Model Output Discussions 12z 03/05/2016

[northwestsnow]

Well well well, GFS is late season tan-tastic this morning, pretty much high pressure all the way into lala land, these sept anticyclones are becoming quite common in recent years!

Hopefully ECM agrees !

[knocker]

Today

Some showery activity clearing the east of the SW region quite quickly but threat of some heavy downpours in the Midlands. Hottest temps probably around Tunbridge Wells.

A quick look at the GFS

In the ten day time frame it's basically the classic scenario of a N/S split with Azores ridging influencing the south and systems tracking NE and effecting Scotland and the north of England.

Anyway, showery on Sunday before a ridge moves in the give a fine dry day for most on Monday. A front approaches the NW early Wednesday and tracks SE dissipating as it goes. A small perturbation nips across the south on Thursday before the ridge nudges in from the SW and before the next system arrives in Scotland and the north of England on Saturday. Temps generally around average.

 

[seaside 60]

10 hours ago, knocker said:

Gaston hits the buffers

Just a quick question.
Noticing some of the tracks has it sinking south again.
Has one ever done the full circle, ie dropped south of Africa and reformed.

[knocker]

25 minutes ago, seaside 60 said:

Just a quick question.
Noticing some of the tracks has it sinking south again.
Has one ever done the full circle, ie dropped south of Africa and reformed.

Not to my knowledge.

[knocker]

GEFS - Gaston

[Summer Sun]

High pressure is never far away on this mornings ECM keeping the bulk of any rain / showers in the far north and west though some short-lived unsettled blips further south can't be ruled out

[phil nw.]

A decent outlook according to the latest runs after we get clear of the shallow complex low currently over the UK which is giving rain and some thundery showers.

A look at today's fax and Tuesday next week we can see the low gone and high pressure building across us. 

Away from the north west where fronts will bring some rain at times many areas look quite dry .A look at the London ens for example show reasonable temperatures going into September with very little rainfall expected. 

If anything week 2 of the outputs looks even better with the Azores high frequently ridging across many areas forcing the jet further north.

GEFs T240 from the 06z run.Alongside the 00z ECM mean for T240hrs -good agreement there on the general pattern.

Of course there will be occasions where again the north west will be prone to something more changeable and on occasion further south may see frontal activity but overall it looks like we can expect a number of dry and fine days-pretty good i think. as we start Autumn.

Edited August 27, 2016 by phil nw.

[Singularity]

With so much high pressure in the outlook, and signs that Gaston might behave nicely for keeping that theme going while also increasing the temperatures again, it's a shame that we can never rely on tropical cyclones to behave quite as the models expect!

Certainly a time of great hope for a decent first week or so of September though. Temperatures look to be on the warm side, particularly in the south - warmer than average, certainly - most notably in the east, as one might expect from a weak westerly mean flow.

The heat across Europe is notable in both intensity and spatial coverage. For the sake of balance, this ought to try and find ways to reach the higher latitudes and disperse, be that via plumes or storm genesis. Or indeed both!

[Summer Sun]

The 1st full week of September starts with high pressure taking charge temperatures generally in the high teens to low 20's

[Man With Beard]

Some nice looking op runs tonight for the coming 10 days, but not enough certainty on the ensembles for me once we get past next Friday. A SW to NE flow perhaps the favoured cluster, but it's a bit of a mix really with cut-off troughs causing issues on some members by D8, and a possibility that Gaston may even promote a mid-Atlantic ridge rather than a UK-based one. I'll put my September CET pitch off a bit longer methinks.

An excellent summer week coming up though for many. Turning into quite an August for the south east.

[knocker]

Today

The rain currently effecting North Wales and the north of England (and Cornwall I might add) will move away east leaving broken cloud and showers for many. Temps down from recent levels

This morning's GFS

The week up to the weekend can be summed up pretty quickly. High pressure will prevail in England, particularly the south, whilst Scotland will remain subject to systems tracking NE bringing rain and possible quite strong winds.By Saturday the HP has given way to a new depression that has arrived from the west with the fronts bringing rain to most. Temps generally around average, possible a little above in the south.

Now this is where it may become interesting. Looking at this morning's GEFs anomaly and to a lesser extent last night's EPS in the 7-12 period, with the trough south of Greenland and height's building to the east, we could have the not unfamiliar scenario  of systems continuing to track NE effecting Scotland but a slack area of low pressure to the south which could once again encourage thundery outbreaks moving north and some quite positive temps.

[Summer Sun]

ECM shows pressure building quite strongly from D8

GFS goes for 30c next Sunday & Monday in parts of the south

 

[Captain Shortwave]

There is certainly a trend for the first week or so of September to see a fairly widespread anticyclonic spell across the UK with a ridge building over Scandinavia with this influencing the UK for a good deal of the time.

      

The two complicating factors are firstly Gaston which will take some time to resolve its exact track, the second is the chance of a trough sinking south and becoming cut off near the UK at the end of the week.

GFS and GEM

   

You can certainly see how the heat shown in the post above comes about as the low gets cut off west of the UK setting up a very warm south easterly flow, the GEM would be cooler and showery for a time before pressure builds back in. The ECM however doesn't do this and keeps a stronger jetstream which simply keeps pushing the Azores high north east until the latter couple of days where the high displaces across the UK and Europe.

    

A lot of settled weather on offer at the moment from the models, just in time for the kids to go back to school. How typical.....

It must be said however that this coming week looks pretty decent away from the north west.

Edited August 28, 2016 by Captain Shortwave

[Singularity]

Great analysis as usual CS 

The past 6 weeks have seen a repeated tendency for the models to assume a fairly straight forward SW-NE jet passing NW or across the N of the UK, with ridges extending all the way from the Azores to eastern parts of Europe via the UK or at least E&W, only for a break in the jet stream to be introduced nearer the time, with trough disruption bringing the potential for a low to drop to the SW of the UK and bring about a hotter but more unstable outcome.

GFS has now made such an adjustment to waft in another round of continental heat, but ECM would rather stick with a strong SW-NE jet passing well NW of the UK and working in combination with ex-Gaston to bring a large wedge of subtropical air to the UK. The two solutions are equally valid at this stage - trough disruption nearly always keeps us guessing until pretty short range, which is what makes them so entertaining in winter (!) 

[johnholmes]

This is the idea that ECMWF-GFS show along with that from NOAA

EC-GFS much like that shown by CS above. NOAA is less keen on the idea of any marked 500mb ridging as you can see below.

One would expect the majority to be nearer the pattern day 6-10 but I tend to err towards the NOAA outputs. Be interesting to see which model is closer to the upper pattern in 6-10 days though. And, as always, in the hurricane season, all it takes is for one to get into the north Atlantic and relative chaos will develop in the models for a few days.

http://www.cpc.noaa.gov/products/predictions/610day/500mb.php

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

[knocker]

Well I don't think this morning's EPS is a million miles from NOAA. Yes it does have the Azores ridging into the UK with some not unpleasant temps particularly in the south but it's not sustained. It's essentially from T192-T252 before the pattern flattens and the upper flow veers a tad. This would not necessarily show up on the NOAA charts.After that we are back to LP to the NW and HP to the SW scenario but with HP to the east still ridging into the northern Baltic this keeps the upper flow south westerly so temps quite reasonable.

[Nouska]

While it's quiet and not everybody visits the tropical section - a nice close-up of the hurricane (Gaston) we are mentioning in model discussion.

Cannot credit the image as it is on Imgur but borrowed from S2K tropical forum.

Edited August 28, 2016 by Nouska

[knocker]

And latest GEFS guidance

[Tamara]

On ‎18‎/‎08‎/‎2016 at 14:53, Tamara said:

The cooling off trend suggested beyond the day 10 period reflects the discussion in recent posts with regard to the evolving progression of the amplified Atlantic ridge - and how evolution of the upstream pattern ties in with direction of travel of atmospheric angular momentum.   The continued amplitude of convection in the Western Pacific over the medium term looks wholly supportive of propping up the atmospheric circulation with sufficient westerly wind propagation to prevent slipping back into -ve GLAAM territory . So supplying the downstream movement of Rossby Waves that sustain the indicated very warm meridional pattern in the Atlantic and European sector through next week, and which follows the interruption spoiler courtesy of a weekend hooligan.

Its a continued watch as to how much amplification can be squeezed out of this, and for how long. The likelihood remains that following the Bank Holiday period, the tropical forcing signal will relax, as the current activity in the Western Pacific ends and starts another cycle in the Indian Ocean. This will have the effect of a renewed slide in angular momentum and, eventually the movement of the Global Wind Oscillation more decisively into Phase 1.  Until this time, tropical forcing will offset parity of the GWO at a neutral signal on the pattern, and the status quo prevails.

The Bank Holiday is here, and after what for some of us at least has been a truly Mediterranean type week, thankfully the status quo still prevails. 

Accordingly, as long as the sq lasts, NWP will keep putting off any suggestions that change of official season also means widespread change for UK and western Europe away from the outgoing season weather type.  Of course in saying that, parts of northern UK have not been fortunate to see the considerable lasting improvements that August has brought further south in the UK and over much of the mainland parts of the continent.

In terms of the bigger tropical forcing picture that has helped drive these changes, whilst reasonable, logical and sensible to carry on anticipating the eventual return of tropical convective forcing towards the Indian Ocean, there is a weak signal not yet faded completely in the Western Pacific and so continues to help support global atmospheric angular momentum at the fairly neutral levels maintained since a recovery first started from a low position mid summer. 

Tropical convection forecasts typically vary, and should not be taken at face value alone without examining the extra tropical forcings that when combined can constitute wider scale weather pattern changes - but this is not yet the more definitively expected Nina atmosphere/ocean controlled state that seasonal modelling envisaged evolving into autumn looking forward from the end of Spring.

  

This recovery from the lower angular momentum levels that had greeted the first half of summer and had appeared to signify an increasingly Nina-esque type cool and unsettled season across UK and Europe, has instead offered during later season the northwards and eastwards propagation of Rossby waves from tropics to mid latitudes, far enough downstream to the European sector to help try to relieve/offset a persistently and stubbornly flat Atlantic jet pattern. The flatter pattern that has also particularly affected parts of Scandinavia a lot of the time as well as Northern Britain.

So whilst it hasn't been any 1976 or 2006 - it has been far from any 2007 or 2012. And with the help of August 2016, its been better than 2010 and 2011 which had stronger Nina influence than this summer.

As official summer 2016 comes very close to its end, last but by no means least, an unpredictable watch over tropical storm and hurricane activity in the tropical Atlantic has now also entered the fray to help prop up the downstream ridging potential that keeps hopes of the weather ignoring season changes alive.

A combined sum of factors such as these will always gives chances to arise for very warm and humid air to be pumped towards UK and NW Europe however late in the season. However, on the most micro scale level, the boundaries of jet amplification and associated warm air advection potential has focussed right across the UK all summer (as it too often does) and has led to some quite starkly different outcomes and fortunes over a small Island - according to whether one is north or south of this jet boundary.

Notwithstanding the differing domestic outcomes for Net Weather members up and down the nation from the most northern coast to the most southern coast - on the more macro level I think that NWP has nevertheless been shown up at least a couple of times since mid summer for not picking up the greater latent meridional aspect available until at shorter notice.   These warm air advections have shown up quite clearly in shorter term intra day NWP modelling, but while the upper air anomaly charts at greater ~ 8 to 14 day period distances have correctly and reliably kept identifying the persistence of the default flat westerly pattern, they also have somewhat disguised/detracted from the amplification potential available from mid latitude ridging that The Global Synoptic Dynamical Model (GSDM) had already identified by this time.

The tropical convection signal alone from mid July was flagging up this possibility with suggestions of forcing from the west Pacific which would help boost angular momentum and in turn supply rossby wave propagation needed to buckle the jet and boost warm air advection potential available from the greater northward amplification of downstream Azores/European ridges. In suggesting a better parity of AAM , it also gained favour for the expectation of eastward ridging alignment of the Azores High rather than any retrogression allowing the jet to dig even further south. This has proved to be the case - to better extent (for the south of the country at least actually) than had started to seem possible at the mid summer point

The GSDM, though use of the Global Wind Oscillation ( a phased plot representation measure of a total budget tropical and extra tropical forcing momentums that influence global jet stream strengths and trajectory) provides a highly useful starting point for assessing whether NWP is with, or behind, the game in terms of judging jet stream patterns and their amplification potential in terms of the associated placements of upper air features that result from these calculations.

The various phase plots also give an indication where in the hemisphere such amplifications may occur and whether the pattern is a forward one (westerly wind additions/ higher momentum) or a retrogressing one (easterly wind additions/ lower momentum)

This is the most macro scale starting point possible.

On the theme of hidden upsides, its also true I think that some seasonal outputs were over pessimistic of expectations for the UK as a whole (within the parameters of a forecast for whole of Europe). There is one at least I certainly have in mind here. If taken literally at face value these underplayed any warm air advection amplification advection potential of the jet anywhere in the UK - and restricted it to continental indicators, implying something akin to another 2007 or 2012.

However, more and more so since the mid summer point we have seen how relatively small amounts of amplification to an otherwise flat pattern can make considerable differences over short distances where the jet boundaries exist (such as the UK!). Even within the same general overall changeable westerly pattern that has occurred and which many expert predictions correctly made.

Hence the care that is needed with interpreting these broad-brush predictions too much at face value when applied on the smallest scale - especially towards a very small country that borders a great expanse of cooling moist ocean on one side and a very rapidly heating large expanse of continental land-mass on the other.

The butterfly effect fast comes into play if NWP calculations of this macro starting point are even slightly out in projections up to 14 days hence. Its one thing applying that butterfly effect to a whole hemisphere, but if as one tiny part of that whole hemisphere the UK is just one persistent focal point for where the jet ribbon lies in its global travels, its no surprise that some of the greatest "local" anomaly differences can appear.

So with all this in mind, I think the same alertness to read between the lines continues to be justified in not taking future flatter pattern modelling at face value when applied to our own neck of the woods in current and forthcoming output.  As discussed by others today, there is disagreement about future amplification of the pattern. But as rightly stated in these posts, with Gaston in the mix for the coming 10 day period and beyond this serves to stress greater caution still.

The ECM ensembles for London show up the differences between the GFS (blue line) and the ECM in the 10 day period in terms of further warm air advection potential. But even assuming the flatter and stronger jet profile of the ECM these are surely a very good set of numbers to begin autumn with and better than many of the earlier summer ones - even if they only are representative of south east England. Lots more very dry conditions to come these suggest as well. Assuming current modelling suggestions of Gaston holds sway in the days to come, the ECM suite is increasingly supportive, anyway, of the jet moving further north in association with the extra help from Gaston. 

 

With AAM supported at least at parity into the medium term, and therefore the GWO prevented from moving decisively into another Phase 1/2/3 orbit as suggested as soon as might imminently occur in the last update - its logically reasonable to not expect any upstream retrogression signal, just yet, to further amplify the Pacific and as a consequent downstream sequence response to such a process, pull our anticyclone too far west. 

Therefore, simply put, this means that the theme of eastward Azores ridging should be able to keep going for a while yet. It also means in terms of the current modelled suggestions with regard to Gaston, this should hopefully promote further the chances of an inflated UK/NW Europe ridge rather than an inflated retrogressed Atlantic one which would risk much more putting us nationwide the "wrong" side of the jet stream in terms of any late seasonal warmth.

Last but by no means least, while the percentage play currently points to continuing most changeable furthest north west - it might well evolve that a break from the sequence of Atlantic troughs arrives here too for a while at least in week 2.

Edit: pm was sent to blizzard in reply to post below

Edit 2 Mon a.m :  Reaction to face value intra day NWP is not sensible at any time, but especially with a tropical feature in the mix.

Edited August 29, 2016 by Tamara

[carinthian]

Hi Tamara, interesting comparison of how the flat jet you mention produces a widely different summer, not only on the bigger view of Europe but more locally. Looking at reports from the UK , I would suggest much of Northern Britain has had a poor summer with regular top of rainfall and lack of heat and sunshine. In the other hand lack of rainfall and increasingly hot summer days in pockets of Southern Britain. However, probably not an usual summer scenario. You mention Scandinavia in the same boat, regions further west and north cool , dull summer and even Stockholm not having the best of summers, yet areas further south , like Malmo receiving pulses of intense heat at times this summer. Here in Austria , a indifferent summer, not the best and after lasts years record heat and drought a bit of a shock.Likewise parts of Germany and France have had great diversity in summer weather. On a more upbeat note for the wider influence of a nice spell of prolonged weather for the British Isles and to include much of Western Europe. There is now positive indications the flow in the Upper Atmosphere will begin to undulate with a greater prospect of warm air advection poleward , with the resultant strengthening of the high pressure zone in the area you have mentioned in your latest analysis. Thanks for all that work you put in your posts and best regards from Austria( still in the influence of the easterly drift, us being on the wrong side of the jet ! )

 C

[blizzard81]

Hi Tamara

Thank you for another fab, informative post. When you allude to "certain" other long term Summer forecasts/indications coming unstuck, are you referring to the met office?

Edited August 28, 2016 by ajpoolshark
removed original post as no need to repeat it

[knocker]

Now this is an interesting chart

[blizzard81]

7 minutes ago, knocker said:

Now this is an interesting chart

Indeed. A very nice first week of Sept if these anomalies come to fruition.

[Summer Sun]

GEM shows high-pressure building as we go into the 1st full week of September

[Summer Sun]

ECM has something different tonight with low pressure over Iceland moving SE and ending up over Scandinavia leaving high pressure to the west of the UK leaving us with a northwesterly to northerly flow of air

 

 

 

Edited August 28, 2016 by Summer Sun