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Some useful tropospheric developments upcoming which are likely to have stratospheric impacts towards the end of November and more particularly into December. A strong convectively coupled tropic

so after many days the GFS & FNMOC & canadian finally now follow the Euro with 44 out 64 Members with a split at day 9- The ECM is day 8. We will call it - SSW & Split for 1st Ja

For all that watch the zonal winds. Let me urge you to look at the geopotential heights more. At least as far as weakening/strengthening trends go. Because as the polar vortex cries for help, you migh

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Posted
  • Location: Rotherham
  • Weather Preferences: Snow, severe frost, freezing fog and summer sunshine
  • Location: Rotherham
    5 minutes ago, stodge said:

    Afternoon all ?

    I fear I'm a novice at this as well and I don't understand the optimism of some on here.

    To me, we are seeing (and still in FI) a strong warming from the Eurasian side - all that will do is displace the PV back to Canada where it will strengthen and re-form in situ and inevitably the trop and strat vortices will connect and the jet will fire up.

    We need two or three of these to weaken the PV enough to dislodge it further west and encourage blocking either over Scandinavia or perhaps Greenland.

    I accept there may be a lot else going on at different levels and at different ways but I wonder if this is where the UKMET's mild winter forecast originates - a powerful displacement which doesn't split the stratospheric PV but sends it back to Canada where it strengthens and locks us into a zonal Atlantic spell.

     

    6 minutes ago, stodge said:

    Afternoon all ?

    I fear I'm a novice at this as well and I don't understand the optimism of some on here.

    To me, we are seeing (and still in FI) a strong warming from the Eurasian side - all that will do is displace the PV back to Canada where it will strengthen and re-form in situ and inevitably the trop and strat vortices will connect and the jet will fire up.

    We need two or three of these to weaken the PV enough to dislodge it further west and encourage blocking either over Scandinavia or perhaps Greenland.

    I accept there may be a lot else going on at different levels and at different ways but I wonder if this is where the UKMET's mild winter forecast originates - a powerful displacement which doesn't split the stratospheric PV but sends it back to Canada where it strengthens and locks us into a zonal Atlantic spell.

    Doesn't this chart posted by knocked show more of a warming over Canada though? I did see charts earlier in the week which showed a eurasian warming so not sure if something has changed or just different models showing different outcomes...

    ecmwf-deterministic-nhemi-t10_anom-5028800.webp

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    Posted
  • Location: County end Oldham 202 m Above sea level
  • Location: County end Oldham 202 m Above sea level
    9 minutes ago, stodge said:

    Afternoon all ?

    I fear I'm a novice at this as well and I don't understand the optimism of some on here.

    To me, we are seeing (and still in FI) a strong warming from the Eurasian side - all that will do is displace the PV back to Canada where it will strengthen and re-form in situ and inevitably the trop and strat vortices will connect and the jet will fire up.

    We need two or three of these to weaken the PV enough to dislodge it further west and encourage blocking either over Scandinavia or perhaps Greenland.

    I accept there may be a lot else going on at different levels and at different ways but I wonder if this is where the UKMET's mild winter forecast originates - a powerful displacement which doesn't split the stratospheric PV but sends it back to Canada where it strengthens and locks us into a zonal Atlantic spell.

    That is what i fear may happen.

    But like you i am but a novice ...

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    Posted
  • Location: Ashbourne,County Meath,about 6 miles northwest of dublin airport. 74m ASL
  • Weather Preferences: Cold weather - frost or snow
  • Location: Ashbourne,County Meath,about 6 miles northwest of dublin airport. 74m ASL

    Is it rare to get 3 winters in a row having an ssw?

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    Posted
  • Location: Netherlands close to the coast
  • Location: Netherlands close to the coast
    4 minutes ago, sundog said:

    Is it rare to get 3 winters in a row having an ssw?

    2/3x2/3x2/3= 8/27 consecutive 3 winters will have 3 ssws in a row 

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    Posted
  • Location: Wantage, Oxon
  • Weather Preferences: Hot, cold!
  • Location: Wantage, Oxon
    1 hour ago, mushymanrob said:

    hi

    am i correct in assuming that if we do have a ssw in mid/late december (or even early new year) and it fails to produce a cold spell for us, then its game over for a stratospheric induced cold spell for this year? do we get only 1 shot per season? or is it possible to get another warming event later in the season ?

     

    I believe it is possible to have two SSW events during the winter, this link might help, suggests this happened in 98,99 

    https://www.earth-syst-sci-data.net/9/63/2017/essd-9-63-2017.pdf 

    Looking at the trop model output this morning, it may even be that this warming event, if it happens,  goes alongside a shift to a cold blocking pattern anyway.  Speculation of course, but interesting times.

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    Posted
  • Location: Beccles, Suffolk.
  • Weather Preferences: Thunder, snow, heat, sunshine...
  • Location: Beccles, Suffolk.

    And it's certainly possible to get spells of cold, snowy weather without an SSW: 1968-69 had several (five or six?) such periods between November and March...They cannot all have been SSW-related.?

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    Posted
  • Location: Longton, Stoke-on-Trent.
  • Location: Longton, Stoke-on-Trent.
    5 minutes ago, Ed Stone said:

    And it's certainly possible to get spells of cold, snowy weather without an SSW: 1968-69 had several (five or six?) such periods between November and March...They cannot all have been SSW-related.?

    December 2010 wasn't related to a SSW either.

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    Posted
  • Location: Wantage, Oxon
  • Weather Preferences: Hot, cold!
  • Location: Wantage, Oxon
    1 minute ago, Ed Stone said:

    And it's certainly possible to get spells of cold, snowy weather without an SSW: 1968-69 had several (five or six?) such periods between November and March...They cannot all have been SSW-related.?

    Well it was, Pete, I'm less convinced it is now for the UK.  More recently it seems to me to have been the case that the kind of major atmospheric upheaval caused by a SSW does seem increasingly to be a prerequisite for snowy weather in the south of the UK.

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    Posted
  • Location: Sedgley Black country 731ft 222 metres
  • Location: Sedgley Black country 731ft 222 metres

    Whilst  Glossea  isnt at the moment showing a SSW  what it does seem to agree on is  weak zonal winds  at the start of December    Still quite a bit of interest in this for me. 

    Edited by weirpig
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    Posted
  • Location: Bedford, 30m asl
  • Location: Bedford, 30m asl
    1 minute ago, weirpig said:

    Whilst  Glossea  isnt at the moment showing a SSW  what it does seem to agree on is  weak zonal winds  at the start of December    Still quite a bit of interest in this for me. 

    You beat me to it - on the plus side you can indeed see quite a slow down in zonal winds forecast on GLOSEA into early December, fairly in line with the GEFS mean really, which may in itself be enough to help us achieve something interesting in the troposphere as per current modelling.

    However, it then goes on to show a mean increase in zonal winds through the rest of the season - and given that is beyond the range of any medium range NWP suite that us mere mortals get easy, regular access to stratospherically, it could well be that the GEFS mean is indeed correct in its guidance, but in the longer term a technical SSW is never achieved.

    Regardless of any of this, whilst every little helps, for as long as we see a decoupled Strat and Trop, we needn’t worry too much about the longer term Strat outlook as far as the first half of December goes for now. One does suspect though that the deeper into winter we go, the more help from above we will require - and I’m not talking divine help here.

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    Posted
  • Location: Near King's Lynn 13.68m ASL
  • Weather Preferences: Hoar Frost, Snow, Misty Autumn mornings
  • Location: Near King's Lynn 13.68m ASL

    Enormous spread on those Glosea ensembles after about D14. That's not a criticism, and it's to be expected at that range. In the shorter term, it shows a weakening of the SPV which is in concert with all the other output we see? It would be nice if we got to see the temp and GPH anomalies as the U-component of the zonal mean at 60N/65N doesn't tell the whole story.

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    Posted
  • Location: South Oxfordshire
  • Location: South Oxfordshire
    4 minutes ago, Kirkcaldy Weather said:

     

    I just read the mention of 1987 by Ventrice and posted in the tweet thread, very interesting. 

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    Posted
  • Location: Manchester Deansgate.
  • Weather Preferences: Heavy disruptive snowfall.
  • Location: Manchester Deansgate.
    19 minutes ago, Griff said:

    I just read the mention of 1987 by Ventrice and posted in the tweet thread, very interesting. 

    Unfortunately that is Dec 1987 not Jan 1987.

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    Posted
  • Location: South Oxfordshire
  • Location: South Oxfordshire
    1 minute ago, feb1991blizzard said:

    Unfortunately that is Dec 1987 not Jan 1987.

    I stand corrected several times ? 

    They all seemed magnificent as a kid, or maybe I'm getting old and forgetful. ?

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    Posted
  • Location: Manchester Deansgate.
  • Weather Preferences: Heavy disruptive snowfall.
  • Location: Manchester Deansgate.
    1 minute ago, Griff said:

    I stand corrected several times ? 

    They all seemed magnificent as a kid, or maybe I'm getting old and forgetful. ?

    To be fair there was an SSW in Dec 87 as well (i think) and i did get a dumping of snow in Jan 88 so that was not as bad a winter for me as others although probably not relevant in this thread as i am not sure at all it was related to the stratosphere.

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    Posted
  • Location: chellaston, derby
  • Weather Preferences: The Actual Weather ..... not fantasy.
  • Location: chellaston, derby
    50 minutes ago, feb1991blizzard said:

    To be fair there was an SSW in Dec 87 as well (i think) and i did get a dumping of snow in Jan 88 so that was not as bad a winter for me as others although probably not relevant in this thread as i am not sure at all it was related to the stratosphere.

    i remember that , i remember michael fish pointing to some very cold air over scandinavia and telling us its 2got our name on it" . we had a lot of deep snow here in derby and some extremely low temps, -12c i think. but it didnt last long, from the 12th to the 20th.

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    Posted
  • Location: Strood, Kent, 19 feet above sea level
  • Weather Preferences: Snow, Thunderstorms,
  • Location: Strood, Kent, 19 feet above sea level
    20 minutes ago, Mike Poole said:

    And today's NAM plot is totally different:

    image.thumb.jpg.5abf8480e55e259bfb39e12011edf111.jpg

    These charts change as often as the op but that's an impressive -NAO signature from the Trop all the way up into the strat!!

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    Posted
  • Location: Wantage, Oxon
  • Weather Preferences: Hot, cold!
  • Location: Wantage, Oxon
    2 minutes ago, Met4Cast said:

    These charts change as often as the op but that's an impressive -NAO signature from the Trop all the way up into the strat!!

    I think that is maybe where we are headed though....

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    30 minutes ago, Mike Poole said:

    And today's NAM plot is totally different:

    image.thumb.jpg.5abf8480e55e259bfb39e12011edf111.jpg

    Interesting ~2.5 week periodicity in the tropospheric NAM in which case the strat probably irrelevant in the forecast. Note on that run the NAM was influenced by a large cut-off high in the Arctic giving -ve AO, but there was a +ve NAO.

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    Posted
  • Location: Clayton-le-Woods, Chorley, Lancs
  • Weather Preferences: Snow
  • Location: Clayton-le-Woods, Chorley, Lancs

     

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