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Model output discussion - the beast arrives


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Posted
  • Location: Cottingham
  • Weather Preferences: Cold Snowy Winters, Hot Thundery Summers
  • Location: Cottingham

    image.thumb.png.c55619133e431dac084597df54a606b0.png

    06z for midday saturday, is cold air still holding on? A few more do, thanks to the secondary channel low that forms on Friday, many of the GFS runs however show the incoming main low curving back westwards before reaching Ireland meaning its hard for cold uppers to return.

    Not a bad 06z but could be better, what I'd like to see is major trough disruption as it heads towards the channel, then forcing the low eventually eastwards instead. May still happen.

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    Evening Guys  Officially signing off for the winter from my window - still all but 5 inches on the ground - have a great year ! Current   favourite   See

    First rule of GFS model watching. Never trust a dartboard low....... But especially in this type of set up.

    See you next Saturday then, Steve?

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    Posted
  • Location: Exeter, Devon, UK. alt 10m asl
  • Location: Exeter, Devon, UK. alt 10m asl
    4 minutes ago, Quicksilver1989 said:

    image.thumb.png.c55619133e431dac084597df54a606b0.png

    06z for midday saturday, is cold air still holding on? A few more do, thanks to the secondary channel low that forms on Friday, many of the GFS runs however show the incoming main low curving back westwards before reaching Ireland meaning its hard for cold uppers to return.

    Not a bad 06z but could be better, what I'd like to see is major trough disruption as it heads towards the channel, then forcing the low eventually eastwards instead. May still happen.

    The gap is closing! Bit like watching the poll trackers prior to a general election:)  Quick Qu Quicksilver - in terms of deciding what member is what, what time frame are you looking at - i.e Fri/Sat or further afield?

    Edit sorry reread your post so ignore the Qu

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    Posted
  • Location: Castle Black, the Wall, the North
  • Weather Preferences: Spanish Plumes, Blizzards, Severe Frosts :-)
  • Location: Castle Black, the Wall, the North
    5 minutes ago, icedust said:

    Polar Low?

    Re the possible polar low overnight/early tomorrow. Investigating the upper air it seems the trough is under a minimum of 500mb temperature (about minus 36) which is moving west under the otherwise undisturbed baroclinic flow. Baroclinic to those not in the jargon means thickness lines being advected, in this case cold advection slightly wobbling, maybe wobbling enough to generate the surface trough, not evident higher up. In short, a small area of increased instability moving west to southwest will pep up  and merge the showers in this trough (may become a very small centre). This instability is being extra invigorated by the surface trough dragging in warmer surface air ahead of it from the north. So a polar low? well may be a case of semantics, but it is definitely away from frontal zones and will be unstable; so yes Polar Low will do.Print

    Thck 500-1000hPa GFS Tu 27.02.2018 06 GMTHeight/Temp. 500 hPa GFS Tu 27.02.2018 06 GMT

    I only called it a polar low because I heard a professional weather forecast presenter earlier this morning call it a polar low..anyway, whatever it is its going to dump up to 8 inches of snow across northern england tomorrow!...model output is incredible for this week, especially further north in terms of potential longevity..exciting stuff is an understatement!..bitter cold incoming.:):cold:

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    Posted
  • Location: Darlington
  • Weather Preferences: Warm dry summers
  • Location: Darlington

    Fairly solid agreement now on the London ens for less cold air to arrive in the south later this week until about Monday after this it looks like it could turn chillier again just how cold remains open to question

    gefsens850London0.thumb.png.7b78bbe0a476a5c4ac375b55c5783db7.png

    Edited by Summer Sun
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    Posted
  • Location: Santry, Dublin, Ireland. 50 metres ASL.
  • Location: Santry, Dublin, Ireland. 50 metres ASL.
    1 hour ago, icedust said:

    Polar Low?

    Re the possible polar low overnight/early tomorrow. Investigating the upper air it seems the trough is under a minimum of 500mb temperature (about minus 36) which is moving west under the otherwise undisturbed baroclinic flow. Baroclinic to those not in the jargon means thickness lines being advected, in this case cold advection slightly wobbling, maybe wobbling enough to generate the surface trough, not evident higher up. In short, a small area of increased instability moving west to southwest will pep up  and merge the showers in this trough (may become a very small centre). This instability is being extra invigorated by the surface trough dragging in warmer surface air ahead of it from the north. So a polar low? well may be a case of semantics, but it is definitely away from frontal zones and will be unstable; so yes Polar Low will do.Print

    Thck 500-1000hPa GFS Tu 27.02.2018 06 GMTHeight/Temp. 500 hPa GFS Tu 27.02.2018 06 GMT

    Has this been officially classified as a polar low?

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    Posted
  • Location: NW LONDON
  • Weather Preferences: Sun, sleet, Snow
  • Location: NW LONDON

    Where do we stand then with the end of the week, has the GFS proved to be correct with less cold or even mild air moving into the south by Saturday?

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    Posted
  • Location: Shorne West, Kent
  • Weather Preferences: Sun in summer, Snow in Winter
  • Location: Shorne West, Kent
    2 hours ago, Frosty. said:

    We almost get 499 dam thickness on the Gfs 6z on wednesday and some fabulous sub zero maxima of minus 3 or 4 c with heavy drifting snow and severe wind chill making it feel like minus 10 to minus 15c in the gale force easterly winds!..can't believe it's so quiet in here!:cold::D

    Maybe in Yorkshire Frosty, but down here in the SE we have barely seen a covering this winter, let alone drifts.

    we ve been let down too many times ...still hoping though 

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    Posted
  • Location: Darlington
  • Weather Preferences: Warm dry summers
  • Location: Darlington
    11 minutes ago, lassie23 said:

    Where do we stand then with the end of the week, has the GFS proved to be correct with less cold or even mild air moving into the south by Saturday?

    Less cold in the south does look to be the form horse at the moment so Kudos to GFS for spotting this first

    UKMO for Thursday and Saturday - London goes from -1c on Thursday to 6c on Saturday and 7c on Sunday based on the current thought's of the met office

    UW72-7.thumb.GIF.8a9f3584ce36b55fa914723eb1fd7152.GIFUW120-7.thumb.GIF.bf89c36fdadda97c707115dc89a927e7.GIF

    Yorkshire north you are likely to remain in the colder air albeit the 850's won't be 'as low' but still a chance of snow

    Edited by Summer Sun
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    Posted
  • Location: West Kirby,Wirral 1m ASL
  • Location: West Kirby,Wirral 1m ASL

    The GFS keeps up it's trend for Friday "correcting" the low and the snow northwards, while the ICON keeps it further south.

    The first is good for me (and much of the country) and the second is not, don't know much about the ICON and so far this season all the GFS snow events have been exaggerated for my location (nothing stuck).

    So which model is the best for accuracy, does anyone know, do we need to get Harry Hill to decide?

     

    Edited by johnwirral
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    Posted
  • Location: Darlington
  • Weather Preferences: Warm dry summers
  • Location: Darlington

    Friday could see a spell of freezing rain in the south as the transition to less cold air begins this could cause major issues and needs to be monitored closely

    The freezing rain shows as green

    tempresult_xad4.gif

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    6 minutes ago, johnwirral said:

    The GFS keeps up it's trend for Friday "correcting" the low and the snow northwards, while the ICON keeps it further south.

    The first is good for me (and much of the country) and the second is not, don't know much about the ICON and so far the season all the GFS snow events have been exaggerated for my location (nothing stuck).

    So which model is the best for accuracy, does anyone know, do we need to get Harry Hill to decide?

     

    Here the forecast is 7c and easterly on Friday, Rain. Saturday Southerly 9c rain. So much warmer than it has bee or will be for a few days. . Northern CI’s Snow forecast 10cm today into Tuesday,  Southern CI, maybe the odd shower, so a few miles makes a difference. All CI’s  have Thursday as the big snowy event. Guess our forecasters are with GFS! We shall see! 

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    Posted
  • Location: Abbeymead ,Glos Member Since: July 16, 2003
  • Weather Preferences: Hot and thundery or Cold and snowy.
  • Location: Abbeymead ,Glos Member Since: July 16, 2003

    So GFS shows the show the low going up into Ireland and the icon shows its moving east along the channel...

    Clearly some major changes going to happen over the coming days.

    I personally dont like to trust the GFS when we get easterlies.

    It just doesn't cope well at all with it and is always more progressive than the other models back into warmer temperatures.

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    Posted
  • Location: Preston, 19m ASL when tide out :(
  • Location: Preston, 19m ASL when tide out :(

    I find it ironic that looking past this week and the trend for a breakdown of sorts to less cold conditions, that it can be blamed on the lack! of a Canadian vortex, so the block to our north makes a rather speedy move west in its absence . How many times does this chuffin seemingly endless vortex scupper our winters? Now we get the mother of all easterlies and the darn thing ain't there to block or hold off the speedy westward progression. that's my rather simple take on it anyway

     

    Still an amazingly cold week coming up!

    Edited by Nicholas B
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    Posted
  • Location: North East Hampshire
  • Location: North East Hampshire
    52 minutes ago, johnwirral said:

    The GFS keeps up it's trend for Friday "correcting" the low and the snow northwards, while the ICON keeps it further south.

    The first is good for me (and much of the country) and the second is not, don't know much about the ICON and so far this season all the GFS snow events have been exaggerated for my location (nothing stuck).

    So which model is the best for accuracy, does anyone know, do we need to get Harry Hill to decide?

     

    Surely the exact opposite of what you say is true?

    The low staying south keeps the UK in colder air for longer.

    Edited by Johnp
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    Posted
  • Location: Shorne West, Kent
  • Weather Preferences: Sun in summer, Snow in Winter
  • Location: Shorne West, Kent

    Strange winter......-NAO for the first and last days of the season only. 

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    Posted
  • Location: Castle Black, the Wall, the North
  • Weather Preferences: Spanish Plumes, Blizzards, Severe Frosts :-)
  • Location: Castle Black, the Wall, the North

    Feels like minus 35 / 40c (actual minus 22c) where our air is coming from in russia which is why we may see sub 500 dam thicknesses on wednesday as the 6z showed, certainly potential for it..such an exciting week with disruptive snow / drifting as well as sub zero maxima especially wed / thurs with frequent snow showers further east and blizzards spreading north across the uk later this week!:cold::)

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    Posted
  • Location: West Kirby,Wirral 1m ASL
  • Location: West Kirby,Wirral 1m ASL
    19 minutes ago, Johnp said:

    Surely the exact opposite of what you say is true?

    The low staying south keeps the UK in colder air for longer.

    Not really if you live in the east of the country then there will be frequent snow showers and opportunities for them to merge together, these don't deliver for my part of the world and the further west you go. While the longevity will be shorter much larger area of the country is forecast be the GFS to get the frontal snow and possibly extremely rare blizzards, which was originally only impacting the south, and areas further north will stay in the cold over the weekend or longer. I'd rather igo out with a bang than a wimper...

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    Posted
  • Location: Dundee - 140m ASL
  • Location: Dundee - 140m ASL

    I notice the UKMO run was very consistent with yesterday's 12Z but the fax charts look similar to the ECM run. Will be interesting to see what the UKMO 12z does - it's not exactly alone as the GEM isn't dissimilar and ICON too.

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    Posted
  • Location: East Ham, London
  • Location: East Ham, London

    Afternoon all :)

    If a week is a long time in politics, it's going to seem like and eternity in here as we watch the tribulations, machinations, projections and confusions of the Atlantic onslaught scheduled for a few days hence. Done and dusted it certainly isn't, "game over for the south", "all rain south of the M4" - bold calls for an event very difficult to predict.

    The ENS are clearly calling for a slackening of the frigid air - no surprise, 72-96 hours of -10 to -15 uppers in late February is unprecedented and unsustainable so the coldest of the air would ease eventually. Whether that translates to "less cold" rather than "mild" depends on your perspective and perception I suppose but within an overall context of heights to the north and east, cold air isn't likely to be far away and it's quite possible some northern areas will never lose the cold.

    Anyway, a quick look at some medium-range model output looking today forward to Thursday March 8th:

    ECM 00Z OP at T+240:

    ECM1-240.GIF?26-12

    A complex evolution and very interesting. Pressure is high to the NE with a new HP developing over Scandinavia and to the far NW with a complex trough in mid-Atlantic and a shallow LP over SE England. Uppers over the country range from just below zero across the south to -6 or -7 over Scotland. It's entirely possible a T+264 chart would see rising pressure to the NE and the LP heading SE (along the line of the trough) toward Iberia.

    GEM 00Z OP at T+240:

    gem-0-240.png?00

    Another interesting evolution. LP is centred over southern England and is moving slowly ENE. A chain of shallow LP extends SW from the Azores while pressure if high to the NW with a new HP cell coming off the eastern seaboard. The weather over the British Isles would be unsettled with rain for southern and eastern areas (based on positive uppers) and more wintry conditions further west and especially north.

    GFS 06Z OP at T+234:

    gfs-0-234.png?6

    A complex trough controls the weather over the British Isles with one centre to the NW of Ireland a new LP moving from the SW. Pressure is higher to the NW and is building via a mid-Atlantic ridge. The British Isles is in 0 to -4 uppers so rain or showers for many with snow restricted to higher ground. Further into FI and the trough pulls away east and south re-introducing colder air even as new Atlantic systems approach from the SW but look set to move SE into Europe.

    GFS 06Z Control at T+240:

    gens-0-1-240.png

    A complex trough sits just to the east with two LP centres over Scandinavia (really ?) and a smaller deepening LP to the SW but a transient ridge from Greenland covers the British Isles settling things down and re-introducing colder air with -8 uppers so frosty for most. Further into FI the battle between colder and milder air-masses continue but with warmer air coming across the British Isles from the SW by mid month.

    The 06Z GEFS at T+240:

    http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=240

    Surprisingly little spread so general agreement on LP dominance over the British Isles with a cold trough setting up as LP is held to the south or east. One or two members try to introduce milder conditions by forcing the trough north in mid-Atlantic but there's not much support for that at this time.

    In summary, part of the process of winter becoming spring is the battle between the colder and warmer air-masses and the fascinating synoptics and weather these can produce. We are looking at it in microcosm this weekend but it's the dominant feature of the weather stretching through the first third of March. This week's exceptionally frigid air will pass but there's no rapid transition to spring on the cards - rather, any milder incursion (IF it happens) looks to be brief with a strong signal early next week for colder (if not as cold as currently) conditions to return with the mildest temperatures likely next Monday (10-11c in the south so only just on average) and values set to fall from there.

    Clearly, the further north you are the more likely to remain in the colder air-mass so little chance of an appreciable warm-up in Scotland going forward. Further south it will depend on how the models end up dealing with the initial onslaught on Friday - it may be even if the bulk of the milder air stays to the south there will be a clear slackening of the frigidity in the south but the complexities of judging snow/rain/freezing rain events I'll leave to others at this time. ECM goes strongest on a return of heights over Scandinavia and some of the trough modelling from the other outputs just doesn't look feasible to me. As a final point, it might also be worth considering the accumulations of rain and snow-melt and the possible flooding implications if we get a protracted "battle ground" scenario between the competing air-masses.

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    Posted
  • Location: Castle Black, the Wall, the North
  • Weather Preferences: Spanish Plumes, Blizzards, Severe Frosts :-)
  • Location: Castle Black, the Wall, the North

    Looking at the GEFS 6z mean, northern uk stays very cold throughout the weekend and next week too whereas further south temps recover closer to average following the freeze although the mean shows it turning colder from the north again next week..longer term the temps recover generally but there are still some very cold blocked members out to mid march but with more milder options too..Enjoy this week coldies!:cold::)..if you're in the southeast, enjoy the Thames tickler!!:D

    Edited by Frosty.
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    3 hours ago, icedust said:

    Polar Low?

    Re the possible polar low overnight/early tomorrow. Investigating the upper air it seems the trough is under a minimum of 500mb temperature (about minus 36) which is moving west under the otherwise undisturbed baroclinic flow. Baroclinic to those not in the jargon means thickness lines being advected, in this case cold advection slightly wobbling, maybe wobbling enough to generate the surface trough, not evident higher up. In short, a small area of increased instability moving west to southwest will pep up  and merge the showers in this trough (may become a very small centre). This instability is being extra invigorated by the surface trough dragging in warmer surface air ahead of it from the north. So a polar low? well may be a case of semantics, but it is definitely away from frontal zones and will be unstable; so yes Polar Low will do.Print

    Thck 500-1000hPa GFS Tu 27.02.2018 06 GMTHeight/Temp. 500 hPa GFS Tu 27.02.2018 06 GMT

    Not totally convinced, compare with this case study - Snow and gales in eastern England from a North Sea polar low: 6/7 January 2010 - http://onlinelibrary.wiley.com/doi/10.1002/wea.740/full

    Typically a warm core system, it wouldn't be under a 500mb temperature minimum, though this system is very shallow.

    The 850mb Theta-e chart below shows a frontal structure already this morning along the west Norwegian coast (might well have been initiated by land/sea temperature/wind contrasts)

    nmm-5-1-0.thumb.png.9d59eb84116a828b8a465dbedbee43d9.png

    This is following a line of vorticity advection -

    euro1_24hr.thumb.png.902b325a8817bc340e261167810c87ff.png

    Edited by Interitus
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    Posted
  • Location: st albans
  • Location: st albans

    IMO, the only reason this is being described as a polar low is because it originated in the arctic !

    its a feature that has been predicted from the middle of last week - I was always of the mindset that polar lows form without such predcitivity ?????

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    Posted
  • Location: Grays, Thurrock
  • Location: Grays, Thurrock

    Icon at just T-33 interesting look at much further SE the energy disrupting is going and its actually not far from phasing with that small low over Greece now that would be backtrack from models if we get clean undercut. I doubt they will go that far but shows just how nothing decided for weekend yet as massive changes even within 24 hour timeframe

    12z

    iconnh-0-33.png?26-12

    12z

    icon-0-33.png?26-12

    6z

    iconnh-0-39.png?26-06

    6z

    icon-0-39.png?26-06

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    7 minutes ago, bluearmy said:

    IMO, the only reason this is being described as a polar low is because it originated in the arctic !

    its a feature that has been predicted from the middle of last week - I was always of the mindset that polar lows form without such predcitivity ?????

    It's well know it's incredibly hard to predict Polar Lows. In my opinion this isn't one. PL's are from a strong Arctic Northerly flow - This isn't. It's really that simple. 

    It's already exited Norway now so lets see how it looks on the radars. If it's strong which I suspect it will be in this cold flow crossing warm waters, then somewhere is going to get buried. 

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