Catacol

January 4

Vortex split right through the layers to 20hpa (I'll just show the 20)

and vortex clearly very stretched.

ECM signal for fast dropping overall windspeeds at this point midmonth is growing

= little to no top down frictional support for a return of westerlies any time soon.

Meanwhile, as I suggested might be happening a few days ago, relative AAM is on the way back up. Still negative, but climbing and by the time we get to the end of next week I would hazard a guess that the next spike in AAM will be in the wings.

So....playing a game of lag: really cold air jumps onto Scott's bandwagon about 15th Jan at a time when the vortex is gasping for air, and at the same point pacific momentum begins to climb again. Remember the Webb prediction of a +EAMT mid month too. This means reamplication roughly from week beginning 29 Jan. Can the cold pattern survive 2 weeks until we get that resurgence?

No way to be sure, other than to look at the products available that are trying to calculate the physics of this. Not surprisingly EC weeklies read week 1 of this pattern as a definite cold to very cold NE for us

by week 2 of the phase a much more muted signal

but hardly one that looks mild. Tentative signs of breakdown? Maybe....but by golly it might be a very snowy breakdown and hardly a breakdown at all given NWP then sees a reignition of those Greenland Heights as we head into February.

I'm going to call it now. I think we have week of cool down with the odd white surprise next week followed by 3 weeks of cool/cold/very cold with snowfall events along the way. I'm not sure there is much of a signal for anything else right now. How much snow falls and where it falls - well, who knows. But snow will be the theme.

And 3 weeks might be pessimistic, because by week 2 of Feb the impacts of the next pacific wave will be in town, and the block will be getting fed plenty. NWP agrees for now.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4994847

January 4

@Scott Inghamday.

Vortex split right through the layers to 20hpa (I'll just show the 20)

and vortex clearly very stretched.

ECM signal for fast dropping overall windspeeds at this point midmonth is growing

= little to no top down frictional support for a return of westerlies any time soon.

Meanwhile, as I suggested might be happening a few days ago, relative AAM is on the way back up. Still negative, but climbing and by the time we get to the end of next week I would hazard a guess that the next spike in AAM will be in the wings.

So....playing a game of lag: really cold jumps onto Scott's bandwagon about 15th Jan at a time when the vortex is gasping for air, and at the same point pacific momentum begins to climb again. Remember the Webb prediction of a +EAMT mid month too. This means reamplication roughly from week beginning 29 Jan. Can the cold pattern survive 2 weeks until we get that resurgence?

No way to be sure, other than to look at the products available that are trying to calculate the physics of this. Not surprisingly EC weeklies read week 1 of this pattern as a definite cold to very cold NE for us

by week 2 of the phase a much more muted signal

but hardly one that looks mild. Tentative signs of breakdown? Maybe....but by golly it might be a very snowy breakdown and hardly a breakdown at all given NWP then sees a reignition of those Greenland Heights as we head into February.

I'm going to call it now. I think we have week of cool down with the odd white surprise next week followed by 3 weeks of cool/cold/very cold with snowfall events along the way. I'm not sure there is much of a signal for anything else right now. How much snow falls and where it falls - well, who knows. But snow will be the theme.

And 3 weeks might be pessimistic, because by week 2 of Feb the impacts of the next pacific wave will be in town, and the block will be getting fed plenty. NWP agrees for now.

January 4

Very very good EPS at long range. Note the growing depth of the low pressure signal over the near continent, unusually deep given these signals usually fade the further out they go.

Got to be about the best long range EPS signal for a midwinter spell in the last dozen or so years.

January 4

1 hour ago, BleakMidwinter said:

I'm clueless when it comes to interpreting charts, but one thing I have become aware of, trying frantically to keep up reading, is just how many of the posters here whose knowledge I really respect have posted in the last day or so to say that they have never seen charts like this, never seen this kind of run for January, can't remember this or that in recent decades, etc.

We have seen charts as good as this before BUT:

1. 2018 was a March event. Warm air intruded fast on a near perfect setup.

2. 2010 was December, and for parts of the south (certainly where I was) it took a while to get the overall temps down so that snow would stick, and once the pattern started to shift away the winter disappeared fast.

Both the above were awesome events though, and the winter of 09/10 was generally good.

What is potentially (and we have to say that here because the main surge of cold, if it comes, is still more than a week away) about to happen is that it is positioned in the heart of winter and looks like it could potentially tap into air over Scandy that has been cold all season and is particularly cold right now. The Baltic has frozen already (fastest in 12 years) and Sweden has just broken an all time cold record. So - if things line up with the luck that we will always need in the UK to turn a very good looking macro pattern into a micro pattern that delivers this forthcoming spell has the potential to be one that is quoted often in years to come.

And if an SSW comes out of left field - because as Met4 has pointed out today the number of members seeing a technical 10hpa reversal is back on the rise - then we could really hit the jackpot. A split has been modelled on and off since the New Year up through the layers, sometimes as high as 10hpa, but not with a reversal attached. If this is back on the table then watch out for early February I'd say....

January 4

29 minutes ago, Jason M said:

If forecasters were expecting severe wintry weather or even possibility of it, they would be signposting this by now in forecasts.

Not sure about this though it depends a lot on timescale. I'm not the MetO media advisor - Marco Petagna would be good to tap up on this is a quiet moment.... - but because of the way the media reacts to snow, and because of the way the outward facing elements of the MetO have reacted quite aggressively to tabloid weather posts, I think they will need to be 110% sure of severe wintry weather before signposting it. Doing what they have done so far, listing it as more likely than normal but still low probability, is about as front foot as they will go until the snowflakes are almost literally gathering on the horizon. We might see a change of emphasis once 15 Jan (assuming for a moment that 15 Jan is when the serious stuff starts) is at 144h range, but until then I'd say no. If I was that media advisor I would be smiling at the forecasters and saying "I hear what you are saying - it is likely to get very cold with snow in the mix....but let's not mention it yet. 11 days is a long way off...."

There is a balance to be struck of course because heavy snow will tend to translate quite quickly into amber warnings, but we dont get these usually until 48 hours before in any case. For now I think the MetO text is fantastic.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4994614

January 4

29 minutes ago, Jason M said:

If forecasters were expecting severe wintry weather or even possibility of it, they would be signposting this by now in forecasts.

Not sure about this though it depends a lot on timescale. I'm not the MetO media advisor - Marco Petagna would be good to tap up on this is a quiet moment.... - but because of the way the media reacts to snow, and because of the way the outward facing elements of the MetO have reacted quite aggressively to tabloid weather posts, I think they will need to be 110% sure of severe wintry weather before signposting it. Doing what they have done so far, listing it as more likely than normal but still low probability, is about as front foot as they will go until the snowflakes are almost literally gathering on the horizon. We might see a change of emphasis once 15 Jan (assuming for a moment that 15 Jan is when the serious stuff starts) is at 144h range, but until then I'd say no. If I was that media advisor I would be smiling at the forecasters and saying "I hear what you are saying - it is likely to get very cold with snow in the mix....but let's not mention it yet. 11 days is a long way off...."

There is a balance to be struck of course because heavy snow will tend to translate quite quickly into amber warnings, but we dont get these usually until 48 hours before in any case. For now I think the MetO text is fantastic.

January 4

2 hours 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.

Awesome post @MattH - not much more needs to be said!

Time to batten down the long term hatches and get stuck into the next 10-14 days. What happens in February can wait a bit for me now! - I want to see if I can make a snowman on 15 Jan

January 4

1 hour ago, Battleground Snow said:

@Scott Ingham day is inevitable!

It's uncanny isn't it. Modelling at this range just isnt accurate or consistent....and yet again and again we are seeing this for 15 January

00z

06z

January 3

Just now, Rob 79812010 said:

Question for long time model watchers. When the charts consistently showing colder temps out in F1 which then come into the medium term, is it still feasible it can all go belly up??

Oh yes. Certainly can. But we are getting better I think at interpreting the broad forcings and drivers than we were back in 2012 or 2006 or 2001. And the broad setup for the next 10 days is good to very good. Taking my party hat off for a moment, there will be question marks emerging for the final third of January because to my eye those forcings get less attractive. This is why any block we get in the next week or so needs to get to high latitude and tuck into the tasty post Xmas morsels left by a weakened vortex...allowing it to stick around and hold on just long enough to get the next round of momentum lined up as a reinforcement. That could potentially go pear shaped - too far off to be sure. But there are plenty of reasoned posts knocking around on this forum from the last couple of weeks pointing to the upcoming phase as one with a great deal of upstream support. I don't think it will go belly up this time around. I'm peering hard at the ointment....and can't see the fly.

January 3

1 minute ago, TSNWK said:

I did think that, but thought I was missing something else

Nah - just a bit of fun. No widespread blanket this time but I wouldn't rule out a bit of upgrading from that chart. There is a definite kink over central France that might develop a few showers within the flow.

January 3

And here we have it - @Scott Inghamday once again. There is a bit of a theme growing here....and all fun aside 15 Jan is rather consistently looking very tasty. Scott - how much for a day with your crystal ball?

January 3

1 minute ago, Northern Sky said:

Regardless of whether it actually happens or not, watching this GFS run come out is a beautiful sight.

My wife introduced me to Ginny and Georgia over the holiday. Can't say I was upset to meet Brianne Howey on screen for the first time.

GFS today is better.

January 3

2 minutes ago, Catacol said:

Hehe - what did I tell you.....

Now then.....will it????

Ha - @northwestsnow - you can come out from behind the sofa now

It's a Bob the Builder run for sure.

January 3

3 minutes ago, northwestsnow said:

Well....

Hehe - what did I tell you.....

Now then.....will it????

January 3

Jan 9 2024

Feb 7 1991

Could just do with the models picking up and growing the little kink in the 2024 isobar over the Massif Central....

January 3

MetO are very slow today. Is anyone else visualising a cobra style meeting with a screen showing -15/-20 850 values over a wide swathe of the country on @Scott Inghamday... chewing over how best to frame the text?

January 3

27 minutes ago, northwestsnow said:

Owwww hope so C

96h - we'll take that.

January 3

Just now, northwestsnow said:

Owwww hope so C

Ha - famous last words probably and I rarely enter into the game of frame by frame pinpoint staring....but at 72h I'm seeing more amplification.

January 3

This GFS is lining up to be a good one....

January 3

1 hour ago, nick sussex said:

Same old story ! These cold pools are so sensitive to minor changes in the position and orientation of the high .

Still not possible at this point to forecast if there’s going to be any decent convection off the North Sea .

The ECM brought a chance for the far se , the GFS 06 hrs has some flurries for the east .

Hopefully we can get a resolution to this tonight as it’s now around T96 hrs .

With the current setup looking like this I doubt it.

Will not resolve until under 72h I reckon. So much dramatic change in a short period of time - tiny, tiny differences in the alignment of the momentum surge and response of the wave break will have big implications a few days down the line. A fascinating watch continues.

January 2

Still looking good @Scott Ingham

January 2

While celebrations abound - this is significant perhaps. Frictional torque already on the turn, looking like its drift into negative territory has bottomed out:

Similarly the crash in momentum has possibly also bottomed out:

Overall GLAAM has not dived too much, though it will go down a bit further from here

and the extended EPS showing this for mid month over China

I'm seeing the potential here for another +EAMT event (to be honest Eric Webb spotted it first....)

In plain speak? The higher we can keep the base GLAAM state the better our chances of maintaining amplification with the jet pushed south, and even when the MJO enters phases less helpful in terms of wave position if amplification is sustained then our block gets trapped. Will bounce around - Tamara and Scott have flagged it as a possibility already - and then when AAM increases once again in line with a +EAMT event mid month (hopefully with the MJO pushing through the maritimes once again) we get a resurgence of the blocking signal just where we want it. If the block has ended up in a less favourable slot as the MJO sits in the IO (and that is an if and not a when) then this serves to bring it back where we want it.

The chances of extended cold are always slim, but the picture this paints is plausible and it could certainly happen. These teleconnective signals do not always stay in the trench as hoped for - sometimes Vadar and his two wingmen swoop down and shoot them back out - but right know we are in the trench and the exhaust port is not a million miles away. By this time next week we will have a good sense of where the block is going on the second pulse helped by vortex weakening or even splitting, and how these signals may be lining up.

It's all good.....so very very good....

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4992610

January 2

While celebrations abound - this is significant perhaps. Frictional torque already on the turn, looking like its drift into negative territory has bottomed out:

Similarly the crash in momentum has possibly also bottomed out:

Overall GLAAM has not dived too much, though it will go down a bit further from here

and the extended EPS showing this for mid month over China

I'm seeing the potential here for another +EAMT event (to be honest Eric Webb spotted it first....)

In plain speak? The higher we can keep the base GLAAM state the better our chances of maintaining amplification with the jet pushed south, and even when the MJO enters phases less helpful in terms of wave position if amplification is sustained then our block gets trapped. Will bounce around - Tamara and Scott have flagged it as a possibility already - and then when AAM increases once again in line with a +EAMT event mid month (hopefully with the MJO pushing through the maritimes once again) we get a resurgence of the blocking signal just where we want it. If the block has ended up in a less favourable slot as the MJO sits in the IO (and that is an if and not a when) then this serves to bring it back where we want it.

The chances of extended cold are always slim, but the picture this paints is plausible and it could certainly happen. These teleconnective signals do not always stay in the trench as hoped for - sometimes Vadar and his two wingmen swoop down and shoot them back out - but right know we are in the trench and the exhaust port is not a million miles away. By this time next week we will have a good sense of where the block is going on the second pulse helped by vortex weakening or even splitting, and how these signals may be lining up.

It's all good.....so very very good....

PS - a little addendum while I think of it. Those that remember the amplification event of Dec 2010 will know that we all felt the timeline was finite. The signals were lining up to flatten out the pattern and following that spell we had a winter pretty much to forget afterwards. Not so this time. I do not know whether the amplification on the horizon will give us anything close to what happened then, but I do know that the signals are lining up in quite an opposite frame to those back in 2010. Dont forget the seasonals also saw a very blocked March....

January 2

Oooooo who needs @Scott Inghamday when GFS can give us this 48 hours before

What is it about watching bumper model runs - that have a low probability we all know of working out exactly as they suggest - that is so addictive? Hehe - we would be digging parts of the U.K. out of the drifts if this one came off….

January 2

30 minutes ago, Dennis said:

deeply winter forseen from midmonth

Dennis - that’s the second time you have posted that 850 chart for the equator. To my eye it is not good - it shows strong trades in control and little in the way of any westerly wind burst activity with the MJO stuck in the IO. It’s a GFS forecast so I’m not expecting it to be accurate…but what are you thinking will happen as a result of those strong trade winds and likely crash in GLAAM (if it were to be true)?

Sign In

Forums

Blogs

Gallery

Events

Learn About Weather and Meteorology

Community guides

Posts posted by Catacol