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  1. 122 points
    An ode to the model output thread... "In days of old, when Thatcher was bold and Kettley was a weatherman, Tales are told of winters cold, and snow lay everywhere, man. The World Wide Web and ECM were yet to be invented And weather forecasts at the time were often quite demented! But there's no doubt, the records show, that winters then were colder And five foot drifts were commonplace - they came up to your shoulder! For years and years all we've had is windy wet and mild And although it's not all been bad we crave a winter wild.... Now... The models hint that Scandinavia could maintain a block To curb Atlantics bad behaviour - that would really rock! But... The GEM can't be trusted; the GFS is dire The ECM has often busted; the CFS? - a liar! So on UKMO we must rely but wait - is it cursed? More runs needed, standing by.... let's get the cold in first! Hope you all have a great weekend of model watching!
  2. 114 points
    Evening All Ice Cold hope your still with us .... So the much touted SSW is coming into view & here’s my thoughts + timelines of when / where to expect it... We have seen lots of posts & comments on it - but whats the reality likely to be -??? The Omni present warming in the GFS charts is usually due to the model & its poorer vertical resolution V the ECM, as a result there is an over reaction / over estimation of how much a warming is going to impact the zonal wind @10MB - so because of this 'bias' when viewing the mid / long term outputs churned out by the GFS we have to be a little on the sceptical side as these are normally moderated & scaled down even wiped out ! However we have now seen the evidence in the Berlin site that a downwelling SSW event will make it to the 10MB level & indeed go on to challenge the date record for the time lf year- ( this is NOT the same as the usual deceleration of the zonal wind we see at this time of year as that is more of a gentle reduction all the way to mid april when the vortex breaks its annual westerly influence ) So as highlighted we have passed the point of no return in the stratospheric modelling where a SSW is now just 5 days away for the 12th Feb *** Take note of this date -- The plots below show steep downward curve of a signature warming Note the main black line being Climo - but the ensemble mean from the GFS running out at mid -20 to -30 M/S... The clustering is quite close - further backed up by the another illustration of the ensembles from the hannah attard site With the mean bottoming out at -32M/S *The date record for this time is ~ -17 M/S & the all time record low ( using Merra data ) is -35 M/S The ECM berlin forecast below is not as bullish as the GFS coming out around -17 M/S @10MB but none the less still classed as significant event... So what we have in modelling terms of a SSW due is * The first one in 9 years ( I dont think last year was classed without checking ) * Possible record breaking reversal of tge zonal wind... If your thinking whats best in terms of impacting the UK its simple- The lower the negative number the better... - record breaker ? yeah I will take that please... Why?... The bigger the negative number the stronger the easterly flow is across the mid lattitudes. !! ( think feb 63 / jan 85 & so on ) Whats the models churning out then? The SSWs are classed as 2 types - Wave 1 displaced vortex or - Wave 2 Split Vortex .. This is whats expected - A classic wave 2 Split vortex- with 2 clear areas of poleward flux - over the far East & canada- Now luckily for me the historic SSWs have already been classified -we are looking for la nina years / W2 / split vortex- 6 years appear as matches - 28 Jan 1963 - 7 Jan 1968 - 18 Jan 1971 - 1 Jan 1985 - 21 Feb 1989 - 24 Jan 2009 Below are the 10MB increase in temps at the time when the zonal wind hits 0M/S Obviously they all have 1 thing in common- The huge rise in temps across the pole - Now the Date of the zonal Mean hitting 0M/S isnt the day of peak blocking - Looking at the dates above peak blocking appeared 7 - 11 days post Reversal - see below day 11 charts from the above warmings ( 500 MB anomaly ) Whats apparent is HLB is quite prevelent & most are centered ( for us ) around greenland & Western Scandi - Also all 6 Splits have varying levels of troughing to the south - but all have an anomaly- So that really leaves with a level of expectation that should at least give us some confidence for Feb over the following dates- 12 Febuary : is 'R' Day- as in the reversal of the 10MB zonal wind where the eastward progessional component is replaced by a westward one 13/14 Febuary : is peak 'R' days where we will know the magnitude of the warming & just how much westward ( reversal ) component there is - Sub -20 M/S is the date records & anything below is the jackpot - 16-18 Febuary - Mid to high lattitude transitioning - This is where depending on how lucky we are for our area we will see MLBs start migrating North to the pole as zonal wind lag filters through the lower layers of the atmosphere & support builds for HLB - look for the 3 key wave patterns ( atlantic / Scandi & pacific (-EPO) The UK can get very cold in this period if the migrating highs are favourably positioned from the outset.... 20-24 Feb - Peak HLB blocking across the NH - peak -AO signature & peak cold overall for the mid lattitudes ... *** IF the GFS lands with the depth of negativity then Late Feb early march will be on a par with 2013 for AO negativity & possible / probable UK cold / snow.... if the negativity is watered down then the cold signature will be watered down & less dominent in western Europe... Best S
  3. 96 points
    Good afternoon gang ,its nice to be back reading all the posts again ,although i have been lurking .(Thanks to all friends on here for my much appreciated messages over the loss of my wife recently ,THANK YOU ALL ) .Its great to see that the charts are showing some Winter weather , really warms the cockles of my heart .And its the charts which keep us interested not always showing us what we want ,and i,m certain that over the coming winter there will be Prozack moments and of course STella times ,so with the Meteorological Winter looming we can look forward to 364 roughly Runs of the good old GFS ,182 of the ECM , AND HUNDREDS OF OTHERS .Looking around the Internet back last year i looked at many weather forums etc ,and found that ours is by far the best and most interesting around .In my next post i will stay on Topic ,just wanted to start with a light Hearted post today .Let the hunt for Winter Synoptics commence ,Curtain twitching ,hiding behind the settee etc ,cheers gang ,.
  4. 80 points
    Well it's probably fair to say that I've been rather quiet on these forums for the last few years really, especially since 2013. After 15 years of internet weather watching, and more importantly, having witnessed the incredible run of winters we had from 2009-2013 (vs the more Ian Brown style winter in the preceding 10 years), it really takes something now to get me to show more than a fleeting interest in what's on offer. Now it's safe to say, regardless of geographical bias (bearing in mind I now work in Central London and live on the SE'ern edges of our ever-warmer capital, so I am pretty neutral when I say this) this winter has, thus far, been the most productive for watchers of a colder persuasion since March 2013, with many parts of the country seeing at least a covering and some lucky folks through Central England seeing 3 pretty decent, if temporary, snow events (of course those further North and more vertical than the rest of us have seen far in excess of this, but those lucky b******s get to see this most years). But what we stand on the cusp of, what is being modelled within a pretty reliable timeframe, is reminiscent of those days back at the beginning of this decade where the sun went to sleep and cold chaos ensued. It is far to say that, beyond just the pure pornographic synoptics, the likes of which we had not seen for many years previous, 2010 ruined the laws of model watching in so many ways. Forecast models are not supposed to pick out the correct pattern at +360 and run with them pretty much right through to +0. They're supposed to tease us with big greeny highs, fallible dreams of the biggest snowstorms of the last 100 years (circa December 2012) and then leave us distraught, crying in the corner of the shower, attacking the 'mildies' on here with our not-quite-waterproof smartphones (what a long way we have come...) at even the merest hint of an 'I told you so'. And I genuinely think the 2010 episode of near flawless modelling has left a lot of people on here far too expectant of the capabilities of predicting the friggin future with a lot of electronic circuitry and fans. This is why, more so than at any time in the past 5 or so years, this current phase of modelling really has my interest. We are on the cusp of something which, pre the 2009-2013 phase, would have had me online from 8am-10pm (which, if memory serves, is when the old BBC slowwatch forums used to shut for the night) in a far too nerdy way (nobody ever understands our snow obsession right?). Some members on here can be accused of being just that little bit too optimistic when it comes to cold and snow chances, but those same people are very much correct in these sort of short-range cold shock scenarios - whilst the models might not yet show anything significant snowfall wise, they never do until much closer to the time. In fact, if we think of events such as Jan 2003, Jan 2004, Feb 2005, Feb 2009, Jan 2010 and even in to Feb 2012, Jan & March 2013, all of them had modelling which at face value painted a cold and dry scenario....which continued until a few days before unexpected features popped up in an increasingly unstable flow given a significantly lower than usual upper temperature profile. When you combine that with the anomalously warm seas surrounding the UK right now, there is an inevitability about unexpected short range snow events. Beyond just next week, we also have a pretty consistently modelled significant warming into the stratosphere, which should yield an interesting second half of February, combined (or perhaps even coupled?) with one of the most significant MJO episodes we have seen to leave us on the cusp of a pretty memorable February overall...now when have we seen that before, with a declining solar profile...memories of 2009. Enjoy the next few weeks everyone, I will certainly be more active on here as we stand on the edge of what, from 15 years of experience, feels like a pretty significant period of wintry weather for our humble little island.
  5. 79 points
    In days of old, When nights were cold, And models weren't invented, We might have hoped, we might have prayed, But we didn't drive ourselves demented. The MJO the QBO, No wonders such as these, All we had back then my dears, Was Uncle Bert's dodgy knees. He'd hobble along with back bent low, Telling all who passed 'it's goin ta snow' 'They're aching bad' he'd say, 'eee I wish I were fitter', 'You mark me words ma lass, tis goin to be bitter'. More often than not he was right, A deep white carpet fell through the night, We'd wake up to an eerie glow, First words of the day...'Yippee, SNOW!' Those days are gone, but not forgotten, Few snowy days now, seems so rotten, What will it take to make dreams come true? A long fetch beast, a bolt from the blue? A slumbering Sun? A boiling hot strat? A volcanic eruption? Dear God please, give us all that. When I was little, I'd be told, 'Yer won't like it so much when you're old' Mummy dear, I'm afraid it fell on deaf ears, I'm as bad as I was, so I'm here with the seers, I look at the charts with their purple and blue, It's all double dutch, I'm reliant on you, I've read and I've studied, I've tried and I've tried, Still makes no sense, my brain must be fried I understand there's lows and there's highs And a beast from the east makes white stuff fall from the skies But down here in the soggy south west I fear it will mean just slush at best I'm not giving up on those dreams from before, When I lived further North, instead of south of the M4, It must still be possible to get a battleground, Hopes of it happening are still around Down here we must settle for the dribs and the drabs, Seems snow is still out there, it's up for grabs, What must we do to get it to come here? Or do we just get to drown our sorrows with beer? The easterly beast that all winter's been bumbling, Will it get it together or carry on rumbling? How hard can it be to waft this way? All together now, let us pray. There'd be whoops of delight and cries full of cheer If we wake up one morning and find that it's here Open the curtains, let out a shout, 'See, I told you that's what the models were on about' Oh how I hope those dreams come true, But as I said, I'm reliant on you, Please be honest, please don't bicker, It makes reading these pages so much quicker. So finally before I go, To dream of the day we do get snow, To Paul and the Mods, be kind, please, Just lightening the mood of the FI tease.
  6. 76 points
    You know what - I havent seen 1 hopecast on here. People have put all their points of view across in a pretty good mannor- infact its been pretty good debate. The only post that sticks out a mile as pointless is the one im quoting...
  7. 75 points
    Well - ho hum - let's have a sit rep. My eyes are hanging out on stalks. The pacific first - engine of the climate system. How is our AAM looking in the face of the current high amplitude MJO? Tendency off the chart. How is our mountain torque input responding to the parallel rise in frictional torque? Off the chart. And the MJO itself? Well - not off the scale but not far off it. What does this mean? In a nutshell - strong pacific signal for high latitude blocking as AAM in northern latitudes falls and sub tropical high pressure gets the rug pulled out from underneath. Wouldnt it be great if this could happen in tandem with positive developments in the arctic stratosphere? Ummm - ok - funny that... 100% support now from the GEFS for a reversal at 10hpa 60N as a result of this: Huge burst of flux energy being punched straight into the vortex in the next week or so resulting in all the pandemonium on twitter today from the strat brigade. Flux angle is straight upwards - smashing into the poor vortex and giving it all kinds of grief End result: Vortex split in half in about a week's time just prior to the reversal. Proper SSW in sight - even the MetO have publicly advertised this today. What does this mean on the ground? Double whammy. Pacific forcing is pumping up high lat blocks - phase 7 composite for Scandy - while up above the vortex splits, slows, gets all in a muddle and ends up dropping one shard of the vortex over Russia and perhaps European Russia. End result - even stronger signal for the Scandy high that is already in place thanks to pacific forcing.... and a reversed flow via displaced vortex shard encouraging cold continental easterlies under the block. Length of spell hard to be precise... but certainly more than a few days. A double whammy like this would leave a strong blocked signal in place for more than a week at least - maybe longer depending on just how battered the vortex is and how quickly it could reform. Eyes still out on stalks. This is definitely a one in 10 year event - and actually it might be more than that. Cohen is advertising 1985 as the last time we had a vortex split like this one... and we ended up with this around 2 weeks later Response time for our current event looks likely to be less than 2 weeks - Chio reckons pretty instantaneous. So - are charts like this on GFS for the return to school after half term likely to come off? Yes they are. Potential is there for this to be one of our big periods of weather that gets marked in the history books. 81, 85, 87, 91, 96, 10 - and maybe now 18. Can it go wrong? Of course - as fast as it went right... but who gives a stuff about that right now. The dominoes are currently aligned... so no gloom required. And the dominoes are looking steady.... Funny. 10 days ago I was gloomily expecting the final pacific cycle of the season to be as tame as the last 2 and to give us at best a mid lat block in the face of unremarkable looking conditions. Omega block... bit of frosty gloom... the best of a poor season thought I. Strat forecasts looked moderate - no sign of a reversal if we are honest... MetO forecast nowhere near mentioning "very cold." And now we are looking at something potentially special (though note this is NOT a snow forecast because getting the cold in is only half the battle... the other half is getting the precipitation and that requires some luck.) Now... where's my hat and gloves? Not needed them in Somerset for a very long while.... tropical moths probably got 'em.
  8. 74 points
    I quite often agree with your sort of sentiment, as I'm one who opts to look at the most likely solution to fit the signals rather than the preferred one But, equally impartially and with intended objectivity (hopefully): The situation at present is a highly unusual one and the risk of some astonishing late season wintry weather is much higher than usual, certainly than often seen in these cases where deep cold pool advection flirting with the UK graces the perimeters of more 'reliable' NWP The repercussions of this SSW are going to be sustained. The clock starting ticking back in January and carried on through this month with extreme instability of the atmospheric profile with the tropics and extra tropics being subjected to opposing high amplitude states of angular momentum tendency. The impact on tropospheric global wind-flows (the Jetstream) has been significant, in addition to the detonation of some intense cold pooling over the polar field (relative to the modern day generally warmer arctic) : more especially across the Canadian arctic as multiple programmes of hot needles are probed into the polar stratosphere The result of extreme tropical momentum and stratospheric implosion implies high impact weather events on a broad-scale. Some places are going to get bitterly cold and some weirdly warm. In this day and age fewer parts of a hemisphere can get cold with less to go around than used to be the case maybe. But this programme of events strongly favours the European sector to become bitterly cold from what looks to be an impressively large breakaway cold pool for the time of year from Siberia. While its true that the envelope of this cold has boundaries that shift in intra suite modelling, the focus of the BI being impacted in inclusion, is much higher than other situations where lesser broad-scale drivers have been in evidence Ramping indeed requires a justification - I think this situation fits that criteria. Areas of land mass infrastructure most at risk aside from weather impacts (hopefully with least human welfare risk), the synoptic blocking pattern and its associated reverse polarity from one side of the Northern Hemisphere to the other - is not something seen on an every day NWP menu
  9. 73 points
    Cold - Yes Instability - Yes Prolonged - Yes I just wet myself - Yes!
  10. 73 points
    Right time to knock it on the head. I am not interested and neither are most of the posters on here interested in how climate change may or may not be influencing SSW impacts. Keep your bickering to the climate change forum and let us concentrate on whether or not we will have a productive easterly or not. Thnk you.
  11. 72 points
    netweather members celebrate when the long-awaited easterly finally arrives...
  12. 72 points
    Still coming slowly off a cautious fence Long term total global atmospheric angular momentum trends can tell you a lot about pattern changes due to the effects the rises and falls in global wind-flows have on jet stream patterns. Total AAM refers to the net balance of easterly and westerly flow in the atmospheric circulation and the outcome tells you which direction the atmosphere is presently headed and which has initiative forward momentum Latest levels, assisted by a second tranch of eastward moving tropical convection since October has taken total global AAM back to parity, with even a hint of peeping a head above the parapet. This is to be set as disconnect against the negative (easterly) La Nina base state. Its no surprise that the sometimes pausing, but still steady upward trend overall, began from early October and why the pattern has been increasingly amplified over this time The importance of these feedbacks keeps being stressed repeatedly I know in these posts, but they are very important in terms of recurrence patterns that can give a good insight into how future patterns may play out. On the basis of the seasonal wavelength cycles spoken of again yesterday, the start of the winter (like any other season) is one of those especially important times when trends within the layers of the atmosphere can be especially augmented by natural seasonal wavelength cycles. Behind the rises in total AAM is continued buoyant AAM tendency as a result of positive torque mechanisms which are programming swathes of amplification poleward. This begins in the tropics c/o of the MJO cycle and propagates to the extra tropics and then from the latter c/o mountain torque into the stratosphere to sustain a destabilised profile. The momentum being created is starting to assure a cold pattern persisting longer and longer through December and slowly cancelling out cautious notions that the traditional base state might interfere and de-amplify the pattern in the ways described previously. As a consequence of the atmospheric flux, the Global Wind Oscillation (a representative plot of rising or falling AAM and global windflows) has continued to stretch its Phase 4 amplitude and enlarge the disconnect with La Nina. In synoptic terms, the implications of this are for an upper flow into Europe that looks likely to continue to be somewhat flat against the Atlantic ridge and troughing to the NE(hence some of the apparent stubbornness for breakaway lows heading from upstream to deconstruct and take optimum southerly most tracks each and every time). But with the upstream +PNA pattern assisting split flow it continues to favour the angle of the jet stream to be on a NW-SE trajectory, its set well for increasing upper cold air in tandem with surface cold to become more and more in situ and increase the possibilities of surprise more widespread snowfalls popping up more and more as time goes by. This leads to the extended period. In December the NAO has a low relationship in its response behaviour to the state of the polar field (the AO) However this starts to rapidly change as New Year arrives and the relationship, as such, consolidates much more tightly in January. Hence another aspect of this crossroads theme referred to so often. The feedbacks in process are starting to suggest with a bit better confidence that lagged effects of these amplification programmes will help prime a cold pattern to sustain or recur heading into the New Year. Assuming the atmospheric circulation doesn't deviate much from the present (and in this respect its still necessary to monitor AAM as tropical convection returns to the Indian Ocean as a potential fly in the ointment), then the effects of seasonal wavelengths bring those height rises to the NE into the equation, and the implication of this is to repress the Atlantic ridge, with less mixing of milder air in trough disruption occurring and better and better chances of snowy undercuts.
  13. 70 points
    Dear wife, Due to the netweather code of conduct I am unable to tell you this directly now as, otherwise, this will go pear shaped and as we haven’t seen lying snow for 5 years... I can’t risk that. If today’s icon/gfs 00z (17/02/18) charts verified, we could be in for the snowiest spells of weather we have seen in our 40 years living in the south and this could pretty much be a nationwide event. I know that you hate and loathe cold, snowy weather but all I can say is........ get to Tesco’s and stock up on supplies, alcohol and logs as we’re in for the long haul!!! All things going well, I will show you this message on Tuesday/Wednesday as I may be allowed then!!! Amazing charts today, not sure the ecm 12z from yesterday could be beaten but it may have been by icon/gfs 00z runs. Great to see the ukmo onboard, need the ecm back on board later today. Enjoy the ride! Clem (suffering in silence!)
  14. 70 points
    Sorry, I just thought I’d walked into the moans threa.. oh wait. <passes around a big bag of grips> No sooner do we get a cold spell within sight it astonishes me that time and time again some people seem hell bent on being the first to find signs of it unravelling. Is there some kind of prize for this I don’t know about? We don’t live in Siberia. We are never going to have three month of bitter cold. We all know this! It’s one run. 48 hours ago some of you were dismissing the idea of an easterly entirely based on the output. Maybe when the hangovers and cruddy moods have lifted this will improve the quality of posts?
  15. 70 points
    00z EC showing interesting battleground snow event for the north and west next Tuesday, as Atlantic frontal system moves in from the west and bumps into the cold air If only my wife could understand my fascination of looking at weather charts ...
  16. 70 points
    We should rename thread the ‘miserable git’ thread - So much negativity & misery in here I’m surprised people even make it out of bed. updated 06z JMA joins the euro party to 84
  17. 69 points
    In the name of sanity can people please not quote the whole of bb6263s excellent posts
  18. 68 points
    Posted February 10 Irrespective of what the ECM goes on to show shortly and irrespective of what my head keeps telling me of how the effects of this SSW could be mitigated, I am not sure I have seen anything programmed quite like this thing. Polar easterly reversals are often enough mitigated at least to some degree by other tropospheric drivers, but I am beginning to come to round to thinking this may not be one of them where that happens so easily and its going to take over a lot of the NH for some time. it could be the case that it would start to be more prudent not to underplay the SSW, than place caveats as to what might mitigate it. On that basis maybe its me who should have a bit of a ramp, and not others who should restrain themselves However it plays out in terms of what comes out of the sky in the coming weeks - and despite the fact that the actual phenomena of SSW's is not new, this is quite a significant specimen indeed we are watching unfold ............................................................................ A week on, and a crazy amount of pages later, what has changed? Well I haven't had another ramp, and the deepest cold is still 9/10 days away But what has become clear in the course of a week is that the first stratospheric break-down salvo is set to verify for certain this week - and that day 9/10 day period marks Phase 2 and the time when the Canadian vortex to the NW should finally back off and the down-welling process of -ve zonal wind anomalies really start to make themselves felt in out part of the Northern Hemisphere On that basis we can give credence to the shape of the mid and higher latitude pattern and emerging block alignment with the deep cold backed up like a dam waiting to be unleashed I am amongst the most sceptical of day 10 UK deep cold in NWP and very often based on the realistic signals, barely take a second glance, if even much of a first glance at all But this SSW is a significant specimen indeed, and no further deep analysis is needed. On that basis I will be taking this particular day 10 deeper cold rathe more seriously as a contender The fact that Phase 2 marks the time when the strongest sibling vortex lobe starts to finally cave in after its winter rule, increases the chances of deeper cold air advection at that time-period not just because the block to the NE can start to orientate in ideal position as polar jet energy is finally being squeezed out, but because the chances of retrogression are also much higher so that at some stage re-loading deep cold has a heightened chance of finding out even this little Island. Probably the most simplified basic principle post you will get from me - but less is more sometimes and nothing else needs to be added
  19. 68 points
    Afternoon All - A frantic few days on here with pages & pages of posts flying through in a matter of hours- I think we have 2 main discussion points at the moment- 1) The short to medium term prospects for the UK covering the next 10 days 2) The medium to long term thoughts on December & Winter as a whole... Short term then whats the bad news- well is there much to be frustrated with? only the fact I guess that the megasnow charts that appeared for a day or so have been moderated - Thats because even though the overall pattern is near as damn it identical - the timing & phasing of the jet + low pressures has been modified just slightly to reflect a slightly slower progression south of the cold air- The initial prognosis for the cold was always Thurs PM into the Eve- well now potentially the GFS just holds this off another 12 hours due to a track of that low not being as efficient for cold air advection alligned to the UK- This aside though the potency of the Northerly looks pretty substantial- at this early phase of Winter if you can get the -8c line to the South Coast then your doing very well- We deliver that with other areas of -9 & possibly the magical -10c The flow looks very unstable to me - bringing a rash showers across the usual places exposed in a NNW flow - NI included- perhaps some of the posts & general frustration today has reflected some IMBY desire for snow - well thats life. * In terms of more organised bands of snow I suspect the models havent quite resolved the finer detail yet so I believe we will see some kinks & troughs forming ... It will be all about timing and intensity as that whether areas further south can get any snowcover ! For Scotland & parts of the North /NW sustained snowcover looks a possibility from overnight Thurs onwards for at least 4-5 days... 'The slider lows' - personally I love the name - a potential again for some snow pushing across the UK ( mixed into rain ) for the western portions - The models havent got a grip yet of how these will develop- they are beginning to see the Energy & rough location of development - however angle of the jet is very much up for grabs -indications being the first system will slide past the UK- or possibly into the west, keeping the UK on the very cold side of the jet- although some runs do bring a higher chance of snow across the UK with a shallow system & acute angle... after that it is usually difficult to keep the jet attenuated enough for 2 sliders but we will see... * Post next weekend & more long term the prospects for sustained cold is highly probable- The starting point would be - how many times in the last 2-3 weeks have you seen a return to normal NH zonal conditions past day 10- the answer is probably very low.. From the top down we are seeing the GFS continue to show no coherent downwelling of any meaningful positive westerly winds, with infact a second bout of negativity building in the 10-30 HPA layer at day one 12 -16 The models have been a bit flip flop with this so its not a given- However even with the possible bonus of another reduction of the zonal wind the models persist with the disturbed hemispheric pattern. The H5 anomalies show considerable blocking across the Pacific / pole / Russia & a segmented vortex mostly languishing across the other side of the globe- Whats key here & the reason why we are seeing the models choose the 'non toppler' scenarios is because of how I believe the energy within the zonal wind is being distributed- when we have a high Westerly phase of the zonal wind the Easterly component ( moving west to east ) is very uniform & theres minimal deviation away from that direction- IE minimal poleward vector- In reduced phases & the highly desirable negative phases you have maximised poleward & equatorial vectors & no Easterly Vector- So for December in General we have a zonal wind that kicks on around 30-40 M/S - where currently its heading to around 10 M/S- Thats where all your Easterly progression has gone... Factor in the weak La nina base state which if you use the general analogues you will find a pretty good match for a negative December AO & cold in the mid lattitudes- With that in mind the odds of a below average December are high - with H2 of the month of particular interest as the Russian high starts coming into play potentially backing the pattern up even more... so.. for a change increase your expectation towards cold for the remainder of the month-blocking peak 9th Dec - with maybe a short relaxation before going again towards the 15th ish on the run in to the festive period.... S
  20. 67 points
    Afternoon All I guess a few of you/us are wondering whats going on with the weather this weekend & into next week... Strange, almost 'texbook' cold charts appearing in the models & actually landing with some degree of accuracy.... Well like many - you are probably wondering if its a precursor to the rest of the winter or a lucky double 6 roll in November.... Based on the information at hand I would say the nina base state forecasts of mild westerlies into december & throughout are going to be wrong & on very shaky ground - Looking at the current picture & the run up to the start of the winter season I commented on TWO about NW winters getting more extreme - The NOAA data for AO & NAO show the modes of these metrics becoming more & more diverse & when in a particular phase ( whether that be pos or Neg ) so the metrics would be topping / bottoming out at at close on record breaking levels - The whole post was in reference to the M.winter theory from IBrown To underpin this ( but without the data ) in the last 15 years we have smashed the AO record at both ends so many times - months like Dec 10 / Mar 13 spring to mind- but also the extreme mild ones as well ! However also in the post was the fact that steadily the incidence of Negative months had reduced in favour of more positive ones- so with Heinsite the M.Winter theory carries some weight but poorly communicated without all the facts- What also has become Crystal clear is the fact that the M.Winter or whatever you want to call it could be under attack by more front loaded cold winters especially when the total atmosphere favours a negative state of AO/NAO with winter 17/18 being just that- Post M.Winter ....? The fallout from the polar ice melting is creating massive impacts on the way the jet behaves in November in particular - The fuel needed to ignite the jet is simply missing in action - probably due to the self perpetuating feedback loop that develops at the same time as when the jet & vortex should be positioning over the pole ( Early Nov ) The chart below shows the current surface temp anomaly for November up until 22nd The green scaling is about 7-8c the orange & red 10-15c vice versa blue about negative 5-10 If you look close at the map the dividing line is generally alligned to 60N where the jet is usually located. We have a reducing in measured gradient by around 15-20 degrees > this essentially acts as a neutraliser on the jet- for which we are now feeling the benefits. This troposheric lead feedback is a far larger beast than El nino or La Nina - it covers the entire space North of 65N & a large part of Russia - It certainly needs a name so I am calling it this - Calido el hielo !! What we have is a troposheric feedback loop that feels lime it can run disconnected to the strat until the anomaly becomes muted but the inevitable increasing gradient as we had further into December & the strat can work its way down... So a watch out for future Novembers that Calido el Hielo may be creating more blocked extreme ( warm or cold ) Novembers.... Moving back to the hear & now we are in a rare situation, one of only 6 occasions since 1979 in winter ! of these 6 the EQBO years being just 2. 1st Jan 85 ( Front loaded EQBO ) 20 Feb 01 - So whats infront of then ? A troposheric induced stratospheric splitting event - the net being a massive deceleration of the zonal wind lagged about 10-15 days later. I would go with our splitting event to be dated 29th NOVEMBER !!!! ( This is why I kept referring to 31st Dec 84 in the model thread ) Here was the Jan 85 & feb 01 charts & the associated stratospheric response ( lag back down ~ 10-15 days ) Then importantly the following months anomaly After +10days lag * The key notes here are that the troposhere is primed for polar blocking with a core towards Greenland- Also low euro & Azores heights present... Now, Taking our event to be 29th of November we should see an immediate stratospheric collapse of the zonal wind & from about the 4th-5th & The blocking anomalies to be present from anywhere around the 8th onwards- Lets look at this mornings outputs - these are GFS based & depict a total collapse of the zonal wind - with this depiction being the daddy - showing a -35 M/S hit on the zonal wind which is a reversal at 10MB .... Jan 85 Merra data shows a reversal down to -15M/S Feb 01 shows bottoming out -3M/S So this is why the GFS / ECM are spewing out all this blocked data for first / Second week of December- Based on the science of the lagged troposperic response the 6-12th Dec will be peak for blocking & subsequent cold UK potential with Greenland being the favoured location a Below ave December / Front loaded winter is odds on favourite for me with a high probability of some very special charts appearing! fingers crossed.... Best S
  21. 62 points
    Must say considering I have only been home a few days following a spell in intensive care, I am finding the output very pleasing and healing at the same time. Can someone bring me up to speed though. When was the potential E,ly first modelled and by which computer model. I won't be contributing much to this thread as im still very weak. Just enjoying the contributions from others especially Steve M who is equally obsessive about E,lys as I am.
  22. 62 points
    Find 1 post that I said it would be a convective Easterly - The problem with you ( & many others ) is you read one thing but assume another. The forecast was a blend of the GEM / ECM here is that model run ( ECM ) at day 8 & here is current day 4 run if if you want to pick holes in that 8 days out then be my guest. Instead of preeching to me you might want to ask your self how many times the Northwesterly has been put back - were probably about 3 days now. An evolution you continually went on about every post- but you don’t see me quoting you every 5 mins that your wrong - because that isn’t me. It seems your far more worried about what I’m doing rather that how your lucks going if you don’t like it stick me on the ignore list- therefor you don’t need not worry what I’m doing.
  23. 61 points
    Hello to the Net Wx comic, I suppose it's not tea you are drinking A Good to see you on form and markedly misunderstanding the models as usual take care young fella oh just to confirm that the flow is going to come from east not west from later this week and into March, below the links to the latest NOAA 500 mb anomaly charts. They have been consistent for several days now with what they show this evening. Just how cold and how much snow not even Anyweather has any real idea. The synoptic models will to and fro about this over then next 4-5 days. So really interesting model watching. http://www.cpc.noaa.gov/products/predictions/610day/500mb.php
  24. 61 points
    imagine the scenes if the GFS was to verify. M1 Northbound - just south of the M4 -
  25. 61 points
    Having followed all the output and read all the posts these past few weeks I thought I would make my first post of the winter. A few points I wish to raise. 1. Current output does not suggest a major cold spell. 2. The NW,ly this Fri/Sat will bring snow showers to the favoured locations and may even spread SW through the cheshire gap towards even London. However many locations will remain dry and sunny with max temps of 2/3C. The snow showers will not be as extensive as some have suggested. 3. Beyond NW,ly the jet stream does appear to be taking a NW-SE track so slider low pressure systems bringing a risk of snow is possible. Remember though your location dictates whether a model run is good or bad based on the track of the low. 4. The risk of cold and snowfall from this pattern looks likely to extend into mid Dec. However I fear beyond this a return to a milder weather, flatter jet stream, lower heights to our NW/N is likely towards xmas. Love to be wrong. So a summary is this is much better than last year but certainly no repeat of 2010!
  26. 60 points
    I don't think there are any words that can describe these synoptics, lol. All my SSW dreams coming true - this is the perfect SSW trop response that excited me so much 2 weeks ago. Can't believe that it can come true - Can it?
  27. 60 points
    The idea that the signals 'have gone wrong' and previous posts don't tally with earlier posts would be laughable, if it wasn't so misleading and demotivating to (all) those who have made those posts. For my own part, I'm very deliberately posting 'the whole book' written one month past which assessed the possible problems the patterns this season might encounter in terms of the favoured cold weather this thread (largely) craves. Its staggering, frustrating, very annoying and equally demoralising that so much time can be wasted attempting to provide so much information in voluntary time but to persistently find a name banded around with quite different interpretations - and especially an inability to take one post in context of the next - some simply lazy and glazed over and can't be bothered to read, and others which are frankly trolling deliberate misinterpretations. So, another long one (I'm afraid) of intending to manage expectations before returning back to the rollercoaster sidelines My own perception of the start to winter. (like any other season in terms of weather preference), largely differs from most because I am far more interested and curious how the signals play out (either way) and not how cold and snowy it might get. So I will have to be forgiven for a different tone that frankly intends to neither optimistic or pessimistic, but simply hopeful objective how I see it. There is neither the time or inclination to get absorbed in the daily swathes of NWP operational and ensemble suites - but instead the usual non NWP approach is most helpful to me. In the final analysis anyway, the signals dictate the models, not the other way around. Apparently consensual ensemble suites gauge assessment based on a moment in time captured, but they are prone to switch direction like shoals of fish when they realise something different may be going on... So, for what it may be worth: Sorry no time for links. Atmospheric angular momentum tendency (essentially in context referring to the turning force of the jet stream) has tumbled back with lack of tropical convection (MJO) focus allowing easterly wind inertia to return to control the atmospheric circulation in line with La Nina consolidating at all levels in the Pacific. The SOI is consistently +ve and there are colder waters to upwell and strengthen La Nina into the close of the year The Global Wind Oscillation (which represents a plot representation of global wind flows as referred to above) in reflection of all this, has progressed from quite an amplitude Phase 8 and is set to hover around Phase 2 for a while. This slow/stationary orbit underpins the modelling over the coming days in terms of the very big signal for a very amplified holding Atlantic ridge - and certainly favouring a cold pattern sustaining into the medium term as the vacuum occurring upstream slams on the brakes with jet flow rapidly decelerating In terms of the stratospheric feedbacks though, the question mark in my mind is the extended hints of the Pacific pattern starting to show the first signs that La Nina is going to tighten its control from upstream with the building of the Alaskan ridge. On that basis a highly anticipated two week stratospheric forecast is just that, and on the basis of potential upstream changes that ultimately spell return of the jet, it cannot be wholly assumed it will automatically favour this side of the pole as the Pacific pattern starts to take control. So I don't personally agree with some of the views being expressed that this is a "good thing" for downstream prospects in terms of sustaining a cold weather pattern beyond the early to (possibly?) mid December period. Its a typical La Nina development that often happens as wavelength cycles occur with the change of month and season and has the effect of increasing Canadian cold and re-booting the energy into the downstream polar jet. Such inications are minority model solutions at the moment that show increased upstream flow in FI, but I think its not a case that they are automatically wrong, simply maybe on the progressive side. And I would be highly cautious of 100% confident assumptions then return energy will automatically split and encourage trough disruption under the Atlantic ridge On that basis I'm not sure that any equal assumption (however valid) can be made that the present amplified pattern has a sustainable feedback. Or at least not sustainable without a further eastwards moving MJO catalyst, to engineer further tropics>extra tropical rossby wave train and set up further downstream amplification via +ve MT and then, just as importantly in turn externally pressurise the polar stratosphere. Even the freeze of 2010 ended on the basis that no follow up occurred to the high amplitude MJO event of October and that led to the rapid taking of control of the default La Nina Pacific ridge and return of polar jet flow after Christmas So the La Nina default will not favour any undercut of -NAO automatically. The upcoming pattern is a traditional (extra amplified) mid latitude ridge pattern. The irony is that the higher AAM pattern we have been seeing of late has actually featured something of a Greenland High and an attempted -NAO (albeit west based). Its no coincidence that falling AAM redistributes the blocking pattern into the Atlantic. I think this has already been forgotten by quite a few because of the pretty charts at the moment However much the warm air advection from this ridging may perturb the troposphere/boundary and help prop up the poleward nature of the ridge in the short and medium term, the increasing upstream amplification in the Pacific that will carve out the default La Nina ridge will, eventually, increase cold air advection upstream and focus jet energy into the polar branch. That is not going to assist cold air advection downstream and both negate stratospheric destabilisation this side of the pole, and transfer the weakness to the Pacific side. This is an old and familiar story, and though we are certainly in a different place to last winters weak La Nina, the possibilities remain the same with the arctic in such an alarmingly fragile state. Its getting increasingly hard for the whole hemisphere to be cold - there is simply not enough cold air to go around. Something, and somewhere, has to give The importance of the Aleutian Low and Siberian High moving forward in terms of cold air feedbacks have been identified a few times on here as a means to sustain a cold pattern into winter proper. Any Pacific heights, as a key part of an arrangement of circumglobal La Nina mid latitude ridges and polar jet flow, are counter intuitive to this. The stratospheric pathway can certainly override the tropospheric winter La Nina effects, but its going to require tropical forcing to play ball and come into play just at a time when the upstream pattern shows signs of coming back to life once more. Strengthening La Nina and changing seasonal wave length changes are going to become increasingly resistant to this the further we head towards January and especially beyond. There is no certainty either way, and whilst the pattern could sustain in a few ways yet - the "quick fix" I spoke of in the MOD a couple of weeks could easily still be just that. At the moment I see things much as I would at the end of a warm La Nina Spring, that so often does not transfer to a warm La Nina summer. That said, there is more to encourage a cold pattern, certainly to start, beyond what the weak La Nina went on to deliver last year - but I don't see the straightforward path to sustained cold nirvana many others see. Ciao I could have posted much more from various other posts which have gravitated and returned back to this theme, but it still wouldn't increase the chances of having them put in the right context. Now, a whole lot of signal evolution and model output has obviously gone under the bridge since even the last week of November and many, many others have contributed large amounts of time to try to give best perspective. Lots of different posters, some with great NWP insight, others using non numerical methods. But in between the ever increasing signs of a theme towards possibilities to cold weather as a recurring theme this winter, there have been REPEATED posts that have returned to the early cautionary theme of the whole bolded post above. Simply speaking, there are still uncertainties ahead which some are rightly referencing, but that crossroads I banged on about is arriving and frankly there should be no surprise that the signal, tea leaves, teleconections (call them whatever) have come to roost in the way described above and are not necessarily following the 'straightforward path to sustained cold nirvana many want to see' that was posted 4 weeks back Please, to those with lack of attention span, note the italics in the previous sentence. There is of course a whole lot of this season to go yet, and much can still (and will) happen either way - and who knows sooner or later. But please no-one act surprised or blame the 'tealeaves' for being wrong. Blame a skewed, frost tinted or addled mind instead - the pendulum has swung to and fro with the upsides and downsides (this is the UK after all) but don't anyone tell me (or anyone else) they have been misled. Its not my fault (or anyone else) there are selective agendas and a few who are so insecure they need constant 'will it snow' updates who only want to hear what they like. There is the weather, and there is also a life. One that is often more serious, more problematic and can have much greater repercussions than whether or not it snows. I've seen it said that weighting two different scenarios is some kind of ploy so as not to be wrong either way. Er,no - its simply saying things as they are and giving an honest opinion. Like lots of other opinions. Its not about right or wrong, its meant to hopefully be about informative contributions, and not to pander to tribal allegiances. I'm not wasting any more time and energy with further explanations or even current analysis - its a hiding to nothing continually having words put in mouth by a vocal percentage who keep acting bemused or even cheated because (allegedly) they had been promised their cherished weather and its disappeared, or hasn't happened yet. Whatever. Or who offers nada themselves but sit and carp at others efforts. Why bother? But there are plenty of very good (also equally non-egotistical) posters on this forum, many of them on this page each day. I suggest keeping looking out for who they are and those referred to above maybe who, either deliberately or simply lazily have selective thinking, paying them the respect they deserve. Otherwise they too are going to get fed up very fast and not bother also. I know some who already feel that way - so this is not just another one-off paddy fit. To the rest (of the large majority) on here, I hope you all have a lovely Christmas
  28. 59 points
    I think BA is simply reinforcing the point that it’s not really worth attaching too much credence to current output, where there is clear inconsistencies being exhibited. It really is more about broader trend and the eventual path, whereas the journey to get there remains fluid and undecided. 12z EC could correspond with its peers or it could reinforce its 0z signal and advertise a more subtle path. What I would strongly disagree with, is NWP assertion of a quick return to mobility (or milder weather) That evolution doesn't correspond to mid range products at all, and can quite confidently be discounted as models reverting to type and to some extent underestimating the degree of in situ blocking. This behaviour has been seen previously so reasonable to view a rapid breakdown with scepticism. What an exciting end to winter! SB
  29. 59 points
    I'm sorry but teleconnections are useful for both medium and long range forecasting and over a long period of time those using how the tropical momentum anomalies spread to the poles and slow down/ speed up will have better forecasting abilities than those who don't. I feel that you are becoming like a stuck record peddling the same message year after year. We get it! You don't believe that teleconnections are of any benefit whatsoever and you would rather bizarrely use seaweed to forecast the weather in two weeks time. The last time I saw a bit of seaweed I did ask it what the weather forecast would be for a fortnight and it just looked blankly back at me. The fact is, that there are many factors that determine the global weather patterns from stratospheric influences to tropical Ocean temperature anomalies and solar influences. So those attempting to put these pieces of the jigsaw together should be lauded and not dismissed. Scientists may take a whole lifetime to prove a hypothesis with many failures along the line, but without this we wouldn't advance as a society. So, Yes using teleconnections to forecast in the medium ranges is going to have its ups and downs, and yes there is a chaotic system out there, but there is order to that chaos and the challenge is always to find that order and why certain weather patterns exist. To suggest that ignoring (for instance) the stratospheric influences on our weather pattern in two weeks time, is now accepted as being short sighted and ignorant and I am sure that you are neither, TEITS. So why the continually knocking of those using medium range teleconnections? It very much reminds me of the attitude I faced when opening the first strat thread, and how those doubters have been proved wrong now. For every teleconnective forecast that doesn't deliver there is a learning opportunity for the future. I have learnt nothing from seaweed.
  30. 59 points
    JUST BEFORE I LEAVE TO GO TO THE FAMILY, I'LL GIVE OUT A FEW CHRISTMAS PRESENTS TO SOME OF OUR FAITHFUL MEMBERS Dec 25th 1878: min -18.3c: For those up north the coldest on record: Dec 25th 1981: lying snow 47 cm For our friends in Scotland, the snowiest 47 cm (and 43 cm at Buxton): Dec 25th 2009: lying snow 43 cm and more recently, for England, Malham Tarn (N. Yorks) again 43 cm: Dec 25th 2010: sunshine 7.5 hours Not everyone likes cold and snow, so just for @knocker the sunniest on record, actually at Camborne: ! Ooops, sorry that was also very cold and snowy (the snowiest in Wales - 45 cm and Northern Ireland -17 cm) !!! Dec 25th 1920: max. 15.6 C (60 F) So for Knocker as well as Sidney, here's the warmest (Killerton, Devon): Even though it's Christmas, this is a model discussion thread and to keep the moderators happy, let's have a look ahead with a few post Christmas surprises for some of you. From the 6z GEFS ensemble suite I have the following presents for Wednesday, December 27th (and don't forget to "discuss these models"): For Wales and all of northern England, I give you perturbation 6: For The Midlands and southern England, I give you perturbation 3: For the Home Counties, London and the south-east, I give you perturbation 4: For those further south-west, I give you perturbation 13: Finally, for those that have missed out, I give you this: Have a great Christmas
  31. 59 points
    This thread is a mix of analysis and the occasional toys out of prams. We’re not the BBC giving a forecast . And the ups and downs and some of the melodrama and humour in here are part and parcel of the success of these forums . Coldies in here are not your average members of the public , the majority are snow lovers who are passionate and so no I don’t want a dry humourless emotionless thread just discussing the track of a low. Yes of course you want to see some analysis and there’s lots of that in here, but at times it’s going to happen that we might lose it and and have the occasional moan.
  32. 59 points
    So sorry to hear that mate Dont want to clutter up this thread but im sure i speak for everyone in wishing you the very best and hope you will be ok.
  33. 57 points
    I know it's an absolute disgrace and a complete waste of public money when they refuse to tell us what we want to hear,
  34. 56 points
    For those getting up to have a sneaky peak at the Gfs 0z go back to bed and sleep well. It’s awesome!
  35. 56 points
    What we are witnessing from the 18Z is a stunning synoptic evolution. Enjoy it.
  36. 56 points
    This is not the BBC forecast thread, please stop replying to the (already deleted) post about it! Thank you
  37. 56 points
    Evening All Many many pages on here today driven on at a frantic pace - FWIW here’s my analyis- The evolution from mild to cold is pretty much set now all be it with still minor resolution on whether the first batch of cold makes it to the far south at the first attempt - There’s a slight concern that the full deep cold ( sub -6c polar air ) may not make it - before its started to get mixed with the continental air- seen here It’s not to much to worry about as the continental air will be cold - just not mega cold initially- there is reasonable continuity from the models around this but post 120 they part company. Post that we have to heavily rely on historic performance in this scenario. For me that stems back of about 13 years - & there is always a couple of consistent themes. * ECM / ECM operational usually leads the mean but the mean is usually catching the OP up the day after - The mean is also less volatile. * GFS is without fail awful in ANY scenario relating to undercutting - so many people have short memories of just how bad it is - *** in particular 06z & 18z ensembles *** the GFS / GEFS will be up to 3 DAYS behind the ECMs correct solution. * GEM / JMA - are usually a lottery. * UKMO usually close to the ECM. I think personally we are on the cusp of a classic cold spell in terms of 500MB height appearance - The ECM 144 & 168 would certainly not look out of place in the archives Whats not quite as classical is the upper air temps, we don’t get the full -10c uppers from the East- so convective snow ( at the moment ) looks a bit limited to more granular flurries. Surface temps will however be very cold circa 0-2c. Based on the ECM the best opportunity for proper convective snow is day 6 into 7. Post 7 onwards - undercutting YES..... Forecast summery: GFS - will correct throughout Weds- GEFS will correct Weds- Thurs however the meeting point to the ECM may not be all the way to ECM there may be a 70/30 meeting point where the ECM / GEM blend backtracks slightly. ^^^^ This is more towards the undercutting - don’t waste your emotions or time on your the GFS... The caveat to that is the ensembles will transition towards the expected scenario but it will be jagged & slow with some suites better than others. The distribution of energy into the Northern arm is expected to gradually be modelled back south. EXPECT THE UNDECUT.... Best steve
  38. 56 points
    we have an SSW forecast- a Sudden Stratospheric Whale....
  39. 55 points
    WOAH, WOAH, WOAH GUYS. I have NEVER seen a chart quite like this one... hold onto your pants... the Polar Vortex has only gone and turned FULL LOBSTER 😵😵
  40. 55 points
    I'm here - been working and have also had to pick myself off the floor after checking the 12Z. Best ever trop response that we have been able to track following a SSW, oh those of little faith lol. I did think of buying all the snow shovels and salt in B&Q yesterday and then selling it back to them next weekend.... I have been convinced of an epic cold spell for a long time now (since before the split but my resolute belief was reinforced when I saw the residual Hudson Bay daughter vortex getting taken down). It may have taken the best part of 10 years but finally we are seeing the makings of an epic spell when you take the strat vortex out of the equation. Even @TEITS may finally have to concede that there is something in this teleconnections Malarkey!
  41. 55 points
    ECM a bit disappointing tonight because any showers between days 8-9 could be a bit sleety..... ........(Can't remember seeing such a great run for a very long time if ever on internet)
  42. 54 points
    Comes in, has a little look at the 12Z GFS and has a little chuckle to himself.
  43. 54 points
    As always, to try and take stock of NWP means instead of trying to second guess it (and its ensemble suites) at face value, it means instead attempting to step back away from it and try and do an assessment of the factors that are driving it These factors are vast and hugely complex to say the least and there is literally no-one who can make solid definitive predictions, (though some may try regardless of course), based on such an extremely loaded atmospheric profile that has been pulled in two quite different directions over such a relatively short period of time. But that loaded state still has to be assessed against the fairly recent history that has been equally as volatile as the present - and may still have a say in the way ahead in the context of the SSW. The Global Wind Oscillation plot orbit emphasises the contrasting forces that have been taking the atmosphere in two very different directions one after the other over just a ~ circa 6 week period. Two high amplitude directions - one opposing the other. . We have seen strong easterly trade winds from late December and the start of the New Year plunge the atmospheric state into a deeply low angular momentum state reflective of La Nina registering a stronger forcing relative to the official weak base ocean state. This beefed up a profile of sub tropical ridging and more enhanced polar jet flow that kept an average to milder in the south and often colder in the north zonal flow pattern flatter than otherwise might have been the case. Then, in complete contrast to this, a record breaking MJO amplitude wave has subsequently attempted to imprint on the top of the robust Nina profile of January, stretching the atmospheric profile in completely the opposite direction with a markedly +ve AAM disconnect to the base Nina state instead of a markedly -ve one . This has seen quite a change in the zonal wind profile across the Pacific with MJO derived +AAM anomalies replacing the swathe of -ve AAM anomalies (La Nina easterly trade winds) We have been seeing this tropical momentum process work poleward since the last week or so of January and the signals for stratospheric upheaval come into play to join the highly stretched rollercoaster of opposing forces the troposphere has been subjected to. I am deliberately paraphrasing and dumbing down the technical processes involved here to keep emphasis on the huge complexity and conflicting natures of the pattern. These technical processes have been discussed in detail over many previous posts anyway If we take the above GWO trace plot at the top of the post literally, then NWP to date has traced it perfectly. Flatter, faster zonal under the low AAM phases 1,2,3 during January - and then increasingly amplified in the last week as atmospheric angular momentum has shot up with the Scandinavian ridge of this week verified - viewed of late as generally as an appetiser to something better c/o SSW. So far so good. But this is where it gets very very difficult and why some caution needs to be applied in terms of trying to read between the lines of tropospheric reactions to the SSW The ying-yang of the atmosphere and its instability related to the fixed parameters that govern its wind-flow exchanges between tropics>extra tropics mid and higher latitudes>stratosphere) are working on an intricate series of different timelines that take the representative synoptic pattern in the troposphere to different places at different times. Its here that we cannot ignore December and January's past history as much as we cannot ignore the meltdown in the upper atmosphere that is up-comimg The Scandinavia block hasn't sustained (as expected) due to the brief nature of the peak of the +AAM spike above. The direction of travel is descent from here - but how much? This is discussed further down. But back to the context of the SSW for a moment, because global tropospheric wind-flows (as measured by the GWO) and the net outcome of those (flatter -ve AAM flow vs amplified +AAM poleward transport) are to be measured against the polar -ve anomaly easterly period at highest latitudes that the SSW will be yielding (over however many days it has technical reversal) There is surely no doubt that a high latitude block of some kind will emerge based on a reversal of zonal winds at the highest latitudes - it would be counter intuitive to suggest otherwise. But what is highly uncertain and questionable is how the whole troposphere profile responds based on the possible default tendency of the atmospheric circulation to default to La Nina once again as the latest amplifying poleward tropical momentum transport process concludes. We cannot assume 100% that the latest poleward forcing c/o MJO will automatically imprint a sustainable impact on the atmosphere (and hence the tropospheric synoptic pattern) based on this alone. Contrary to what is often assumed on here, MJO lags alone will not account for all this - we have to take the extra tropical reactions into account as measured by the GWO. On that basis we cannot make assumptions of sustained cold pattern verifications based on dateline convection if the extra tropical GWO is not conducive to this. Feb 2009 with its noteworthy SSW and very fast response time in the troposphere did not actually sustain anything like as long in terms of cold air advection to this latitude in terms of depth as its strength of destruction, but was instead diffused and watered down beyond the initial Scandinavian High pressure that gave the easterly and snow in the early part of February. There was something of a disconnect between the high latitude block profile over the polar field, and the pressure arrangement across our mid latitude which didn't reflect the type of classic -NAO response and undercut looked for in terms of sustaining a cold spell. Ultimately, a WQBO and La Nina profile thwarted any sufficient weakening of the +NAO profile. This winter so far, irrespective of E/QBO state, we have again seen how low angular momentum regimes when unsupported by amplifying actions of tropical MJO forcing (changing the traditional Nina profile of the Pacific trade easterlies) have easily reverted the atmosphere and tropospheric state to an unremarkable one at our mid latitudes. In many ways we are in similar place to where we were at the peak of the last tropical MJO phase in December - where the route to follow of AAM is always down - towards the return of the MJO to the Indian Ocean and start of the next phase. The difference to then, and it is of course quite a large difference, is that we have implosion forthcoming of the stratospheric vortex. Its hard to envisage absolutely nothing exciting happening isn't it? Isn't it? To take NWP into context, and why despite some charts which do suggest it will do what is expected and anticipated and yet others seem (almost annoyingly out of spite) seem to keep a stubbornly underwhelming profile, its necessary to look at how far angular momentum might fall back again at the conclusion of the latest MJO wave, however huge it has been and however imposing the SSW may look. Total GLAAM, relative to where it was at -3SD has sky-rocketed as shown in the timeline plot above - and best reflects the sheer size of the poleward tropical momentum transport that has taken it there. Another measure of the latest +AAM forcing is the Southern Oscillation Index (SOI) - spiking as much -ve now - as it was +ve during January https://www.longpaddock.qld.gov.au/seasonalclimateoutlook/southernoscillationindex/ The plot above for the GWO illustrates how rapid the orbit continues to race through the higher AAM phases - and this reflects the default reality that although showing distinct signs of decline, there still remains a La Nina signal firmly in the background to steer AAM budgets (net total global wind-flows) and suggest that an easterly trade wind bias *may* try to re-emerge around the time the SSW is trying to flex its effects in the troposphere. How much, if at all, this happens will have significance on the mid latitude profile and either offset or assist the tropospheric effects So its way too early to know, but any drop-back in AAM *might* be a factor that *could* work against effectiveness of blocking at our latitude and, such as happened in Feb 2009 under weak La Nina, with some residual splintered pockets of vorticity aligning some stubborn polar flow that scuppered sustained cold air advection furthest south- beyond the initial easterly. The significant snowfalls of that event are remembered, but what is less than remembered is that it was relatively unremarkable to follow Its hard to be sure at this stage, but set against the effects that the latest MJO will have had in terms of moving warmer waters eastwards from the Western to the Central and Eastern Equatorial Pacific, and also aiding upwelling of warmer sub surface waters (and hence limiting rather more any resurgence of easterly trades), then this, plus the legacy of +AAM anomalies scrubbing out so much previous easterly Nina inertia in the atmosphere should be enough to prevent angular momentum falling back too far. Ideally though, at least in my opinion, the best timing for the SSW would have been in the last 10 days, in tandem with the massive AAM surge and GWO in most amplified phases. All possibilities, including good ones remain, but I think its important to gauge the SSW against what has been and gone and how the cyclical nature of the atmosphere may influence (mitigate or enhance) the tropospheric effects of the implosion within the polar field. On a thread which is, alas, hyper sensitive to any pitfalls and resistance to anything that doesn't suggest cold - this is simply, as per usual, a little heads-up to the type of thing that might happen. Its because of this that so many of the key words are italicised. History always shows that such a sensitive emotional environment as this leads to all sorts of misconstrued and knee-jerk assertions further on. One cannot manage expectations and thrills and then disappointments for others for them, but it is possible to try to do ones best to tell them in advance. The rest is up to them.
  44. 54 points
    Remember reminder: Its only an island if you look at it from the water Feb 2018 : Massive poleward tropical momentum transport + tidal surge of +AAM tendency > +MT > fast orbit Phase 5/6 GWO Nino attractor in extra tropics (this weeks easterly 'jab around the edges') >stratospheric pathway dissolution/feedback from dateline convection > -AO/-NAO. Allowing for some deterministic model variations of forecast, based on the fundamental changes that are underway in the Pacific eastern and central waters, good supporting reason to 'cherry pick' the ECM to illustrate impending ultimate change downstream in terms of the state of Annular Mode I don't make forecasts as such, but lets just say the Global Synoptic Dynamical Model (GSDM) timetable is evolving very close to its defined timeline schedule from inception date ~ 22 January when the starting pistol was fired in the tropics c/o the MJO and the poleward momentum process was underway. The extent of the extra tropical +MT propagation sure reflects the huge amplitude of the tropical convection rossby wave trigger Back to a previous posted comparison made in last 2 weeks: Feb 1978: Spent most of the month in GWO Phase 5/6 c/o high amplitude MJO and led quickly to a strong -AO/-NAO combination. Differences? There was no La Nina lag underpinning an entrenched sub tropical ridge +NAO pattern and so the tropospheric/stratospheric pathway was unhindered to a much greater degree. Well, that and of course the absence of so much anomalous homogenous warming of tropical oceans which are skewing and rather neutralising the natural effects of strong tropical poleward feedbacks - in addition to the alarming atrophy of sea ice which correspondingly unbalances expected albedo feedback relationships to an increasingly unprecedented state : Feb 2018 is indeed proving to be a slower burner with, overall, increasingly less cold air relative to 1978 in the NH to share around in terms of cold air advection from the pole and which inevitably therefore favours much less dilution through continental landmasses like Canada, than downstreamacross oceans) But, all that said: There is an abundance of pretty cold air to the NW as we watch the next phases of trough disruption. Based on the spatial arrangement of cold vortices which look set to ultimately implode - that doesn't mean (by any means) that the UK and Europe won't yet see their coldest weather of the winter, as the end of official winter gets closer and closer March 2013 provided this on the Costa del Cinq Ports of the SE: It was even worth capturing some So, still very much the sort of thing that is more than possible late winter 2018, a few weeks earlier than the fun and games of March 2013 - and so there is no need for anyone to be miserable
  45. 54 points
  46. 54 points
    WINTER 2017/18 REPORT No. 3 WITH DECEMBER 3rd INPUT PART 1: As this will be a long report (even by my standards!) I am splitting it into to two parts. Part 2 will probably be posted much later on this evening. It will include an updated analysis of the Arctic, European and Asian snow, ice and temperature profiles. A REVIEW OF THE MODEL OUTPUT OVER THE LAST FEW DAYS Another extraordinary week in the volatility of the model output and continuing uncertainties even for later this week. In response to all this the general mood on this forum has gyrated from agony to ecstasy and back again – at least amongst many of those seeking cold and particularly snowy weather. I broke one of my golden rules during the week and produced a one liner with a single chart while an ECM run was in the middle of being churned out. The comment proved pretty inaccurate on the very next chart! I’ll endeavour to leave the instant reactions to others but for any cold and snow starved “coldie” it’s so easy to get sucked into the frenzy. I shall stick to these occasional (perhaps weekly) long reports with some shorter interim posts when I feel that I can add something to the overall discussion which hasn’t already been covered. There is much still to be decided in the short term. The period around Thursday to Saturday, December 7th to 9th had been identified a few days ago as being critical in terms of determining the direction of a broader pattern change. Most of the models (including the big 3) swung at some stage between a longer lasting northerly, a much briefer northerly and no northerly at all for the end of this week. Just as one or more of the models moved in one direction, at least one other moved in the opposite direction. Then about 2 days ago it at last looked like we had some general agreement on a decent Arctic outbreak towards the end of this week. There continued (and still does now) to be considerable variation on its longevity and its potency. For several days now, most of the models have shown a LP crossing the country from south-west to north-east on different paths and at different strengths with the northerly sweeping in behind them. Just small variations in the path, speed and intensity will make huge differences in terms of how much precipitation there might be, how much (if any) cold lies ahead of the system, how quickly the cold moves in from the north, how much it might undercut , how much snow there might be and how windy it might get. Several GFS runs showed the LP deepening rapidly and crossing the centre or south of the UK. At one stage it showed an intense LP in the south North Sea which, if it verified, would probably have led to a substantial tidal surge with high Spring tides due mid-week and still high tides during the critical period. I did a short post on this potential threat on page 81 of this thread. Fortunately for those in the firing line, the intensity of the LP has been considerably downgraded. Just ahead of the Arctic air stream the south in particular, is likely to see some pretty mild conditions. Whatever path the LP takes (unless it goes much further south) it has really looked like rather too much of this mild air would initially mix into the system which would almost eliminate any “early” snow prospects over lowland areas (at least south of the Scottish border) ahead of the Arctic air arriving. Again, several GFS runs showed much lower temperatures at an earlier stage with considerable widespread snowfall. Many on here (including me) did get very excited about this prospect but a number of the wisest posters (and perhaps also several who are more pessimistic or even “warmies”) did warn us to manage our expectations. Even the GFS (at least at the time of writing this part of my report – it’s currently 1030 with the 6z output still rolling out) has moved away from the early snow scenario. Much will then depend on how quickly any mild air is forced away by the surge of Arctic air and the depth and intensity of this incoming cold air and also how long the LP hangs around close enough to our east to produce more widespread wintry precipitation and not just wintry showers close to exposed western, northern and eastern coasts. Another factor will be whether there are any troughs or minor disturbances (even the outside chance of a Polar Low) embeded in the northerly flow. At this stage most of the potential for “widespread” snowfall for next weekend has been downgraded by GFS and the other models, several of which never really showed it in the first place. Obviously there is still huge uncertainty and things can easily change again even within the 24 to 48 hour period particularly in terms of snow events. Nobody can seriously rule it in or out at this D4 to D7 range given the current set up. It still looks like there will be some snowfall but how much of the country will see it? Stay tuned to this forum all week for comments and analysis from our regular (and occasional) posters for the latest developments! LOOKING FURTHER AHEAD Things still look very interesting going beyond next weekend and current uncertainties continue which is hardly surprising given that the next few days are still to be decided. There seem to be far greater than usual complexities. The main overnight runs have shortened the direct northerly to just several days. The GFS and ECM 0z runs both continue to show a pretty cold pattern even though the jet stream appears to strengthen considerably with a lot of energy moving over the top of the Atlantic HP and flattening it to a lesser or greater extent. With a likely north-west to south-east jet and the UK remaining on the eastern side of it both models in their own way show a succession of LPs moving down over the vicinity of the UK and engaging some of the colder air remaining over us. The “potential” for snowfall almost anywhere in the UK will continue as long as this broader pattern is maintained. We cannot see what the UKMO shows beyond T+144 and their longer range outlooks have varied somewhat in recent days. Several models like GEM as well as a few of the GFS and ECM ensembles have gone for a much flatter flow with a much more direct jet stream pushing almost all before it. Let’s have a look at some of the different possibilities predicted for the jet stream using the control run and several perturbations from the GEFS ensembles from today’s 6z run which has just rolled out (currently 1145). GEFS 6z on December 3rd Jet Stream Predictions: T+0: Control – current: T+144: Control Perturbation 5 Perturbation 7 Perturbation 13 T+180: Control Perturbation 5 Perturbation 7 Perturbation 13 T+264: Control Perturbation 5 Perturbation 7 Perturbation 13 T+384: Control Perturbation 5 Perturbation 7 Perturbation 13 I selected these particular perturbations as they show quite (or very) different outcomes and routes of getting there. The time periods chosen are to show the position around the start of the so-called critical period for a possible pattern change at T+144 and the interesting changes just 36 hours later at T+180. I found more variations around T+264 and towards the end of the run at T+384. I will not comment on all the detailed charts (until part 2 of this report), they are simply there to show the significant range of variations going forward after around T+144. One of the causes frequently cited of a strengthening jet stream is the North American temperature profile with the conditions down the eastern side contrasting to the adjacent much warmer Atlantic Ocean. The greater this contrast, the greater the likelihood of establishing or maintaining a stronger jet stream. It is much more complicated than just this and this is in danger of getting rather above my pay grade and technical ability, so I shall keep it simple for my sake as much anyone else’s! In recent winters we have got very used to seeing the jet stream frequently roaring across the Atlantic and blowing away everything in its path, although last winter saw long periods of MLB but very little in the way of any deep cold (just surface cold at times). This winter does seem to offer something rather different. The strong and quite persistent Pacific and Atlantic ridges have not only caused significant MLB but, unlike last winter, have so far caused the jet stream to buckle leading to some greater amplification and a much more meridional pattern. Now let’s have a look at the North American temperature profiles for the same time periods as I used for the jet stream predictions. I could have taken the temperature predictions several days ahead of each jet stream chart as there is usually a delayed response from temperature changes but the five time periods from T+0 to T+384 should give a rough idea of the predicted changes for each model run. Again I shall comment on these in part 2 of this report. GEFS 6z on December 3rd 2m Surface Temperature Predictions: T+0: Control – current: T+144: Control Perturbation 5 Perturbation 7 Perturbation 13 T+180: Control Perturbation 5 Perturbation 7 Perturbation 13 T+264: Control Perturbation 5 Perturbation 7 Perturbation 13 T+384: Control Perturbation 5 Perturbation 7 Perturbation 13 GEFS 6z on December 3rd 850 Temperature Predictions: T+0: Control – current: T+144: Control Perturbation 5 Perturbation 7 Perturbation 13 T+180: Control Perturbation 5 Perturbation 7 Perturbation 13 T+264: Control Perturbation 5 Perturbation 7 Perturbation 13 T+384: Control Perturbation 5 Perturbation 7 Perturbation 13 I think that this will be the first and last time that I do such a detailed overview with so many different charts! Apart from the time to prepare and post them, it is difficult to look at all the changes and comment on each run. Hopefully the end product will have made it all worthwhile! Part 2 to follow this evening – quite late.
  47. 53 points
    Dear forum members, For the hardship caused to many of you over the weekend period by my, what I can only describe as, schoolboy efforts: I would like to offer the below as a means of apology... I hope you will see it to yourselves that I was having a bit of an off spell, having been out on an all night bender on Friday night with the GFS 18z. I believe I have learnt the error of my ways and hope we can continue on, as we left off, before this whole sorry debacle. Yours, The ECM
  48. 53 points
    Apparently a lady rang the Met Office earlier this week and said there is an Easterly on the way. Don't worry there isn't......
  49. 53 points
    OK - let's do one of these long posts. Best pacific data very slow to update this week but there is enough out there to put forward a teleconnective update. Not about to contradict anything GP or Tamara have said already today - so forgive a slightly cracked LP feel to things... Much keeps being said about pacific forcing via vertical wave effect of the MJO. With a NH vortex still decidedly unimpressive such forcing perhaps becomes a more significant factor. Current MJO image here as GP already posted: Notice this is a strong signal for significant convective activity. To add to GP's earlier post for those with beginner knowledge the negative blue anomaly just to the NNE of Australia is the specific zone for a 7/8 orbit of energy that pulses north into high latitudes. If anyone wants to see an image of this sort of thing occurring then search for Antony Masiello on Twitter and look at the images he has up on his feed showing wave breaking on the back of the recent Asian MT event and consequent extension of jet energy through the pacific - you see very clearly wave eddies firing north and helping create the Alaskan ridge. Anyway to add a bit more flesh to this... the SOI has flipped negative over the last 3 days following a month of moderate Nina style positive values, indicative of pressure patterns shifting towards a more Nino-esque style, tying into the MJO 7/8 orbit which is also more of a Nino signal. Once again, as Tamara has already described, evidence of the very east based nature of our Nina and how in the western pacific we are actually experiencing higher than expected AAM input than in a "standard" Nina year. This graphic from last week shows the above average surface SSTs in precisely the MJO 7/8 sector with colder water further to the east - and recent running graphics show this colder anomaly perhaps to be fading further to the east Consequent MJO forecast looks like this - and it seems to me that after a long spell of misreading the pacific signal the ECM ensemble has latched onto this 7/8 phase. Note what I said the other day too - latest CPC MJO update is expecting the progression from 7 through 8 to be slow. If you want cold this is good news. The longer it sticks in a 7/8 orbit the better.... All of this would lead to reasonable speculation that reamplification is imminent. I use a fairly blunt JMA tool for MJO composites, but phase 7 broadly speaking pushes high pressure towards our N and NE: and once into phase 8, perhaps around Xmas, the forcing is trying to bend the pattern like this: = a cold signal. Once we transition to January then this lovely forcing appears: What else can we glean? Look upwards we have a vortex profile very much in sync with these tropospheric forcings. Vortex below 50hpa has nothing at all impacting to our west in terms of encouraging a strong westerly pattern: taking the day 5 forecast at the outer edge of reliability the vortex is clearly off centre towards Asia and run forward to the 10d forecast and this is enhanced further: and meanwhile closer to the surface patterns we experience the 10d forecast is demonstrating that the vortex remains a very poor player this year in terms of driving westerlies at us: Notice the ongoing strong signal for wave 1 warming... most certainly going to be reinforced by the alaskan ridge set perhaps to retrogress, allowing opportunities for a bit of aleutian low "kick the vortex where it hurts" action as we approach New Year. I believe the Met have gently indicated their models are seeing some warming impact - it will be this north pacific situation creating it. Is there anything left to throw a spanner in the works? Only really that the best pacific data we have on torques and the angular momentum budget globally has not updated now for 7 days. That is a frustration... but looking at all this other evidence I am not expecting an update suggesting a swift return to anything suggesting a flat response. I sincerely hope I'm not deluding myself... but regardless of flip flopping model runs trying to get a mathematical hold on these signals I am as confident as I can be that amplification impacts are coming, and that climatological and statistical evidence points to blocking to our N and NE with the atlantic cutting in underneath. The vortex profile to my eye makes this even more likely. Timescales still a bit murky... but model divergence in the days before Xmas now suggesting it may appear prior to New Year and then extend through into January. These teleconnective signals can change.... but as far as my amateur eye feels confident to read them I see no return to sustained westerly mildness. Next week is merely a reset - and once we get blocks in place then microscale analysis comes into its own. Happy watching at the moment. Anyone like to guess what might happen were the wave 1 warming over the north pacific to make a significant... and perhaps mortal blow to the vortex? I'm getting ahead of myself here - but factor this in on top of a trop pattern with blocking in place and cold air established over Europe and..... well..... you get it I expect. I'm going to say nothing more. There arent too many analogues for a weak Nina profile working alongside a weak vortex that is hit by a major warming in January on the back of a favourable trop pattern. Go find some... :-)
  50. 53 points
    Always worth taking a lead from the GSDM (Global Synoptic Dynamical Model) at all times in my opinion, but in the context of current discussions then NWP may be especially likely to oscillate in the period ahead, both with the tropospheric pattern, but also across the polar field in terms of the AO benchmark. Each post for quite some time from my own point of view has, in anticipation of possible outcomes, focussed on the upsides and then the downsides in terms of where atmospheric angular momentum is to be led during the upcoming transition of the MJO (tropical convection) from the current wave to the start of the next one. As stated yesterday, definitely coming off the fence with this one, though still stressing the need, as expressed in each post, to monitor how far AAM falls from the maximum disconnect with the La Nina base state currently happening - to the cyclical ebb as the tropics re-set patterns through the mid period of this month. The Phase 4 Global Wind Oscillation (at present) orbiting to Phase 8 and then in turn back to Phase 4 (and not heading back into Nina Phases 1,2 and 3) will underpin the bullish notions that the atmospheric circulation wants to continue to pave the way towards an even colder trend heading towards and into the New Year as the North Pacific ridge and Canadian vortex configurations relax sufficiently to allow height rises to the NE but without too much northern branch of the Jetstream to spoil deeper sources of upper cold air advection to head south-westwards across the North Sea. We could espouse the easterly of late December 2005 as an example of this sort of thing, but not at face value in terms of "intensity" (or otherwise )of cold air and snow distribution necessarily, or indeed replica precise timing to take too literally. It still has good purpose for illustration use though of how things could conceivably evolve in principle. I expressed slowly growing confidence in this sort of evolutionary possibility to NE heights yesterday. However the UK initially fares, the jist of it is that a deep source of cold air would be in place in this scenario that is highly unlikely to move very far in these circumstances and sets up a very very interesting January scenario Still with the attached caution caveat that prospects of a fall back in AAM sufficient to take the GWO back to Phases 1,2 and 3 is becoming less likely with each passing day of positive data - *should* this occur then the more traditional La Nina pattern would re-surface which implies the North Pacific ridge and Canadian vortex combo not retrogressing and in this way pressurising the polar jet and neutralising an -AO profile. At the same time, the Azores/Atlantic ridge would be ascendant at the expense of greater influence of heights to the NE and too much energy transport to the N to allow the pattern to back deeper cold air advection westwards Its highly possible that the models will show especially erratic trends on the way to the final destination, notwithstanding that as posted earlier on this thread, the GEFS suite is pointing a way towards the upside scenario in the extended period. But as a precaution anyway, in terms of keeping a sanguine open mind to keep enjoying the ride, I would suggest not allowing any model vicissitude to correspondingly engulf human emotions into equal vicissitude. On that basis best also to take AO/NAO forecasts with an equal pinch of salt - these will simply reflect the swings of NWP, and equally, ensemble suites The theme is the same old for me - the signals lead the models, the models don't lead the signals. Highly interesting start to the winter (for a change), if you don't let every model suite overwhelm you, whichever way