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Model Output Discussion - 31/10/2014 and Beyond

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Looking at the NAEFS spreads there's quite a bit of divergence around the UK. I imagine due to solutions varying between high pressure over/near the UK and the jet tracking further south putting us into an Atlantic onslaught. That split can be seen in the GEFS.




Less uncertainty over the bigger picture though with the vortex getting organised and those low heights to the NW.


naefsnh-1-0-180_zit1.png  naefsnh-1-0-240_fro5.png  naefsnh-1-0-384_ryp9.png


So the main uncertainty is regards to what latitude the jet tracks over the UK when it fires up.. which is of higher confidence.

Edited by Bobby
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To be honest the 12z op is probably on the extreme end (opposite to the 00z run albeit) of the set. Weak heights over the pole should probably prevent a full onslaught if this were to pan out. We still probably see an unsettled spell into week 2 with winds from the south west, but maybe not to the extent of the weather we saw last winter.


That said the recent output does suggest that Arctic blocking can result in pretty awful conditions for the UK, a NW Canadian/Siberian cross polar ridge is about as bad as you can get as the ridge directs all of the cold Siberian air towards Canada which in turn drives an increasingly mobile pattern.

How long will this last? Probably not too long (a week or so). But a lot can change.

If you look closely at the charts Matt has posted here ... does much actually change by T240? Split vortex, with Canadian and Siberian centres. Lows still being spat out under the tip of Greenland. Low Aleutian heights, high heights through eastern Europe towards Scandi. Still possibly holding onto -AO. That doesn't mean any change in the weather here, but also means the PV isn't firing on all cylinders.

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From 144 to 192 on some of the output today just doesn't look right. Too much Atlantic progression, the shape and angles don't support that, neither does all the variability and uncertainty. I can see the trough stalling in the Atlantic more, as it has done more and more the last week or so. We will end up with a 'battle-ground', that will bring us quite chilly, mixed, not too dramatic weather. 'Typical' for the time of year. We might actually get a proper frost or two.


Can't see that meridional flow just disappear so quickly. Then again, these are modern times, so who knows?

Edited by Altohumorous
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GFS 18z continuing the theme with some very disturbed zonal weather taking over. The parallel essentially the same. Atlantic moves in at 144hrs




Day 10 GFS op and parallel

gfs-0-240_jis0.png  gfs-0-240_hhn1.png





The process that led up to 144 is far from "Atlantic moving in" in the sense that you intimate. Anything beyond that is too far to call, especially as far as day 10, as we've seen over the past few weeks and otherwise. That trough at 144 has wandered around for 2 days already, even gone a bit west from where it is at 96 and 120, according to the output.

Edited by Altohumorous
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One thing that is noticeably different to last winter is the absence of the N Pacific/Aleutian heights, which lasted all winter, making the jet stuck in that same position (sending all the cold NW/SE and then generate those monster Atlantic lows). 

If we keep low heights around the N Pacific, then that certainly puts us in a more favourable position in building more in the way of heights over Canada and perhaps Greenland at some point.

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The process that led up to 144 is far from "Atlantic moving in" in the sense that you intimate. Anything beyond that is too far to call, especially as far as day 10, as we've seen over the past few weeks and otherwise. That trough at 144 has wandered around for 2 days already, even gone a bit west from where it is at 96 and 120, according to the output.


That low forms from cold air ejected from Canada engaging with tropical air being sucked up from around the Azores.  See at 120hrs. I don't see how that can be described as anything other than an Atlantic low pressure moving into the UK?


gfs-6-120_pze1.png  gfs-7-150_lfu6.png

Edited by Bobby
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Morning all,


AO forecast to go positive for a while,Lots of cold air upstream over the states and Canada that spewed off the pole though.Thats where our weather looks likely to come from now and we can see from the ECM that the air is cold to say the least.


The atlantic will dilute the cold as it crosses but to me it looks like its going to be colder than anything the east had to offer from our earlier hopes.


If the posted chart were to verify it would be hardly mild with isobars stretching back to what could be termed a cold pool.Northern hemisphere temp profile highlighting its colder to our west than east,


I for one wont be too dispondant

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THE CURRENT GENERAL SITUATION. A large depression covers the Atlantic ocean with a series of fronts crossing North and slowly East across the UK both today and tomorrow.


MODELS-2 WEEK HEADLINE  Remaining largely unsettled with rain at times, heavy in places and coupled with spells of strong winds in near to average temperatures for all.


THE JET STREAM ENSEMBLE FORECAST The GFS Jet Stream Ensemble forecast shows little sign of any significant shift in the flow from it's 50-55 deg North location with a particularly strong phase of the flow crossing the Atlantic to a position close to Southern Britain through Week 2.


GFS OPERATIONAL The general message from the GFS operational this morning is for a sustained period of unsettled and Low pressure driven weather with rain or showers at times for all. A short quieter phase is shown briefly at the start of next week as the current Low pressure fills up near to Southern England before a renewed Atlantic drive from intense depressions to the NW delivers severe gales and very heavy rain and squally showers in temperatures gradually falling closer towards the seasonal average after the weekend.


THE GFS PARALLEL RUN The GFS Parallel run is very similar to the operational with the only slight difference being the emhasis towards the heaviest rains and the strongest winds focused more towards the North and West though all areas are shown to come under repeated attacks of wind and rain in a very volatile and mobile Atlantic.


THE GFS ENSEMBLES.  The GFS Ensembles are likewise similar to what I have already printed in the above text with strong winds and heavy rain being the driving force in a more mobile pattern following the current unsettled and more locked pattern with temperatures close to average.


UKMO UKMO today illustrates the quieter phase in the weather shown by most models early next week as our current deep Low has drifted down towards Southern England while filling bringing lighter winds but still some rain early next week at the top and tail of the UK. The Day 6 chart shows a deep Atlantic Low approaching Western Britain later to renew the drive of Low pressure based weather later in the week.


THE FAX CHARTS  The Fax Charts maintain that the UK skies will be governed by Low pressure with concoction of troughs moving gently North and NE across the UK. Innitially there will be strong winds and heavy rain in places but later pressure becomes slacker as Low pressure is shown to fill near Southern England with rain at times still for the South and far North well into next week but with quieter weather in Central areas permitting frost and fog possibilities night and morning for a time.


GEM  GEM shows Low pressure governing the UK weather over the period but does differ in as much as the Low pressure areas come in on more Southerly latitudes and slower in movement maintaining rain and showers for all areas at times in a cyclonic airflow and temperatures close to average.


NAVGEM NAVGEM is very different than the above models this morning in that once the current Low pressure complex fills near Southern Britain early next week pressure rises further with slack High pressure covering many parts a week from now with dry and benign weather with mist, fog and frost patches much more likely than rain a week from now away from the far SW.


ECM  ECM this morning has finally shown closer resemblance to the majority of output this morning in ratcheting up a more powerful series of Atlantic storms later next week crossing quickly East between Scotland and Iceland and delivering Westerly gales and heavy rain and showers in temperatures falling back from the somewhat mild conditions currently to values much closer to what we expect at this time of year. All this follows the current more locked pressure pattern which in itself continues to give heavy rain and wind at times between now and then especially over the South.


THE ECM ENSEMBLES  The Ensembles point to a SW flow across the UK in 10 days time in association with Low pressure most likely to lie to the NW of the UK. In this pattern one can only expect unsettled and relatively mild weather to persist in spells of rain and strong winds for all.


NOTABLE TREND CHANGES FROM PREVIOUS RUNS The trend today generally focuses on maintained unsettled weather but with a change of emphasis of rain shifting from the West and South to all areas as gales develop widely later.


MY THOUGHTS  I suppose the main focus for people who read my reports daily is when will the weather turn more wintry and cold but more concerning than any of that is the concerning charts this morning that show the UK is likely to experience a lot more rain and wind with likely flooding issues likely to develop in areas that least need it as the current locked pattern of Low just to the West and SW is replaced by a much more mobile Atlantic and powerful Jet Stream still quite well South. This pattern in some ways mirrors what we were under repeatedly last Winter. This will encourage some powerful storm systems to develop to the NW of the UK as the High pressure block to the NE collapses next week. All areas will then see further spells of heavy rain and squally winds with brighter and more showery weather in between. There is little sign of any dry weather over the UK over the next few weeks with the exception of early next week when a Central swathe of the UK sees a drier and calmer phase before the aforementioned pattern develops. Temperatures will fall back somewhat from this weekend towards a point close to the seasonal average and in the strength of the winds likely later next week I'm sure it will feel chilly with the chance of mountain snow at times across the North. NAVGEM is the only model that does suggest higher pressure from the block to the NE developing later next week but does look very isolated in it's evolution and is best disregarded this morning. So going back to my early point about when the UK can expect to see cold weather arriving my answer would be as far away as ever this morning as all the building blocks shown late last week and to some degree early this week are largely removed and in their place we have a powerful Jet flow next week winding up powerful storm systems which look like battering Britain from the West in the second half of the period shown by the models this morning.


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Over the next 8 days the 2m temps are shown to be above normal for large parts of Europe, of course surface temps for some parts of Europe won't be overly high given the time of year, for the UK temps should be in double figures fairly frequently




Normal 2m temps




Expected 2m temps




Across the pond its a different story with 2m temps well below normal in places, you have to travel over towards the far west to find 2m temps slightly above average



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GFS has been showing the re-organisation of the PV for sometime in FI; not to a normal state, but more of a driver. You can see from the five day difference here that it is quite a marked development and a notable trend towards a Greenland/NE Canadian main lobe:


post-14819-0-94770500-1415874399_thumb.p  post-14819-0-83595800-1415874408_thumb.p


Its very rare once the Atlantic dominates the output that it will flip flop back to something more blocked, unlike the other way when it seemingly always does. ECM handling of heights again has been very poor and we will have to continue to be wary through the coming Winter. Its D10 mean supports the op:




The JMA monthly has just been updated and as expected temps look around average (to slightly above) with little sign of any winter pattern developing. Week 2 ties in with the GFS F1 of an active Atlantic and W3-4 suggests a calming down of that flow, and that ties in with the less than organized PV:


W2: post-14819-0-10540600-1415874790_thumb.p  W3-4: post-14819-0-17563700-1415874804_thumb.p


The GFS op is continuing to trend to send the ex-US cold pool (PV lobe) towards the UK, from around D8:


D8 post-14819-0-29144900-1415874896_thumb.p D10: post-14819-0-31521100-1415874921_thumb.p


D12: post-14819-0-69672900-1415874933_thumb.p


Parallel has the jet slightly further north, but basically a wet outlook: post-14819-0-04212400-1415875664_thumb.p


If there wasn't a Strat warming event that would be a nasty pattern setting up. However although indications are that the warming may not have much legs (GFS op for instance), ECM may give us a split which should reboot the following winter pattern. So the next 5-7 days the interest lies in the strat. as we look out for some potential very heavy precipitation from week 1-3.

Edited by i'm dreaming of...
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Big difference between last November and this November for us is quite clear. 


Last Year

  • Steeper Temperature Gradient between the Azores and the Atlantic
  • Vortex Structure




This Year

  • No structure in vortex
  • Disrupted jetstream





Looking at the GFS 06z you can quite clearly see some significant changes in the vortex that appears to be getting stronger in 192hrs, to significantly weakening by the end of November. Whilst quite far out you can see from 300hrs to 384 hours it completely starts to disintegrate, this must be Wave 2 activity affecting the vortex as mentioned in the Strat thread.







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There are interesting differences at 144h between GFS Op and P, quite a large difference in where each places the surface low centre. EC for comparison is between the 2 on its 00z run, but nearer the P position.

This may well make a difference further down the line perhaps. Way down the line these differences will merge very probably?

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Looking at the CFS Daily  to see if the strat. has an effect as we move into December and to be honest there is no sign of HLB'ing. It still has the signal (in line with the MJO) for heights to build at the end of week 1 in December for the UK region:


 post-14819-0-82133200-1415879267_thumb.p For a week or so: post-14819-0-42884500-1415879211_thumb.p


No sign of an Arctic based PV through the run. However no cold for the UK up to the New Year. But there are two more Arctic plunges for the US in the next month including a Christmas one:




As CFS is based on the GFS op and that op has only a displacement at the moment it may not be significant (though the Parallel also eases off on the warming in late FI), so assuming the displacement is fed into the CFS then the UK not benefiting much from the warming. ECM's wave 2 is therefore under scrutiny and we will see in the next few runs if this is not another false dawn.

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