Model Output Discussion - The final stretch to Christmas

[Severe Siberian icy blast]

I think (and anybody can only think at the moment) that the depression dropping s at the w/end (assuming it does) mustn't be viewed in the way we would normally do. Ie. system dropping to our west will bring snow to the east of it as the less cold air is held to the west. The warm uppers that head north and engage the depression dropping se out of the arctic will bring a warm sector in ahead of the deepening system. hence, the cold will remain to the north and nw of the low. hugely complicated and not really worth analysing where the warm/cold uppers are in relation to any wraparound until we get the track agreed upon. Yes, the threat of some snowfall but perhaps not as threatening as ECM might appear. next week does look chilly though for the most part.

Btw, the latest ec32 looks cool zonal weeks 3 and 4 on the mean/anomolys with not too much sign of any blocking though there could be some clusters

Absolutely pointless in analysing where snow will fall , let's get all models agreeing on where the storm track is .

The one I prefer would be South/southeast , we have a chance of developing a Scandi high , with low pressure to its South then we stand a good change that the low pressure will prop the high up and stop it sinking over the top of us . We all no how the models are chopping and changing so nothing's off the table . But with what's going on in the strat things should continue to and get even more interesting . Let's split this vortex and watch it come to its knees . Don't be fooled by a compact vortex been shown at t200 things will look completely different in a wks time I feel .

And re the ECM monthly , like you say it's difficult to dissect without seeing the clusters . Not sure I'd buy into a zonal flow in jan much at all tbh.

[TheBigFreeze]

Hi there, 

 

Been watching the forum for a couple of years now and am only just starting to get a bit of an idea [i think / hope] with regards to some of the models, so please be kind! lol

 

Am I right in thinking that the UKMO has the low running South/South East down the North Sea at 96-120 hours with the centre staying closer to the UK, although not as deep as GFS, which has the centre track more in the direction of Holland, and as the low sinks it is replacing warmer air with the 850 uppers only just reading -4/-6 ahead of the low any snow would be more likely to the North of the system where there has been more prolonged colder air, resulting in a wet/sleety scenario for most as opposed to a white one, or would the potential Easterlies [depending on the track of the low] bring in enough cold air to make it a snow event ? 

 

Also, and for me and much more of a concern, wouldn't either of those tracks the low takes produce a storm surge down the North Sea. which is a little concerning at this would also coincide with a large tide, which could prove devastating for the East Anglian coastline which is very close to me and where I have family and friends who have not long recovered from last years surge?

 

Apologies if I am way off of the mark, but am very new to looking at weather models, and please correct me if i am wrong.

[I remember Atlantic 252]

Prefer ECM to GFS on the 00Z's, ECM potentially very cold under the high, GFS just westerly and mildish

[johnholmes]

Btw, the latest ec32 looks cool zonal weeks 3 and 4 on the mean/anomolys with not too much sign of any blocking though there could be some clusters 

I would agree with that idea

The anomaly charts, well the NOAA 8-15 day chart,suggests this. Certainly no sign of any marked northern outbreak either from the NW or NE if that is a correct portrayal of the upper pattern into the New Year?

link below

http://www.cpc.noaa.gov/products/predictions/610day/500mb.php

[Mucka]

Hi there, 

 

Been watching the forum for a couple of years now and am only just starting to get a bit of an idea [i think / hope] with regards to some of the models, so please be kind! lol

 

Am I right in thinking that the UKMO has the low running South/South East down the North Sea at 96-120 hours with the centre staying closer to the UK, although not as deep as GFS, which has the centre track more in the direction of Holland, and as the low sinks it is replacing warmer air with the 850 uppers only just reading -4/-6 ahead of the low any snow would be more likely to the North of the system where there has been more prolonged colder air, resulting in a wet/sleety scenario for most as opposed to a white one, or would the potential Easterlies [depending on the track of the low] bring in enough cold air to make it a snow event ? 

 

Also, and for me and much more of a concern, wouldn't either of those tracks the low takes produce a storm surge down the North Sea. which is a little concerning at this would also coincide with a large tide, which could prove devastating for the East Anglian coastline which is very close to me and where I have family and friends who have not long recovered from last years surge?

 

Apologies if I am way off of the mark, but am very new to looking at weather models, and please correct me if i am wrong.

 

 

Hi TBF

 

Your observations are all valid in my humble opinion.

re track of low and amount of mixing etc, well that is the million dollar question but the general idea that snow to the North and west of the low as it sinks is correct as the warm sector is pushed South ahead and colder uppers filter back in behind on an Easterly flow.

 

You are right about the track the UKMO currently shows, give or take, and yes a storm surge would definitely be a concern.

I think we can expect to hear more about that from Ian Ferguson if things continue along these lines a bit nearer the time.

 

Certainly a very interesting period of weather coming up one way or another.

[nick sussex]

Regardless of the differences in low track this morning it at least looks like turning colder.

 

Amidst the obvious attention on what happens over the UK something that's gone largely under the radar is the initial edging ne of the Azores high just after Christmas doesn't remove the cold from central and eastern Europe, the low on the ECM/UKMO is expected to bring lots of snow to that area and this will help if the flow then goes round to the east, lower dew points and that cold pool will help the UK as the low drops into France.

 

The models generally then edge high pressure in with some frosty conditions, to get the high into Scandi and staying there is dependent on the jet upstream and how much digging south we see and whether some energy can disrupt underneath the high.

 

Overall given what could have happened at least we're talking about some cold and snow possibilities so Amen to that!

[IDO]

Noticed that too BA strange.

IDO:Zonal in FI....there's a turn up for the books.

The modelling of the exit of the depression is keenly anticipated and could mean plenty of snow for the Pennines but is a way off being nailed.I will be travelling to the Dales Saturday so of particular interest.

 

Yes I know, default GFS. I can only highlight what is showing up but I did mitigate that with the D10 trend to build heights to the NE and its fail at D12 (all but 2) so maybe thats FI. However the PV looks like building over Canada in the next 10 days so the GEFS default to zonal may not just be default in this setup. Sort of ties in with Dr Cohen's reading of it.

 

Where as GFS has consistently split the low's energy before it sinks south the ECM splits into two lows as it arrives in the Midlands on Saturday. Very complex and borderline 850s for snow throughout:

 

 

ECM still flapping around on how the Low acts at the weekend. The D5 clusters show the op is in cluster one of five different outcomes: http://old.ecmwf.int/samples/d/inspect/teasers/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!120!pop!od!enfo!enplot!2014122300!!/

 

The ECM mean has switched to a sinking LP system for the weekend compared to last night:  

 

The mean clears next weeks high faster than the op and the D10 mean is closer to GFS so something in between may be the call:

 

Edited December 23, 2014 by i'm dreaming of...

[Captain Shortwave]

The ECM ens are certainly shifting towards the op

 

Northern European block the favoured outcome

So a chilly pattern with surface cold dominating rather than a true snowy easterly. But that could change if we see a more favourable split jet upstream to allow heights to edge a little further north. At this present time the strat signals are pointing to the polar vortex relocating to the Canadian side so we will see what kind of a fight that high has in it, I wouldn't be calling a zonal pattern just yet.

The start of 2015 I believe will be a cold and mainly dry one for the majority of the UK.

 

Last thing from me, if the Euros are correct then the issues of coastal flooding will be negligible as the winds will be lighter, still strong and quite gusty but nothing on some of the output a couple of days back. 

Edited December 23, 2014 by Captain shortwave

[Banbury]

ECM and UKMO both bring in a brief easterly.

 

UKMO 120 is snowy for some in S England.  

 

One to watch.

Certainly is WI, much better than last year for sure

[Man With Beard]

Hi there,

Been watching the forum for a couple of years now and am only just starting to get a bit of an idea [i think / hope] with regards to some of the models, so please be kind! lol

Am I right in thinking that the UKMO has the low running South/South East down the North Sea at 96-120 hours with the centre staying closer to the UK, although not as deep as GFS, which has the centre track more in the direction of Holland, and as the low sinks it is replacing warmer air with the 850 uppers only just reading -4/-6 ahead of the low any snow would be more likely to the North of the system where there has been more prolonged colder air, resulting in a wet/sleety scenario for most as opposed to a white one, or would the potential Easterlies [depending on the track of the low] bring in enough cold air to make it a snow event ?

Also, and for me and much more of a concern, wouldn't either of those tracks the low takes produce a storm surge down the North Sea. which is a little concerning at this would also coincide with a large tide, which could prove devastating for the East Anglian coastline which is very close to me and where I have family and friends who have not long recovered from last years surge?

Apologies if I am way off of the mark, but am very new to looking at weather models, and please correct me if i am wrong.

Hi Big Freeze. Good questions - ones that we've all been trying to work out over the last 50 pages of model output discussion, so it's not just you!

The snow question is tricky. Yes uppers look marginal for snow but they aren't the only factor (e.g. nighttime cooling, cold undercutting a front, lower pressure levels) - Ferguson from the MET has been on here confirming that charts such as the UKMO could bring widespread snow (based on last night's chart, but today's looks similar IMO). Your assessment of where the snow is likely to be seems reasonable to me.

Any possible storm surge looks a little less likely thus morning - the tightness of isobars around the north of the developing low pressure seems less on all models, particularly when the storm reaches the north sea.

[dragan]

Looking at the models, to me anyway, it seems after the low/potential storm, there is a brief high pressure then back to south westerly's.

It seems to me that a lot of people on here take the uncertainty of the models to mean that the atlantic weather probably wont happen, and use conjecture to fantasize what happens next.

Maybe im wrong, but surely considering this country gets south westerlies the vast majority of the year, this means beyond the low then high pressure this coming weekend, chances are we will back to 'zonal' given that models also show this??

[johnholmes]

Hi there, 

 

Been watching the forum for a couple of years now and am only just starting to get a bit of an idea [i think / hope] with regards to some of the models, so please be kind! lol

 

Am I right in thinking that the UKMO has the low running South/South East down the North Sea at 96-120 hours with the centre staying closer to the UK, although not as deep as GFS, which has the centre track more in the direction of Holland, and as the low sinks it is replacing warmer air with the 850 uppers only just reading -4/-6 ahead of the low any snow would be more likely to the North of the system where there has been more prolonged colder air, resulting in a wet/sleety scenario for most as opposed to a white one, or would the potential Easterlies [depending on the track of the low] bring in enough cold air to make it a snow event ? 

 

Also, and for me and much more of a concern, wouldn't either of those tracks the low takes produce a storm surge down the North Sea. which is a little concerning at this would also coincide with a large tide, which could prove devastating for the East Anglian coastline which is very close to me and where I have family and friends who have not long recovered from last years surge?

 

Apologies if I am way off of the mark, but am very new to looking at weather models, and please correct me if i am wrong.

 

First of all welcome to posting after lurking. Don't be afraid to answer questions, use your pm to the poster if you prefer. As to will it snow. No one can say where, how much or indeed if for at least another 24 maybe 48 hours. What has to be worked out first is the exact track of the low-still open to various solutions, then when that appears decided the even more difficult ideas on will there be precipitation in a specific area. have a look in the Guides section for 'will it snow' or soemthing like that. We have to get at least 7 maybe 8 variables correct for it to be snow!

good luck and enjoy.

[Betleyblizud]

Confused.com we seem to have two polar views this morning...

Good point. however whenever we have a chance of something snowy and cold getting closer bear in mind we get the IMBY process. As such Midlands north may be getting 6 cms of snow (so the charts are great)whilst south of Oxford its rain so the charts are shocking" ""poor"etc or vice versa. I think the trick is to look at the trends and the weather picture for the UK and Ireland as a whole before deciding that the models are 'good or bad'.

[marksiwnc]

*if* it does snow quite widely and *if* the high pressure comes in afterwards will this not enhance the block due to cold surface temperature. I have seen something similar before can't remember when it was last sorry no pics on my phone. But what are the odds of this block being stronger than everyone anticipates??

[karlos1983]

Good point. however whenever we have a chance of something snowy and cold getting closer bear in mind we get the IMBY process. As such Midlands north may be getting 6 cms of snow (so the charts are great)whilst south of Oxford its rain so the charts are shocking" ""poor"etc or vice versa. I think the trick is to look at the trends and the weather picture for the UK and Ireland as a whole before deciding that the models are 'good or bad'.

 

With charts like this, to say it is a North of Oxford snow event only is probably a tad premature. This I believe will very much come down to now casting. Although I'm sure the M4 will work it's magic for anyone south of it 

above image taken from www.weatheronline.co.uk 

 

After re-reading your post, I realise you weren't actually making a forecast,  , but my point still stands, that anything really could happen from this system, especially as the exact track is not even nailed yet.

Edited December 23, 2014 by karlos1983

[Dr. Astro]

ECM is showing a very settled & cold spell of weather coming up, perfect for those that like a good frosty morning and ice days.

 

Plenty of sunshine, plenty of dryness & cold to v. cold in some parts.

 

This, of course is just one outcome, it all really depends on which track this weekends LP system takes, as we could be looking at something completely different in due course.

[Nick F]

Well, still none the wiser this morning over the track of the weekend low. GFS ens members give little support for ECMWF deter and ECMWF EPS members give little support for GFS op/para but more support for UKMO track. So possibly UKMO could actually be on the ball with the inbetween track?

 

00z GEFS and EPS postage stamps for t+120

 

Like I mentioned last night, the low's track and deepening hinges on its phasing with a S/W upper trough dropping SE from Greenland as shown on the map below.

 

 

00z EC/UKMO deterministic runs seperates/ejects the S/W trough from the arctic 500mb upper vortex to our north, so we see the S/W and surface low dive into mainland Europe while pressure rises quickly to the N and NW once the low clears, with a mid-lat high taking over on the Euros.

 

00z GFS, on the other hand, keeps the S/W upper trough intact with the vortex/low height circulation to our north for longer just to our east and also has more shortwave energy upstream over the Atlantic, so we don't see the pressure build in the same way as the Euros.

 

It turns colder Sunday on all the ops, GFS has Sunday and Monday with max temps struggling to get much above freezing both Sunday and Monday. Tuesday, GFS sees it turning milder from the west, but the EUROS have high pressure building over the UK, locking in the cold surface air - so it would probably continue cold right up until New Year's Day.

 

Difficult call where we go from early next week, but my money's on the Euros for now and not because I have a cold bias. But I could be wrong!

[Duane S.]

Looking at the models, to me anyway, it seems after the low/potential storm, there is a brief high pressure then back to south westerly's.

It seems to me that a lot of people on here take the uncertainty of the models to mean that the atlantic weather probably wont happen, and use conjecture to fantasize what happens next.

Maybe im wrong, but surely considering this country gets south westerlies the vast majority of the year, this means beyond the low then high pressure this coming weekend, chances are we will back to 'zonal' given that models also show this??

Yes but on the flip side a lot of people on here take the uncertainty of the models to mean that the Atlantic weather probably WILL happen.

Assuming the chances are we will go 'back' to zonal because the models show it is also fundamentally wrong. The models will almost always show zonal outcomes, they won't always show cold ones. We can't deduce anything from that other than if a run shows cold outcomes it is because it COULD happen. Last year we didn't get a lot of eye candy chart output and there was a very good reason for that...

[Nick L]

With charts like this, to say it is a North of Oxford snow event only is probably a tad premature. This I believe will very much come down to now casting. Although I'm sure the M4 will work it's magic for anyone south of it 

 

I think the poster in question was referring to a hypothetical situation re. Oxford, rather than making an actual forecast.

Edited December 23, 2014 by Nick L

[IDO]

With respect to the ECM op HP after D6 I would expect this to be over done as usual by the ECM Op. The mean and the Control show the pattern is more mobile and not a stalling MLB. The Dutch ensembles have the control as a westerly along with the mean:

 

 

Nearly every ECM op run for the last week has been close to an extreme or an outlier so I am not expecting them to go sensible today. More likely a few days of Higher pressure as the ML high moves west to east then maybe a SW to NE split for another couple of days before the pattern flattens (IMO).

[Gibby]

HERE IS MY LATEST ANALYSIS FROM THE OUTPUTS OF THE WEATHER COMPUTER PREDICTION MODELS FOR TWO WEEKS FROM 8AM TODAY TUESDAY DECEMBER 23RD 2014.

NEXT UPDATE WEDNESDAY DECEMBER 24TH 08:00

THE CURRENT GENERAL SITUATION A cold front across Southern Scotland and Northern England will move SE tonight and tomorrow replacing the mild SW flow in the South with colder NW winds for all tomorrow.

MODELS-2 WEEK HEADLINE Continuing changeable with some dry and fine rather cold days and some rain at times in milder temperatures at other times. A brief much colder period could occur for a time post Christmas.

THE JET STREAM ENSEMBLE FORECAST The Jet Stream Forecast is for the flow long term to maintain a fairly brisk West to East flow in the vicinity of the British Isles lying between Low pressure to the NW and High over the Azores and parts of Europe.

GFS OPERATIONAL The GFS operational this morning shows the deep Low post Christmas sinking SE over Europe late this week taking it's cold Northerly flow with it and it's attendant innitial rain and strong winds then wintry showers. Thereafter the flow backs Westerly under a toppling ridge scenario with mild SW winds and rain at times through the New Year. Incursions of High pressure continue to affect principally the South at times and a build of pressure over Europe is also shown later, but too far South to bring the UK any signifiacant cold conditions as the Jet continues flowing North of the UK in balmy South or SW winds at times.

THE GFS PARALLEL RUN The Parallel run sings the same song overall with only small differences in specifics but maintaining the trend of a brief cold shot under Northerly winds and some snow showers before High pressure to the NE collapses under the weight of a powerful jet stream riding over it and returning mild SW and rain at times for all later with some powerful storm systems crossing East to the North of the UK by the end of the run.

THE GFS CONTROL The GFS control run doesn't need going into detail with today as it replicates the theme of the other partner runs in a broad sweep colder then milder theme.

THE GEFS ENSEMBLES The GFS Ensembles do show the temporary chance of cold weather from quite a few members post Christmas with the overlying trend thereafter for the cold to lift out in preference to milder Westerly winds between High to the South and Low to the North into the New Year.

UKMO UKMO shows the quiet Christmas weather giving way to Low pressure sliding SSE down across the UK and the North Sea bringing a short shot of cold North or NE winds on it's back edge with the chance of some wintriness in places before the run ends next Monday with a large and strong UK anticyclone delivering bitter cold conditions with severe frost by night and no doubt some persistent freezing fog patches for a few.

THE FAX CHARTS The Fax Charts today keep the story of the operational run with High pressure keeping Christmas dry and crisp for many before a Low moves across the North of the UK deepening rapidly with rain and strong winds likely for many next weekend.

GEM GEM today shows the post Christmas storm sinking South across the UK post Christmas with rain and strong winds followed by colder air with a few wintry showers to exposure briefly before all areas fall back into a mobile Westerly flow with rain and strong winds at times in average temperatures.

NAVGEM NAVGEM looks much like UKMO this morning with it's modelling of events which take us out of the Post Christmas storm. After a chilly but fine Christmas for many a period of very wet and windy weather will be sewpt away by a brief cold interlude with some wintry showers for almost anywhere before High pressure takes control later over the UK with widespread sharp frosts and freezing fog as we approach the New Year.

ECM ECM this morning also shows a UKMO and NAVGEM type evolution bringing a sharp rise of pressure following the storm as it slips South away from the UK. There is a period when some snow could affect any part of the UK on it''s back edge as it slips away South, this quickly quashed by High pressure developing strongly over the UK for the remainder of the run with severe frosts and freezing fog a major issue especially in the South.

ECM 10 DAY MEAN The ECM 10 Day Mean Chart is made up of a varity of options but with an increasing trend to develop higher pressure over Europe than over Greenland where pressure is likely to stay quite low. The positioning of such a European rise of pressure is instrumental in surface conditions over the UK and in that resolve the jury is still out.

NOTABLE TREND CHANGES FROM PREVIOUS RUNS The trend this morning has been to extend the length of cold across the UK somewhat as High pressure becomes established over us or close by. The path towards mild SW winds to return though towards the New Year remains a possibility.

MY THOUGHTS  While there is some unison over the path of the post Christmas depression event moving SE the exact positioning remains uncertain with the Americans wanting to push the Low SE over Europe and giving no more than a glancing blow from a cold North or NW flow before a flattening pattern behind a toppling ridge reverts the UK back to default mode of West winds, average temperatures and rain or showers at times. On our side of the pond the UKMO and ECM both drop the Low South across the UK quite quickly filling it as it does. In this period there is a strong possibility of a spell of snow on a short sharp and strong East or NE wind which could occur almost anywhere before rapidly rising pressure clears this away South to leave the UK under very cold clear air where surface temperatures under High pressure could drop very low overnight. Areas of freezing fog could also become an issue, failing to clear in places under the light anticyclonic winds. Within the ensembles the GFS group are not supportive of much in the way of persistence to this High pressure block preferring to sink everything South and set us up on what could be another prolonged Westerly phase of wind and rain and average temperatures. However, within the ECM pack are much more resilience to this theme in holding High pressure over Europe. Although this is a dangerous game for the UK as we could end up on the mild side of a Euro High it could provide dividends if it is allowed to ridge North to Scandinavia and allow at least some continental cold to seep into at least Southern areas with a more seasonal mix of frost and fog patches by night. However, for those looking for any significant amounts of the white stuff outside of a 12 hr window somewhen post christmas the charts longer term don't paint a very Christmas card type scene this morning I'm afraid. Still the interest values are high at the moment and I'm sure we'll see more twists and turns over the coming days output as the situation which involves the rapid development of the post Christmas Low comes nearer.

[Matty M]

One thing to note this morning is that the models and ensembles have tended to move away from forecasting a very deep depression on the 27th, and are showing a more moderate low pressure system.

 

This may change, but model guidance does not favour anything disruptive at this point.

[bluearmy]

Karlos - you have attached the spread on uppers rather than heights. More difficult to deduce too much on uppers spreads

The height spread on ecm shows a fair cluster going for a deepish depression headed w to e well to our North

[Mucka]

Looking at the models, to me anyway, it seems after the low/potential storm, there is a brief high pressure then back to south westerly's.

It seems to me that a lot of people on here take the uncertainty of the models to mean that the atlantic weather probably wont happen, and use conjecture to fantasize what happens next.

Maybe im wrong, but surely considering this country gets south westerlies the vast majority of the year, this means beyond the low then high pressure this coming weekend, chances are we will back to 'zonal' given that models also show this??

 

 

Funny thing, the models chop and change their predictions and are often wrong.

 

Truth is, there is plenty of room for conjecture or a more pragmatic reading of what the current output shows and so long as people make clear what is supposition and what a chart actually shows I don't see a problem.

 

On the one hand you accuse people of using uncertainty to promote a more wintry possibility (which is a fair observation but I don't see a problem) yet on the other you promote the likelihood being southwesterlies and ignoring that uncertainty? What makes that view more pragmatic or more valid?

 

And actually UKMO and ECM do not show a return to zonal conditions next week anyway so perhaps you should provide your own caveat that you are taking one GFS op run as being the  way forward and ignoring the trend within the Euros?

 

There is uncertainty and maybe we will get a drift back to a zonal set up as with GFS or maybe the pattern will be more amplified as with ECM/UKMO.

 

As far as I see it you are speculating with your mild SW zonal flow just as much as anyone who is speculating about a more blocked pattern being possible which is fine but don't pretend yours is the scientific approach while other opinions are mere speculation.

Edited December 23, 2014 by Mucka

[Summer Sun]

Saturday still looks the best chance for some snow

 

 

Snow depths are nothing to major just 2 to 4cm at best for higher ground, with rain shown to be proceeding any snow its going to struggle to lay unless its heavy and persistent

 

 

Temperatures too high for snow away from high ground initially in England and Wales

 

 

Colder later on so any rain would start and turn to snow

 

 

A cold start for the revelers out early NYD away from the south west where its milder

 

 

2015 starts chilly for all bar the SW

 

Edited December 23, 2014 by Summer Sun