Model Output Discussion - The Run In To Christmas

[fergieweather]

An awful lot of focus here on how pronounced any cold might be.... but arguably, one of the most eye-catching forecast issues amongst ensembles is one of possible explosive cyclogenesis (vast majority of EC-EPS members from 00z suite producing lows from Boxing Day onwards, some very deep indeed, and all considered likely to entrain sub-zero theta-w irrespective of track). So, for us it's a story of potentially bad weather across a fair scope of outcomes (gales/severe gales/heavy rain/snow) rather than a myopic focus solely on snow. Whilst I appreciate some people merely seek the latter to the exclusion of all else, there is a resultant risk of not seeing the woods for the trees in terms of the potential (still highly uncertain) evolutions and how these might provide a very interesting / volatile period meteorologically, irrespective of how cold it proves.

Edited December 19, 2014 by fergieweather

[Weathizard]

Still differences in the ensembles as to be expected, ECM makes more of the ridging in the Atlantic whereas the GFS looks messier, just scanning the perturbations I think we are no closer than we were 3-4 days ago.

Especially as the mouth watering stuff keeps getting pushed back, the Azores high is my number one winter hate, seems like it likes to rear it's ugly head whenever other things fall into place it thinks 'I think NOW is my time to shine', ridge north or sod off mr Azores.

[inghams85]

The thing is you state 'Another bite of the cherry should do it' before you know it another week ot two have passed'

 

There hasn't even been a bite of the cherry yet. The anticipated spell is just after christmas and has always been touted as that.

 

The cold charts showing prior to that were a surprise to those of us who could see the pattern panning out. Don't look at the christmas week projections as a failed attempt. It wasn't expected in the first place

Whilst i very much appreciate the effort who base their lrf's around factors as previously mentioned because it does statically aid and improve chances of the pattern painted becoming a reality it does not mean however it will happen as projected.

There have been past examples where we have had all the *key ingredients* however something has scuppered our chances for example being on the wrong side of favourable blocking synarios when the pv has been disjointed following a strat and continued strat warming.

As i say in my view its a aid and a big aid of that and to have such great input from those in the know is invaluable however it is not a decider and we still require a high element of luck to produce the goods. This is why i am always very sceptical of people using the phrase 'Another bite of the cherry should do it' before you know it another week ot two have passed.

Grab every opportunity what arises..

[gottolovethisweather]

An awful lot of focus here on how pronounced any cold might be.... but arguably, one of the most eye-catching forecast issues amongst ensembles is one of possible explosive cyclogenesis (vast majority of EC-EPS members from 00z suite producing lows from Boxing Day onwards, some very deep indeed, and all considered likely to entrain sub-zero theta-w irrespective of track). So, for us it's a story of potentially bad weather across a fair scope of outcomes (gales/severe gales/heavy rain/snow) rather than a myopic focus solely on snow. Whilst I appreciate some people merely seek the latter to the exclusion of all else, there is a resultant risk of not seeing the woods for the trees in terms of the potential (still highly uncertain) evolutions and how these might provide a very interesting / volatile period meteorologically, irrespective of how cold it proves.

 

In plain English (only teasing, but was kind of lost in your translation there) I believe this suggests a continuation of where we currently are with Northern parts favoured for further snowy periods on occasions, with perhaps a ramping up of the Jet and its associated deep lows. I am sensing an increasing dry but cool signal for most of the UK for Christmas Day itself and perhaps Boxing Day, do you concur with this aspect Ian and is it the wider viewpoint of the UKMO, do you know? Still D6 and D7 of course, so plenty could change.

 

Fascinating times ahead whatever and looking forward to some more widespread snow post Christmas if things fall right. I sense it will be a long road ahead for my neck of the woods in seeing any lowland snow, however. 

Edited December 19, 2014 by gottolovethisweather

[gottolovethisweather]

I would throw this out there

'Does the behaviour of the shortwave(s) prevent the onset of the broad long wave pattern for nw Europe completely or just delay it?

Sort of 'all roads lead to Rome' situation but are we going via the A roads or the motorway . (Seems the flight got cancelled !)

It's a potentially complex answer but maybe only as complicated as the higher res models want to make it ........

 

If it is the initial shortwave/depression/surface low, i.e. the one I mentioned a few days ago as being positioned South of Greenland come midnight tonight (still modelled as such), then yes it could tip the balance, one way or the other all IMHO. I can't pretend to know either way but the way in which the GFS P 12zs have modelled it in particular makes me wonder how things will develop further on.

Edited December 19, 2014 by gottolovethisweather

[nick sussex]

The best thing all round is that people don't have a lot of drama over Christmas so I think we should wish for the snow minus deep low situations suggested by Ian F.

 

I suspect what Ians talking about ( not sure Ian if you're allowed to tell us the clusters in the ECM ensembles) is several different options regarding low track, likely to form to the sw, and run in towards the UK.

 

Because of the steep thermal gradient with that cold air digging into the mid Atlantic via the western based negative NAO at that time these could deepen rapidly.

 

As cold air is very close to the north these could engage that on the northern flank of the low some heavy snow, rain and gales on southern flank.

 

The headache I expect at the UKMO is the wild variations in low track, looking at the ECM De Bilt clusters, re wind direction, dew point its evident that from around the 27th theres a huge spread in those wind directions, these are probably allied to the said low track into the UK, the wind cluster more towards east/ne would take lows across the south of the UK.

 

The same south track can be correlated with the snow spikes for De Bilt, if at the end of the day the ECM operational run moves towards the main cluster then the low track currently shown by the operational run is too far north.

[Tamara]

.....

All bets are off indeed and rapid changes in modelling in conjuction with the pattern change have kicked off in the earlier timeframes of expected developments. Look out for some lively atmospheric ying and yang commencing from the festive period and taking us right into the New Year

Whatever the outcome, some utterly compelling MOD days ahead of us that is certain

Negative AAM and GWO phases 1/2 have duly supplied the long awaited amplification signal in the Atlantic. Recent negative mountain and frictional torques as discussed in previous post(s) will reinforce sending the GWO into high amplitude phase 3/4 as now forecasted and imply a strong Mountain torque (MT) as snowking mentions this morning.

 

The implied MT strongly underpins the signposting of robust wave 2 activity as discussed on the stratosphere thread and it is on this basis that we can continue to reason that the vortex might be receiving its last rites in the early part of the New Year....

 

On this proposed basis though, the poleward westerly momentum flux associated with Phase 3 heading into 4 that might ordinarily threaten greater flow through the northern arm and break down the amplification, will instead be meeting an increasingly hostile reversing polarity zonal wind environment as the tropospheric spoke into the stratosphere stuns the already weak vorticity spinning wheel in its tracks.

So, a sharp decline in momentum is likely to ensue as these attempts at westerly additions are rapidly removed from the atmosphere. Against the background of low AAM, this supports latest GWO forecasts (as above) for a return to high amplitude phase 1-2

Fast orbit Phases 1/2 towards 3/4 before rebound into Phase 2 suggests and supports high impact weather events. With the stakes upping all the time, i.e that the nadire of the polar vortex is approaching (SSW?) the implications for the Northern Hemisphere are especially greater in terms of high impact weather

On this basis, no surprise that the METO have an eye out during the whole festive period for snow and also rapid low development along the PFJ gradient and on the left advancing axis (atlantic) gyre of the Scandinavian/UK troughing. A lot of polar air spilling south and meeting air of sub tropical nature.

Should stratospheric detonation occur in tandem with the atmosphere in this ying and yang state, then as snowking rightly hints, this will have even better omens..... with renewed and ever more vigorous blocking signals (at return to Phase 2) enhancing and further sustaining (next time around) upper Greenland heights rather than amplified Atlantic ridging.

 

A lot to happen before we get here and we should exercise large caution with such a chaotic programme unfolding.

 

We must exercise such care in expectations because the sheer complexity of upcoming events will almost certainly contain possible pitfalls - but it should not be a surprise to see such spectacular charts as we have been seeing in the GFS (P)

 

 

And so the gas is getting turned up higher....

 

As suspected from earlier analysis, quite a collision course increasingly seems to heading towards our patch of the NH between Christmas and most especially the closing days of the year.

 

Despite the (apparent) dissonant operational output from one model to another and from one suite to another, emerging signs of those potential high impact events suggested yesterday are filtering through as a powerful cocktail of densely cold arctic air spills south and meets a sub tropical west based -NAO regime air mass during the Christmas/New Year week period. There are plenty of such solutions in GEM and GEFS suites and I imagine that the METO will be looking at their extended maps, as well as ECM, they have access to as well. Along the boundary of these two air masses, we are looking at the distinct possibility of a deep low crossing the UK (track uncertain) with associated high impact weather, and cutting off into Europe.... with very cold arctic air sitting in its wake. 

 

Models are closing in gradually on the greater aspect of the amplification signal, so the boundaries are being drawn between a very mild airmass (to the south) and surprisingly cold boundary not far at all to the north... setting up in the region of the UK.

 

The question is how far in the medium term can the cold air sink? And how far east and south could the troughing get to clear the greater part of the UK?

 

With negative AAM tendency persisting and a raft of signals tensing atmospheric responses like a taut rubber band, the GWO in tandem with stratospheric trends continue to be where we should look for likely answers to these questions, and what else might happen in general.

 

Think renewed upstream amplification to kick the cold further south and east - this is what we need.

 

Portends here in terms of further amplification, still hold good.

 

Return to phase 2 (renewed atlantic amplification signal) still set to follow brief orbit to 3/4 and interestingly poised on a collision course with a New Year polar vortex blitzkrieg and resultant tearing split. Timing and placement of these developments very important for the UK - because right time and right place puts us in a position where, as Chiono and Tony have suggested, the UK freezer door is wide open for a possibly sustained January cold spell.

 

The renewed amplification signal upstream plays a very important part first of all though. If that verifies, and we can keep the very favourable stratospheric programme as suggested atm - then watch the dominoes fall... 

 

Edit: Updated very latest AAM/GWO suggests continued rebound to amplified Phase 2 and deeper still negative tendency state.

 

 

With the above in mind, everything but the kitchen sink comes into mind as we head into 2015...

Edited December 19, 2014 by Tamara תָּמָר

[Captain Shortwave]

Well at least the complete bust should be off the table. Christmas day looks fine and sunny for most. Beyond we see cold polar air clashing with mild air pushing north. Where these two meet we will likely see some lively weather develop. Going to be worth watching how this pans out. Those in the north may get a surprise.

[legritter]

An awful lot of focus here on how pronounced any cold might be.... but arguably, one of the most eye-catching forecast issues amongst ensembles is one of possible explosive cyclogenesis (vast majority of EC-EPS members from 00z suite producing lows from Boxing Day onwards, some very deep indeed, and all considered likely to entrain sub-zero theta-w irrespective of track). So, for us it's a story of potentially bad weather across a fair scope of outcomes (gales/severe gales/heavy rain/snow) rather than a myopic focus solely on snow. Whilst I appreciate some people merely seek the latter to the exclusion of all else, there is a resultant risk of not seeing the woods for the trees in terms of the potential (still highly uncertain) evolutions and how these might provide a very interesting / volatile period meteorologically, irrespective of how cold it proves.

Thanks for your time and much appreciated interesting information ,looks like the uk could be in for an interesting newsworthy time ,on as you say several interesting synoptic situations possibly panning out , looking at the charts are fine on paper but what a massive area they cover and of course on many different MB levels ,interesting days ahead ,thanks again . :smiliz39:

[Man With Beard]

An awful lot of focus here on how pronounced any cold might be.... but arguably, one of the most eye-catching forecast issues amongst ensembles is one of possible explosive cyclogenesis (vast majority of EC-EPS members from 00z suite producing lows from Boxing Day onwards, some very deep indeed, and all considered likely to entrain sub-zero theta-w irrespective of track). So, for us it's a story of potentially bad weather across a fair scope of outcomes (gales/severe gales/heavy rain/snow) rather than a myopic focus solely on snow. Whilst I appreciate some people merely seek the latter to the exclusion of all else, there is a resultant risk of not seeing the woods for the trees in terms of the potential (still highly uncertain) evolutions and how these might provide a very interesting / volatile period meteorologically, irrespective of how cold it proves.

Thank you as ever Ian, yes easy to forget, looks stormy too, and if the North Sea lows verify, east coast flooding could be another concern I imagine

[Weathizard]

Ensembles look massively scattered & fairly poor for London to me, compared to yesterday morning. (I use London as it's the capital, saves IMBY arguments haha)

Edited December 19, 2014 by Weathizard

[london-snow]

The thing is you state 'Another bite of the cherry should do it' before you know it another week ot two have passed'

 

There hasn't even been a bite of the cherry yet. The anticipated spell is just after christmas and has always been touted as that.

 

The cold charts showing prior to that were a surprise to those of us who could see the pattern panning out. Don't look at the christmas week projections as a failed attempt. It wasn't expected in the first place

Yes and i am by no means stating that there has been winter offerings for us thus far except for those in the n/nw. I am just stating that to the original poster key and favorable ingredients doesn't mean or lead us coldies into glory we still require that luck..

Things seem to be coming together in relation to the strat thread and all the wonderful work and effort they put in. Let's hope it pays out in billions of white 50p pieces

[West is Best]

Ensembles look massively scattered & fairly poor for London to me, compared to yesterday morning. (I use London as it's the capital, saves IMBY arguments haha)

 

Phenomenal 06z operational, and excellent Parallel, but this does not alter the point from this morning, and as you rightly highlight Weathizard: the models are as scattered as Kevin Pietersen's boundaries.

 

Nothing is remotely clear beyond 3 days and I'd politely urge people to avoid soothsayers who say otherwise until we start to see a tighter ensemble grouping in the model runs. I'm not convinced that will occur before Monday. This output variation does happen when there are significant pattern changes, particularly the jet buckling upstream. So, as they say, we shall see.

Edited December 19, 2014 by West is Best

[weather_it_will]

Ensembles look massively scattered & fairly poor for London to me, compared to yesterday morning. (I use London as it's the capital, saves IMBY arguments haha)

That's the 00z.

[ukpaul]

Still no sign of the latest ensemble run, whatever data issues they are having, they seem to have knocked it out longer than they suggested. I've not seen them forego a run completely, maybe they'll have to run it alongside the 12z (or retrospectively).

[bluearmy]

Dribbling out now - up to day 5 so far

[Harsh Climate]

My view on the recent output is there will be some cold of cold spell/snap 26DEC - 31DEC then a return to zonality for who knows how long ?? 

 

From looking at the model runs again, there is certainly the potential for a cold/snowy few days at the end of the year. But on the side of realism there just isn't a big enough signal for things to quiten down upstream for a lengthy block/cold spell into january. Even in deep FI we aren't seeing stella blocking/cold. Yes it's deep FI but I think we could do with seeing this change soon if january is going to deliver  .

 

I think those calling for a cold/blocked January are just guessing or been hopefull, as there just isn';t enough evidence to suggest so. Even the met office think along these lines in there extended outlook (with there multi-million pound number crunching computers.)

 

''

UK Outlook for Friday 2 Jan 2015 to Friday 16 Jan 2015:

The most likely scenario for the coming New Year is for a continuation of changeable, and at times windy weather coming from the Atlantic with the wettest weather probably across western parts of the UK, and eastern parts most likely to see the best of any dry weather. In between the wetter periods there should be drier, brighter, and colder spells. Temperatures are most likely to be around or slightly below average for the time of year with overnight frosts and some snow over the high ground expected. There is a chance of some overnight and morning fog in places too. However, there is a low likelihood that the drier spells will become more prolonged between weather systems. ''

 

Not trying to put a dampner on things are this is still very much wide open, but caution and realism must be kept in mind regarding the evolution of our weather over the next month or so.

[ukpaul]

Dribbling out now - up to day 5 so far

 

Dribbling? The run, some 20 minutes later is finished, now that's speedy!

 

Control is a doozy by the way, moves swiftly from a west based NAO to a northerly.

 

[Lincstim]

I'm taking that the lack of charts for the 25th -28th is basically saying that all has changed and we are now in search for the next potential cold blast?

[johnholmes]

It's a stunner at day 9. Big Greenland ridge and bitter arctic air sweeping down. What a turn around. Surreal situation this is turning out to be.

day 9-my and how likely is it to verify do you think?

[ukpaul]

I'm taking that the lack of charts for the 25th -28th is basically saying that all has changed and we are now in search for the next potential cold blast?

 

No, and it depends where you live, this is North Lincs for example.

 

Edited December 19, 2014 by ukpaul

[IDO]

The GEFS as expected are a mixed bag. The hi-res have flipped back to a Northerly by D11-12 but there is only limited support from the ensembles. Expected as we are now back out in FI looking for cold and its now a case of monitoring for the pattern to establish in the next 3-5 day. Deja Vu again. 

 

No need to argue over where the spread is: 

 

Great uncertainty and wouldn't take a lot to flip back to a flatter pattern.

 

 

[johnholmes]

 

 

IF these charts verify, itll give very strong backing to johns findings that when in agreement and are consistent, the noaa anomaly charts DO pick up long term upper trends better then the ops and are therefore more reliable.

 

will be posting shortly after reading through x pages since I did a breif post this morning!

[Backtrack]

Really can't understand who is feeding the fire, but telling people to discount a run just because it's an 06Z or an 18Z because it doesn't have balloon data is just plain wrong, and this is coming from a non-bias point of view, whether the models are showing the deepest cold or the mildest December synoptics ever seen. A run cannot simply be overlooked, the GFS is ran four times a day for a reason. Instead of discounting a run, compare the four which run each day and take the average, and that's more than likely the closest to accurate one can get.

 

Sorry for the rant but it's annoying, especially when I see EXPERIENCED members who have been here for years asserting people to 'BIN' a run for whatever stupid reason that may be.

[Lincstim]

No, and it depends where you live, this is the North East of England for example.

I love all things weather but I'm not massively clued up like everyone in here. Love reading and waiting with anticipation (just hoping we get something that resembles winter)

I've said before that me been on here and reading all these posts is like watching a foreign movie but without the subtitles.

I love it even though most of IT goes way over my head lol

Anyhow less interruptions from me and back to the weather ....