Met4Cast

January 4

Deterministic a clear outlier during the 'messy' period now which does unfortunately mean we can't take much stock in what it goes onto produce in the latter part of the run.

Though, i'm not sure we would have done anyway..

January 4

The messier evolution of the Det doesn't seem to be supported within the GEFS with many inc. the control opting for a much cleaner route to Greenland. Det is at the top of the pack pushing outlier territory during the transition period.

January 4

This chart rivals anything we've seen in the past few decades. This is the holy grail.

January 4

Just now, northwestsnow said:

Its prerty much porn at this point..

the slower evolution seems to produce even better results...

The Riley Reid of weather charts..

Incredible how we've managed to go from something that looked like going wrong to that absolute belter! This evolution whilst messy would probably end up being snowier than the cleaner route.. risky though.

January 4

1 minute ago, TSNWK said:

True.. but we used a fair amount of contingency to avoid a different pattern... not much left in the bank on the 12z

The bank is preparing to open for business, but exact opening times may shift..

January 4

Encouraging that despite the wheels almost falling off we still end up in a situation with Greenland blocking and cold air aimed directly towards us. So often we see the wheels fall off entirely but that's not happened here, just a slightly different evolution with the end goal still reached, to me, that's very promising that this is a strong and (to quote our former prime minister) stable signal.

GREENLAND MEANS GREENLAND etc.

January 4

Just now, sheikhy said:

Also i think its about time we took this low to the southwest thing seriously cos it could ruin everything lol!!!!

The low coming in from the SW helps, it undercuts the high pushing energy NW to Greenland, on this run though it seems the GFS is struggling with the undercut portion.

Lets wait for the ensembles.

January 4

1 minute ago, frosty ground said:

So at 132 the cold uppers over the north of England have pretty much mixed out but by 138 they intensify and I can’t see why

nothing major just a curiosity

Cooling in situ underneath a cold area of high pressure.

January 4

39 minutes ago, MattH said:

Hi.

I just wanted to create a post from an educational perspective and also be a point of reference regarding the importance of the GSDM and the AAM on the medium and long term. Hopefully, anyone who questions this should change their mind after reading the below. The reason it is worth doing this is because there is no better, clearer, example of the importance and connections between those upstream, Pacific developments and the downstream influence.

I'll attempt to highlight and stitch this together using some of the usual plots and charts which tell the story so very well indeed and it is this which, hopefully, helps people to at least better understand the influences of the GSDM and what to look for moving forward.

OVERVIEW: Firstly, we have just endured a very wet December, this comes as no surprise given what happened to the AAM in late November. Interestingly, seasonal models all pointed towards December being a +ve NAO month, in keeping with the long-term teleconnections with regard El Nino and a +IOD in early winter. The late Nov and early Dec cold spell can be linked back to the behaviour of the GSDM too, while what followed through much of December certainly can and what is happening now and looking ahead, most certainly is. Despite a weakened stratospheric polar vortex, it is the troposphere that is 'leading the dance' rather than the stratosphere for the most part even though it is lending a hand.

The late Nov/early Dec blocked pattern has links to the temporary rise in the AAM in mid-November, with the usual lag in place. We can see this first evolution in the below plots...

The second and more obvious evolution was then the more pronounced fall in AAM through late Nov as the MJO returned to the W Hem and westerly inertia was removed from the GSDM budget and, as usual, AAM fell along with a -FT (Frictional Torque) and -MT (Mountain Torque) event. The result was, as ever, propagation through the extra-tropics and then into the mid-latitudes of more westerly momentum, propped up by easterly momentum at circa 30-40N - Remember the inflated Azores high in the run-up to Christmas? - We can see how the +AAM anomalies, in particular, were distributed through the atmosphere within the usual window of approximately 14 days. No surprise we then saw an enhanced period of +AO and +NAO conditions just before mid-December onwards.

Lastly, comes the 'big event' within the last week or so in terms of the pronounced rise in AAM. Once again, in complete contrast to what happened through mid-November, with a lag of course, we can see how the marked rise in AAM has allowed the propagation through the sub-tropics and into the mid-latitudes of more easterly inertia (-AAM) very well indeed, this is particularly obvious on the relative AAM transports plot, as highlighted below. Once again, no surprises at all and of which has been documented by the usual few on the group we are now seeing a complete reversal of that +AO and +NAO period with an array of mid-latitude and, eventually, high latitude blocking patterns.

We can also see this visually on the zonal wind plots at 100hPa (top of the trop/bottom of the strat) too.

While like in many areas of meteorology, there is never often a usual "a+b=c evolution", but this is about as close to that as you can get. We have certainly had help from the stratosphere here mind because a robust stratospheric polar vortex that is downwelling westerly winds into the troposphere can often be the dominant player, overriding what has occurred over the last month. There is likely to be some 'help' here from the El Nino and eQBO combination this winter as the sPV continues to remain disorganised and far weaker than it can be at this point in the winter with far less influence on the troposphere too.

When it comes to the AAM it is crucial to be able to accept and acknowledge when there are other overriding influences and counterbalances. Tamara et al often talk about not taking the MJO at 'face value', it is similar with the AAM, but when you combine the usefulness of the GSDM and all it incorporates then, as I have perfectly examined here, nobody can ever say the likes of the GSDM and the AAM is "flawed or useless" when it comes to pre-empting NWP, at times, and also gauging how the broader patterns may evolve and shift.

As I mentioned at the start of the post, I wanted to put this one together because there is no better example of the usefulness of the GSDM than what has occurred over the last month or so. The evolution and 'story' of the atmosphere have been well played out in these plots.

For those who want some winter weather after the last few weeks of very wet conditions then 'this is your time'. We approach mid-winter with such solid footing for cold synoptics that it should be a pleasure to watch the more unusual patterns being modelled in NWP and, interestingly, this continues to link in well with the majority if not all of the seasonal models with regards to how Jan and Feb and perhaps even Mar should progress. Winter is about to start...

With regards, Matt.

This is one of the best posts I think I've read on this forum in explaining the GSDM & how it can be used as a fantastic tool to gain insight to the sub-seasonal forecasting timeframe and it's usefulness.

A few on here in recent weeks have snubbed the idea of using teleconnections because it hasn't necessarily 'gone right' in terms of their expectations/biases but this post perfectly demonstrates how this upcoming period of blocking has been well advertised within the teleconnections (AAM, MJO, GWO etc) and that has done well to provide context to what NWP modelling eventually begins to show.

I'm still learning how to put this stuff into practice & this has been a great winter to properly throw myself into it, I've bookmarked the post so I can come back and re-read it at some point, I think others who wish to learn should definitely do the same!

January 4

The difference between the 00z and 06z is absolutely tiny but makes all the difference.

I think we've *probably* come to the end of the NErly shifts in the high now, cold at the surface but the idea of getting lucky with something more convective appears to be fading with modelling beginning to converge.

January 3

Yet another GEFS shift north with the high.

A few more days like today and we'll be looking at a more widespread snow shower risk across E/SE England..

January 3

Interestingly -ve AAM tendency appears to have bottomed out and is climbing again, I suspect helped by a broadly weakly +ve MT.

This suggests total AAM may not fall quite as far as anticipated & instead the GWO will remain firmly routed within a Nino-coupled base state, with a likely +EAMT event towards mid January and a further Pacific jet extension coupled with MJO progression eastwards broadly speaking westerly momentum within the atmosphere should remain +ve with further wave breaking events to come down the line with renewed poleward propagating +AAM anomalies.

This I believe is the @Tamara's signal for shuffling heights between Greenland > Iceland > Scandinavia.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4993935

January 3

Interestingly -ve AAM tendency appears to have bottomed out and is climbing again, I suspect helped by a broadly weakly +ve MT.

This suggests total AAM may not fall quite as far as anticipated & instead the GWO will remain firmly routed within a Nino-coupled base state, with a likely +EAMT event towards mid January and a further Pacific jet extension coupled with MJO progression eastwards broadly speaking westerly momentum within the atmosphere should remain +ve with further wave breaking events to come down the line with renewed poleward propagating +AAM anomalies.

This I believe is the @Tamara's signal for shuffling heights between Greenland > Iceland > Scandinavia.

January 3

You’re never going to see a stronger day 10 mean than this from the 12z ECM.

I’ve been chasing this cold spell since September after making some assumptions on the MJO cycle & likely progression of the AAM towards an El Niño base state so it’s really wonderful to finally see something concrete appearing within the model outputs.

A 3 month long chase but we’re finally getting there.

January 3

We can add MOGREPS to the list of models deepening the cold.

January 3

If the latest CANSIP seasonal is anything to go by blocking could last through February & March.

Current MJO/GWO progression does favour the likelihood of repeated periods of blocking/cold spells with a waxing & waning of blocking inbetween.

We are entering the most exciting winter period probably since 2009/2010.

January 3

Met office keeping the dream alive despite a very late update!

What an evening. Lets hope the ECM continues with the theme.

January 3

I know the attention is on the quite frankly insane det run but the GEFS mean now has an easterly flow across the UK from the initial high so an improvement across the board. I'd expect to see a much colder ENS suite in general here.

Boom boom boom.

January 3

Impressive cross polar flow on this run with retrogression brought forward a day or two!

January 3

Suble upgrades to ICON, GFS and GEM. I said yesterday any further shifts and we'd be looking more towards Scandi high territory and the GEM is essentially producing just that.

So much for a sinking high and strong Iberian heights..

January 3

A more amplified high initially and easterly flow doesn't mean we wont see retrogression later on, I'm not sure where this either/or idea is coming from.

January 3

1 minute ago, prolongedSnowLover said:

I’m not sure with pressure too high and not cold enough for convective showers.

The ECM shows absolutely zilch.

Certainly cold enough on this ICON run with -10c 850hPa moving in. ECM still has the high further south, ICON is much further north.

The placement of this high is still yet to be resolved.

January 3

Given this mornings 06z GFS and now the 12z ICON i think the trend towards something wintry in the E/SE day 4 into 5 is beginning to grow.

January 3

A couple of points re: the MJO, these snippets taken from the recent CPC weekly report.

Quote

Dynamical and statistical model guidance continue to reflect continued MJO activity; however,
the GEFS and ECMWF ensembles now depict a much slower evolution across the Indian
Ocean over the next two weeks.

and

Quote

A weakening +IOD response may be playing a role in the forecasts for slower evolution, as
well as destructive interference between the MJO and the ENSO signal, which favors
suppressed convection over the Maritime Continent

A suppressed signal as this next MJO wave pushes across the maritimes isn't ideal and neither is a slower progression. I had hoped for a faster transition to see a faster uptick in +FT and +MT in order to prevent total GLAAM from falling too far but that now seems less likely, though GEFS still favouring something more amplified than the ECM.

What does this mean? Potential for blocking to wane in the 2nd half of January with the Atlantic jet beginning to return back northwards, however; continued uncertainty in the MJO progression does make this a low confidence forecast and any returning Atlantic jet will likely be bumping into very cold stagnant air.. i.e, high impact snow events possible.

Nothing to be too concerned about at this stage but worth flagging nonetheless, a possible +EAMT event (flagged by Eric Webb & @Catacol yesterday) c/o a Siberian High builds into East Asia should be enough to keep overall westerly momentum up regardless of MJO activity. The GWO continues to remain in a high AAM orbit and I'm not expecting any dramatic changes to that at this time.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4992976

January 3

06z det can't decide whether to send the high to Greenland or Scandi so it's trying to do both.

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