Model Output Discussion - The Run In To Christmas

[nick sussex]

So another day of model watching to come and we're no nearer to the outcome post Xmas than we were  a couple of days ago. I've always favoured a cold snap quickly followed by the familiar mobile Westerly regime but this still could go either way at this stage and won't be resolved until early next week IMO. I must say I've never seen such a huge difference between the ECM and GFS in a log while, talk about polar opposites.

It really depends on whether the GEFS is too flat. Judging by comments from NCEP they think that might be the case and also the GEM ensembles because they have factored in more of the ECM ensembles than the GEFS/NAEFS to their outlook.

 

The ECM operational run days 9 and 10 is a mild outlier:

 

http://www.weerplaza.nl/15daagseverwachting/?r=midden&type=eps_pluim

 

Something has to give here, and we need it to be the operational run climbing down and edging the pattern further south and east.

[knocker]

Last four days ECM anomaly starting at T216. Spot the subtle differences.

Courtesy weatherbell

 

 

[bluearmy]

Yes knocker, as the time ticks by, the euro heights hang in longer. Hoping that the Atlantic ridge will retrogress the western chunk whikst the Eastern drifts se.

I get your point though.

[Snowman.]

Which of this mornings run would support those remarks I wonder? Nothing we have seen would support..

 

That's because it's 16 days out and the GFS is likely barking up the wrong tree.

 

I'm not talking about the cold spell for Christmas period I'm talking about after that.

[Frank Trough]

I've probably got completely the wrong end of the stick but i'm not really seeing all that much uncertainty in the overall pattern up to Christmas and the period immediately beyond? what happens then may be more interesting (I hope). Uncertainty in the day to day details of course, but to be honest the last couple of days the direction of travel for the period up to t+240 has been away from any significant cold (especially for the south - might be different for Scotland), whatever the details.

 

Up until a couple of days ago there were some really cold charts on offer for the immediate post xmas period - this one just plucked at random because I remember viewing the run and being excited:

http://modeles.meteociel.fr/modeles/gfs/archives/gfs-2014121700-0-252.png?0

 

But we're not really seeing those now. So, unless we see a flip back then the direction has been pretty clear.

[phil nw.]

Looking at the next 10 days the trend to mute any real Atlantic blocking has continued this morning Still some idea of ridging but nothing like the upstream buckling of the jet that was evident in all the models 48hrs ago.

It looks very much like we are heading towards a dry and frosty type of Christmas before we revert to the fairly average westerly  type of pattern we have seen so much of this month.

[BLAST FROM THE PAST]

I've probably got completely the wrong end of the stick but i'm not really seeing all that much uncertainty in the overall pattern up to Christmas and the period immediately beyond? what happens then may be more interesting (I hope). Uncertainty in the day to day details of course, but to be honest the last couple of days the direction of travel for the period up to t+240 has been away from any significant cold (especially for the south - might be different for Scotland), whatever the details.

 

Up until a couple of days ago there were some really cold charts on offer for the immediate post xmas period - this one just plucked at random because I remember viewing the run and being excited:

http://modeles.meteociel.fr/modeles/gfs/archives/gfs-2014121700-0-252.png?0

 

But we're not really seeing those now. So, unless we see a flip back then the direction has been pretty clear.

Generally I think you are reading it reasonably well

 

BFTP

[Mair Snaw]

I seem to remember well the cold periods of 2013 being much like this ECM picking up a pattern then the GFS would join in then UKMO would join the party and the GFS would go off on one for maybe 6-8 runs then it would slowly start to come back towards the others....I think it happened every single time...now im not saying that this is the case for the up coming period but I think it is certainly something to bare in mind....

[Gibby]

HERE IS MY LATEST ANALYSIS FROM THE OUTPUTS OF THE WEATHER COMPUTER PREDICTION MODELS FOR TWO WEEKS FROM 8AM TODAY FRIDAY DECEMBER 19TH 2014.

NEXT UPDATE SATURDAY DECEMBER 20TH 08:00

THE CURRENT GENERAL SITUATION A cooler NW flow will weaken tomorrow as a ridge of High pressure crosses East over the UK.

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 between High pressure over Europe and  near Greenland and Low pressure to the North of the UK.

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 and temperatures recovering to the mild side of average for many.

THE GFS PARALLEL RUN The Parallel run is less bullish on holding mild weather exclusively across the UK after Christmas alternating spells of it with brighter and colder conditions with night frost but very limited precipitation of a wintry note, even over the North. The run ends on a mild and breezy note with a long fetch SW flow between High pressure to the South and Low to the North.

THE GFS CONTROL The GFS control run too shows a lot of mild SW or West winds across the UK through the two weeks with some rain at times more especially across the North and West. A few brighter and chillier spells are shown too especially early in the period coinciding with the Christmas break.

THE GEFS ENSEMBLES The GFS Ensembles do show the temporary chance of cold weatehr 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 a mild SW flow early in the week is replaced by a drift into colder conditions with frosts at night and wintry showers over the North and East on Christmas Day.

THE FAX CHARTS The Fax Charts today show a cold front clearing the SE today with a brief chillier NW flow ahead of another broad warm sector especially across the South before finally colder air from the NW drifts down behind a series of cold fronts from the NW towards Christmas..

GEM GEM today shows a colder interlude at Christmas with overnight frosts gradually giving way to milder SW as pressure falls ro the NW gradually developing into a deep centre and delivering spells of gales and heavy rain to the UK on a SW flow late in the year..

NAVGEM NAVGEM's run today shows a chilly Christmas and a weak trough crossing the South could give a spell of rain for a time on Christmas Day before a frosty period develops by Boxing Day under a chilly NW flow..

ECM ECM this morning shows that after a quiet and anticyclonic Christmas with frost by night and cold bright days the weather turns potentially quite wet and stormy from the NW between Christmas and the New Year.

ECM 10 DAY MEAN The ECM 10 Day Mean Chart supports the highest chance being that High pressure will lie to the West of the UK with a trough to the East of the UK supporting a Northerly component most likely over the UK. This supports a mix of cold and bright weather with some wintry showers with the Jet Stream at Southerly latitudes to the East of the UK and higher over the North Atlantic with the UK lying on the cold side of the flow.

NOTABLE TREND CHANGES FROM PREVIOUS RUNS Trends this morning have been watered down considerably in the incidence of cold weather post Christmas and while some cold options are still shown from reliable Ensemble data there is an equal amount of milder weather shown too from our American partners.

MY THOUGHTS I was very careful with my wording yesterday and chose to use the word potential wisely because that is what was shown. Much of the output today has either watered down or indeed removed the risk of marked cold weather over the UK that was shown yesterday and preferred instead to maintain High pressure to the South and SE of Britain. Pressure does rise over the North Atlantic sufficient from some output to at least give a window of opportunity for something to at least try to come down from the North and the ECM Ensembles support at least a period of chilly Northerlies post Christmas though in the transitory period a spell of high winds and rain is probable. GFS today has gone totally Atlantic biased bathing the UK in mild SW winds for much of the time and this is supported from it's ensemble group too on the whole. I'm afraid the problem as I have indicated all the time of late is the Jet profile across the Atlantic post Christmas is not conducive to give us a lengthy cold spell while the flow stays North of an Atlantic High pressure. While the flow does move South over Europe towards the Meditteranean it seems unable to ridge North far enough North over the Atlantic long enough to stop the inevitable collapsing ridge pattern that we have seen all too often. The net result is from GFS that the pattern flattens out entirely with the polar vortex returned to the North and High pressure to the South bringing balmy SW winds and rain at times to the UK. The one thing that has been removed though is the Azores High for now and it seems very unfortunate for the UK to have it replaced by a European version to hinder an otherwise good chance of cold given that the tendency is to want to bring pressure higher to the NW which would otherwise have opened the door fully from the North. However, we have to sit and watch as things unfld over the coming days as things remain far from certain post Christmas. I would strongly urge folks to not take each run literally as there are a lot of wild swings from run to run and model to model currently and while the good charts of yesterday have been suspended for now I wouldn't be surprised if they don't return again over the next few days but I will withold my input until tomorrow morning before giving a more definitive report on proceedings likely up to the New Year over the UK.

[MR EXTREMES]

Last four days ECM anomaly starting at T216. Spot the subtle differences.

Courtesy weatherbell

in the broad sense the last chart looks the best with weaker heights to our south and stronger heights to our nw but atleast its not a west based nao but everything has swiftly dropped the idea of sustained decent hlb.

 

be interesting to know why the sudden drop in the charts we see 48 hrs ago.

although you cant say the rage of the polar vortex is really the biggest thorn in the coldies side so rather dissapointing but hey thats the uk weather,

i would certainly like to see the guys who have worked hard with there LRF,s get some joy.

 

i think i need to go read the strat thread see if theres any light at the end of the tunnel

 

also worth noting that the azores and heights into europe se europe do seem to be coinciding with higher sunspot and solar activity as in cycle 23 the azores was very much a pattern driver in both winter and summer and it seems to be a factor again.

 

but of coarse this is not the only reason but we would not have a climate if we didnt have a sun.  

Edited December 19, 2014 by emotional rollercoaster

[picog]

Ensembles are divided between milder and colder after Dec 24th-ish, so looks like it could go either way.

Edited December 19, 2014 by Paul

[TonyH]

Next week could be another mild one overall in spite of all the expectations to the contrary over the past week:

Sunday through to Tuesday night mild to very mild over Wales and England with some more really mild nights:

Then a cool down luckily for the festive period but not especially cold:

Hopefully a fine bright Big Day for many, but this may be scuppered by a waving front over the south which could give some parts a chilly wet day:

What could turn out to be the only decent frost of the week for southern and central parts overnight Thursday:

Boxing Day looks the coldest day of next week and hopefully quite sunny where fog clears:

More speculative by this stage but a deep mild SW flow could well be on the cards for the weekend prior to New Year:

Double digit maxima once more which would tip the balance for the week into the mild category:

However the split in the ENS does suggest a colder unsettled evolution is possible post Boxing Day:

Edited December 19, 2014 by TonyH

[Paul]

Can we keep this vaguely about the models please - picking out a 140 word un-model related tweet from someone and trying to analyse the ins and outs of it to the extent you're trying to read wasn't isn't actually there and in some cases trying to put your own words in someone elses mouth, is never going to work.

[Banbury]

Looking beyond 5 days is a gamblers game, the ENS suggest such a split at 120 hours.

[offerman]

Certainly looks milder than the charts suggested two days ago.

[snowking]

It really depends on whether the GEFS is too flat. Judging by comments from NCEP they think that might be the case and also the GEM ensembles because they have factored in more of the ECM ensembles than the GEFS/NAEFS to their outlook.

 

The ECM operational run days 9 and 10 is a mild outlier:

 

http://www.weerplaza.nl/15daagseverwachting/?r=midden&type=eps_pluim

 

Something has to give here, and we need it to be the operational run climbing down and edging the pattern further south and east.

Couldn't have put it any better Nick

There is always a concern when the higher-res operational run sticks to a consistent theme for several runs, as you have to make an assumption that its superiority is picking out the key detail and may have the right answer....

However, the crumb of comfort for me is that the control is not following the op - if you have the two high res runs vs the ensemble consensus in these kinds of delicately balanced situations then you start to suspect that the lower resolution of the ensemble members is the cause (and is likely to be incorrect). But conversely in this particular situation they have been fairly steadfast in a colder scenario (be that from MLB or HLB) alongside the control.

One key thing to remember is that low angular momentum situations throw the model suites in to chaos - and that is where we find ourselves right now.

For your own sanity, wait until at least the other side of the weekend before making too many judgments on the upcoming spell

SK

[Shunter]

Is there a delay to the GFS 6z ( somebody giving it a good kick hopefully )?

[Banbury]

Is there a delay to the GFS 6z ( somebody giving it a good kick hopefully )?

Just been notified NCEP is having major problems and data is being delayed by up to 2 hours at the moment. This will impact GFS/GFSP and GEFS.

 

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ From Brian on TWO

[frosty ground]

Just been notified NCEP is having major problems and data is being delayed by up to 2 hours at the moment. This will impact GFS/GFSP and GEFS.

 

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ From Brian on TWO

http://www.wetterzentrale.de/pics/Rtavn1201.gif

Out to 120 Hours.

[Banbury]

http://www.wetterzentrale.de/pics/Rtavn1201.gif

Out to 120 Hours.

Thanks Brian

[bluearmy]

'one set of extended ecm ens doth not a winter make' .

 

very hard to read too much from a mean and some weakish anomolys but if this suite is on the right track, we could be looking towards a ridge to our northwest stretching to our northeast with a southerly tracking jet into europe and very cold air being dropped into the back of the block to be advected west. thats beyond the fun and games this side of new year

 

thats my only ramp for now and as i say, tough to read that from a 51 member ens mean. (however, the mean jet and normalised anomolys help a bit)

[damianslaw]

Lots of chopping and changing from the models over recent days when it comes to beyond reliable timeframe, as ever, best sticking to the reliable timeframe roughly 144 hours and expect the models to keep churning out various scenarios beyond this.

 

Its a difficult situation at the moment, a fine line between a much colder evolution or more of the same mild/average conditions of current, making any prediction beyond Christmas day at this stage should have a massive disclaimer of 'subject to change' attached to it.

 

So with this in mind expect more wild swings from the models.. frustrating for those wanting to see a clear pattern emerging.

[Iceberg]

Improved 06 GFS upto 120, small changes, but big impacts, very much a nod to the ECM and UKMET. GFS has struggled with the strength of the ridge being thrown up by the cut off low mid atlantic.

[iamgazza]

Improved 06 GFS upto 120, small changes, but big impacts, very much a nod to the ECM and UKMET. GFS has struggled with the strength of the ridge being thrown up by the cut off low mid atlantic.

 

Haha lets hope you've not cursed the run by praising it so early

[karyo]

Improved 06 GFS upto 120, small changes, but big impacts, very much a nod to the ECM and UKMET. GFS has struggled with the strength of the ridge being thrown up by the cut off low mid atlantic.

Once again it is shortwave galore around southern Greenland and Iceland. Doesn't look good to me.