Model Output Discussion - heading into April

[Singularity]

Interesting to see discussion of anomalously strong ridges across Europe for the time of year being modelled, as this is a plausible climate shift associated with  warming of the Arctic more than the tropics - as we’ve been seeing generally for over a decade now. It’s to do with the Hadley Cell expanding, shifting the location of the subtropical highs northward.

Not a certain thing but recent years have shown some alliance to such a tendency.
 

A noteworthy theme in extended modelling of high pressure fighting back whenever it gets pushed away from the UK. It may not always locate in a warm position for us but it appears dry weather may remain abundant for the late stages of May.

[Tamara]

Following very similar April's in both 2007 and 2020 in terms of degree of anomalous warmth and the distribution across Western/Central Europe of that warmth - the script heading towards early summer 2020 is proving quite different to the former.  There is no sign, at this stage, of a strong e/QBO stratospheric lead on the Northern hemisphere pattern - leading ultimately towards an unstable polar pressure field and mid latitude troughs across Europe. Such a development coming about through a collapse in global atmospheric angular momentum and enabling coupling of that to the cooling trend within the Pacific and a rapidly strengthening La Nina. Such as happened in late Spring/early Summer 2007.

At least not yet.

Despite the cooling within regions of the ENSO zones of Pacific , more importantly the tropics as a whole continue to reflect above average heat content across the I/O, the Maritime Continent, the Western Pacific and also the Equatorial Atlantic. A strong convectively coupled kelvin wave (CCKW) is at present passing the I/O and generating powerful westerly wind bursts in association with the deep thunderstorm development created by atmospheric engagement with such a large oceanic heat and moisture environment. These westerly wind bursts tend to forge and migrate rossby waves poleward to the extra tropics with time and reinforce on-going amplification of sub tropical ridge development at mid latitudes - in the absence of any unstable -AO forcing on the polar field.  The WWB'S are depicted by the strong red/flame colours on the wind-anomaly Hovmollers plot. A swathe of countervailing easterly winds (in blue) at present lie ahead of the CCKW and indicate stable tropical convective suppression. NB: GFS forecasts tend to have a -ve bias to trade wind forecasts

 

These types of vigorous intra-seasonal kelvin wave tropical convection events are often progressive with eastward propagation and the negotiating of trade wind suppression barriers ahead of them and their associated wind shear. Deterministic MJO modelling tends to unreliably depict eastward propagation beyond about 5 days, with the terrain of the Maritime continent region adding to this difficulty with propagation forecasting - but nonetheless, they are starting to track the event eastward right across the tropics.

 

The result of this tropical forcing is to sustain angular momentum budgets within the global atmospheric circulation. Global AAM levels remain on the whole rather above average - depicting an atypical warm/neutral aspect to any attempted Nina-esque ocean lead in the Pacific..... 

…..precisely what is required to prevent/delay any collapse towards -ve inertia within the atmosphere and force La Nina switch, drive unstable e/QBO stratospheric influence within the polar field, and a much cooler/wetter tropospheric pattern change at mid latitudes heading into summer.

With tropical>extra tropical developments in mind as described,  CFS AAM forecasts have been persistently correcting forecasts upwards in the medium to longer term - and now reflect a sustained momentum budget through to end of May. Trends thereafter are advisedly treated with caution and subject to change - but no signal for collapse evident.

 

The tropical activity stateside and its expected track and phasing with the macro scale Atlantic pattern over the coming week is creating uncertainty to modelling in terms of the medium term impacts to sensible weather and surface details for the end of the week and the weekend for NW'ern peripheral parts of Europe such as the UK. But overall, based on the Atlantic trough and downstream ridge arrangement dominating the European sector of the hemisphere, it should be viewed as a helpful aid to perpetuating a virtuous early summer season pattern of trough to the west and ridge to our east (and an ongoing SST arrangement across the mid Atlantic that helps perpetuate the pattern).

As long as angular momentum trends remain stable, and no sustained fall is induced through the mechanisms described, then this trough/ridge pattern bodes very well for cyclical northward propagation of building heat into the first part of the summer. Therefore, whilst the UK will tend to inevitably see breakdowns arriving from the west in a default pattern such as this, any suggested breakdown that the modelling overall is showing to follow the present warming trend and fine weather, should be viewed not as one individual fine increasingly warm event with an ending to follow late week - but within a rinse and repeat perspective

 

[Mike Poole]

Great update from @Tamara, thanks!   That really sets the scene for what we might expect to see in the models, and now the 12z runs unfold...first up as always is ICON, and here it is a case of a brief incursion of unsettled weather punctuating a mainly settled picture, I would say:

[Djdazzle]

ICON also pushing the mini-breakdown back slightly.

[carinthian]

10 minutes ago, Mike Poole said:

Great update from @Tamara, thanks!   That really sets the scene for what we might expect to see in the models, and now the 12z runs unfold...first up as always is ICON, and here it is a case of a brief incursion of unsettled weather punctuating a mainly settled picture, I would say:

Hi @Mike Pooleyes Tamara is a great asset to the model discussion. She produces some real in depth knowledge in her up dates and from little I can understand of the latest one, I think the picture shown on many of the ICON runs indicate the point made about rinse and spin perspective. I like the ICON time limit of up to 180 hours forecast charts and has for quite sometime produced some good results with these charts. In many ways , I am happy to look no further then this outer time span as charts beyond AT 240h and plus ,often hardly verify, that's from my observational point of view. . From what I can gather over here you lot for quite sometime now are not having a bad spell of weather, temperature and sunshine wise. Long may it continue.

 C

[Mike Poole]

At T96 you can see the block is stronger on UKMO than GFS, where this will lead, we will see...

[shaky]

6 minutes ago, Mike Poole said:

At T96 you can see the block is stronger on UKMO than GFS, where this will lead, we will see...

Pretty horrible ukmo at 144 hours!!!only positive is a ridge  of high pressure could be about to build from the south at 168 hours!!!gota say gfs has surprised me and made me eat my words!!!well done to the gfs so far as all other models have come in line from this morning!!!sods law that it shows the more unsettled weather  coming true where as if it was the other way around then it probably wouldnt lol!!

[Djdazzle]

Huge difference between GFS and UKMO at 144. UKMO looks like going down the ICON route.

Enough evidence already that GFS doesn’t have this sussed.

[Mike Poole]

7 minutes ago, shaky said:

Pretty horrible ukmo at 144 hours!!!only positive is a ridge  of high pressure could be about to build from the south at 168 hours!!!gota say gfs has surprised me and made me eat my words!!!well done to the gfs so far as all other models have come in line from this morning!!!sods law that it shows the more unsettled weather  coming true where as if it was the other way around then it probably wouldnt lol!!

UKMO looks like getting the worst of the unsettled weather through quickly, should bounce back from there, although we've all been wrong in predicting the next chart, and in this case we don't get to see it.  But I think the UKMO run is OK if we accept there is a brief unsettled incursion?

GFS on the other hand, is starting to look nasty, T180:

Edited May 16, 2020 by Mike Poole

[Methuselah]

Wel, the 12Z looks to keep warm air in place for a wee while longer than before; but just how warm it'll have time to become, is still in question:

    

In the longer term, will the large-scale teleconnections (ENSO and QBO) override the smaller scale, but much closer, Southeastern European heat dome...or will the heat throw a proverbial 'spanner into the works'? I dunno!

Edited May 16, 2020 by General Cluster

[mb018538]

So - settled until Wednesday. Thursday might just about squeeze another fine day in the east, before it turns unsettled from the west. Friday perhaps unsettled, but not guaranteed.....but UKMO looks primed to rebuild the high into the weekend.

[Zak M]

The GFS 12z shows the unsettled weather, that is supposed to be forecast after the warm spell, not lasting for too long as high pressure starts to build over the British Isles again!

   

[Djdazzle]

GEM also shows a brief unsettled incursion before HP builds in strongly. GFS has a longer unsettled spell before even it starts to bring back HP.

Edited May 16, 2020 by Djdazzle

[Mike Poole]

12 minutes ago, Djdazzle said:

GEM also shows a brief unsettled incursion before HP builds in strongly. GFS has a longest unsettled spell before even it starts to bring back HP.

Yes, the GEM is an example of what I now think is roughly the expected evolution, a brief unsettled spell in the middle of some really settled and fine weather, here it is:

It is consistent with ICON and UKMO even if the exact timescales vary a bit.

[Methuselah]

The back-end of the GFS 12Z holds a lot of promise...Or it would were it not so far out in La La Land!

     

[damianslaw]

3 hours ago, Tamara said:

Following very similar April's in both 2007 and 2020 in terms of degree of anomalous warmth and the distribution across Western/Central Europe of that warmth - the script heading towards early summer 2020 is proving quite different to the former.  There is no sign, at this stage, of a strong e/QBO stratospheric lead on the Northern hemisphere pattern - leading ultimately towards an unstable polar pressure field and mid latitude troughs across Europe. Such a development coming about through a collapse in global atmospheric angular momentum and enabling coupling of that to the cooling trend within the Pacific and a rapidly strengthening La Nina. Such as happened in late Spring/early Summer 2007.

At least not yet.

Despite the cooling within regions of the ENSO zones of Pacific , more importantly the tropics as a whole continue to reflect above average heat content across the I/O, the Maritime Continent, the Western Pacific and also the Equatorial Atlantic. A strong convectively coupled kelvin wave (CCKW) is at present passing the I/O and generating powerful westerly wind bursts in association with the deep thunderstorm development created by atmospheric engagement with such a large oceanic heat and moisture environment. These westerly wind bursts tend to forge and migrate rossby waves poleward to the extra tropics with time and reinforce on-going amplification of sub tropical ridge development at mid latitudes - in the absence of any unstable -AO forcing on the polar field.  The WWB'S are depicted by the strong red/flame colours on the wind-anomaly Hovmollers plot. A swathe of countervailing easterly winds (in blue) at present lie ahead of the CCKW and indicate stable tropical convective suppression. NB: GFS forecasts tend to have a -ve bias to trade wind forecasts

 

These types of vigorous intra-seasonal kelvin wave tropical convection events are often progressive with eastward propagation and the negotiating of trade wind suppression barriers ahead of them and their associated wind shear. Deterministic MJO modelling tends to unreliably depict eastward propagation beyond about 5 days, with the terrain of the Maritime continent region adding to this difficulty with propagation forecasting - but nonetheless, they are starting to track the event eastward right across the tropics.

 

The result of this tropical forcing is to sustain angular momentum budgets within the global atmospheric circulation. Global AAM levels remain on the whole rather above average - depicting an atypical warm/neutral aspect to any attempted Nina-esque ocean lead in the Pacific..... 

…..precisely what is required to prevent/delay any collapse towards -ve inertia within the atmosphere and force La Nina switch, drive unstable e/QBO stratospheric influence within the polar field, and a much cooler/wetter tropospheric pattern change at mid latitudes heading into summer.

With tropical>extra tropical developments in mind as described,  CFS AAM forecasts have been persistently correcting forecasts upwards in the medium to longer term - and now reflect a sustained momentum budget through to end of May. Trends thereafter are advisedly treated with caution and subject to change - but no signal for collapse evident.

 

The tropical activity stateside and its expected track and phasing with the macro scale Atlantic pattern over the coming week is creating uncertainty to modelling in terms of the medium term impacts to sensible weather and surface details for the end of the week and the weekend for NW'ern peripheral parts of Europe such as the UK. But overall, based on the Atlantic trough and downstream ridge arrangement dominating the European sector of the hemisphere, it should be viewed as a helpful aid to perpetuating a virtuous early summer season pattern of trough to the west and ridge to our east (and an ongoing SST arrangement across the mid Atlantic that helps perpetuate the pattern).

As long as angular momentum trends remain stable, and no sustained fall is induced through the mechanisms described, then this trough/ridge pattern bodes very well for cyclical northward propagation of building heat into the first part of the summer. Therefore, whilst the UK will tend to inevitably see breakdowns arriving from the west in a default pattern such as this, any suggested breakdown that the modelling overall is showing to follow the present warming trend and fine weather, should be viewed not as one individual fine increasingly warm event with an ending to follow late week - but within a rinse and repeat perspective

 

Very good read, might we on borrowed time in June though... increasingly unsettled summer?

[Mike Poole]

34 minutes ago, damianslaw said:

Very good read, might we on borrowed time in June though... increasingly unsettled summer?

What is it with you and unsettled, @damianslaw?  Does lake Windermere need a top up?  To me it looks likely that June will be a hot month, and the issues around falling AAM related to developing La Niña probably won't manifest themselves until later in summer, mid July maybe my estimate?  BTW I do accept there might be a north/south element in the difference between our views!

Edited May 16, 2020 by Mike Poole

[mb018538]

Decent ensemble support from GFS to build pressure back in after the blip late next week. Mean well above 1020mb by Sunday.

[Mike Poole]

Here's my regular update on CFS predictions for June, here's z500 anomaly for the last 8 runs as usual:

Still very positive for a settled month, 7/8 have above average heights over the UK.  

[MATTWOLVES 3]

26 minutes ago, damianslaw said:

Very good read, might we on borrowed time in June though... increasingly unsettled summer?

Damien I'm surprised you can make a statement of perhaps an unsettled summer, when summer is yet to start.. It would be no different then if I was to say, we are looking at a 95 or 2018 repeat.. Its basically impossible to predict that far out. Your a good poster and I enjoy your posts, but there is a lot of legs left in this coming summer just yet. 

GFS 12z mean brings us a blip and mainly to the W/NW.. I've noticed even Exeter have low confidence on this and they are probably the best there is.. Either way things look to quickly turn settled and warmer again.. Its a good mean overall. 

[damianslaw]

4 minutes ago, Mattwolves said:

Damien I'm surprised you can make a statement of perhaps an unsettled summer, when summer is yet to start.. It would be no different then if I was to say, we are looking at a 95 or 2018 repeat.. Its basically impossible to predict that far out. Your a good poster and I enjoy your posts, but there is a lot of legs left in this coming summer just yet. 

GFS 12z mean brings us a blip and mainly to the W/NW.. I've noticed even Exeter have low confidence on this and they are probably the best there is.. Either way things look to quickly turn settled and warmer again.. Its a good mean overall. 

My post was just a musing, not a statement or prediction, I'm none the wiser with the summer. It was just a musing based on Tamara post, which suggests should anticipated state of background teleconnections ENSO and QBO imprint on the pattern as we move further through the summer, then the base state going into the summer may change towards something more unsettled rather than settled as time move on, 'hence phrase borrowed time', conversely if they don't imprint then this reduces risk of an ever increasingly unsettled summer.

 

 

[Methuselah]

19 minutes ago, Mike Poole said:

What is it with you and unsettled, @damianslaw?  Does lake Windermere need a top up?  To me it looks likely that June will be a hot month, and the issues around falling AAM related to developing La Niña probably won't manifest themselves until later in summer, mid July maybe my estimate?  

That's why @Tamara's updates are so good: she doesn't simply right off the entire summer (or predict another 1976) just because there's an arcane analogue-agreement with, say,1859, she acknowledges the fact that the world, in 2020 (with all its quirks and nuances) isn't the same as it was in the 19th Century...

IMO, it's always the same few members that 'call' every summer 'cool and unsettled', in April or May; a time when absolutely no-one (professional or amateur) has the ability to do that...

Me? I don't know how July and August will pan out...all I do know is that there is, now, an anomalous amount of heat building-up to our south...?

[Djdazzle]

To be fair to @damianslaw, he does try to justify his views.

[Mike Poole]

ECM: Better angle on things at T96 than even the UKMO, comparison:

[Cheshire Freeze]

22 minutes ago, Mattwolves said:

Damien I'm surprised you can make a statement of perhaps an unsettled summer, when summer is yet to start..

 

There is little to suggest that this will be a sustained dry summer but more evidence to suggest that there is a risk summer deteriorates as we progress. I think people like Singularity have pointed this out and reading between the lines, I think Tamara is suggesting the best of summer may well come more immediately than later into the season. 

In the mean time there is plenty of very useable weather to be had between spells of slightly more unsettled conditions.