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Model Output Discussion - The Start Of Winter


Paul

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Posted
  • Location: North East Cotswolds, 232m, 761feet ASL
  • Location: North East Cotswolds, 232m, 761feet ASL

I know its at the end of the runs but the GFS, and GFSP both seen to have high pressure building into the west of Russia, this backed up by a few GEFS members. Not sure if this is where we should be looking if we want cold later in Dec.

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Posted
  • Location: Carryduff, County Down 420ft ASL
  • Location: Carryduff, County Down 420ft ASL

Not one member has the NAO going negative over the next 15 days and until it does there can be no sustained spell. At least there will be some lowland snow in the North West from the brief passing cold air as lows move North of Scotland...

 

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.shtml

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Posted
  • Location: Aviemore
  • Location: Aviemore

Nick's posted his latest 14 day synoptic outlook:

https://forum.netweather.tv/topic/81941-synoptic-outlook-for-next-14-days-2nd-december-update/

 

"A transition to a less blocked outlook, with more in the way of wind and rain but also cold weather at times with snow over northern hills."

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Posted
  • Location: st albans
  • Location: st albans

Not much to choose between the ECM and GEFS anomaly. . The ecm has the temps below average towards the end of the run.

Charts courtesy weathebell

 

It does ?? (day 10 yes, but day 14 no)

 

the 00z suite has lost the upper ridge over w siberia so for the moment, i think we can discount yesterdays 12z  as being progressive in week 2

 

as week 2 looks to become more mobile, so we see the london temps easing upwards.

Edited by bluearmy
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Posted
  • Location: Aviemore
  • Location: Aviemore

There'll be a few delays to the GFS-P this week, including a period of 4 days where it won't be run:

 

As we have mentioned, the GFS parallel is running on our backup

supercomputer.  This week NCO needs to do work on the backup computer
related to our pending supercomputer upgrade.  This will impact the GFS
parallel in the following ways:

Today, 12/2   the 12Z GFS parallel output will be disseminated late.

Wednesday 12/3 - Sunday 12/7  The GFS parallel will not be run after the
06Z cycle on 12/3.  We will resume the parallel on Monday 12/8 once the
system has been returned to service and all data has been caught up.  We
will send an announcement when the parallel dissemination resumes.
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Posted
  • Location: Heckmondwike, West Yorkshire
  • Location: Heckmondwike, West Yorkshire

The AO looking more predisposed to go negative as we head to mid-dec.

Just one member staying positive by the 16th Dec.

 

post-12941-0-19050100-1417528509_thumb.g

 

 

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

Back to the models and nothing really showing in the anomaly charts to suggest any marked change within their time scales. Also EC seems at odds with the other two which is never a reliable sign when one differs from the others. It has but rarely been correct with the other two following.

links

ECMWF-GFS

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

and NOAA

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

Edited by Paul
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Posted
  • Location: Camborne
  • Location: Camborne

It does ?? (day 10 yes, but day 14 no)

 

the 00z suite has lost the upper ridge over w siberia so for the moment, i think we can discount yesterdays 12z  as being progressive in week 2

 

as week 2 looks to become more mobile, so we see the london temps easing upwards.

 

I was referring to T240, I should have been more specific.

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Posted
  • Location: Eastbourne and Larnaca,Cyprus .
  • Location: Eastbourne and Larnaca,Cyprus .

In terms of comments from NCEP alluded to by OMM I think this could bring some reliability issues upstream in the NWP.

 

Theres often a problem deciding on whether you get an interaction between the northern arm of the jet and the STJ, this is important in terms of depth of any low pressure there and its track.

 

Although the general pattern over Europe is generally agreed on across the model suite the upstream area may well alter the jet track  into  western Europe, low pressure in the eastern coastal USA will effect the Azores high, so the interaction between those jets is pretty crucial.

 

You can see further into the NCEP discussion they're already discussing the will it won't it interaction:

 

...ONCE THE SOUTHERN JET MOVES INTO
THE SOUTHERN TIER STATES...DOES IT PHASE WITH THE NORTHERN
BRANCH...AND IF SO...AT WHAT LONGITUDE IN THE WESTERN ATLANTIC
WILL THE PHASING TAKE PLACE.

 

Below is the ECM T168hrs chart you'll see the STJ and the PJ:

 

post-1206-0-56018900-1417528332_thumb.gi

 

 

The phase point for those jets is important, for those hoping for something a bit colder you'd preferably want any phasing further west and one low developing thereafter which can effect the Azores high, so as an example I've superimposed the effects here:

 

post-1206-0-02079900-1417528849_thumb.gi

 

If you get a deep low there the natural effect is generally for this to travel more ne than east so you might then get some temporary ridging further north of the Azores high and more dig south downstream of troughing.

 

However theres not much chance of any longer cold interludes in the expected mobile set up, effectively you're just trying to squeeze out as much wintry interest as possible.

 

Longer term if the Siberian high does edge west then these phasing interactions upstream would prove even more important but with that strong STJ at least this throws in a variable, at this point some uncertainty is welcome given the general theme of the outputs.

Edited by nick sussex
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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Afternoon all :)

 

I'm loath to make one of my rare contributions here given the quality of posts such as Dr Astro's and others. Looking at the GFS 06Z output (both Op and Parallel) I was struck by the progression of the strat temperatures.  

 

http://modeles.meteociel.fr/modeles/gfsp/runs/2014120206/gfsnh-10-252.png?6

 

The Parallel at T+252 puts the coldest part of the stratosphere over Northern Greenland and NE Canada which would suggest a strong PV in that area but follow the progression to the end of the run

 

http://modeles.meteociel.fr/modeles/gfsp/runs/2014120206/gfsnh-10-384.png?6

 

The coldest part of the stratosphere is now over Scandinavia and on the main charts the Op and Parallel both draw the PV out of Greenland and Canada and place it more over the Pole.

 

Here's the same timeframe on the Op:

 

http://modeles.meteociel.fr/modeles/gfs/runs/2014120206/gfsnh-10-252.png?6

http://modeles.meteociel.fr/modeles/gfs/runs/2014120206/gfsnh-10-384.png?6

 

The coldest part of the stratosphere finishes over NW Russia. My initial thought is this will encourage anticyclonic development rather than usher in deep cold.

 

Here's where we were a year ago:

 

http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013120306-10-252.png?6

 

Note the much warmer temps over North America.

 

http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013120306-10-384.png?6

 

Note the much warmer temperatures over Eurasia and Russia.

 

I'm an ignoramus in these matters but the movement of the coldest part of the stratosphere was affected by the presence of the warmer areas. The warmer areas over North America pushed the PV east, then the Asian warming held it and pushed it back NW so it concentrated around Greenland and NE Canada. Not happening this year it would seem.

 

In the absence of any anomalous areas of warmth at present, the coldest area meanders east as you might expect.

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Posted
  • Location: Dousland, South Dartmoor 205 m/asl
  • Weather Preferences: The fabled channel low
  • Location: Dousland, South Dartmoor 205 m/asl

Somewhat confusing these two posts. Are we to suggest that looking forward that the models are struggling a wee bit?

 

 

The AO looking more predisposed to go negative as we head to mid-dec.

Just one member staying positive by the 16th Dec.

 

attachicon.gifao_sprd2.gif

 

Not one member has the NAO going negative over the next 15 days and until it does there can be no sustained spell. At least there will be some lowland snow in the North West from the brief passing cold air as lows move North of Scotland...

 

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.shtml

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Posted
  • Location: Aviemore
  • Location: Aviemore

Somewhat confusing these two posts. Are we to suggest that looking forward that the models are struggling a wee bit?

 

One's AO and one's NAO - which are both quite different, more info about them here:

 

AO

https://forum.netweather.tv/topic/81903-the-arctic-oscillation-ao/

 

NAO

https://forum.netweather.tv/topic/30315-ao-el-nino-la-nina-nao/

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Posted
  • Location: Newton in Bowland
  • Location: Newton in Bowland

I received an email with regards too my enquiry about the GLOSEA 5 from the MetO  today. Hope it's ok here Mods,

 

Thank you for your email.  I have received the following response from our Climate scientists:

 

"The GloSea5 forecast is initialised with observed conditions. Unlike most short term forecast systems, which usually use an atmosphere model with specified sea surface temperatures for the period of the forecast, GloSea5 uses a fully coupled ocean-atmosphere dynamical model. Coupled models tend to ‘drift’ from the observed climatology, so to correct for this, a set of retrospective forecasts (often referred to as hindcasts) are run. From these we can estimate the drift and then calibrate the forecast. In this case the calibration period is 1996-2009. 

http://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/user-guide/technical-glosea5

 

In making the forecast there are a number of sources of information taken into consideration: the current observations, known forcing factors (or drivers) and, importantly, several dynamical forecast models. For the forecast for DJF 2014/15, issued 20th November 2014, there was good agreement across these models for enhanced likelihood for the positive phase of the North Atlantic Oscillation (NAO), cyclonic westerly circulation and warmer than average conditions for northern Europe. In addition, models had shown a very consistent signal for early winter in this respect for the past few weeks.  Of course, this doesn’t rule out the possibility of blocked conditions and a cold winter. It can be seen from figure T2 in the Temperature Summary that some forecast ensemble members lie in the lowest temperature quintile, but overall the probability distribution has shifted from climatology to favour a greater chance of warmer conditions.  Note that this forecast is regularly updated for the risks of cold/warm and wet/dry as the atmosphere evolves so do look out for the update in December.

 

Initial analysis of the forecast from the GloSea5 system suggests that the positive NAO signal may, at least in part, be driven by teleconnections from the tropics. In particular, there was a clear wave train in the upper level troposphere emanating from the tropical Atlantic and supporting the positive NAO. The forecast also showed anomalously high rainfall in the far west Pacific, associated with warmer than average sea surface temperatures in that region. 

 

Understanding the drivers of predictability is an important part of the forecast process, although it’s useful to bear in mind that they may not act together in a simple linear manner. Dynamical models are the best method we have for studying the interactions between the different drivers and there is a continual programme for the development and improvement of these models."

 

I hope this helps.

 

If you have any further questions or need any additional information please contact the Weather Desk on 0370 900 0100 where one of our advisors will be happy to help you. We are open 24 hours a day, seven days a week.

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Posted
  • Location: Carryduff, County Down 420ft ASL
  • Location: Carryduff, County Down 420ft ASL

Somewhat confusing these two posts. Are we to suggest that looking forward that the models are struggling a wee bit?

Hi festivalking

 

A negative AO is good in that it means cold air will be spilling from the Pole into the mid latitudes, however, only the presence of a negative NAO will bring it the direction of these islands of mid latitude.

 

So, whilst the AO is keen to go negative by mid month we need that NAO to go negative as well.

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Posted
  • Location: Crewe, Cheshire
  • Weather Preferences: Snow, storms and other extremes
  • Location: Crewe, Cheshire

Excellent post as ever Tamara and you highlight and explain the disconnect between the seasonals and the other factors very succinctly. I guess there has to be a risk that the modelling could come up trumps in terms of the incessant +NAO signal. It's a shame that a good winter month in December looks a no go in terms of proper winter potential and my fear now is that any potential SSW either fails to occur at all or occurs too late into the season for us to really benefit from it. There's certainly nothing in the NWP to suggest anything of a significant wintry note in the next 10-14 days and that's half of December down the drain!

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Posted
  • Location: Reigate Hill
  • Weather Preferences: Anything
  • Location: Reigate Hill

Great post by Tamara. Thank you. Yes early signs have been dampened as per a December cold spell. The ECM weeklies highlight this. The temp anomalies are average to above: 

 

  WSI_EuroEnergy
Low pressure keeping wet/windy weather with temps around normal/slightly above for NW/C Europe mid-late December! http://t.co/OJUhHvhf00
02/12/2014 15:13

 

I do not know for sure why we had such a poor Winter last year, but I believe it was something to do with above average rainfall in the Pacific. So signs of this repeating do not bode well. With the bottom up warming to the strat currently slowing, just when a bit more would have killed the PV is disappointing. But fingers crossed a SSW will still happen in January.

Edited by i'm dreaming of...
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Posted
  • Location: Kirkburton, Huddersfield - 162.5mtrs asl.
  • Weather Preferences: Winter synoptics.Hot summers.
  • Location: Kirkburton, Huddersfield - 162.5mtrs asl.

The positioning of the PV has never really concerned me when ever we have the Aleutian low/scandi/russian high scenario.

 

During the Slow burning winters,which many will not remember,the above were common place.

Lets face it if this chart was out now the Bartlett brigade would be weeing and the raging PV brigade s.o.s- ing Nick Sussex.So a typical example of a slow burning winter here:

http://modeles.meteociel.fr/modeles/reana/1977/archivesnh-1977-12-15-0-0.png   however notice the Aleutian low.

 

So lets move it on to New year...

http://modeles.meteociel.fr/modeles/reana/1978/archivesnh-1978-1-7-0-0.png

Not many left on the thread by this time the slow burner still on and a raging PV. BUT the Aleutian low still everpresent with heights to our n/e

http://modeles.meteociel.fr/modeles/reana/1978/archivesnh-1978-1-7-0-0.png

 

Wave breaking events were probably taking place throughout December as they are at present because of this combination which ultimately leads to this dramatic pattern change and Winter starting. 

 

http://modeles.meteociel.fr/modeles/reana/1978/archivesnh-1978-1-12-0-0.png  we went from this Northern Hemispheric pattern to this

http://modeles.meteociel.fr/modeles/reana/1978/archivesnh-1978-1-27-0-0.png       and then by mid Feb

 

Bingo....http://modeles.meteociel.fr/modeles/reana/1978/archivesnh-1978-2-19-0-0.png

http://modeles.meteociel.fr/modeles/reana/1978/archives-1978-2-19-0-2.png

 

That is just an example but 78/79 winter evolved with the Aleutian low in situ as did 86/87 and did i mention 46/47 in fact all of our classic slow burner winters had the same combination.  NCEP archives well worth a peek.There was always pain before gain but i did not have access to all these charts so patience was not an issue.

 

 

 

EDIT:Super post Tamara puts mine to shame :good:

Edited by winterof79
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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

 

thanks for sharing that HP, well worth reading everyone and shows just how much goes into seasonal forecasting especially if you read the link given earlier to their winter forecast.

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Posted
  • Location: Crewe, Cheshire
  • Weather Preferences: Snow, storms and other extremes
  • Location: Crewe, Cheshire

On a side note, that potentially nasty low looks to be heading further S on the 12z GFS and hasn't developed yet from a wave feature (upto about 120 hrs). Eyes down to see whether it now deepens over the UK.

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Posted
  • Location: west yorkshire
  • Weather Preferences: extreme weather
  • Location: west yorkshire

The potential storm on the gfs 12z looks to be heading further South on this run. Hope we aren't seeing the first signs of dec 2013 again.

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Posted
  • Location: Reigate Hill
  • Weather Preferences: Anything
  • Location: Reigate Hill

Deep depression gone on the 12z!! Fi probably at 120 hours right now!!

 

 

????

 

post-14819-0-33498800-1417537068_thumb.p  post-14819-0-73421200-1417537250_thumb.p

Edited by i'm dreaming of...
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