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  1. 112 points
    So a rather long post ( Will also clip into the winter forecast thread ) However just an update on saturdays post, a large debate around models - & I took the day 6 UKMO & GFS charts to compare for verification- These were both of the 6 dayers GFS on the left. Note GFS flat with no heights in Greenland, UKMO more amplified with heights - Also a circular vortex North of Scandi. UKMO has energy seperation & a closed low - GFS just sends a 'block' of energy through - Look at todays UKMO 72- Comments: -Circular vortex just North of Scandi -Closed low traversing East towards Iceland - Residual heights over Southern Greenland - Arctic High 1040MB. Conclusion UKMO is a clear resounding winner here- every element that differentiated from the GFS is still apparent in the T72 chart, this is a big thumbs up for the UKMO, proof ( on this occasion ) that the GFS clearly has an eastward bias & why looking at developing heights over the pole ( NB UKMO 144 today ) The UKMO resolves energy better... So, onto the SSW it seems an eternity since the first warming started showing up way back in December - but now we are day +6 since the wind reversal- Much of the discussion has been about the 'slow' response in terms of downwelling in terms of creating a significant AO - This is depicted nicely on the NAM index which I have saved from the other week- The GFS bias initially showed minimal downwelling, however gradually ( like the comparison with the UKMO above ) has slowly come into line with a more 'propergating' feature. I think we have been unlucky with the QTR - sadly the NOAA composites page isnt available, however twice there has been significant mid lattitude blocking developing in the locale forecast as a QTR relating to the strat split- However the blocking has been just to far East for us to really gain any benefit - *but* as far as Europe as a whole is concerned in terms of snow this winter could challenge the record books in terms of sustained depth from mid Jan onwards- My memory ( from the old teletext days ) was that St Anton could reach 600CM on the tops by the end of Winter- By the end of this week it will be North of 400CM Also records going in Greece with snow in Athens & -23c reported North of the region- So whilst the QTR missed us that release of deep cold didnt miss everyone... The next stage of this SSW / Split will be crucial for winter as the norm here would be a gentle recovery from the PV ( not to normal strength ) - however if like me you were hoping for something that lasts longer than a few days - IE 1 MONTH then a secondary warming & further splits would be the upper cut to the PV that would knock it out for the rest of the Winter. However just before commenting on that lets see the progression of the downwelling- The charts at the top are from around NYear- now look at the NAM index from the GFS today ( remember its still not the best model for coupling the Strat > Trop ) Here is the NY 100HPA profile V todays Lots more clustering below 5M/S- some below zero. This is why we are seeing the GEFS respond post 192 - Note the AO Ensembles - Starting to gain momentum towards -4. Moving through day 9 on the ECM strat from yesterday we see that the Uwind is still negative but importantly the allignment of the vortex lobes are significantly different to this week - encouraging blocking- Red is the left lobe allignment Blue is the right lobe allignment Yellow is the blocking potential- Its quite apparent that despite a split the current shape of the lobes means that the U wind off the states doesnt support blocking, but day 9 ( alligned to the trop response ) allows for a different pattern that is complimentary towards the jet being sheared up the western side of Greenland & also residual flow alligned SE in the atlantic - We should also see the vortex 'throwing' Scandi Deep cold SW across Europe - This is the jet flow -( yellow ) & associated areas of deep cold. This is a solid -AO / + PNA / -NAO pattern. This is why the models have suddenly flipped to that sharp NW > SE allignment If you are looking for sustained cold then a SSW split + follow up warmings & continual negative zonal winds are the hallmarks of LONG cold spells, * with the usual caveat that we are the SW point of the cold & could always see some milder air pushing back west * This could be a crippling final quarter of Winter for Europe & the Balkans- Best S
  2. 103 points
    I assume the overnight ECM has (temporarily at least) put an end to the glass half empty stuff from some posters yesterday. I'm sure the next variation in op run will bring them back out - but if you are on here to learn and are hunting snow/cold (sad to see that thread go....) then here's a bit of learning for you. The overnight chart from ECM at the later stages of medium range reliability is fabulous. What you are looking for here is the source of the air in situ over the UK - and the angle of approach from the system in coming...and where it will pull its air from. Note here at 216 you have a generally slack E/SE flow over the UK established from the back end of the week to come, with air being drawn to us broadly from Scandy and Northern Europe - already both snowbound and across a north sea that is not especially warm. Meanwhile the incoming low has purples in it in terms of pressure - meaning it has been drawn directly from the deep vortex low over Canada. As it approaches and disrupts against the higher pressure ahead of it - it "slides" southwards and the winds from that system turn to the SE, pulling dry continental air up from France. The final image shows how the moist, atlantic air (still pretty damned cold because of its Canadian origins) has dropped into France. Eastern UK has a feed straight from central Europe - western parts of the UK from a slightly milder France - but the combination is such (especially in January) that snow is likely countrywide. This is a "slider" low - precisely because the atlantic system has come from the NW and literally slid down the face of higher pressure ahead of it. Are there historical parallels? 3 from my memory that show a variety of similar events. The most similar to the one progged here would be Feb 1996 where we had a very similar setup a couple of weeks later in the season. Note again the deep origins of the sliding system (purples) and the cold air in situ from a SE feed. 1996 brought huge snowfalls to some parts - myself fortunately included this time around while in Dorset. Slightly different, but no less impactive in terms of snow, would be 1985 and 1979. 1979 first. Note here that the incoming system is a lot flatter - it's approaching from due west and meeting the trough in place over scandy. On this occcasion the deeper cold was in the resident scandy lobe and less in the approaching system. Note the isobars ahead of the atlantic system turn, once again, to that SE flow and as the higher pressure ot the south drew away plenty of snow fell. Feb 1979 was full of such events - they kept repeating over and over giving blizzards to all parts. This image below, again not a million miles away from where we are heading but with a very convenient wedge of higher pressure just to the north of the UK - brought some of the heaviest snow falls in the last few decades, especially a few days later around Valentine's Day. And last of all 1985. A bit different this one - but if you are wanting to learn about snow giving conditions good to dig out. This time the system approaching from the west runs up against a block that is much more entrenched to our NE - but the effect really is the same. Moist air from the west disrupts against the colder, denser air in a block ahead of it and slides underneath. Because of the angle of trajectory these are sometimes described as channel lows because the atlantic system's slide angle takes it through northern France as it pulls continental air up ahead of it into its moist lead edge, turning all that moisture to snow. Bottom line is - we are approaching a pattern which could replicate any or all of these situations because of the forcings which are in operation. However - and it is a big however - for every one of these big snow makers there are plenty of historical near misses......either because too much warm air gets wrapped into the system or because pressure to the south remains too high and continues to feed warmth up from the south. Putting my own neck on the block here - I don't think these are going to be a factor this time around because of the forcings I described last night at some length....but they MIGHT be. Dont shoot the messenger if it all goes wrong - but if I'm honest I'm feeling pretty good about the alignment of things at present and in particular about the longevity of what may occur. Bear in mind that week beginning 21st January is likely NOT to be the peak of the process. If you prefer computer driven analysis then just look at the oft shown EC images for end of Jan into Feb for evidence....but the downwelling impacts of the SSW and the next phases on pacific forcing say to me that the peak will be somewhere in the last few days of Jan and on into the first couple of weeks of Feb. Historically probably the UK's sweet spot in terms of snow fall. Watch and enjoy the ride.
  3. 98 points
    It's all good folks - we are about to get slammed Think March 2013 imprinted on the middle of winter - what's not to love ! The slider solutions are dialled in as the wave guide changes, NW SE sliders will be the key feature of the next 6 weeks as the canadian vortex drains itself via downwelling. No it's not 62 or 47 or 2010 But what it actually is an SSW which we all now respect and have learned from, and have the nuance to watch in real time, spilling its arctic cold guts all over the mid latitudes. I am sorry for those of you who think , nope this is not a driver, nope AAM isnt a driver, MJO isnt a driver, Nino - isnt a driver - you get me? Simply put - they are - and always will be and GWO and AAM possibly the most reliable of the lot! Do not discourage in weather that which you have yet to understand - this science is difficult, no one is ever right, no one is ever perfect, no one on here alludes to that What I want to say is- for us afficiandos of cold, us dedicated individuals, hunting, searching, wanting looking and dissecting everything. We are all good Its near solar min, monster SSW, monster Split. NWP - Bring IT !
  4. 94 points
    Last one from me for 6 weeks before I leave in the morning for Canada . Our experts we use in resort have told me that todays upper air soundings over the Russian Arctic are showing Easterlies now established at 10mb level. They expect this flow direction to run down to the troposphere in the coming days ( the start of the reversing the westerly flow for much of Northern Europe including the British Isles ). This will impact on the models in the next 48 hours. So hopefully some good looking winter charts for you lot just around the corner. Will be watching from far a field with great interest. Bye for now and a happy New Year to all our forum members, young and old ! C
  5. 89 points
    For those who think the SSW was a bust take a look at this at T+3 Then look at the NW/SE jet axis over us, then look at the fact that the downwelling has been delayed but is just underway, and winter is not over by a long way. Then go and read up a bit about SSW's so next time you make a sweeping statement you are doing so from a position of greater knowledge. Thank You
  6. 89 points
    C'mon guys lets give @Paul and the mods a break with the bickering and personal digs type of posts after all it is a WEATHER forum and this thread is for WEATHER MODEL discussion I can only imagine how hard it is for newbies to try and decipher what is going on among all those types of posts so if anybody has any issues with posts / members perhaps it would be better to use the report post button / ignore member button or try and settle it like adults through PM's and also remember the couple of banter threads that exist Now onto the models I will refer back to my post from 8th Jan some statements / thoughts that I made in the post on 8th Jan "I still believe that any low pressures that do develop will begin to take an ever increasing NW - SE track (with the majority perhaps struggling to get much past the UK) resulting in some northerlies / North westerlies bringing the first hints at something cooler / colder to the UK " "My key period for this would be 17th Jan - 21st Jan " starting on this point, I am fairly happy with this still as we move towards those dates as it looks like around the 17th will be the first (of what I think could be quite a few within the next few weeks) at a sliding low attempt dont take the position / strength of the low too seriously as this is still changing from run to run but the NW > SE movement is there and a run showing possible north westerly / northerly / north easterly air by around the 21st onward for a few days onto my next statement / thought from 8th Jan "So what could happen after that?" "Well IMO it looks like being the last week of Jan from around 24th Jan - 31st Jan that the possibility of some fun and games with blocking and colder charts will reach its maximum potential so far this winter." Again I remain pretty confident with this, why? IMO there is still a signal for the last week of Jan for blocking to start to develop / take hold there are some more ensembles showing this but I think this demonstrates my point clearly enough AO still set to nosedive first hints that the NAO might head the same way And with the MJO looking like possibly heading back toward / through phase 6 / 7 by then that could also help aid blocking (again I am only going off my limited knowledge on the MJO and also might need to factor in some lag time) (some of the other MJO forecasts look a bit more uncertain / slower to go toward those phases ATM) Also still worth factoring in effects from the strat warming event(s) that have took place during late December / Early Jan. some more thoughts / statements that I made on 8th Jan "A word of warning / potential spoiler would be a west based - NAO which remains a possibility http://theweathercentre.blogspot.com/2012/10/east-based-v-west-based-negative-nao.html Key Points keep an eye on these beginning to nosedive once the blocking gets nearer https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.shtml be wary of the west based -NAO" All of the above are still true / possible IMO but with regards to the west based - NAO perhaps the chances of this wont be know until nearer the last week of Jan and where the models are seeing the potential blocking setting up / developing keep an eye on the ensembles for more and more BOOM type charts appearing in the run up to the last week of Jan I think the first area to focus on ATM would be the potential for slider lows and the possible snowy conditions that they may bring but I still believe the amount of BOOM charts will be on the rise the nearer we get to the last week of Jan. A few extra points I would like to make 1. I wouldn't worry too much about differences in each GEFS suite on the graphs (rises in 850 hPa temps) as slight changes in positions of possible slider lows and later on blocking highs can shift those 850's heavily in one direction or the other and I think we are seeing the usual ebb / flow of the models trying to grasp exactly where each low / high is likely to set up (possibly whilst trying to factor in ongoing effects from start event(s) and MJO etc) 2. How quickly have we seen in the past that things can change and head down a colder / much colder route a la Nov / Dec 2010 & Feb / March 2018 etc (yes there have also been occasions where charts such as "that ECM" where the cold looked like it was on route to the UK and suddenly diverted but I much prefer to look at things with a glass half full rather than immediately thinking that we have no hope / chance of the cold / snow reaching our shores / back gardens) using the 2 years mentioned above as examples and again I am not saying that anything of that severity is heading our way I am just highlighting how much can change within the space of a few weeks (using today's date 14th Jan and 2 weeks from now would have us in the last week of Jan , 28th Jan) taking the 25th November as the end date as that was when the colder air was spreading right across the UK then 2 weeks before was the 11th November 11th November 2010 > 2 weeks later 25th November 2010 11th November 2010 25th November 2010 an example of how quickly things can change / blocking can develop February 2018 - again I will use the 26th February as the end point as this was when the colder air was spreading across the UK so 2 weeks before was the 12th February 2018 > 2 weeks later 26th February 2018 12th February 2018 yes there was some snow around for some but I am highlighting how quickly more blocked conditions can develop 26th February 2018 Keep calm everyone and try and enjoy how the rest of January and beyond plays out, I still think we are in for some fascinating model watching. And I just want to remind people I am certainly no weather expert, I am just having a go at trying to predict where we are heading and seeing how close or far away I am (and if I am miles off the mark I will own up and try and examine the charts to see what happened and how we ended up with scenario A or scenario B etc) ensembles GEM 0z ensembles FNMOC/NOGAPS 0z
  7. 89 points
    After a health scare I have had the best news ever and been given the all clear. What a year it has been weather wise.Just like to take the opportunity to wish Paul,all The moderating team and all the members a very Happy Christmas,Have a break from The forum and enjoy the day with your Family's. Let hope for all us coldies January is a cold and snowy one. All the very best to you all C.S
  8. 86 points
    The Models Are Just Starting to Sniff Out the Major Pattern Changes - Better Late Than Never! As expected the models were almost certain to struggle dealing with the exceptional changes in the background signals - they almost always do. There are even inconsistencies within the same models' different type of output on the same run which is almost unbelievable. I will start with GFS who have struggled more than most. I'll refer to today's 6z run. We know that they have been indicating an SSW for several weeks now. Their strat charts have played around with the timing, the extent and the type of SSW but their pressure charts still bear little resemblance to their strat charts. The same goes for their mjo output which is the polar opposite to what the pressure charts are showing. Always useful to remember that it is the background signals to controls the model output (when the models take note!) not the other way around. The SSW is taking place now and some of the GFS strat output is already showing an imminent wind reversal (see the strat thread for details) and the earliest signs are already been seen in North Asia (more on that below). This 10hPa chart is for day 10 and shows a thoroughly disrupted SPV (stratospheric polar vortex) with both a displaced and split SPV. At no stage in this run does GFS show wind reversals at the surface in the Arctic on their pressure charts (this was the same in the run up to the "beast" following the February SSW until about a week before the full surface impacts). The day 10 chart on the op run actually shows a reasonably well organised PV with a default westerly flow and no reversal. Some HP has built across from both the Alaskan and Siberian sides of the Arctic but this chart is so far from correlating to their strat and mjo other output that it only serves to magnify the serious deficiencies in the main model and it seems clear that their nwp either does not have a sufficient data feed of both the strat and the tropical atmosphere or it is far too biased with the default always towards climatology. This is the GEFS panel for the same time. None of the ensemble members show a full reversal at the surface but about 6 or 7 do have HP building northwards or north eastwards which is a move in the right direction but even these do not represent their other data. GEFS has been going for steadily higher amplitude as the MJO progresses through phase 5. In fact it goes off the scale through phase 6 during next week and is predicted to enter phase 7 at near record high amp much as it did back in February during the last SSW. The chart is actually the "bias corrected" version! The ECM chart has the MJO at much lower amp and is more progressive through the phases but it has been slowly increasing amp during the last couple of days. The tropical forcing has been suggestive of a generally higher amp but GEFS is still the only model to go for the "extreme" outcome. It may well be that we'll see a model convergence with reasonable amp (more like the JMA position below) but week 2 MJO forecasts are notoriously unreliable and subject to change. Overall, the current consensus would be to progress towards phases 6 and 7 (and later on to 8 and 1) as we move though the first week of January and increasingly favouring HLB with a few days time lag to likely impacts - perhaps around days 10 to 15 or January 6th-11th which has been the more widely favoured period for some time. The other models also show a mix of outcomes although most show the HP to our south building northwards (not always decisively) and the trend is now suggesting that they are just beginning to pick up on some of the changes in the background signals. Most of the other charts have already been posted on here and it's encouraging to see ECM trying to produce a more amplified scenario, so I will move on to several other "key" charts. The "StormSurf " charts are based on NASA output but I'm only looking at current and short term changes. In my recent posts, I've been referring to the vast expanse of HP over much of central and northern Asia, Russia and Siberia - well that is now even more intense exceeding 1060mb in northern Asia. It's that area which is seeing the initial impacts from the SSW. Strong northern Asian blocking is one of the precursors to the lower tropospheric layers being receptive to propagation from the stratosphere and full coupling. Now the highly important influence of GLAAM (global atmospheric angular momentum) and the torques. Total GLAAM is still +ve but has fallen recently. The relative GLAAM tendency anomaly was +ve, then fell back very briefly to quite strongly -ve and is now rising strongly again precisely as anticipated. FT (frictional torque) is also rising. I have not shown the latest AAM and FT charts this time but I'll move on to MT (mountain torque). In my last couple of updates, I said that +ve EAMT (east Asian mountain torque) was extremely important in both this part of the process as well as playing an assisting role in triggering major SSWs. The previous spike in GLMT (global mountain torque - the black line) was around Dec 7th. It then nose-dived to be temporarily strongly-ve around Dec 19th and was predicted to bounce back very quickly to go strongly +ve again around now. The charts are always 2 days behind and are usually updated at around 1430 GMT - so this one is yesterday's chart for Dec 24th. It looks like GLMT is already +ve and probably still climbing right now. EAMT (the red line) has been following GLMT as a main component of it. If you refer to the top part of the chart which shows the regional torque latitudinal distribution we can see that the last +ve EAMT event is depicted by the deep red blob around Dec 5th to 10th and centred around lat 32N to 45N - which is just north of the Himalayas and across the Tibetan Plateau up to the Mongolian Mountains. The uplift from that event fed planetary waves right up into at least the upper stratosphere and this (with the time lagged response of a few days) helped to further weaken the SPV. Then we had that short period of -ve EAMT depicted by those blue blobs in the same region. Now we are seeing the next +ve spike which may well be as strong as or even stronger than the last one. This is perfect timing as within a day or two it is likely to send up further vertically propagating planetary waves which should help to finish off the SPV during next week if it still needs a final attack. The other benefit is that the strong +ve EAMT right now and for several more days is part of the surface pressure process propping up the huge HP block to the north. It's all more complex than this and I'm still learning about these processes. Just accept that what is going on now is part of a much larger process and it's all helping to "prime" the surface layers for SSW impacts. Although no atmospheric changes in our meteorological world can be predicted with absolute certainty, the changes in the background signals and the broader pattern reset gives us a real insight into what we are "likely" to see several weeks ahead. The models almost always struggle to take full account of these changes often up until a week or so in advance. This is a very significant SSW event but there "were" problems with timing issues, strength, type (displacement and/or split), the extent of downward propagation and the position and longevity of surface impacts. While that is still not 100% resolved, things are a lot clearer now. The tropical forcing and the teleconnective link between AAM, the torques, the MJO and the strat are all coming together more or less as predicted several weeks ago. I expect the models to increasingly factor in the significance of these changes during the next few runs. By the time we reach the New Year we "should" be very close to the fuller impacts showing up on the day 7 charts. So expect a mix of eye candy and less progressive runs and the usual roller coaster on here for a couple more days as they adjust. I remain very confident of a pretty prolonged cold spell in Europe, the UK and the eastern CONUS starting to take hold as we move into early January. Monitoring all the changes will be incredibly fascinating. I'll leave you to it for a few days and hope to come back to a much more optimistic thread. David
  9. 85 points
    All roads lead to Rome - or in this case a cold spell. There have been some odd comments on here today, given we are on the cuspy of only our second significant cold spell since 2013, and so I'm going back on my last post - and instead of looking only at short range charts from here it might be good to make some connections and map out the road ahead. Strat first of all. We have seen a slow downwell - no doubt about that - and a fairly chaotic displacement/split event that was uncertain for a while. But the mists have cleared, and the downwelling is finally going to impact more substantially on the trop pattern in the coming days. The atlantic profile for midweek is still fairly flat but the split has worked in our favour, with the Canadian lobe remaining in situ but the more substantial Siberian shard pushing back east towards the pacific. The 150hpa forecast 5 days later quite clearly shows this and you can see the push of energy at 30hpa moving away from Europe over the eastern Siberia with the Canadian shard sitting in place The signal for a resurgent midatlantic ridge up to the N/NW is quite clear. Picture those EC46 images showing more robust northern blocking by month's end - part of downwelling strat forcing. But we have a pacific signal that looks to be marrying up. Our current high has been resilient, but at too low a latitude for our liking. No getting away from that - forecasts a month ago saw the blocking, but saw it further north. The slow speed of strat impacts probably wrecked this possibility. Now torque effectis, apart from in the tropics, have been on their way down....but before long the bounce back up will begin again, and lag effects will time perfectly with maximum impact of strat downwell So we have the beginning of strat impacts to come in 7 - 10 days followed by GLAAM support 7 - 10 days after that. All good. But the story does not end there - the MJO, which on its own was not enough in early Jan to override other factors, is heading swiftly back around to phase 6 - 8 in time for February....so that just as the atmosphere needs a bit more of a bump to keep blocking in place - it gets it. Note also that the MJO is remaining generally active, and poleward wave activity is therefore going to remain a factor in preventing any flat pattern from getting a hold once again. Ventrice filtered plots remain quite impressive So - this takes a pattern of parallel forcings supporting a meridional signal and anything but a westerly atlantic pattern well into February. But let's finish on the strat…..because of all the factors that drive our weather it is becoming increasingly clear that impacts on the vortex that downwell to the trop are dramatic and forceful. The warming that started well over a week ago is just past its peak, but winds at 10hpa are set to remain easterly until the back end of the month, give or take At the same time westerly winds will return at the top. Bad news? Not at all. A return of westerly winds at the top will form part of the ongoing downwelling process - and just as we had a flushing process of westerlies pushed down into the trop round about now, helping neutralise attempts at mid atlantic to greeny height rises, so this flushing out of easterlies will serve to force them onto the trop pattern. Given that the 10hpa pattern will have been reversed for the best part of 4 weeks, we are facing a long process in this regard...and so the gradual recovery of the vortex will actually sustain a reduction in tropospheric westerlies for a long time also - I'd suggest most of February. And then in March the vortex is fading anyway. Will we get anything like enough westerly momentum to change the pattern out of the entrenched cold cycle? I'm not sure we will.....but that is a bit far off to be discussing in detail now. So - forget op runs in 8 or 9 days time that are making it look as though a resurgent trop vortex driven from Canada is about to fire through the atlantic. It isn't. a Canadian trough will remain in place as the strat image is imposed upon it - but the door in the atlantic is going to be slammed shut, and cyclonic energy will have to circulate around the edges. Cold northerlies or undercut scenarios. And if we can get slices of that cold Canadian vortex firing moisture down into Europe over the top, or later on potentially underneath, the block then we get the precipitation we want in a cold phase. This on top of the impacts of deep European snow cover that will help provide a very cold feed off the continent at times when the winds turn E/SE. Long post - apologies - but everything is in place for something a bit special. Stop worrying about NWP. It doesn't get a handle on all these processes well....and while there is no way I would want to call the microscale specifics at anything more than 72/96 hours (and always from UKMO and ECM) - we can sleep easy knowing that the macroscale factors are lining up in favour of snowy goodness for the second half of winter.
  10. 85 points
    Meant to post this last night but some forecasters saying mild Christmas. At this range ,about any thing could turn up ,strange year weather wise so far ,snow in the forecast tomorrow , STORMY with it ,plenty of rain next week and signs now of cold cyclonic next weekend . Our local squirrel s took BEDDING to their winter homes last week , yesterday they threw it out to the local polecats and like ,Today they are collecting it all back .went up woodshed just before sunset today and local vermin were BUSY storing winter food .some very interesting weather ahead I feel ,Stellas all round gang ,I'm usually lurking about as weather is always on my mind ,miss my dear late wife . It's great having this great forum , cheers all .
  11. 84 points
    LOOKING FOR SSW SURFACE IMPACTS NEAR THE POLE IN THE MODEL OUTPUT - COMPARISONS TO EARLIER EVENTS - PART 1: 2019 AND 2018 I'm writing this post for two weather forums (US and UK) but most of it is relevant to both N America and UK/Europe. I will be mainly drawing on charts produced by Meteoceil and these + archived charts from the NCEP reanalysis show the Northern Hemisphere from the UK perspective. Abbreviations used in this post: SSW - Sudden Stratospheric Warming SPV - Stratospheric Polar Vortex TPV - Troposheric Polar Vortex HLB - High Latitude Blocking QBO - Quasi Biennial Oscillation MJO - Madden-Julian Oscillation COD - Circle Of Death SOI - Southern Oscillation Index GWO - Global Wind oscillation GLAAM - Global Atmospheric Angular Momentum FT - Frictional Torque MT - Mountain Torque EAMT - East Asian Mountain Torque What I want to examine are the surface pressure patterns and charts in relation to previous SSWs and to show what to look out for in the current output. My focus will be for signs of the reversal propagating down to the surface in the high Arctic and close to the North Pole. I will look at charts around the time each main SSW event started, at the time of the specific types developed (ie: the displacement and/or the split), the time that surface impacts were beginning to show up and one or more later chart(s) to see how blocking patterns fell into place. I will divide this post into at least 3 parts over several days to cover separate SSW events. In part 1, I will look briefly at the current set up and then focus on the February 2018 SSW. In part 2 I'll focus on the 2013 SSW and in part 3, the 2009 SSW. Later on, I may move on to several earlier events - time permitting. Firstly, we need to see the dates, type and length of each event. I repeat this table for reference: This only goes up to 2010. Malcolm @Blessed Weather has kindly helped me obtain similar data for the 2013 event and there is plenty of data available on the Feb 2018 event. If nothing else, these posts will confirm that every SSW is different in many ways. The type of warming with the displaced and/or split vortex events as we know are highly important with the latter "usually" leading to more extensive HLB. The propagation and down welling of the wind reversal to the surface is often far from straight forward and precise timings are extremely difficult to nail down even within the D5 to D7 period. 2019 SSW: SSW started in late December 2018 (precise date to be confirmed). Type - Split, circa January 3rd, 2019. MJO - phases 5 and 6 with 7 and 8 predicted at moderate amp; ENSO - weak El Nino developing (there is a minor blip right now but do not get hung up on the SOI and on some of the S Hem ENSO impacts); wQBO (descending); solar - near minimum. I'll start with the current "ongoing" event which I'll call the "2019 SSW" to avoid confusing it with the earlier 2018 event although the warming in the upper layers started in mid/late December 2018 with repeated attacks on the SPV. GEFS and ECM are much more closely aligned now compared to the last couple of weeks but there is still some uncertainty over how fast the progression will be. In the second half of January we would normally expect this to favour HLB. As this SSW looks like being a long (or even very long) event it would not be too bad if the MJO misses out on its 1 to 4 phases and re-emerges in phase 5/6 again for a repeat performance (perhaps at higher amp) during February to give us a second bite of the cherry. I appreciate that on our side of the pond phases 7 and 8 (and 1) are better for blocking patterns while in N America phases 8 and 1 (and 2) are better. The GWO is now strengthening again and progressing through phase 5 and looking set for phase 6 (if it's not there already with the 2 day chart time lag). The relative GLAAM tendency anomaly has been rising again as is total GLAAM. That's encouraging for +ve tropical forcing but there has been a timing issue. Ideally, we would want to see the SSW surface impacts more or less coincide and it is not completely certain that GLAAM will be maintained in an elevated for more than the next 10 days or so. It is, however, pretty likely that the GWO will perform in a similar way to the MJO and it has been on a repeat cycle since early November. So we might see both January and February impacts. FT (not shown) remains +ve. A reminder of the GWO phase chart. Then we have further good news. Global MT (black line) is +ve and just recently, rising further. This should prevent EAMT (red line) from falling back too far and it'll likely remain +ve for even longer. The strongest signal is at 30N to 40N (the red blobs in the upper part of the chart) centred around the Tibetan Plateau (see my early posts for greater details on this). The +ve torques should assist in keeping GLAAM +ve for an extended period with perhaps only a short weaker or -ve blip. Now to relate this to the models. I prepared this post based on today's 0z and 6z output and I know that the 12z will be out by the time I've finished. As there has been considerable run to run variability this does not really matter as output is likely to remain volatile for at least several more days and possibly rather longer than that. What I noted however, was some remarkable "consistency" on the day 5 output (something not seen at all on previous runs with considerable disagreement): I'll just show the GEFS 6z "mean" for today. The moderate amplification that we've seen so far has been related to the +ve GLAAM, torques and the MJO at decent amp through phase 6. This has produced some quite stationary or slow moving ridges and troughs and the recent cold plunge into Europe which looks set to be repeated during next week. I'll leave it to other posters to comment on their shorter term "home" patterns be it UK, Europe or N America. I'm really focusing on the high Arctic. There are just hints of HP building closer to the North Pole. Now the January 9th chart. HP is building right over the pole. and the TPV is looking set to split just to the south. This is the mean chart but every GEFS ensemble member has HP over the pole at this time (see below), plus the control run + the GFS operational run. Here's the panel: EDIT: I had saved the 6z but the gif updated to the 12z which still has all the members with HP building around the pole. Moreover so do "all" the other main models - GFS (parallel), ECM, GEM, NAVGEM, JMA and ICON. As you'll see when I cover the 2018 and earlier SSWs, these are important early signs. This coupled with the latest news on the stratosphere suggesting that the reversal is now down welling through the troposphere with several commentators suggesting that this may only be 3 or 4 days away. Now, please do not take this as definite - things can still go wrong or at least we may have further delays. The fact that all the models agree on around day 5 for the first signs of polar impacts is encouraging. Rather than pushing things back, if we can move things forward then we'll get the best combination of GLAAM and the torques with the tropical forcing with stronger HLB much more likely and assisting better strat-trop coupling. The full story is still in its early stages. Will the existing amplified pattern link up to HLB? Will there be a transition of a few days with a flatter pattern? Where will the blocking set up? How severe will the cold be and how long will it last? "If" there is a further delay, things still look good into February. So the 2019 SSW still teases us but I remain very optimistic of widespread cold weather going forward with some earlier rather than delayed impacts. 2018 SSW: SSW started during February 2018. Type - Split, circa February 12th, 2018. MJO - phases 3, 4, 5 and 6 at increasing amp and entering phase 7 at around record high amp (see below); ENSO - moderate La Nina (but with a weaker phase in January) eQBO; solar - weak and falling. Note that the MJO was in high amp phase up to the time of the initial triggering of the SSW on February 12th, then continued at weaker amp through to phase 8 (ignore the forecast "green" bit as I'm looking at what actually occurred). The time lagged impacts on HLB fitted in very nicely. This chart from the archives (see below) shows that the MJO continued through phase 1 at increasing amp then onto phase 2 (good for N America which saw the SSW impacts a week to 10 days after the UK and Europe) and briefly into phase 3 before passing through the COD and back out to phase 7 towards the end of March. Here's a link to the archived NOAA weekly reports going back to 2006 and these contain the phase charts and a lot more. http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/ARCHIVE/PDF/ Unlike the current event, GLAAM had been strongly -ve through much of January 2018 and rose strongly at decent amp through phase 4 and 5 into early February and at moderate amp through phases 6 , 7 and into 8 by February 10th. So pretty strong and with +ve torques in the build up to the SSW. The spike in global MT and EAMT in early February and with that 10 to 14 day time lag almost certainly helped to trigger the SSW on February 12th. The next spike may well have assisted the secondary warming. I covered this in more detail in my last post. Now the models. I'm using the excellent NCEP reanalysis charts from the archives. You can trace the whole of the 2018 SSW and much more on this link: http://www.meteociel.fr/modeles/archives/archives.php?day=12&month=2&hour=0&year=2018&map=4&region=&mode=2&type=ncep The SPV split on February 12th and models were generally showing pretty mundane output (seems familiar?). We had some polar maritime air in the UK and central/eastern CONUS and Canada had a "standard" (not SSW related) Arctic outbreak. Just one week later and the models were starting to sniff out something going on and there were signs of the pattern reversal impacting with the build of HP at the pole but only very modest amplification of the Azores HP. Strong HP over central and northern Asia and building across from Alaska. This post is already getting very long but for those of you who want to see how variable the model "forecast" output was a few days before, run through the archived "forecast" charts - here's a link: http://www.meteociel.fr/modeles/gfse_cartes.php?jour=7&mois=2&annee=2018&heure=12&archive=1&mode=0&ech=6&runpara=0&carte=1 You can play around with all the output and reset the date ranges etc. A further week on and it's getting very interesting. Arctic HP extending to Iceland and Scandinavia. The "Beast from the East" was just awakening over Europe and the UK. Note that the TPV was still over northern Canada but it was shortly to be on its journey across to Siberia. Just 4 days later and the TPV had migrated across to Siberia. A true Greenland HP had developed. The surface flow reversal was now pushing on right through CONUS. The beast is at its most intense over western Europe and the UK. Three more days later and the reversed flow at the surface shot through Europe, the UK, across the Atlantic, Newfoundland and through to central CONUS. After weakening somewhat, the SSW (with its secondary warming impacts) is having another go. The "Mini beast" (or beast 2) hits Europe and the UK Canada and central CONUS saw the most severe impacts during much of April 2018. Although the current and the February/March 2018 SSWs were both "split" SPV events you can see that the build up had some similarities but also many differences too. One can see how quickly the model output changed and how dramatic these events can be. I hope that we will see something very special from this event. Watch out for those Arctic profiles and the HP building there. Next up in part 2 (tomorrow) I'll look at the 2013 SSW which had a displaced and a split SSW with separate impacts over a prolonged period. David
  12. 83 points
    New EC weeks 3 and 4 as you were. High pressure in all the right places.
  13. 82 points
    I'm starting think that for some in here following the models is a form of self-flagellation. I mean, you have lots of expert views giving lots of details on the overall signals and direction of travel at the moment and you have that same general theme showing on virtually all of the models a lot of the time. And still on every single run, there are the same people over analysing them to the nth degree either getting caught up in will it won't it snow / how much in various localities at 10 days or so out (always a pointless exercise), or on milder runs it's like that particular model just shot bambi and is responsible for the end of any cold weather ever. Things are happening in the atmosphere right now, the most likely direction of travel is a cold one. The models are a bit up and down due to all that's going on, and so therefore, surely, unless you just want to create drama the answer is to accept that fact and not get hung up on every single run of every single model?
  14. 80 points
    Afternoon so 2 hours on the train should be plenty of time for a post- The last 2 weeks the projected SSW has gradually worked through the models & is now 'imminent' ~ 30hours away is when we go negative on the zonal wind @10HPA/ 60N. But I guess many onlookers will be wondering why the distain for the GFS V the Euros, is it really that bad. Well sadly yes it is. The failure of the GFS is going to be 2 fold here. 1) Identity of type of SSW - Split or displacement. 2) Non propergating ENSEMBLES. So going by the first point, this refers to a models ability to 'see' what that Stratospheric energy & warming looks like at the height of the strat, you have 'high top' models - highest being Glosea then ECM, you also have non High top - GFS which IIRC is 64km V Glosea ~80KM. IIRC ECM vertical resolution is closer to the Glosea. The GFS being poor resolution & the ENS being even lower resolution means that the ability to resolve / locate & then split energy is much inferior to the Euro model, as a result the model will see a 'blob' of warming however wont be able to see the warming plus energy splitting, thats above its means. So the GFS can be scored reasonable for the 'identification' of a warmer- even taking into consideration the errors in actual timings - however its score rapidly decreases if you want resolution to a Split V Displacement- NB here is the GFS elipses about 10 days ago- You will see the GFS ENS green & operational orange not being able to pinpoint a split - ( which the sparked masses of debate on twitter from people who should know better than to use the GFS ) If we compare this to the high top ECM, whilst similar to the GFS in timing errors the actual resolution of the SSW was pretty much bang on. Why is this important - What we are currently seeing is a QTR to the split as the Troposhere mirrors the stratosphere split, however why did it take days for the GFS to see the first ridge & cutting trough over Scandi- Why was it always East!???? Simple- The 'Eastward' (E) energy from the zonal wind was incorrectly modelled - NB GFS model 'E' v ECM (E) * remember take the Eastward component * The poor modelling of the (E) component for about 5 days up until about Fri Eve / Sat AM drove a fairly uniform Eastward motion around our part of the globe, hence with the scandi tough there was a fairly amplitude inflection point meaning its bend & southerly element was low -GFS catapulting it Eastward- Then slowly as the warming proergated down from 1HPA to lower 5HPA & into the GFS comfort zone so the GFS picks up the split- We now look at todays elipses - for day 4/5 Its finally caught up 96/120 & hey presto its on the same page as the Euros now.... ( At least for the time being ) So onto point 2 - GFS propergation issues. The modelling of the strat is generally difficult especially the coupling of a downward propergating SSW to the troposhere, so again only the highest resolved models will pick it up- it appears the GFS has coupling issues as the its ENS suites for the past 5 days have stopped it fully propergating ( again creating much speculation on here & twitter ) all again annoyingly GFS based- Here is the NAM index which shows how the SSW is progressing with negative vales indicating propergation NB GFS ENS 3 - 7 days ago = Non propergation. 100HPA is where we want it to reach ! Notice it stops short - So the ensemble suite from maybe Weds onwards up to around Yesterday wasnt seeing that wave come down - hence a lot of people were looking 10/12/14 days out in the ENS for high lattitude blocking when infact it was never going to appear- Whilst the ECM had already picked up the deceleration at 100HPA for day 10 ( 26/12 ) day 1 & day 10 char So again, ECM was already factoring in a decelerating jet - hence the operational model runs showing a maintained blocked response out to day 10 with higher & higher potential. The GFS has cottoned on now though- Todays ENS @100HPA show the GFS dropping nicely ( NB how poor the operational is though in orange ) Pic 1 ENS from 5 days ago flatlining the 100HPA wind V todays dropping it from 10 to around 4 M/S The main dip comes down around the 8-10th & guess what thats why we are seeing High lattitude blocking now appearing in the GFS ENS - its not a coincidence !!!! Now that the split is in range & the GFS is picking up on the correct outcome in terms of deceleration so the gulf between the GFS v the EUROs should reduce this week as they are working on the same stratospheric & zonal wind speed data now -But never forget how bias the GFS is in terms of powering up that jet.... Propergation is alligned to the 10th Jan - ( which is about 2-3 days later than initially progged ) Dates for propensity of lowest -AO values 10-20th Jan.... Cheers S
  15. 78 points
    I'm sorry for being off topic but I'm sure mods will forgive me for this one. Very sorry to hear you're missing your wife, this time of year can be especially hard and you can't just switch off that sort of emotion. That said, I always smile when I read your posts and I'm sure many others feel the same. All the best. It's always a pleasure having you around.
  16. 77 points
    Pondering evolution and longevity today. It's taken it's time in coming - and I will do a longer post later tying in the thoughts of December and early January into what is happening now - but the gloom of 5 days ago seems a distant memory as the blocks begin to drop into place. In Dec 2010 we got a very swift transition to a deep scandy trough supported by a very sharp and strong greeny high - but it wasnt particularly long lived. It started to fade within a week because all the drivers were moving things back to a mobile pattern, and then the rest of the winter was unmemorable. This time around we have a much slower evolution - but the blocks are in place for a much more sustained affair. The initial cyclonic euro/scandy blast wont be quite as severe or swift as 2010 because we havent got the same strong block surging up over greeny BUT we are in the heart of winter rather than at the outer edge and with pacific signals remaining on track and a slow strat process suggesting slow but positive evolutions ahead we could find ourselves in a pattern that sustains the cold and, at this time of year, brings plenty of snow from this predominantly cyclonic signal, at least in the medium term. Might we see mention of blizzards in parts? Quite possible. Longer term more entrenched cold, maybe a bit less precipitation. The potential for a noteworthy spell of weather that can be mentioned in the same sentences as Dec 10, Jan 13, March 18 looks on the cards. I'm breathing a sigh of relief and putting the knitting needles away - for a short time doubt began to creep in as to whether synergy of pacific and strat would work out as all instincts and understanding suggested - but today all is clicking nicely. I wouldnt bother wondering or asking where it will snow for a good while yet - but with a bit of luck and a half decent roll of the synoptic dice we can get at least one solid front to cross the country to give everyone a shot, and plenty of convective action pushing inland. Window of opportunity from Friday next week - but probably midway through the following week for maximum chances. And dont expect this pattern to return anywhere close to mild (or even average) for a while. For a little bit we can afford to put the teleconnective charts away and forget macroscale pattern drivers, and instead enjoy a bit of fax chart scrutiny, weather radar updates and even some lamp post action. Lovely.
  17. 73 points
    MY CURRENT VIEWS ON THE MODELS AND THE OUTLOOK That was a great post @Kirkcaldy Weather and should be read by all those who are moaning about the output. I have very little time now or for a few days - so rather than show loads of charts, I'll make a few bullet point statements on the background signals, the model output and several general comments. No two SSWs are alike - I do not know how many times that has to be said. In my last two posts I tried to show what to look out for with comparisons to the current set up and charts with the 2018 and 2013 SSWs (part 3 on 2009 with likenesses and differences to 2019 to follow by next weekend). What those archived charts showed was just how quickly the HLB patterns developed and the whole northern hemisphere set up changed and evolved. I noted John's @johnholmes comments this morning wrt examining archived "forecast" charts prior to earlier SSW events - something I suggested too - they're available for most of the models now and certainly the big 3. John also queried whether or which previous SSWs had failed to deliver any significant cold here in the UK. I'll just repeat a table here: We know that 2018 and 2013 delivered big time and they were split SSW events (2013 displaced and then split) and so did 2008//09 and 2009/10 both also split. The last displaced SSW was in 2007/08 and I believe that can be considered a failure but for that and earlier events, we need to check the archives - and I haven't got time for that but anyone can go by the table above and check the archive charts for the whole SSW period. Here's the link again: http://www.meteociel.fr/modeles/archives/archives.php?mode=2&month=1&day=20&year=2008&map=4&type=ncep I set it to Jan 20th 2008 to get you started. We can take comfort in the fact that most (perhaps almost all) split SSWs have produced decent periods of HLB which have delivered cold to the UK. The teleconnections have NOT let us down at all and contrary to what the usual suspects might be saying through their impatience. In fact they are almost spot on in terms of what we expected from them - there's a slight problem over precise timing but that's always the case with SSWs and such dramatic pattern changes (which the models cannot handle). The next three comments were confirmed to me by @Tamaraby PM and I hope she doesn't mind my referring to them as she will continue to avoid this thread with all the confrontation and I fully sympathise with her (our loss). The tropical/extra tropical cycle and forcing has been sufficient to amplify the tropospheric pattern and it's just that the polar field has not "yet" been conducive for HLB and stratospheric dimuition. She thinks that in January 2013 the tropopause was more receptive at this stage than it has been so far this time. She feels that "its still barely into the second week of January and there is far too much overreaction in general". Back to my own comments: That means in both directions - no cold patterns showing or a Siberian wasteland - we're somewhere in the middle right now. We've a substantial split event ongoing and the best news is that this SSW seems likely to be very protracted, perhaps approaching the 2013 record length and some records are already being achieved up there. We should have at least two or three bites at the cherry. The lagged impacts of the MJO through phases 6, 7 and now into 8 may show up within the next 7 to 10 days - favouring HLB. I see that for once the GEFS (bias corrected version) and the ECM are both in broad agreement for a change (long may that last but do not hold your breath) and week 2 MJO forecasts and notoriously unreliable.. Although they dive into the COD soon, they both look set to re-emerge in phase 6 and maybe for a quick "rinse and repeat" through phases 6, 7, 8 and 1 again in early Feb.(perhaps later). Something to keep an eye on for sure. The lagged effects of the GWO in phases 5 and 6, albeit at slightly weaker AAM than we had expected is still strong enough to have +ve impacts for the next two weeks. This cycle is likely to repeat in or by early Feb too. The temporary weakening in the El Nino seems to be over and it looks sets to strengthen again - a better tropical state with a weak Nino - gentle forcing but not too strong like the 2015 super Nino.. Meanwhile, the SPV destruction continues and may take many days, weeks or perhaps not at all to reform into a more organised fashion. Overall - an exceptional and truly fascinating period for all the atmospheric processes with an extremely high chance of cold patterns setting up later this month and perhaps for much of February too.. We are about to see a transition to a less settled phase but this is probably a sign that there are changes to feed through from the Arctic and towards the mid latitudes - merely timing issues IMHO. Looking at the models, I see that a good number of ensemble members show charts which develop HLB blocking patterns - some as early as day 7/8 and building on the Arctic outbreak, others do this later on in the run. If you study those charts from 2018 and 2013 and indeed some other pre/during/post split SSW events, you'll see that the initial impacts can almost always be seen close to the pole. Several GEFS ens show a "yellow" HP - a strong sign of a full reversal reaching the surface. Some show heights building towards a proper Greenland HP and some towards Scandinavia. Do not worry about the TPV still looking immovable on our side of the Arctic. What should happen is as (when - not if IMHO) the wind reversals reach the surface is that those low heights are displaced southwards - almost bulldozed out of the way. Quite often a lobe drops into Scandi and it "looks" like we'll see a true northerly but that would likely be short-lived and transitory but not the normal "toppler type" either. What happens is that HP builds around the top of the LP and pushes that south into central and southern Europe. Then that opens the pathway for Siberian and Russian heights to push westwards (which occurred in dramatic fashion to create the "Beast" last Feb/Mar.). Although easterlies have been a rarity in the last 30 years they were much more common back in the '60s to '80s and even mild winters saw several outbreaks. Those associated with SSWs are usually very potent. Then the HP can build towards Iceland and Greenland letting in a true Arctic air stream with north to north east winds - many of our coldest winters see an easterly/northerly combo. When will all this happen? I'm very confident of "this" winter and well before Spring. No guarantees - there never can be but the current set up is on the verge of something quite dramatic. Frankly, with the strat state as it is and taking account of the other teleconnections, I'll be astounded if we do not see a memorable cold spell in much of Europe, the UK and eastern CONUS, eastern Canada as well as large parts of Asia/Russia/Siberia - not all at the same time but we should all see periods of extended wintry weather. So, please, please be patient and accept that the models will struggle - which I and others have been saying for a while and I've shown that there has been a slight delay - not for weeks on end!. When I'm on here again at the end of this week, I hope that we can all be focusing on some much more attractive output in the mid term. David
  18. 73 points
    UPCOMING COLD SPELL - TELECONNECTIONS UPDATE WITH YET MORE ENCOURAGEMENT I just posted this across the pond on a US weather forum - I copy it here unedited. This is an update to my last two main posts: From December 11th entitled "Looking Great for Extended Cold Spell in Europe and East CONUS from Xmas Onwards" (direct link: https://www.33andrain.com/topic/868-teleconnections-a-more-technical-discussion/?do=findComment&comment=110591 ) From December 13th entitled "A Major Sudden Stratospheric Warming (SSW) Later This Month? Testing an Important Recent Theory" (direct link: https://www.33andrain.com/topic/868-teleconnections-a-more-technical-discussion/?do=findComment&comment=110901 ) Since then, I have read numerous posts on several threads and many of which IMHO are showing far too much negativity and this seems to be largely due to the model uncertainty which is often at its greatest just before some important broad scale pattern changes. I hope to allay many of those posters' and readers' fears in this post. In the last few days we have seen some great posts by our Teleconnections and Stratosphere specialists with a real consensus firming up of the anticipated cold spell. Today we have seen some great updates from Tams @Tamara, Tom @Isotherm, Zac @Snowy Hibbo, John @earthlight and James @Singularity as well as some others. Everything looks good to me and there is some remarkable agreement on the forthcoming cold spell and if anything, the view is even more bullish than just a few days ago. The only differences are over precise timing issues. I'll run through some of the charts with brief comments below each one. The GWO looks to be looping back up again and we'll be back in phase 5 and rising again quite soon. Note that the total GLAAM anomaly has remained +ve. GLAAM fell back and then rose again and has levelled off. Relative AAM tendency, nose dived and then spiked briefly before falling back slightly but with a renewed spike already underway. FT has stopped falling and has levelled off. The huge spike in global MT (black line) had already ended when I last reported on it but it looks like it has already turned upwards again without going -ve. The key regional torque, EAMT (red line) peaked last week and is falling back as expected. It may go briefly -ve but it looks set to rise strongly again within a few days. Note that the previous strong spike was the one that should have created that powerful uplift from the Tibetan Plateau and Mongolian Mountains with those very strong vertical rossby waves which should impact on the stratosphere around Dec 22nd-24th. The further spike may well produce a similar response in very early January (more below on that). Jet stream looks strong over Himalayas and Tibet now (above) and again (predicted) at T+180 (below). Link to gif for animations: http://www.stormsurfing.com/cgi/display_alt.cgi?a=nindi_250 Remember from the paper that I referred to - the lower part of the jet is obstructed by the very high Himalayan peaks and is partly channeled and funneled across the Tibetan Plateau and rushes northwards until it is uplifted by the Mongolian Mountains. It is that range (the Altai in particular) that is believed to generate the greatest uplift of all and it was probably no coincidence that the strongest EAMT (the red blob on the MT chart centred around 40N to 45N) was right over that range last week. The lower charts suggests a repeat in about 7 to 8 days time and if this is roughly correct, that should coincide with the next spike in EAMT in that area (more below). As I said a few days ago, the Russian HP is hanging on - in fact it is building slightly. As our specialists have said, some HLB looks likely to be in place "before" we get the "top up" benefit from the SSW itself. Link to these two charts for animation: http://www.stormsurfing.com/cgi/display_alt.cgi?a=nindi_slp W Russian HP builds and a new even stronger cell develops from the north and from the south. The lower troposphere and the surface look nicely prepared and conducive to further blocking. The MJO is playing ball too. It's progressing though the "Maritimes" phases 4 and 5 at decent amp. ECM take it to phase 6 and towards phase 7 around the New Year - further supporting HLB. Given the other background signals, it's quite likely that we may see a further increase in the week 2 amp. GEFS is similar - perhaps slightly higher amp but holds it in phase 5 for longer. Several other models are more progressive and closer to the ECM forecast. Expect further evolution during the next few days - week two MJO forecasts are notoriously unreliable and the main models have still not factored in the broader pattern changes in any event. All the above is already suggestive of a fairly blocked pattern becoming established even without the help of a major SSW. In fact most of our strat specialists should note that the troposphere would appear to be even more conducive to a decent strat/trop coupling than it was in the early 2018 events. The latest strat charts (GFS and ECM) and comments seem to be going beyond just a wave 1 displacement and the repeated attacks on the SPV will be reinforced by lasts week's EAMT spike around this weekend. That may well be enough to trigger a major SSW with splitting. Some wave 2 action is starting to look more likely and reasonably early on. So, the SSW perhaps starting over Xmas and reversal and surface impacts perhaps around New Year. The renewed spike in EAMT should help to finish off the SPV as we enter January if it manages to survive the Xmas attack. This time the trop patterns + the repeated strat attacks look very likely to produce a much longer cold spell compared to the early 2018 events. There is so much to be excited about for those seeking cold. We still need to wait for the precise timing - it may be a few days later than I suggested. Then we need to see exactly where the troughs and ridges set themselves up. Given the vast Russian HP, it seems highly likely that we shall see that push westwards. It may retrogress to Iceland or Greenland for a while too. According to several specialists, this may well follow the pattern set up during the 2009/10 SSW when we saw many weeks of cold and snow in both Europe, the UK and the eastern CONUS. Too early to be certain of that yet. So, the next few days are likely to see a flatter pattern with higher temps and pretty unsettled and windy at times too but that is all part of the build up to the "re-set". If anything this more zonal pattern is looking to be even briefer than suggested a week ago. Watch out for some big changes in the models later this week with some exciting charts showing up for just beyond Xmas. David
  19. 72 points
    Feel I have an apology to make. If people are wondering why this thread vanished for almost an hour, basically I went ahead a locked the thread first. Then, went and hid it. Was feeling fed up (partly due to the way this thread was going and for other reasons). Regardless, I shouldn’t have taken out my frustrations on here by vaporising this thread and leaving people feeling confused and worried as to what happened. It wasn’t fair and I didn’t let any members of my team know what I did. Nor anyone on here. I’m sorry for behaving that way and wouldn’t blame anyone for being annoyed. Not really a great example for a mod/host to set. While I appreciate some of the damage I likely caused (even though some will probably look back on the mysteriousness of the missing thread and laugh), I will make sure it doesn’t happen again. After all, this thread is meant to be a laid back and fun place for you guys to chat about the models, and would hate to ruin that mood. Could have chosen not to have said anything at all, but feel you guys deserved to know the truth!
  20. 72 points
    Evening Based on the pretty successful thread around the current seasons NH patterns I thought I would lay out the thoughts for Winter 2018. Headlines - Following on from Autumn > Winter 18 Globally is set to smash records- From record warmth to record cold, record rainfall & record drought... This will be driven by weak westerlies & a possible SSW in mid December- Teleconnection notables **could** be * Lowest negative AO on record ( or at least a challenger ) * Lowest & or most positive POL on record ( this metric can be good for us in either positive or negative mode, however its the extremes of pressure that support the -AO ) * Most negative 100 or 10HPA zonal wind on record in Merra2 data at any point during the Winter ( most likely earlier rather than late ) UK wise - The overall theme is a very high probability of a below average winter with the sub 3c breeched twice - ( maybe 3 times ) Winter NH patterns For a winter forecast this last 10 or so years a traditional method by most has been adopted - taking the state of the Teleconnective background signals & matching them to analogue years in the 1900s - & I still believe there is some merit in this especially when we are in very high NINO index years as this can be the overuling global driver over & above any favourable ones - The last 5 years or so have seen attempts to create a winter forecast by morphing analogue years for the stratosphere - again with some limited success- However there is one fundemental issue with using these analogues which is the assumption that should the same metrics repeat themselves then the tropospheric responses would all align & the H500 height anomalies would be at least very similar across the NH. Well now, as we get better understanding of how climate change is impacting the weather (most notably the ice & arctic heat ) then all these analogues potentially become redundant due to the troposphere becoming more & more independent in relation to not allowing the stratosphere to downwell - ( otherwise known as being 'decoupled' ) The main driver of this is the surplus warmth left over in the arctic at the end of the summer & Autumn as well as the record breaking ice loss along the peripheral ice edges - Not only this, as the mid lattitudes heat up we have grown larger more 'intense' areas of high pressure transporting yet more heat upwards into the pole- ( NB even now this week in November we see record High pressure developing towards Scandi pumping more warmth upwards ) The feedback then becomes self perpetuating- I would also like to add to this the 2018 'spin' that not only does this year have a massive heat anomaly,but perhaps ( IMHO ) a dipole of heat / cold across the areas with early ice build up V no early ice What you then allow is even more inconsistency with heat creating vast gradients across the pole allowing for yet more blocking - & because of the dipole the balance of heat then allows potential displacement of the tropospheric vortex - Its no wonder then that we see the amount of wave 1 & wave 2 blocking attacking the early vortex & the inability of the stratosphere to couple downwards as the resistence upwards is balancing it out - What you get as a net of all this is no tropospheric analogues because there isnt a teleconnection that quantifies Arctic Amplification ( AA ) & there are no stratospheric analogues because if the strat cant downwell then its overall strength is much less impactful on the troposphere - - So as mentioned then- Autumn has been one of blocking highs - even when the stratospheric jet has increased along its seasonal pathway the troposphere has refused to couple with it- ive highlighted this is due to the anomalous vertical heat flux & perpetual bombardment of upward waves thats served to offset the downward propergation of the strat leaving the polar cap sitting in equilibrium Seen here ( Source AER ) Also shown is the continual warmth in waves pushing upwards from the troposphere - & now potentially down from the strat- Remember the upper vortex is *Stronger* than average this year so while its vulnerable to attack - early displacement to russia * Isnt * the same as a SSW split - for this we need to see a reversal of the zonal wind @60N/10HPA * Classic winters like 1962 had early warming over the canadian side which took the vortex out for the entire winter then went on to allow for blocking to remain in situ for long periods of time- I believe this winters signal of a tropospheric decoupling could allow for a similar scenario especially if the SSW underpins it - QBO support - The initial concern is that a downwelling WQBO would omit us from the chances of a SSW however we are still in the transition phase where 30MB moves to positive but the 50MB lower down holds negative- The impacts of this are that the QBO will not act as a blocker early on the potential SSW this winter - Ive uploaded the image & I should have shortened the timeline but hey ho! h Possible Strat warming ~ Mid December... The strat as we know has been under attack this winter & the lower vortex especially has recently born the brunt of any deceleration - dropping to around 5M/S where as higher up the 10HPA wind has remained less impacted The day 16 disks which when the next wave of vertical flux peak starts to show a canadian warming & relocation of the vortex - So worst case scenario a dipsplaced vortex towards Russia, best case is a split & even less eastward zonal wind speed !! ** Key date proposed for major displacement / poss warming Dec 15th but remember because of the decoupling this may only serve to reinforce the blocking thats already there - ** DJF UK CET - Viewpoint & Anomaly plot The seasonal winter CET stands from Hadley @ 4.13C broken down into D 4.7 J 3.9 F 3.8 Statistically across the last 100 years sub 0c months are - 8/300 which is about 1 every 40 years ~ 2.5% chance. sub 1c months are 17/300 which is about 1 in every 18 years ~ 6% chance sub 2c months are 29/300 which is about 1 in every 10 years ~ 10% chance. So we can see the numbers are low- in terms of our chances I try to quantify this winters numbers by saying that a sub 2c is as high as 50/50at this stage ! & sub 1c maybe 25% - Sub 0c maybe 10%... Overall projected winter CET SUB 3c ~ 2-2.5c Overall pressure anomaly locations for Winter 18- These may wax & wain however general locations feel about right- Storm track is in green - Cold winter for central states as well as possibly the east depending on whether the blocking is more East based towards a +PNA or more west based -EPO ( the further west you get the -EPO you do encourage a ridge on the SE coast ) UK sits on the NW side of the low anomaly in Europe - so in that respect continental air is sent west in our direction- which will drive snow events- Europe as a whole cold & below ave - especially central & Western, however places like Greece / Turkey could benefit from warmth up from the south - It is my belief that confidence in the projected patterns for this winter are about as high as they can be in terms of potential blocking- especially in the locations we need it - what you will see from the models is perpetual ridging to the pole from every angle across the globe ( -EPO / -NAO / -POL ) If the vortex remains uncoupled then the speed of the 100HPA vortex is more crucial than the 10HPA one higher up- This will continue into December where the idea of a 'front loaded but possibly fully loaded winter comes from' - The nature of reduced westeries also impacts the UK around rainfall- Mean averages especially for the NW will be lower however what you lose over a month in terms of loss of westerly driven wind & rain events may well be offset by slow moving PPN events ( The same as Autumn ) So there you have it - 2018/19 Global extremes of weather & for the UK higher probabilities of exceptional weather which for once is more in favour of exceptional cold instead of warmth.. S
  21. 71 points
    Roll on 4 days, and if seems that we are seeing just this. I think that we have seen that the ECM has the tendency in the past to overplay amplification and blocking scenarios........but, and a big but, when we have downwelling strat events the ECM picks these up a little better because of the better strat resolution. Now we may not see a classic evolution as seen in this latest run, but my feelings are that we will see a block to our north somewhere in a similar position. No need to comment on every run, but imo we see the trend increasing as expected, and I suspect that most of us will witness a significant snow event before the end of winter and most likely before the end of the month. And with a locked in omega type block, that snow isn’t going to disappear quickly......
  22. 71 points
    REALLY GREAT NEWS! Now many of you will not realise the significance of this: Those of you who have been reading my posts and those from the likes of @lorenzo, @Catacol and others who comment on the key teleconnections will know that we've been banging on about about +ve EAMT (East Asian Mountain Torque) in particular. We could see this event unfolding a few weeks ago as part of the GSDM (global synoptic dynamic model), the GWO (global wind oscillation), GLAAM (global atmospheric angular momentum) and both FT (frictional torque) and MT (mountain torque) which all link in with tropical forcing, the ENSO state and the MJO. These charts are produced 2 days after the actual position - so this afternoon's chart (above) shows the position as on Dec 29th. In my previous posts I said that EAMT was already rising strongly and that could be seen in the pressure distribution over eastern Asia (I showed the StormSurf charts, most recently yesterday). Well, EAMT is not just rising but it's sky rocketing as can be seen by the red line in the chart and looks set to climb quite a bit higher, in fact with that 2 day chart time lag it already is. I'll not go into the complexities but +ve EAMT events have an extraordinary influence on all levels of the lower and middle atmosphere and especially on the northern hemisphere global weather patterns and many of these assist directly or indirectly with setting up ridges and troughs and blocking patterns. Here are some of them: 1. A "major contributor" to wave breaking in the stratosphere (there are other influences too, of course) and vortex attacks by creating huge uplift and vertically propagating planetary waves from the Tibetan Plateau and particularly (as discovered more recently) the Mongolian Mountains, which can reach the upper stratosphere and even the lower mesosphere before reaching the "critical level" which is effectively "wind shear" in the troposphere as shown in this chart. In the stratosphere the critical level has the easterlies above it which are the reversed winds and the planetary waves cannot break through it and are reflected (or even deflected) back down and they break at increasingly lower levels. This produces one or more attacks on the spv (stratospheric polar vortex) and prolonged events can send up further planetary waves with attacks from above and below. The last surge in EAMT occurred during Dec 4th to 12th and peaked around Dec 9th/10th. A few days later we saw some attacks on the SPV. 2. Now we have a further event which is likely to repeat the exercise and if there's any problem with the split or the downward propagation this may well deliver the final blow to the SPV in a few days. In fact the timing is almost perfect with the split (if it happens) predicted for later this week. 3. EAMT also influences the tropospheric patterns with lateral planetary waves influencing the jet stream and downstream patterns in winter across the North Pacific and into N America. This can help the jet stream to meander and/or buckle. This action in association with other factors can have knock on effects setting up the pattern and distribution of troughs and ridges around the hemisphere. 4. In the summer half of the year EAMT has a powerful influence on the Asian Monsoon. 5. The planetary waves also spread polewards and this is where it gets very interesting. Some of us will have heard of and studied Judah Cohen's theories on early Asian Snow Cover extent and the greater likelihood of SSWs. He recently admitted that it is more complicated than that and it was not a perfect correlation but nevertheless it does seem to work more often than not.. Over some years and particularly more recently, research has strongly suggested a link between North Asian blocking and the priming of the lower tropospheric layers and the surface to be receptive to a down welling SSW. In several of my recent posts I've been showing those Asian pressure charts and the extraordinary expanse of HP over almost all central Asia northwards, Russia and Siberia. I've been looking at the timing of these events and I'm pretty sure that it's no coincidence that a combination of +ve EAMT, extensive Asian snow cover (well above average right now as I showed yesterday) and the blocking regime are all coming together to make the patterns receptive or even highly conducive to downward propagation of the SSW to the surface. This obviously needs to be explored much more extensively and research into earlier SSWs (including near misses and failures) need to be considered. Another factor is GWD (gravity wave drag) which is mostly generated by the the east Asian mountains as well. That will be one of my 2019 projects. Malcolm @Blessed Weather and I have been studying these events and found that they fitted in perfectly to last February's SSW. Here's the MT chart for back then: Note the 3 spikes in EAMT. The first one around Feb 1st to 5th and the SSW was triggered a week later on Feb 12th. The second one around Feb 20th-25th and we saw the full propagation down to the surface and just a few days later with the "Siberian Express" rushing westwards and producing the "Beast from the East" in the UK and progressing around the hemisphere to N America about a week or so later.. The final spike was March 5th-10th and the "Mini Beast" followed about a week or so later. Overall, some of this is still theory but the extraordinary influences of +ve EAMT events have been studied for over 20 years. Now more of you might realise why I'm so excited about this month's two +ve EAMT events. The models simply do not have much of these influences factored into how they churn out their nwp solutions and it's why they often need a few days to adjust to changes in the background signals. Before long we are likely to see some much more sophisticated models being developed. The next few days of monitoring the model output will be totally absorbing and fascinating. Finally a Happy New Year to everyone and what a January we have in store for us! David
  23. 69 points
    I love having the FV3 now. There used to be that dead time between the end of the GFS and the start of the ECM where I had to talk to the wife. Not any more
  24. 68 points
    Leaked express headline for tomorrow. #sorrynotsorry
  25. 68 points
    UKMO amazing - snow event followed by more snow events + longivity of cold What more could we be asking for...
  26. 68 points
    Last one from me for a few weeks. Spending Christmas in the East Sussex Weald, thats ,if I survive a drone attack at Gatwick battlefield ! Then on to British Columbia to see my new grandson during January. Going to ski for a few days in a new resort called Big White but most of my time in Vancouver. I know you cold lovers find the hunt very frustrating, having to wait for weeks on end for it to arrive and then just watch it melt away in a matter of an eye blink. Like the Japanese water drip punishment, a slow painful pulling of the teeth or waiting for Brexit to conclude ! You lot deserve better and fingers crossed for a proper cold and snowy spell to surprise all soon as the picture below shows , when it comes there is no where nicer than the British village. So no snow for my short visit to Blighty but the welcome sight of a nice pub, log fire and fine pint of Sussex Best Bitter awaits. Have a merry Christmas and good New Year and may the snow gods be with you . Cheers, C
  27. 66 points
    Well forgive this old fella asking what all the fuss is about over the 12Z, but just what re the 12 V 06 out to 144h please? I’ve looked at the overall pattern of the 558 DM line and the isobars for the 500-1000 chart. Also the same times for the 850-1000. Slight differences but why the posts that have phrases like’game over’ and such? These do not help new folk understand what is happening. I honestly cannot see that, in the time scale I mention, there is much that is markedly different on the two runs. If you are commenting beyond T+120-144, and in this fairly volatile state of the northern atmosphere perhaps even near T+00 then you MUST compare like with like. It is way too far ahead to use the argument that the run has the most up to date data and therefore must be more accurate. It does not hold, believe me, sorry to be a bit dogmatic but 20+ years of forecasting makes me feel you may just bear with me over that. Come on I posted this morning about the overall upper air signals, yes the run to run of the models may well vary but the cold is here for 2 weeks possibly longer. To be sure of what values in each of our back gardens or even more so will it snow/when/how much then be realistic. Models 2x or 4x daily will NOT be accurate for temperature before about T+72 and for ppn of whatever type before T+48 and sometimes not even T+12. If you can accept these restrictions life on here can be enjoyable and useful for learning for us all with no loss of enjoyment. Shall we try this for 24 hours or so.
  28. 66 points
    I've just read through the last 10 pages or so. Some of you seriously need to think about taking a break from watching the models and taking every run as gospel. It's gone from euphoria to throwing toys out the pram in the space of a few hours! Walk away from the computer, life is too short!
  29. 66 points
    Things are looking very much better than many on here seem to realise "including" the GFS 0z run! Although this model thread is intended for scrutinising and commenting on model output, I feel that many of the golden rules of model watching are being ignored by some of you. When we are looking for signs of broad scale pattern changes, we should be focusing on the wider picture and not the micro detail. We are hoping to see signs of the wind reversal from the SSW in the high Arctic and close to the pole - so this means studying the northern hemisphere profile and not the UK/Euro charts (they will come into play once the pattern reset evolves). We know (or at least should know) that the models struggle with pattern changes, especially when we have 2 major upcoming changes in the background signals which are well underway - the SSW which has been well broadcast and the tropical forcing/influences which have been been referred to by only a small number of us and yet they are key (and this is not just the MJO which is only a part of the processes involved in the GSDM - Global Synoptic Dynamic Model including GLAAM - Global Atmospheric Angular Momentum and the torques). I will not comment on these in this post other than to say, that what we expected is falling into place and I believe (as I've said in a number of recent posts) that the tropospheric surface layers are much more conducive to downward propagation of the wind reversal than some think. The expected surge in EAMT (East Asian Mountain Torque) is nicely underway and this will play an important role during the next few days and into early January. The SSW is happening right now and a split looks likely around Jan 1st to Jan 3rd. We should know very soon whether and to what extent that happens and then it'll be a question of how long it lasts. The SPV (stratospheric polar vortex) will be undergoing further attacks but these may well not be necessary with the damage already likely to have been done. To keep this simple, I shall now only focus on the models and what I feel we should all be looking out for. The models have been tending to show slightly more amplification in recent runs anyway and this is not due to HLB (yet) but to how primed the lower atmosphere is with a generally weaker jet stream. It is possible that we might see several days of greater Atlantic influence during the broad scale pattern transition. The models have (correctly IMHO) been narrowing that gap and extending the longevity of the current MLB and only modest amplification. All this is happening in the 7 to 10 day time frame. I will focus on day 10 to see how things are progressing in terms of what the models are showing but remember, I feel that they are not even half way there to factoring in all the background signals right now. Several of you have already posted the ECM chart and as GFS has been coming in for a lot of stick (including by me) I shall look at their 0z output. Day 10 - T+240 The GFS op run is very much an outlier but even this shows some amplification. The key thing is that it is building HP near the pole - in this case on the far side. A key sign of SSW surface impacts will be HP building strongly around that region - ideally centred nearer to or right over the pole. This will be strong signs of the wind reversal and surface polar easterlies. The GEFS control run is more amplified with some ridging through Scandinavia and starting to build HP right over the pole. Even this is an outlier! This is the mean chart which shows an average from all 24 ensembles + the control run. This should always be viewed carefully as "averaged out" pressure will not be the best way of of interpreting the actual flow. What it does clearly show is that HP is building around the pole. Now I "cherry pick" perturbation 11 to show what we are looking for - a full and strong reversal at the pole and already extending its influence with a proper Greenie high developing. That's a split SPV and a nicely coupled strat/trop with the main vortex into central Europe. This evolution would start us off with a northerly but as the HLB really gets going, pressure should rise strongly around the top of the LP and then through Scandinavia with an easterly becoming established..... ...just like this on the day 16 - T+384 chart. Returning to day 10 - here's the ensemble panel. All bar a couple have HP building over the pole and it's just the timing and stage of development that varies. If you want a closer look - here's the link: http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=6&ech=240 Click on the first chart and use the double white arrow (pointing right) at the bottom of the close up chart to run through all of them. I'm running out of time again. For those that might accuse me of "ramping" I am trying to show what we should be looking out for. I am also saying that GFS is starting to embrace the changes. If their 6z run was to be more like perturbation 11 then this place would be in meltdown. Then the following run might revert back to something much less exciting for coldies. The main thing is to watch things evolve over several days. Much will be decided by around Jan 2nd/3rd in terms of the split. Yes, there could be a delay but I actually feel that things will be brought forward when we factor in the +ve GLAAM and the +ve torques as well as the MJO. It can go pear shaped but I believe that there are so many background signals more or less in sync and playing ball this time that we'll be treated to something very special. David
  30. 66 points
    Awful Lot of folks on here this morning with an opinion about how silly looking at day 10 models are. Interestingly not many of them had much to say on any output analysis at all until now. Amazing how we have a slew of new experts when the models don’t behave as expected if you’re in that camp of ‘day 10 model watching is pointless’ then might I suggest you stick to watching the televised weather forecasts and basking in the knowledge that you will probably always be right, and then you can leave those who like to make a stab at a forecast based on output analysis alone to pursue a hobby they enjoy. nobody gets a prize for being right or wrong and it’s frankly just a bit poor if you enjoy being the person who takes pleasure in saying ‘I told you so’. there’s lots of other places on the internet for your badly articulated ‘realism’. Thanks.
  31. 66 points
    We still believe, we still believe… We still believe, we still believe… It's coming home, it's coming home It's coming, summers coming home It's coming home, it's coming home It's coming, summers coming home Tears for netweather Skies are grey No plans to go out today Barbecue summer drifting away… There could have been storms Lightning that couldn’t be beat Waiting was nearly complete GFS FI was so sweet And now I’m singing… Three models as they were ECM still gleaming No more years of hurt No more need for dreaming Talk about Summer coming home And then we all thought it won’t But high pressure was strong It had grown And now I see UKMO’s showing more GFS is good as before NAVGEMs certain to score And Summer suns screaming Three models as they were... ECM still gleaming No more years of hurt No more need for dreaming This is our chance A better summer then France It's coming home, it's coming home It's coming, summers coming home It's coming home, it's coming home It's coming, summers coming home It's coming home, it's coming home It's coming, summers coming home
  32. 65 points
    Thanks for this excellent post Malcolm. This is just a very brief comment from me. As some have said the GFS op run continues to be a big outlier and the 6z was an extreme example of this. Almost all the GEFS ensemble members show HP building close to or over the pole. Let's look at one of the key periods - the day 10, T+240 "mean" chart: Several others have already "cherry picked" some of the perturbations showing a full reversal and a split right down to the surface. The "mean" shows that most members are well on their merry way to this - the later output is likely to adjust (some already looks great) "if" day 10 is anywhere near right (it may be too conservative or there might be a further delay). Contrary to what some of the most impatient members have been saying - the timing issues have hardly changed all the way through this long build up. We've spent some weeks watching the strat with interest. The timing of the SSW (when the warming occurs up there - not the surface impacts) was mostly expected from around Xmas or shortly afterwards. A few models were forecasting it for slightly earlier than that and a few for around the New Year. It "has" happened and now we await whether we shall see a full split of the SPV or a displaced one. The vortex is still under attack and if they're needed another shot of planetary waves will be sent up by the very +ve EAMT event which is now well underway (time lagged response of a few days to a further hit). Yes we have issues over downward propagation and this is where the tropical forcing can really help. I've posted on this a number of times and that is all going in the right direction. In fact, even without an SSW, the current +ve momentum and torques and their interaction with the MJO would deliver a decent colder spell in any event. This current HP is starting to amplify. The strong HP and ridging over the UK, Europe and northern Asia is making the surface very conducive to at least some blocking and assuming that we get that final propagation to the surface (which I believe will occur due to the tropical forcing, existing blocking and +ve torques) the surface pattern looks great for producing HLB setting up in a very favourable position. We should be looking for the split over the next few days to firm up on that and particularly the timing. Then watching for the downward propagation and then the blocking patterns setting up. I would say that the time range might be any time from Jan 10th to 20th and perhaps most likely around mid month. If it takes a little longer, so be it. This is all happening now and during early January not after Easter! Last week some of us (including myself) were saying that we would start to see the models beginning to sniff out these changes from around or just after Xmas and that is precisely what has been happening. While anticyclonic gloom seems to be prevailing both outside and here on this thread both types of gloom are totally uncalled for. Some arctic air is about to be injected and this will clear the gloom and producing some brighter and frosty weather (but with some fog too). Meanwhile, as we await the changes, this is a totally fascinating period meteorologically - why not start to understand, embrace and accept that and consider how unusual the set up is both high up in the strat and down here on the surface? Watch the models trying to factor all this in and accept that we'll see some more ups and downs for at least several more days. Then if we are to see the full SSW impacts, there may well be a transition period with several days of more unsettled "Atlantic" weather. This period has been steadily shortening and it's possible that the HP will hold on and link up to the HLB as it develops. Overall there is so much to be excited about right now. David EDIT: Whilst writing this post I see that @Dancerwithwings is wondering if I wrote a post referencing the GEFS rather than the op run. - a bit like I did just now! Well, not for any other reason than to show that many of the ens were showing what I said we should be looking out for. Here's the link to that post so that you can see exactly what I said. D https://www.netweather.tv/forum/topic/91032-hunt-for-cold-model-discussion-heading-into-christmas/?do=findComment&comment=3947020
  33. 65 points
    I think it's "hold your breath" time.... I've just spent some time scanning the better minds out there on the twittersphere. and checking the recent model runs - and I'm not sure I can ever remember reading/seeing such a collection of differing views and mostly open acceptance that we have an evolving situation that is so hugely complex that we don't really know how it will pan out...and I'm damn sure NWP doesn't really have a scooby either in terms of anything past short range. 2 salient factors for me. Firstly background (strong?) pacific forcing that is going to want to throw up a high lat ridge. Secondly the very difficult predictors of the extent to which downwelling can successfully impact on the troposphere under a wQBO regime where splits such as we are (probably) about to have are so rare. And where into all this does declining solar impact sit.....and the sharp see sawing of mountain torques over the last 2/3 cycles? GLAAM operating at particularly high levels this winter season. I'm still sitting on the cold side of the fence, even if timing is being skewed later. But the uncertainty is there for sure. If we end up with a +NAO signature by mid Jan after all the build up and cumulative signals for blocking - and the sustained MetO long range calls via Glosea for cold continental feeds then a good many people are going to end up with eggy faces. Some people seem to dislike forums where hyperbole becomes the norm. Don't really get that myself....particularly when the interest is so intense. Enthusiasm is always a good thing. The weather outside our windows may appear very dull right now - but up top and out in the pacific as another significant east Asian surge is underway it is anything but ordinary. Long live hyperbolic enthusiasm....and bring on the cold.
  34. 65 points
    I came back on here tonight hoping to see some positivity. (I shouldn't really, I've been here long enough to know how it works), yet we are in the midst of a December SSW, a very rare beast. It could and should, give us the winter we've been waiting for, for years. It might not... however, we are in the best position we've been in for years. The models are struggling with an outcome and it's a fact that an SSW will play havoc with numerical weather prediction. We (My family) are losing our home on the 7th January. We will be ok somehow. One of our Netweather members has just been given the all clear from cancer. Is it really worth any animosity over the weather? Something which is out of our control? It's Christmas eve tomorrow, real winter weather is coming (allegedly at some point...) Just enjoy the hunt for cold and have a merry Christmas....
  35. 64 points
    Beginners guide to the psyche of a model watcher in Winter..... 1) A cold spell is shown in FI - "it will never verify it will all go pear shaped" 2) A cold spell moves into the reliable timeframe - "that run looks very dry hardly any snow showing there" 3) The snow arrives after the commencement of said cold spell - "it maybe snowing outside but this cold spell looks like it will be finished next week" We are at Stage 2 at the moment! A very decent start to the day today model wise. I would be very happy in the event the ECM verified and it would seem that all roads lead to cold this morning. Indeed the GEM is a cracker following the durge it produced last night! But will it snow IMBY?
  36. 63 points
    EC Ens up to 6 on the clusters, but the key stand out is the blocking platform across them, atlantic is primed, AAM has spiked precisely when the downwelling advertised on the paint drip connects - Genuinely cannot see a road back to the flatter solutions from here. I think 'That ECM' will get usurped in the not too distant future.
  37. 63 points
    No charts tonight - on a train and on my phone which is tedious... But did want to post some text. My eyes are moving beyond the trough now - I was pretty confident in it at the weekend and am now certain. How much snow will we get? David's post highlighting the arrival of the expected next pacific spike is very timely. While we were wading through the tedious first half of the month the pot at the end of the rainbow was always the potential for a downwell that synchronised with a powerful pacific spike. It's taken the third time of asking to arrive - but it's here. This is going to mean reinforcement of the Euro trough at the same time as a push for stronger heights to the north, and this at a time when the ssw has already begun to affect the pattern. And this in turn I think is going to mean quite a steep pressure gradient and some really quite cyclonic continental weather as the trough beds down. I'm still thinking that the block has to setup over greeny rather than scandy in the medium term, though at the start of the season I did admit to being frustrated at an inability to get ridge positions exactly right and I want to get better at this - modelling appears to be favouring more of a scandy block at the moment - but in the end ridge position when the Euro trough is deep is probably not so important overall as the feed will be cyclonic and bitterly cold at this time of year either way. And all this adds up to some considerable snowfalls I think. Someone next to me on the train just said "it's supposed to rain on Tuesday..." and I was close to grinning at him and offering an alternative view....but let's just watch it unravel. I suspect the next few weeks won't be especially dry or especially wet. Something else.
  38. 63 points
    Update on the Background Signals and Looking at the Interaction between the Likely SSW Impacts and the Tropical Forcing Firstly, that was an excellent update on the SSW on here by @lorenzo. I have just posted on a US weather forum Teleconnections thread and I feel that this will put a little flesh on some of the points that I've made in some recent posts on this thread - I copy it below. I've edited it slightly to better fit the UK position but I do not have time to do a complete re-write. I will not explain everything again except the really key points. I posted this morning on here (on page 119) wrt to the model output and this post relates to some of those as well as my earlier comments - here's the link: https://www.netweather.tv/forum/topic/91032-hunt-for-cold-model-discussion-heading-into-christmas/?do=findComment&comment=3948800 Just to add a little more to Tom's @Isotherm excellent update and several updates today - things do seem to be going very much according to plan with perhaps some real clarity likely to emerge during this week. EDIT: and while writing this I see that Tams @Tamara has just posted with some encouraging comments but with some wise words of caution too. An excellent post as usual and an interesting comparison to the 2012/13 SSW and the key teleconnections at play back then compared to now. Right on with my post and I'll make brief comments below each chart: The total GLAAM (global atmospheric angular momentum) anomaly which has remained +ve all month but eased back recently is now rising again. The strongest +ve anomaly is currently at the equator.  The relative GLAAM tendency anomaly which spiked for 5 days, remains +ve but has levelled off. This has been in association with rising torques. FT (frictional torque) has been rising strongly. Note the orange colours (in the upper part of the chart) showing around 25N to 35N. That's part of the poleward progression from the tropics (see below). GLMT (global mountain torque - the black line) has continued its recent spike and is now +ve. Of the regional torques, the strongest rise showing is the highly important EAMT (East Asian mountain torque - red line) which is +ve and climbing steadily - this is exactly what I was hoping for, with perfect timing. The highest values (red blobs) are once again being seen over the Tibetan Plateau and (with the 2 day time lag in these charts) is almost certainly over the Mongolian Mountains right now. More below on this. As I expected (well hypothesised) GWD should be rising in that same area just before EAMT is at its strongest and indeed it is and also around 35N to 50N. More below on this. Just a reminder of the GWO (global wind oscillation) phase chart as part of the GSDM (global synoptic dynamic model) which incorporates GLAAM and the torques and takes account of and influences (and is influenced by) the ENSO state and the MJO. The most recent GWO chart is below. The GWO has stalled temporarily in neutral orbit (a bit like the COD on MJO charts) but looking set to emerge in phase 5. With rising AAM and the torques we are likely to see the GWO rising though phase 5. I do note several comments on this with some views expressed going for a slightly longer delay in this progression and we'll need to see exactly what unfolds during this week. I feel that the key torque right now is EAMT but it is unwise to separate out any part of the whole GSDM process and we must consider all aspects together. So, I'll rephrase that and say that +ve EAMT has some very strong influences on planetary waves - lateral (eastwards impacting on the Pacific patterns downstream and beyond), northwards (to aid North Asian blocking) and vertically (strong uplifting often into the upper stratosphere and lower mesosphere). I see that the latest MJO charts have been posted this afternoon and both the RMM phase charts as well as the VP200 output have been shown - so I won't repeat them here. I feel that both types of charts have their place and pros and cons The GEFS bias corrected RMM version maintains its strong amp through phase 6 and into 7 before stalling there and maintaining amp. ECM continue to go for a faster progression through phases, 6, 7, 8 and at decreasing amp and entering the COD later than on recent runs. Most of the other models are somewhere in between the big 2 and there may well be greater convergence and model consensus as the timing of the pattern reset becomes clearer during this week. That vast expanse of high pressure extends across almost all eastern, central, northern and western Asia , Russia and Siberia and has pushed even further westwards. Strong blocking in this region is considered to be a key precursor for SSW impacts and very likely to assist with strat/trop coupling making the lowest layers more receptive to the lowest stages of the downward propagation. This + the spiking EAMT and GWD are very encouraging right now and set to improve even further. I posted this chart recently but the northern hemisphere snow cover has extended even further south and looks really impressive before we even consider the SSW and tropical forcing impacts.  Global surface temps and particularly N Hem temps have fallen close to their lowest levels since Feb/Mar at the time of the last SSW. The trend in much of Europe and the UK is a downward one for the next 7 days but this is due to slightly greater amplification under the existing HP and not HLB (at this stage). There are some low anomalies over Alaska and -ves over SE and parts of eastern CONUS. The lowest anomalies of all are in the key North Asian/Russian/Siberian region with some parts seeing -ve anomalies approaching 20c below average. I also note that the Arctic has turned much colder with overall -ve anomalies developing there (Greenland remains +ve). The more cold to be displaced from the Arctic the better. I will do an Arctic update within the next few days. It's not just global land temps that have been falling, global SSTs have continued to fall back steadily almost all month and if anything the trend is accelerating again. They are close to their lowest values for 5 years as shown below. This may be a temporary trend and is something that we'll need to examine more closely on the Teleconnection thread but it's good to see some respite from the global warming trends. Overall, in the context of the SSW, the tropical forcing and the other key teleconnections there are some very encouraging signs and a lot might be revealed during this week. Look out for what I suggested in my model post this morning. David
  39. 63 points
    We're going to run a competition this afternoon with the winners getting special pre-Xmas thread bans, woohoo!! To win, those who keep posting solely about Met Office forecasts and the like with scary regularity, despite various requests to stop and the big notice at the top of every page in here, just have to keep doing it. Good luck to all those taking part
  40. 63 points
    A MAJOR SUDDEN STRATOSPHERIC WARMING (SSW) LATER THIS MONTH? TESTING AN IMPORTANT RECENT THEORY I just posted this on a teleconnections thread on a US weather forum and thought that you might like to read it over here. For the second time this year we are seeing a significantly weakened and disrupted stratospheric polar vortex (SPV) with many specialists forecasting a very early substantial warming event and a probable major SSW. We know from past experience that we have seen some "near misses" with the wind reversals in the stratosphere struggling to propagate through to the lower tropospheric layers right down to the surface. With my fairly limited stratospheric knowledge (still learning), it's beyond my pay grade to comment on the main reasons for this. From the papers that I've read and accounts of earlier SSWs, I can see that although forecasting these events has seen huge improvements in recent years, we still have a lot to learn about the latter stages - the type of SSW, the timing and extent of propagation (or lack of it) to the surface and where, how much and how widespread will the high latitude cold be displaced towards the middle latitudes. There have been some fascinating recent studies into what causes the final triggering of a major full on SSW and I will focus on this very important aspect of the whole process in this post. Malcolm @Blessed Weather and I each produced very long posts on this topic as part of our "2018 SSW Debate" back in April. They both appear on page 3 of that thread and as I will be be referring to both of them in this post, here are the direct links: Malcolm - A Review of events leading to the 2018 Sudden Stratospheric Warming (SSW) https://www.33andrain.com/topic/868-teleconnections-a-more-technical-discussion/?do=findComment&comment=86401 David - 2018 SUDDEN STRATOSPHERIC WARMING DEBATE - EVOLVING THEORIES ON SSW CAUSES AND MORE ON MOUNTAIN TORQUE https://www.33andrain.com/topic/868-teleconnections-a-more-technical-discussion/?do=findComment&comment=86675 To summarise very briefly, Malcolm, in his superb post, examined the state of the stratosphere right through the 2017/18 winter season and focused on the main teleconnections and the key role that they played in assisting the development of and impacting on the 2018 SSW. This included the ENSO state (La Nina at the time but a temporary easing in January), the east based (Quasi Biennial Oscillation) eQBO, the low Arctic ice extent, the "uncoupled" state of the strat and trop, the "Aleutian high" causing the main SPV to shift to the Siberian side, the blocking high over north Asia (assisting further vertical wave activity flux) the MJO moving through its Indian Ocean and Maritime Continent phases of 3, 4 and 5 at increasing amplitude and then on to phases 6 and 7 at even higher (record high) amplitude (favouring high latitude blocking), the Global Wind Oscillation (GWO) moving through phases 3, 4 and 5 with rising relative Global Atmospheric Angular Momentum(GLAAM) from a low point, with rising Frictional Torque (FT) and rising Mountain Torque (MT) with the usual 10 to 14 day time lag, with East Asian Mountain Torque (EAMT) being particularly strong. All this showing how the main components of the Global Synoptic Dynamic Model (GSDM) were all playing out exactly as would have been expected with almost perfect timing. The southerly east Asian jet stream branch was blowing strongly across across the Himalayas and the Tibetan Plateau and there was a huge spike in EAMT around February 2nd/3rd. The 100hPa zonal winds were at a record high (since 1979) on February 10th and this triggered a dramatic collapse during the next 2 days in the zonal winds at 10hPa (60N) which went negative (reversed to easterly) on February 12th and the 2018 SSW was underway. I have over simplified the events and I strongly recommend that anyone interested in this (learners as well as specialists) to take time out to read Malcolm's post which is so clearly laid out with numerous annotated charts. Malcolm and I had already been studying the impacts of MT spikes on SSWs prior to the 2018 event. It was very timely that Malcolm found a brand new paper entitled: Orography and the Boreal Winter Stratosphere: the Importance of the Mongolian mountains (click on the title for a link to the abstract in the Research Portal where there is a direct link to the paper). I was preparing my very long post (which took over a week to research) and this paper was so relevant to our research and it was written "before" the 2018 SSW event. The last part of my huge post covers a detailed review of that paper and I shall return to it below. The first part of my post (which in hindsight should have been split into at least 2 posts!) looked into the history of SSWs, the development of understanding them, the causes and the evolving theories. I referred to a couple of excellent papers by Amy Butler including this 2017 paper: A sudden stratospheric warming compendium (portal link). I reviewed those papers and I also referenced and reviewed this 2012 paper by Thomas Ehrmann: Identification and Classification of Sudden Stratospheric Warming Events (portal link). This includes this table: Very briefly, this shows us that early major SSW events were quite common in the 1970s to 1990s but much rarer this century. The last one with a central date in December was 2001 (day 361 = Dec 27th) and only 2004 (central date Jan 3rd) started in late December since then. The lack of major "early" SSWs this century looks to be far more than just a statistical quirk. It may be due to the warming Arctic and reduced ice extent or to more indirect factors or natural variations. Anyway, if we do see a major SSW within the next 10 days or so, it'll be the earliest since at least 2000 and probably the 4th or 5th earliest since 1978 when the continuous satellite records began. Most of my post covers MT. I examine all types of mountain waves with numerous charts - look at wave breaking, critical layers and much more. I refer to and review some important papers covering MT and these include the highly acclaimed papers by Dr Klaus Weickmann (who developed the GDSM and GWO phase charts with Ed Berry while they worked at NOAA from around 1999 to 2015). Klaus was amongst the first to identify that EAMT had much more influence on SSWs than the other torques. I went into a lot of detail explaining the different torques and 85% of all global MT is produced by EAMT and NAMT (North American Mountain Torque). The original thinking was that meridional mountain ranges like the Rockies and Andies (SAMT) had far more impact on generating vertically propagating rossby (or planetary) waves by being perpendicular to the jet stream. This earlier research could not explain why EAMT had such a strong impact as most of that mountain massif was more east/west or west north west/east south east, such as the Himalayas. It was known that these mountains have powerful influences on the south Asian jet stream with strong impacts on the Asian and Indian monsoon seasons. In winter time, it was also recognised that EAMT impacted on the down stream flow right across the Pacific and on into western North America. More recently, the Tibetan Plateau was identified as a major source of EAMT and then in the last year or so, the very latest research identified that the most powerful uplifts were generated by the Mongolian Mountains and particularly the Altai range. In fact, the whole central and east Asian mountain massif is by far the largest elevated area in the world. I reviewed several papers on this in my post and especially the one referred to above. What actually happens is that the powerful west to east (sometimes south west to north east) jet is obstructed by the vast Himalaya range. The jet is forced over it. Then the lower past of the jet descends rapidly across the Tibetan Plateau while the upper part continues on its merry way. The plateau is the largest in the world and is generally 3,500 m to 5,000 m high sloping slightly downwards north from the foot hills of the Himalayas which are on the southern boundary. The lower part of the jet is effectively channelled or funneled northwards and north eastwards and continues until it hits the Mongolian ranges to the north. It is then forced upwards again with some huge uplifts generated - thought to be the strongest anywhere in the world. This uplift catches up with the upper part of the jet stream and generates powerful vertically propagating rossby (or planetary) waves. Under the right conditions these waves pass through the troposphere, often right through the stratosphere and even into the lower mesosphere. They then reach the "critical level" (see my main post for a fuller explanation) and the waves start breaking and gradually start falling back down, breaking at lower and lower levels. A prolonged and powerful EAMT event will continue this process for several days. I quote this from my post which I extracted from the paper: "- Flattening orography results in substantial differences in stratospheric flow from October - May, with the greatest differences in November - December. - Contrary to expectations based on mountain heights the Mongolian mountains have the largest impact on stratospheric flow. - The effect of the Mongolian (Tibetan) mountains is to decrease the flow significantly. - The Rockies produce no significant zonal wind changes. - The Mongolian and Tibetan mountains both produce anomalous convergence near the region of largest zonal wind. - Changes in horizontal divergence dominate the response to Mongolia while both vertical and horizontal divergence changes are important for the Tibetan response. - In contrast to the Asian orography, the Rocky mountains slightly increase EP flux divergence in the stratospheric jet region. - The presence of the Mongolian or Tibetan mountains produces a strong increase in wave activity propagating upwards from the surface into the upper troposphere. - Orography induced EP flux anomalies have generally different propagation pathways from the troposphere to the upper stratosphere than climatology. - Mountains also induce changes in wave propagation paths. - Orography induced changes in EP flux divergence cannot be attributed solely to the orography acting as an additional source of Rossby waves. - The Mongolian mountains allow more wave activity to propagate vertically into the stratosphere. - The Tibetan mountains have a similar spatial structure to the changes due to the Mongolian mountains but are of smaller magnitude. - Compared to Mongolia or Tibet, the Rockies have a much smaller impact on the stratospheric zonal wind. - These results indicate that changes in refractive index are of central importance for the impact of orography on the wintertime stratospheric circulation. - The Mongolian mountains have a greater impact on the upper tropospheric wintertime circulation than the Tibetan plateau. - Without the Mongolian mountains, the frequency of SSWs drops from 0.6 SSWs per year to 0.08. - Removing the Tibetan mountains also reduces the frequency of SSWs, albeit weakly compared to the Mongolian mountains. - Removing the Rockies has no statistically significant impact. - The presence of mountains causes no significant change in the date of the seasonal vortex breakdown at the end of polar winter. - The delay in the switch from westerlies to easterlies when the orography is not present is not statistically significant with 40 years of data. - Reductions in both displacement and split SSWs occur when the Mongolian or Tibetan mountains are removed." I highlighted the key point in bold. The experiment simulated the impacts of the main mountain ranges and looked at what would occur by removing each range in turn. Without the Mongolian Mountains, the frequency of SSWs drops from the average of 0.6 events per year to to just 0.08 per year - a huge difference. Furthermore, the enormous uplifting is almost always associated with the major SSW events - the stronger the EAMT the stronger the impact on the SPV. This is no "one off" piece of research. The experiments have been tested and verified by some other specialist in this field. A whole host of papers are now in the pipeline, not least linking this research to the 2018 SSW. When Malcolm and I examined the precursors to the 2018 SSW, we were amazed how everything fitted into place. Although it is too early to draw absolute conclusions from this, it's a fascinating piece of research and it almost blows away some of the early theory out of the window. many scientists will need time to comment on this and react to it. Now, we can put this theory to the test again with the probable upcoming SSW event due later this month. Although, there are some slightly different parameters and teleconnection fundamentals this time around, if anything we have an even better fit that the February SSW event. In stead of a La Nina we have a developing weak El Nino - often considered to be the best ENSO phase to favour SSWs. We have shifted during the summer from an eQBO to a wQBO. The former is much more supportive of SSWs but the transition has only recently been completed and was not considered to be particularly relevant (as shown in several tele and strat thread posts during the last few weeks/months) and only yesterday (just above this post) Steve @Superstorm93 referred to a tweet from Sam Lillo stating that "the latest MQI phase space plot shows the QBO in westerly shear mode, which when compared to a climatology of stratosphere vortex weakening events, is consistent with increased favorability in December." A whole raft of recent forecasts are showing a thoroughly disturbed SPV. The preconditions are building. Now let's sprinkle a little MJO, AAM, torque and jet stream activity into the mix of ingredients. The MJO is currently at moderate amplitude in phase 3 (the I/O) and all the models predict it to rise through phase 4 into phase 5 (the Maritime Continent). I show GFS and ECM which predict moderate amp but weakening slightly during week 2. Several other models (not shown) show the MJO continuing at decent amp. I posted the AAM and FT charts just 2 days ago. They showed a big spike in GLAAM tendency and a rise in FT from it's low point last week (albeit not a particularly strongly +ve phase). The GWO has seen Total GLAAM remain +ve (the relative GLAAM tendency anomaly went -ve and then spiked to strongly +ve). It's emerging in phase 5 which is strongly suggestive of rising MT (reminder in chart below). Then we have this amazing and extremely timely MT chart: GLMT (black line) dipped to its lowest level of the year 2 weeks ago and spiked to its highest level a couple of days ago. EAMT (red line) has spiked more than the other regional torques. Now, looking at the upper part of the chart (the dates from the bottom still apply) we can see where this is occurring. Around Dec 2nd EAMT was -ve as shown by those blue blobs at 30N to 40N. Then we have the spike to Dec 11th (still rising slightly at the end of the run) and we have deep red blobs from 28N to 48N and at its strongest around 40N. The main Himalayan peaks are around 28N and the majority of the Tibetan Plateau is around 29N to 37N. Mongolia is mostly between 42N to 52N and the Altai range is around 43N in the south east and 48N in the north west (there are other ranges too). I provide other maps and much more detail in my main post. The strongest EAMT is centred right over the Altai range! I compare the current EAMT event to last February (see Malcolm's April post for full details). EAMT peaked around Feb 2nd/3rd 2018 - 9 to 10 days prior to the SSW. it saw another (even larger) peak around Mar 7th with a secondary warming (or further SSW impacts) around 10 days later. Going back to the current (2 day time lag) MT chart, a similar time lag for triggering the upcoming SSW would be around Dec 20th to 22nd with "possible" surface impacts a few days later (perhaps around or just after Xmas). This ties in with the strat predictions. What can possibly go wrong? Remember this is all still based on theory and is yet to be fully proven. If we do get an SSW, just how/when will it propagate down to the surface and where will it impact? Given that we are seeing such a strong EAMT event right over the Mongolian Mountains (stronger even that the ones in February and March during the last SSW event) I shall be following this very closely and half expect us to see a major full on SSW! Some readers will be more familiar with the jet stream charts. I recently found a good site showing the jet over the east Asian region. It's part of the excellent "StormSurf" site. Here's the link: http://www.stormsurfing.com/cgi/display_alt.cgi?a=nindi_250 I've set it to the jet from now until T+180. It's animated but I cannot copy a gif link - so I show the T+0 and T+120 charts below (and you'll need to go to the site for the animation): A very powerful west/east jet streak has been passing over the Himalayas and Tibetan Plateau region during the last few days. This is predicted to continue through to at least day 5 - making it a prolonged and very strong event and consistent with the really strong EAMT event. Another feature often associated with SSW precursors is the high pressure (HP) blocking over central and northern Asia - there is anomalous fairly high pressure there but we can see a strong belt of HP stretching from west to east centred around 50N to 60N. No coincidence, given the well defined and powerful jet to the south. By day 5 the belt of HP continues but has built strongly to the west and north west with a new cell developing over western Russia - perhaps another good sign as a precursor to renewed Russian blocking and well primed for high latitude blocking (HLB) following the expected SSW impacts in 12-15 days time. Overall, a lot to follow, a lot of interest and perhaps the perfect set up for a great Xmas present for cold and snow hunters in Europe, the UK and eastern CONUS. Things are looking really interesting for the run into the New Year and through at least the first half of January. David
  41. 62 points
    The problem is, we have many spending hours on this forum, explaining why things may and may not happen. The pros, the cons with a certain setup. The background signals, from Pacific forcings to Solar to the Enso state.Going to great lengths to point out the mechanisms, the caveats, the opportunities. I understand why some feel, why do I bother? 95% are here to do exactly what the forum title says, 'HUNT FOR COLD'. Whether that is looking for a glimmer of hope in a flat zonal profile with poor background signals or in more interesting times, aka right now, it is the whole point of being here on this forum surely? Clearly this forum would be redundant if we all lived in Antartica, but we don't, we live in an area that is usually beyond the reach of any easterly train from the east and with a continuous warm belt of water being pumped up from the Gulf of Mexico to our west. The odds are stacked against us right from the off. The dice are heavily loaded and they are not in our favour. And that is the thing, the crux, the whole point is the chase itself. I won't go as far as to say the cold actually landing is secondary, but before it does, the chase, the hunt, the hope, the despair, the rollercoaster, that is why we torture ourselves on here every winter. I am a die hard lifelong Spurs fan, so that probably makes me a masochist! But the fact remains that for the 95%, just seeing those cold charts appear gives us the buzz we all crave at the time. That may make me look like a total fruit loop in 'real life' but I know full well most of you know exactly where I am coming from!! It is a shame then that we will always get one or two miserable posters who take a few op charts as gospel and on complete face value. Bad enough but to then, through no skill but their own negativity, extend that op chart out to several weeks / months beyond is what really gets people's backs up on here.
  42. 62 points
    Output is beginning to recognise the significance of the timing of +MT, MJO progression, background Nino and impact of heat transfer onto the vortex. Height rises out west to drive the trough further south, followed by invigoration of that trough via falling momentum phase - and meanwhile Greeny and Scandy height rises begin to link up. It's a near perfect sequence - and once again for all those moaning last night about how we cant predict anything and its all random blah blah - nonsense. There are spanners that regularly get thrown into the works and mess things up...but broadscale prediction is getting ever more possible with better and better tools. And this is one instance where we havent had a sudden uptick in solar activity, or a tropic storm in the wrong place....and the cold pattern will be completed on schedule. You have done well Lord Teleconnect....and now I sense that you wish to continue the search for the split vortex.... Hehe. Such fun. But to anchor my mid afternoon drivel into something with a graphical solidity about it - how about a GFS image. Usually ECM gets the bigger coverage, but I think GFS has been handling the extended picture rather better in recent days. By the end of next week we have a very good signal for a cold trough with signs of continental cold being able to back west ....and then within a few more days the heights back further west to Greenland and begin to pull in an ever more frigid flow from the E/NE Being brutally honest cold rain for many will have to be endured as we progress through this phase - but the end result looks like an increasingly cold and wintry one. Patience my friend. In time the Beast will seek you out, and when he does, you must bring him to me. He has grown strong. Only together with the additional benefit of a downwelling split vortex can we turn him to the Dark Side of The Force.......
  43. 61 points
  44. 61 points
    My take on the upcoming cold spell using the usual 500 mb anomaly charts Looking at the latest upper air, 6-15 days from now. The usual 500 mb anomaly charts. Not that they have been either consistent or a good guide at times but the three I use have been slowly converging over the past week into a more coherent and agreed pattern. One item that has been consistent is the gradual lowering on all 3 of the contour heights. A week or so ago the heights just south of the UK with above 558 DM now they are predicted to be closer to 546DM or lower, ECMWF-GFS Today it is the turn of GFS to show the most meridional and cold pattern. Previously it had not had much in the way of this ridging over the western Atlantic into the Greenland area but now it does. Not sure if this will stay although judging by the EC and NOAA this is where it should be. NOAA Their 6-10 still shows a more Atlantic type of PM pattern with some ridging into Greenland, similar to how it has dealt with the pattern for about a week. +ve heights are shown off Newfoundland and these have also steadily increased over the last week on its daily output. Likewise the actual contour heights (just south of the UK) are showing at 546 DM some 10-12 DM down on earlier predictions. The 8-14 is a pretty similar chart in the pattern and positions of any ridging/troughing. Perhaps most of us might be more relaxed about this upcoming cold spell if these two charts from NOAA showed similar meridionality to EC/GFS. However, to me, the consistency of NOAA gives some confidence in the cold spell being something that is going to be there two weeks from now. How marked the cold will be, where any snow falls, is of course not for this type of chart but from the operational ones closer to T+00. My own punt would be for a cold, sometimes very cold period of at least 2 weeks for most areas. Only temporary breaks in it for parts of the west and SW, unless a very active system breaks NE from the Atlantic. Then the usual problem of show or rain ahead and/or behind it. All full of interest for all those cold fans and for anyone with a weather interest. http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php
  45. 61 points
    You have been repeating this for as long as I can remember. And yet again I feel that a response is required. If we go back 10 years to when I first started the strat threads, you weren’t alone in your thoughts that this teleconnection did not influence the trop and made repeated attempts to knock this extra knowledge as a forecasting tool. Yet, in that first year we observed a record split in the SPV and were able to demonstrate quite easily how that split brought about an almost immediate trop response with the Feb 2009 easterly. Then we have the early winter splits of the next couple of years. We have also demonstrated in futher years how cold strat temps led to periods of vortex intensifications and a resultant strong trop +NAO. I am sure that if you put it to the floor on Netweather then the vast majority would agree that analysis of the strat will assist in longer range trop forecasts. And we know that every SSW is different and there is still a lot to learn. But our ignorance should not put us off that quest for extra knowledge, nor should it deny us acknowledging that the link exists even for our small island. So, the same can be said for the links between the MJO and GWO. The phases of each have been shown many times to be linked to a certain planetary wave pattern. I do not understand every little nuance of these factors but I know that they do have a bearing on our small island and in years to come I hope that the acceptance of these interactions will be as mainstream as the strat is now. In fact I feel particularly proud when I see nw members warning that not every SSW leads to a trop response. I feel that those years weren’t wasted. Back to today now, and after a little wobble yesterday the strat charts still look conducive to providing a downwelled trop response. The only difference being is that we are 3 days closer so I would be expecting changes in the output from days 12-17 now.
  46. 61 points
    Reading this thread tonight has been a real rollercoaster....have to wonder why those who believe the weather is nothing but chaos with no discernible pattern bother to spend time on a forum where the main thrust is to try and make sense of complex signals and decipher a path forward - but there you go. Takes all sorts I guess.... ...and on the subject of signal deciphering all still looking pretty good, isn't it? I have a slightly warm and fuzzy feeling at the sight of this EPS chart for the 18th Good to know that GSDM theory has a basis that produces the goods. Signal for isolation of the trough underneath a growing band of high lat blocking is growing, and on schedule. To reinforce the fundamental reasons for this - time to post the MT chart that David has already put out there tonight...just for double emphasis It's a really very impressive spike at 30N - and to summarise David's detailed argument into a brief sentence - it very much increases the chances of our strat warming becoming a major one. This sharp increase in momentum will do all kinds of nasty to the vortex - but it also creates a signal for increased atlantic blocking as eddies downstream of the spiked pacific jet form. NWP has been slow to pick up on this - but that EPS chart suggests we have increased clarity now. From here? EPS at 10 days suggests again that the expected pathway may be accurate. The trough will sink south, and with it will come increasingly cold air and wintriness to high ground. This is the start of our winter proper (at least in my eyes) but don't expect widespread snow at low levels quite yet. However - this period will signal the start of the real cooldown. And from there? Time to return to GSDM forcing because strat reinforcement of the pattern will be a little way off yet. Tendency of AAM will begin its next downward cycle soon. This will signal in effect a reduced momentum signature at 30N and opportunity for enhanced momentum further north. However the difference this time is that our next MJO cycle has kicked off, with moderate wave activity emanating once again from the pacific. This will aid in preventing the pattern from becoming too flat, and I would suggest we will see a reinvigoration of the atlantic as we head into Xmas week (despite the higher than average pressure anomalies out west on that EPS chart) but with the trajectory to the south rather than through the heart of the UK (as is happening this week) as heights to our NW serve to deflect the jet on a NW/SE axis. Shamelessly cherry picking a GFS extended image from the 18z rolling out now this chart for Xmas eve would be about what I would expect though perhaps with a greater maintenance of heights over Scandy Systems tracking beneath the block heading towards mainland Europe. Polar maritime airmass mixing with a trough that is beginning to pull in air from the NE. In essence becoming progressively colder on average. So - when does all this give us snowfall at low levels in the south? Don't know yet - don't want to guess. Depends on how quickly cold air can be absorbed from the NE and just how entrenched the block becomes. But chances certainly exist prior to New Year if the flow is right. If not it wont be long after NY before we see 850s in the right kind of zone with a flow that will be evermore easterly on average. And all this being forecast on 13th December rather than 13th February. Warm and fuzzy all over again....
  47. 60 points
    The warmer air creeping east today with the font And to digress for a moment. I was in a taxi just now and the driver started wittering on about how he loved cold weather. I thought, 'the bloody nutters are every where', as i deleted the taxi firm from my contacts.
  48. 60 points
    Atmospheric Customer Services. If you are concerned by the lack of Winter Weather at the minute then please call this number: 0000 -1 -2 -3 -4 Option 1: ICE Option 2: Snow Showers Option 3: Heavy Snow Option 4: Blizzards Option 5: 1963 Option 6: 1947 Please press 0 to hear these options again or alternatively Nick Sussex is on line 7 to take orders for Prozac. We apologize for the lack of Winter Weather and our engineers are fixing the problem..... PLEASE HOLD... ESTIMATED FIX TIME: 10 - 15 jAN...
  49. 60 points
    LOOKING GREAT FOR EXTENDED COLD SPELL IN EUROPE AND EAST CONUS FROM XMAS ONWARDS I posted this on a US forum teleconnections thread and @Raythan asked me to copy it on here. It does relate to both US and UK/Euro patterns. I shall not edit it and it was rather rushed. At last, the AAM, torque and GWO charts have all just updated to Dec 9th and they are almost entirely in line with Tams' @Tamara and Tom's @Isotherm predictions and very good news for those hunting the main cold spell starting around or just after Christmas in the eastern US and a few days later in western Europe and the UK. Total GLAAM having fallen back is on the rise again. Following the huge fall in the relative GLAAM tendency anomaly it's bouncing back equally strongly exactly as they predicted. FT rose and has gone +ve albeit briefly. The rising FT (from its low point) has led Global MT up (with the usual time lag) and that's another huge spring back and leading NAMT and EAMT upwards. The GWO did not go -ve while it has moved from phase 8 and has pushed through the COD and is re-emerging in phase 5, exactly as Tams predicted. It's set to rise at increased amplitude through phases 5 and 6. I've run out of time (incredibly busy this week) to say any more but with the MJO also playing ball (entering a higher amp run through phases 5/6/7) and the signs of a significant strat warming (if not a major SSW) make me feel really bullish about a significant cold spell - probably in Europe/UK and the eastern CONUS. I'll leave it up to the rest of you to scrutinise the finer detail. I wonder how quickly the models will "fully" factor this in? David
  50. 59 points
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