SSW, the appearance of vertical coupling is less likely, at least initially. The same is true for the NAO: if a negative NAO is present at the time of the SSW, the downward coupling is instantaneous but short-lived, while otherwise the negative NAO often appears after the SSW event (Domeisen et al., 2020). The stratosphere is one of several factors influencing the NAM, with most NAM variability being generated within the troposphere (and from surface interactions). The stratospheric influence becomes clear, only statistically, in regressions or in composites of many SSWs. Specifically, the concept of surface amplification of the polar pressure signal (Figure 3) will not be apparent during every SSW, but it becomes clear when averaging over many events. This is because the troposphere is highly variable, and the stratosphere represents a modest influence that is active during the cold season.

Just a moment...

AGUPUBS.ONLINELIBRARY.WILEY.COM

 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4983681

[Eagle Eye]

In case the vortex needed anymore destroying, a fairly rare wave-3 triple appears to be coming up on the forecasts now for the mid Troposphere and should connect up. If that comes off then we would probably have the best chance for the vortex to be completely destroyed and the best chance for a good Trop response to occur. 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4984280

[Eagle Eye]

Not surprised we're trending away from a SSW on the EC46, it's gone from Wave-2 to Wave-1 and the members are struggling to work w/a strong Wave-1. However, the trend is looking towards a Wave-3 in the Trop later into the forecast which is where our potential cold spell also comes from. That Wave-3 should push into the Strat as a tripole beyond the current forecast time and I suspect a lot of those members don't have that signal yet. However, if we continue to move towards it then there's nothing to worry about, essentially it's a delay, which happens with most things forecasted. Anyway, the vortex is likely to stay weaker than average throughout the next while, meaning a better chance of cold even w/out or a delayed SSW. 

 

Could still get a SSW first time if the Wave-2 is stronger (mainly the wave around Greenland needs more strength) than its currently forecasted. It's been forecasted to be stronger than it currently is being forecasted to be to be fair. 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4984402

[bluearmy]

I think the debate about the 12z eps is interesting

no way should we be taking the ec46 data ahead of the eps 12 hours later. The eps is still a large sample at 51 members and it is much higher resolution. 

BUT the 12z run is quite a flip and we should always wait to see the following run after a flip before going overboard 

the eps suite has a habit for the ens members clustering around an erroneous solution when it throws out an unexpected run.  I’d be quite dismissive but then the gefs are still not reversed on the mean and the op swings back and forth. 

I think there is a little too much confidence at the moment on a reversal - however there is also the point that if we see a strong reversal get down to 70N then it will probably not make much difference and could even be more effectual than a tech reversal which is fairly tepid and doesn’t last too long 

2 minutes ago, blizzard81 said:

So....... Can somebody clarify if the EC46 is still run from 00z data or not?

It’s a 00z model and is completely separate from the eps 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4984532

[Catacol]

Jittery in here tonight - even X is causing some angst! For what it is worth the 4 people on X I follow with some genuine respect are Simon Lee, Anthony Masiello, Eric Webb and Amy Butler. Amy has gone quiet this season and I think Anthony has abandoned X for now, but both Simon and Eric are very active and worth following. 

Those questioning - will it, won't it....and it hasn't happened yet might perhaps reflect on the much wider context. I put out a post last night that gave a pretty full analysis of what is going on - but to reiterate in brief: NWP output is not produced in a vacuum. There are processes and trends going on that are still identifiable from a human perspective in a way that computer modelling doesn't see, and the context at the moment is strong for northern blocking in the medium term. Momentum is high, the pacific jet is extended, the MJO is in a good place right now. These don't guarantee a cold block because twists and turns happen but I think estimates of 10-20% chance of cold/snow are miserly. We probably had that kind of % over the Xmas period once the MJO began to falter, remembering that the longer term drivers were not anywhere near as well aligned in mid December as they are now. I think chances of cold given the current context must come in at better than 50% and I'd be tempted to go with 70%. 

And this is without an SSW. If we get it, and the odds are in favour, then we have a split driven through the north atlantic sector that must - as Eric Webb has posted today - increase the chances of extended Greenland blocking. And if we get that 2018 style shard from the split dropping down into Russia then we can expect frictional forcing to support frigid easterlies. This will be further down the track and we must watch closely what happens in the strat in the next 7-10 days, but the trends are looking rather good I'd say.

For those who feel NWP is the only way to go and are not sold on the stuff above, let's just go with the EPS for now. The trend towards northern heights before we get to the end of week 1 January is bedding in. If you don't value the drivers that make things happen, then let the computers provide some confidence.

By Jan 10 the signal is strengthened further.

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4984601

[Met4Cast]

Personally I'd prefer a SSW doesn't happen (though I would 100% take a very, very weak SPV)

We've got some very, very favourable trop led drivers coming into play during January without the help of a SSW, whilst a SSW could potentially amplify the cold signal/prolong any cold/blocking we end up getting, it could also "reshuffle" things into something unfavourable for us. 

SSW's are always risky.. exciting when nothing else is going our way but always a concern in situations like the one we're looking at going into January. An extraordinary amount of luck and January could be very, very special.. 

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4984505

[Catacol]

2 minutes ago, Battleground Snow said:

Maybe she's reading your posts

Just posted 

Ah - missed that one so thanks. She is great. Very knowledgeable and passionate about the stratosphere. We have all the big guns posting with confidence about what is about to transpire despite the earlier Huffman tweet.

From my very amateur perspective the flux she discusses here, which I also put into a post last night, is not well modelled by NWP. It is an area that is perhaps open to human interpretation more than others. When one factors in the consistency of the Ural/Aleutian pattern in recent weeks and then the magnitude of the jet extension happening now as a result of a huge +EAMT event I think we can be confident that the strat is about to hit very hard indeed, and perhaps harder than modelling is projecting still. Given that NWP underestimates flux impacts on the strat at long lead times we have a modelling context in situations like this where output is constantly playing catch up. I remember the same in 2018...at least I think I do!

GFS modelling on 24/12 and 25/12 was better for a strat split than today. If we get a return of the split profile tomorrow, making 3 out of the 4 most recent op runs seeing a split, then I will start to breathe a little easier. If we end up with a reinforcement of today's less bullish runs then it will be nail biting time.

But even without a split we are looking at a context very favourable for cold down the line. However, I'm greedy. I want that split because I want to see chances of something akin to 2018 but 4-5 weeks earlier happen if at all possible!

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4984618