Model discussion highlights

[Nick F]

Morning, the EC ensembles point to it turning milder after next weekend

Glasgow                                   London

But I don't think the Atlantic is totally resolved beyond this week, as other have indicated, UKMO maintain blocking around Greenland for longer and thus delay the phasing of the Atlantic low with the upper trough and low pressure over the Norwegian Sea and I still think this is an option on the table that can't be discounted.

GFS and EC are keen for to pull the +ve heights away from Greenland next weekend, as the ridge builds north across Alaska towards the pole, this allows pressure / heights to fall over the far north Atlantic with the phasing of Atlantic low and low pressure to our north and northeast. But this is quite a change for EC compared to the 12z yesterday, which kept a blocking wedge to our NW, stronger TPV over Canada and less poleward ridging over Alaska.

Expect more twists and turns...

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4761704

[mushymanrob]

Sorry, too much to wade through so sorry if this point has already been made...

Which ECM run to believe?
Well as this concocted frame below illustrates, IMHO the ECM 12z is close to what the NOAA charts are predicting. The Anomalies are centred on the 18th, the two ECM charts are the 12z and 00z for the 18th.

IMHO the current ops are over stating the incoming atlantic system, the Anomaly charts does not support a low of that depth, but suggests the ECM 12z is closer to the mark.

Plus..... deep cold doesnt usually get swept away so easily, theres often a lengthier battle, thats experience talking! I dont believe the current ops.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4761962

[bluearmy]

35 minutes ago, FetchCB said:

Reading the Met Office further outlook seems to suggest that they believe that the low approaching from the south west will slide into France as the only mention milder in the south and west and cold in the North. This scenario which would drag colder air from the North. 

They have more data than we do but have to react to changes in the modelling 

I suspect they see any relaxation of the cold behind next weekend being a temporary thing - it’s not easy to paraphrase the forecast for the whole country over a 10 day period! 
 

the phasing of the low heights to our west looks pretty certain now. Ukmo is isolated on this. But that doesn’t necessarily lead to what the ec and gfs ops are showing. There remains lots of moving parts on the evolution -  getting the trough to clear further east (because heights look to stay reasonably high to our northwest) seems pretty important to get cold back across nw europe 

as others have pointed out, the NH profile offers much encouragement for amplification to continue 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4761885

[Paul]

Really interesting set of ECM ensembles this morning. If you just took the line graph, you'd be forgiven for thinking it was carnage - a distinct jump to milder temperatures then who the hell knows for London. 

But, strip the noise out a bit, and there's a reasonable pattern in there. A definite uptick in temperatures during and after next weekend. But then, a cooling off again does seem most likely, with the level of cooling the biggest question. The bottom end of the 90th percentiles take it potentially about as cold as it is now, but with plenty of uncertainty around that, as you'd expect at this stage.

The uptick in temperatures is most pronounced and a little longer lasting the further south you look, as you'd expect.

London:

Derbyshire

Highland

So, we have a week of cold air still to come, with interest in terms of patchy snowfall, very low minima and freezing fog in that period. We'll maybe need to watch for transient snowfall as that milder thrust arrives (assuming it does), and during the next few days, the longer range pattern is likely to become clearer too. Will the milder air materialise? (Looks pretty likely at the moment).  If/when it does, we'll need to answer the question as to how mild and how far north than mildness gets?  And how long it may last before the cold attempts to return?

Interesting times..

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4762002

[Catacol]

No snow here yet, and the winds steadfastly refuse to ease in from the east so a bit frustrating currently for the East Midlands in general. Still - the little mini experiment regarding whether the U.K. can build its own cold pool I think is complete. Coldest here on Thursday, a bit warmer Friday, warmer again yesterday and today the car was thawed before 10am. Conclusion - even with zero wind and a December sun the cold gets mixed out steadily. We need reinforcements to maintain our cold when sat in the eye of a trough as is the case in Lincolnshire right now.

This the chart key for me today.

 

The Atlantic profile on a knife edge….but old hands know that high pressure sticks around more than models tend to spot, and so my take would be that a southerly adjustment is likely. Remember what happened to the modelling of the Azores Low for midweek - classic case in point. Now forecast to be nearly a non event. I wouldn’t be at all surprised to see a gentle rise in 850s for the south in particular next weekend, but nothing especially “mild” in the mix.

Meanwhile upstream the next pacific amplified wave train kicks off. Note the substantial trough coming out of Asia, the Alaskan High being pushed up ahead of it and then, at the end of the run, a substantial Aleutian Low signal in place.

 

Extended modelling of course - and the arrival of this next phase is a little later than I had expected it to be - but it is incoming. Whether we get proper cold hanging on or not next weekend will be a close run thing, but I expect the return of blocking for the Xmas period. This could be the previously advertised Scandy High or, depending on the context across the US, it could be a surge of Greenland heights once again particularly if that Alaskan eddy cuts so far north that we get some cross polar flow. Will have to wait and see. But I don’t expect any “mild” phase next weekend to last long at all - assuming it arrives in the first place.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4762338

[blizzard81]

53 minutes ago, bluearmy said:

A little adjusted as per the mean re the phasing 

a little less troughy across the U.K. by day 6 

The updated ecm 06z control at 144hrs compared to the 00z control this morning for 150hrs. You can see the improvement for those of a cold persuasion. The ridging down from our north west is more pronounced. This will put more pressure on the atlantic low as it moves towards us and also keeps the cold flowing in from the north. This trend is exactly what we need to see continue on the 12z runs. 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4762519

[Cold Winter Night]

With FI still at 96h, max 120h if you're stretching it, we can be sure of cold until the end of the reliable, because the cold is here now.
Maybe not as cold as you hoped, maybe not with snow for everyone, but it can't be denied that it's here.

Perhaps comparisons to 2010 or the like are always a bit unfair. Many Decembers of the past have seen cold episodes like the one we're in right now and for some they end up being more special or memorable than the Big Ones.

A face value evaluation of the ensemble output suggests we're going milder, especially the further South and East you are, without a return to real cold before Christmas.
The De Bilt 2m plume is ugly in that regard. The KNMI (Dutch Met Office) speak of a 70-80% chance of milder and unsettled later on.

A return of the cold would take a big swing in the ensemble.

However, in the 96h+ timeframes much depends on the handling of the Atlantic. Many posters have discussed this in great detail, but whether the block is stronger, or better placed than models show, makes all the difference both in that mid term and in what follows longer term.

To many observers it may seem like many in here who expect a better setup than the models show are being silly, or even in denial, but tendencies to underestimate blocking and cold are not without precedent.

Even comparing the EC 0z T+144h of 6 days ago to what it actually looks like today at T+0h reveals a lot:

- The Greenland block is stronger, in better shape and more East-based than EC Op 'thought.'
- That infamous tropical storm low is much smaller and less deep (location is spot on though).
- There is an Alaskan ridge and associated trough along the US/Canadian Pacific coast, which ECM did not foresee 6 days back.
- The Russia/Kazakhstan High has been pushed slightly more SE than foreseen.

For De Bilt that results in the next few days being colder than forecasted based on the 5 December 0z EC/EPS.

So, my point is, there's still a lot of interest in the models, because of the NH pattern, we may see surprising shifts in the output.
Maybe already in the next few hours of 12z's, maybe over the upcoming week, or maybe not! Isn't that the fun of model watching?

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4762561

[johnholmes]

I hate to spoil the party but the predicted 500 mb flow on my usual charts (NOAA 500 mb anomaly charts) for several days has slowly but surely dropped any ridging E or W of the meridian. Instead it has over those days gradually delivered what looks like a mainly westerly flow from where the main trough is placed (eastern north America) out into Europe.

This is also backed up by the 10 day ECMWF set of charts (the show 500 mb flow, surface pattern, along with the 850 mb temperatures.

The general date for this to be fairly well installed looks to be settling down to around 17 perhaps 18 December. By the second date the -5c 850 mb temperature is shown well north in the UK.

Of course they may both be wrong but in my view that is rather unlikely, but I'll come on here and accept it if this prediction is way off the mark.

Sorry about not being able to show the ECMWF charts other than as very small maps.

http://www2.wetter3.de/Fax/00_ECMWF_ENS_p0_500hPa+144_240.gif

NOAA charts 6-10 and click on it for the 8-14 output

Climate Prediction Center - 6-10 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

 

 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4762596

[Kirkcaldy Weather]

51 minutes ago, IDO said:

No sugar coating, the models, if correct they look bad for the foreseeable, the rest of December. No sign of any HLB'ing, and the Arctic wedges (high) never really create much unless accompanied by mid-high-lat forcing. The wedge in Greenland forces nothing instrumental to change away from a west-based flow for the UK.

The doubt about the Alaskan ridge (overplaying heights by the usual suspects) looks like a strong possibility, now more a belling mid-lat omnipresent HP cell based on the Eastern Pacific conus.

UKMO D7 charts (or D6 come to think of it) def have a garden path aura, so I would not hang my hat on that chart.

The D8-16 GEFS mean: 

That has a familiar early winter look.

The usual caveats, that nothing is set in stone and that this is based only on a few recent runs by the models.

 

I'm not sure what's so bad about the modelling, weather always has a constantly evolving nature even in blocked setups like we have currently, interesting how December 2010 also had a brief warmup before the 2nd cold plunge arrived. AO running similarly negative to Dec 2010 

There is high latitude blocking aplenty in the outputs which is likely to be getting a boost from the substantial +EAMT event setting up at the min and MJO progression through a number of phases. 

Possibly we see the US benefit most from a cold and snowy setup initially but could also see potential routes that provide us with a pattern not too dissimilar to current conditions 

With the above ingredients at play we likely should look for a high from the Pacific moving into the Arctic and towards Greenland 

ECM 

GEM Ensemble Mean 

And if we look at where we were 2 weeks ago ..

Those who were doubting the Greenland High development then as they were with the Scandi high beforehand might again be unwise to continue that downbeat attitude

 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4764182

[MattH]

Morning...

The evolution this weekend and into early next week is not yet completely resolved. While, overall, the most likely outcome is a SW'ly flow and a breakdown in the prolonged cold spell, there remains enough intricacies within this evolution to not yet write off something like the 00Z UKMO run. It remains a problematic area for some models, in particular, developing lows and cyclogenesis from the SW and it is interesting to see how the UKMO model splits the lows and has the more northerly low on a more easterly position, clearly the end result is a quick return to cold.

There remains a handful of MOGREPS members as well that maintain this evolution, as can be seen below by Monday of next week and, once again, a week in meteorology when it isn't a standard, dominant W'ly regime is a noticeably long time.

In terms of details, in particular, confidence is very low for next weekend. Subtle changes to the flow, whether a more directly S or SW'ly or any sort of SE'ly element could mean the difference between little or no snow on the breakdown, to a significant snowfall event, albeit brief. Primarily, more consistency is required as to how the broader evolution will progress first, before any sort of details arrives for next weekend. Despite the ECMWF and other models blowing the cold air quickly, it also remains interesting to see a significant spread there as well for next weeked, albeit with a clear grouping (10-30%) showing the rise in 850's. N England example...

Where we go from there is anyones guess, but I would certainly put money on the outlook NOT being dominated by a sudden shift to a robust +ve NAO pattern through the rest of December. Therefore, please do ignore some of the posts suddenly writing off the rest of December, etc, as there's just no evidence for such an evolution given the broader signals.

It is also now interesting to see a clearer and cleaner signal for the MJO to get on the move, now that the I/O cyclone has stopped muddying the signal. Both the EPS and the GEFS signal a decent -ve VP200 signal towards phases 4-5-6 looking ahead. This may well have implications on late December and into January, depending on how it evolves.

So, to quickly summarise - The emphasis is on a change this coming weekend, in some shape or form, but do not yet write off the evolution of the UKMO just yet, as much of an outlier as it is because how the breakdown takes place is very complex in terms of cyclonic development and evolution from the SW, plus also this separate low to the north. Beyond that and my money is firmly on further potential blocking patterns through the rest of December and into January and for us not to suddenly shift to a +ve AO and +ve NAO outlook as can often dominate this time of year, etc.

Kind regards, Matt.

 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4764298

[mushymanrob]

Well it has to be said...my favoured NOAA charts failed to spot the deep Atlantic trough and have had to back peddle over the last 24 hours.
The GFS picked it up first, and the ECM and EPS followed soon after...
The attached charts illustrate how they played catch up ...... But like i/we have always stated, they/no model prediction suite is right 100% of the time... and in this occassion the NOAA charts lagged behind the others.

Talking of which, im liking the EPS, it seems to be accurate although ive only just started using it. But i like the way the slider covers every day seperately so we can see the development of the pattern. It makes it easier then relying solely on the NOAAs mean charts centred on days 8 and 11. Plus it gives a better idea beyong day 11 where the mean gets dodgy.

When the EPS and NOAA agree on days 8 and 11, thats added strength to the synoptic patterns accuracy...

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4764556

[Kirkcaldy Weather]

2 hours ago, Gowon said:

The Beast is waiting to pounce.

Just wanted to add to this, whilst it might not be directly relevant to our setup at the mo should we see blocking align favourably we are already at close to record intensity to the cold over siberia 

 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4764775

[Tamara]

Just wanted to wrap up some recent analysis by way of conclusion: This was posted a week back in the old thread:

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

I continue to think that ultimately following attritional battleground forcing (and a very wet and muggy period of weather in my SW Europe locality) there will be something of a lifting of the cold air from the south for parts of NW Europe, including obviously the UK. Clearly the further south one is most likely to see this. 

A downstream ridge building from the sub tropics into Iberia (following the low-pressure sequence) could well then build northwards. Much a similar sequence as occurred from last weekend and early last week.

As stated in the last post - it is a case of how any energy put back from the sub-tropical -ve NAO jet regime into the polar jet then interacts with this process and how much unstable-ve zonal wind inertia remains at higher latitudes. This sensitive balance of opposite forcing, meaning the difference between a European mid latitude ridge and Atlantic trough, or a re-connection of a northward building ridge to arctic high pressure and cold pooling. How far this cold pooling is dislodged through attrition is finely balanced. 

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

 

The ultimate attritional nature of the breakdown is set to be rather less than perhaps anticipated,  but the broad thrust of that analysis looks set to verify closely for the coming weekend with the suggested return of an Iberian ridge now clearly modelled. With that in mind the 'fork in the road' discussed in a few other posts also comes clearly and precisely into view.

The re-building downstream Iberian/Euro mid latitude ridge interestingly has been poorly modelled in extended modelling (e.g the ECM monthly modelling) but a rinse and repeat of the last week of November heading into December modelling (which commenced with a building Iberian ridge that moved poleward to connect with heights to the north east_ was a self-evidently sound pitch based on tropical>extra tropical forcing and how much +ve AAM inertia had accumulated in the atmospheric circulation.

This next time around, with the next building sub tropical ridging, continues to look much more problematic to call than the poleward ridge that built to Scandinavia the first time around. On the one hand, and unlike last time much more cold air has amassed close to NW Europe to re-advect, (should there be a reloaded -ve AO/NAO pattern) but this time with angular momentum now at a lower base state (one has to consider wind-flow in the extra tropics as well as just the MJO) and (personally) still not sold on the next round of propagating tropical convection through the Pacific having the same 'teeth' as the previous mini ENSO cycle, there is more work to do to reload the pattern sustainably. Much was spoken about MJO periodicity (timeline re-cycling of amplitude tropical convection waves) if anyone wanted to look.

Commitments and other matters here in Portugal mean no further updates but a close watch from afar when time allows will be interesting to see how things pan out. Enjoy the rest of the winter whatever the weather patterns evolve.

Best wishes to all for Christmas and into 2023.

 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4764784

[weatherguy]

Hi all, taken a few days off to avoid model fatigue and to actually enjoy the coldspell that has taken hold - some lovely scenery around up here the last dew days!

Anywho, let's take a look at what the models are indicating in the medium term, using +72h as the starting point...

The GFS 72/96/120/144/168/192/216/240

The cold air established over the UK starts to see its influence wane as heights slowly build over the continent, and due to the angle of the incoming LP from the west (caused by the absence of a significant block) we establish a S/SW flow going into Sunday.  Interestingly, the warm uppers don't last long as, while we appear to enter a more zonal phase, the atlantic is very low-power for the time of year due to the core of the PV remaining on the Asian side and the emergence of an Aleutian HP system.  This means that we are subjected to a period of "cold zonality" with shots of PM air from the north-west as we move through the +144-+240 time period.  With a cut-off HP effectively acting as sticking a rod into a bike wheel, we can again see signs of more northerly blocking across the NH profile as we move into the more long-range period.  

I won't go into huge detail with the ECM as the 12z will be out soon, but we see a similar outcome here.

ECM +144/192/216/240

Again, S/SW flow established into Sunday, followed by the introduction of PM NW airflow (interspersed with TM SW airflows).  We also see the development of a combined Aleutian cutoff high and some renewed ridging towards Greenland.  

Something to keep an eye on is the state of the sPV, given the stress that the tPV is still under. 

 

This +168h chart shows the sPV is quite elongated after sustaining some mild wave 2 activity.  No signs of an SSW just yet, but this is not looking like the typical raging December PV, and this can only be good news for longer term cold prospects.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765058

[Uncertainty]

The next steps we take this winter have been very challenging to forecast - unlike the present cold / blocked spell which was very well highlighted by seasonal, sub-seasonal and analog modelling. For me, given the weakening east-based La Niña, a second ‘bite at the cherry’ in early January has always been plausible. The ec 46 has been consistent on this since the period came into range and today’s model continued the trend.

 

There have however, been two highly notable shifts in the output between runs:

1) The mjo 

There is now a reasonably strong signal to take the mjo into the WP around the new year. This would, all other things being equal, suggest a renewed effort to reinforce blocking signals and - more sceptically - serve as the precursor to an ssw later down the line, especially if high amplitude can be achieved in p6/7. Compare this to the last forecast (perhaps sullied by tropical systems in the IO?) which had a more -AAM look and a stay in phase 3/4

In my experience, a protracted stay in these phases usually correlates to an extended westerly phase for us. 

 

January Phase 5, 6 and 7 Nina composites, on the other hand, suggest a blocking signal.

I am not suggesting a 2+2 = 4 relationship with these mjo charts, more the simple fact that a reasonable amplitude run through p5-6-7 is far more preferable for blocking than an extended stay in phases 3 and 4.

The other major change is upstairs, where a significant uptick in zonal wind speed is noted. It doesn’t last, but date records could be threatened. This is not what one usually sees before a notable cold spell!
 

The trop charts for early Jan do not presently indicate a fully coupled strat and trop though, and blocking is still very much evident.

W4

W5

The precip charts for early Jan also indicate Hp to the NW and perhaps low pressure over S Portugal then the med.

 

So our interesting winter isn’t over yet. I’ve always been keen on an ssw this winter - the wqbo/low solar, favourable walker circulation combo and past analogues back this up. But it’s clearly not going down w/o a fight. Were one to occur, soon after the anticipated early Jan blocking wanes, then we could end up with our first -NAO or even colder than average winter for many years. Equally the power up could proliferate through the levels; the mjo WP progression could falter and we’re back at pv of doom purgatory once more. 
 

As ever, the Xmas period could well be crucial in determining which direction the fork in the road takes us.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765372

[Singularity]

Just realised that if you run through the GFS 12z days 8-14 on the N Hem view, you can see a really neat example of a longwave upper ridge retrograding from the Pacific side to Scandinavia. Such longwave features do in fact behave like that, the big question then being whether the polar jet forces it quickly south or allows it to hold at the mid-high latitudes long enough for cold continental air to work its way across to the UK.

Just one of many possible ways in which the highly amplified Arctic patterns might play out during the 2nd half of the month.

We might instead see the high on the Pacific side try to link with an Atlantic ridge.

Either way, seems to be a more dynamic half to the month coming up, with a higher propensity for milder interludes in the south but also increased scope for collisions and interchanges with cold airmasses.

Consequentially, it's not looking as dry overall (which is not saying much where I am - all that's accumulated to date is fog and frost!).

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765393

[Cambrian]

Halfway through advent, the 12z ECM ensemble mean out to day 12 is fitting viewing with a good glass of wine, some crackers and cheese.  I admit that I’ve not captured the last three days of the run as it descends into the usual norm-seeking stagnation, but in the modellable period, Greenland heights look to be relaxing just enough to let the Atlantic in for a while. 

From this at least, the current very cold spell ending next weekend, milder with a southwesterly then westerly signal for a while, a bump of heights from the south around day 10, but then potentially colder again from the north via the northwest under the influence of a renewed Norwegian Sea / Scandinavian trough (a tendency throughout for this to set up there) being pressed from the north by a robust looking polar high, southern European heights the big unknown.

 

Plenty to play for with the Northern Hemisphere profile though, the PV getting its Arctic coverage back together somewhat (only to be expected after this exceptional period), but around an emphatic polar high, and even away from there, at day 12, the pressure over Iceland is higher than over the UK and Ireland. 

At day 12, Christmas Eve (good Lord, how did we get around to that again so quickly?) on the 12z GFS ensemble, a very similar mean to the ECM, but with the anomaly with it, higher heights beginning to work their way through Iceland again, joining those all the way from the Atlantic through Greenland, the pole and eastern Siberia. Interesting too how that purple blob of lower heights over Arctic Canada doesn’t even show up as a weak negative anomaly, weakly positive if anything. 

 

The signal is resoundingly neutral. At this time of year, with no imprinted jet stream pattern, in that space between the northern block and the weak, frequently fragmented jet, we’re likely to see plenty of shallow low pressures milling around in cold air looking for somewhere to dump their wintry loads.

And so a reasonable chance we’ll be back in business for more seasonal weather through the Christmas period Whatever else at this stage, a properly cold start to the winter, no swapping out of the template, and plenty of road.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765444

[Uncertainty]

13 minutes ago, feb1991blizzard said:

Quick question - would a phase 3 MJO not be favourable for triggering an SSW - it just seems logical that a storm track in that part of the world could lead to an East asian mountain torque event, caveat being we would want it to do a circumvent carrying on its merry way right round to the high numbered phases at high amplitude and not die a death.

Google Scholar

SCHOLAR.GOOGLE.COM

Have a look through this Feb. Backs up what you’re saying that a full progression from p3-8 at decent amplitude often precedes SSWs. I personally feel that the ideal trop config is a strong scandi-Greenland dipole, followed by high amp p6/7. Much like we had in Jan 18. The west based -NAO / Scandi trough we have now does the reverse (perhaps why we are seeing a strong uptick in SPV strength in the coming weeks).

Also there looks to be a significant +EAMT event over the next week or so, these often precede SSWs but no sign of one in the next 3/4 weeks at least.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765411

[MattH]

Just a quick one, but there is cross-model agreement on the amplification once again into early next week, but what is lacking is consistency, so despite some of the usual silly posts in here, rest assured the outlook isn't confused and it is one of interest still with regards to the N or NW'ly flow that has an increasing probability once the weekend's low pressure has cleared away to the east.

The 00Z GFS Det is, clearly at one end of the scale, in terms of the amplification of the pattern, but in this regime we need to keep an close eye on the orientation of the troughs and associated lows over Newfoundland and far E Canada. These can be crucial in determining whether any N Atlantic ridge is flattened or whether, in association with WAA, the ridge builds, clearly the 00Z GFS Det does the latter, in a significant way.

To me the atmosphere remains pre-disposed to amplification. There is no obvious strat and trop connection and as mentioned yesterday my money remains firmly on a pattern that is more 'unusual' than 'usual' for the time of year, we all know what 'usual' means in this instance.

The overnight monthly remains very interesting indeed, with extensive +ve anomalies, both MSLP and 500mb across the N Hem looking ahead. As usual the exact positioning of these ridges and associated troughs will determine the sensible weather as the next few weeks progress, but there remains clear evidence (despite with some on here suggest) that the way forward is further amplification, in some shape or form which maintains a higher than usual risk of further cold synoptics.

Just to highlight a couple of stand-out plots to me from overnight are the MJO RMM signal once again, which has high confidence now of phases 4-5, but with clearly interest (green and blue dots) for getting around to phases 6 and 7 looking ahead, which is still expected, despite what some may suggest and the ever useful regime plot clearly highlights a bias on blocking patterns as well.

A fascinating and interesting outlook remains...

Cheers, Matt.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765745

[nick sussex]

This is the likely evolution if there was a ECM day 11.

The first chart which is day 10 shows the direction of the shortwave running ese.

This would run into the base of the Scandi trough and become absorbed . The Arctic high to the ne should extend its influence sw . 

The next chart shows the likely day 11 chart .

You’ll have trough ne Canada , high pressure to the ne extending a ridge sw to the west of the UK and then deep trough to the east .

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765740

[Nick F]

Some encouraging trends / upgrades from the models this morning, GFS in particular. Think James (Singularity) did mention to look out for the Euro high to be flattened more and that's what we are seeing, which allows a less mild outlook, with potential too for cold arctic air to return from the north. 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765699

[bluearmy]

Not sure if it will be right but I have noticed renewed hook up of the developing Canadian segment and the Aleutian low - itself connected to the Asian segment. Creating a ring around the Alaskan ridge which looks likely to retrogress to Siberia (which I think closes the retrogressive trip around the hemisphere which started with our scandi ridge around the 25 nov - not seen that features make it west from there before ) 

Anyway, if the link up does verify then it draws some energy west from the Canadian which is even more support for amplification in our sector of the NH to close the year. 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765782

[Mike Poole]

ECM clusters T120-T168:

Still considerable uncertainty about the extent the two lows in the Atlantic phase, and it really matters for the UK.  Looking at T144, here are the 4 clusters in the same order in detail:

Clusters 1 and 3 have the lows phased by this point, and the WAA (black arrow) builds the European high as well.  Clusters 2 and 4 retain the southern low as a separate identity, and pump up the European high much less, while at the same time allowing CAA (yellow arrow) to begin to restock the UK’s cold from the NW.  

The trend of the last 24 hours, is towards clusters 2 and 4.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765790

[TEITS]

Promising set of model runs this morning.

I think its pretty clear any mild spell will be shortlived before the cold returns via a N/NW,ly. Now if I remove my cold ramping hat off for a minute, I would say the outlook in the medium range is uncertain and comparing the 0Z ECM +240 N Hemisphere to the 12Z highlights the big difference between runs. I shall add that Nick S is exactly right with regards to the ECM and what would happen beyond +240.

So in summary if you're a fan of cold weather then you should be pleased with the output. The ingredients are there for a classic cold spell. What I will say is contrary to what someone was saying the output is not your typical UK winter weather patterns. Viewing the models from a N Hemisphere perspective clearly shows this.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765833

[chionomaniac]

1 hour ago, georgiedre said:

Come on give us your excellent assessment of how you think it will end 

All down to the MJO, this one. And if you ignore the CFS and look at the 850 u wind alongside the 200u wind forecast anomalies in the western Pacific then we have movement on this front. So simply put, we can welcome back the cold for Christmas, and this then will give the Strat another push towards breakdown of the stressed upper vortex, probably early Jan for that though. 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4765817