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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: Sussex
  • Location: Sussex

    65278032

    At T84 the low appears to be further away on the colour Fax charts, Im not whilst the upper warm front is unwelcome, If the main warm front was to align NE/SW close to the coast of Kent we could have a hell of a lot of snow ahead of this with a stiff NE wind.  This chart does seem at odds to the Met Office forecast which implies the snow moves up from the SSW. Unless they are linking the snow to the Occlusion following the surface warm front. What a messy situation this is. If only that Scandi High could be 400 miles further SW...

    Edited by Snowbound
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    A POSSIBLE RARE FREEZING RAIN OR ICE STORM EVENT ON THURSDAY TO SATURDAY?  A COMPARISON TO THE FAMOUS JANUARY 1940 EVENT 

    While I'm awaiting some decent snow down here in Exmouth, I thought that some of you might like to read this. In this post I will consider the "possibility" of a freezing rain event suggested for the far south and south-west in the current set up for the end of this week. I will then compare this pattern to the UK's most famous example of this phenomena - the January 1940 "ice storm". Before I go any further, I must stress that this is not a forecast and these events are so rare that the chances of having a major event, even with the current synoptic patterns on offer, are still relatively slim. It is also dangerous to use any analogues with past events as there are always some differences. I will endeavour to point these out later on. I shall start with a look at the current output for the critical period before moving on to the 1940 event. Finally, I'll make the comparisons and highlight the differences.

    The Current Output for the Critical Period: 

    All the models currently show an Atlantic LP somewhere around The Azores (that makes a change doesn't it!) with an exceptionally cold easterly flow established over the UK. In fact it is sourced from Siberia and stretches through Russia, Scandinavia, Europe, the UK and more than halfway across the Atlantic. Then most of the models show the LP moving east or north-east towards Spain and Portugal and on into Biscay. It's possible that the output will change and the LP will not make any inroads into the cold block at all. This, right now, seems the least likely of all the scenarios. I shall assume that it does arrive on our door step. It is how the models handle developments from there that will be critical and I shall pick it up from there. I have already written four posts on this subject on the MOD during the last week. One comparing the current set up with the extremely low 850 temperatures to similar patterns in previous severe winters and the others mentioning the output and my views that the deep cold block might take a lot of shifting - the final one with a greater degree of balance. Let's have a look at some of the charts:

        MetO fax for 1200 Thur 1st March             MetO fax for 1200 Fri 2nd March                  UKMO 0z for 0100 Sat 3rd March            UKMO 0z for 0100 Sun 4th March         

    20180226.0520.PPVL89.png       20180225.2132.PPVO89.png     UW120-21.GIF     UW144-21.GIF

    This is not one of my cross model analyses (that'll save for another time). I wanted to pick two models with slightly different solutions. I'm going with the MetO//UKMO 0z and the GFS 6z output but I could just as easily have picked on any of the other models. The MetO fax charts show the "potential" micro set up very nicely. Note that their charts up to T+84 updated this morning but the last two do not update until much later today. The two fax charts show a "ghost" warm front rather than a fully blacked-out one. This leading edge of less cold air may be unable to penetrate the block and is effectively lifted off the surface and over rides the surface cold. If this occurs then we could easily see a heavy snow to freezing rain event. The air aloft might be warm enough to produce rain rather than snow at times. This then falls through the still sub zero freezing layer. It freezes on impact when it hits any solid surface. 24 hours later the first front is shown to have stalled around the north Midlands. The occluded front behind it appears to be stalling in the English Channel. This would probably have less cold air behind it at the surface but if its stalling, it might not even reach the south coast. On this chart, just the extreme south-west appears to be in this less cold sector. The later position is shown in the UKMO charts. They do not show the fronts (which are key) but suggest that the stalling continues for several more days at least. With such a depth of cold in this block it might take a much stronger push to displace it or a series of attacks over a few days.  Although the less cold air would start to mix into the system, there would equally be an opportunity for the dense cold air to mix into the system from the north and east.

    This set up may be on a knife edge from Thursday and right through the weekend until it is resolved.  There could be various scenarios. The LPs completely stalls and slowly fills in situ; they are deflected away north-westwards or south-eastwards; they eventually push into the block and make much more progress across the UK; or that the LP doesn't even get close too our shores. Now, let's look at the GFS charts for the same period. Please note that it doesn't matter if the 12z output currently rolling out paints a very different picture. The models are highly unlikely to properly nail this micro set up right up to T+24 or even T+0! I just want to demonstrate the possible consequences..

          GFS 6z for 0100 Thur 1st March                GFS 6z for 0100 Fri 2nd March                   GFS 6z for 0100 Sat 3rd March                 GFS 6z for 0100 Sun 4th March     

     gfs-0-66.png?6      gfs-0-90.png?6      gfs-0-114.png?6      gfs-0-138.png?6            

    The GFS starts off with the LP slightly further north than the MetO but it is not quite so deep. By Friday they have LP in a similar position to the MetO off the south-west approaches and a similar strength (note that the fax charts are for 11 hours later, so adjust accordingly but the last two charts and all the 850s below are exact time matches). By Saturday GFS has the LP further north-west than UKMO but has developed a second, smaller LP cell centred over Brittany. The UKMO had a larger flabby area of LP with three cells within in. In actual fact the differences are not that great. We cannot see the fronts on the GFS charts but it looks like their pattern is all slightly further north and just 50 to 100 miles can make a huge difference in this highly marginal set up. By Satruday, GFS is starting to pull in more of a southerly flow, whereas UKMO have  some slack LP drifting around mostly just to the south of us, suggesting that the less cold air has hardly made in roads. To get a better idea of all this, let's examine the 850s for the same period. I'll leave the charts directly below each other and then comment.

        UKMO 0z for 0100 Thur 1st March              UKMO 0z for 0100 Fri 2nd March                UKMO 0z for 0100 Sat 3rd March             UKMO 0z for 0100 Sun 4th March         

     UW72-7.GIF      UW96-7.GIF      UW120-7.GIF     UW144-7.GIF  

           GFS 6z for 0100 Thur 1st March                GFS 6z for 0100 Fri 2nd March                   GFS 6z for 0100 Sat 3rd March                 GFS 6z for 0100 Sun 4th March     

      gfs-1-66.png?6     gfs-1-90.png?6     gfs-1-114.png?6     gfs-1-138.png?6

    We start off with most of the UK engulfed in sub -14c 850s. Both UKMO and GFS show the 0c 850s pushing into the far south of the UK and displacing the lowest values slightly north-eastwards with a very steep gradient over the country. There would be slight mixing in the boundary layers. By Saturday, UKMO have the 850s dipping slightly again but only to around -2c in the south and still in a similar position on Sunday.. GFS retains the 0c isotherm near to the south coast through the weekend. Now we would normally think that the uppers are now too high for snow but this may not be necessary for a short period. With the milder air at least temporarily likely to be lifted over the cold dense surface air and as long as there remains a partial feed from the continent, dew points might still be at or below zero. Stalling fronts and LP systems can produce heavy precipitation for a number of hours and radiative cooling.(melting snow progressively cools the layers below it until snow reaches the surface). Fronts and troughs can wriggle around slightly northwards and southwards and that can produce rain to snow to rain events with a number of changes.  Then of course we might get a prolonged period of freezing rain, which takes me on to the 1940 event. 

    The January 1940 Ice Storm: 

    This remarkable 48 hour event started on January 27th 1940 with snow turning to freezing rain and then back to snow with a severe blizzard. Let's set the scene. There is an excellent summary of that month here:

    https://www.theweatheroutlook.com/twoother/twocontent.aspx?type=tystat&id=1180&title=January+1940

    I copy a summary from the monthly weather report:

    "...January 1940 was a severe wintry month with frequent frosts and heavy snowfalls. The CET for the month was -1.4C, the first sub zero CET month of the 20th Century and the coldest month since February 1895.
    On the night of the 23rd, a minimum of -23.3C was recorded at Rhaydaer(Powys) a record low for that date. Other lows include -20C at Canterbury, Welshpool, Hereford and Newport in Shropshire.
    The Thames was frozen for 8 miles between Teddington and Sunbury and ice covered stretches of the Mersey, Humber and Severn.
    The sea froze at Bognor Regis and Folkestone and Southampton harbours were iced over. The Grand Union Canal was completely frozen over between Birmingham and London. Central London was below freezing for a week and there was skating on the Serpentine on 6" ice. 
    However January 1940 will always be remembered for the Snowstorm and Icestorm that struck the UK.
    SNOWSTORM
    On the 26th, two occlusions were moving up from the SW engaged the cold air over the UK. At the same time, the anticyclone over Scandinavia was intensifying blocking the fronts from pushing through the UK, they became stationary over Wales and SW England. This resulted in a great snowstorm across many northern and eastern areas.
    Vast areas of northern England reported between 30-60cm of level snow, the higher parts in excess of 60cm+. The snow drifted in the strong SEly wind even in the centre of London. Other reports of snow depths include Eastbourne:- 25cm, Pontefract:- 37cm, Malvern:- 60cm and Exmoor:- drifts of 2.5m. The snowfall lasted to the 29th of January.

    ICESTORM
    On the low ground in the south, the preciptation fell as freezing rain. The raindrops were of the supercooled nature, so when the rain hit the surface it would freeze instantly. This is a rare event in the UK and the 1940 is reckoned to be the severest that has struck the UK in recorded history. The duration of the storm was remarkable lasting up to 48 hours in places. For instance at Cirencester, 48hrs of freezing rain fell in temperatures of between -2 and -4C. The effect of this prolonged icestorm was severe and damaging. Many telegraph poles and wires were snapped unable to cope with the weight of the ice. Flora and fauna suffered as well, many tree branches were snapped off by the enormous weight of ice, birds were unable to fly because ice accumulated on their wings. Travel was next to impossible as roads and pavements became skating rinks. Any sloped surface was impossible to climb...".

    There is also an excellent archived NetWeather thread on the ice storm and here's the link (just click on the chart below):

     

    Now the fascinating bit. I've dug out some charts from the archives and I show them below (EDIT: I'm afraid that these archive charts do not have the run through white arrows):

    Jan 1940:        22nd                                                       25th                                                      26th                                                      27th

    archives-1940-1-22-0-0.png  archives-1940-1-26-0-0.png  archives-1940-1-27-0-0.png  archives-1940-1-28-0-0.png 

                             28th                                                       29th                                                    30th                                                      31st

    archives-1940-1-28-0-0.png  archives-1940-1-29-0-0.png  archives-1940-1-30-0-0.png  archives-1940-1-31-0-0.png 

    Jan 1940:        22nd                                                       25th                                                    26th                                                      27th

    archives-1940-1-22-0-1.png  archives-1940-1-25-0-1.png  archives-1940-1-26-0-1.png  archives-1940-1-27-0-1.png 

                              28th                                                       29th                                                    30th                                                      31st  

    archives-1940-1-28-0-1.png  archives-1940-1-29-0-1.png  archives-1940-1-30-0-1.png  archives-1940-1-31-0-1.png

    Jan 1940:         22nd                                                       25th                                                    27th                                                      29th

    archives-1940-1-22-0-5.png  archives-1940-1-25-0-5.png  archives-1940-1-27-0-5.png  archives-1940-1-29-0-5.png

    Look at those Jan 22nd 850s 3 days prior to the event. Now if you looked at those charts before the event, you would say that they must be bringing in milder air, rain, a thaw etc. What we will have by the end of this week may be very similar. A frozen and snowy country. A streak of the southerly jet  pushing towards us (I show the current jet stream charts below). South-westerlies or southerlies pushing into the south-west and highly marginal 850s arriving in the south. This is where there is a huge difference between just surface cold and extremely deep upper cold - an immense block. I still feel that it would take a big push from a more direct jet to shift a block like this completely.

         GFS 6z for 0100 Thur 1st March             GFS 6z for 0100 Fri 2nd March                GFS 6z for 0100 Sat 3rd March              GFS 6z for 0100 Sun 4th March     

    gfseu-5-66.png?6   gfseu-5-90.png?6   gfseu-5-114.png?6   gfseu-5-138.png?6

    There were several significant differences in the broader patterns - 1940 doesn't seem to have a west based -NAO negative North Atlantic Oscillation). Just compare the charts below which show the beginning and end of the key periods for both now and back then. All the way during the 1940 event the Scandiinava HP was intensifying which helped to maintain the block and prevent any LPs making significant inroads. With our current set-up, the sudden stratospheric warming (SSW) impacts have been so strong and so progressive that the HLB is being pushed west towards Greenland and predicted (on most models) to go even further towards north-east Canada and Newfoundland. This is the -NAO with the normal LP in the Atlantic being replaced by HP. With HP over there, this can allow LP to make progress in our part of the Atlantic. This is not nailed on but we would need to see our Scandi HP hold on at lest to some extent. The next part of the SSW (further warming or multiple warmings) has been taking place just now with the strat guys expecting it to impact in about  another 8 to 10 days or so. This might re-invigorate the same blocking pattern (it might set up slightly differently) and it might lead to a re-load of the cold pattern. Even if this happens it may be too late to rescue the current blocking and in any event, the days are drawing longer and further blasts from the east may not be as cold as we are seeing currently. In March 2013, the cold pattern hung around until mid April..It is unknown if there was an SSW in January 1940. Sea surface temperatures were rather lower back then too. 

    Whatever transpires this will be a fascinating period. The 1940 event proves that a strong cold block can hang on against all the odds. I know that both 1947 and 1963 produced loads of these "cold southerlies" (a term that I first used last February - wrongly with the surface cold but no deep cold uppers) which in the former only brought milder air in after a 3 week struggle and never in the latter!  

        GFS 6z for 0100 Thur 1st March               GFS 6z for 0100 Sun 4th March                           Jan 22nd 1940                                        Jan 29th 1940

    gfsnh-0-66.png?6    gfsnh-0-138.png?6    archivesnh-1940-1-22-0-0.png    archivesnh-1940-1-29-0-0.png

     

    Edited by Guest
    Correct typos and check charts & links
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    Posted
  • Location: Stroud, Gloucestershire
  • Weather Preferences: Extreme!
  • Location: Stroud, Gloucestershire

    GFS ensembles slowly seeing the fact the warmer uppers may not make it as far north as it previously predicted.

    definite shift, clustering of the warmer runs subsiding and more members quickly returning cold after the low edges in

    IMG_3377.thumb.PNG.de729d0efec28eb46ae320ef325b105c.PNG

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    Posted
  • Location: Cambridge, UK
  • Weather Preferences: Anything out of the ordinary!
  • Location: Cambridge, UK
    24 minutes ago, nick sussex said:

    Without the first warming the UK wouldn’t be seeing this cold spell. And you often get a second one after the first .  They often come in pairs.

    The issue isn’t the second warming happened but just the block goes too far west, However we’ve seen improvements over the last 24 hours with the jet now edged further south .

    We might now be seeing the lagged effects of the unexpected move of the MJO into phase 1 , originally the models had that going into the COD.

    And that means it’s premature to throw the towel in. :)

    Not sure why the GFS is taking centre stage and driving the mood in here.

     

    Quite right nick. GFS consistently verifies as worse than ecm and ukmo, yet people hang on it’s every word (or run). If all three showed the same then panic stations, but as they don’t, best to just wait and see how it pans out.

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    Posted
  • Location: Calgary, Canada. Previously, Saffron Walden (Essex/Herts border), United Kingdom
  • Weather Preferences: Continental:Warm dry summers, cold snowy winters
  • Location: Calgary, Canada. Previously, Saffron Walden (Essex/Herts border), United Kingdom
    1 minute ago, Dominic Carey said:

    Which means? 

    keeping it a mainly snow event. From what i'm aware of, the snow won't turn to rain unless the 0C line crosses over

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    Posted
  • Location: Burton-on-Trent
  • Location: Burton-on-Trent
    3 minutes ago, Man With Beard said:

    ECM 12z:

    0C uppers line DOES NOT get across the channel on Friday.

    Yes it does look as though we manage to keep a bit more of a continental influence on this run.

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    Posted
  • Location: st albans
  • Location: st albans

    ecm consistent with its earlier run to day 5. not sure it will shear the trough away on this run in the same way so expect things to be further north by day 6. 

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    Posted
  • Location: Wellington, Somerset
  • Weather Preferences: Thunderstorms/Snow/Hail & Strong Winds
  • Location: Wellington, Somerset
    4 minutes ago, Man With Beard said:

    ECM 12z:

    0C uppers line DOES NOT get across the channel on Friday.

    Important step forward, however, we are unable to see the uppers into late Thursday/Early friday which is a little annoying. 

    Edited by MattTarrant
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    Posted
  • Location: NR LOURDES SW FRANCE
  • Location: NR LOURDES SW FRANCE

    The ECM and UKMO are closer together re the pattern to the ne at T120hrs especially with the direction of the PV lobe heading sw.

    Edited by nick sussex
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    Posted
  • Location: Cornwall
  • Location: Cornwall
    4 minutes ago, Man With Beard said:

    ECM 12z:

    0C uppers line DOES NOT get across the channel on Friday.

    Is there a chart we can possible see? and what would be the meaning of this?

    What about Us Westerns?

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    Posted
  • Location: Drayton, Portsmouth
  • Location: Drayton, Portsmouth
    1 minute ago, Snowy L said:

    Yes it does look as though we manage to keep a bit more of a continental influence on this run.

    Looking on weather.us, I think it may get above freezing for a few hours on Thursday night (between the Meteociel frames), but it's back to snow by Friday morning south of M4 except in extreme SW.

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    Posted
  • Location: Darlington
  • Weather Preferences: Warm dry summers
  • Location: Darlington
    1 minute ago, Skullzrulerz said:

    Is there a chart we can possible see? and what would be the meaning of this?

    What about Us Westerns?

    2

    Yeah

     

    ECU0-120.GIF.png

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    Posted
  • Location: st albans
  • Location: st albans
    3 minutes ago, Skullzrulerz said:

    Is there a chart we can possible see? and what would be the meaning of this?

    What about Us Westerns?

    Worse than the previous run though it does return south 

    374211DA-BC57-438D-A59F-625A9C808D05.thumb.jpeg.d1182f065fbe055b65e197f3c07c7023.jpeg

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    Posted
  • Location: Raynes Park, London SW20
  • Location: Raynes Park, London SW20

    ECM doesn't quite make it on this run - by day 6, mild uppers encroach a lot of England.

    Guess there wasn't enough trough disruption along the front between days 4 and 5?

    If only the pattern was 200 miles further south!

    Edited by mulzy
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    Posted
  • Location: Liphook
  • Location: Liphook
    6 minutes ago, Man With Beard said:

    Looking on weather.us, I think it may get above freezing for a few hours on Thursday night (between the Meteociel frames), but it's back to snow by Friday morning south of M4 except in extreme SW.

    Yeah almost getsupto 2C by the south coast, 0C isotherm gets to London-Bristol roughly BUT not much precip about. What precip there is is freezing rain.

    Probably 5-8cms would be a guesstimate from the 12z ECM verbatim, but I think you'd have to think the front would be weaker as it is coming up against dense dry cold air, so real figures maybe lower.

    Not too different from the GFS it has to be said in how it handles everything with the front coming across in a similar way.

    Edited by kold weather
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    Posted
  • Location: Cottingham
  • Weather Preferences: Cold Snowy Winters, Hot Thundery Summers
  • Location: Cottingham
    5 minutes ago, MattTarrant said:

    Important step forward, however, we are unable to see the uppers into late Thursday/Early friday which is a little annoying. 

    Its possible to via this link

    https://weather.us/model-charts/euro/england/precipitation-6h-in/20180302-0900z.html

    Looking at the dew points and air temperature I think it would all fall as snow north of a line from Bristol to Dover, further south it goes from a snow to rain to snow event with temperatures in the far south upto 2 or 3C

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    Message added by Paul

    Please only post model discussion in here! 
    Other options:
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    For more focused short-range model discussion:
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