Model Output Discussion - 28th November

[BLAST FROM THE PAST]

I must be completely imagining the split vortex and the cold spell that is about to ensue.

Just because we are not seeing a glowing orange beacon over Greenland does not imply no blocking.

The GEFS mean height and temperature anomalies continue to advertise a well defined trough signature across Europe throughout the 15 day period with temperatures well below average. Whether this is the '2010 factor' at work I don't know but we must consider that this is late November and early December and we are looking down the barrel of a sustained cold spell, unusually so for the time of year.

Looking at short to medium term those small scale adjustments in the track of the low driving down from the NW continue almost on every run so by the time we get to 2-3 days out, could wel be interesting, especially with the trough engrained over Europe.

Looking further ahead, we have the strong teleconnector in the North Pacific and downstream ridge over the North Atlantic south of Greenland. That essentially keeps us locked in a cold puddle of air for the duration. The AO looks on the negative side too which is a bonus for December as far as I'm concerned given other factors.

GP

Thanks for your thoughts and as it suggests cold an awful lot of 'likes' too...put me down as a like. Lets see how this develops and hope you are right. Correct, blocking is around but its getting sheered off ....the question was - what is in place for cold blocking to occur next time and hold after this current failure to what models forecast, not that any 'forecast' of it happening is nonsense. I couldn't see what is supporting prolonged cold...

BFTP.

Edited November 28, 2012 by BLAST FROM THE PAST

[Continental Climate]

well i thought that we would be experiencing very cold and prolonged wintry conditions starting the 5th of december but i realise that no way is that going to happen now, so i was wrong about that. Our experts say that everything is primed for cold to start in 10-14 days and i still believe that this will be the case!1 I just hope that im not setting myself up for another fall here!! I remember 09/10 very well cold weather started on the 17th december ands never really relented in durham until mid january!! So if the experts say mid december now i will agree with that but if we get to the 15-20th december with no cold spell in sight and having experienced more last minute letdowns i will resign myself to another so near yet so far winter!! I really cant be bothered chasing cold for the next three months!!

[Jezzer]

Just seen this tweet from Ian:Ian Fergusson â€@fergieweather "@terryhood73: met office say cold easterlies 2nd half dec what do you say" I think N / NE'rly their latest prognosis; cold generally, yes

[andymusic]

Personally I feel we are now entering the real cold phase - ie - a finely balanced cold which at a moments notice could produce alsorts of wintry precip anywhere in the UK - so it'll be watching the detailed nae/nmm and also ultimately keeping an eye on those lamposts - could be a very tiring winter this year if we stay on this knife edge - but I think ultimately rewarding because like other posters have said we are normally looking down the barrel of mild westerlies/south westerlies and moaning on about no cold showing up at all - now we are debating the balance between the chances of wintry precip and sleet or rain - I'd say we don't know how lucky we are with all this and that in the next few weeks the chances of everyone getting some snowy weather are extremely high - just enjoy!

[Zakos]

Im sorry but the GFS at least almost invariably underestimates the block. Of course there will be times that it will be right, but I think it is quite clear that on almost ever single run the arctic high is upgraded, even if only slightly.

Wrong? it is not yet December, shall we wait and see what happens, before we start claiming who is "wrong"

I havent wavered from my initial thoughts; a prolonged cold spell in early/mid December. The fact that the Atlantic has delayed the arrival of this potential cold spell by a few days doesn't really matter

I ask you to cast your mind back to this February with the "phantom easterly". for weeks it had been predicted, only getting pushed further and further back into FI . It did however eventually materialise. Thats not to say that this time it will follow the same pattern.

my point is models often have difficulty in determining the arrival of a cold spell.

Oh and for your information, the atlantic hasnt "smashed" through anything. yes there was a ridge in the Atlantic but not a true block. there is no block to our east. There is however a powerful Arctic high.

Solid support for a negative AO

what we dont have is a sufficiently negative NAO

]

It is predicted to rise to positive as that low crosses past Iceland, it may well turn negative again if that low takes a southerly track.

With a continual sign for a negative AO, i wonder how long it will be for the NAO follows suit.

[swfc]

well i thought that we would be experiencing very cold and prolonged wintry conditions starting the 5th of december but i realise that no way is that going to happen now, so i was wrong about that. Our experts say that everything is primed for cold to start in 10-14 days and i still believe that this will be the case!1 I just hope that im not setting myself up for another fall here!! I remember 09/10 very well cold weather started on the 17th december ands never really relented in durham until mid january!! So if the experts say mid december now i will agree with that but if we get to the 15-20th december with no cold spell in sight and having experienced more last minute letdowns i will resign myself to another so near yet so far winter!! I really cant be bothered chasing cold for the next three months!!

Hi cc.Primed for cold in 10-14 days?I think we have just been down this road over the last ten days or so.Given the time of year i think its inevatable that we will get a cold snap"snow ete" but generally if you keep throwing a dice a six will come up.If it does not then the guys forecasting this and other scenarios will say it was bad luck it didnt come off!!!! Edited November 28, 2012 by swfc

[Isolated Frost]

+24

+48

+72

Here is an alternative view of upper air temperatures around Europe- you can really see the progression of the colder air quite clearly on here- and the movement of warmer air out of eastern europe.

quite nifty

Edited November 28, 2012 by Isolated Frost

[Continental Climate]

Im sorry but the GFS at least almost invariably underestimates the block. Of course there will be times that it will be right, but I think it is quite clear that on almost ever single run the arctic high is upgraded, even if only slightly.

Wrong? it is not yet December, shall we wait and see what happens, before we start claiming who is "wrong"

I havent wavered from my initial thoughts; a prolonged cold spell in early/mid December. The fact that the Atlantic has delayed the arrival of this potential cold spell by a few days doesn't really matter

I ask you to cast your mind back to this February with the "phantom easterly". for weeks it had been predicted, only getting pushed further and further back into FI . It did however eventually materialise. Thats not to say that this time it will follow the same pattern.

my point is models often have difficulty in determining the arrival of a cold spell.

Oh and for your information, the atlantic hasnt "smashed" through anything. yes there was a ridge in the Atlantic but not a true block. there is no block to our east. There is however a powerful Arctic high.

Solid support for a negative AO

what we dont have is a sufficiently negative NAO

]

It is predicted to rise to positive as that low crosses past Iceland, it may well turn negative again if that low takes a southerly track.

With a continual sign for a negative AO, i wonder how long it will be for the NAO follows suit.

It could be a long time before the NAO follows suit ZAKOS if that residual energy centered around southern greenland keeps spawning those low pressure systems and spitting them into the north atlantic http://www.wetterzentrale.de/pics/Rtavn1201.png!! This chart is a very good example of that

[swfc]

It could be a long time before the NAO follows suit ZAKOS if that residual energy centered around southern greenland keeps spawning those low pressure systems and spitting them into the north atlantic http://www.wetterzen...s/Rtavn1201.png!! This chart is a very good example of that

That chart shows exactly the problem.Its like a conveyor for the low pressure areas to slide threw!!! Edited November 28, 2012 by swfc

[Zakos]

It could be a long time before the NAO follows suit ZAKOS if that residual energy centered around southern greenland keeps spawning those low pressure systems and spitting them into the north atlantic http://www.wetterzen...s/Rtavn1201.png!! This chart is a very good example of that

I did notice that yes, splitting up over the southern tip of Greenland, it is certainly not a great sign. This residual energy is the main feature which is preventing the cold from on advancing on the UK, for now.

perhaps that tropical depression could be the trigger if it dives below the block a la GFS 12z

[paul tall]

I think we really need concentrate our efforts between 120-168hrs

Did you really just say that?

[Snowy Easterlies]

can someone tell me where this powerful arctic high is, because i can't see one in the reliable time frame, and even if there is one its not having a real affect on our island for next week

your right Zakos, there is no strong block, its just a ridge to the north west now, but the models were showing a stronger block some days ago, so my belief on the models overestimating heights SOMETIMES holds some validity

[swfc]

Just seen this tweet from Ian:Ian Fergusson â€@fergieweather "@terryhood73: met office say cold easterlies 2nd half dec what do you say" I think N / NE'rly their latest prognosis; cold generally, yes

Oh god not again.There updates change so often im wondering what they base it on.For the love of god i hope it does not say a trend!!!!

[Dean E]

I did notice that yes, splitting up over the southern tip of Greenland, it is certainly not a great sign. This residual energy is the main feature which is preventing the cold from on advancing on the UK, for now.

perhaps that tropical depression could be the trigger if it dives below the block a la GFS 12z

The GFS normally under plays the strength of a block, so I wouldn't say that this is a new trend or anything.

I do agree with you on the Low moving SE just to the South of us, could be a very important feature. Has been on many of the runs now.

SM

[Zakos]

The GFS normally under plays the strength of a block, so I wouldn't say that this is a new trend or anything.

I do agree with you on the Low moving SE just to the South of us, could be a very important feature. Has been on many of the runs now.

SM

it most certainly does!

yes, this has been a peculiar feature, one which I have been watching with great interest.

It seems to form a kink in the jet-stream, here we can see it west of Ireland.

As it dives south, it takes the jet stream with it

This needs watching as it could turn out to be an important trigger low for the cold spell.

[pyrotech]

What we need is Europe landmass to cool down, The cold air is too shallow and weak right now for us in UK to benefit. Europe is due to cool quite signifigantly now and that will help us.

I feel that the synoptics shown for this weekend would have given an edge to the marginal temperatures required for any Attack from the Atlantic to be more interesting. In my opinion if this had happened as set to, in two weeks time things would be very different.

We had almost the right set up and conditions, just not a cold pool of air over Europe.

So i see these conditions fluctuating over then month ahead, but Europe will see a fall in temperatures that will make the next few weeks interesting.

The models have all struggled at times with the blocking and i do not its resoved yet, but if the biggest land mass to us is less cold we will struggle here with sea temperatures around us at 10c. North Europe mainland looks set to start cooling this weekend, even night time teperatures are currently warmer than ours. This then gives less modification to any North Easterly flows, but also helps if we have cold air over the UK as its harder for the warm Atlantic air to shift it. The warm air then pushes over the cold air longer before pushing it back. Allowing marginal events to become more likely.

We need all the ingredience right and thats one major factor that is missing right now, so in my opinion we have so much that is going in our favour we just need to be patient. Lets get the cold into Europe.

[Dean E]

it most certainly does!

yes, this has been a peculiar feature, one which I have been watching with great interest.

It seems to form a kink in the jet-stream, here we can see it west of Ireland.

As it dives south, it takes the jet stream with it

This needs watching as it could turn out to be an important trigger low for the cold spell.

One thing to note, it does seem to be loosing intensity every run, Which is another area to watch...This change in wind direction (NW from the more anticipated NE) just goes to show what a small change can do! As others have said, blocking is going to remain high to the North and the cold uppers are there...

Just a matter of time.

SM

[Catacol]

Scanned all the ops after checking the ensembles - none the wiser really for next week. Track of low uncertain; strength of height rises in mid atlantic and possibly over scandy also uncertain; I'm also not sure that the models are doing a very good job of reading the split vortex: they seem to be wanting to reform it out in FI all the time, and that just doesnt seem likely.. I have just trawled back through the archives on Meteociel and stopped at 1972 - there isnt a year anywhere in the archive that matches the severity of the current vortex disruption and others more knowledgeable than me are saying that disruption is going to get worse. With this in mind do I think the models, with a definite zonal bias in FI (120h plus really) can get a proper handle on all this? No.

So - agree with a few on here that the energy being fired out of Canada is the spoiler at the moment, but also less than convinced that the pattern will be as flat as is being modelled. I also think that height rises could be sudden and quite sharp in this scenario.

Basically I'm off to bed pretty convinced that next week is wide open.

[Dean E]

What we need is Europe landmass to cool down, The cold air is too shallow and weak right now for us in UK to benefit. Europe is due to cool quite signifigantly now and that will help us.

I feel that the synoptics shown for this weekend would have given an edge to the marginal temperatures required for any Attack from the Atlantic to be more interesting. In my opinion if this had happened as set to, in two weeks time things would be very different.

We had almost the right set up and conditions, just not a cold pool of air over Europe.

So i see these conditions fluctuating over then month ahead, but Europe will see a fall in temperatures that will make the next few weeks interesting.

The models have all struggled at times with the blocking and i do not its resoved yet, but if the biggest land mass to us is less cold we will struggle here with sea temperatures around us at 10c. North Europe mainland looks set to start cooling this weekend, even night time teperatures are currently warmer than ours. This then gives less modification to any North Easterly flows, but also helps if we have cold air over the UK as its harder for the warm Atlantic air to shift it. The warm air then pushes over the cold air longer before pushing it back. Allowing marginal events to become more likely.

We need all the ingredience right and thats one major factor that is missing right now, so in my opinion we have so much that is going in our favour we just need to be patient. Lets get the cold into Europe.

I can see what you mean, but you don't need Continental Europe to be under a cold pool to still gain from a cold weather pattern. As in this cold spell modeled last week, we had our cold uppers coming from the NE over Scandi, which is never warm this time of the year (very often anyway), so we would in fact get the cold pool way before Continental Europe would. Continents will always cool down much faster than area over the North Atlantic for example, so can take only a matter of days for a cold pool to appear over the continent if conditions were favourable.

SM

[pyrotech]

I can see what you mean, but you don't need Continental Europe to be under a cold pool to still gain from a cold weather pattern. As in this cold spell modeled last week, we had our cold uppers coming from the NE over Scandi, which is never warm this time of the year (very often anyway), so we would in fact get the cold pool way before Continental Europe would. Continents will always cool down much faster than area over the North Atlantic for example, so can take only a matter of days for a cold pool to appear over the continent if conditions were favourable.

SM

I agree to a large extent. However firstly Euro mainland is rather mild at the moment. I am talking about a large cold air mass over Europe. Then cold air into uk . Its then much harder to breakdown. During 2010 the models tried to show a breakdown too early. And it failed partly due to this. We had an undercutting low which then brought snow in the south. Models adjusted very late. Large pools of cold air much harder to move due to density. Plus even an easterly now would need to be sustained longer than if Europe was colder. To bring snow.

[Fozfoster]

http://modeles.meteo...nh-0-162.png?18

Possible crazy pub run coming with a vertical allignment of advection signalling pressure rising.

S

Hi chap yeah, but i have just got in from the pub run .................;-)

Good night all........

Edited November 29, 2012 by Fozfoster

[Duane S.]

can someone tell me where this powerful arctic high is, because i can't see one in the reliable time frame, and even if there is one its not having a real affect on our island for next week

your right Zakos, there is no strong block, its just a ridge to the north west now, but the models were showing a stronger block some days ago, so my belief on the models overestimating heights SOMETIMES holds some validity

Here is an Arctic high at the whopping range of T+0

Correct, it is not having much "effect on our island". Direct effect that is. Just to remind some on here that an Arctic high/ Mid Atlantic high//northern blocking/-AO/-NAO/trough disruption off the eastern seaboard/wave events/SSWs/e-QBO/favourable MJO phase and so on etc etc are not, have never been, nor will ever be any sort of guarantee of cold to the UK. But anyone of the above, combined with or without other factors usually (but not always) increase our chances. That is all, that is the best it will ever be for us in the UK, sorry.

So much anger from so many just because the models aren't yet showing the right charts in the reliable. I say, save yourself the angst guys, pop back in a few days because this ridge will not hold, a drift of energy across the Atlantic is going to happen and it will spell a mild(er) blip. We were unlucky this time around, no matter how you want to see it. But with the pattern setting in, it is unlikely we will be this 'unlucky' a second / third time. Cool/cold/cool/cold December (interspursed with 2-3 day milder blips), default will not be mild zonal for once. Happy days ahead, the models just don't know it it yet.

The jet is the key. Watch for an increasingly meridional flow and what happens when (if ?) a tipping point is reached with the southern arm carrying enough of the energy, in the blink of an eye the charts could quite easily flip overnight from a cool wet zonal feel to the end of hi res and into FI to a bitter easterly. And stay there.

[Dean E]

I agree to a large extent. However firstly Euro mainland is rather mild at the moment. I am talking about a large cold air mass over Europe. Then cold air into uk . Its then much harder to breakdown. During 2010 the models tried to show a breakdown too early. And it failed partly due to this. We had an undercutting low which then brought snow in the south. Models adjusted very late. Large pools of cold air much harder to move due to density. Plus even an easterly now would need to be sustained longer than if Europe was colder. To bring snow.

Indeed, but you've got to remember the November 2010 event started with a NE/N wind direction, pulling in some very cold uppers from Scandi and Svalbard/Arctic regions. It wasn't until the first week of December when we got a renewed shot of cold air from the East. But at this time Russia and Siberia had the cold pool already in place.

This time, like you said, its very different, Central Europe is very mild thanks to a vigorous Low in the Med and to some extent, preventing a Sandi high to develop which would drive cold uppers into the mainland.

With the only cold pool available to the NE and N at the moment and a large upper low to our South East, blocking to our North, we are open to the Atlantic just enough to get these pesky Lows from Southern Greenland. These will end up in Europe and keep the mild air around for now and be more zonal for that area.

SM

[Jupiters Winter]

Nice looking GFS after T150, Decent Atlantic block with Uppers of -10 towards the northeast. Probably flattens out towards an easterly with the block sinking. Never the less seen similar pattern om ECM on previous charts and now on the GFS.......

Edit: Typed to soon as soon as it hits low resolution it just bounces towards default. Typical GFS probably better for it to stop at 192.

EDIT NO 2 - UKMO t144 Also inlines with GFS t180 to some extent but UKMO very nice for progress. All on that low towards the South West, If that runs on the jet then crashes into the UK killing the block and if it runs over the block and slides/undercuts then we could be in business, but even a slide of that low can bring in greenland lows into the atlantic. So a improvement in pattern with many risks of similar failures of this upcoming cold few days.

Edited November 29, 2012 by Jupiters Winter

[The Eagle]

UKMO a big upgrade at 144hrs. Very useful.