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

[Biggin]

A new model for people to use now is the UKMO euro 4 which is now available here http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=euro4&MODELLTYP=1&VAR=prec&HH=3&BASE=-&WMO=&ZOOM=0

Shows well the "feature" moving across the South after the front has gone through

Edited December 18, 2013 by Biggin

[nick sussex]

I think todays headline for coldies should read How Much Interest Can You Squeeze Out Of A Poor NH Pattern!

 

Because realistically this pattern isn't great for any lengthy cold spells, its a damage limitation exercise in lowering expectations so that any snow that does fall is seen as a success rather than a disappointment as it won't last long.

 

So with my optimistic goggles on rather than my grumpy tone from earlier in the week I'll try and highlight any even fleeting snow chances!

 

Starting with tomorrow, still some uncertainty here because of the marginality, a chance for higher ground towards the sw, inland along the M4 corridor into the northern Home Counties and towards the east.

 

For northern areas some squally heavy showers, some wintry snow over higher ground.

 

After this some milder mush before some cooler conditions once again, throughout the next ten days it is likely that especially the north will see some snow falling, again though generally transitory in nature away from much higher ground and because of the fast flowing changes we have to be talking about cold blips rather than even snaps.

 

In terms of Xmas Day especially towards the overnight period and into Boxing Day my eyes are drawn to both the ECM ensemble spread and operational:

 

In terms of spreads we do see a cluster of solutions bringing low pressure on a more southerly track:

 

 

Then if you look at the ECM operational run, this takes low pressure further  north, in terms of snow again we are talking marginal but the 850 spreads suggest possibly some interest on the northern flank, again though I think you'll need some help via evaporative cooling,  for newbies you'd have to be situated roughly in the red area to the north of the low centre:

 

 

Indeed with this type of set up theres  likely to be several lows running east along the base of the main trough, the models however will chop and change with track etc so its difficult to put too much detail on things.

 

In terms of who has the best chance again its all to do with track, the ECM ensemble spreads would suggest the south prone to that the operational any snow for northern areas, basically just look at the low and pick the northern flank, that will give you an idea.

 

Going forward there is no sign of any major change to the overall pattern, the PV is in angry mood and looks to stay that way, in terms of colder prospects or any further snow even transient this relies on the PV not becoming a single entity to the north, To get the jet further south and stop the  slug high from becoming a main player again its imperative that we see one of two things, either some pressure rises near Svalbard to help cut some energy se into Europe  or at least the horseshoe low heights set up to the north.

 

 

 

 

 

 

 

 

 

[Purga]

Worth noting the EURO4 model differs from the raw NAE, with snowfall forecast further SW, over the moors of Devon & Cornwall especially;

image.jpgimage.jpg

Interesting times ahead though, a respectful possibility of some white stuff for some lucky southerners!

Now if GB was about 800 miles further NW we would be in business!

[Tamara]

 

The pattern, that has been keeping the core of the polar vortex pinned towards Siberia, is now in the process of changing, with the vortex relocating to the 'wrong' side of the pole. The question is how long will this change in the vortex profile persist?

 

In this sense, it is obvious that concerns are arising, at least amongst some, that the upcoming Euro High/Canadian and Greenland vortex pattern doesn't keep overly flattening for any undue period of time during December and then let the polar vortex boss the show for too much of the duration of the winter. This is where the MAD thread nightmare posting has its origins

 

The AO has been strongly positive for November and tools such as the Snow Advance Index (SAI) and October Pattern Index (OPI) all increasingly now appear to suggest a more predominantly positive phase for the winter. This is following what appeared to be a very encouraging start to the autumn on the Snow Advance side of things over Eurasia. With this in mind, and the fact we have a very organised and quite stable vortex on the wrong side of the pole, then we know that things are not going to be great (for a while at least) on the basis that the vortex is relocating

 

We need sustained wave activity on such a concentrated vortex. The upcoming pattern is perhaps a crossroads to what lies ahead in terms of its longevity. There are signs in the upper stratosphere that increased zonal westerlies could fuel an even more organised and problematic vortex

 

We are not there yet of course, and it might not prove to be the case, but it is worth bearing in mind. We have to be aware of what could go wrong as much as what could go right

I've copy edited a few extracts from this post from 10 days or so ago because clearly we have seen just how organised, immensely strong and stable this vortex is proving to be and what could go wrong, as suggested, has indeed gone wrong.

 

The Euro High set-up, as unpopular as it was (and remains an unpopular prospect for most) was actually a damage limitation exercise (in both senses of the word!) in keeping at least some quiet inversion cold over at least a reasonable part of the UK, from what is the most unfavourably positive AO (Arctic Oscillation) profile there could be.

 

Indeed regular updates from behind the scenes at METO HQ have slowly been shifting their expectations of the zonal pattern extent over the last fortnight or so (anyone remember the Scandi High suggestions that were being posted?..it seems a long time since then) in line with the adjustments the models have been making as time has progressed in terms of just how strong, flat and fast these polar westerlies are now proving to be.

 

Clearly any such blocking suggestions was just the dream it was suspected to be. Unfortunately.

 

These adjustments, almost insidiously over this period, have moved to the point that ANY ridge at any latitude is flattened completely and a formidably powerful, and actually pretty scary, jet streak is aimed right at us and other parts of western europe courtesy of all that bottled up densely cold air pouring out of the Canadian arctic, meeting an acute temperature gradient on the south western gyre of the vortex, and igniting and exploding one furious secondary low after another.

 

The only route out of this stormy, and potentially dangerous, seasonal winter pattern is to have the Canadian cold blowing machine switched off with the Pacific ridge re-loacting back further north towards the Aleutians, re-amplifying the pattern, splitting the jet stream energy and thus reducing its energy, and re-jigging the vortex profile at the same time. The pattern might be giving snowballs that side of the atlantic, but downstream it is sending us very tightly packed furballs instead!

 

There is a suggestion in the models that the jet stream will head far enough south to send us a colder zonal pattern. We are wary of course of modelling further out and the continual conveyor of secondary lows around this vortex will keep being picked up as we get into the more reliable time period, and limiting the southern extent of colder upper temperatures. The very low geopotential heights of course make snow potential in the colder sectors of these low, a transitory possibility (as early as the next 36 hrs or so f.e). This looks set to continue to form the maximum level of expectation we should expect from a wintry precipitation perspective especially further north - but overall the main theme that dominates is the worrying aspect of storm strength from these secondary low pressure systems on the anti clockwise section of the southern orbital perimeter of the PV M25.

 

Its a pattern that is so tightly wound up, it is going to take some time to blow itself out. It could be that some will be thinking of how, f.e, winter 1994/95 evolved and the wintry potential that developed from that very vortexy winter during January. Its hard to see any cold blocking evolving for some time to come yet, that seems quite certain.

[Iceberg]

GEFS fully backs up the stormy Christmas Day/Boxing Day. The operational 06z was not extreme far from it, with Various members brings much deeper(if thats possible) and stronger winds, with the lowest member bringing 918mb on mainland UK, but a few 930mb or below.

Regardless to say this would likely be the lowest pressure ever recorded on the UK mainland. However still too far off to be anything but interesting.

 

A very stormy distruptive Christmas seems likely unfortunately.

[nodrog]

UKMO interestingly has the weakest primary low and probably lends itself to a higher chance of snow from the secondary.

 

 

I'm sure we had a similar event in the 90's then turned cooler as I'm looking for a repeat for New Years eve also, again to compare. Thank you for the links.

[shedhead]

Now if GB was about 800 miles further NW we would be in business!

Yep and if yer Auntie had balls she'd be yer Uncle....

[carinthian]

I've copy edited a few extracts from this post from 10 days or so ago because clearly we have seen just how organised, immensely strong and stable this vortex is proving to be and what could go wrong, as suggested, has indeed gone wrong.

 

The Euro High set-up, as unpopular as it was (and remains an unpopular prospect for most) was actually a damage limitation exercise (in both senses of the word!) in keeping at least some quiet inversion cold over at least a reasonable part of the UK, from what is the most unfavourably positive AO (Arctic Oscillation) profile there could be.

 

Indeed regular updates from behind the scenes at METO HQ have slowly been shifting their expectations of the zonal pattern extent over the last fortnight or so (anyone remember the Scandi High suggestions that were being posted?..it seems a long time since then) in line with the adjustments the models have been making as time has progressed in terms of just how strong, flat and fast these polar westerlies are now proving to be.

 

Clearly any such blocking suggestions was just the dream it was suspected to be. Unfortunately.

 

These adjustments, almost insidiously over this period, have moved to the point that ANY ridge at any latitude is flattened completely and a formidably powerful, and actually pretty scary, jet streak is aimed right at us and other parts of western europe courtesy of all that bottled up densely cold air pouring out of the Canadian arctic, meeting an acute temperature gradient on the south western gyre of the vortex, and igniting and exploding one furious secondary low after another.

 

The only route out of this stormy, and potentially dangerous, seasonal winter pattern is to have the Canadian cold blowing machine switched off with the Pacific ridge re-loacting back further north towards the Aleutians, re-amplifying the pattern, splitting the jet stream energy and thus reducing its energy, and re-jigging the vortex profile at the same time. The pattern might be giving snowballs that side of the atlantic, but downstream it is sending us very tightly packed furballs instead!

 

There is a suggestion in the models that the jet stream will head far enough south to send us a colder zonal pattern. We are wary of course of modelling further out and the continual conveyor of secondary lows around this vortex will keep being picked up as we get into the more reliable time period, and limiting the southern extent of colder upper temperatures. The very low geopotential heights of course make snow potential in the colder sectors of these low, a transitory possibility (as early as the next 36 hrs or so f.e). This looks set to continue to form the maximum level of expectation we should expect from a wintry precipitation perspective especially further north - but overall the main theme that dominates is the worrying aspect of storm strength from these secondary low pressure systems on the anti clockwise section of the southern orbital perimeter of the PV M25.

 

Its a pattern that is so tightly wound up, it is going to take some time to blow itself out. It could be that some will be thinking of how, f.e, winter 1994/95 evolved and the wintry potential that developed from that very vortexy winter during January. Its hard to see any cold blocking evolving for some time to come yet, that seems quite certain.

 

Thankyou Tamara for your very interesting and informative post. I have sent a copy to our expects to divulge. As part of our Portal service a winter prediction is most value. There is different thought regarding the speed of evolution to cold blocking. They have a 60 % chance for a Arctic blocking to take place in January and expect the Atlantic flow to weaken soon after the start of the New Year. The predictions so far have provided a high success rate from this source.

 C

[bluearmy]

notice the little pool of higher heights ejected into the arctic tomorrow n of scandi, meanders around and becomes a shallow upper ridge off e greenland by day 10. (ref ecm ens).this helps to send the jet on a more southerly track to our west and as heights drop a bit over europe, we end up with the jet over the southern half of the uk, if not south of us completely, there will be attempts to bring the pfj back north post boxing day and into new year. that presents an opportunity for snowfall on the northern flank as per nicks earlier post. infact, i would suggest the possibility of something notable 29/30th dec somewhere between a line mid wales - mid EA at the southern extent and the english/scots border the northern end. the ops will play with this over the next few days but we could end the year on a very wintry note across a fair sized chunk of england. thereafter, the likelihood that the jet manages to stay south is pretty uncertain. would seem to be a lack of any strong anomolys post new year.

[Summer Sun]

Looking at today's met office update the risk of very strong winds from Christmas day onwards may transfers south with colder temperatures in the northwest allowing snow to low levels here, rather than just over high ground.

 

As we move towards the new year the risk of severe gales is likely to reduce

[egret]

Carinthian,

I m trying to get my head around the current position and exactly what processes might initiate Arctic blocking. Do you know what changes your sources see as causing such blocking and the indicators that this will happen?

 

I ask this as one the one hand I feel that the current set up appears pretty 'locked in' whereas weather often starts to change early in the New Year.

 

I have always assumed that those changes stem indirectly from the effects on the atmosphere of sea temperatures and seasonal changes in solar warmth. I.e things that are difficult to pin down with scientific evidence due to the indirect way in which the effects lead to measurable change.

[R.P. McMurphy]

 

Lots of colder scatter options showing now on the Ens, nothing remotely mild appearing.

[shedhead]

 

Lots of colder scatter options showing now on the Ens, nothing remotely mild appearing.

Agree re some colder scatter options, but not sure you can say 'nothing remotely mild appearing'...some of those runs maintain temperature level close to where they are presently.

[R.P. McMurphy]

Agree re some colder scatter options, but not sure you can say 'nothing remotely mild appearing'...some of those runs maintain temperature level close to where they are presently.

 

Which going by recent temps and feel, its cold !  

[R.P. McMurphy]

 

DeBilt also firming up for much colder weather.

[shedhead]

Which going by recent temps and feel, its cold !  

There is still nothing in the current short, medium or long term modelling to suggest it will be cold Glenn. Temps look set to be near average across the northern half of the UK and still on the mild side generally for the southern half, though it will of course often feel cold in the wind and rain.

[carinthian]

Carinthian,

I m trying to get my head around the current position and exactly what processes might initiate Arctic blocking. Do you know what changes your sources see as causing such blocking and the indicators that this will happen?

 

I ask this as one the one hand I feel that the current set up appears pretty 'locked in' whereas weather often starts to change early in the New Year.

 

I have always assumed that those changes stem indirectly from the effects on the atmosphere of sea temperatures and seasonal changes in solar warmth. I.e things that are difficult to pin down with scientific evidence due to the indirect way in which the effects lead to measurable change.

 

 Hello Egret,

The thermal gradient is likely to reach its peak across the North Atlantic over the next 10 days, hence the powering up of the Atlantic storms. The current synoptics across Europe and including the UK have been spot on ( rather mild ) with the modelling showing a rise of pressure across Europe with the jet deflected poleward in its seasonal  prediction.. A change of the course of the low pressure systems southwards are projected in January with a consequence rise in pressure over the Arctic. Confidence from our expects remain high for this to happen and I cannot argue with their advice, but is always open to be questioned.

 

c

[Snowmaggedon]

 

DeBilt also firming up for much colder weather.

And the plot thickens...

[nick sussex]

 

DeBilt also firming up for much colder weather.

Have you looked at the wind direction ensembles, the control run looks a bit interesting in terms of where it tracks another of these fast running lows.

 

 

Given the precip spike in relation to the wind direction we can see the flow over there moving round to the east then north around the 29th.

 

Low pressure wise that looks like a runner through southern areas, very hard though to have too much confidence in detail as these lows are likely to be modelled differently between outputs.

 

If theres two things to keep an eye on in tonights outputs its what happens to the northern chunk of Greenland and the configuration of low heights, the horseshoe with gap over northern Greenland is okay to keep the jet further south, also an elongated area of higher pressure near Svalbard, you have to see one of those two to continue with at least some chances for snow and colder interludes in the UK.

 

If the PV becomes uniform to the north like last nights hideous T240hrs ECM output then its game over. Thankfully the ECM dropped that this morning and we certainly don't want to revisit that horror chart tonight.

Edited December 18, 2013 by nick sussex

[shedhead]

 

DeBilt also firming up for much colder weather.

Again not really the case imo Glenn - marginally colder overall post Xmas, but much colder no, with shedloads of milder members still evident right out until the end of the run.  Nothing really significant here yet that I can see.

[R.P. McMurphy]

There is still nothing in the current short, medium or long term modelling to suggest it will be cold Glenn. Temps look set to be near average across the northern half of the UK and still on the mild side generally for the southern half, though it will of course often feel cold in the wind and rain.

 

The current & medium term certainly looks to be on the Chilly side, unless you can show me otherwise? I woke up to a Frost yesterday, and it was bitter this morning, with potential snow predicted during the storm, i'd call that not average.

 

You are correct in assumption, some days will "feel" a little warmer, but I suppose that depends where you are, certainly not even close to mild weather.

 

Chilly & thats MAX.

 

 

Chilly, and thats MAX.

 

 

Chilly, and thats MAX.

 

 

Chilly, and thats MAX.

 

 

Towards the end of the run... Cold...

 

Not sure what else to show to prove the way we are heading?

 

Debilt & Ens again, just got fun.

 

 

[Mucka]

Unless we are suddenly able to predict the weather one  month in advance then I would keep an open mind as to whether any blocking will develop through January.

 

We all have are own method of weighting the various teleconnections, and deciding which is cause and which is effect, which may give us a different perspective on how things may develop but I'm sure none of us would wish to stake our lives on a predicted outcome.

Yes it is fair to say the current situation is not good and things will need to change for any developments regarding blocking but the weather not only changes it often surprises.

As far as this pattern being "locked in" goes then there is some sense to that and the second half of December can almost be written off entirely regarding chances of prolonged cold but will things still be the same come the end of December with the zonal flow in full control for as far as one can sensibly predict from that time? Personally I doubt it and hope to at least see some more favourable conditions for blocking develop even should we not ultimately benefit from it.

 

I get the doom and gloom and that there is more a degree of realism than pessimism regarding prospects in January but I really do not think things are that bad that we should be considering writing January off. Yeah it may turn out zonal but there is still a reasonable chance it may offer a decent cold shot.

 

Regarding the GFS 06z, again on face value it is poor but when we look at the ensembles (This has already been stated by someone, sorry for not trawling back and finding out who) then it does show a cooling trend after boxing day (no doubt associated with the jet pushing South) and the mean does not get above 5c even for London, colder in the North with just one or two colder options starting to sneak into the output.

Now if you are in the South that means you will need to get very lucky to see snow falling to low levels let alone have a chance of settling but in the North and on high ground especially there is the potential for some pretty decent transient snowfalls - at least it wont be mild.

 

Given that we know there is no potential for proper cold until after New Year we may as well accept that reality but stay positive about January prospects for now and let's not forget there is a potential snow event tomorrow for central/Southern areas that came unexpectedly - I may be getting old but I'm pretty sure I can remember worse output.

Edited December 18, 2013 by Mucka

[johnholmes]

notice the little pool of higher heights ejected into the arctic tomorrow n of scandi, meanders around and becomes a shallow upper ridge off e greenland by day 10. (ref ecm ens). this helps to send the jet on a more southerly track to our west and as heights drop a bit over europe, we end up with the jet over the southern half of the uk, if not south of us completely, there will be attempts to bring the pfj back north post boxing day and into new year. that presents an opportunity for snowfall on the northern flank as per nicks earlier post. infact, i would suggest the possibility of something notable 29/30th dec somewhere between a line mid wales - mid EA at the southern extent and the english/scots border the northern end. the ops will play with this over the next few days but we could end the year on a very wintry note across a fair sized chunk of england. thereafter, the likelihood that the jet manages to stay south is pretty uncertain. would seem to be a lack of any strong anomolys post new year.

 

yes the anomaly charts have 'toyed' with this possible set up, no continuity with them just yet so I am reluctant to make anything of them. But it is something I have been watching for several days, sometimes the 6-10 NOAA, more usually it seems the ECMWF-GFS. Another thing that counts against this at the moment is  the 8-14 is not yet picking this signal up, it did not last evening so watch for the 8-14 NOAA this evening?

Edited December 18, 2013 by johnholmes

[shedhead]

shedhead, on 18 Dec 2013 - 14:24, said:

There is still nothing in the current short, medium or long term modelling to suggest it will be cold Glenn. Temps look set to be near average across the northern half of the UK and still on the mild side generally for the southern half, though it will of course often feel cold in the wind and rain.

 

 

Glenn W

The current & medium term certainly looks to be on the Chilly side, unless you can show me otherwise? I woke up to a Frost yesterday, and it was bitter this morning, with potential snow predicted during the storm, i'd call that not average.

 

You are correct in assumption, some days will "feel" a little warmer, but I suppose that depends where you are, certainly not even close to mild weather.

 

 

 

Those charts are often innacurate Glenn, but I guess if you're using words like 'bitter' to describe conditions this morning you are clearly concentrating on how things feel (and are likely to feel) as oppose to how they actually are (and are likely to be).  

Edited December 18, 2013 by shedhead

[LomondSnowstorm]

Well tomorrow certainly looks to be below average temperature wise for most of the country, and for Ireland in particular I'd go as far as to say cold and even rather wintry - the Euro progs maxima at no higher than 4C for Scotland and as far south as the Midlands, with Wales also struggling (away from the coast where obviously coastal modification and increased mixing will keep temperatures a degree or two higher). An ice day for the Grampians and Northwest Highlands down to even about 400m or so and even at low levels in northern Scotland and Ireland temperatures will be no higher than about 2C:

The snow accumulation charts also paint a very interesting picture, with significant accumulations right down to low levels by 6am Friday everywhere northwest of the Highland Boundary Fault and also for a large chunk of Northern Ireland and the Republic. Accumulations also signalled (albeit maybe 2-5cm at most at this stage) for the central belt, the Eastern Borders, the Pennines, elevated parts of the Midlands and in particular the Cambrian Mountains:

 

Obviously these will probably change around a bit, and as this is the first day we've had access to the Euro4 it will be interesting to see how well it fares, but it is illustrative of the fact that we don't *necessarily* need blocking to deliver at least a modicum of wintriness to the British Isles, particularly the northern and western parts.