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Model Output Discussion - Snow for some, but what else is in store?


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Ok, I have a bit of an update. Looks like the correction westward for today got the predicted snowfall about right . Nowcasting really comes into its own for this weekend. The team think another corre

Please allow me this small divergence mods... I feel like the last 3 weeks have been a bit of a blur. I caught Covid tail end of 2020 and was really rough with it. Low oxygen levels leading to in

I have had it once in October and again December the 30th. Theres a bit of chat over whether i have had it once had long covid and tested positive again as symptoms came back in December or caugh

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Posted
  • Location: Stroud, Gloucestershire
  • Weather Preferences: Extreme!
  • Location: Stroud, Gloucestershire
    1 hour ago, kold weather said:

    If you want a really good demonstration as to why the surface airflow is SO important, take a look at Saturday:

    GFSOPEU06_24_1.thumb.png.0cd0dc42cc70380986e7f59aedd4e367.png

    You'd look at that and say there should be no chance really of snow.

    850hpa temperatures are somewhere between -1/2c for areas that are at risk of snow, which typically would be too warm from this sort of set-up.

    BUT what isn't shown all that well is there is a slight sharpening of the low pressure area as it comes through, which switches the winds towards a more southerly direction which then keep the airflow from getting too much of an Atlantic influence ahead of the feature and keeps more of the continental flow going.

    The earlier that happens, the further south the snow risk will extent. That combined with a signal that the front edge of the precip shield will also strengthen as it comes further east as well, probably in response to the sharpening and strengthening of the wave feature previously mentioned.

    Absolutely right.

    Also important to point out for anyone learning about the processes, is that the "continental flow" you describe is a much dryer airmass with colder dew points/wet bulbs and a lower freezing level which allows for snowfall in less cold 850s. We have had the 850s debate many time this year, but when the airmass is less maritime the parameters for snowfall change, and the 850s don't need to be as cold.

    Edited by chris55
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    Posted
  • Location: Reigate Hill
  • Weather Preferences: Anything
  • Location: Reigate Hill
    4 minutes ago, MJB said:

    Wouldn't the milder weather be because of the Southerly tracking LP's 

    The mean in FI suggests the easterly flow of the NH is setup North of Scotland and we will get a westerly undercut:

    gensnh-31-1-336.thumb.png.e60992a0fb520e6f72a367bd77068dfc.pnggensnh-31-0-336.thumb.png.c354a3a949c1f76f68158c251cfd28d2.png

    These are for circa d14. The axis of cold veering towards Asia<>Canada. This is looking like a development for post-d12? The gefs support the likely outcome though the op is less progressive and the control a variation on that outcome which is a bit colder:

    gensnh-32-0-336.thumb.png.c90e1d14529c4073eb6a5bba35dfccbe.png

    The areas of max uncertainty are on the above cold-axis, not for the UK outcome. Assuming the gefs are right, and this is currently trending, then a warming up period maybe inevitable and we can just hope this is not the blocking pattern signature.

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    Posted
  • Location: 50/50 Greece/Germany
  • Weather Preferences: Cold winters, hot summers
  • Location: 50/50 Greece/Germany
    29 minutes ago, sebastiaan1973 said:

     The distribution of area's of high/low pressure has been okay for some of us (still waiting for the first snowflake) but they weren't good enough for all of us. Mostly polar maritime air.

    Well, you live so close the the "hot" sea, what do you except? M-Europe climate is ALWAYS domintated by ATLANTIC REGIME due the gulf stream. Climate changes do the rest (ice coverage, sea ice cover etc).

    The idea of prolonged ice-cold spells that last over weeks, well, that is history now. I did not have significant winter since years, and I am in the middle of Germany, even farer away from the boiling north sea...

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    Posted
  • Location: Stroud, Gloucestershire
  • Weather Preferences: Extreme!
  • Location: Stroud, Gloucestershire
    1 hour ago, MJB said:

    image.thumb.png.9e2d13e7db5243da47d3bc27028e9249.png

    Control is more than interesting 

    I think a cold easterly is a good punt going into February, but long way off.

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    Posted
  • Location: 50/50 Greece/Germany
  • Weather Preferences: Cold winters, hot summers
  • Location: 50/50 Greece/Germany

    2 Scenarios for +240 with a 72% Cluster is 😛

    spacer.png

    FI

    spacer.png

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    Posted
  • Location: Liphook
  • Location: Liphook
    32 minutes ago, sebastiaan1973 said:

    With a synoptical heaven you don't need luck 😀

    Oh for sure.

    However, for large snowfalls you definitely don't need synoptic heaven either.

    Some of the Uk's greatest ever snowfalls have come right on the borderline between mild/cold. We came very close in the last week to something that could have delivered UK some very decent snowfalls, but it was indeed just a touch too warm. Could just be bad luck in terms of the upper lows not quite placing themselves correctly, or could indeed by AGW to some extent (if you have a situation that is about 0.5c cold buffer on average for snow, then you warm it by 1c...it then becomes a sleet/rain event rather than snow as your now +0.5 of that buffer...I know though thats a simplistic approach!)

    Edited by kold weather
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    Posted
  • Location: Gorslas 178m abs
  • Location: Gorslas 178m abs

    Has anyone got a small pin to push into the back of our 'Winter hopes' router and press reset?

    Model volatility is huge and post 120 hours very uncertain, I think for many of our own sanities we'd be best freezing this forum until Monday, let's see what we have to contend with then, all this bickering and downbeat sniggering, does nobody any good. 

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    Posted
  • Location: Banbury
  • Weather Preferences: Deep Deep Snow causing chaos
  • Location: Banbury
    2 minutes ago, Adam lufc said:

    The MODEL OUTPUT for up here has been fantastic. Weve had four big snow events in 3weeks already. A beautiful day today with 6inch laying snow all around.

    I take it you are in Yorkshire ? 

    Can you please add your location to your profile 

    Cheers 

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    Posted
  • Location: Near Gouda, Holland 6m Below sea level
  • Weather Preferences: Sun, snow, ice. Very hot or very cold.
  • Location: Near Gouda, Holland 6m Below sea level
    34 minutes ago, Man Without Beard said:

    Right this is a pure speculation post, based on something I've noticed on the GFS parallel in FI:

    image.thumb.png.91ede030752400cc15e0d971b48920df.png

    Notice that little area of surface high pressure poking from Russia back to the North Sea? Back-door cold very nearby? Combined with low pressures running regularly into Southern Britain?

    Will probably come to nothing but I will be looking out to see if this pops up again!

    Please don't take this too seriously as this is purely for enjoyment (the European part of the chart, not the Greenland part!), but...

    image.thumb.png.d24e70a2b4545a5e5d5d85532c59ee6e.png

     

    ECM had something similar at 240h two days ago.
    In that massive, deep low all sorts of smaller features pop up and together they can create a High.
    With a little more CAA the formation of a proper Scandi High is not unheard of.

    I think that is what makes this setup still fascinating. There is the large scale setup, which most of us hope will put Greenland Highs and Arctic Highs in the best location for cold coming our way, but on the smaller scale there can be interesting developments too, that might have large repercussions for us.

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    Posted
  • Location: Brighton, East Sussex
  • Location: Brighton, East Sussex
    3 minutes ago, Frosty Winter said:

    ‘Nothing to suggest otherwise.’

    The actual models:

    F8A93371-E345-450D-9BB2-3EA803C2104B.thumb.gif.385f58f5db2a89c18093b80ca9b3e058.gifA317F9C9-7E62-4558-AE25-80A3137C6EEA.thumb.png.651be0f978c8b83429c951ae43b2383e.png

     

    Not to be obtuse but day 8 charts all winter have been utterly useless, here’s the ECM for 192 now here it is 4 days later, all winter the models have overdone these ridges and attempted HLB

    EBE39086-84AB-4F5D-B2BE-1391D2F91B44.jpeg

    961B8FF1-6EAA-4346-9D52-2B1A930E9940.gif

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    Posted
  • Location: Hinckley
  • Location: Hinckley
    10 minutes ago, Adam lufc said:

    The MODEL OUTPUT for up here has been fantastic. Weve had four big snow events in 3weeks already. A beautiful day today with 6inch laying snow all around.

    Cheers for rubbing it in

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    Posted
  • Location: Roznava (Slovakia) formerly Hollywood, Co Wicklow
  • Weather Preferences: continental climate
  • Location: Roznava (Slovakia) formerly Hollywood, Co Wicklow
    1 minute ago, Roger J Smith said:

    This modern warming doesn't necessarily mean less snow for everybody. There is probably a decrease in many climate regions, but the northeastern U.S. have seen an increase. I've got a thread on historical trends at Toronto and NYC over in the climate science forum. Toronto recently have seen a 20 to 30 per cent decrease in mean annual snowfalls. NYC on the other hand has seen a return to levels attained in the late 19th century. The average of all years annual snowfall 1869-2020 is 28.6" and for 1991-2020 it was 29.9" ... for 1961-1990 it was only 23.9" and temperatures have actually warmed slightly despite those snowfall values. There is a lot of variability recently, several winters have had very low totals (2019-20 was only 4.8") but several others notably around 2010 to 2016 had huge snowfalls by their standards. Feb 2010 and Jan 2011 both set monthly records for snowfall at NYC. 

    There has been a significant decrease in snowall in Central Europe over last decade or so. High Ground above 1000m.asl not so much but lowland areas hardly see more then few days of settled snow all winter. There are a lot of situations with precipitation but we are most of the time on the wrong side of marginal for sure, similar setup would have produced snow in past. The problem I see is that we can not settle in a synoptic which will cool down the surface and the spells of milder weather are very effective in quickly draining precious cold weather. Example will be next week when we will go from -15 uppers which last for days in to mild rain within a day, not even a dumping of snow before the front reaches us.

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    Posted
  • Location: Liphook
  • Location: Liphook

    The other thing about snow event that are marginal that is often overlooked is TIME.

    ARPEGE ensembles have a great example of this. These two scenarios are broadly very similar, including intensity of front and also 850hpa profile is not that different for both their times.

    pearome-1-19-0-4.thumb.png.2b7296cc67098e6518353df00ce62411.pngpearome-1-23-0-7.thumb.png.544c9999a8546eb9ce6f39347a67208c.png

    The major difference is the time of arrival.

    The left hand chart has the front interacting with the cold air still during the peak overnight hours where the air is at its coldest.

    The right hand chart is for 9z. Whilst its only just a touch after that early morning period, there is already enough warming at the surface to already reduce the area of snow for the south.

    When we are in a *really* borderline snow situation, even what looks like a relatively small shift in timings can make a major difference to how much snow actually falls.

    Edited by kold weather
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    Posted
  • Location: Buxton
  • Location: Buxton
    8 minutes ago, kold weather said:

    The other thing about snow event that are marginal that is often overlooked is TIME.

    ARPEGE ensembles have a great example of this. These two scenarios are broadly very similar, including intensity of front and also 850hpa profile is nearly identical for both thier times.

    pearome-1-19-0-4.thumb.png.2b7296cc67098e6518353df00ce62411.pngpearome-1-23-0-7.thumb.png.544c9999a8546eb9ce6f39347a67208c.png

    The major difference is the time of arrival.

    The left hand chart has the front interacting with the cold air still during the peak overnight hours where the air is at its coldest.

    The right hand chart is for 9z. Whilst its only just a touch after that early morning period, there is already enough warming at the surface to already reduce the area of snow for the south.

    When we are in a *really* borderline snow situation, even what looks like a relatively small shift in timings can make a major difference to how much snow actually falls.

    Yes, the timing is related to the speed of the front which I discuss here.

    The set up tomorrow relies on cold surface air which is shallower further west. This means, following any temporary front edge light snow (poss 30 mins), the situation will become quite marginal with heavy precip producing snow, moderate precip producing rain. Nonetheless accumulations of 3-7cm above 250m and 1-4cm in some areas below 250m are possible in this central zone covering Yorkshire (east of Manchester), the Central Midlands and parts of Central Southern England. East of the A1, especially into Lincolnshire and East Anglia the cold air is colder and more expansive in the atmosphere. The front is also slowing down. This will produce more conducive conditions for longer below 250m. A prolonged spell of moderate to heavy snow is therefore likely across central / southern Lincs and East Anglia. Also parts of the SE, here mostly above 250ft favoured due to a southerly wind. Totals here are most likely to fall between 1 and 5cm for roughly 60% inland to higher levels above 100-150m up to 8cm possible. Again some uncertainty related to the speed of the front too fast and it will remove the surface cold too quickly and slower will allow more snow. The first would drastically limit snow totals.

    Edited by Kasim Awan
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    Posted
  • Location: Aberporth S W Wales
  • Location: Aberporth S W Wales
    42 minutes ago, Vikos said:

    2 Scenarios for +240 with a 72% Cluster is 😛

    spacer.png

    FI

    spacer.png

    Unfortunately its the smaller cluster 27% at 240 we need, well most away from then north do anyway.

    Edited by KTtom
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    Posted
  • Location: Nr. Tunbridge Wells (150m/450ft asl)
  • Location: Nr. Tunbridge Wells (150m/450ft asl)
    13 minutes ago, Kasim Awan said:

    Yes, the timing is related to the speed of the front which I discuss here.

    The set up tomorrow relies on cold surface air which is shallower further west. This means, following any temporary front edge light snow (poss 30 mins), the situation will become quite marginal with heavy precip producing snow, moderate precip producing rain. Nonetheless accumulations of 3-7cm above 250m and 1-4cm in some areas below 250m are possible in this central zone covering Yorkshire (east of Manchester), the Central Midlands and parts of Central Southern England. East of the A1, especially into Lincolnshire and East Anglia the cold air is colder and more expansive in the atmosphere. The front is also slowing down. This will produce more conducive conditions for longer below 250m. A prolonged spell of moderate to heavy snow is therefore likely across central / southern Lincs and East Anglia. Also parts of the SE, here mostly above 250ft favoured due to a southerly wind. Totals here are most likely to fall between 1 and 5cm for roughly 60% inland to higher levels above 100-150m up to 8cm possible. Again some uncertainty related to the speed of the front too fast and it will remove the surface cold too quickly and slower will allow more snow. The first would drastically limit snow totals.

    And yet presumably faster also means it arrives earlier when the air is colder, whereas slower means it arrives later when the sun has had the chance to warm the air just enough to be the wrong side of marginal...

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    Posted
  • Location: Buxton
  • Location: Buxton
    6 minutes ago, wellington boot said:

    And yet presumably faster also means it arrives earlier when the air is colder, whereas slower means it arrives later when the sun has had the chance to warm the air just enough to be the wrong side of marginal...

    The solar heating wont mean too much as the front will produce an adiabatic temp. Imo it's the speed of the front which will affect how much evapo cooling will occurr and how quickly the cold layer is mixed.

    Edited by Kasim Awan
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    Posted
  • Location: County end Oldham 202 m Above sea level
  • Location: County end Oldham 202 m Above sea level
    49 minutes ago, Battleground Snow said:

    Excellent MJO update by the ECM. We are still in 3 now, but look how fast it is predicted to skate through cod in just a few days and towards phase 6 and 7.

    Matt H tweeted more information about the MJO which I'll pop in the tweet thread.

    I think we will start to see some better blocking in the Atlantic sector based on this.

     

     

    ECMF_phase_MANOM_51m_full (1).gif

    Potentially big news!!

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