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Model output discussion - after the beast, what next?


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Posted
  • Location: Cambridge, UK
  • Weather Preferences: Anything out of the ordinary!
  • Location: Cambridge, UK

    No comments always means nothing exciting on these forums!

    I'm actually quite surprised how strong some of these lows are, considering the jet is so far to the south and it's not especially strong. The weather out to the middle of March looks dodgy to say the least.

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    The UKMO 144 has teased me out if hibernation - for a comment. 144 shows a very meridional flow across 50N with deep cold filtering into Scandi- could be a sharp transition from mild to cold

    No mate, I'm still in winter mode as long as the Gfs shows potential arctic blasts..hope it continues!❄❄❄❄❄

    Ahhh another chocolate teapot in your post... I believe the last one froze. It seems that we are seeing the second response to the SSW with another surge of negative zonal mean u winds heading fo

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    Posted
  • Location: st albans
  • Location: st albans
    25 minutes ago, Man With Beard said:

    The ECM mean chart for mid March is pretty much as it has been for days:

    ec-ens_nat_mslstd_mslmean_hres-msl_20180

    The clusters suggest it does not hide any wild variations in potential patterns

    ec-ens_nat_z500scenarios_2018030600_360.

    So just a bog-standard wet period looks like extending well into March, average temperatures at best, just a small chance of the Azores High making a resurgence later on but wouldn't hold your breath. Spring well and truly on hold, and winter pretty much gone too.

    It does look a bit indeterminate and unconvincing  - to me, the euro troughing seems to be increasing in the extended period and whilst there is no strong signal for HLB, wedges would be sufficient to allow something notable - moreso further north. I think we need to be patient to see what features become the major players through week 2.

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

    The 06Z Control follows on from the 00Z OP building heights to the NE and SW forcing the trough into a NW-SE alignment across the British Isles before disrupting it to the west. Here's a dream chart for fans of cold rain:

    gens-0-1-384.png

    Uppers of -4 to -8 late March - would it be rain ?

    Not worth the time it's taken to produce this post at this time but a trend of sorts starting to emerge.

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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 6z op is trough dominated but again there is arctic weather in FI with very disruptive snow..it's enough to keep me interested in what could happen next week!:):cold:

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

    GFS 06z mean shows the Op is on the cold side towards the end of the run

    GFSAVGEU06_270_2.thumb.png.9f4a6d227aec18cc61a6e7152d576d45.pngGFSAVGEU06_300_2.thumb.png.9107043fff24ae37052f202dd30f6a5f.png

    GFSAVGEU06_348_2.thumb.png.8dcdded5e52ccbbec076d521a174ba70.pngGFSAVGEU06_372_2.thumb.png.8f54d1d28a391ba982cb77fab4401eab.png

    Still the chance of snow in Scotland and higher ground further south but elsewhere the snow risk is generally low

    gefsens850Inverness0.thumb.png.eea9bf64cc6a779d28dda4ec079d710a.pnggefsens850Newcastle0.thumb.png.c96cc17984dfc77813412d4f321d4d68.pnggefsens850London0.thumb.png.90b1e6daf95db9e194b25768d53ad45f.png

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    Posted
  • Location: Manchester
  • Weather Preferences: Sunny and warm in the Summer, cold and snowy in the winter, simples!
  • Location: Manchester

    Certainly lot's of "interesting" weather to come if the models are to be believed.

    Three main takeaways for the run up to mid month are the possibility of storminess as systems develop rapidly and cross the South of the UK, the potential for very high rainfall associated with these systems and the increased possibility of blocking, most likely Atlantic ridge mixing in some cold air from time to time.

    The combination of these could mean some surprise heavy but transient wet snow to low lying areas central/Northern UK and likely heavy snowfalls on hills in the North, 

    Around or a little after mid month the weather may begin to quieten down with blocking becoming more of a player with a chance of colder weather returning (though nothing close to what we just experienced)

    I wouldn't exclude the possibility of West based neg NAO developing after mid month either which could flip the weather to Spring like with long fetch Southwesterlies but that seems fairly low probability at the moment while pressure remains low over Europe and low pressure systems pushing through rather than stalling to the SW.

    Plenty there for us to get our teeth into over the coming week or two.

     

    Edited by Mucka
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    Posted
  • Location: East Ham, London
  • Location: East Ham, London
    13 minutes ago, Summer Sun said:

    Still the chance of snow in Scotland and higher ground further south but elsewhere the snow risk is generally low

    gefsens850Inverness0.thumb.png.eea9bf64cc6a779d28dda4ec079d710a.pnggefsens850Newcastle0.thumb.png.c96cc17984dfc77813412d4f321d4d68.pnggefsens850London0.thumb.png.90b1e6daf95db9e194b25768d53ad45f.png

    To clarify, the chart I posted was from Control which only foes colder than the OP at the very end while the OP has a long colder spell before going milder at the very end.

    Oddly enough, we end up pretty much where we are now - there's a clear warm up over the weekend coming but after that much less clarity as you would expect. We'll see if both the midweek warm up next week and the general cool down from mid month are trend setters or red herrings.

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

    Would be ironic if some had the worst of snow in mid March. GFS 06Z does that buries NW England 47mm in 12 hours major cities like Manchester severely affected, this will probably be gone in next run. However it exemplifies risk of widespread snow event(s) the snow will likely melt quickly, but all is not lost for coldies yet.

    316131E2-50D9-49C3-8E0B-756894EBAED9.thumb.jpeg.1d8b13fa9e088dd010bb1b7f676b5083.jpegDE594C0A-129E-4F47-A4C8-3CFD6B7E453F.thumb.jpeg.190bf179d849241857b543c84be1d9cf.jpeg

    Edited by Daniel*
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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

    I wouldn't rule out a return of cold blocked conditions this month, the GEFS 6z shows examples of this becoming re-established!:):cold-emoji:

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

    There definitely seems to be a trend for chillier conditions around mid month. ECM shows increasing cold air pushing south implying a good chance of snow in northern areas. Getting in mix of southerly tracking lows areas further south too may have a chance of some wintriness too.

    Safe to say I can’t see spring warmth! Possibly even into April...

     

    Edited by Daniel*
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    Posted
  • Location: Western Isle of Wight
  • Weather Preferences: Snow, Storm, anything loud and dramatic.
  • Location: Western Isle of Wight

    Looking at the GFS the latest trend is lots of rain. Flooding will be the next weather headlines quite possibly.

    West country looks worse at first IMO.

    I threw my last snowballs of the Winter/Spring for the dog today,  wishful thinking perhaps.

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

    Frustrating in mid winter there would likely have been cold air aloft instead cold rain on UKMO.

    95B3E812-3098-4141-84DB-DFEAE364F625.thumb.gif.becfc4c30b6bf8077266c50d1e8b367f.gif2FA3825A-E516-44E6-B1B4-0C5424830599.thumb.gif.af368c5bc6d59496431c04f0c7e95f25.gif

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

    A cold snap mid month is gaining traction. GFS opens the arctic floodgates again, similarly to ECM this morning. It definitely suggests a wintry picture persisting in the far north especially. 

    BE0DE3D2-775F-427D-A51E-B84CEB57FAF2.thumb.png.44e3de0e24513993de9bda80a8a4ce2a.png51E6A925-0951-4E50-94B1-2E3397769021.thumb.png.4350166558be8bef67db53d443617e99.png

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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

    Great to see the Gfs 12z continuing the theme of eventually shunting the complex trough to the east allowing arctic air to flood south with snow and sharp frosts, just as the 12z did yesterday..I'm not ready to let go of winter and seemingly, neither is the Gfs!:D:cold:

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    Posted
  • Location: Mytholmroyd, West Yorks.......
  • Weather Preferences: Hot & Sunny, Cold & Snowy
  • Location: Mytholmroyd, West Yorks.......

    The GFS MJO tweet from M. Ventrice has me a bit twitched. over 5 s.d. is a 1 in 3,500,000 shot so not a common occurrence at all? The 4 s.d. that propagated the SSW was a measly record 4 s.d.'s and that looped the jet toward the pole before plunging it way to our south. Could the jet, like a swing pushed too hard, make it right over the pole and so out the other side?

    This would place us well on the summer side of the jet and open the doors to African WAA until the Jet can slip back.

    I'm not liking these obscene excursions of atmospheric angular momentum at all ( and I won't tell the usuals "I told you so!") but it is new to me!

    The plot on the graph shows today well beyond 2 s.d.'s and the 7th is off the plot so we won't have long to see if the excursion verifies but I have no idea just what it will unleash?

    Edited by Gray-Wolf
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    Posted
  • Location: East Ham, London
  • Location: East Ham, London

    Afternoon all :)

    Worth keeping an eye on the rainfall numbers with the south catching most:

    Modele GFS - Carte prévisions

    As for the extraordinary amplification this is how the 12Z GFS OP shows it on the Pacific side:

    gfsnh-5-102.png?12

    Look at the jet streak buckling north over far eastern Siberia and Alaska and then moving south in the northern Pacific. Doesn't seem to impact our side of the globe much at all but that's because it's in Phase 4/5 whereas the amplification from the SSW led to high amplitude Phase 7/8 which allowed the Scandinavian HP to set yp.

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    Posted
  • Location: Manchester Deansgate.
  • Weather Preferences: Heavy disruptive snowfall.
  • Location: Manchester Deansgate.

    Hefty cluster advertising the possibility of Greenland height rises towards the end of the GEFS suit.

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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

    My feeling with the Ecm 12z run so far and indeed the models in general is we coldies would have to be extremely unlucky not to see further cold / snowy spells this month with the jet generally so far south!..hope we see something from the arctic either next week or soon after!:):cold-emoji:

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    Posted
  • Location: STEVENAGE, HERTS (100M ASL)
  • Location: STEVENAGE, HERTS (100M ASL)

    Potential from the ECM for an end of the month cold spell? 

    D2D85D67-91FA-43F1-9CB7-BAE3D2DA201A.png

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    MY TAKE ON THE CURRENT UNUSUAL PATTERNS AND WHAT WE MIGHT SEE UNFOLD DURING THE NEXT FEW WEEKS

    I am not surprised that all the threads are very quiet so far this week following the MOD and the regional threads being frantic during last week. Many of us are exhausted and suffering from model, posting and reading fatigue. Almost everyone who was looking for cold and snow got their fix in abundance. Unfortunately there is always a downside during severe weather events with some lives lost and quite a few suffered badly from being cut off, stuck on roads or rail or through loss of vital services like water and power as well as burst pipes and flooding. Many of you will be happy to see some early spring warmth but the weather will do what it wants to and it may well be a few more weeks until we see some more seasonal conditions. In this post I will look at the current set up. Then I will give my view on how I expect things to evolve during the coming weeks. I shall examine the evidence from various sources as well as completing one of my cross-model analyses.

    WHAT JUST HAPPENED?

    We were given pretty good advanced noticed of the Sudden Stratospheric Warming (SSW) event by many of our strat specialists. The final timing of the surface impacts were very well forecast with a full flow reversal in the Arcitc and the associated HLB patterns being established with much of the cold being displaced towards the middle latitudes. A vast belt of HP developed from Siberia, through Russia, Scandinavia, Iceland, Greenland and on towards north-east Canada. The long lasting Canadian vortex was displaced across the pole and towards north Russia and Siberia. The very cold dense surface air with extremely low upper temperatures surged westwards from Siberia, through Europe, the UK and even half way across the Atlantic. It was a record breaking SSW and the impacts were very strong - almost too strong. I liken it to the Siberian Express steaming though so quickly that it overshot the UK platform! It gave us a week of exceptionally cold weather which would have been very severe and unusual even if it had occurred in January. We smashed many UK temperature records for late February and early March, especially the lowest day time maximums. The very low uppers saw the 850 temperatures below -14c across the whole of the UK for a while with a very brief period of sub -16s over a few spots.

    These conditions were conducive to the extraordinary amount of low level convection. The extremely cold and very dry continental air rapidly became unstable in its surface layers as it crossed the relatively warm seas picking up a lot of moisture. Snow streamers and bands of snow showers affected many coasts exposed to winds from an easterly quarter. We saw the now rare event of a full English Channel snow streamer and the even rarer Bristol Channel snow streamer. Then "Storm Emma" decided to do battle with the "Beast from the East" producing blizzard conditions with large and widespread snow accumulations and severe drifting. This paralysed  vast swathes of the UK and Ireland. Some parts, like down here in Exmouth, saw about 12 hours of heavy powder snow dumping 10 to 20 cm of level snow with 2 to 4 foot drifts (much more further inland). This was followed along much of the south coast by about 10 hours of freezing rain coating all surfaces in 1 cm to 1.5 cm of ice. Then the thaw started over the weekend gradually pushing northwards and eastwards across the country. I wrote several posts about the types and causes of freezing rain on the south-west regional thread.

    THE CURRENT SET-UP:

    What we have been left with is a very odd looking pattern. Let's have a look at a few of the current charts:

     Euro Pressure 24 hours to 1210 Mar 6th       Met O Fax 0z for 0600 Mar 6th                   GEFS 6z T+0 for 0700 Mar 6th                         Same but annotated                         GEFS 6z T+0 for 0700 Mar 6th 

       tempresult_raf4.gif    20180306.0645.PPVA89.png    gensnh-0-1-0.png   5a9e87cfe24dd_gfs6nannotated.thumb.png.a4519332456a0e55081442bb849fcae7.png   gensnh-0-3-0.png 

    The pattern has got into a bit of a rut. Emma has almost stalled in situ over the UK. She keeps spawning minor cells of LP within her circulation. One is currently to her north-west but most have been to her east and south-east. The faithful Scandinavian HP that maintained the easterly flow for so long steadily declined, also more or less in situ. Pressure has started building again slightly up there during the last 24 hours through Finland and ridging soutjh-eastwards into western Russia and the far north-east of Europe. This is also well represented on this morning's fax chart. 

    To better understand the pattern, we must look at the northern hemisphere view and I've picked the current GEFS charts (late morning right now). Again you can see the wider circulation around Emma with the fairly slack LP centred over us, with (now) much lighter winds. What I want to highlight is the continuing flow reversal around the Arctic. I'm useless at drawing and I'm not sure if the same "annotated" chart has been copied properly so that it'll enlarge - I hope it does. I have drawn two red lines with arrows indicating the direction of the flow. Firstly, I show the cut off HP which remains sitting over the pole. Then look at the flow reversal extending around the whole of the northern hemisphere sandwiched between various HPs from Siberia, over the Arctic, Greenland, northern Canada and through Alaska and beyond, with relatively lower pressure (mostly) further south. Overall, the HLB is weaker than it was last week and the flow reversal is not quite reaching so far south towards the middle latitudes right now but it remains intact. This is all the continuing signature of the SSW impact.

    The jet stream remains on a very far south track around almost all the northern hemisphere. Apart from a small area just south-east of the Kamchatka peninsular it is mostly moderate in strength. It is so far south of the UK that it is passing over north Africa and the southern Mediterranean. In fact if goes any further south, the Sahara Desert might see quite a bit of rain! This hemispheric far south position is due to the huge SSW impacts. There is a sort of void area in between the northerly HLB and the southerly jet. For much of the last week this void has been filled with mostly fairly weak and slow moving LPs. Emma was rather stronger for a while as it moved northwards on a temporary breakaway streak or loop of the jet.  This is fizzling out - you can see it now moving east out of north-east Europe. I shall come back to the jet and pressure patterns in the next section.

    Euro Temps 24 hrs to 1200 GMT Mar 6th Euro Temps at 1150 GMT Mar 6th          Euro temps at 0650 GMT Mar 6th    GEFS 6z 2 m Temps T+0 for 0700 Mar 6th GEFS 6z 850 Temps T+0 for 0700 Mar 6th       

    tempresult_szm6.gif   temp_eur2-12.png  temp_eur2-07.png  gensnh-0-4-0.png  gensnh-0-0-0.png

    I adjusted the times in the headings to GMT (1 hour behind French times shown in the charts). if we allow for the daily min/max temp changes, the 24 hours changes to lunchtime today show the extent of the cold over much of central and eastern Europe has changed little since yesterday. The second charts will be close to today's maximum values and the third chart close to this morning's minimums. The south of the UK is seeing temps almost up to normal today for the first time in nearly two weeks. There is some uncertainty over the current forecasts just for several days ahead with either milder conditions over much of England or becoming rather cold again. I think that the milder conditions, whether 1 day or over several days may prove to be very short-lived and these (in this short spell) might be the highest max temps that we shall see for quite some time (reasons later on in next part). Meanwhile Scotland has hung on to colder conditions and there has been quite a bit more snow there today. The northern hemisphere charts are for 0700 this morning - so closer to minimum values. There are low surface temps over much of northern Russia, Siberia and now across the Pole (unlike  two weeks ago at the start of the SSW when surface temps were close to zero) as well as Greenland and the far north of Canada. The deep cold in northern Russia still extends into north-west Russia and Scandinavia as well as southwards into south-west Russia and the far north-east of Europe (as shown in the Euro temp charts). The very low 850s haven't been pushed too far away. There are sub -24s over north-west Russia, sub -20s extending into northern Scandinavia and southwards with sub -12s still showing over southern Scandinavia, western Russia and north-east Europe.

    THE NEXT WEEK UP TO DAY 5:

    I highlighted the jet stream which is relentlessly tracking far to our south and, with the continuing flow reversal, I put this down to the ongoing influences of the record SSW impact. The obvious question is how long might this broad pattern continue. From now on I will only look at the wider northern hemisphere charts as the micro detail for the UK in this extremely uncertain set-up is unlikely to be nailed by any model for quite some time. So let's look ahead to day 5 with one of my cross model analyses. With times adjusted to match each output, these are all charts for 0100 on Sunday:

                    GFS Operational                                                    ECM                                                              UKMO                                                              GEM

    gfsnh-0-114.png?6?6      ECH1-120.GIF      UN120-21.GIF      gemnh-0-120.png

    The main differences close to the UK are the position and the depth of the LP. Some have it close to or over us with a cyclonic or south-easterly flow. Some have it further to our south-west with either a southerly or more of an easterly flow (mostly over the north). Some have quite a deep feature while others have a very weak feature. Several earlier runs had moved it further east with a northerly pushing down across us. At just 5 days out this shows up the huge uncertainties. There is rather more agreement over the broader pattern. All the models maintain the Arctic HP and to a less or greater extent the flow reversal is still evident, although taking a rather more meandering route.. Most models are building HP just east of Scandinavia or over north or north-west Russia. 

                         NAVGEM                                                            JMA                                                       GEFS Control                                          GEFS Ensemble panel

    navgemnh-0-114.png      JN132-21.GIF      gensnh-0-1-114.png      gens_panel_css8.png

    To enlarge the panel members, go to the link, click on the first panel and then use the run through double white arrows at the bottom right of the chart:  http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=6&ech=114

    WEEK 2 UP TO DAY 10: 

                       GFS Operational                                                 ECM                                                             GEM                                                              JMA     

    gfsnh-0-234.png?6?6     ECH1-240.GIF     gemnh-0-240.png     JN252-21.GIF 

    Note that UKMO (to day 6) and NAVGEM (to day 7/8) are no longer available: There is greater diversification by day 10 but the flow reversal is becoming rather less evident or taking a far less direct route. There remains a cut off HP over the pole. GFS has the LP out in the North Sea with a northerly flow becoming established over the UK and further LP to our north. ECM is broadly similar with a rather slacker LP and a different (more north to south Arctic profile and there are signs that the LP to our east will bring down a north-easterly flow in its rear (this is a synoptic pattern that would fit in more with my own take as outlined in the next section). GEM offers a rather different solution. On the one hand it has intensified and expanded the Arctic HP but then has introduced an even wider middle latitude pattern with a plethora of minor LPs. JMA still has the Arctic HP and some strong HP building in north-east Canada (ignore their unadjusted for altitude HP over the Greenland plateau and thick ice sheet) and HP in northern Asia but they have LP further north in the Atlantic and a weak westerly flow over the UK. The GEFS control has the LP just to the north of the UK with the Arctic flow diverted further west and coming into us on a west-north-westerly in its circulation. It also has a strong build over pressure over Russia and Siberia. The ensemble members show a variety of evolutions mostly within the range outlined in the other models.

                          GEFS Control                                     GEFS Ensemble panel                        GEFS Ensemble panel  Jet T+114            GEFS Ensemble panel Jet T+240

    gensnh-0-1-240.png      gens_panel_rna9.png     gens_panel_wru1.png     gens_panel_ptx1.png  

    The links to the GEFS panels:

    Pressure at T+240:   http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=6&ech=240 

    Jet at T+114:   http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=3&ech=114    

    Jet at T+240;   http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=3&ech=240

    The last two charts above show the GEFS ensemble members for the jet stream at day 5 and day 10. At day 5, all the members keep the main branch of the jet well to our south. Several members do spin off small loops or weaker streaks to the north but these generally fade out quite quickly. By day 10, the main theme is largely maintained but with a little more buckling rather than a straighter west to east southerly jet. A few members have a slightly stronger streak much closer to the UK or even pushing through the UK.

    Overall, not surprisingly the inconsistency continues. Although UKMO only goes up to day 7, the uncertainty is reflected in the text of their extended outlook. They suggest some very unsettled weather from the weekend into next week and then they cover almost all bases in their 15-30 days. So equally inconclusive..  

    LOOKING AT SOME OF THE KEY INFLUENCES AND THEN FURTHER AHEAD:

    With the models so uncertain, I will now look at other factors. In the run up to the record strength SSW, the models really struggled to cope with the pattern reversal. GFS toyed with the idea and then moved away from it before returning to it once the other models firmed up on more of the detail less than a week before the event. Even then it took several more days until the location and extent of the HLB was more accurately predicted and finally it became clear that we would be heading into a very cold easterly spell. With the flow reversal still present now, the models will still be encountering the same problems. There is always a tendency to revert to the seasonal or climatological norm.

    There were a combination of factors as to what might have caused such an extreme SSW and this will the subject of much debate as well as what triggered the event, what caused a fairly quick propagation down to the surface and what caused the impacts to progress so rapidly eastwards from Siberia. We still do not know how the impacts will continue. I feel that there remains a very strong imprint on the tropospheric pattern with the reversal and there is still HLB in the very high latitudes and then why does the jet continue to track so far southwards for such an extended period? This can only be due the SSW impacts. Furthermore, I just do not see the current pattern of a "stalemate" continuing indefinitley, with rudderless, meandering and slow moving LPs sandwiched in between the HLB to the north and the southerly jet. Something will have to give before too long. Unless the flow reversal ceases and the jet resumes a more seasonal mid latitude position, I can only envisage further surges of colder air spreading westwards and southwards. These will almost certainly not be as cold as the record breaking spell we have just seen but still probably cold enough for further snowfalls and frosts. It will not take much to nudge the HLB back into a more favourable position. How can I say all this when the models do not agree on any particular outcome? Well, I might be wrong but let's have a further look at some of the evidence.

    The strat specialists are talking about further and final warmings. On top of this we will shortly be getting to the normal seasonal breaking up of the stratospheric PV and this year it is probably much too late for it to reform properly anyway - although I gather that there was a brief attempt at this. I believe that the latest suggestions are that a further warming might impact by or just before the equinox (March 21st) around the end of week 2. I freely admit that I still have much to learn in all of this and I'm still fairly weak in terms of understanding many of the stratospheric processes and so I'm guided by opinions of a few of our more knowledgeable members. I have had some help from a few very patient members in much the same way as I received a lot of help learning much more about atmospheric angular momentum (AAM), frictional torque (FT) and mountain torgue (MT) earlier this winter.

    Another key factor that we saw was a near record strength MJO signal when it reached phase 7 in the latter part of February. This along with interacting with other drivers was supportive of HLB patterns. Right now the MJO signal is very weak and it is pretty inactive. The latest weekly NOAA MJO report was published yesterday. Here's the link:

    MJO WEEKLY NOAA REPORT:       http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjoupdate.pdf

    Here's the summary: "OVERVIEW  The MJO continued across the Indian Ocean during the past week while showing signs of weakening. The signal appears most tied to anomalous upper-level divergence and to a lesser extent upper-level zonal winds and low-level anomalous westerlies.  Tropical Cyclone Dumazile in the southern Indian Ocean may be partially responsible for the apparent character of the aforementioned wind fields by enhancing upper-level divergence and convection over the Indian Ocean but encouraging low-level easterlies near the equator. Low-level easterlies over the Pacific have also been relatively weak.  Dynamical models continue to propagate the intraseasonal signal eastward during the next two weeks but at reduced amplitude, suggesting a possible return to a weak MJO state after active conditions during the past 3+ months"

    We also need to factor in the underlying ENSO state where we have had a fairly weak but pretty longer lasting La Nina. This has been very much east Pacific based. That initially favoured a front loaded winter but giving way to a strengthening PV and then a more varied period as the jet stream and PV naturally start to weaken towards the end of the winter season. The La Nina has been weakening steadily in the last few weeks and the latest weekly NOAA report makes for some fascinating reading:

    ENSO WEEKLY NOAA REPORT:         http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

    This shows that La Nina has further weakened in the last few days and will become less influential. NOAA feel that its well on course for the ENSO state to return to neutral during March to May. With this slight acceleration in the weakening we might see this occurring during April. Just to raise the interests of those now looking for some spring warmth, the Nina to neutral phase at this time of year is often associated with relatively fine, dry and warm conditions.

    Right, bringing all the above factors together, I will attempt to summarise the overall order of events that brought about this unusual pattern change in a very simplified way (I'll use the abbreviations, so please refer back to the earlier text for the full wording):

    La Nina starting to weaken; AAM having been negative for a prolonged period spiked upwards in early Feb; this +AAM lead to +FT followed by +MT with the usual 10 to 14 days time lag response; the +MT was, along with other factors (which I have not referred as even the specialists are debating the causes) partly responsible for helping to trigger the SSW by sending forcing wave snot only through the middle and higher latitudes (Rossby Waves) which impacted on the strength and position of the jet stream but also high up into the lower stratosphere; the MJO fits into to this process with the +AAM/FT/MT and weakening La Nina combo all playing their part, although there is again much debate as to why the MJO managed almost record strength amplitude (this has been partly explained to me but it is quite complex); then the SSW impacted on the surface creating a full pattern reversal and establishing HLB patterns and displacing cold to the mid-latitudes; this particular pattern arrangement was perfectly aligned to allow a surge of exceptional cold surface and upper air to push westwards from Siberia and right through to the mid Atlantic; the jet stream was forced well to the south; much of Europe and the UK saw a week or more of strong easterly winds with some large snow accumulations; storm Emma engaged with the deep cold block and produced blizzard conditions and freezing rain in places too; than a thaw commenced with less cold conditions moving in from the south; now we are left with a very uncertain outlook with the legacy of the SSW still in evidence, the jet stream; far to the south and LPs taking up the void. So, what happens next? 

    If we do see another hit from the SSW with renewed cold weather, this could last for a few more weeks. We might see quite a sudden switch perhaps later in April from cold to warm. Nothing is ever guaranteed but one to look out for. In any case, the continent starts to warm up rapidly as we move through March and into April. Any flows from an easterly source will be far less cold by then. The delay in warmth would come if we see something of a repeat of the March/April 2013 prolonged cold spell. That spell was also triggered by a significant SSW. No two events are ever identical. I do see some similarities now though. For much of the 2013 spell the winds blew from the north-north-east or due north-east and not from the east. As we progress through March into April this is often a colder direction than a straight easterly with the  NE flow originating from the Arctic but then mostly making it here over a land crossing. Here's a reminder of several of the charts from that spell with pressure, jet stream and the 850 temps:

                     March 18th 2013                                             March 31st 2013                                            April 6th 2013    

    archivesnh-2013-3-18-0-0.png         archivesnh-2013-3-31-0-0.png       archivesnh-2013-4-6-0-0.png 

                    March 18th 2013                                              March 31st 2013                                             April 6th 2013   

     archivesnh-2013-3-18-0-5.png       archivesnh-2013-3-31-0-5.png         archivesnh-2013-4-6-0-5.png

                 March 18th 2013                                              March 31st 2013                                             April 6th 2013    

    archivesnh-2013-3-18-0-2.png       archivesnh-2013-3-31-0-2.png         archivesnh-2013-4-6-0-2.png  

    I must stress that analogues can only ever be used as a very general guide. There are some similarities but there are differences. The SSW in 2013 started in January and there was some earlier very cold weather well before the main event. The long cold spell started over 2 weeks later than our spell. After some milder days the current pattern reversal may behave quite differently to that of 2013. Only time will tell.

    Just briefly back to the models to take a look at deep FI. Only GFS goes out that far. Out of curiosity more than anything else, I show the day 16 GEFS panels for pressure, the jet stream and the 850s to see whether there's any hint of the next possible SSW impact showing up at all:  

    GEFS Day 16:

    gens_panel_ywx7.png     gens_panel_kux7.png          gens_panel_yev7.png                                                  

    Pressure at T+384:    http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=6&ech=384 

    Jet at T+384:              http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=3&ech=384

    850s at T+384:           http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=5&ech=384

    Many members do still show a flow reversal. There is some HLB and there are a few Scandi HPs. There are also a few with a LP trough over Scandi and indeed some have a north-north-easterly flow. Definitely not enough support for any type of solution and extremely mixed overall. If we see an evolution towards the 2013 type of set-up or HLB in other places then the models, as with the main SSW event, may not properly pick up on the signals until its within the 7 to 10 day period.

    There is some support for this more north-easterly cold pattern, this time from Judah Cohen in his latest "AER" Arctic report. Last winter I regularly used to quote these in my MOD reports. His latest weekly report was published yesterday. Here's the link:

    https://www.aer.com/science-research/climate-weather/arctic-oscillation/

    Judah feels that the HLB will initially weaken during the next week or so with both the Arctic oscillation (AO) and North Atlantic Oscillation (NAO) trending positive and a slow relaxation of the cold over the UK and Europe at first.. He feels that HP will remain on the Eurasia side of the Arctic and this will force lower heights and colder conditions westwards from northern Asia and through into Scandinavia, Europe and the UK during the next two weeks. I show his summary below:

    ...."Summary

    • The Arctic Oscillation (AO) is currently slightly negative and is predicted to trend positive.  The positive trend coincides with the weakening of the signal associated with the downward propagation of atmospheric circulation anomalies related to the polar vortex (PV) disruption.  
    • The current negative AO is reflective of positive pressure/geopotential height anomalies across the Arctic and negative pressure/geopotential height anomalies across the mid-latitudes of the North Atlantic. The North Atlantic Oscillation (NAO) is currently also negative with positive pressure/geopotential height anomalies across Greenland and Iceland and negative pressure/geopotential height anomalies across the mid-latitudes of the North Atlantic.  The forecasts are for the NAO to also trend positive the next two weeks.
    • The models predict that over the next two weeks with weakening high latitude ridging/positive geopotential height anomalies in the North Atlantic the current cold pattern across Europe, including the United Kingdom (UK) will relax. However predicted more persistent positive pressure/geopotential heights across the Eurasian side of the Arctic will force negative geopotential height anomalies and cold temperatures across Northern  Asia and Scandinavia over the next two weeks.
    • Currently amplified ridging/positive geopotential height anomalies stretches from the Aleutians will slowly slide westward allowing for troughing/negative geopotential height anomalies in the Gulf of Alaska. This will favor ridging first in Western North America slowly being pushed eastward with troughing initially in the Eastern United States (US) eventually shifting offshore. This is will result in generally normal to above normal temperatures for western North America and normal to below normal temperatures in the Eastern US.
    • I continue to believe that the weather for the remainder of the late winter will be dominated by the response to the ongoing significant PV disruption.  The pattern of high heights in the Arctic with lower heights across the mid-latitudes in particular the Eurasian continent but focused across Siberia is the tropospheric response to the ongoing significant PV disruption.  This pattern typically persists for four to six weeks following a PV disruption and though the cold response is often focused across Eurasia, with time usually includes the Eastern US"....

    Judah's full report goes on to discuss the impacts and he states that this type of pattern can persist for 4 to 6 weeks.  He shows a lot of charts which are mostly based on the GFS and GEFS models. His views, just like all the models, the strat forecasts and more especially my own (far less experienced) views, have a higher than usual degree of uncertainty. I will be monitoring developments closely and bearing in mind much of what I have covered above, I will be looking for any hints of either pattern changes (to a warmer solution) or for a resumption of the cold. I must admit to having a somewhat divided opinion about renewed cold prospects. I'm certainly attracted to the possibility of the cold spell, whenever it ends, being quite quickly replaced by some decent spring and early summer warmth.                                    

     

    Edited by Guest
    Correct typos and check charts
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    Posted
  • Location: Windermere 120m asl
  • Location: Windermere 120m asl

    A very 'cyclonic' outlook - 2018 certainly delivering a variety of synoptical set ups. Long wave trough wrapped up in itself, held by heights to our NW and the jetstream anchored well to our south.The result, meandering low pressure reinforcing itself, a messy set up at anytime of year. Surprised too at the depth of low heights being shown by the models for the weekend, given the temp profile differences are not significant and we have no long drawn polar or tropical maritime air invading. I suspect these will be weakened at the time comes. Conversely a deeper low pressure system would enable stronger ridge to build to our North west, which in turn would force the trough to pull down into Europe enabling the colder arctic evolution shown by some of the models long term. 

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    Posted
  • Location: Rotherhithe, 5.8M ASL
  • Location: Rotherhithe, 5.8M ASL
    3 hours ago, Tim Bland said:

    Potential from the ECM for an end of the month cold spell? 

    D2D85D67-91FA-43F1-9CB7-BAE3D2DA201A.png

    There are thirty-one days in March that takes us mid month.. :laugh:

    A most terrible outlook if you want something drier and warmer, unsure whether this is fiction but do poor springs correlate better with decent summers? Suppose you have to have some balance. Summer of 2013 maybe I’m losing my mind but I think that was a pretty decent summer, with some long sunny warm spells across country. 

    It seems the polar front wants to push more south with more colder air in the mix. I can see an April showers, showery set up, however with it comes chance of rain, sleet, hail and snow just about anywhere. At least it will be interspersed with sunny spells, here’s hoping we see a clean northerly airstream.

    Edited by Daniel*
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  • Location: Mytholmroyd, West Yorks.......
  • Weather Preferences: Hot & Sunny, Cold & Snowy
  • Location: Mytholmroyd, West Yorks.......

    I still think with one of the drivers showing a deviation over 5 s.d.'s from the norm takes things beyond the programming capacity of the current models?

    They will run at their extreme numbers for that input but not the 'real' numbers?

    As such I think we're back down to 3 days ahead?

    Will the energy give a push so hard as to flip major cold for major warmth?

    Watch this space!

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    Message added by Paul

    Please only post model discussion in here! 
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