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


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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
    1 minute ago, samadamsuk said:

    Yes good call SteveM, clocked that post (my god you do stick your neck out sometimes! Why not though hey..). Interesting to see if the block modifies those warmer 850s as they come in to range - ensembles run on the same but simpler dna so even when unanimous they're not necessarily real odds. 

    Interesting times! 

    :) Samos

    Is that the SM 10.30 post, can't see it anywhere.

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    Knee-jerk, a joke!?...if that is what you believe then simply don't follow. I was simply highlighting what the EC ENS are showing and to be honest certain people need to read before commentating, perh

    Yes, I recognise these sage pieces of sentiment so well. The signals are always wrong, and the professionals (and others) who try to present and explain them, when an operational appears to take away

    This is an unusual set up for the UK, hence the model variations. The bigger picture according to seriously knowledgeable people like @Tamara tends to suggest that the hemispheric factors that actuall

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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

    The Gfs 18z deserves a Boom for Saturday across parts of the north:bomb: Quite a bit of snow:shok:

    18_93_preciptype.png

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    Posted
  • Location: Heckmondwike, West Yorkshire
  • Location: Heckmondwike, West Yorkshire
    1 minute ago, Frosty. said:

    The Gfs 18z deserves a Boom for Saturday across parts of the north:bomb: Quite a bit of snow:shok:

    18_93_preciptype.png

    Mainly on high ground unfortunately. Uppers just a tad too high for most of us.

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    Posted
  • Location: Cirencester
  • Weather Preferences: Supercells
  • Location: Cirencester
    4 minutes ago, snowray said:

    Is that the SM 10.30 post, can't see it anywhere.

    It was before the easterly came in to the charts - atleast as far as I could tell! :)

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    WHY THE ECM 12z IS "NOT" MILD!

    There has been quite a lot of nonsense spouted on the thread today and I have found some of it quite exasperating. I am about to prove why the ECM 12z run is not a mild one. I do not want to sound like I am preaching but I feel that a few basic lessons in understanding the charts is required. Several of the 12z models such as the GFS and ECM have shown the Scandinavian HP sinking south-eastwards from around D6 to D8 introducing more of a slack south-south-easterly flow for several days. Yes, this does temporarily cut off the direct supply of the deep cold from the north-east and the 850s do mix out and warm up to some extent but that's about it. I have tried to explain for several weeks now how surface cold will become entrenched and that much of Europe is likely to have at least some snow cover by early next week.

    Let's accept for now that the ECM evolution is accurate, although I find part of it rather questionable. I have heard several comments that the air is going to come from North Africa! Just because the flow appears to come from a south-south-easterly direction does not mean that this is the wind or temperature source. A basic principle is to understand the coriolis force. In simple weather terms we see winds blowing towards a LP system and away from a HP system at the surface. The winds do not blow parallel to the isobars but they are "backed" across them to some extent. For example, a southerly flow would typically have south-easterly winds. When we have a particularly large area of HP this displaces more air from its centre to its periphery in the surface layers (at the surface and slightly above it). The backing or cross isobar effect is even greater. Take the T+192 chart below which shows a slack south-south-easterly flow with the HP centred over Germany and Denmark. The winds will be east-south-easterly and the air will be coming from central Europe, let's say Switzerland (I am not going to go into possible Alpine fohn effects which may or may not have a small impact). The immediate source of the air will be from under the HP. The original source would actually be much further east with the air slightly modified but flowing around the southern flank of the HP before it migrated further south. This surface layer would appear to have very little wind to shift it. At this time of year, it is likely to remain very cold and dry with very low dew points. Yes temps would rise briefly above freezing in any sunshine but with severe overnight frosts. In cloudier conditions the daytime temps would be lower but with only slight frosts. Any freezing fog would keep daytime temperatures well below freezing. A rather different scenario to north African zephers (somebody even mentioned Saharan dust!).

    Of course much will depend on how cold it gets over most of Europe during the next 5 days. If you have followed my daily Euro temp and pressure watches which I post around 0730 each morning, you will see the answer is likely to be very cold. Now let's go through the charts. Another point, I notice that most of the European charts posted on the thread are the default ones from Meteoceil. If you click on "Europe 2" you can get a wider picture (not the northern hemisphere view) but one that goes further in each direction, like the charts I show below. This feature is available for most of the models except UKMO and, strangely, the GEFS ens means. The position up to T+120 is still showing the cold easterly. I pick them up from T+144. The HP has sunk southwards but is ridging across the UK. So, if this verifies, the cold air would be able to stagnate right over us. This continues into T+168. Then at T+192 through to T+216 the flow veers to a more south-south-easterly one. I have already described the likely surface conditions for this period. Then the T+240 chart starts to show two possible much colder evolutions. The main Atlantic LP systems are way out west, closer to North America. The small slack area of LP to our south looks like it will perform an undercut as it can hardly move northwards with the strong build of pressure towards Greenland which developed from T+192 to T+240. It is strengthening a south-easterly flow (with easterly winds) dragging in air from the near continent. If this continued it might re-introduce an easterly. The far more likely evolution going by the T+216 to T+240 charts would be the deepening low heights to spill down into Scandinavia with the Greenland HP starting to exert its influence and we move into phase 2 with the northerly streaming down across the whole of the UK probably by around T+288.

    The 850s do mix out and we might see them in the 0c to +4c range for a few days if those charts verify. Meanwhile, let's look at the surface temps. ECM do not publish these on their free-to-view Meteoceil charts so I found a similar pressure chart to the ECM 12z T+192 with the GFS 12z T+192. This also has the HP just to the east of us and a gentle south-south-easterly flow. The 850s are quite similar too. The T+192 shows temps across much of the UK around 4c and up to 8c along the south coast. This is a 1300 chart which would be close to max temps, so I include the T+186 charts with 0700 temps which will be closer to min values. This shows most of the country around or slightly below freezing. These charts almost always understate any surface cold so I would say that these are about the highest possible values under the GFS and ECM evolutions at that time. So definitely not mild!

    ECM 12z Pressure:

                                    T+144                                                   T+168                                                T+192                                                 T+216                                                T+240

            ECE1-144.GIF     ECE1-168.GIF     ECE1-192.GIF    ECE1-216.GIF   ECE1-240.GIF

    ECM 12z 850s:

                                    T+144                                                   T+168                                                T+192                                                 T+216                                                T+240

            ECE0-144.GIF?07-0     ECE0-168.GIF?07-0     ECE0-192.GIF   ECE0-216.GIF    ECE0-240.GIF

    GFS 12z:

                                 Pressure  T+192                                           850 Temps  T+192                         2m Surface Temps at 1300 T+192               2m Surface Temps at 1300 T+186  

                gfseu-0-192.png?12               gfseu-1-192.png?12              gfseu-9-192.png?12                gfseu-9-186.png?12    

    I believe that the ECM evolution is a complicated one and may not be right but that's more of an opinion and unlike my analysis above, I cannot really back that view up.I know that much of the other 12z model output has been inconsistent. and whilst writing this, I have not yet had a chance to view the GFS 18z but judging by the number of new posts (over 60 in the last hour or so) I'm assuming that it's an upgrade. overall, I firmly believe that the upcoming cold spell will be a good one with a few snow chances. I think that the HP will not sink nearly so quickly and I'm expecting the phase 2 northerly (and possibly a further easterly later on) to deliver something even more special. Cold or very cold throughout but perhaps a couple of slightly less cold days during the transition. I'll be back in the morning with the latest on the HP and the deepening cold block

    EDIT:  Wrong assumption by me. The last half of the GFS 18z is struggling with the phase 2 cold spell. It looks like it makes an attempt to bring in a northerly but then backs off. Where on earth is that Atlantic flow coming from? Some quite extraordinary things going on. The models are going all over the place from D6 onwards for at least the next few runs. Be careful not to over react to a single model run. Now to quickly spin through over 70 posts. I hope there are rather more better quality views expressed.

    Edited by Guest
    Correcting typos and to ensure that all the links and charts work properly.
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    Posted
  • Location: New Ash green 150M / 500 FT
  • Location: New Ash green 150M / 500 FT
    20 minutes ago, snowray said:

    Is that the SM 10.30 post, can't see it anywhere.

    Starting it now :( - its probably been covered anyways...

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

    For want of a bit of clarity...this is a dead ringer for ECM mean that all the hoo harr was about earlier

    gfsnh-0-240.png?18

    EDH1-240.GIF?07-0

    As you can see, Greenland heights fail to establish and a day later you get this

    gfsnh-0-264.png?18

    Case closed your honour.

    Edited by CreweCold
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    Posted
  • Location: Isle Of Lewis
  • Weather Preferences: Wild!
  • Location: Isle Of Lewis
    1 minute ago, nick sussex said:

    The GFS looks similar to the ECM upto T240hrs, the models still reluctant to send energy se'wards and want to keep high pressure over southern Europe. This is likely to change as they start modelling the phase 8 MJO.

    The MJO is expected to be robust and have an effect on the USA pattern going off comments from NCEP and that's good news for us in western Europe.

    Expect bigger jumps forward to high pressure to the north over the next few days in the outputs.

    I can see the high pressure to the north evolvong sending down a very potent nly blast +240hrs. 

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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
    4 minutes ago, Steve Murr said:

    Starting it now :( - its probably been covered anyways...

    Ahh ok, thought I had missed it somewhere.

     

    The 18z Hirlam is another upgrade, showers turning wintry by tomorrow evening and some of them look like they will be a bit more than just "flurries", maybe super flurries.:)

    hirlamuk-1-28-0.png

    hirlamuk-1-32-0.png

    hirlamuk-1-41-0.png

    hirlamuk-1-48-0.png

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    Posted
  • Location: Heckmondwike, West Yorkshire
  • Location: Heckmondwike, West Yorkshire
    4 minutes ago, CreweCold said:

    For want of a bit of clarity...this is a dead ringer for ECM mean that all the hoo harr was about earlier

    gfsnh-0-240.png?18

    EDH1-240.GIF?07-0

    As you can see, Greenland heights fail to establish and a day later you get this

    gfsnh-0-264.png?18

    Case closed your honour.

    Fair point Crewe but cmon, this is the pub run at 10 days out. If I remember correctly, the 18z consistently never went for the upcoming easterly.

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    Posted
  • Location: Crewe, Cheshire
  • Weather Preferences: Snow, storms and other extremes
  • Location: Crewe, Cheshire
    2 minutes ago, blizzard81 said:

    Fair point Crewe but cmon, this is the pub run at 10 days out. If I remember correctly, the 18z consistently never went for the upcoming easterly.

    It was to highlight how that ECM mean was possible with only 9 Greenland High scenarios. There could have been a large cluster showing similar to what the GFS has shown this evening i.e heights almost making it to various degrees.

    Thought it was an apt time to illustrate seeing as we've just seen an op run which produces an almost exact replica of that mean chart.

    Edited by CreweCold
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    Posted
  • Location: Pershore
  • Location: Pershore

    A quick reminder:

    1. If you want to moan, ramp or just banter randomly about the weather/models etc then this isn't the thread for it, the banter/ramp and moans thread is (clue is in the name :D)

    2. If you are getting annoyed by the off topic moans etc, then don't make it worse with your own off topic moan about them please. 

    3. If you report a post, please give us a chance to respond - reporting, then posting a reply to the post 2 minutes later kind of defeats the purpose and makes you part of the problem.

    4. If you want to chat about bbc forecasts, met office forecasts and the like please head over to the relevant threads in the winter forum.

    Banter thread:

     

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    Posted
  • Location: NR LOURDES SW FRANCE
  • Location: NR LOURDES SW FRANCE
    2 minutes ago, snowbunting said:

    I can see the high pressure to the north evolvong sending down a very potent nly blast +240hrs.

    Yes that's the plan! the GFS lower resolution falls of a cliff which is what it tends to do in these situations. The MJO is moving at some speed so the models will be playing catch up. And what tends to happen is that they get caught between the impacts of one phase that's why they want to leave higher pressure over southern Europe. That's the leftovers of phase 7. Once the phase 8 starts becoming the main player we should see energy heading se first towards Iberia and then further east.

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    Posted
  • Location: Heckmondwike, West Yorkshire
  • Location: Heckmondwike, West Yorkshire
    1 minute ago, CreweCold said:

    It was to highlight how that ECM mean was possible with only 9 Greenland High scenarios. There could have been a large cluster showing similar to what the GFS has shown this evening i.e heights almost making it to various degrees.

    Fair point, cheers

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    Posted
  • Location: st albans
  • Location: st albans
    1 minute ago, nick sussex said:

    Yes that's the plan! the GFS lower resolution falls of a cliff which is what it tends to do in these situations. The MJO is moving at some speed so the models will be playing catch up. And what tends to happen is that they get caught between the impacts of one phase that's why they want to leave higher pressure over southern Europe. That's the leftovers of phase 7. Once the phase 8 starts becoming the main player we should see energy heading se first towards Iberia and then further east.

    The modelling has a transitory look about it - has done for a while now. That's why I'm not bothering to make any in depth analyses.  the only unexpected thing that seems to have ticked down well from the eps is the higher heights and associated  rising uppers east of the Iberian trough. 

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    Posted
  • Location: Heckmondwike, West Yorkshire
  • Location: Heckmondwike, West Yorkshire
    2 minutes ago, Nick F said:

    Tomasz Schafernaker not particular excited by the upcoming cold 'snap' other than some flurries, so lets see if we can be more enthusiastic than Tom re: snowfall?

    T+72 fax chart shows a developing warm front moving west from N Germany and Denmark toward the UK, IMO this marks a plume of moisture being drawn NW out of central Europe and, with lift from the 500mb trough and surface low moving east over the N Sea will probably enhance snow showers Friday PM and Friday night into Saturday morning

    t+72 fax and PWAT (Precipitable Water)

    20170207_72.thumb.png.aa4d337b4107cf41d097fbe6a8afefa7.png72.thumb.png.235e86760cdeaca93dfd663a99220870.png

    A look at forecast skew t for Essex Friday PM shows increase in moisture in lower layer (more snowfall) between T+72 and T+82 i.e. where dew point line (left) is merged with temp line (right) the air is saturated ... notice thicker layer of moisture at T+84 between 950 and 800 hPa. This fairly representative for eastern coastal counties of England

    skew72.thumb.png.9defce290403c476d608a03863b944a7.pngskew84.thumb.png.88a59f2c5542a7eba63f9805609103c0.png

    T850s down to -11C across England Friday night and not often we see partial thicknesses (850-1000hPa) 127 gpdm

    thk81.thumb.png.2a2ced99c3b95feced2d7d9b0c6537a1.png81.thumb.png.ef0707ccf0b1a89fb150da3082d653b5.png

    500mb trough providing plenty of lift Friday

    H500.thumb.png.8ce0645776a9bedbaa22d201c0228113.pngrv500.thumb.png.a495843eb69a1ccde829836fd1a070e0.png

    So looks like there is the dynmaincs there to pep the snow showers Friday night and probably through Saturday too as that trough and increased moisture moves in.

    I think I trust your judgement more than Schafernaker. He promised me a metre of snow back in Feb 09 on one of his ramp forecasts. I got 4 inches lol.

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    Posted
  • Location: Eshaness, Shetland Islands
  • Weather Preferences: Cool and Stormy
  • Location: Eshaness, Shetland Islands
    5 minutes ago, snowray said:

    Ahh ok, thought I had missed it somewhere.

     

    The 18z Hirlam is another upgrade, showers turning wintry by tomorrow evening and some of them look like they will be a bit more than just "flurries", maybe super flurries.:)

    hirlamuk-1-28-0.png

    hirlamuk-1-32-0.png

    hirlamuk-1-41-0.png

    hirlamuk-1-48-0.png

    Yes. Wednesday evening until Friday evening is where there is the *opportunity* for some light sleet and snow showers along eastern coastal counties I.e. Northumberland, Durham, Yorks, Lincs, Norfolk....however, low *risk* of anything meaningful. Unfortunately, snow prospects for the weekend have, in my opinion, downgraded due to the slightly warmer sectors and higher dewpoints from the small low off the east coast on Saturday. Again *low* risk at sea level with rain being the likely outcome. Opportunity for some snowfall on the eastern slopes of the Pennines say 200m+

    It will still feel raw with high windchill and a strong breeze off the sea in the east. Western areas may stay dry and bright. 

     

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    Posted
  • Location: NR LOURDES SW FRANCE
  • Location: NR LOURDES SW FRANCE
    1 minute ago, bluearmy said:

    The modelling has a transitory look about it - has done for a while now. That's why I'm not bothering to make any in depth analyses.  the only unexpected thing that seems to have ticked down well from the eps is the higher heights and associated  rising uppers east of the Iberian trough.

    Yes I think transitory sums it up well. It was notable that the chief forecaster talked about the MJO effecting the temp profiles for the USA because that's the first time this winter that the MJO is expected to have a proper impact over there. It can't have an impact there without effecting us in western Europe given the response towards the eastern USA.

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    Posted
  • Location: Caterham-on-the-hill, Surrey, 190m asl (home), Heathrow (work)
  • Location: Caterham-on-the-hill, Surrey, 190m asl (home), Heathrow (work)

    IMO seems to be a theme in the GFS in particular today, as played out by the 12z GEFS z500 and now 18z GFS, to go from an east based -NAO on to develop a west-based -NAO with time?

    gfs-ens_z500a_nhem_fh72-192.thumb.gif.2eced3112d9b5653eab0ad0839945149.gif

    We start off with Iceland/Greeny height rises in next 7 days as east coast trough amplifies flow downstream, with increasingly -ve NAO, but strengthening southern stream over N America may pull back west the troughing over SW Europe too.

    Not ideal, just have to hope the trop PV can drop down into Scandi quickly like EC high res day 10, certainly supported further by 10-15 day 12z EPS z500

    eps.thumb.png.ba7aeec55769a32804e3307cfc5661fe.png

    Edited by Nick F
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    Posted
  • Location: Saltdean,Nr Brighton,East Sussex,Hither Green,SE London.
  • Location: Saltdean,Nr Brighton,East Sussex,Hither Green,SE London.
    On Tuesday, February 07, 2017 at 20:38, Summer Sun said:

     

    In reality  a block over Greenland appearing at 240 hrs is going to take another 4 or 5 days to start to influence our UK weather, so it would still come under the late February/early March cold snap as the tweet eluded too.

    I think some folk are just hoping for  things to swing in our favour 'ovenight' or rather from less cold 13th- 17th, to bitter on the 18th!

    This current Scandinavian High with its 'Nicki Minaj' backside hanging down into Europe was never going to produce deep cold and snow.

     It's been a long time since I've seen a 'sleek' Scandinavian  High form over that way, a flow straight from the Russian steps.

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