Model Output Discussion 18th Nov.2013-12z onwards.

[Severe Siberian icy blast]

Not too far off a bartlett high type set up looks a temporary set up though, with it comes the milder air

what we have gav is a very very disturbed vortex that is actually very close to bringing very cold air to us. You zoom in and show what you want it to show but we really need to look at the bigger picture.

[Methuselah]

I think there ought to be a bit more reading between the lines that there are some who post on this thread who like to try and suggest how the pattern may evolve some time ahead based on attempts at reading background factors and potential atmospheric signals -  but that these are used as a measure of progress to test against and are not intended necessarily to be taken at face value as any definitive long term forecast. This isn't crystal ball gazing - and should not be confused as such, and not discouraged in any way as such posts from members like these can prove useful for discussion and as a learning tool.

Why should we have to 'read between the lines', Tamara? Why can't 'experts' simply express themselves in plain English?

[Ǝssex Ǝasterly]

Because it will have impacts on what happens to the general pattern I believe. It certainly won';t be bringing us snowmageddon.

 

Ok thanks, this is because when a front comes in from the west it will usually drag with it milder air displacing our current cold snap, whereas a front from the north or NE/E would commonly prolong the spell of cold?

 

Is that correct, sorry for my noobiness! Trying to get the hang of things

 

PS: I know it's a lot more complicated that how I've explained it

 

none, but ex tropical storms are in plain English-bloody sods to try and predict, they tend to scupper or at least mess up most model predictions. This is partly due to the huge amounts of moisture and heat they inject into the north Atlantic area once they move into that area.

 

Thank you both, very informative!

Edited November 19, 2013 by Essex Easterly.

[Mucka]

MetO pretty awful, sends the shortwave NE instead of SE at 120

 

[Cecil Hogmanay Melchett]

Well after today im going to take time out to enjoy some much more seasonal weather.

Hand on heart its a long road back to HLB from the charts im seeing today.

 

Exeters view of the cold becoming diluted looks a pretty good call to me,hopefully an Atlantic influence will be shortlived.

[sunnijim]

GFS aside, in nearer-term the 12z NAE signals a small-scale low associated with the occlusion wraparound as it moves SE'ward tomorrow afternoon-eve. WBFL's circa 500-600m in zone between this feature and the cold front (which itself has strong line convection signal)..... we anticipate some wet snow approx Cotswolds down across M4 corridor to the SE as it runs south, aided by slack wind environment. Critical PPN rates only around 2-4mm p/hr needed to help turn this to snow.

Very interesting thankyou,we actually have some potentialy wintry weather in the next 48hrs,snow,severe gales,ice,squall line with hail,and folk here are banging on about winter synoptics at 384hrs that may or may not happen!

[phil nw.]

The anomalies are usually a good indicator of what's to come and are a good go to when the operationals are uncertain.

The cold upper air they showed to be -4 to -6C today for the UK has arrived bang on cue.

 

If we recall they never promised a prolonged Arctic burst.The coldest air will be somewhat mixed out by Thurs as that developing low moves down the east coast bringing some hill snow with it.

The fax at t84 is a good illustration of the often talked about split flow btw

 

see the lows n and s with the high inbetween.

 

Thereafter we see the much talked about Atlantic block moving in keep it rather cold with an increasing risk of frosts and some freezing fog.

UKMO T120

 

Pretty much as expected days ago.

 

[karlos1983]

MetO pretty awful, sends the shortwave NE instead of SE at 120

 

 

Yes it's not great, Over to you ECM, It will interesting to see how it deals with the same time frame.

[radiohead]

12Z GFS opens up the vortex then splits it. It just happens in such a way that doesn't impact us much, but you could easily imagine it happening in a slightly different manner...

Should be interesting to see if there will be any support for this idea in the ensembles.

[shaky]

Ukmo keeps it settled all the way and I dont think its gona be mild.more like cold and frosty with high pressure slap bang over us!!

[Purga]

Oh no a mild December!

 

 

 

Joking! Seriously though this type of amplified pattern could easily turn into something severe

 

 

In the meantime cool and occasionally frosty but mostly dry.

[nick sussex]

Yes it's not great, Over to you ECM, It will interesting to see how it deals with the same time frame.

Really the problems are twofold, the shortwave energy to the sw doesn't head east and this is a problem as it runs anti-clockwise putting pressure on the high and keeping the tilt positive, thereafter the shortwave which needed to head se to have any chance of giving the high a chance to ridge north heads ne. Game over at that point with the high taking up limpet position over the UK, could still be cold with frost and fog but its really hard to see any sort of decent easterly from there. The best output of the evening so far is the NAVGEM which at least might bring some excitement for those in the se but is to put it mildly only a model to turn to in desperate times when everything else is underwhelming! It's basically cat litter, they really should just put it out of its misery and give up!

 

The GEM just trundling out now but as Princess Leia said help me ECMKINOBE you're my only hope!

[NorthernRab]

MetO pretty awful, sends the shortwave NE instead of SE at 120

 

 

Though more crucial is the northern hemispheric set up, we're seeing quite a distressed polar vortex on this run which could have implications for model accuracy until we get a clearer picture. 

[Purga]

Really the problems are twofold, the shortwave energy to the sw doesn't head east and this is a problem as it runs anti-clockwise putting pressure on the high and keeping the tilt positive, thereafter the shortwave which needed to head se to have any chance of giving the high a chance to ridge north heads ne. Game over at that point with the high taking up limpet position over the UK, could still be cold with frost and fog but its really hard to see any sort of decent easterly from there. The best output of the evening so far is the NAVGEM which at least might bring some excitement for those in the se but is to put it mildly only a model to turn to in desperate times when everything else is underwhelming! It's basically cat litter, they really should just put it out of its misery and give up!

 

The GEM just trundling out now but as Princess Leia said help me ECMKINOBE you're my only hope!

If the best output so far is from NAVGEM then things must be in a bad way. 

[john mac]

Though more crucial is the northern hemispheric set up, we're seeing quite a distressed polar vortex on this run which could have implications for model accuracy until we get a clearer picture. 

I agree with you the that chart shown has a lot of potential, as said early its all about the bigger picture not the small details at medium and long range.

[Frosty.]

The Gfs 12z op run is pretty cold and anticyclonic, even more anticyclonic than the 6z and just when you think the atlantic might break through, high pressure builds strongly to the east and brings a mexican standoff, the atlantic keeps trying and eventually gets through but it's far from smooth progress, so there are significant obstacles put in the way of a change to zonality on this run and there is nothing mild here, it's rather cold with widespread frosts from later this week onwards.

[Tamara]

Why should we have to 'read between the lines', Tamara? Why can't 'experts' simply express themselves in plain English?

You haven't interpreted/represented correctly what I was trying to say - but best to keep the thread on topic without further explanation.

 

The hints as expressed by some Met Office ensemble data of hints of a more progressive westerly type to follow is maybe showing its hand on both the GFS and UKMO this evening. I wonder how much of this is exacerbated due to unfortunate placings of pockets of residual vorticity energy towards Greenland in connection with the disturbances to the polar vortex from the lower stratosphere activity.  Its too early to be certain and could well be over progressive in timing, even if the evolution is ultimately correct

[Catacol]

Why should we have to 'read between the lines', Tamara? Why can't 'experts' simply express themselves in plain English?

 

Because weather is not black and white; it is grey... and I for one often post possible interpretations based on model runs rather than straight forecasts of what will be. There is a difference.

[bluearmy]

it seems the canadian segment of the p/v is too close to greenland to allow any decent ridging north. the jet energy coming off the eastern seaboard is strong and flattens the weak ridge that has built. not as flat as some models showed earlier in the week but certainly the ecm op's first test of whether it is still prone to over amplification returns a 'yes'. the modelling of the p/v in fi is promising but if we cannot get the canadian p/v to relocate closer to hudsons or weaken markedly, we will struggle to get upper cold from any vortex split/displacement.  on the plus side, the fact that we are even talking about the vortex in this way in the third week of november is promising and it is possible to get a decent easterly, even with a vortex close to greenland.

[Duane S.]

You haven't interpreted/represented correctly what I was trying to say - but best to keep the thread on topic without further explanation.

 

The hints as expressed by some Met Office ensemble data of hints of a more progressive westerly type to follow is maybe showing its hand on both the GFS and UKMO this evening. I wonder how much of this is exacerbated due to unfortunate placings of pockets of residual vorticity energy towards Greenland in connection with the disturbances to the polar vortex from the lower stratosphere activity.  Its too early to be certain and could well be over progressive in timing, even if the evolution is ultimately correct

 

 

This happened quite a lot last winter as well if memory serves. It would seem that, in low res at least, the models almost disregard the influence of residual energy from the vortex when the main vortex is Scandi-based. Come hi-res and it starts getting a correct handle on it.

[Methuselah]

Because weather is not black and white; it is grey... and I for one often post possible interpretations based on model runs rather than straight forecasts of what will be. There is a difference.

Indeed CH, it is not...But clear and concise English still helps any explanation get across IMO...Unless, said explanation is really designed to confound? Inferring what may - or may not be - 'between the lines' is neither here nor there?

 

As they say, in academia: Keep It Simple, Stupid...KISS!

[nick sussex]

Crucial 144hrs out soon on the ECM, shortwave near southern Greenland, if it heads ne game over , se a small chance of still getting an easterly.

[Tamara]

This happened quite a lot last winter as well if memory serves. It would seem that, in low res at least, the models almost disregard the influence of residual energy from the vortex when the main vortex is Scandi-based. Come hi-res and it starts getting a correct handle on it.

I suggested yesterday that the ECM probably had the best handle on the movements of the vortex in response to its disturbance from the lower polar stratosphere but I will readily admit that looks not to wholly be the case today and the greater weighting that the GFS gave to the Canadian lobe of the vortex is looking to be more prominent as it has been suggesting over the last day or two. The fault of the ECM to over amplify the pattern towards the FI part of output is, as bluearmy alludes to, in prominence here yet again.

 

I think its modelling of movement of a portion of vortex over to Siberia has been correct - simply it has overdone this through over amplifying the pattern. In reality the High is keeping at lower latitude through enough energy remaining over Canada and Greenland to hold the High further south. The more progressive westerly solutions will be picking up on steepening temperature gradients into the atlantic as a greater amount of cold air spills out of the Canadian artic than anticipated and this will spawn lower pressure to the NW.

 

The 12z ECM also backs this rather more progressive trend as suggested by the other models by day 6. High pressure still in charge but a lot more energy appearing over the top of the High

 

Edited November 19, 2013 by Tamara תָּמָר

[Frosty.]

Tonight's ukmo 12z shows our weather settling down by the weekend with high pressure taking total control with long sunny spells, overnight frosts and an increasing risk of fog which will be slow to clear, some areas would be cold and foggy or at least misty all day and temps would be struggling close to freezing if that happens since we will have low level cold air in situ. Into next week and high pressure continues to dominate but even by T+144 hours there are signs that the anticyclone is starting to drift slowly southeastwards with the far northwest becoming breezier and cloudier as the atlantic influence grows but most of next week looks fine and calm the further south and east you are with the fog and frost but bright and sunny in some areas, however, the orientation of the atlantic high may mean we pick up more cloud, especially for more exposed sw/w areas. We have seen significant changes today since the 12z runs last night, the high has been shunted further east which will probably make things easier for the atlantic to eventually come back through early to mid december.

[radiohead]

12Z ECM T168 broadly quite similar to the GFS now on the NH view.