Model discussion highlights

[Catacol]

33 minutes ago, feb1991blizzard said:

what do you make of the run though? its nearly split practically all the way through the atmosphere from about 150000 feet to the trop.

I'm at work and I need to get out my office to do a walkaround so no time to dig into too many tools - but I guess I'm not totally surprised that we are seeing such a comprehensive split forecast given a few factors:

1. We have had a precursor split pattern repeat really quite extensively this winter so far. It didn't deliver in December and then the vortex recovered as the North Pacific ridge appeared and the Scandy High signal retrogressed swiftly to Greenland - but up at 1hpa there was an extensive attack from the late Nov pattern and a sign of what can be achieved with a Ural/Aleutian combo. That combo has returned in January.

2. Taking a speculative guess at something that I'm sure the real scientists might analyse at another time and that I mentioned yesterday - the astonishing wet pattern over the Western US driven by a very active Pacific Jet must be having a warming impact. All that moist, warm air hitting the mountains in near record breaking quantities I am going to guess is the source of the intense wave flux forecast we saw the other day. Did we see this US flood and record level snow event for the mountains coming? In truth no - we all saw an extended Aleutian Low signal and knew it was likely to provide warming - and I pointed out my very amateur interpretation of patterns around Nepal that suggested to me +EAMT would create an active Pacific Jet starting a few days ago...but the strength of that jet has taken everyone by surprise I think. CC in action? Probably. Back in 2018 the big split has been attributed partly to a very active system in the Atlantic that fired warm air up off high ground to do a similar thing. Very active cyclonic systems have a major part to play in sudden transformative events perhaps? We are in a Nina ENSO pattern but the atmosphere has been Nino all the way. More CC in action? Guesswork - but probably. Amplified patterns, jet energy - all in plentiful supply this winter. Goodness only knows what happens when we next get an actual strong ENSO Nino....

3. More knowledgeable folk than me - Chio especially - have always said that there is no such thing as a vortex than cannot be shattered and brought down if the hit is big enough. He cited 2009 earlier in the winter and I have seen charts posted of that remarkable event when a very active vortex was shattered in very short order. The flux forecast yesterday was 6SD above normal hence my "zoiks". Even the toughest nail can be bent by a big enough hammer.

 

I'll really enjoy looking at this later - and from a selfish angle I'm pleased to be seeing some of the thoughts from a week or so ago actually line up and begin to come good because what happened over Xmas was a knock to the confidence a bit (though in hindsight probably the loss of the precursor pattern quite quickly in December should have been seen as more damaging to prospects later in the month than some of us thought at the time). We are all amateurs searching for more knowledge and if we get a split in 2/3 weeks time our knowledge will be grown further. Can't ask for more than that! (apart from a few snowflakes on top, of course....)

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788452

[Kirkcaldy Weather]

2 hours ago, Allseasons-si said:

Finished work early today

the gfs going for a split now in fl just like some of the 00z ens showed by @Kirkcaldy Weather who posted them earlier...

Appreciate the mention Si

Plenty of mega enticing output which will keep increasing IMO, I've posted the majority of my thoughts for the next 2-3 weeks throughout my recent posts though one biggy I keep thinking is the initial sight-setting to the East&NorthEast is most likely purely MJO driven which gives us huge opportunities that any SSW related downwelling from strat>trop could either enhance or provide further blocking + cold conditions as I believe the typical period for the warmings fully making it to surface patterns averages anywhere upto 4 weeks unless it's a QTR (quick tropospheric response) I've not researched QTRs fully yet tho I think 2009 was in that group.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788463

[Catacol]

1 hour ago, Battleground Snow said:

Beat me to it Feb... This is what it looks on meteociel....

When do you think we would feel the affects of a split? Late Feb or early march?

Yes - Amy Butler wasn't posting for no reason last week. She is the SSW bloodhound....

Impacts all depend on speed of downwell. Phrases like "flushing out" of westerlies would begin to be thrown around (the downwell impacts have to force out any westerly influence lower down first) and then the crucial reality of where vortex shards end up has to be waited for. In 2018 we got the perfect shard that spun to Asia and then tracked west....bringing a large wedge of cold and snow with it! A fast response would be 2 weeks but 4 weeks perhaps more likely. A split on 27th Jan might see a flush effect of enhanced westerlies in the first third of February before the reversal impacts take hold in the middle to final third. Approximately!

But GFS extended is not reality yet.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788438

[snowking]

What a thing of beauty to watch unfold. Relentless pressure on the stratospheric vortex. Wave 2, followed by a huge Wave 1, whilst flirting with the idea of a return to Wave 2. All still way out there by NWP standards, however if this were to bear any sort of reality then the PV is well beyond just being on the ropes.

A fascinating watch upcoming, with something of a wintry flavour in the shorter term to keep us satisfied while we watch.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788477

[Catacol]

Excitement regarding an SSW needs to be held in check because it is right at the outer edge of GFS modelling - and that needs no further comment. But looking for progression and trends is important. A stretched vortex as the first stage has been flagged for many days and by Cohen for over a week. Vertical profile for 192h clearly shows the stretch beginning

This is yesterday's run incidentally. Then we can see, as we get to the less reliable timeframe, the lower vortex gets shunted over the Asia by the power of the warming from below while the upper vortex stretches and twists. Clear stress through the column

Finally, right at the end of the run, meltdown becomes clear. Upper vortex has split with a secondary appearing off to one side and the rest of the vortex as a whole is horribly mauled. 

Today's run, when it appears on this site, will be more dramatic again I think.

Important though to note that prior to yesterday there was little sign of this. GFS forecast had the vortex largely intact bar signs of that stretching. We will need to see the trend of yesterday and today gather momentum and consistency until it gets to within 240h. If this kind of impact can get below the 240h threshold then we can begin to contemplate another 2009/2013/2018 scenario for February. Meanwhile, this week, we have MJO lagged impacts reinforced by the strong downstream impacts of the pacific jet hammering the US to contend with and try to resolve. Cold for a few days next week - Scandy High after that not out of the question.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788517

[bluearmy]

38 minutes ago, Allseasons-si said:

I tell you what,...if these charts keep on showing in fl then i will start to take notice,the prev runs had amplification too so is the gfs sniffing out something,...QTR(quick trop response)?

It’s not a QTR in the sense that the zonal reversal up top downwells at great speed. But the 06z showed the whole atmosphere top to bottom in reversal above 70N.  I would suggest that the strat is weakening to the extent that it won’t provide any westerly momentum above 60N which allows massive amplification in the trop.  Still waiting to see the zonal flow cross section chart for the 12z gfs  

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787918

[Mike Poole]

The change in the strat charts which changed on yesterday’s GFS 0z from run-of-the-mill warmings to something rather more organised, and then went on to the next level on the 6z this morning to a split, had me running for the archives to see what things were like in 2018.  Here’s the charts for the day of the SSW:

Well the trop chart is very similar on a NH scale re the location of bits of vortex to where we are headed right now, choosing GFS T240 as representative of the likely way forward after our cold snap:

So this is what to look for on the strat charts - vortex to be split wide apart in two roughly equal parts, here’s where we were at from the 6z T360:

So, work in progress at the moment, after the first hint on an op run - on future evolution of this potential warming event.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788594

[Eagle Eye]

120E-180 Pacific jet retraction looks quite strong compared to the late December and that's been the shared view with a relatively large loss of AAM.  The -VE EAMT shifting and retracting the Pac jet and leading to the eventual loosening of the Californian Atmospheric River into probably quite a drier period perhaps persistently. The shifting of the jet might be persistent with cyclonic wave breaking linked with the eventual move towards +VE mid-high lat North American heights and so consistent with Trop-Strat coupling for a quasi-stationary link between the +VE Alaskan Block and the forcing on the Strat pattern for the Wave-1 warming. More importantly, it helps with the shifting of the warming Wave poleward and shifting the Vortex but it needs to be a much stronger secondary Wave pushing towards the Scandi-Ural region then it would be a split. Though at this range, the forecast is likely to be well off, in this situation I wouldn't expect that much of a split though as the Wave-2 in Europe doesn't look that strong but if we can get a Tropopause Eddy Heat Flux re-driving towards the Scandi-Ural region then in the forecasted situation; that's the best option. For now it's unlikely but by no means impossible whatsoever...

 

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788814

[Mike Poole]

ECM clusters, and as you might expect from watching the runs all day, a swing towards the scandi high option in the extended.

T120-T168:

Clusters 2 and 3 favouring the early link up between the Azores and scandi, op is in cluster 2.  Cluster 4 we hang on to our atlantic ridge a little longer.

T192-T240:

Pretty much all headed towards scandi block by various means, apart from cluster 5 which doesn’t really show much in the way of high heights, only 5 members in that one.

T264+:

Blocking to the NE on both, cluster 1 probably closer to impact the UK, improvement on this morning’s 3 way split.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788791

[bluearmy]

23 minutes ago, feb1991blizzard said:

While nowhere near a split, this ain't too bad.

That’s quite close to a displacement reversal 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788816

[Catacol]

Anyone doubting the amplification on offer this winter - another extraordinary EPS from last night.

And an extraordinary Pacific pattern too - not often seen such a line of low pressure from Siberia to California like that. And the overall pattern is another snapshot of precursor strat pressure.

The winter started with excitement....drifted to misery as the vortex escaped and reformed - and we are back now in a very very interesting setup. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789006

[bluearmy]

28 minutes ago, Catacol said:

Next 10 days of modelling I think is the winter crossroads. EPS at 240h

Lagged impacts of favourable MJO coming to an end....retraction of pacific jet in clear sight as the north pacific ridge returns. Scandy anomaly in place. So......if the current assault on the vortex over the next two weeks does not shred it then I think it recovers. And if we have not got a high lat block in place by this point then flatter patterns courtesy of MJO IO phases and reduction of overall AAM return.

Best case scenario = vortex binned and continental flow in place. Sets up a cold phase into February. Worst case = vortex still in shape, UK under mid lat high influence ensuring westerly dominance. First half February at least then won't be cold.

We could do with the targetting computer hitting the exhaust port first time....

So much in agreement with this 

can see some wintry broad patterns setting up for last week Jan on the gefs and eps clusters 

watching the zonal cross sections to see how much westerly momentum is being flushed down by the reversal up top on gfs ops - whilst we may not yet be seeing technical ssw reversals, we are seeing a reversed upper strat above 70N and that will feed down in some way.  As I mused a few days ago, it could interfere with a scandi ridge setting up and not allow it to gain enough northerly traction - a few indications that the strat pattern at the back end of the month would be fine for Europe with an Asian master and little left over Canada and as such a reversal wouldn’t be required to bring winter (which would be first half feb rather than later feb) 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789024

[Catacol]

Next 10 days of modelling I think is the winter crossroads. EPS at 240h

Lagged impacts of favourable MJO coming to an end....retraction of pacific jet in clear sight as the north pacific ridge returns. Scandy anomaly in place. So......if the current assault on the vortex over the next two weeks does not shred it then I think it recovers. And if we have not got a high lat block in place by this point then flatter patterns courtesy of MJO IO phases and reduction of overall AAM return.

Best case scenario = vortex binned and continental flow in place. Sets up a cold phase into February. Worst case = vortex still in shape, UK under mid lat high influence ensuring westerly dominance. First half February at least then won't be cold.

We could do with the targetting computer hitting the exhaust port first time....

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789018

[Nick F]

24 minutes ago, blizzard81 said:

I see the age old problem of a massive chunk of vortex plonking it's backside over Greenland. You can see this happen from day 5 onwards on the ecm op and gets bigger and more expansive up to day 10. This is a massive obstacle for us as it means we will probably have to endure the boring sceuro high for quite some time from day 9 onwards. Eating into what's left of winter. 

I don't share such pessimism. I've noticed a trend in recent extended  GEFS, and now extended EPS catching on to the idea (who'd of thought it?), of the TPV over Greenland retrograding into northern Canada, which allows heights to build over NW Russia and  Scandinavia. The retrogression of the upper pattern likely in response to the -EAMT / lowering pressure over East Asia and the resultant Pacific jet retraction. The jet extension bringing the copious rainfall to California eventually fading as the jet retracts, but allowing a ridge to build there as the upper trough over the NW Pacific retracts, but also the upper pattern downstream retracting too.

So potential that the days of the Atlantic domination are numbered with increasing influence from HP to the east. Whether the block developing to our NE brings deep cold and snow remains to be seen, if it does it may take a while if the block holds, but can now see increasing signs that it may influence our weather for the last 1/3rd of Jan.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789130

[mbrothers]

Just now, winterof79 said:

Cracking chart and people need to look at the bigger picture so i dont see why this thread continually  descends into despondency

Agree but sadly it’s the same folk all the time

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789111

[bluearmy]

beginning to get a feel for later week 2 to evolve in a similar way to late nov into dec …… whether we actually see a scandi ridge retrograde is another matter but there are some jigsaw pieces falling into place 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789140

[blizzard81]

Unfortunately I trust the gfs 06z as much as I trust Matt Hancock. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789105

[Eagle Eye]

Teleconnection forecasting right now is difficul there's so much going on dynamically so I won't even bother but the signal for the -VE EAMT would usually suggest an extension of the Atlantic jet but given the base state of the Pacific, it may enhance retrograde WAA into the East of North America whilst extending the Equatorial Atlantic Jet and backing the Eurasian feedback to affect the high pressure cell expansion into SE Europe. Theoretically, that creates the backing for a Scandi based Scandi-Ural Blocking signal with the in-situ Atlantic high also pushing into the UK and eventually poleward to work with the poleward forcing of the Scandi-Ural high to force an Easterly. That would rely on strong extra-tropical forcing by an amplified Tropical-Extratropical forcing causing a quasi strong unstable inertial forcing across Europe and the in-situ trough acting to force an Easterly despite the general AAM signal being against us. Based off the MJO amplification alone that's unlikely but its not impossible as it's being modelled. It mostly relies on how the meridional jet reacts to how the Equatorial jet interacts and that's complicated Physics that I don't know yet. I suspect the Easterly shown the GFS is very unlikely but its in the hat of possibilities. Needs a lot to work in our favour though.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789177

[Nick F]

33 minutes ago, alexisj9 said:

Thread is unusually quite for when we are about to hit a cold snap/spell, more signs at times the SE might stay cold. I'm not sure people are seeing the potential around now.

I guess because there's not really many features to bring snow on offer away from the usual spots of northern Scotland and windward coasts that see wintry showers.

But there is a few features to watch out for, more certain is a frontal wave moving SE across central areas that looks to bring a spell of sleet/snow to N. Ireland Sunday afternoon / evening then down across N Wales and N England Sunday night. Also a developing low running through the English Channel, but most likely just rain/sleet if it gets inland across  S England

Tuesday a small low running SE across SW England on some models, could bring some snow to SW / CS England if as far north as 00z EC and 03z UKV.

Wednesday may see further troughs / fronts drop south as winds veer northerly

A few lucky areas seeing some snow in the upcoming cold snap, but by no means is a risk of snow looking widespread. Particularly inland parts of Britain.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789176

[Mike Poole]

ECM clusters this morning, T192-T240:

Equal split into 2, the op in cluster 2 which shows the evolution to scandi high.  Cluster 1 maintains separate highs over UK and Russia.

T264+:

Options in the mix this morning are with decreasing likelihood: scandi high, UK high, retrogression to Greenland high - and - dross.  

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789007

[phil nw.]

Quite a messy picture in the next few days as the low crosses the Uk and drags in the cold air behind it.Looking at a couple of fax's we see a number of fronts and wave developments heading down in the cold north west and then northerly flow.

The Arctic air established pretty much countrywide by Monday.No doubt some locations will see snowfall but as ever more than a day or so out tricky to forecast where and how much.Even the short range models vary on this.

Looking at the daily temperatures next week it like being the coldest period since early December with max's further north around zero and low single figures elsewhere.Sharp night frosts expected. 

The Warks.ens show the change to cold.

Looking ahead current outputs favour a pressure rise towards the weekend with cold upper air being pushed away.As can be seen on the graph some recovery in daytime max's towards average are showing.

EPS day 10

Currently favouring the high near the south with milder Atlantic air across the north.

Where this goes beyond remains to be seen.With later mean anomalies showing ongoing Scandi.ridging we can never rule out this building west as zonal winds continue to reduce.

Warmings continue above and these may come to our aid just as the effects of the last mjo on this side of the hemisphere die away.

One good thing is that this current low looks like it's the last one to affect us for a while as it heads away towards Norway early next week.Thank goodness after all the rain we need a break.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789173

[Catacol]

1 hour ago, Penrith Snow said:

I think there is too much emphasis put on SSWs, winters were often cold and snowy between 1962 and 1987 but very few had SSW’s.

This emphasis on SSW is all down to the link identified with the BFTE in 2018 but the Trop that winter was already set up for HLB hence the cold spells well before the SSW occurred 

This winter is very different and with the El Nina signal of positive AO and NAO late winter I really don’t expect a notable cold spell in February 

Andy

1980s SSWs =

Feb 79, Feb 80, Feb 81, Dec 81, Dec 85 (split), Jan 87. 6 SSWs in 8 years that had frequent cold spells. In the last 8 years we have had Feb 18 (cold that followed), Jan 19 and Jan 21 (chilly, very close to cold but didn’t quite land.) Three. Correlation is not the same as cause but the idea that the “cold” and seasonal 80s happened in the absence of strat action is not correct.

Pre 1979 data is much less available but there was certainly a Canadian Warming in Dec 62 and 8 warming events in total across the 1960s.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789775

[Sweatyman]

1 hour ago, Kasim Awan said:

Looks like another dissapointing spell snow wise.

Like i said it would be. As rubbish as the last 'snap'

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789694

[Catacol]

EPS this morning painting a knife edge scenario

We have low pressure where we want it over Italy and we have a momentum pattern that is retracting, allowing (in theory) the pattern at high latitude to back west where eddies form. But any blocking that sets up near Scandy is perilously close to being too far south. Part of the cause, as BA has already correctly stated, might be the fact that - as movement towards a potential SSW gathers pace - the lower TPV is being forced towards Russia and acting against tropospheric forcing that I am sure favours heights in that area. Note however that some modelling is also splitting that low TPV as it is pushed towards Moscow

 

Short term pain for long term gain? Or short term pain on top of long term failure? U.K. cold weather fans could be excused for claiming that “if it can go wrong it will go wrong” - we will just have to wait and see. Those who have been on here a long time are hardened now to cold fails. But….the dice are still rolling on this one and I’m still seeing (as I always do) the chance of a double six. Scandy High = cold continental feed followed by SSW that drops a daughter vortex into Asia backing west. That will do fine and dandy thanks very much!

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789796

[Penrith Snow]

I think there is too much emphasis put on SSWs, winters were often cold and snowy between 1962 and 1987 but very few had SSW’s.

This emphasis on SSW is all down to the link identified with the BFTE in 2018 but the Trop that winter was already set up for HLB hence the cold spells well before the SSW occurred 

This winter is very different and with the El Nina signal of positive AO and NAO late winter I really don’t expect a notable cold spell in February 

Andy

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4789734