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Model Output Discussion - The Run In To Christmas


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I think topple is the buzz word of the Gfs this morning, looked through every 00z perturbation and the ones which didn't show high pressure building from the south showed a vigorous depression on the 27th tracking east with a brief backwash of Northerly winds before an atlantic ridge topples in and we start all over again. Perhaps it's true that the computer models have now backed away from any deep sustained cold to something more transient which is the usual uk default pattern but dec 27th, highlight that date in your diary because it could be stormy but then again, it could be a storm in a tea cup.

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So to sum up the likely conditions for the 28th December from the overnight runs......

 

Temperatures will range from 2 to 14c in a slack southwesterly flow or a storm force northerly. It could be dry and sunny or very wet with blizzards in the north!

 

That clears things up!

 

:w00t: That's about the sum of this morning's runs. A complete dog's breakfast. Having said that, on balance the models are tending to show no more than a fleeting cold snap northerly just after the big day. A couple of the models look odd: the GFS transition from super-storm northerly to mild south-westerlies looks too fast between T192 and T220 and the ECM is still quite odd with its Caribbean conveyor belt (it actually has a feed from the equator).
 
The contrast between GFS and ECM at T192 is worth displaying again because it is pretty damned remarkable!!
 
Evil ECM:
 
Glorious GFS:

 

Edited by West is Best
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Still think my post from yesterday morning is the most likely outlook and pretty much reflects this mornings ECM. However a couple of things I am unsure of is how long will the spell of SW,lys last and will a severe storm develop i.e GFS 0Z. At the moment I would say the mild SW,lys will last for around 2-3 days and then the cold returns around the 29th. I am more concerned with the storm that will blow E Anglia away because the GEFS control also develops this.

 

http://modeles.meteociel.fr/modeles/gens/run/gens-0-1-180.png?0

 

So I continue with the same outlook but im not totally dismissing the storm that the GFS predicts!

 

Yes you said Dave that 27th/28th/29th December would see 'a return of mild westerlies', so you're sticking to the ECM route rather than GFS by the looks of it? Fair enough but the T192 range is incredibly split with the models at the moment. GFS is the opposite of your ECM solution.

 

I'd encourage those who love cold not to lose heart: the variation I posted earlier shows how volatile is the situation. I don't think anything will be 'fixed' for the relevant period until the overnight runs for Monday morning.

 

(p.s. good to be debating these things with you again: just like the old days!)

Edited by West is Best
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ECM ens now starting to smell a brief warm up on the 27th/28th before turning cooler again from the north west, but again this looks transient.

EDM1-168.GIF?20-12

EDM1-216.GIF?20-12

 

So the 28th/29th looks earmarked for the potential for severe weather as this low could deepen to produce some strong winds and also potentially some snow following on the western flank as it clears.

 

Yes BA, there is a shallow secondary low which moves south-east on Christmas night which could if cold enough deliver snow to low levels in the north if it verifies. I also mentioned in my regional of maybe a few wintry showers in coastal areas on the big day (SE thread)

Edited by Captain shortwave
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HERE IS MY LATEST ANALYSIS FROM THE OUTPUTS OF THE WEATHER COMPUTER PREDICTION MODELS FOR TWO WEEKS FROM 8AM TODAY SATURDAY DECEMBER 20TH 2014.

NEXT UPDATE SUNDAY DECEMBER 21ST 08:00

THE CURRENT GENERAL SITUATION
A cool NW flow will back SW and strengthen further as a warm front sweeps East over the UK tomorrow, active in the North but very weak in the South.

MODELS-2 WEEK HEADLINE Remaining changeable with rain at times especially across the North and West. Possibly becoming more generally colder and unsettled post Christmas with some snow and ice in places, at least for a time and chiefly over the North.

THE JET STREAM ENSEMBLE FORECAST The Jet Stream Foreecast is for the flow to gradually be squeezed further South than currently lying near or to the South of the UK before a trend to shift it back towards the North somewhat later maintaining a pattern of Low pressure to the North of the UK and High to the South after a brief hiatus..

GFS OPERATIONAL The GFS operational this morning shows a mild SW flow in the run up to Christmas before Christmas itself turns rather chillier with overnight frost but bright crisp days as High pressure moves over the UK from the West. This then steadily collapses away SE in the post Christmas and New Year period with rain at times in the North and West spreading to all areas with a cold plunge of air from the North post Christmas with snow showers in places. This pattern then collapses South to reinstate mild and windy weather under a Westerly flow to end the run with rain at times.

THE GFS PARALLEL RUN The Parallel run also shows a shot of cold Northerly winds under a powerful Low pressure just to the East of the UK post Christmas with snow in places, considerable for a few. Later in the period the pattern resets and flattens as the Low to the East moves away with a cpollapsing ridge over the UK and a mild SW flow with rain at times returning as we move into 2015.

THE GFS CONTROL The GFS control run too shows a brief colder period when strong winds and some snow are possible across the North and East after Christmas but High pressure and frost quickly takes over from the West which in turn becomes followed by milder weather with rain at times under an Atlantic flow later.

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 today shows the weather turning colder as we move towards Christmas as High pressure lies close to SW England by Boxing Day with frosty nights but with any wintry showers for the North in the NW flow on Christmas Day dissolving away later as cloud reaches the NW at the end of Boxing Day with milder SW winds developing here.

THE FAX CHARTS The Fax Charts today show a sustained warm sector period of weather across Southern Britain between tomorrow and Christmas Eve as moist SW winds blow strongly with rain and drizzle over the hills. The fronts straddling the North will give heavier rain before they all clear SE over Christmas Eve to leave Christmas itself in rising pressure and a chilly NW wind with wintry showers for a time over the North likely on Christmas Day

GEM GEM today shows a much more classic Wintry evolution over the UK post Christmas as the chilly anticyclonic Christmas period gives way to a brief milder day or so with rain before cold Northerly winds with widespread strong and cold winds delivering plenty of snow showers to all areas especially heavy and substantial across the North and East with sharp overnight frosts for all. The end of the run shows High pressure strong and locked in across Greenland.

NAVGEM NAVGEM's run today shows a very similar Christmas to the rest before a deep Low over the North Sea brings rain and cold NW winds down across the UK post Christmas with wintry showers in the North and West but not as pronounced or severe as GEM.

ECM ECM this morning shows that the mild SW winds after Christmas quickly become replaced by a chilly North flow with snow showers in places with a deeper dig of cold over Europe. The UK lies on the Western periphery of this with snow showers restricted to Northern and Eastern parts and frost at night more widespread rather than snow.

ECM 10 DAY MEAN The ECM 10 Day Mean Chart is not as good for coldies today as the pattern is flatter with a NW flow across the UK rather than a direct Northerly. High pressure is stubbornly High down to the SW and pressure is becoming lower to the NW all spelling less cold conditions following any colder period post Christmas.

NOTABLE TREND CHANGES FROM PREVIOUS RUNS Trends this morning show strong support for a cold post Christmas period with much disagreeance on how much, little and how long this influences the cold conditions across the UK post Christmas.

MY THOUGHTS The Jury is still out on the details surrounding the period Post Christmas with all models indicating cold weather coming to the UK over Christmas itself although this will be the largely dry and frosty kind of cold. Then as a milder blip crosses with some rain a more serious plunge of cold North winds is possible with gales, heavy rain and snow all possible for a time. It's at this point that all models show difficulty in finding an agreed solution to this phase of the weather with some hanging on to the cold and potentially snowy theme, notably GEM while GFS quickly changes to pattern back to a mild Westerly type as we move into the New Year, a theme supported by it's ensemble data too by quite a few members. ECM doen't look that alarming to me today and it, although being a bit divergent run to run like the rest lately is I believe one of the best model to use for guidance in these conditions.   So taking all this morning's data in a nutshell it looks like changeable weather with marked temperature variations will be maintained over the run up to Christmas and the period thereafter too with the chance of a strong surge of cold and potential snowy weather especially in the North for a time at least later. More runs are needed to pin down the detail of the events after Christmas and the New Year though if I was to put my spin on things today I feel that while a period of cold weather for all is coming post Christmas when we all see a little snow falling I don't somehow feel comfortable in saying anything other than it will be a more pronounced but short interlude of Winter than of late before the milder Westerlies return but I hope I'm wrong.

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I think it might be time to wave the white flag on a northerly shown by the GFS. Any northerly will IMO be delayed as its really just the GFS that develops this in that timeframe and its NH profile goes down hill quickly after this so to be honest I'm not sure I'd want it to verify anyway!

 

The ECM has refused to back its ensembles for several days and this is always a bad sign, ironically part of the many problems is that upstream it has a sharper more amplified USA troughing at T120hrs which then takes the shortwave to the nw south rather than se and the Atlantic low sends another shortwave more ne in a response to that more amplified upstream pattern.

 

As for the UKMO I think that's completely lost it over the USA, NCEP prefer the more amplified solutions and that really goes AWOL.

 

In terms of Christmas and Boxing Day the ECM actually looks the coldest and at this point it may have been better if there wasn't this middle ground solution, if we're not to see a northerly it would have been better if the high at T120hrs was further north and west to increase the cold around that time.

 

After the will it won't it northerly the ECM is an improvement on last nights run especially to the north, the GEM I suppose is a sort of ECM beginning with that train of shortwave energy which splits, with strong block over Greenland.

 

Overall the outputs still a mess but I think it would need a miracle for the GFS to be right here and perhaps we might have to look at it another way, part of the reason its right is because its flatter over the USA and any northerly is shortlived and its profile over the pole is underwhelming after that.

 

I'm not sure now I'd even want it to verify as shown!

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Miserable charts this morning after the snow fest ones a few days ago. When will we ever learn, the good charts were always in FI and really we should ignore anything beyond 168 hrs. Sometimes I wish the models never went beyond that time it would certainly help my nerves!

I am hoping that this winter will follow the path of 1977/78 which was mild and benign until the 10th January when all he'll broke lose and snowfalls came thick and fast after that.

Andy

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Whilst the ECM ens continue to point to a scandi trough/Atlantic ridge and cold few days 7/10 for the uk, the way we now get to this position means the colder air is held up further north and gets into the mix later than originally modelled a few days ago. The nett result of this means we are less likely to see cold enough temps to guarantee snowfall, even though the Synoptics may look good. There remains a cluster of runs, vsisble on the spreads, that takes the trigger depression on a se track across the uk, ending up in the Low Countries by day 8. That would be of higher wintry potential for more of the uk.

The ECM ens spreads remain large and whilst the mean is no doubt wintry looking later on, many will have lost confidence in its ability to deliver after the past few days.

Still much to resolve and despite the trend of the past couple days, the mean isn't so bad and, in tandem with the anomolys, is something that most would have taken a couple of weeks ago.

Incidentally, amidst all the concerns about a west based -NAO, the reality looks like ending up the usual 'action to our east ' whilst we look at the pictures from eastern and potentially central Europe.

The extended ECM ens slowly drift the Atlantic anomoly towards us (sinking at the same time) whilst intensifying the sceuro trough to our east. We end up too far west (for the time being)

Edited by bluearmy
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Far too early to bring out the razor blades, I am a weather enthusiast as opposed to an expert but that ECM just doesn't feel right, the system from the Caribbean to Russia, yeah right as if. Plus the ECM is notoriously bad post 144 so anything it is showing then should be treated with scepticism

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You can see by looking at the ECM postage stamps still quite a split in terms of solutions at T120hrs, some of those could deliver a White Christmas for favoured areas if projected forward to T132hrs.

 

post-1206-0-10059000-1419066024_thumb.gi

 

It's a difficult halfway house situation because the colder Christmas/Boxing Day scenarios come with the more amplified high to the west which means less chance of the GFS northerly.

 

So you either want the ECM to flatten the pattern out somewhat or just increase the amplitude even more of the high to the west, it depends really on what you'd prefer to see.

 

 

 

 

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So the ECM looks like been right again. It is the top performing model so we shouldn't be surprised. All the talk last night of blizzards snowdrifts cold here to stay now seem a million miles away. Stick to t96 and don't get sucked in by the gfs fantasy island charts because otherwise you will drive yourself mad.

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Does anybody know where the GEM stand in the verification stats?

The GEM has an annoying habit of predicting warmer 850mb temperatures than what actually verify,even at short timescales,so as a result is not on my christmas card list. :laugh:

 

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Quite a few have mentioned it will be cold on Christmas Day but GFS has been showing these sort of maxima:

post-2595-0-80775200-1419067655_thumb.pn

Only cold over Scottish Highlands. The 'cold' we are in today as modelled a week ago has turned out rather mild (8 to 10c max today in reality), so the Big Day may end up no 'colder' than average.

Edited by TonyH
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I don't know why so many are despondent as this never looked like anything other than a cold snap, the eye candy charts were always in FI as they usually are. I sense a return to the mobile westerly regime we've been accustomed to throughout this month, and IMO it looks like a pattern that could be with us for some considerable time until events in the Stratosphere play ball with us and at least give us a possible bite of the cherry.

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HERE IS MY LATEST ANALYSIS FROM THE OUTPUTS OF THE WEATHER COMPUTER PREDICTION MODELS FOR TWO WEEKS FROM 8AM TODAY SATURDAY DECEMBER 20TH 2014.

NEXT UPDATE SUNDAY DECEMBER 21ST 08:00

THE GFS PARALLEL RUN The Parallel run also shows a shot of cold Northerly winds under a powerful Low pressure just to the East of the UK post Christmas with snow in places, considerable for a few. Later in the period the pattern resets and flattens as the Low to the East moves away with a cpollapsing ridge over the UK and a mild SW flow with rain at times returning as we move into 2015

Thanks for the summary Gibby, but just to point out that the GFS Parallel is not running this weekend due to technical issues so the run you reference in your post is actually Friday's 12z.
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The GEM has an annoying habit of predicting warmer 850mb temperatures than what actually verify,even at short timescales,so as a result is not on my christmas card list. :laugh:

 

attachicon.gifcor_day6_T_P850_G2NHX.png

 

What is that blue one?.. FNO or FNG, it seems to be doing well of late.

 

Edit- After looking again, its FNO :doh:

Edited by Vivian
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Looking through the output again this morning the longer term outlook is a complete mess. I've never really been that enthused by this northerly as tbh it's never really looked anything other than pretty standard winter fare in my mind (from a temperature perspective). Obvoiusly a deep low off the coast of East anglia is somewhat unusual but I can't see it bringing blizzards to most, rather just a wintry mix with meaningful snow to high ground. Oh, and damaging winds! -4 to -6 850s on a maritime influenced flow simply won't cut it for widespread lowland deep snow in most places. Some snow would fall but how much would settle? Some crazy ramping over the last few days!

What occurs after the northerly is of more interest to be honest and I still think we will end up with an easterly. The Gem ensembles have some support for HLB and I suspect the destination will look more like the chart I've linked below.

http://www.meteociel.fr/modeles/cmc_cartes.php?code=16&ech=384&mode=0&carte=

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One good thing, the track of the potential vigorous low at the end of next week isn't nailed yet so we could still be looking at a significant winter storm event with heavy snow in the mix too.

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