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Model output discussion 25th Jan - The final third of winter beckons..


Paul

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Posted
  • Location: UK/ EU resident in Almeirim de Fazendas, Portugal
  • Location: UK/ EU resident in Almeirim de Fazendas, Portugal

    Lots of uncertainty but signs that the atmospheric circulation is going to mirror stratospheric turmoil and wind itself up for some elastic band rebounding that suggests some interesting and contrasting surface detail fall-out to come for the last third of winter

    This is one of those occasions where falling torques and atmospheric angular momentum tendency in the first instance and then a consequent sharp rebound of torques and atmospheric angular momentum in the second, might engineer catalyst to snap the NH pattern out of its seasonal rut.

    Cued by tropical forcing in the Indian Ocean, -ve balance of frictional torque has been leading mountain torque decisively downwards over recent days. A considerable -ve mountain torque has occurred over the Rockies and rapid removal of westerly winds from the atmospheric circulation is occurring.

    gltauf.90day.gifgltaum.90day.gif

    This has signalled a drop in relative angular momentum tendency

    gltend.sig.90day.gif

    With (approx) two day lag plot showing the Global Wind Oscillation heading towards low amplitude Phase 1

    gwo_90d.gif

    Taking into account response timelines to -ve mountain torque this advertises an upstream amplification over the Pacific to occur around the 6 day period which will have downstream ramifications in terms of retracting the Azores High westwards and taking the Jetstream southwards across the Atlantic as fuelled by the displaced Canadian lobe of polar vortex.  No surprise to see some distinctly unpleasant weather modelled in the next weekend period in the first stages of this process

    However, the upstream jet, is set to decelerate rapidly as pressure rises over the Pacific and re-build the Aleutian Ridge.  In the Atlantic sector, the retrogression of the pattern will tend to angle the Jetstream more NW/SE and, conceivably, enable build of pressure over Scandinavia. With time, as the disrupting trough gets separated from the Canadian lobe of vortex, downstream amplification from the Pacific sector becomes possible at the same time as the wave 2 response is activated by rising pressure over Scandinavia to work on the vortex in tandem with the Aleutian Ridge. It is key at this point that the vortex is sufficiently weakened to allow the bleeding of secondary systems to be cut off from the Canadian lobe - and hence terminate the thermal gradient.

    So much for the extra tropics.

    Returning back to the tropics, we have to watch eastward propagation of the MJO towards the Pacific starting to act constructively on the pattern in terms of increasing downstream amplification. With angular momentum, what goes down goes back up again to balance the global windflow budget, and with total angular momentum levels close to parity...

    gltotaam.sig.90day.gif

    then a logical correction to reflect the background ENSO neutral ocean base state can neatly be supplied through eastward moving tropical forcing.

    What does this mean in possible synoptic terms?

    It firstly bolsters/re-enforces the inflection point of downstream amplification into the Atlantic as, ultimately, transferred by a decelerating jet from the Pacific - which then encourages a follow-up link up (over the top of cut-off disrupted troughing heading into Europe) to the pressure rises over Scandinavia. Meanwhile, with (hopefully) a split enabled in the vortex, the chances of the jet crossing through the northern arm with spoiling energy to inhibit amplification are reduced (also assisted by tropical signal progressing through Phases 7/8 which would teleconnect to an increasing -NAO signal and help back cold air advection west)

    This is of course the ultimate prize scenario of what *could* happen through February. Whole timing of all this beyond the point where troughing may start disrupting and reduce the vigorousness of the Atlantic is obviously uncertain this early, and of course much depends on both emerging stratospheric signals and medium to longer term tropical forcing signals both sustaining, and, very preferably upgrading.

    Its a case of looking to an orbit of the GWO to Phase 2 (shaping the Atlantic ridging and as already given credence by latest GFS 06hrs) and then looking to the stratospheric fall-out of the tropospheric uppercut and westward encroaching Scandinavian ridge as tropical forcing moves eastward to the Pacific and hopefully maximised amplification as atmospheric angular momentum tendency returns the GWO through to Phase 4

    But whilst we are familiar with what can go wrong will go wrong, lets consider for a change that this process does, on occasion work the other way too. There is feasibly reasoned GSDM extra tropical and tropical support for both the tropospheric and stratospheric possibilities - and with just the last few weeks of February left of official winter, and whilst we cannot control the elements, frankly there is little to lose in approaching the evolution with a mind-set that is otherwise

    Late edit: GEM 12z and GFS 12z are also trying to read the longer term script...

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    Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
    56 minutes ago, supernova said:

    Great, informative post Chiono. Based on that forecast, would be interested to know if and what blocking might prevail thereafter. 

    Ahh well that is the difficult bit. But what @Singularity and @Tamara allude too. Scandi Block moving westwards with undercutting southerly displaced jet. It could happen with this type of set up, I guess as ever we just need the resultant daughter vortices to be in the right position and strength for that to occur, because we all know that near misses are far easier to achieve than a direct hit. But there is definite interest in this projected set up.....

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    Posted
  • Location: NR LOURDES SW FRANCE
  • Location: NR LOURDES SW FRANCE

    I'm wondering whether we're seeing a closer match to an MJO phase 5 lower amplitude signal.

    If you compare the GFS 06hrs run at T240hrs and compare it to the MJO lower amplitude you get this:

    gfsnh-0-240.pngfeb.gif

     

    If we see less interference to the MJO signal then we should be seeing that closer match. Last weeks NCEP update mentioned less interference in week 2 and if this does verify then chances for something colder to develop should increase.

    PS I've edited the MJO to give an easier comparison.

     

     

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    Posted
  • Location: Erith. SE London/kent 40m asl
  • Weather Preferences: Winter Snow, extreme weather, mainly sunny mild summers though.
  • Location: Erith. SE London/kent 40m asl

    Today's set of 12z runs will be of particular interest to me since we are now going out to the 14th of February, halfway through the last month proper of Winter, no leap year this year.

     It would be nice to see a continuation of these more positive charts and a firming up of maybe a trend of a Scandi high, or even a split in the PV, something along the lines of this chart which is from Autumn 2015 would be really nice for a bit of late Winter fun. I'm not saying this is going to happen, just something to look out for out around the 2nd week of February should the SSW play ball and favour our snow starved Isles. :)

    gfsnh-0-120-5.png

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    Posted
  • Location: Stroud, Gloucestershire
  • Weather Preferences: Extreme!
  • Location: Stroud, Gloucestershire

    Some trough disruption at day 7 on the GFS 12z,

    GFSOPEU12_144_1.png

     

    it seems to me we are now tentatively trying to pick out the next phase of the pattern from the ops, this mornings ECM and the GFS 06z both hinting at a pressure rise to the north east as the jet digs south east in the mid range.

    00z ECM

    ECMOPEU00_144_1.png

    ECMOPEU00_168_1.png

     

    Though UKMO quite progressive on the 12z

    UKMOPEU12_144_1.png

     

    Certainly some interest to be watched, but very early stages. Some favourable background signals though. Lets hope the ECM 12z continues its theme from the 00z.

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    Posted
  • Location: Norway
  • Location: Norway
    4 minutes ago, chris55 said:

    Some trough disruption at day 7 on the GFS 12z,

    GFSOPEU12_144_1.png

     

    it seems to me we are now tentatively trying to pick out the next phase of the pattern from the ops, this mornings ECM and the GFS 06z both hinting at a pressure rise to the north east as the jet digs south east in the mid range.

    00z ECM

    ECMOPEU00_144_1.png

    ECMOPEU00_168_1.png

     

    Though UKMO quite progressive on the 12z

    UKMOPEU12_144_1.png

     

    Certainly some interest to be watched, but very early stages. Some favourable background signals though. Lets hope the ECM 12z continues its theme from the 00z.

    true the JS should be given more south.....

    76.png

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    Posted
  • Location: Newton Aycliffe, County Durham... 90m asl
  • Weather Preferences: snow and thunderstorms :)
  • Location: Newton Aycliffe, County Durham... 90m asl

    So some small but deep lows developing to the south of the main trough in the atlantic as we head into next weekend running across the uk which could bring some very unpleasant weather with warnings likely to be issued, wind a key feature of the weather with everything but the kitchen sink mixed in dependent on location.

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    Posted
  • Location: Erith. SE London/kent 40m asl
  • Weather Preferences: Winter Snow, extreme weather, mainly sunny mild summers though.
  • Location: Erith. SE London/kent 40m asl

    Its trying to get there, but all the deep cold back down towards Greece again on this run.

    gfsnh-0-234.png

    gfsnh-1-234.png

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    Posted
  • Location: st albans
  • Location: st albans
    1 minute ago, snowray said:

    Its trying to get there, but all the deep cold back down towards Greece again on this run.

    gfsnh-0-234.png

    gfsnh-1-234.png

    Eyes on the prize snowray - that isn't the deep cold most are looking at with the hemispheric pattern being painted longer term! 

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    Posted
  • Location: Pembrokeshire
  • Weather Preferences: Snow
  • Location: Pembrokeshire
    1 minute ago, snowray said:

    Its trying to get there, but all the deep cold back down towards Greece again on this run.

    gfsnh-0-234.png

    gfsnh-1-234.png

    I think your clutching at straws there tbh - way off the mark - we need to see what mid/late feb brings 

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    Posted
  • Location: Erith. SE London/kent 40m asl
  • Weather Preferences: Winter Snow, extreme weather, mainly sunny mild summers though.
  • Location: Erith. SE London/kent 40m asl
    3 minutes ago, bluearmy said:

    Eyes on the prize snowray - that isn't the deep cold most are looking at with the hemispheric pattern being painted longer term! 

    Problem of course is no undercut this time.

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    Posted
  • Location: Croydon. South London. 286 ft asl
  • Weather Preferences: Thunderstorms, snow, Ice days, warm sunny days.
  • Location: Croydon. South London. 286 ft asl

    Good trends again from the 12z.. The GEM also looks good.

    gemnh-0-240.png

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    Posted
  • Location: Erith. SE London/kent 40m asl
  • Weather Preferences: Winter Snow, extreme weather, mainly sunny mild summers though.
  • Location: Erith. SE London/kent 40m asl

    Yes its the trend that matters at this stage of course, and GEM coming on board is good news.

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    Posted
  • Location: Stroud, Gloucestershire
  • Weather Preferences: Extreme!
  • Location: Stroud, Gloucestershire
    6 minutes ago, D.V.R said:

    Good trends again from the 12z.. The GEM also looks good.

    gemnh-0-240.png

    Now that's more like it!

    We start to get the elusive undercut at 168!

    gem-0-168.png?12

    But as ever these are just the op runs "toying" with the new signal. 

     

     

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    Posted
  • Location: st albans
  • Location: st albans
    22 minutes ago, snowray said:

    Problem of course is no undercut this time.

    It's not bad considering what was being chucked out only 24/36 hours ago

    be interesting to see how many ens runs begin to smell this pattern. If it's only a few, then likely the op is just coming off that shelf and will revert to less blocky tomorrow 

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    Posted
  • Location: Tamworth, Staffordshire (83m ASL)
  • Weather Preferences: Heat, Thunderstorms, Snow
  • Location: Tamworth, Staffordshire (83m ASL)

    Noticeably more interesting Northern Hemisphere charts appearing.

    This is what we have been lacking recently.

    We have been hoping for a cold spell relying solely on the jet playing ball rather than having the building blocks in place that would ensure a less risky route to cold, longer too.

    P8 = LOADED

    gens-8-1-276.png

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    Posted
  • Location: Erith. SE London/kent 40m asl
  • Weather Preferences: Winter Snow, extreme weather, mainly sunny mild summers though.
  • Location: Erith. SE London/kent 40m asl

    Well I guess all eyes on the ECM then....More eye candy on its way.....I hope!:D

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    Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
    33 minutes ago, D.V.R said:

    Good trends again from the 12z.. The GEM also looks good.

    gemnh-0-240.png

    Cracking demonstration of a complete wave 2 split that chart. Wave 2 upwelling splits have often delivered the best results in term of cold since I started monitoring the strat. Hopefully the Canadian daughter vortex won't be too top heavy.

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    Posted
  • Location: New Forest (Western)
  • Weather Preferences: Fascinated by extreme weather. Despise drizzle.
  • Location: New Forest (Western)

    Some very 'fiddly' undercut processes offered by GEM and GFS this evening, but remember, these are models that are known to struggle with such developments. To be fair, they all tend to have a bit of a 'mare these days.

    As usual we're left wondering of modelling shortfalls are weighted more towards not disrupting troughs and sliding secondary lows readily enough, or getting a bit carried away with the emerging blocking signal.

    Historically, when wave-2 upwelling is on the scene, it has been one of the few times when the more extreme model output in terms of a meandering jet stream etc. tend to be the form horse. Thing is, it's been quite some time (years?) since this was last the case, and the old rules of thumb have seemed less applicable these past few winters, for whatever reason.

    Even so, I'm feeling hopeful for an 'all routes lead to cold' scenario to develop - but with the magnitude of that cold anyone's guess at this time.

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    Posted
  • Location: Orpington Kent
  • Weather Preferences: Snow freezing rain heat waves
  • Location: Orpington Kent

    im going to  stick my neck out and say we are in for a big freeze mid February on wards or later part of Feb with heavy snow showers blowing in from east  high pressure over Scandinavia low pressure pushed south  just my take on things wants going on in the  stratosphere SW . Folks may shoot me down but we have all been wrong  at some point..:D

    IMG_0292.PNG

    IMG_0293.JPG

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    Posted
  • Location: Bournemouth
  • Weather Preferences: Dry mild or snow winter. Hot and humid summer.
  • Location: Bournemouth
    7 minutes ago, abbie123 said:

    im going to  stick my neck out and say we are in for a big freeze mid February on wards or later part of Feb with heavy snow showers blowing in from east  high pressure over Scandinavia low pressure pushed south  just my take on things wants going on in the  stratosphere SW . Folks may shoot me down but we have all been wrong  at some point..:D

    IMG_0292.PNG

    You maybe right and as amateurs we can all "stick our neck out" as we are not accountable. Interesting output and interesting trends. Let's hope we get something, as it will be 10 months until us coldies are back in the game. 

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    Posted
  • Location: Rotherhithe, 5.8M ASL
  • Location: Rotherhithe, 5.8M ASL

    We're seeing a a rather quick downwelling? To the troposphere on GEM most evidently. This thread would be ablaze with activity if it was earlier in the winter, it seems to me the atmosphere is going to be the most inclined towards cold not seen since early 2013.

    Eye catching synoptic in GFS 12z FI northern blocking galore reminiscent to early winter - back in December when EC monthly and glosea were modelling extensive northern blocking, it got the droves out.....round 2? :wink::p 

    IMG_1745.PNGIMG_1746.PNG

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