Model discussion highlights

[Mike Poole]

A lot of interest in the 12z runs tonight, the interest in building a deceptively weak-looking block in scandi, separated from the euro high, as others have posted. 

And GFS later shows the euro high demolished by the low from the NW tracking well SE, with some cold air along with it, T270:

Move forward 10 days, then add in some underestimated MJO amplification, and maybe mid Jan looks a whole lot different to how it did only a few days ago.  

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780476

[Cold Winter Night]

What GFS, UKMO and GEM have in common is those heights generally centered over the Barentsz Sea, the triangle Scandinavia-Svalbard-Nova Zembla.

Arctic Highs have a certain reputation as "good for winter," but many consider that a bit of a hoax, because we've often seen Arctic Highs that don't deliver anything at all, but I think a distinction needs to be made between those nearer the Bering Street (like the past week) and the Barentsz Sea  Highs. The CAA flows moving Southwest along these last ones have a far greater chance of actually reaching us and those are the ones that gave Arctic Highs a good name.

So, it's good to see something like that getting more support across models, although they all handle them quite differently, with GEM currently the best of the bunch.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780481

[Mike Poole]

ECM clusters T192-T240, the op run sits in cluster 4, while the GFS type evolution is the majority one in cluster 1:

The other two pull the euro heights west as the trough moves through.

T264+:

And we’re heading to - blocked.  3x -NAO (detail close to UK notwithstanding) 1x Atlantic Ridge, 1x Scandi block.  All in all, a decent afternoon’s model output, hopefully future runs firm things up a bit.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780643

[Daniel*]

Just now, Kasim Awan said:

...For central Scandinavia. Looks nothing more than bog standard zonal affair for us.

I think you are too much of a surface reader. Adjustments are needed with Atlantic troughing clearly. Hemispherically this has a lot of interest. 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780590

[TEITS]

Quick summary from me because there has been some odd posts tonight and some members must be very confused.

A non biased honest assessment is this. Next week will remain largely unsettled with the N/W being more unsettled than S England who may have a drier week compared to recent days. Around 7th Jan onwards potentially turning cooler/colder and possibly very stormy with gales, maybe even severe gales at times. A greater threat of snowfall especially for the higher ground of Scotland/N England but not exclusively. As the winds start veering from a W,ly to a NW,ly and possibly N,ly then snowfall at lower levels becomes more likely.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780829

[nick sussex]

The UKMO gets the award for a very frustrating set of charts ! 

The upstream troughing is sharper and the intense cold is building to the ne , not enough ridging though  between that and the UK low .

The day 5 screamed potential , but the PV is just too strong and the weak Arctic high can’t disrupt the low as it drops se .

There are differences earlier at day 4 between the UKMO and GFS.

Norway upto Svalbard . The former has a clean flow the latter sticks a shortwave there .

We really want the main high to be as the UKMO has it and not two separate cells with shortwave in between like the GFS . The main forcing needs to come from the ne and the Arctic high given the overall set up .

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780854

[bluearmy]

I mean we actually have a ticket for the raffle of the century ….

It’s only one ticket unfortunately- would like to have a book of tickets but given that it’s the raffle of the century I suppose beggars can’t be choosers

the Siberian vortex is expanding towards nw Russia and ne scandi - it shouldn’t reach that far and a chunk of it should break off and traverse toward n Canada whilst the remainder drifts back east . That’s the expectation- BUT the Arctic high comes into play here and it’s feasible that it prevents that chunk from reversing west and if the AO can be negative enough it could reach scandi/svaalbard/w Russia . If the slp patterns then drop into place then who knows ….

This isnt necessarily a one off one chance in the next week or so opportunity either. The NH profile could try this passage of heights transfer several times - if it’s proceeds as per expectation then it ramps up the n Atlantic jet stream as a chunk of pv passes east to west. 
 

incidentally, the gfs at the v top of the strat is still keen on a massive reduction of zonal flow as the top of the spv ends up displaced to Greenland. A little lower down the repeated warmings are keeping a generally average strength chap displaced around svaalbard. The spv is ever stretched as we head down through the strat.  It still looks like the trop’s dance to me although if we do see some surprise developments high up then that could well shake things up in that respect. Given the lack of coupling this season you wouldn’t expect a quick response but perhaps a strong and v rapid reduction in zonal flow could change the dynamics. 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780875

[bluearmy]

9 minutes ago, Ali1977 said:

Getting hotter still, and slowing edging closer 

The initial warming was progged anywhere between -28 and -4 when it appeared at day 16/15/14.  It looks to verify around -20 to -16 now we see it around day 8/9.  I reckon that should be our current expectation- strong warmings that keep the spv displaced around svaalbard. But if we can get something hotter above zero then we can stretch that spv and who knows, possibly even split it. anyone for a cold spring ???

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780876

[nick sussex]

The GFS 06 hrs run picks up the UKMO baton and almost makes the finishing line ! 

Remember that UKMO tweak I was hoping for , we just need another little tweak this evening ! 

You can see by the ECM ensembles that the mean keeps the rounded troughing and if the ensembles were more bullish on the sharper troughing we might have seen more colder members .

Could there be a dramatic development this evening ?

 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780973

[Allseasons-Si]

Although the 06z gfs is different up top to it's previous run,it does show a near split(altough stretched at this point) of the spv,let's see what future runs produce...

Looking at the 06z gfs for example,you can see the difference from yesterday mornings run at 168 vs this morning run at 144,notice how the heights over N Scandi have moved/backed west into the Norwegian sea putting more preasure on the trough out to our NW,notice how sharper/neg tilted it is

it would be interesting to see how this play's out,can we get more forcing of the trough SE from this wedge of height's to our N/NE,an interesting one to watch.

 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4780970

[Derecho]

4 minutes ago, Battleground Snow said:

Yeh me too, it won't change until they see ec46 on monday

With these updates I think they are just a quick write up based on an operational run in the shorter term and ensemble means for the long term. They will have the longer range MOGREPS to look at. They seem to go for one scenario unless its closer range and there are big implications.

I wouldn't read too much into the longer term text. From my time in working in weather forecasting it is deliberately vague and generic as forecasting at that range is difficult. I'd only write something different if all the ensembles were going for a big storm or there was a good consensus on a major cold spell. 

Even at longer timescales and a good ens signal most of the time I'd just write 'much colder conditions from the east cannot be ruled out'. When writing to clients the uncertainties have bigger implications compared to a weather forum so text is likely to be often underwhelming and just a rough guide from the model output.  

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4781089

[bluearmy]

06z eps tend to slightly stronger block and slightly more push se of the jet ……..………..

and the gfs 06z finally manages to reverse strat flow at the top axross the pole - displaced 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4781667

[Catacol]

HNY everyone - festive season pretty much over...time to return to "normal" (whatever that is...) 

It has been a grim 2 weeks for cold hunters. I have checked into a few charts and data sources over the Xmas period and frankly if it could go wrong - it has gone wrong. Pacific forcing arrived as expected and it has prevented the slide towards a Nina dominated atmosphere. AAM has pushed back up into positive territory

and the GWO orbit started to rise once again, avoiding a slide into flat, Nina territory.

We have even ended up in the fabled ground of MJO phase 7 as many suspected might happen despite the usual crappy MJO model forecasts.

This was probably about as big a jump back up of AAM in a positive pacific context as we could expect. Looks pretty good! We are even looking at a scenario which sees the North Pacific High replaced by some quite long last low pressure....a good precursor for strat forcing

But just take a look - as though we need to - at pressure over Europe. I posted JMA monthly charts that saw this draining away. EC charts showed it draining away. And here we are with the Euro High firmly embedded. It has forced the jet stream further north so that only the Highlands are now seeing what - at one stage - some of us thought much of the UK could see during this current period. Go to the outer reaches of useful EPS modelling and not much change. Euro High in charge. 

It is indeed grim. CC modelling of global patterns over the next 80 years or so sees the growth of the Euro High as a core feature. The fact that we are seeing it so much already, as early as 2022/23, is depressing. Germany breaking temperature records....we had our 40 degree summer just gone. Both courtesy of this growing anomaly. As the world warms the regional implications of this Euro feature are going to become quite profound I suspect.

Where does this leave UK winter? Searching for a SSW. I don't see any way out of a westerly pattern now without a SSW. Really substantial amplification might possibly do it but remembering the failure of the GP +4SD "torpedo" years ago I am not sure modern climate patterns produce the same kind of response as was the case 30-40 years ago, at least in Europe where we have a semi permanent high anomaly bedded in to our south.

A proper SSW - like 2018 - would do it. In such circumstances downwelling impacts of vortex collapse overcome tropospheric forcing and these scenarios are the ones that really significant winter cold will rely on going forward. To have any chance of this in our current winter we could do with seeing high pressure reemerge over Scandy or the Urals as we had in November to pair up with low pressure over the Aleutians which is modelled. As more than one poster noted a month ago - it would have been much better for our winter overall if the Scandy High in early December hadn't retrogressed so swiftly to Greenland. Much better for stratospheric forcing. Right now only half of this pairing is in place - the Aleutian Low. It is forecast to produce quite a significant wave 1 stretch of the vortex and there is a chance going forward of a displacement warming....but a wave 2 split would be much better for us. Note the current 3D modelling of the vortex in 10 days' time - stretch is quite clear and visible.

So - forget the first half of January. I would almost suggest everyone take a week away from the models, maybe even 10 days, and come back and see if any change is in the offing. Pray that the Euro High ridges towards the Urals in the meantime.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4781681

[Catacol]

One little extra post. An area I am trying to improve my understanding is in regards to East Asian Mountain Torque events. In very blunt laymen's terms these occur when vertical wave activity is produced from warm air bouncing off the Himalayas and spearing up into the stratosphere. These ideally need to force that warmth more in a polar direction rather than towards the Equator. I get a bit vague as to the tropospheric shape of patterns to induce polar rather than equatorial wave flux so have to lean on the flux models for this. At the same time the action of the high pressure sweeping across the mountains acts to slow down the rotation of the earth ever so slightly and produce a consequent increase in atmospheric momentum. This is what a "spike" in AAM created by mountain torque means.

These +EAMT events happen when a high pressure cell sweeps across the Himalayas in a NW to SE direction. Not only does this increase wave flux but it also provides a significant boost to the Pacific jet - sometimes posted by Met experts in the form of a "jet extension" in the pacific. This extension is a factor that produces another round of pacific driven amplified wave activity downstream, certainly to the US but hopefully also through to the Atlantic sector (at least until the Euro High puts up the wall!)

ECM modelling of Asia is interesting today. Note the strong high pressure to the NW with a fairly deep trough sinking down the eastern flank

Roll that on a few days and the high pressure has moved ESE, interacting with the mountains.

By Saturday it has passed mostly to the East.

Now - lots of caveats to this, not least the open admission that this is very much an amateur understanding of something that is undoubtedly complex. But if people are looking at straws to clutch away from longer term impacts of an SSW then I would suggest the second half of January might see the reignition of an amplified pattern that might - might - do something to try and shift that Euro anomaly.  

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4781690

[knocker]

1 hour ago, RainAllNight said:

What is meant by "wave 1" and "wave 2"? I've seen Eagle Eye mention these frequently also

Evolution of Warming

During the prewarming stage an intense polar night jet stream with strong vertical wind shear will appear. At this time a blocking situation develops in the troposphere. There is amplification of wave numbers 1 and 2 occuring in the upper troposphere and lower stratosphere. There are two types (Type A and Type B) of wave amplification which takes place during the prewarming period. In Type A, intensification of wave number 2 occurs about 2 weeks prior to the onset of the major warming. This is closely followed by an increase in the amplitude of wave number 1 with a subsequent weakening of wave number 2. During this time, wave number 1 reaches a peak about 1 week prior to the warming. In Type B warming, wave number 1 maintains a large amplitude for a long period. Type A is the most frequently occurring type of stratospheric warming.

An important character of sudden warming is its downward propagation from 45 km into the lower stratosphere. This feature is not zonal in character, but hasnonzonal structure, with a planetary wave tilting westward with height. In the middle latitudes, warming in the stratosphere (40 km) is followed by cooling in the mesosphere (65 km). Simultaneously, the opposite occurs in low latitudes, with stratospheric cooling and mesospheric warming, but the magnitude of the changes in the lower latitudes is one order less compared to that noted in higher latitudes.

Source _ Stratosphere Troposphere Interactions.  K. Mohanakumar

Further to this

The numbers are the "wavenumber". This means that in a given belt of latitude, a wave with wavenumber 1 will have one peak and one trough around the entire world. This is called wave 1. Likewise, a wave with wavenumber 2 ("Wave 2") has two peaks and two troughs as you go around the globe within this latitude belt. And so on. As you can probably see, as you increase the wavenumber, you are cramming more waves in as you go around the world. So the distance between each peak and each trough gets less. This is another way of expressing the relationship between wavenumber and wavelength. Wavenumber is essentially the inverse of wavelength.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4781731

[Eagle Eye]

Upper Stratosphere displacement towards Greenland vs far upper Stratosphere/near Stratopause level displacement towards the North Pacific.

A +60°C difference between the two levels over Europe
Vs
A -15°C drop over areas of the North Pacific.

Vs what it's apparently supposed to look like. (Just what came up when I searched it up) 

So according to the GFS (outdated run), looks like we'll get the biggest abnormal thermal transfer between 10hPa and 1hPa levels at the end of the second week of January but at this range it's still too far out to put numbers to it. Still looks to me like a Wave-1 displacement that doesn't reverse the strat just yet but as long as we can have the Baroclinic Tilt then transfer of heat will be abnormal and the displacement of the Strat should keep weakening it in bouts and the formation of a secondary Wave split may happen . Still a few members showing increasing Wave-2 strength at the end of the run so I'll continue to keep an eye on how this evolves.

P.S If you're interested in Wavenumbers and I mention them but don't explain them in my posts a lot, both @Catacol and @knocker made better explanations than I could ever make further up..

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4781746

[Catacol]

1 hour ago, RainAllNight said:

What is meant by "wave 1" and "wave 2"? I've seen Eagle Eye mention these frequently also

Wave 1 = a single pocket of warmth pressing on the vortex from 1 side. Wave 2 = 2 pockets of warmth acting on the vortex at the same time from different sides of the vortex. Think of an air balloon pinched between your fingers.

Generally a wave 2 warming that causes a vortex reversal is the most destructive and - as in 2018 - can have the most dramatic tropospheric impacts. A wave 1 reversal can essentially be a displacement that pushes the vortex off its perch but often the direction of this displacement pushes it over towards Greenland. Wave 1 SSW therefore probably less attractive in general for the UK.

The 2018 wave 2 destruction of the vortex is a great one to study. The precursor pattern in the troposphere was very evident in mid January. 4 week lag to the warning and then those amazing tropospheric charts as the impact downwelled which produced a reverse flow all the way from Siberia to Canada. Extraordinary. For several weeks the most exciting weather watching of my life, the only negative being that it happened 3-4 weeks too late in the season.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4781726

[Eagle Eye]

AAM has been staying fairly neutral recently and despite the quick rebound it probably wasn't sustained enough as the pressure returned back over the Himilayas as a quick reaction and balancing out of momentum flux and the energy patterns returned back to normal and a loss of torque could be seen fairly quickly. Note that despite this the AAM has remained away from -VE largely and so the atmosphere continues to try and not liken itself with the La Nina oceanic pattern in the Pacific. Over the next fee days the Pacific jet fluctuates a bit and we see the collapse of very cold air but also a sort of collapse of the Eurasian block and thus the cycle of EAMT continues as over time the +VE EAMT and -VE EAMT are usually related quite well. The zonal feedback of a -VE EAMT event is to retract the East Asian Jet and attempt to form some sort of Eurasian ridging in feedback to that which seems to keep the Himilayan pattern in check as long as it sustains. The downstream effects of a -VE EAMT event don't matter too much but it can drag up a Scandi high but most times it results in the horrid Euro ridge that's so hard to replace. However, the collapse of the high pressure feedback as the zonal effects weaken over time can often cause the high pressure vertical wave projections over the Himilayas as the +VE EAMT event forms and the distribution of the Strat pattern especially begins due to this.

The MJO can often gradually influence the pattern so it's important to note the two patterns together as well.

The best lag correlated phases are 6/7/8/1 with the development of that central Asia +VE temperature anomalies though phase 1 is fairly dubious plus its usually noted as being right on the line of COD as its typically a rather nondescript phase in terms of the strength of Convection. Phases 2/3/4/5 probably more helpful in during -VE EAMT events (e.g recent event also associated with phase 4/5 with the colder central Asia temperatures) and can have a negative impact on the initial formation of the Eurasian block though phase 5 possibly less so and so I think the recent -VE EAMT event probably correlated itself well with the quick phase 5 and now we're seeing the effects of phase 6/7 being modelled so how phase 7 typically evolves along with the result of external factors will be how Asia should eventually evolve and so the development of the Himilayan high moving into the week 1/2 boundary is fairly inescapable and that's where the GWO forecast from the GFS also seems to be moving to.

Whilst the MJO isn't significantly strong, it still seems to be helping at least a little bit in the formation of how the events are evolving. Right now we're around phase 7 and should slowly start propagating into phase 8 as we go into mid month which may actually be better as it tends tends build high latitude North American blocking (Canada wise) and even though it may setup a slightly more zonal Atlantic due to typically colder for the East of the USA (or it could build up WAA towards Greenland), the North American high-latitude blocking will continue to drive vertical Eddy's and may support a Wave-2 setup. Though, I think that'll rely on timing with how the EAMT evolves and how strong Phase 8 eventually gets of course.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4781804

[Eagle Eye]

I'm going to copy over my pretty much non-biased (hopefully) texted forecast long-term to one of my friends...

Firstly, we have the Atmospheric Angular Momentum (AAM) which is the amount of torque or rotational force in the atmosphere. Positive AAM (+VE means positive and I'll be using that) typically results in a pattern where +VE temperature anomalies move poleward and see we have hotter than average temperatures over the Arctic whereas the cold from the Arctic falls to the mid-latitudes (including us) and we see negative(-VE) anomalies there (known as Nino-esque). It's important to note that +VE AAM doesn't cause -VE temperatures everywhere in the mid-latitudes, it depends where the warmer air moves into(advects or WAA) the poles and therefore the cold partly falls on the other side of it to somewhere. If this happens over North America that can potentially fire up the Atlantic and for the UK that means the mild and wet that we've been getting recently though we may still get a visit from the Polar Maritime air for a bit. Whereas if we get WAA into Greenland that can often result in the Atlantic effectively being shut off and can lead to cold air falling to the UK in the form of say an Easterly or a Northeasterly and with that there's the threat of snow. It's what happened in early December this Winter.

There's also negative(-VE) AAM which results in a fairly flat and 'normal' system (known as Nina-esque) where we in the UK usually get mild and wet though it depends on the strength of the -VE AAM.

Right now though, it's fairly neutral and so we're relying on 'events' of gain of torque to increase or decrease the AAM and this is where we get to first know the EAMT or East Asian Mountain Torque. A +VE EAMT event is where warm air hits the Himalayas and we find Him a laying in the Stratosphere wave activity moves vertically up into the Stratosphere and we see the gain of AAM in the Trop-Strat this way. On the other hand we have -VE EAMT where cold hits the Himalayas and there's a loss of momentum into the Earth....

With such a fairly neutral AAM it's unlikely to be the main driver but as a basic signal it's fairly good at explaining how things work.

Right now and in the mid-term forecasts, for the end of the first week of January it's looking like we will get warm air moving upwards into the Himalayas and a propagating vertical wave vector into the Stratosphere fairly quickly which results in a +VE EAMT event and an increase to +VE AAM. This will probably result in an extension of the zonal jet in the Pacific. Normally, an extended jet globally is the last thing that we want but just over the Pacific it's fairly good and as I noted +VE AAM tends to drive poleward warm air influence and we don't want that to be over the Pacific (an extended Pacific jet tends to stop that from happening) and instead would prefer it to be towards Greenland for cold for us. 

Now it's time to combine this with the MJO signal...

Combining the MJO with an EAMT event is fraught with danger because that event can shift the Rossby wave (a ridge and a trough or rather a high on one side then a low on the other sort of) pattern from each of the MJO phases and Rossby waves help shift energy throughout the Atmosphere. Luckily, the Atmosphere is being fairly helpful to me and offering me two patterns that come to roughly the same conclusion with the +VE EAMT and MJO phase.

 

There are 8 different MJO phases

 

Phase 1 is fairly non-descript for us though I find it to usually be mild and wet may just be because that's how the 'average' part of Winter is for us.

Phases 2 and 3 tend to drive the mild and wet muck that not many people like and you can probably include phase 4 in that. As these seem to help +VE Azores region Hadley cell development and the Euro high tends to form because of this.

Phase 5 is fairly non-descript.

Phases 6 and 7 are heralded mostly by UK cold lovers because they help with warm air advection towards Greenland (known as a -VE NAO) or sometimes Scandinavia(?) and that often results in a colder pattern for the UK as air can move in from the East/Northeast.

Phase 8 drives high-latitude North American blocking and potentially a west based -VE NAO as well. Though a west based -VE NAO is dangerous for cold as it leaves the door open for the Atlantic as well and so in a strong westerly system (depending on how the East of North America evolves as well) it can end up being a 'wasted' solution and we revert back to type (mild and wet). Although, this type of far west based -VE NAO (so far that it doesn't count) can still be cold with quick shots of Polar Maritime air as it's more North West centred so the air coming down is potentially from a colder place with a steeper gradient and so areas such as the North and Scotland do best from this and even places as far as the south might be able to escape the mild and wet. Instead it may be cold and wet or if it gets cold enough, cold and sleety/snowy. Polar Maritimes aren't always the best but they're the best we're probably going to get soon...

Currently, the forecasts suggest that the +VE EAMT event will coincide with phase 7/8 and high latitude North American blocking looks to be the most driven solution out of this despite both being fairly under amplified because putting them together and you've got yourself poleward driven warm air around North America. This is slowly evolving now with the MJO phase 6/7 lag over the coming days building mid-high latitude blocking and as phase 7 properly pushes in, I think long-term and we'll get increasing Polar Maritime(PM) potentially as this acts like a far west based -VE NAO. It doesn't look overly like zonal mild and wet though a quick Southeast US trough linking up with the Canadian low may mean that for a time that returns very strongly.

So still looking fairly mild and wet long-term especially in the south but further North may actually fare quite well and I don't see why some of the cold can't make it far south enough to bring the midlands or even the south some snow for a time. I think the GFS going for a large -VE NAO long-term is fairly dubious. My thoughts are more along the lines of the MJO progressing more quickly than the forecasts are showing into Phase 8 and that continues to interact with the +VE EAMT reaction forming North American blocking but no large -VE NAO. Though, if the current MJO projections are correct then we stay largely in Phase 7 with it amplifying for a time and so maybe we can get a -VE NAO and cold via an Easterly/Northeasterly that way. If it does interact with how the Pacific jet evolves that way then we can get excited about Tropospheric based significant cold potential for late January but for now I don't think it's going to be amplified enough nor under-progressive enough for that to happen. Instead PM may be our best chance of cold at least away from the Stratospheric pattern...

The Strat pattern continues to show signs of displacement as the main part of the vortex appears over Greenland area and displacement is a good thing as it generally leads to the weakening of the Strat westerly winds (zonal winds) due to abnormal Rossby wave thermal transfer and the resultant net easterly force from Rossby waves. So, a slowing down due to displacement but not a sudden warming just yet. A sudden Stratospheric warming (SSW) is characterised with the reversal of the Strat zonal winds between 60-65N (apparently) and typically that happens with a large displacement or a split. Generally a split right down the middle of the vortex, perhaps a displaced vortex is more associated with a major SSW and a large displacement with minor SSW's but I think I've heard of one or two major SSW's that were displacements but I don't think it's enough to just rely on a displacement especially to get one in the first place. The polar-night jet formed very strongly recently and we have an anomalously +VE Strat zonal winds in the first place so to get a SSW from just a displacement alone is probably unlikely though it does look like it's going to weaken it quite a lot to perhaps below average but beyond that relies on how the Trop pattern evolves...

If Wave-2(2 warming areas, Wave-1 is 1) increases then a split considering the initial displacement is fairly likely if we can get a strong Wave-2. Recent trends have had it increasing at the end of the run going into mid January but nowhere near where need it to be. As the large Pacific wave connects up with the North American response to the +VE EAMT and MJO phase 7/8 event, it should start slinking away from Siberia which may be a good thing. A +VE Ural Block (UB) in the Trop pattern could provide the upward wave flux we need for a Wave-2 signal though I think it probably needs to be a lot stronger than where it is currently at on the models, at least it's a start. The 2018 SSW had a persistent UB pressuring the Strat beforehand plus it was Wave-2. A UB isn't the best indicator as it may be the only vertical wave flux and so Wave-1 signal such as the 2019 one which seemed to mostly have been UB based with no other real intense blocking and at the time the forecasts were showing a displacement event. It's important to note that SSW's do evolve relatively slowly as the pressure and displacement increases (especially Wave-1 followed by Wave-2 events) and then the snap happens. 

In the current scenario a split would only really happen if Wave-2 increased fairly significantly and that would possibly be to do with the timing of the UB omega (?) block expansion and the initial warming Wave moving towards the Pacific/North America perhaps negating the need for an Alaskan blocking in the Trop but for now the UB times itself just too early and instead focuses itself on strengthening Wave-1 similar to how 2019 evolved, I think that was a former UB on top of a re-strengthened UB. 

So in other words, it's possible that even if a SSW does happen it could be similar to 2019 but importantly, at this time the zonal wind looks to be around average so this wouldn't be the onset of a SSW, just something to keep it displaced for now. It seems like a wasted +VE UB block but it's important in keeping up the pressure on the Strat and also for the secondary displacement towards Greenland where it looks to shrink back a little bit. This leaves room for what would be the most helpful thing considering the placement of Wave-1. A Scandi high would split the vortex in two but when we need it there's no real sign of it, yet. Although, the stretching of the Strat and the general movement of the Wave-1 heights would suggest that a UB a few days after the end of the GFS run would be a good way to split it  with the increasing Wave-2. It's at times like this where you get a little bit mad at your luck. 

This has looked the case on recent runs but it's still quite far out. Given how everything is timing itself though it does like an increasing of Wave-1 towards North America with the vertical wave flux propagated by the +VE heights over North America and combined with the +VE UB doing similar, the Wave-1 continues to get a lot of support from below it and keeps the Strat Vortex displaced and stretched but no real signs of an increasing Wave-2 strength largely just yet. That's shown well on the image below.

Why do we want a split and major SSW instead of a displacement?

Mainly want a split rather than a displacement because split's generally increase the chance of getting a major SSW and so the zonal wind reversal reaches the Troposphere which is an important area for the evolution of our weather systems. A split rather than a displacement also usually favours a colder pattern for Europe with a displacement favouring North America with it's downwelling effects. It's also the reason that we want Wave-2 more than Wave-1 as Wave-1 displaces the Strat but often a strongly amplified Wave-2 will split the Strat and that's much better for getting a SSW in the first place and for it's efffects for Europe in terms of helping to bring us a generally colder pattern.

Why does a SSW typically bring colder weather to the mid-latitudes?

I sort of touched on it earlier, it's mainly to do with the reversal of the Stratospheric zonal winds and as Rossby waves attempt to move vertically, the reach the reversal, impart their easterly force and break up and this continues until the easterlies are in the Troposphere.

What are some SSW past events?

January 2009 SSW (thanks to Simon Lee's blogs) and the relatively quick revert to the Easterly for the UK though it didn't last for too long, it was a major SSW (I think).

February 2018 (also thanks to Simon Lee), this also occurred right after very strong polar-night jet happened as the Tropospheric Eddy-driven jet pushes up thermal wave flux and we saw the development of a strong Wave-2 split.

So what's coming up?

I think for the Strat it's the case of wait a while and see where we are. The best signs continue to be long-term and there's still no real signs of a SSW just a return to average, perhaps slightly above or below average. Though, the initial warming Wave which is followed by backup is now with about a week but what happens beyond that depends largely on how quickly the North American and Eurasian patterns evolve which I generalised above but there's a lot of potential difference with the actual timing, if it happens at all. That may have a fairly big effect on how things evolve. So for now, it's going to be waiting but I'm still going to be updating you on the trends with how timing is evolving, these are just my general 'musings' that my friend had to listen to me talk about this morning.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4781990

[Duane S.]

It does seem that, whilst there is little appetite for a full on SSW any time soon, the forecast warmings up top could start playing havoc with the SPV, stretching it here and pushing it there.

A slow down up top coming into view. Yes, nothing significant, but maybe it won’t need to be?

And, last but not least,  you’d have to assume this won’t be without huge consequence with regards to the NH atmosphere, off the scale…

My take away is a mobile first half of January but literally anything goes as we get past mid month. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4782023

[Mike Poole]

39 minutes ago, nick sussex said:

Regarding the Scandi high .

I think one more days outputs should decide whether even though unable to directly influence the weather on the ground as it edges east it could hang on in a more favourable position and add more forcing to direct the jet more se into the UK.

After the Scandi high moves  east the models paint an unsettled picture . Some variation though in how much suppression we see of the Euro high .

By day ten the ECM has the more favourable upstream pattern with a better chance of a more potent PM shot .

I’d remain wary though of the Euro high in the later outputs as the models seem to going on recent performance have been premature in either flattening it or displacing it further west and north .

The movement of the MJO does though favour some change so I’d say the odds slightly favour the more amplified upstream solutions .

 

 

I don’t think this early scandi high is going to result in UK cold directly, I think that was always a big ask.  

What it does do potentially, is demonstrate that the atmosphere as of now is perhaps more prone to northern blocking than it appeared because the high has been underestimated by the models.

It also, as it moves east, puts pressure on the strat vortex in combination with the Aleutian low.

But, I think the model runs that have it stronger, also slow the movement east of the big low in the Atlantic, which delays any meaningful PM shot, and also delays eroding the euro high.  But I think these are both delays rather than substantially changing the picture we previously had from several ensemble suites of low heights moving eventually in the direction of Italy.  

If you look at the extended clusters T264+ you still see the euro heights gone on all 3 (apart from the first chart of cluster 1), and - again apart form the first chart of cluster 1, no further +NAO charts, with Scandi high, Atlantic ridge and Greenland block represented. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4782005

[bluearmy]

The upper trough that is going to barrel into the Atlantic sector is currently forming in the base of the pv extension far n of Canada. You would expect the models to have a good handle on this feature but there is still some wriggle room on its evolution and subsequent interaction with the sceuro ridge thrown up ahead of it.  As nick says, perhaps another couple runs to be certain of how that is most likely to play out. (Although the models do seem pretty sure) 

beyond this it looks pretty mobile zonal but mid month begins to smell a little interesting. There are more gefs members than I have seen for some time with notable solutions for that timescale. Awaiting to see if the eps are similar in that respect. The clusters show that they could be. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4782007

[Catacol]

The advice to go and take a break from the models for a week or so CLEARLY wasn't mean't for me - when I look into the mirror all I see is a weather junkie. No end to that in sight. 

A day after posting about a second half of the month potential/straw clutching shift to a new phase being possible....with the need for a Scandy high to enhance our chances going forward.....more interesting developments. 3 x EPS charts for midnight on Jan 10. The 3 runs are midnight ones, on 31st, 1st, 2nd consecutively.

Baby steps - but baby steps undoubtedly in the right direction. Note on each run a progressive suggestion of an elongation of the atlantic trough and therefore - at last (cos we have been waiting an age for this "predicted" context to emerge) - a resultant eddy over Scandy with the first signs of a scandy block being possible in the days that follow.

Long way to go. Need this direction of travel to be sustained. And if my EAMT stuff made any sense at all yesterday - good developments there too. High pressure makes better clear progress over the Himalayas on last night's run with a sharper pressure gradient dropping in behind it. 

More optimistic today that the second bite of the winter cherry might begin to emerge mid month and after. Another chase on the cards....this time with more cold to tap into.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4782161

[MattH]

Good morning...

It isn't looking good at all for the foreseeable for those looking for cold winter synoptics, the opposite viewpoint is in summer, with an often dominated cyclonic pattern and those longing for dry, hot summer days, clearly which does happen as well.

Some of the key points in the last 7 to 14 days have been the expected rise and recovery in AAM, but this being counterbalanced by a fairly decent downwelling event from within the strat to increase the westerly momentum across the northern hemisphere. As ever, it is always a 'battle of the powers' through the medium and long-term to see which can win out. A good example of the opposite of currently is during the first half of December, when the strat and trop where well and truly disconnected and a +ve AAM regime, aided by the MJO, etc, ruled the roost and northern blocking was able to flourish - the opposite is now present.

AAM is now set to fall (see EPS plot below, not a great AAM outlook ahead), we've seen a significant -ve FT event of late as the current, weak and paltry MJO slides its way through phases 7-8 with little impact, especially within an evironment that is dominated by a more 'typical' strat and trop coupling. While this link is far from as significant as it can be, at this time of year, highlighting this change compared with late November is, as usual, the excellent plot below - Note the evolution change in anomaly pattern at the far right of the image.

With AAM set to fall now, as one would expect and with a more likely bias on a more Nina atmospheric response, little in the way of any significant MJO activity, coupled with some influence from the strat and trop then, IMO there is only one primary outlook for the foreseeable and that is a general W'ly flow, but with some, temporary weak amplification to the pattern at times. More wet and windy weather at times, but within a background that isn't quite as entrenched, in terms of a solid, bowling ball resolute trop PV that can dominate at this time of year and exampled many of times over the year too, as an example - https://www.wetterzentrale.de/maps/archive/2020/cfsr/CFSR_1_2020011418_1.png

Where we go from there remains to be seen. All long-standing seasonal data drifted towards a +ve NAO regime through mid to late winter and that, at the moment looks the way forward. The constant talk of an SSW, etc etc, is all good and well but as we all know will only become reality if the trop helps the cause, there is no sign of that either, so the chances of a Jan SSW are waning too, and when I say an SSW I actual mean a reversal of the winds at 60N, etc, not the usual wave 1 pushing and pulling of the strat that is on the way. This can be of interest for down the line, but is not going to bring about an SSW any time soon.

For us coldies then one can often look back, remembering the cold synoptics during the first half of December and enjoying that synoptic spell, but also acknowleding a heck of a lot of winter lies ahead and, as ever, even March too, but those hoping for some proper cold synoptics in the 'heart of winter' are likely to be extremely dissapointed yet again this year and, as we have seen exampled many of times over the years, this is our winter 'default' pattern now and there's no clear and obvious change from this for a good chunk of January.

Cheers, Matt.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4782534

[Ladyofthestorm]

A wee update from the teleconnection models .

 

The forecasters are still expecting disruption to the PV mid January onwards either as a stretching  or splitting ( caused by SSW) 

The EC and GFS are both continuously sniffing these scenarios out. 

LIttle wonder given the forecasts 

1. Neutral to Negative NA0.. watch that trend. 

2. Negative NO .. it's been kicking around all winter.  Look at the ensemble runs. 

 

3. I'm really not convinced with all this doom and gloom expectations 

The MJO looks promising we may still  get a phase 7, plenty ensemble runs suggesting it.  

 

I think though look at the longer term blocking pattern over the arctic. That strengthened PV which we have the now is a sitting leaky duck. 

 

 

Potentially, latter part of January beginning February could see much colder conditions. 

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4782566