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  1. 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
  2. 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
  3. 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
  4. 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
  5. 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
  6. 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
  7. 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
  8. 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
  9. 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
  10. 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
  11. 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.
  12. 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....
  13. 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
  14. 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
  15. 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.
  16. 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...
  17. 54 points
    Decent signal for a strong mid latitude ridge signal across Christmas week in the EPS and GEFS for NW Europe. This looks plausible on tropical and extratropical signals right now. Thereafter, EC locks in a -AO out until February and drives the NAO negative mid January onwards. I would be expect movement of mid latitude ridges north and north-westwards over time as the impacts of the stratospheric warming take effect.
  18. 53 points
    Hi Nick, it's unnecessarily gloomy on this thread. I haven't got time for a full update today but the "tropical response" that you, me and many other coldies are hoping for is looking extremely promising. Even if we do not see a major SSW (and it's almost nailed on - with just type and impact timing uncertainties to be ironed out) the next tropical Nino surge with +ve poleward AAM (atmospheric angular momentum) and +ve GLMT (global mountain torque) and particularly +ve EAMT (east Asian mountain torque) are set to fall into place towards the end of December favouring a pattern reset which is already underway. Currently it has just fallen to strongly -ve relative AAM tendency, -ve GLMT and -ve EAMT and are all about to bounce back (they must do to restore equilibrium) and surge upwards with rapid responses. Almost every winter this catches out the models which do not take anywhere near enough account of these key drivers. It would be looking good for colder patterns anyway through January but the timing of this, with the progress towards a very early SSW (with a full split looking increasingly likely) and the MJO seemingly set to be playing ball too (week 2 just adjusting again to a higher amp pass through phases 5, 6, 7 on the cards), I'm particularly bullish about a prolonged cold spell in much of Europe (including the UK) gathering momentum in early January. This and the last 2 winters have seen only brief periods of "zonal" or really flat patterns and "mostly" weaker and displaced jets. 2016/17 saw an extraordinary amount of MLB but with little HLB. 2017/18 saw periods of both MLB and HLB throughout (November to April) culminating with a rising of AAM, the torques, a spike in EAMT (through late Jan and early Feb with the usual time lagged responses) all helping to trigger the SSW and also helping the MJO advance through its maritime phases at increasing amp to go on to reach near record amp in phase 7 assisting the blocking pattern. The SSW impacts, once the wind reversal reached the surface, spread very rapidly westwards from Siberia/N Asia. That happened with a less favourable "Nina" pattern. This year we have a weak El Nino trying to establish itself - considered to be the most favourable ENSO phase for encouraging SSWs (but not too strong like the 2015 super Nino which blasted the global patterns into oblivion). The tropical Pacific SSTs are all indicative of a Nino event but there has been "until just now" a problem with ocean-atmosphere coupling. The imminent surge in AAM and the current higher amp MJO in the Maritime phases should strongly favour full coupling. The lower troposphere layers will look highly conducive to SSW impacts without the propagating problems that we've seen in some recent years (perhaps the best since 2009/10 - also with solar minimums but no two events are alike and I hate using analogue years when we have impacts from global warming and reduced Arctic ice extent to throw into the mix). The models are likely to struggle for several more days and then we should see some major changes as they start to increasingly sniff out the impacts from the pattern reset and the upcoming broad scale changes leading to an increasingly -veAO and -veNAO as we head into January. A split SPV (stratospheric polar vortex) SSW is likely to produce considerable HLB and widespread Arctic cold spilling out towards the mid latitudes, including the UK. Even a displaced SPV which has come under such persistent attacks could produce the goods this time. Overall, the next week should reveal what lies ahead. If ever there was a time to consider what drives the model output, then this is it. The interaction of the key teleconnection processes on the stratosphere and the troposphere are coming together nicely. In Feb 2018 GFS had several op runs for about 7 days ahead with barrel lows of sub 930 mb showing up just off the southern tip of Greenland. A week later that area had over 1030mb - so just a small error of over 100mb and all due to the pattern reset which GFS and the other models had been struggling with. I noted this in this morning's GEFS 0z run as a perfect example of "What NOT to expect": That's a record breaking Aleutian or Bering Sea LP. This is perturbation 2 for next Sunday - just for fun. With 925mb shown, I would say that the CP would be nearer 922mb or 923mb. The existing NPAC record (excluding tropical cyclones and hurricanes) is 925mb set on October 25th, 1977 at Dutch Harbor, Alaska. That's the "official" record but I believe that there have been several unofficial readings of 924mb with one as recently as December 14th, 2015 during the peak of the super El Nino. An Aleutian low is quite possible but one like that is quite simply complete fantasy. The whole GEFS panel is all over place and covers almost every possible outcome. That should bring home to all of us that we're in a reset period with extreme model uncertainty. If I have time, I'll elaborate on some of this during the Christmas holiday. Meanwhile, I'll wish everyone a very Merry Christmas, a Happy New Year and a period of absolutely fascinating model watching. David
  19. 53 points
    Holding pattern at present. The extent of the hit to the vortex, and whether it splits or not will be a now cast event. However there has been a lot of gloom in here today, and the usual suspects who love to shout “told you so” with little to no understanding of actually what they are telling us have appeared in force. Always makes me chuckle to read posts from those who enjoy pointing out the the UK rarely gets a sustained cold spell and that mild/wet is our default setup....as though we don’t know that already. Really tiresome to have to filter out that twaddle. We didn’t get our block this week - but it was a close run thing. Torques set to re engage very shortly....and the second bite at Pacific led forcing to shunt a block up to the north will be in the period between Xmas and New Year. The fact that a UK high looks likely to be the end product of the current negative torque phase is good news....a much better starting point for the next +MT impacts to work off than the rather nasty trough we had anchored to our west last week. All good still. Strong signals very much in place....but angle of any potential vortex split really will dictate whether we get cold shots or the chance of a properly sustained cold spell of easterly feeds. There are no guarantees here....but we still potentially stand on the cusp of a spell of special January wintriness....
  20. 52 points
    The atmosphere is now reflecting a Nino state and has been for a while - and that chart is a change over the last 30 days chart. The actual anomaly charts look like this Still very much Nino and not Nina. What the oceans look like come March is of zero interest in any hunt for cold now, and any moderation in Nino over the next 6 weeks will not make a real impact on this winter's season. This tweet is frankly nothing more than a scare story. His twitter feed is extremely uninspiring and rather basic. Nothing to see here - move along...
  21. 52 points
    Something is brewing....something perhaps not easily seen right now from NWP operational output. Take a look at the extremity of the most recent mountain torque atmospheric deceleration: Temporarily down to -4SD...with all torques hammering low. In layman's terms what this does as you can see from the negative tendency around 30N is enhance net easterlies and prop up the mid latitude high - and we have our UK mid lat high. So what happens next? With GLAAM tumbling there has to be a counter in the wings as earth and atmosphere continue their ongoing attempt to have earth and atmospheric momentum balance out at 0. Torques prevent this from ever happening for long - and as the atmosphere has slowed at 30N it for sure will come bouncing back up, and on schedule as per previous posts. We can expect to see a rally in MT in the next few days - and perhaps another strong one. We have seen plenty of steep gradients this season. So - imagine a burst of westerly momentum sent through the pacific and on into the Atlantic with our block sat where it is...and now factor in the ongoing pressure on the strat and increasing likelihood of a split. As momentum comes into the atlantic I can see only one impact - and this is the bouncing of this high pressure anomaly up to a higher latitude. And with the vortex collapse imminent this then becomes a pattern that will take some shifting - the block may wax and wane through much of January, but it will become a semi permanent feature. How quickly the vortex recovers (if at all) will determine specific longevity...but as said before: baby steps. Let's see what actually happens to the vortex before getting too excited (at least publicly...…..) And so pacific forcing, with the MJO moving towards phase 6-7-8, set to give a tropospheric lead to the pattern before stratospheric reinforcements arrive. Don't be seduced by the current bland holding pattern. Last week the pacific failed to produce a high lat block in a nearly scenario from the last MT spike - but we were dealing with a deep trough to the west that was unable to progress east. It is a very different atlantic profile developing now, and the impact looks set to be much more predictable. Provided there is an active pacific background signal and a strat under stress there is nothing at all wrong with a growing UK/Euro high...but a little more patience required. Look for the block to begin to extend north as stage 1. Stage 2 will be invigoration of the Euro trough that will replace it - and if the strat splits as the EC is seeing it then expect it to be a vigorous undercut. Downwelling impacts 1 - 3 weeks...so core of the cold potential continues to be weeks 2 - 4 of January. Anything beyond that in the timeline will depend on how badly the vortex gets beaten up and caution required on predicting that. Very exciting times ahead....
  22. 52 points
    Im here & the grass is trimmed ready Im trying to find the time to update the my winter NH thread - However for anyone that didnt read it its here- If anyone does browse - We are homing in fast on one of the key features which was a record breaking negative zonal wind anomaly - The forecast for the SSW for 15 Dec is going to be around a week out- which along a timeline of about 5 weeks is very pleasing The date that the record goes is ~ 22nd to the 1st being the lowest ever- My other highlight being that we could beat the record -AO daily score will be under threat most certainly in January - With an outside chance of the Monthly AO record of Feb 2010 going as well. The fireworks are coming soon guys.... - just not in time for Crimbo.
  23. 51 points
    I don't think there has really been a signal for snow pre-SSW or immediately after, looking in depth at the drivers, I admire your enthusiasm to put a dampener on the outlook despite the overwhelming pointers from the likely impacts from the eventual SSW downwelliing in concert with lag of MJO moving through colder phases (7-8) plus other drivers such as anomalous East Asian Mountain Tourque and +AAM which will help amplify the flow at high latitudes. It has been stated on here by me and others that there was likely to be a few weeks after the SSW started until the impacts were felt in the trop and also the lag of the MJO now headed into 'colder' phases. I think the main reason why we have been stuck and continue to be stuck in this pattern of waxing and waning mid-latitude block with all the upper flow energy over the top, but increasingly flowing NW to SE into the deep eastern Euro trough is to do with not just a strong Pacific jet extension but also the lag effects of the slow MJO stuck in phases 4 and 5 between mid and end of December, these are ‘warmer’ phases that tend to be hostile to high latitude blocking bringing cold to the UK but favours mid-latitude blocking and cold for E/SE Europe. The reason for the slow MJO propagation down to a few likely factors, that were mentioned a while back, including equatorial Rossby waves moving westward along with –AAM which have interfered with the eastward MJO propagation. Also the wave driving into the stratosphere weakening the SPV has probably constructively interfered with the MJO propagation too. However, the MJO now looks to speed up through 7 and 8 and although GFS and EC take into the circle of death (COD) / or MJO dies off over the Pacific, the phase 8 impact on the patterns should remain once MJO has gone into COD, so shouldn’t be duly concerned with this. The downwelling of easterly winds from the strat to trop still forecast and this will be a big driver after mid-month. 9th Jan 14th Jan So although the charts look crap atm, due to the background signal explained above, we should hopefully see the models pick up on better patterns for sustained cold and snow potential for us in week or so as impacts of SSW, MJO colder phases, +AAM/EAMT work through.
  24. 51 points
    Sorry in advance MODS, but it’s comments like these that make brilliant posters like @Tamara stop commenting on here, and this forum is a poorer place for it. It sounds like you have a bit of an entitlement complex. We don’t have a god given right to have cold, snowy weather. We know how difficult it is for everything to fall into place for us to get that kind of weather on our small island. However, as we all know, those “background signals” don’t guarantee cold but make it much more likely. So we should always have that in the back of our minds, and if things don’t fall into place for us then so be it. We have some exceptionally knowledgeable people on this forum who dedicate their time and impart their wisdom to help all of us in our quest for snow. We should be thankful for that, and not moan if things don’t fall into place. As it happens, we are still in with a great chance for a cold, snowy outbreak during the second half of winter. Writing anything off now is madness.
  25. 51 points
    Gosh Fatigue is strong this morning. I think some might need to take a step back for a few days- I’m not sure that restating how disappointing everything is every.single.run. Is necessary/healthy? We get it. It’s not snowing. The output isn’t showing what anyone wants and you feel cheated because we were ‘promised cold’ It’s the weather. You can’t complain to Atmospheric customer services on twitter about not getting what you were ‘promised’. If your post involves a moan about cold being pushed back/the SSW not working/ how bored you are it might be better for the general chat threads OR your innner monologue?
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