Model discussion highlights

[Tamara]

Another brief one-off interjection to the thread as means to measure context of how things have evolved and try and offer some insight to the present:

Posted 29 November:

An attempted musing sees me point to the remaining pockets of -ve zonal winds in the troposphere/stratosphere layer orchestrate with rarified retrogression of the substantial blocking structure to Greenland as inertia across the Pacific weakens (becomes more coupled to base state). Highly likely that this retrogression will eventually edge further east towards Canada (and try and evolve the pattern more -NAO west based)

Further out, an attempt at reload is conceivable with the GWO en route back to Phase 4 and renewed rises in angular momentum tendency. However, heading back to the starting discussion of this post, there is great uncertainty about this - based on the said reasoning for tropical correction to re-assert a further active cycle. The chances are equal that this might not materialise/be delayed.

So to reiterate, at least from my viewpoint, a lot of caution and restraint in over expectations of wholesale stratospheric destabilisation around the end of the year. At this stage, if it is to happen at all, closer to the mid-winter period seems more feasible. However, there are plenty of advanced pitfalls that can be foreseen, notwithstanding it is a ridiculous time period ahead to try to speculate.

..................................................................

 

Posted early December:

The question remains long term how far the retrograde evolves and how the -ve NAO behaves accordingly. The intuitive reasoning remains that attritional battle ground towards NW Europe culminates in an attempted breakdown - which tries to re-set to another Atlantic trough and amplifying downstream ridge. Does the Eurasian feedback reload this as another Scandinavian block, or, does the polar jet then prevail and create a more traditional zonal pattern with heights across mainland Europe?   

Finely balanced in my neutrally objective opinion as much more work will be required from the tropics next time round to assist, with angular momentum at a lower base level than it has been up to this -VE EAMT. Reasoning behind that has been given fully already this week.  I don't personally, at this time, believe the Eurasian feedback signal on its own is enough.

However, all of that is some way ahead. From my own point of view though, the evolution of the diagnostic remains the focal interest.

...........................

In short and as simplified as possible :

1) Tropical convection patterns should be looked at in respect of their periodicity timeline (recurrence) when attempting to look in extended periods. Bias confirmation (weather preference influenced) processes attached to this can skew expectations.

2) Renewed orbit of tropical convection to Pacific is verifying but less coherent as per the caution previously exercised and in tandem with organisational/coupling of polar vortex & troposphere. Neither, genuinely intended in the nicest way, should have been a surprise.

3) According with renewed eastward propagating tropical convection, relative atmospheric angular momentum has seen a rebound and GWO Phase 4 verified as estimated in above summary. This has reloaded the Atlantic trough and downstream ridge scenario as led up to higher latitude scenario of early to mid December when AAM was previously at elevated levels (higher than currently)

4) BUT: Factors discussed in quoted summaries and in points 1) and 2) are meaning that, as suggested previously, that emerging mid latitude blocking scenarios look set to prevail rather than evolution to higher latitude blocking. A case where applying x+y= equations in respect of rising AAM & eastward propagating tropical convection through phases 6/7 etc are not inextricably magic bullets to high latitude blocking & weather preference gratification.

It is very difficult to communicate realities onto ideals in this internet format without sounding like an annoying preacher. I/we all have ideals. However analysis is truthfully not worth the time and effort if it does not suspend preferences & hopes.

Looking ahead: 

Clearly two months left for UK weather watchers to keep looking for the cold weather patterns they hope for. As muted in those early summaries, it could be that another active intra-seasonal cycle of tropical>extra tropical momentum transport re-visits heading into the second half of winter and in tandem with traditional passing of peak upper vortex intensity create another period of instability within the polar field which in turn creates a re-configuration at mid latitudes and implications for polar advection such as seen at the beginning of winter - but this clearly cannot be fleshed out coherently and speculated further about at this time.

Melhores desejos para 2023

 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778436

[mushymanrob]

Nothing of interest?...

 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778493

[chionomaniac]

1 minute ago, Ali1977 said:

Is this good news ref SSW type Synoptics? 

Yes, as it shows a great tilt/stress of the vortex from top to bottom by day 16, whereas today it is a perfect spinning top. 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778594

[Eagle Eye]

3 minutes ago, chionomaniac said:

Yes, as it shows a great tilt/stress of the vortex from top to bottom by day 16, whereas today it is a perfect spinning top. 

Agreed, the polar-night jet sort of helping here because it increases thermal gradient when there are Eddy's integrating into the Strat (polar-night jet oscillation) which could possibly further the baroclinic tilt by helping the misalignment of the thermal gradient. So despite being Wave-1 dominant we may get lucky though I'm not entirely sure of how my mind came to that conclusion it just sort of does it's own thing from piecing together what I remember from reading about the polar-night jet oscillation about a month ago.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778598

[Uncertainty]

There’s a time to throw in the towel and this ain’t it. Sure the most likely outcome is that January ends up milder than avg but we only know the general set up for the next 10-15 days, anything after that and you’re into JMA / CFS / EC weeklies territory.
 

Unlike other Jans, we also have an SPV forecast to weaken (from a v high base), the mjo in a favourable phase for blocking (albeit dubious amplitude) and a NH profile forecast (in the extended) that is not far off ideal for causing an ssw (albeit most likely a displacement). In fact if it weren’t for the info in brackets we’d be heading back to the freezer (damn you brackets!)

In early 2020, we had an mjo forecast to sit in P3/4 and a rampant, record setting fully coupled SPV. If this were the case now there would be justifiable towel throwage, even, in fact especially from me!

The strat for me is ripe for the taking, its present strength is also its weakness you might say. The Aleutian low looks to stick around for there next 10-15 days at least, if we can tag team it with a genuine Scandi - Greenland pattern for a week or so then the long term outlook at all levels would be subject to big changes. 
 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778613

[Met4Cast]

I'm finding the comments moaning about people "writing off January" quite extraordinary given the same people don't seem to make the same observations when people are predicting cold a month in advance. Why is it okay to do one but not the other, I wonder?

Why is it okay to predict cold in a months time but not okay to say cold is unlikely despite both using the exact same teleconnections?

The MJO is likely to move into a more favourable phase for blocking, however; The AAM is low & the MJO amplitude looks to be quite low too. I suspect we'll instead see mid-latitude highs rather than high latitude. I.E a European high extending north into the UK around mid-month seems likely, blocking over Greenland or Scandinavia seems unlikely. 

So.. a zonal, mildish period of weather seems very likely before high pressure builds in towards the middle of the month. There is unfortunately, currently nothing to suggest a cold period is likely in January as things currently stand. 

Average or slightly above seems favoured. The SPV is moving back to Greenland & there are signs the stronger u-winds will begin to downwell. So.. it's going to take a lot more than the MJO alone to shift us into something cold.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778540

[Eagle Eye]

1 minute ago, Ali1977 said:

I’m liking the sound of a Polar Night Jet, she sounds like someone who can pull us out of this (standard U.K.) rut.  

Ironically, it's actually classed as a largely increased Strat jet that half led to this problem in the first place but it's the fact that it's evolving and connecting up with the subtropical jet in the Trop that's directed by Eddy's that means that the North Pole being in daily darkness right now increases the thermal gradient between the cooling Strat vortex due to the polar-night jet oscillation and the thermal Eddy's from the Trop, there's a larger thermal gradient than there normally would be. Which is good for abnormal heat transfer and hence it may help the onset of a SSW.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778611

[Eagle Eye]

Right well it's time for my first proper look long-term since before Christmas so hope you all had a great Christmas and boxing day and are looking forward to the New Year...

Time to watch how the seven nation army are evolving and by that I mean the AAM, MJO, Stratosphere, Troposphere , GWO and I'll chuck in the QBO for good luck!

Starting with the AAM.  Typically if we want a more blocked pattern with colder prospects for us we want a positive(+VE) AAM as the momentum increase which is directly related to the total integration of torque in the Atmosphere as proved by the equation:

dM/dT = r x F

dM being the differentiation of Momentum

dT being the differentiation of Torque

And r x F being the distance from the origin times the Force. r x F being the equation to find out torque.

Hence momentum is the product of the total torque in the atmosphere (well, essentially, there may be more to it)

Equation thanks to Reading University, anyway...

The reason momentum increasing in the Atmosphere is good for blocking prospects is because torque is the rotational force around a pivot point and we know that momentum is directly correlated with the total torque. That torque will draw warm air up and slow down the westerly jet stream due to increased easterly wind integration in the Atmosphere and so an increasing or sustained +VE AAM should theoretically weaken the zonal winds.

Well, if we look at the zonal winds in the Trop pattern from mid to late November through to early December we see a fairly weak zonal pattern evolving just as the sustained +VE AAM at the time suggested there would be. It's good as it shows the link between the two (though this is excluding external facts, the MJO and AAM seem to have been the main reasons for this though) and can be used fairly accurately as a forecasting tool if you include the GWO and therefore you get yourselves a fairly decent signal for working out long-term signals though there are no real numbers that I can put to it in terms of how long or how strong, you've just got to go on your gut instinct. The upper Trop pattern for November suggests that northern blocking is more likely (slower winds typically mean a more oscillating jet and transfer of heat polewards) and we did get a lot of northern blocking especially towards the end of the month. I think the zonal looking Atlantic is mainly to do with how the first part of the month evolved because the second half I don't think saw such a strong Atlantic setup though it did throw a few spanners in the works, that was more due to shortwaves and areas of stretched tropical influence quite late into November/early December (ish) I think it might have been.

The current +VE AAM does look to be slowly fading as we are losing (negative or -VE) some mountain torque (likely East Asian as that seems to be a pattern trend emerging where collapsing waves of energy followed by increased energy waves with other interactions as well are evolving) over the next few days and that will likely mean that early January does not offer us much hope (unfortunately Vortex Intensification or VI in the Strat has dismissed much hope I had of energy being scattered well by the anomalous East Asian Jet Retractions and/or Extensions) but there is the possibility of a Scandi high if we can get a well formed Eurasian Feedback to this loss of mountain torque as the one last time that could have delivered a Scandi high waned slightly too early and we ended up with the dreaded Euro high. Shows how little one thing changing can have either good or bad consequences on how our weather evolves. I'll go over the Scandi high chances later though. As we lose this mountain torque, the AAM may go fairly -VE but I think that's unlikely as it still doesn't want to interact properly with the La Nina oceanic base state and so our +VE AAM chances should remain. Slowly there are tentative signs that we may regain this torque long-term on the CFS and that does make sense with how the repeating rebound pattern we seem to be entering works. The pressure signals are likely quite differing over the East Asian mountains in such an un-amplified but helpful pattern right now as things generally flip-flop when we get into these sorts of situations. Until the AAM or MJO signals get stuck in strongly -VE or phase 2/3 respectively, I think these rebounds will keep happening and if we can sustain one for just long enough at a high enough amplitude, it may be enough to give us some longer-term cold prospects away from a SSW but right now I probably find that unlikely to happen over the coming month or so. Quicker cold events cannot be ruled out of course due to the possibility of a Scandi high and beyond that it's hard to tell with almost all Teleconnections fairly neutral it takes just a little movement to create a lot of 'noise' and we could see the development of a Greenland high though it's looking fairly unlikely for now.

That's three of the 7 nation army done now, onto the MJO...

On the border of phase 5/6 and slowly moving towards being a fairly substantial phase 6 just slightly less amplified than it was in November so under amplified is probably a yes but it's still fairly amplified and we aren't really losing the signal and there's still a few ensembles showing the possibility of it keeping amplification towards phase 7 but the VP shows that we're probably finding the signal beyond phase 6 difficult to interpret and probably we're likely to see it lose amplification and slowly move into the so called COD. So we're probably relying on phase 6 over the next week or so (14-21 day lag probably) and a rebound of AAM (6 day lag initially but can be much longer) to time themselves together and we do get some form of mid to high latitude blocking. An entire pattern flip is probably unlikely as it's usually an amplified phase 7 that we would want for that but that doesn't mean we can't see some form of Scandi or Greenland blocking with a -VE AO by mid to late January. Obviously, the MJO amplification probably won't spike a significant amount of momentum to form that kind of blocking but if it can time itself well with a gain of East Asian mountain torque scattering thermal and zonal energy downstream and maybe allowing for some Eurasian (ish) blocking if it allows for an East Asian Jet Retraction. One of the main reasons why I wouldn't rule January out for cold (especially the second half) is just look at that scatter beyond phase 6 and it's clear that the models aren't handling the MJO well, maybe the ECM is doing better but the amount of spread means that you cannot really be sure off anything so long-term forecasting is likely to be either exactly correct or very far off or anywhere in-between there.

Onto the firth and sixth ones and that's the Strat and Trop patterns...

First thing to note is that Wave-2 does look fairly strong but dips towards the 10th as Wave-1 takes over, I think this is where the initial onset of a SSW would have to happen with strong baroclinic tilting and a large thermal gradient displacing the Strat vortex. The initial onset would then have to be followed by a weakening or dipping of Wave-1 amplitude as we see a second thermal wave forming probably around the North Atlantic area. This would be the best chance of a Polar-Night Jet Oscillation (PJO) type of SSW as that would put a cooling Strat vortex on either side of 'outer riding waves' and that thermal gradient cut push through the middle of the vortex and split it in two. I'm definitely not saying that's what's going to happen here but that is exactly how a PJO onset happens and a PJO is almost entirely linked with a major SSW. So if we can get Wave-1 displacement followed by Wave-2 split then that amount of upward wave flux would likely be enough for strong downwards reflection and a quick weakening of the Strat zonal wind downwards. At the moment that's still unlikely but there's a fair number of ensembles taking the Wave-2 amplitude and ramping it up right towards the end of the run. If that becomes the trend then we can become excited but for now I'd stay calm as that's quite a few hours away.

The zonal winds continue to support the idea that a Wave-1 displacement would at least weaken the Strat vortex and that may translate itself into a slightly weaker (though maybe still zonal) Trop from mid-January onwards but only if we see some downward zonal wind reflection. It means that even if the MJO phase 7 isn't strongly amplified we might see at least a slight weakening of the Trop zonal pattern. So looking long-term is probably our best solution now with a slight increase in cold chances and hopefully a SSW happens with Wave-1 followed by Wave-2 but that'll only happen if we're lucky. We've got to hope that the Eurasian warming signal moving across the Pacific is followed by some sort of North Atlantic (ish) warming signal with increase Eddy's from the North America-Greenland area in the Troposphere and propagating vertically.

In the Troposphere...

Pretty much only the Atlantic is looking largely zonal with the East Asian Jet Retraction helping everyone except us. Still think that the Eurasian feedback across 90E might spread further West and we can get some energy into the Euro high amplifying it but how much is difficult to tell. If we're lucky it interacts with the more Westerly Eurasian Feedback. What looks more likely is the Eurasian Feedback staying too far East and any interaction will be un-interesting and it'll just push the Euro high up slightly. Possibility of a Scandi high remains there but what is most likely is a continuation of this pattern till mid January unless the Eurasian Feedback pushes much further West than is currently forecast.

6 of the 7 nation army done, 1 more to go and that's the QBO...

QBO is still in the Westerly Phase but it seems to slowly be weakening and will likely turn to Easterly but that'll likely be after this Winter is over. Just good that the sleeper signal for the zonal wind is at least weakening and so may start having less of an effect as we slowly go over time. I'm not really focused that much on the QBO as I still don't fully understand how it works.

So overall, the first half of January does favour a zonal pattern as people are saying but the increased tilting between the Trop and Strat layers (especially the upper Strat) could really help with the thermal transfer, in turn weakening the 10-1hpa zonal values fairly well. Wave-1 dominance looks to stay fairly stable so displacement rather than split would be the most likely way a SSW could happen if it does but a few ensembles are showing Wave-2 increasing as Wave-1 and hopefully that becomes a trend but I find it unlikely. What it could do is reflect some of the upward wave movements down and slow down the zonal winds in the Trop pattern so mid-late January we may see that form of downwards (non SSW related) connection between the Strat and the Trop.

Away from the Strat pattern and the Trop pattern will mainly rely on the MJO phase 6 and 7 being more amplified than currently forecast and despite the rebounding +VE AAM, it's probably going to continue to be a forecasters nightmare as per long-term forecasting with multiple contrasting signals and a significant amount of spread on the Teleconnections. As long as it remains fairly neutral then rebounds in AAM from mountain torque events especially can help us in the longer term so it's not all dire in the Trop front but the MJO looks mainly uninteresting unless we get right at the top end of the amplification of the ensembles.

Probably the best Strat pattern is the we see an initial Wave-1 onset causing the oscillation of the polar-night jet and an unstable thermal transfer from vertical Rossby waves and Eddy Heat Flux also increasing into the Strat before Wave-2 splits the displaced Strat vortex. It's unlikely at the moment but not impossible with a fair number of ensembles increasing the Wave-2 amplitude right towards the end of their runs and the 12Z GFS showing the possibility of how one would evolve if the Wave-2's strength did increase (do not take 1 run in isolation, I'm just using this as an example). This would significantly impact the stability and inertia of the polar-night jet and a Wave-1 followed by Wave-2 would likely cause a major SSW as long as it's caused by a fairly strong amount of upwards wave flux.

One of the worse ways that the Strat pattern could evolve would for polar-night jet to continue to intensify and overpower the Eddy-driven subtropical jet and so the amount of thermal flux reaching the Strat would be fairly minimal. This situation wouldn't see a lot of pressure being put on the vortex and it wouldn't be sustained enough to cause that snap. It's a possibility but relies on the polar-night jet's downwelling to the Trop to be fairly continuous which just like the best possible scenario is fairly unlikely.

The most likely scenario right now (in my opinion) is that we see increase Wave-1 strength with a slight increase in Wave-2 after the Wave-1 signal but not enough to cause a split and so at best we end up with a displaced Strat (but maybe not a SSW) and typically the cold is better positioned for North America in that scenario as the downwelling of any zonal changes happens. We do need to check up on how the Wave-2 pattern evolves though because if we do see it strengthen and we do end up seeing the best case scenario that is probably one of the better ways a SSW could set up for us and the large thermal flux and change over time would likely cause a major SSW. Like I say though, that remains unlikely for now. 

The Trop signal beyond the early part of January remains fairly mixed and so I wouldn't write cold off just yet. Without a SSW, I'd say that a zonal setup is slightly favoured right now but that's only because of the seasonal setups and general un-amplified evolving pattern right now and if we can see the AAM rise sharply again relatively soon then we can think about cold prospects away from a SSW for mid to late January so I certainly wouldn't write it off whatsoever.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778855

[Singularity]

Essentially we’ve spent the past week or so tracking whether the MJO might be just about strong enough, in the face of climatology and an ongoing La Niña, to force a sufficient northward advance of high pressure across Europe for a Scandinavian resting point.

Modelling has gradually backed off that and unusually it was ECM/EPS that started out keenest on it (fast & relatively strong), something which had me seeing more of a chance of sufficient MJO activity than I would if it had been GFS/GEFS (they’re usually the overly keen model runs).

The 00z runs look to me to be another step away. In fact, the GFS 00z is more fitting of a return of enhanced convection to the Indian Ocean, something I’ve noticed gaining a little traction in the ensembles lately.

It’s not out of the question that 1st half Jan as a whole plays out very differently to what longer term ensemble means have been suggesting, with a mobile pattern and any colder weather coming via rear flanks of lows crossing the UK as high pressure stays suppressed across southern Europe. 

Remains to be seen how the MJO actually unfolds, mind - there’s huge spread in the ensembles on that matter. Enough runs - possibly including the GFS 06z by the looks of it as of +192 hours - are still finding sufficient phase 6-7 MJO action to keep that outcome on the table… just about. Kind of annoying really as I’d like to be able to settle on a route forward for a while!

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778948

[Eagle Eye]

The models(just the GFS, not sure about the other ones) have been under progressing and/or amplifying the MJO pattern recently. It is possible that they're doing the same for the future as well. Though its unlikely to move away from the so called COD initially, the latest run suggests we may see a re-amplification of the RMM values over phase 7 by the second week of January and if that becomes a trend then cold for late January into early February may be a fair possibility even without a SSW.

ECM extended less interested and probably more likely but still keeps the 'interest' up before moving on to the generally more nondescript phases 8 and 1.

This slow move towards phases 8/1 is likely to happen which generally doesn't fabour -VE NAO though being quite nondescript in nature, will likely not have too much effect until it enters phases 2/3 in the Indian Ocean which favours a +VE NAO signal and by then we'll be ready for another MJO cycle. I'll talk more about the MJO either later today or later this week though.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4779113

[Eagle Eye]

Away from long-term and more short-term, we could see some local date records being broken in Europe with warm air sourced from Africa and just off the coast of Africam its apparent moisture rich look is just because of the time of the year and really its just because theres some moisture adverting from the South West due to the presence of the low and that moisture is slowly transporting across the Atlantic (possible Atmospheric River, the transport looks fairly tight, I mentioned the possibilityof a secondary one a few days ago) so the area its sourcing it's advection from is anomalously moisture rich in the first place.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4779161

[Eagle Eye]

19 minutes ago, Kasim Awan said:

Looks like firm agreement for clustering towards the COD / very weak phase 7/8/1. True strong mjo phasing is unlikely in a strong zonal pattern so I doubt anything to the contrary will happen. COD/ very weak 7/8/1 phasing will not have the required momentum to shift a strong zonal pattern either. For these reasons I think the MJO will be a minimal influencer for the forseeable.

Sort of agree but there are still signs of it re-stengthening in phase 7 like I said and I'd rather that than nothing. It'll still have some backing of an amplified pattern as long as it stays fairly far away from COD anyway as it can still help retract the downstream jet when combined with the East Asian Jet Retraction signal in reply to the -VE EAMT. Of course, the Atlantic zonal pattern still stays fairly strong initially but as the energy starts making its effects downstream it could well weaken the Atlantic zonal pattern assuming it interacts with an in-situ High over either Notth America or somewhere similar. The timing of this is important as to the weakening and chipping away of such an Atlantic zonal pattern but I see no reason as to not keep up hope that we'll get lucky because hope will keep up sane for now. It's not unfounded hope either just relies on a bit of luck to fall our way.

it's not that strong of a zonal pattern beyond mid January anyway. The intiial VI from the development of the polar-night jet should essentially start slowing down soon and the Subtropical Eddy jet upwelling into the Strat could likely pish the polar-night jet abnormally and cause a refracting wave to bend it baroclinically (or however you spell it) and weaken the Strat zonal pattern into the second week of Janaury. Even if this only causes a minor SSW or doesn't cause one whatsoever it doesn't matter much as we could well see that amount of upward Wave flux with an increasing Wave-2 amplification signal to cause the anomalous weak Strat zonal jet to downwell and weaken the Trop to at least fairly average zonal levels.

Plus the GWO may be moving back towards regaining some AAM through a +VE mountain torque event and with this kind of repeating pattern due to the relatively unbalanced balance () over the East Asian mountains and how the pressure evolves, a regain of mountain torque at least once is unlikely. The recent regaining signal was unfortunately overriden by the downwelling of the polar-night jet but if the thermal transfer into the Strat weakens that signal quite quickly then we may be luckier the 2nd time around.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4779138

[Cheshire Freeze]

3 minutes ago, WINTRY WALES said:

We have often heard all about global warming over the past 10 years or so but it seems to be an European warming phenomenon to me. Milder winters through Europe, especially western parts: Hotter and wetter summers….yet the tiger side of the pond seems to have gone the other way. Every year there are historic winter storms. Doesn’t seem global at all! 

I think that’s to do with the expanding Hadley cell and where mean HP usually sits (think Azores and west coast USA). We’re just unlucky as to where we’re situated.

To me it’s pretty undeniable that the Azores cell is moving N year on year.

I think the only thing that can reverse this trend is an expansion of Arctic sea ice back to historic levels I.e back to the levels of the 70s.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4779435

[Cold Winter Night]

Just now, RainAllNight said:

Question, what is the deal with De Bilt, what is special about this location?

De Bilt is a village just outside Utrecht in the Netherlands, where the HQ of the KNMI (Dutch Met Office) is located, just like "Exeter" for the UK.

It's also the official main weather station for Holland, so a long data set is available, and some informative output like on this page:

https://www.weerplaza.nl/15daagse/?type=eps_pluim&r=midden

For you in the UK the De Bilt output can be insightful in Easterly situations, as it's one of the closer continental locations for the SE of England.
(And for me, in Holland, it's also the one that's closest to my IMBY weather anyway)

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4779354

[Eagle Eye]

Less of a large baroclinic tilt on the latest Stratobserve update though the tilt is still there (and holding firm it's just the Trop pattern that's become slightly less stretched), the 'amplification' of the Tilt has weakened some what but we'll only know closer to time whether this run starts the trend away from a highly active polar-night jet oscillation or just a minor wobble as of yet. It may be due to the Wave-1 height decreasing as the Wave-2 becomes stronger so we may still gain ground on putting pressure on the Strat in the long-term though the GFS is largely out on it's own with the increase of Wave-2 at the end of it's run. Nothing to be alarmed at for now as this is still a very good position with the baroclinic tilt still very much being there are the weakening of the Strat zonal pattern still the most likely of outcomes it's just how tilted it gets and how weak it gets. I won't worry too much unless we see the decrease in tilting strength to become a trend in the future; just a minor wobble for now. Plus the GFS looks to be some sort of outlier in most of the fields (I think it's the 00Z run so slightly out of date, Strat looking much better on recent runs).

Today

Vs yesterday, little difference in the Trop pattern so the thermal gradient may be slightly less but it's quite possible the GFS is under-amplifying the Eddy pattern especially long-term.

Surface to Trop -VE NAM (AO) forms possibly due to a kick from the recent +VE AAM rebound, the MJO amplification having some implications and the -VE mountain torque event retracting the East Asian Jet. Unfortunately for us we're stuck on the wrong side of that as the energy is probably scattered to just introduce some more push into the Euro ridge but not really enough to form any Scandi blocking due to a more easterly based Eurasian feedback's properties not being able to push up WAA on it's Western edge into the Scandinavian region and instead the feedback results in the Kazakhstan high that doesn't really help us all that much though the exact formation area is of course fairly dubious. It's still good to know that this sort of pattern does support a sustained amount of thermal wave flux vertically integrating into the Strat and so perhaps the GFS is over-estimating the zonal wind pattern.

This formation of the quickly collapsing high pattern may be enough to re-invigorate some +VE EAMT though I'm not sure what the pressure patterns would have to be for that and it's mainly based on the GWO progression towards phase 4/5 (phase 5 is a gain of mountain torque) and if we can get a significant enough even then slowly AAM could start ticking up fairly well especially if the MJO progression towards phases 6 and 7 is more amplified than currently forecast.  The GFS suggesting that it's a slow movement towards that phase as we wait for the pressure gradient to increase so for now forecasting one would be a big call as it's very possible that it's a quick gain event followed by a loop back round of the GWO as the zonal lengthening of waves in the East Asian region just keeps the repeating pattern going.

The last significant Rossby thermal transfer inducing +VE EAMT event was back in late October. You can see the packet slowly make it's way across the Northern Hemisphere but the stagnant North American trough may have caused it to result in a less helpful Atlantic extension and push back of MJO effects though it did increase AAM and so we were in for a relatively good pattern shape with another wave train in late November that was more helpful in just causing zonal flux havoc across the mid-latitudes and the eventual movement towards the large -VE NAO also linked with the steady +VE AAM state around the time. You can see there's not much of the sorts on the forecast at the moment but keep your eyes peeled because if we're lucky enough to gain +VE EAMT in a pattern where there's high pressure located over North America and the MJO is better placed than currently forecast. So away from the Strat signal and with how slow these things tend to evolve, late January/early February may be the next best time for a cold pattern though I think it'll mainly have to be Rossby packet and +VE AAM as the MJO looks to be in COD by then.

Right now, it's probably highly unlikely as it just looks to be a cycle in the repeating pattern of EAMT events but I want to dream just this once (okay maybe a few times).

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4779591

[damianslaw]

Reading this thread today you'd be forgiven for thinking we never see wet mild atlantic weather at this time of year.. yet it is the norm, 2006, 2007, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019 and 2021 all shared same type of weather to end the year and start the new year and the outlook is not as mild as some of those years or thankfully as stormy.

Back to the models, not much to comment on, case of watching the atlantic do its thing and how it interacts with heights to the south and east, the jetstream looks strong and the depth of cold to the NW is building, a typical westerly airstream. My expectation is for more potent polar air at times first half of Jan, not initially but enough to prevent euro/azores high from ruling the roost. We are seeing signal for secondary lows and runners getting in the mix, and indeed some degree of trough disruption largely due to the strong temp gradient contrasts in the east atlantic, which could enable quite short term developments to make a mockery of medium range forecasting. The north at least could see some quite cold conditions at times first half of Jan.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4779455

[Uncertainty]

Looking to the next regime now, and tentative signs that our +NAO / euro high combo might be waning beyond day 10…
 

 

 

Pretty good support for an MAR and a Baltic trough.

 

Eps not fully on board but 20 odd members go for the MAR. 
 

The mjo has taken on more of a standing wave look to it, reaching but fading in phase 7. As many of the bases for the composite will be based on a more coherent mjo, I’m dubious as to how much influence it’s having. Still, the January p7 Nina composite isn’t totally irreconcilable with the above 

 

I wonder what the 46 will do with the tropical signal (and, perhaps more importantly, what will it do with the strat as BA has alluded to). My punt is it’ll have the strat stronger by the end of the run, but we’ll see.

It looks like the low at day 9-10 will progress E and erode the euro heights. If this verifies it wouldn’t take much to go colder. Best we can do at the moment and probably not great for continuing the WAF into the strat but there is some agreement there. Long way to go though and said low euro heights are notoriously difficult to verify.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4779749

[Nick F]

Nice to see the Euro +heights do one in the medium / longer range from GFS and EC, GEM not so keen.

Getting an upper trough to dig deep across Europe down into the Med is a lot better than hoping a Euro high will build north to Scandi (Sceuro high) - as the latter less likely to lead to a cold easterly with heights still high across central Europe.

Get a trough over Europe and perhaps, eventually, if we get some amplification upstream over the N Atlantic to cut-off the feed of energy from the Greenland TPV, then the trough will cut-off into an upper low over Europe and allow pressure / heights to build to the north or northeast to allow an easterly or northeasterly. It's a tall ask though, no sign of the strong jet slackening off and the flow amplifying yet.

But the best easterlies or northeasterlies generally in the past have had energy over the N Atlantic diving SE into a trough over mainland Europe prior before the flow amplifies and cuts-off the trough.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4779977

[bluearmy]

7 minutes ago, nick sussex said:

A very uninspiring start to the day if you’re looking for some colder weather.

The GFS briefly tries to raise some interest with the Scandi high and the low trying to cut se near the UK but then the Atlantic moves back in .

Even then it’s an outlier solution upstream as it phases that southern stream low with the PV chunk over ne Canada between day 4 and 5 .

No other model does that so this looks like another rogue run . It’s recent performance has been woeful .

The ECM develops a more southerly track of the jet stream by day 10 but I’d be wary of this until this is shown within the day 7 timeframe .

At the moment apart from some brief PM shots there’s really nothing much of interest unless you like wind and rain !

The models do try to develop a weak Arctic high and if the PV weakened in the outlook sufficiently we might see more trough disruption near the UK and a better chance of something colder .

We need to wait and see what impacts if any the MJO might have and exactly how much warming occurs at the strat level .

I was fairly encouraged by it all nick. I’m not expecting anything particularly wintry first half Jan (away from n elevation) so am looking at how things are stacking for the second half of the month. the gefs have not doubled down on us ridding ourselves of euro heights which is a shame but the eps have and I count that as more relevant. 
 

and as you mentioned, a cold Arctic high is beginning to take more interest.  One thing that could be worth watching is if the ridging over the next week or so to our east does manage to drive a cold block n of scandi.  The push of the vortex towards europe would then have to take a much more nw/se track 

 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780216

[TEITS]

Im rather encouraged with the output this morning with regards to trends in around 10 days time. My current thinking is the cooler/cold NW/W,ly will eventually become a much colder N,ly/NE,ly. This is because I can see pressure dropping  across Europe as the jet aligns NW/SE and at the same time pressure increasing over the Arctic with a -AO emerging. So I am looking at around 13-14th Jan when a more significant cold spell could begin.

I shall just add that +240 only takes us to 9th Jan. The fact some have written off Jan and even winter is frankly laughable.

 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780230

[Nick F]

As others have said, nothing particularly cold and certainly sustained likely next 10 days, but the hints of a colder polar martime flow is better than mild SW'erlies. The midnight operational runs have backed off the deeper dig of low heights over mainland Europe in the medium range, but still enough move towards a NW-SE direction of flow to bring chance of colder polar maritime flows, which will bring hill snow in the north, perhaps briefly to lower levels in the north if the air can get cold enough from the NW, especially at night. Trouble is, we get the heights to drop into Europe and rid of the euro high, but with no amplification we are stuck with low heights close to the north.

This rut could last for 10-15 days without a shake-up of the upper flow patterns. However, there was the glimmer of hope from yesterday's EPS extended and GEFS extended MJO plots for the MJO to reach phase 8. So we could eventually see amplification and impetus to build high lat blocking around or after mid-month given the 7-10 day lag response. 

If the extended MJO guidance is correct, it may still be a while until the operationals start to show more amplified scenarios with blocking appearing.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780231

[Duane S.]

59 minutes ago, TEITS said:

Im rather encouraged with the output this morning with regards to trends in around 10 days time. My current thinking is the cooler/cold NW/W,ly will eventually become a much colder N,ly/NE,ly. This is because I can see pressure dropping  across Europe as the jet aligns NW/SE and at the same time pressure increasing over the Arctic with a -AO emerging. So I am looking at around 13-14th Jan when a more significant cold spell could begin.

I shall just add that +240 only takes us to 9th Jan. The fact some have written off Jan and even winter is frankly laughable.

 

Agree with this. People who try and look clever by writing off the rest of January are just looking for kudos and massive pats on the back (often quoting their own posts weeks later) on the back of often very simplistic arguments. Fairly safe in the knowledge they will indeed most likely be proved ’correct’ by nothing more scientific than the default UK January weather being what is usually is. Kudos should be reserved for those who seek and spot opportunities that eventually lead to something substantial. There will always be many more letdowns than victories in pursuit of this, but that’s not the point and all part of the ‘fun’!

Now, there is clearly little chance of any substantial lowland southern snow in the next 10 days, probably a fair bit longer in all reality but that only takes us into the second week of January. And for those further North, write off snow from this potential PM flow at your peril, it has legs.  The tropospheric vortex is not particularly well organised and menacing as we often see at this time of year. The MJO looks like it might offer some help from the Pacific for later on. The SPV looks like it isn’t going to get things easy, as warmings (not significant, yet) disrupt above. AAM seems to be holding up ok, as in not dropping through the floor after it’s exceptionally sustained period recently. Many pluses, none of them standout but combined could certainly produce fun and games later on in the month. 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780258

[Eagle Eye]

1 hour ago, Ali1977 said:

Stratosphere heating up on this run

 

Is this SSW territory?? 

 

This looks to be a slight displacement but notice that the main vortex is placed over Greenland so watch for high latitude North American blocking signals into the future as the upwards wave movement from that direction could potentially split the Vortex but only if the Eurasian-Pacific warming signal keeps putting pressure on the main vortex shifting and hence the vertical baroclinic tilting keeps the polar-night jet from weakening the subtropical Eddy driven jet. If we can get that to happen then that'll be our best chance assuming this is correct.

The UK pattern from the -EAMT relies heavily on the US pattern so I wouldn't start looking at that just yet but note the high latitude North American-Greenland blocking may be a signal with phase 8

Supported (I guess) by the composites though I'm hoping that it acts like a February signal (second image) as the first one might not be a strong enough signal though note that the MJO phase is fairly significant in creating that block in January compared to not really in February. So Im wanting a mix of the two . 

The MJO amplification of that phase is bery difficult to tell though as there's a lot of split at the moment.

Anyway, just my musings on what could possibly go right for us but as we keep up the pressure on the Vortex then I think we'll get a more substantial chance as the NAO looks to be heading more negative over time by mid to late January and that would create a large Trop-Strat temperature difference as well as vortex tilt difference.

I'm waiting for the next Stratobserve update though to see if there's more support from the ensembles for a Wave-2 increase by mid month as that's typically how a PJO (polar-night jet oscillation) influenced SSW happens with a Wave-1 onset before Wave-2 split. Its a lot of hope but the hope does have a little backing at least.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780308

[bluearmy]

32 minutes ago, Ali1977 said:

Stratosphere heating up on this run

 

Is this SSW territory?? 

Any plus zero temp should considered a notable warming.  But as mentioned above, needs to markedly displace the spv or better to split it. No sign of that as yet and the lack of consistency run to run at the back end is also relevant. Yesterday morning I noted the 06z and 18z were much keener on warming than the others. That was less clear yesterday with the 18z not so keen. 
 

Strat zonal flow chart for that run will be out in a couple hours although the straight flow at the back end is 

1hpa  fast decreasing  to around 30 m/s (had surged to 80 m/s 60 hours earlier!)

10hpa 50 m/s  which is well above average although again, it went up from mid thirties a couple days earlier 

30hpa 35 m/s 

looks like that run would have been v interesting had it gone further. 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780276

[Nick F]

Before the 12z GFS / UKMO / GEM / EC roll out, not a bad look from 00z EPS extended day 15 H500, T850 and T2m:

GEFS getting into MJO P8 eventually, as does EC, albeit low amplitude:

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780428