Model Output Discussion

[Optimus Prime]

Still to be honest its pointless wondering about this until the picture becomes clearer.

Exactly. I'm just trying to warn you as I know you like the extreme cold and snow, this is coming from someone that'll have it either way (me)

North Sea Snow Convection, on 09 December 2009 - 23:02 , said:

"Whilst we need a trigger to bring the coldest air in from the arctic across Scandi (Copenhagen) and all routes SW of there, it needs, yes, to be a feature that is significant enough to advect the arctic continental airflow right through the UK but not so over-developed that it becomes like a cyclonic frontal system that takes energy from the 'tropical' side of the system and then sets up a barrier zone to the cold air as it tries to move south and in turn forms a dynamic whereby it stops moving south and halts the progress of the cold air. If you see what my simple mind is trying to say!?

It is very early days, but there is just the hint in my mind that this sort of process as described is being sown and that this north sea low is going to become a more and more significant player (and spoiling nuisance for southern parts of the UK). The time period to get the colder air is not coming nearer, the advecton of cold period should be this weekend for a decisive countrywide event and that may be significant in terms of the extent of this very potent arctic outbreak.

But I think that we will find that the favoured areas will end up being NE parts of the UK (who could see some quite severe conditions)as the path of the low tracks less further south but further west from the north sea into central parts of the UK as the modelling progresses over the next day or so. It could be that SE parts in particular end up on the warm side of the low with a returning flow from the channel (ie a south westerly wind) as the low links up with the advancing southerly tracking troughs in the SW approaches."

That's the post of the day IMO.

Edited December 9, 2009 by Optimus Prime

[PersianPaladin]

Yep I got some overnight rain/heavy snow from that. But we already had the cold over us from the 29th January? And after a generally cold January for many the cold air had little warm air to be mixed in. Hence the reasoning behind those unbelievable temperatures in 81 (max about -4c here falling to -14c)

What we have here is a cold spell over a warm land and sea. We've just come out of the mildest November since '94. It ain't gonna be like coming out of a November like '93.

To be fair, T180+ is far too out to be arguing over this stuff. Albeit, for the sake of argument looking at the shortwave there is some deep cold filtering down and the circulation is reasonably tight. The 0C isotherm boundary may bring marginality for NE East Anglia but its not a marginal set-up given the depth of the cold-pooling: -

http://www.wetterzentrale.de/pics/Rtavn1807.png

However, we are far from there and my worry is that we will be stuck in a col and with the CAA missing us.

[kold weather]

To be fair though Eye, OP does make a very good point in the respect that the boundary level will be very heavily modified indeed, to the point where even under a cold flow we may still struggle at the coast.

The truth is though right now its too early to call, the shortwave will get changed and messed about a lot before we get into closer timeframe...

[Tom Montalbano]

London 18z ensembles.

Regards,

Tom.

[The Eagle]

Ensembles

It's obvious with Aberdeen and Dublin ensembles that a Northeasterly seems the most likely option. It could also end in a Northerly. We seem to be moving away from the prefered Easterly gradually. But a Northeasterly will still deliver. And there is a big scatter there. So all in all a superb outlook. Things will still change remember.

Edited December 9, 2009 by The Eagle

[Tom D]

London 18z ensembles.

Regards,

Tom.

A lot of agreement there, and the operational is perfectly placed between other runs.

[reef]

Just another gentle reminder. If you find your post is missing, its likely it was off-topic and will have been moved to the cold spell discussion thread.

Please keep posts in this thread on the subject of the models. It gets very difficult for anyone who has just logged on to make heads or tails of whats happening when theres multiple conversations going on.

Thanks :lol:

[kold weather]

Of course a well developed shortwave could also allow a stronger cold shot on the northern side of the low, still there is just too many disagreements and uncertainties right now to be too confident.

Ensembles seem pretty solid out to 180hrs, after that the differences in the shortwave do make a difference.

FWIW, I'm willing to bet once the shortwave does either decay or slide southwards enugh we will get a potent easterly on its northern side...this is because I think the 18z evolution is very wrong past 180hrs, all teleconnections would suggest a low pressure over the Azores region, whilst the 18z has a 1025mbs...

[Nick F]

Indeed Nick.I feel the letdowns in the past have probably come out of more marginal setups such as Scandi high`s under pressure from lower Arctic heights.

How often in recent years have we been excited to see a Greenland Block projected at this short range?

http://charts.netwea.../72/h500slp.png

The Steve Murr sausage of 552 up to Svalbard.

'tis a rarer beast the Greeny block than a Scandinavian one .... let's hope the UK can make the most of it while it's around and tap into that deep cold moving SW over NW Russia.

Then again, some of us should be careful of what we are wishing for, particularly as the snow potential that may come could cause alot of disruption and misery for those that have to travel around everyday. There is a downside to our obsession on here! Like there's a downside to me chasing tornadoes as a hobby - there are people who get hurt unfortunately.

[phil nw.]

London 18z ensembles.

http://www.wetterzen....png?6767676767

Regards,

Tom.

Remarkable consistency that the13th has been shown as the day that they dip for about a week now.To me the cold hasn`t been put back like some have contended.

[reef]

Interesting ensembles. The key splitting point seems to be around the 13-14th December still. The GFS 18z run has the initial area of cold air around our high pressure rather further north than the 12z run and indeed, other models. This is shown by the operational run being out of kilter with the majority of the ensemble members which go milder:

http://www.wetterzentrale.de/pics/MT8_Aberdeen_ens.png

Interestingly further south the opposite is the case, which suggests the flow could be a little tighter (larger temp gradient from North to south of the country) than the 18z is suggesting.

http://www.wetterzentrale.de/pics/MT8_London_ens.png

After that its all up in the air, with a lot of scatter. Both the GFS and UKMO go for the shortwave to position itself over the North Sea, delaying the cold somewhat and changing the angle of attack by the cold air to a more North-easterly direction. This is evidenced by the lack of any members above the long-term mean past 16th December in Aberdeen while the scatter further south is much greater.

Id say the initial more marginal easterly flow is nailed now, but anything beyond that should be taken with pinch of salt still

[cold snap]

With all the Doubt regarding 18Z can we say that tommorow mornings GFS will give us a better understanding

18Z maybe one for the Bin

[stewfox]

Do we all agree while being an exceptional setup for the time of year what the GFS is showing this isn't a 1981 and it won't bring us countrywide snowstorms ala Dec 62/78/81? And temperatures won't be that cold.

I fear the party is now in full swing some sober heads are being drown out.

With JH suggesting xmas day wipe outs, go with the flow

Offer asprin in the morning if the hangover is bad for many

Anyway T324 suggest another snow fest

http://www.netweathe...ction=nwdc;sess=

Taxi !

[kold weather]

Just seen the ensembles and it seems clear the problem with the 18z (well relative problem lol!) and the reason why the low doesn't quite get far enough south to really give the country a massive severe cold outbreak is because there is no low pressure heading towards Portugal/France between 192-240hrs. Looking at the 12z ECM what that low does is because absorbed into the low to our east but in turn it still forces the main low to rotate southwards, much akin to the fujiwhara effect (and yes, thats mainly a tropical thing...but in the end they are all low pressure systems, they all work the same in a very broad sense) and that opens the easterly floodgates as well giving a possible attack from the SW.

Thats the holy grail of cold, everything would be building upto that point and thats what required to turn this event from a decent cold spell, to something more exceptional.

OP, I totally agree but there is something that needs to be said...we are only 1 step away from a 81 style event at 192hrs. The 18z doesn't get there but I'd bet the 12z ECM would be real close...and some of the ensembles get there as well.

Edited December 9, 2009 by kold weather

[kumquat]

Just seen the ensembles and it seems clear the problem with the 18z (well relative problem lol!) and the reason why the low doesn't quite get far enough south to really give the country a massive severe cold outbreak is because there is no low pressure heading towards Portugal/France between 192-240hrs.

Hi Kold,

I'm not getting this - to me this seems exactly like a "massive severe cold outbreak" - as a model watcher newb can you tell me what I'm missing? I see this from the 18z at T180:

(looking at 850hPa temps coming around the top of the low)

http://charts.netwea.../h850t850eu.png

Edit mid post -lol- I see the -10 850 recedes massively all of a sudden at 192 - is that what you mean?

http://charts.netwea.../h850t850eu.png

Very excited by all of this and (shame on me) been ramping already amongst friends and colleagues - one time it will pay off and now is as good as ever! (if not the best!)

[kumquat]

Also I'm seeing (and I know I shouldn't look at the precip charts this far out) but I'm seeing low enough -5 850s for snow being shown on the netweather GFS 18z charts for possibly flutters from Sunday Night / Monday / Tuesday. To me this seems like an upgrade for the west country / inland areas of M4 corridor. Seems like SE is getting hampered by sea temps while "us inland" are being given the lower land temps? - Again as a newb I'm saying what I'm seeing from the 18z model output here at NW. I realise nobody gives the precip charts much notice at this range but the 18z seemed to bring in colder uppers for over here in the West/ Southern Central. Could this have anything to do with inversion cold from sitting under the high for a couple of days? Love all the input and all the usual suspects are very entertaining and educational - thank you for that!

Edited December 10, 2009 by kumquat

[snowray]

thanks for that i am not fretting about this run though. it could change and i will get cold where i live so am not worried about that but i would have liked it to visit my neck of the woods before going north lol that's all.

I know its hard to be patient with these sort of charts showing all sorts of Cold and snow Armagedon potential, but I'm quite happy just let things take their course at this stage.

As has been said a few times, the bones are very much there, now a bit of flesh too, but we wont know for sure for a few days yet so its to be enjoyed while it lasts. There may end up being lots of Snow and fun and games for all of us by Christmas.

Had to laugh at the BBC long range forecast this evening:

14th-20th Dec- "light breezes with bright or Sunny intervals".

21st Dec-3rd Jan-"And as usual theres no strong posibility of either wet or white" for Christmas day.

As people have said frequently it has been the GFS parallel run that has led the charge in the Winter Wonderland charts with remarkable consistancy, if things were to go acording to plan, from the 15th of the month this could be a realy great and much improved model, still a pretty big if though of course and the oposite might aply if things go horribly wrong, which I dont believe will happen.

Since just about every other chart imaginable has been posted this evening, how about a very tongue in cheek GFS parallel run for Christmas days PPN. :lol:

Edited December 10, 2009 by snowray

[SMU]

Whos in for the 00z-

T36 has better orientation of WAA up greenland & slightly better orientation...

A very nice start..

S

[SMU]

Mark these words we have seen a very subtle shift over night in the jet energy distribution around 140- we see a lot more flow moving along the iberinan Peninsula & less energy into the loop jet over scandi- as a result that huge pulse of cold air starts to look a though it may not make it. However on the plus side the jet pushing along the southern flank in a surpressed regime is likely to strenthen the Easterly to start with & begin to elongate the troughs over spain & portugal- Whilst this is a slightly risky pattern as it does bring the 0c isotherm back North it also brings a higher potential for a BIG snow event-

& after all thats what were all here for-

GFS control / Operational & PTB 12 !!!! lead the way in the big undercut- if this occurs then there could be some amazing scenes over northern France & southern England-

UKMO on board with this solution as well- great 120 Chart.......

The GEM has picked that up as well-

One final note:the GEFS ensemble mean for Xmas day is now -6C 850HPA

S

Edited December 10, 2009 by Steve Murr

[Altostratus]

The ECM is rolling out. Nervous times. I'm not too keen on the GFS this morning. There is massive potential for a big snow event, but it looks marginal to me in the south.

[Iceberg]

Its been awhile since it can be said but the ops run seems to be a warm outlier of GFS, solid agreement from ENS and meto for the cold and the the snow is now coming into the 144Z range.

Sunday/Monday seems to be getting upgraded for snow in the south by Meto and gfs, With Monday providing quite a few showers now.

[West is Best]

Another excellent duo of runs from GFS and UKMO 0z. The slight change in evolution mentioned by Steve is interesting. It almost makes it look like a double-barrelled blast, with the first shot followed by the second pulling the more intense cold down from the north-east. It does concern me slightly that the migrating hp now starts much further east, but it gets there (Greenland) in the end.

It's all-in-all a stunning run from both models. Let's hope the ECM makes the trio complete.

Talk of snow detail is way too soon. A shift in an advancing low pressure position by 200 miles would make a huge difference on the ground, and there is no way we can be that detailed a week or more from an event.

[Altostratus]

ECM out to T+120:

http://www.wetterzentrale.de/pics/Recm1201.gif

Not a great trend here - looks like the 'real' cold might not make it - if it does, it will be delayed.

Edited December 10, 2009 by Altostratus

[KTtom]

Not sure I can remember such stunning Ensembles or such agreement out untill the end of the run, the Operational even on the mild side. Great start to the day and some of the best model runs being churned out I've seen in my years of model watching....Wait untill the media get hold of these :lol:

[Iceberg]

ECM not as good as yesterday as the link up with the Arctic high doesnt properly happen, still not bad though.

A strange up this, ECM takes the LP at 144Z and destroys it into a weak open wave at 168Z as it clips the south east, all looks a bit suspect to me and stems from the lack of HP link up earlier leading to less cold being dragged down, as bad(relatively speaking) as the 12Z was good, Still not dire by a long way, but shall we say "different".