Model Output Discussion - Spring Has Sprung

[Tamara]

 

@Met4Cast 

You are correct. The equatorward fluxing is very much related to the strongly +AO and vigorous polar jet. It is also true that the longevity of this has been uncertain.

But there are now clear signs of quite a potent momentum surge on the GSDM MT plots and a poleward directional +EAMT springboard and stratospheric pathway.

Those fine lines of synoptic outcome under recent discussion look set to swing a pendulum back again. I have no skin in the game, or interest at all, in respect of favoured weather type across NW Europe, especially living in Portugal, but there looks to be a good match to support extended modelling that migrates high pressure NW'ward beyond (approx) the second week of February.

How that fully manifests at this time, cannot be gleaned by anyone at this time. However the likely repercussions of the momentum transport, based on the updated evidence, looks set for the largest diminution within the stratosphere this season.

On the way towards 22C today. Amazing.

Previsão - Temperaturas podem bater recordes entre Quarta, 23, e Sábado 27 em Portugal - Calor em Janeiro

WWW.LUSOMETEO.COM

---

Previsão de tempo quente em Janeiro, com possibilidade de temperaturas recorde localmente - a Serra da Estrela pode chegar a 15ºC

 

 

[Stephen W]

Heights remaining stubbornly persistent throughout the 6z ensembles to our south and south west up until roughly the 10 day point when there are signs of this retreating west which allows some attempts at a northerly flow and lowering of heights to our east. Too far out for any confidence and the cold patterns that do follow don’t inspire hugely as those heights are never too far away from creeping back towards the UK. At least there are hints of a pattern change towards the end of the 10 day period, just about whether that gains momentum or fizzles out.  Personally, my confidence is pretty low for February now having read the mixed analysis on here the last few days.

[Eagle Eye]

Not all down, trending towards a Greenland high for mid February which I mentioned as a general possibility might be showing now. Not much to add for now.

[northwestsnow]

6z control is a beauty

Day 8 - day 10

then...

looks very cold

[Met4Cast]

@northwestsnow

If that’s the best synoptic we’re seeing within NWP modelling currently then it’s a concern. We know how blocks are often “watered down” and that’s barely a block to begin with

Really want to see NWP modelling throw out some more extreme blocking scenarios at that range. Can’t say i’m overly excited by the prospects of another dry northerly.. 

 

[bluearmy]

@northwestsnow just noise for now but it’s our task to judge if the noise is getting louder or indeed if we can begin to hear the makings of a tune ……

bit like the classic Eric morecambe line - ‘ all the right notes but not necessarily in the right places’! 

@Met4Cast

25 minutes ago, Met4Cast said:

If that’s the best synoptic we’re seeing within NWP modelling currently then it’s a concern. We know how blocks are often “watered down” and that’s barely a block to begin with

Really want to see NWP modelling throw out some more extreme blocking scenarios at that range. Can’t say i’m overly excited by the prospects of another dry northerly.. 

 

At day 8/10 you wouldn’t expect to see any HLB ??

and You can highlight the post if you want to 

[Kasim Awan]

@Met4Cast I do think another bout of amplification is possible. Often cold snaps tend to repeat synoptically around 3-5 weeks after. I can think of countless examples. So from a predictive statistics perspective I think a northerly spell is very possible into February at some point. Probably watered down by the strong signal for Iberian heights though.

 

[Met4Cast]

7 minutes ago, Kasim Awan said:

@Met4Cast I do think another bout of amplification is possible. Often cold snaps tend to repeat synoptically around 3-5 weeks after. I can think of countless examples. So based on that I think a northerly spell is very possible into February at some point.

I agree about the quotes.

I’m certainly not ruling out another cold spell, just not entirely buying it just yet. Especially given the uncertainty wrt the MJO at the moment. 

Sustained HLB seems a lower likelihood outcome but another boring northerly is a possibility. 

 

[ANYWEATHER]

@Met4Cast you can actually Quote what you want by using the Quote function by keeping your finger for a few moments on the sentence etc . I’ve had a go and it works really well, as Paul said gets rid of a lot of clutter on members posts ……

[Eagle Eye]

@Met4Cast

Agree with you w/uncertainty but at least we're not guaranteed to be zonal for the rest of Winter is all I can say. Long-term it is mostly guess work based off the slightly most likely outcome at the moment.

[Kasim Awan]

6 minutes ago, Met4Cast said:

I’m certainly not ruling out another cold spell, just not entirely buying it just yet. Especially given the uncertainty wrt the MJO at the moment. 

Sustained HLB seems a lower likelihood outcome but another boring northerly is a possibility. 

I'm not buying into anything just saying it's possible. It's mid winter it's possible every year, though probably lower this year compared to most.

Edited January 24 by Kasim Awan

[Paul]

There is some thought behind the change to the quoting system, and it is something used on other forum software very successfully, so perhaps give it a chance to bed in and see what you make of it at that point. There is a thread covering it on the go (along with a big banner on every page, pointing to it), so if you have comments or questions about it please head there and don't put them in here as a. it's off topic and b. it's less likly your questions and feedback will be seen, discussed or acted upon.

 

[Rain All Night]

15 hours ago, RainAllNight said:

Deterministic runs, Wed 24th to Tue 30th

If it weren't January, then there might be some more interest in what the low pressure that appears in the Atlantic on Sunday will do... most of the models send at least a part of it to the southeast to become a cut-off heat pump low... "lol". Some have it kicking a surface high over the UK too.

Ensemble means, Wed 31st to Tue 6th

It looks as though "peak bulge" over the UK may be Wednesday & Thursday next week, offering us benign beginnings to February. By that weekend, we see the lowest heights to our northwest having migrated to our northeast, perhaps indicating the possibility of a cooler pattern emerging?

Deterministic runs, Wed 24th to Wed 31st

Each time it looks as though a sustained dry spell might build, something comes along to interfere with it. Still, there are plenty of shorter dry periods showing here, especially further south.

Ensemble means, Wed 31st to Wed 7th

The PV seems to go east, only to then possibly come back west again soon after. The heights to the south seem to gradually recede from their peak at the beginning of this period.

Edited January 24 by RainAllNight

[bluearmy]

13 minutes ago, Met4Cast said:

Especially given the uncertainty wrt the MJO at the moment. 

Todays updates on the bc aren’t great as they trend to cod in 7 without any decent amplification 

the non bc output is decent amp in 7. 

Weeks 2 and 3 on ec 46 (which are usually fairly reliable) are indicative of 7 and then 8 but judging amplification is going to be the issue at this range . I’d like to think that just as we had general agreement that the current run through the Indian Ocean would die in 3 (was wrong ) corrected to a high amp through 4 and 5 , so we can see this death in the w pacific overplayed too. 

Edited January 24 by bluearmy

[Met4Cast]

@bluearmy I’m having flashbacks to the previous cycle when many of us thought models were overplaying the signal decline but modelling ended up being right with that, albeit the atmospheric state is very different now compared with then. 

A case of waiting & watching, again!

[CoventryWeather]

Weren't there always a signal for a cold spell around mid February - if so then they've done well with it, even if the past week they've moved away from the solution. LRFs also rather consistent still. 

Edited January 24 by CoventryWeather

[Eagle Eye]

Using verification, the GEFS has generally trended -VE of the actual strength of the wave propagation, the GFS slightly above but as we go further towards the future, they move very close together and phase 5-7 are more responding to a quickly falling -VE IOD (a fairly strong wave strength response but it's not the only variable, just 1 of the MJO spread inputs) so potentially may be underdoing the strength of the active western Pacific response further away from the western Maritime region slightly infiltrated w/dry air occluded into the far western Maritime region likely in response to the trend away from a +VE IOD, not a full on dry response but not as +VE wet as the normal composite and that dry air into parts of the Maritime region. Whereas a wetter than normal eastern Maritime and western Pacific that has been characterised poorly by the GFS so far. Theoretically leading to a larger response in phase 7.

Edited January 24 by Eagle Eye

[Rain All Night]

1 hour ago, Tamara said:

But there are now clear signs of quite a potent momentum surge on the GSDM MT plots and a poleward directional +EAMT springboard and stratospheric pathway.

Those fine lines of synoptic outcome under recent discussion look set to swing a pendulum back again. I have no skin in the game, or interest at all, in respect of favoured weather type across NW Europe, especially living in Portugal, but there looks to be a good match to support extended modelling that migrates high pressure NW'ward beyond (approx) the second week of February.

How that fully manifests at this time, cannot be gleaned by anyone at this time. However the likely repercussions of the momentum transport, based on the updated evidence, looks set for the largest diminution within the stratosphere this season.

How can we assess the likelihood that this will occur, with respect to the earlier suggestions of high pressure to the north at an earlier timeframe (i.e. between the cold spell which has recently ended, and the timeframe of this new suggestion now being made) which it now appears will not occur?

[Mike Machin]

27 minutes ago, bluearmy said:

Todays updates on the bc aren’t great as they trend to cod in 7 without any decent amplification 

I thought they looked a bit fishy!

[Tamara]

Another way of looking at the potential perturbing effects of rossby wave transport at high levels of the atmosphere is to look at this gravity wave drag plot.

In simple terms this refers to the strength of upward propagating waves that are created through torque deflection of wind-flows against very tall mountain ranges (e.g Himalayas and Rockies) and indeed wind shear c/o tropical convection (whose inflection point(s) of convergence zone(s) creates the eddies which propagate into the extra tropics in the first place)

Gravity waves at high amplitude induce high turbulence proportionate to the ever higher levels of the atmosphere they propagate into.  The trend on the latest GSDM GWD plot shows the torque friction effects occurring at the latitudes of the East Asian mountain ranges.

There is quite the whiplash effect of global wind-flow in progress here. Recent deeply inverted reflective fluxing spilling from the stratosphere into the troposphere - now being sharply reversed by equally very strong +ve gravity wave propagation into the stratosphere. Strongly +ve AO to potentially robust -ve AO? Based on the lag time of the +EAMT.

In that respect, the poleward amplification mechanism has already undergone starters orders and is embedding within the global circulation - and this needs to be taken into account when pondering the eventualities of the MJO progression through the Pacific.

Yet again to say, the MJO, might be a catalyst for future wind-flow changes set in motion within the tropics - but in isolation it is not the be all and end all.

@RainAllNight This post may help answer your question in another way

Edited January 24 by Tamara

[Catacol]

@RainAllNight - Tamara has answered your question and I'll add a bit to it. Recent discussion around failed blocking at the end of this month has not centred on a "failed" process. Indeed, as expected, the pendulum nature of momentum swings started back in favour of blocking at about the expected time (ended up 16 Jan, could have been a day or 3 earlier but this fits within the noise) but what changed was the overriding strength of a reflective stratospheric event that was not forecast. I'll go a bit further than that - unless you are Simon Lee who has written on this subject I'm not sure that the way the stratosphere responds to vertical wave assaults is well understood at all. Simon himself, a pretty modest and helpful X poster, would probably quickly agree that there is a lot we still need to learn.

So - this reflective event has overridden the tropospheric signal that started as expected. The week we are in now was always flagged as vulnerable to a flattening pattern, and the strat response has flattened it hard and fast. The impacts of that flattening will now endure through next week it appears....but all the while the forcings pushing us towards renewed northern blocking are gathering in strength as many of us thought they would through this period and out into February.

The question will be - can the bottled up effects of a momentum surge overcome the strat quick enough to make an impact before we get too far through February? Earlier this week I felt quite glum about that - chances in my mind reducing. I look at strat forecasts for the month and am still not confident that these tropospheric forcings can seize control from the strat once again....but I feel a bit more optimistic about that today. Why? Well - not as a result of this chart which looks horrendous...

but more maybe as a result of this - already posted by Tamara

and linked to that the high spiking nature of the calculated tendency which is, without doubt, going to drive us back towards a tropospheric disposition towards higher lat blocking.

That MT spike is very significant. It has arrived as expected but looks bigger to me than I expected and that is good for winter fans.

I cannot help but curse our luck this month. First a failed SSW, and noone expected it to fail - indeed the strat big guns all came out and started to celebrate in the run up - and then a really positive tropospheric setup that has been undermined and stalled by an unexpected and not fully understood impact of strat developments. It could all have been so very very different!

Watching battle commence between this momentum-led forcing and the strength of the SPV will be an interesting watch if nothing else. We can but try and learn. Perhaps, after 2 bouts of poor fortune and a truncated cold snap sandwiched between them, we can strike it lucky in February. I remember some epic snowy February weeks - 1991 and 1996 at the top of the pile and it would only take a week like that to save this winter from mediocrity. 

[Met4Cast]

4 minutes ago, Catacol said:

The question will be - can the bottled up effects of a momentum surge overcome the strat quick enough to make an impact before we get too far through February? Earlier this week I felt quite glum about that - chances in my mind reducing. I look at strat forecasts for the month and am still not confident that these tropospheric forcings can seize control from the strat once again....but I feel a bit more optimistic about that today. Why? Well - not as a result of this chart which looks horrendous...

Great post!

This part is particularly worthy note & sums up my current thinking too. Given current strat forecasts & continued MJO uncertainty and how this will factor into the broader windflow framework I'm not confident we'll end up in a situation with sustained HLB this time around. The strong +MT event is certainly of note though and like you, I wasn't expecting the event to be quite this extensive but I suspect an amplified MJO has helped this, combined with probably a little bit of luck. The Pacific Jet extension will once again begin to feed anomalous warmth across the USA perhaps helping to take some of the sting out of the current strong +NAO jet raging across the Atlantic. 

It does seem the current +NAO will run out of steam but I'm yet to be convinced that this will then translate to a strong -NAO or robust blocking in places capable of feeding properly cold air south (or west) into the UK. 

[Eagle Eye]

7 minutes ago, Catacol said:

Perhaps, after 2 bouts of poor fortune and a truncated cold snap sandwiched between them, we can strike it lucky in February.

And then I woke up

In all seriousness. The amount of detail on that post is top notch, well done. The amount of high-level posts on here recently have shown how complex the second half of this Winter is. "Set in stone, February is not" as Yoda would say. 

[Daniel*]

Starting to head in right direction worth noting the GEFS seem to have identified the likely return of -NAO/-AO before EPS.

[bluearmy]

  @Daniel* maybe a day ahead on the AO (20th against 21st).  Can’t really see that the NAO is a definitive call yet as marginally neg for now 

Edited January 24 by bluearmy