Model Output Discussion 17th Dec.2013-12z onwards.

[Mucka]

We heard this kind of thing ad nauseum at the start of Dec, but here we are closing in on Xmas and the the charts are looking exactly the same...if not worse for sustained cold.  We all know charts 12 days hence will not verify as shown, but they can and often do give very good pointers to the overall pattern at that time and given what I can see now any positive spin is precisely that...spin! 

 

Could you point out precisely what is spin and where and when anyone has said sustained cold is in the charts?

We can pessimistic or optimistic so long as we are analysing the actual output that's fine.

 

You are entitled to your opinion but if you think nothing has changed in the way the Northern hemisphere is being modelled over the last few days then I suggest you take another look.

Whether we ultimately benefit from that in January is difficult to say but we will certainly be struggling to get any sustained blocking and the sort of rare winter set up and deep cold you appear to be looking for - but then I could of told you that before winter started.

Point being, nobody is saying we will have sustained blocking and deep cold come January as far as I can tell, they are saying that the output is not showing certain zonal doom that was being modelled and that our chances have improved of seeing something of a more wintry flavour in the first half.

 

That signal may or may not get overridden and it is fine to say you believe it will be(entirely possible) but you appear to be denying there is any signal at all?

[Jason M]

Ensembles are fantastic in low res. I still think a. uK high will be the endgame but nonetheless some real eye candy on view.

I think a certain Steve Murr may be around the place over the coming days.

Jason

[Cloud 10]

hgt300.png

 

 

ukwind.png

 

 

 

Why such a contradiction between the Jet and UK Wind Direction charts?

 

Jet showing NW direction on Boxing day UK showing SW?

 

Ian

 

The jetstream chart shows the winds at about 30,000 ft,the second chart shows winds at the surface.

[Ali1977]

Some good WAA into Greenland showing up, think these will be a better set of ens

[Mucka]

Some good WAA into Greenland showing up, think these will be a better set of ens

 

Not bad, these for NW England, but still a way to go before we can get too excited.

 

http://www.meteociel.fr/cartes_obs/gens_display.php?ext=1&x=238&y=38

[Ali1977]

P15 would be nice, with prolonged cold.

[IDO]

My opinion in this current anti-cold pattern still remains around the PV being the driver. Whilst it sits in Canada, even with an Arctic High we still need a spark to get cold to the UK. That's why, even though the ECM was an outlier yesterday, it had the right idea.

 

For instance GEFS 15 has the trigger low ejecting off the PV: 

 

The low heights move south/SE & allow the AH to ridge NE: 

 

And by the end of FI: 

 

So even with a vortex still doing its worse we get probably the perfect outcome for such synoptics. A few days ago all the T384 charts were zonal or UK high so it is a step forward. Of course ECM failed on yesterday's runs, but was probably a bit progressive, due to the current turbo charged jet not really being conducive to the short wave sinking. This is forecast to moderate, so it may enable such a trigger low to change the LW pattern favourably. Of course by T384 there are many potential outcomes and we will need luck for one of these to bring cold to our shores.

 

 

[nick sussex]

Looking at the overall trends from todays model outputs, generally the Azores high is kept displaced to the west, the GEFS mean at T240hrs aswell as the ECM agree on this, that's basically as far as we can look in terms of a more solid trend.

 

Now I think the problem is that sometimes people take the models especially the operationals at at face value, yes of course you can't ignore the trends they show but equally you have to view them with a what can potentially develop from a scenario.

 

Generally speaking the PV chunk over Canada and Arctic high pressure to the ne result in a battle ground being played out over western Europe, in a sense you have two forces working against each other, the PV chunk desperate to send energy by way of low pressure east and the high trying to force the pattern further south.

 

 

The issue of trough disruption in these situations is the one thing NWP doesn't like to deal with, that has to decide where to place the energy, modelling tends to want to send this more north and ne at longer timeframes, this is crucial because if they over do the energy ne and start taking this more east/se low heights begin to drain away from the nw.

 

The actual modelling of the pattern to the ne is often poor because of the lack of observational data in that region, models can often overcompensate in that region or conversely underdo the influence of high pressure there.

 

If you take the Arctic high at face value in terms of its position and strength its very unlikely come T240hrs that the output will show that same set up over western Europe, history in these situations would favour more trough disruption over this region.

 

The more likely synoptic set up if the Arctic high remains in that area circled :

 

 

I've just overlayed that chart, the PV over Canada, the Azores high displaced further northwest, troughing aligned more nw /se into Europe, more amplification over the eastern USA.Historically this scenario correlates quite well with the Arctic high PV combo, now this doesn't mean a pattern change because at this point the amount of trough disruption will determine whether low pressure over the UK is forced se and makes a clean break with low heights over Greenland, if this does happen then heights will begin to rise towards eastern Greenland, the Azores high here acts to slow the next low that is being spawned by the PV.

 

So we have still a way to go before jumping over the first hurdle, the key here is the Arctic high, if that holds out then a chance, if it weakens and moves further north again then the PV will continue to rule the roost.

 

 

 

 

 

 

 

 

 

[Purga]

Great post Nick, well explained and concise. Let's hope the pattern evolves favourably and we all have a nice snowy New Year!

[joggs]

I wont be around for a few days now so would just like to thank everbody contributing in this great thread,and also a happy xmas and new year to all.Stay safe!

[bluearmy]

Good post nick. Fwiw, I think the spread to the west reflects the possible adjustment south of the jet and therefore lower heights than the mean. interestingly, your overall thoughts are not a million miles away from the end of week 2 ECM ens suite. I am rather surprised by the doom and gloom when faced by the current week 2 ens output. I guess we are seeing life without Stewart's teleconnective input!

Why assume we will see a continuation of the pattern? High polar heights are going to become the way forward as we head though the first half jan. that gives us a ticket in the raffle.

[winterof79]

The trend is for the vortex to weaken long term.

http://modeles.meteociel.fr/modeles/gfs/runs/2013122206/gfsnh-0-384.png?6

 

And for the arctic high to start and work its magic and cold to start to push west into continental Europe,which can only be good.

http://modeles.meteociel.fr/modeles/gfs/runs/2013122206/gfsnh-1-384.png?6

 

http://cdn.nwstatic.co.uk/ensimages/ens.20131222/06/t850Moscow.png

http://cdn.nwstatic.co.uk/ensimages/ens.20131222/06/t850Berlin.png

 

I do not care if it is way off,its the trends.http://modeles.meteociel.fr/modeles/gfs/runs/2013122206/gfsnh-10-300.png?6 and open to discussion.

Edited December 22, 2013 by winterof79

[Joe Levy]

The trend is for the vortex to weaken long term.

http://modeles.meteociel.fr/modeles/gfs/runs/2013122206/gfsnh-0-384.png?6

 

And for the arctic high to start and work its magic and cold to start to push west into continental Europe,which can only be good.

http://modeles.meteociel.fr/modeles/gfs/runs/2013122206/gfsnh-1-384.png?6

 

http://cdn.nwstatic.co.uk/ensimages/ens.20131222/06/t850Moscow.png

http://cdn.nwstatic.co.uk/ensimages/ens.20131222/06/t850Berlin.png

 

I do not care if it is way off,its the trends.http://modeles.meteociel.fr/modeles/gfs/runs/2013122206/gfsnh-10-300.png?6 and open to discussion.

I definitely agree about the importance of trends and to that I would add that as far as I am aware, strat forecasts are often more reliable than surface forecasts (someone correct me if I am wrong) so that strat chart is not as 'FI' as we would normally assume with charts at that distance.

[Captain Shortwave]

I think the GFS is going to crank out something really nasty here just after Boxing day

This is much deeper than the previous run

Also the central pressure of this low on this run is dropping 15mb every 6 hours   

[tinybill]

this  the  first storm over scotland 935  mb

 

 

and  the  next  one looks  more south reading 960 at the  moment could cause problem down south  on boxing day

[pip22]

 

Is that a greenland high building over greenland? Lets hope so. We may see a blocking setup.

Edited December 22, 2013 by pip22

[Mucka]

Another bout of WAA about to head up through Scandi, that can help strengthen blocking.

 

Edited December 22, 2013 by Mucka

[Uncle_Barty]

 

Is that a greenland high building over greenland? Lets hope so. We may see a blocking setup.

 

 

 

Probably not. it's not being "supported" by increasing heights in that area - still blues at 500mb, you need greens and yellows starting to show there.

[Captain Shortwave]

Ok I will give this one a chance, hey lets be festive. 

Low north of the UK needs to move west/north west back towards Greenland with the Atlantic low to drive south east into Europe with the Arctic high dropping south into the gap. Strange looking in my limited experience, but plausible I guess. 

Biggest issue is where do we get some proper Arctic air from, though a continental south easterly would be good enough for frontal based snowfall.

Edited December 22, 2013 by Captain shortwave

[Mucka]

So there we have it, a split PV within Hi res and nice Arctic high heading for Greenland,

 

 

Whether we get anything from this or not I think people will have to admit that January suddenly doesn't look like a write off.

[nick sussex]

Exciting stuff by the GFS so far, going in the right direction, the key now is for a separation of low heights so that low near the UK needs to disrupt more and send energy se into Europe, then the ridge to the ne can start to really show the PV whose boss!

 

Its critical to get that clearance and the ridge  further into Greenland before the PVs next missile attack, if you get the ridge further sw into Greenland then even a mean looking PV can get shown the door.

 

Factor in model bias here, the GFS will not want to send the energy se'wards, it will do everything possible not to do that, the key earlier is to get the right alignment of the Arctic high and a bit more amplification upstream. Overall though a decent start to tonights model outputs.

Edited December 22, 2013 by nick sussex

[Polar Maritime]

In reality it never was a write off Mucka, and never will be even before the month starts. And that goes with any month.

Edited December 22, 2013 by Polar Maritime

[Mucka]

Exciting stuff by the GFS so far, going in the right direction, the key now is for a separation of low heights so that low near the UK needs to disrupt more and send energy se into Europe, then the ridge to the ne can start to really show the PV whose boss!

 

Its critical to get that clearance and the ridge  further into Greenland before the PVs next missile attack, if you get the ridge further sw into Greenland then even a mean looking PV can get shown the door.

 

Yeah one step at a time.

We know models handle trough disruption badly at the best of times so other than hoping for eye candy there is little point in being too specific on what breaks in FI.

The main thing is to get some strong HLB going in hi res and see if it can benefit us later.

 

As I keep saying these messy set ups, if it develops, often deliver some big snowfalls because there is plenty of low pressure around to provide the PPN and cold air is never too far away from being in the mix.

[SMU]

http://www.meteociel.fr/ukmo/runs/2013122212/UN144-21.GIF?22-17

 

NICE polar heights on the UKMO @ 144- Strong signal...

 

Also GFS going the same way- with a lobe of the vortex getting stuck underneath the high over Eastern Scandi

 

http://modeles.meteociel.fr/modeles/gfs/runs/2013122212/gfsnh-0-324.png?12

Good chart-

 

Also the stratosphere looking good at 324!S 

[R.P. McMurphy]

 

Looks like another LP System in the waiting.... Ugh..