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Catacol

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Catacol last won the day on January 18 2016

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    Wellington, Somerset
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    History, Rugby, Cricket... and snow. World of Tanks ain't bad either.
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    Frost and snow. A quiet autumn day is also good.

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  1. Folks - apologies for not contributing more in here at the moment. I'm seriously busy at work and struggling for energy.... One area for discussion I'd like to float is the oceanic-atmospheric coupling that we see occur and discusssed. I know what it looks like, and I know what it looks like when coupling is destructively interfered with - but can anyone begin to explain to me what affects the strength of the coupling? The GWO is a measurement of global winds that, in essence, are a a reflection of the closeness of the coupling - but I am at a loss to understand why, for example, the coupling this season has been so strong when Nina itself has been comparatively weak. I was very interested early season in the easterly nature of the Nina pattern, and wondered (and read from others more qualified than me) that the warm waters around the maritime continent might serve to overwhelm the Nina signal as convection moved into the pacific. It hasnt happened. So - why has the coupling been so strong... and why, in some years, do we see a-typical responses that can create a pattern like Feb 96 that I see mentioned earlier today? There are a couple of interesting posts over on the strat thread regarding geomagnetism and solar forcing. This is going to be an area of focus for me through the summer as I try and fight my hatred of hot, sunny days with associated burn, sweat and lethargy... but does anyone have a theory worth putting out in public now? (One thought - we spend hours and days talking about the pacific, but rarely about the atlantic. Are we guilty of paying too little attention to atlantic influence?)
  2. Really interesting post. I have my summer research project now mapped out for me prior to next winter.....
  3. Well - there's no getting away from the fact that the outlook over the next 10 days is disappointing and not what was hoped for. For those watching snow fall in Scotland and the north - ignore this of course. The embedded Nina pattern is bringing cold enough air a-plenty for numerous wonderland pictures on social media, and watching the machinery at Scotstoun on Saturday sucking snow off the pitch prior to the game with Exeter Chiefs illustrated the point exactly. But for snow starved southerners such cold zonal patterns rarely deliver. What's happened? Remember the elastic band analogy with reference to the angular momentum budget? In simple terms it scarcely had the spring to pull the momentum gradient back to neutral, let alone spike pacific forcing enough to help support scandinavian heights. Hindcast data shows it very well: Frictionals never got going properly - notice the near 20 day negative slide and as a result little in the way of spiking mountain torque. Note east asian conditions in negative territory Overall then the relative budget held firm in negative to neutral territory and as one twitter guru posted a few days ago "the earth is spinning faster than the atmosphere right now." End product is dominant easterlies overall at the equator serving to enhance the strength of sub tropical high pressure and, in turn, add further weight to westerlies at higher latititudes. The signal for a scandy block was blown away. Key to this has been the strength of trade winds in the pacific, clearly highlighted here: Our current MJO cycle has a lot of these to combat as it tries to push in the western hemisphere - but the hopeful picture of around 10 days ago has certainly been turned on its head. So - the atmospheric elastic band barely made an impact, and our Nina pattern has entrenched solidly as the atmosphere remains coupled to ocean forcing. MetO forecasts now at last see Nina fading - but one has to conclude that this will be too late for this winter to recover from Nina dominance It is interesting how strongly coupled the atmosphere has been to what looks like only a weak Nina - but coupled it most certainly has been. Where does this leave us? Wave 2 forcing on the stratosphere will start to fade soon as the favourable tropospheric pattern begins to dissolve. We can expect a renewed cycle of torque impacts as nature tries, once again, to balance the GLAAM budget in the face of Nina forcing, and there is the hope that the MJO can force its way to a 7/8 orbit - but after two failed opportunities (Xmas week and the week ahead) the sense that high lat blocking is going to elude us strengthens. EPS date sees the departure of the West Russian high receding taking pressure off the vortex, and the azores high strongly in place. Can we break out this pattern? Mother nature can always spring a surprise... and MJO phase 7/8 might give us something to work with in February, but right now we will need to see the next cycle of pacific forcing do much better than the last 2 against dominant Nina trade winds in the pacific if we are to see anything change substantially. I suspect the passage of the MJO will aid in development of high pressure in or around the UK, and the MetO text forecast suggests as much at the moment, but a high lat block to pull in cold continental easterlies? Not in sight at present. Those in northern England and Scotland - enjoy your polar westerlies!
  4. Strange comment. Ian has laid out why the forecast has changed... and anyone claiming that a forecast has to stay fixed in stone whatever the medium range developments is wanting more than any forecast can give!
  5. Handy link that Knocker. Relevant at the moment is the strength of trade easterlies in the central and eastern pacific. Heavyweights from across the pond are noting them with raised eyebrow (at least in my mind that's the body language :-) ) and how much progress the MJO can make to 7/8 in the face of such strong Nina opposition remains to be seen. I had a good pm exchange with Tamara early season about Nina forecasts and my expectation that Nina would start to wane by now. In fact that hasnt quite panned out. It has shifted a little further east opening the door through the maritimes, but where it is in force it has actually strengthened a little more than expected. I wonder how close to moderate it will get once this winter is archived post-hindcast. It certainly isnt helping with those forcings trying to amplify the atlantic.
  6. Going to cross post this thread from the MOD - not sure how the MOD thread reacts to this kind of thing... but for those interested in pacific forcings very glad to have comments, disagreements, embelishments on what is below. We never stop learning - me especially when it comes to weather - so all debate is healthy debate. I posted this: "Time for a post. A lot happening in background forcings at the moment. Remember the elastic band? So - frictionals look to have turned to an upwards movement (though a bit slower than expected if I'm honest) with graph now heading back up and mountain torque also on the up. Andean South American torque in the wrong hemisphere for us, but note East Asian and Rocky Mts trending upwards once again leading to the global spike MJO moving through the Indian Ocean and still forecast to cross the maritimes into the western pacific with, to my eye, amplitude sufficient to impact on NH circulation All of this serving to increase angular momentum to a position where it can begin to impact on high lat circulation via poleward wave propagation. Note the steep spike here - though my previous post of "how high" can it go and for how long will it be sustained remains extremely salient All this pretty much as expected with timescales remaining relevant... so given lag time we are experiencing a key resultant response not this week but next. However absolutely no getting away from the fact that ensemble data today has shunted the wave pattern a good bit, and ECM ensemble runs for the start of week beginning 22 Jan are not as pretty as they could be or were a day or so ago. Note the deep dig of the trough into Europe as expected, but it is currently forecast to be too far east to assist sufficiently in supporting height rises over Scandy. In simple terms the horseshoe of heights to the north remains but with more azores high influence and flat Nina forcing in the atlantic still present. I'd emphasise the word "currently" because this is an evolving situation. ECM operational chart for 192 this morning to me reflects a whole basked of uncertainty - its a curious chart prior to NWP turning on the atlantic "tap" once again afterwards.... but it says to me that week beginning 22 Jan remains far from resolved. Without doubt pacific forcings are impacting on NWP at this point... and the question "how high" can AAM ping back and how sustained can ongoing MJO activity be in the face of the same cold Nina waters that blocked it in Xmas week retains key significance. NWP is simply a reflection of these equatorial and ocean/atmospheric battles that are ongoing. And what if it goes wrong - and Nina wins out again? We would move back into another waiting game of cycles. We would need to wait another fortnight for frictional/mountain torque activity to come back around... and for MJO (hopefully) to reach the ideal 7/8 orbit in early February. Note quite interesting stratospheric developments as signposted by far more knowledgeable people than me with the Jan 23rd chart showing a decent wave 2 signal for vortex attack.. and lag effects of this would also point to early/mid February impact. And so this winter keeps giving and giving in terms of interest. So far no snow IMBY but plenty of knife edge interest on a week by week basis. I hope readers of this thread can keep perspective going forward - we have been close to some excellent synoptics this season so far, and close enough for many regions to see some decent if rather transient snowfall. High ground to the north has been pasted consistently and Scotland has had a "proper" winter for sure. This is already better than any of the last 4 winters and we still have plenty of interest on the horizon. Even if southern England ends the season without a winter wonderland experience it will have been a fine run thing... and as we head into the solar minimum, forecast to bottom out in Oct 2019, we can expect winters more conducive to less atlantic impact over the next few years. Scant compensation for those wanting "snow tomorrow" I suppose... but for those who acknowledge the reality of our atlantic climate and infrequent brush with very cold airstreams it is actually something to look forward to! Anyway - all eyes on the pacific surge and MJO battle. Model output will reflect how these drivers evolve. Cold zonality this week, and then next week still up for grabs I think."
  7. Time for a post. A lot happening in background forcings at the moment. Remember the elastic band? So - frictionals look to have turned to an upwards movement (though a bit slower than expected if I'm honest) with graph now heading back up and mountain torque also on the up. Andean South American torque in the wrong hemisphere for us, but note East Asian and Rocky Mts trending upwards once again leading to the global spike MJO moving through the Indian Ocean and still forecast to cross the maritimes into the western pacific with, to my eye, amplitude sufficient to impact on NH circulation All of this serving to increase angular momentum to a position where it can begin to impact on high lat circulation via poleward wave propagation. Note the steep spike here - though my previous post of "how high" can it go and for how long will it be sustained remains extremely salient All this pretty much as expected with timescales remaining relevant... so given lag time we are experiencing a key resultant response not this week but next. However absolutely no getting away from the fact that ensemble data today has shunted the wave pattern a good bit, and ECM ensemble runs for the start of week beginning 22 Jan are not as pretty as they could be or were a day or so ago. Note the deep dig of the trough into Europe as expected, but it is currently forecast to be too far east to assist sufficiently in supporting height rises over Scandy. In simple terms the horseshoe of heights to the north remains but with more azores high influence and flat Nina forcing in the atlantic still present. I'd emphasise the word "currently" because this is an evolving situation. ECM operational chart for 192 this morning to me reflects a whole basket of uncertainty - its a curious chart prior to NWP turning on the atlantic "tap" once again afterwards.... but it says to me that week beginning 22 Jan remains far from resolved. Without doubt pacific forcings are impacting on NWP at this point... and the question "how high" can AAM ping back and how sustained can ongoing MJO activity be in the face of the same cold Nina waters that blocked it in Xmas week retains key significance. NWP is simply a reflection of these equatorial and ocean/atmospheric battles that are ongoing. And what if it goes wrong - and Nina wins out again? We would move back into another waiting game of cycles. We would need to wait another fortnight for frictional/mountain torque activity to come back around... and for MJO (hopefully) to reach the ideal 7/8 orbit in early February. Note quite interesting stratospheric developments as signposted by far more knowledgeable people than me with the Jan 23rd chart showing a decent wave 2 signal for vortex attack.. and lag effects of this would also point to early/mid February impact. And so this winter keeps giving and giving in terms of interest. So far no snow IMBY but plenty of knife edge interest on a week by week basis. I hope readers of this thread can keep perspective going forward - we have been close to some excellent synoptics this season so far, and close enough for many regions to see some decent if rather transient snowfall. High ground to the north has been pasted consistently and Scotland has had a "proper" winter for sure. This is already better than any of the last 4 winters and we still have plenty of interest on the horizon. Even if southern England ends the season without a winter wonderland experience it will have been a fine run thing... and as we head into the solar minimum, forecast to bottom out in Oct 2019, we can expect winters more conducive to less atlantic impact over the next few years. Scant compensation for those wanting "snow tomorrow" I suppose... but for those who acknowledge the reality of our atlantic climate and infrequent brush with very cold airstreams it is actually something to look forward to! Anyway - all eyes on the pacific surge and MJO battle. Model output will reflect how these drivers evolve. Cold zonality this week, and then next week still up for grabs I think.
  8. No time for lots of reading or long post tonight, but Nina base state pattern set to deliver cold zonal next week with snow for some and then we have signs of ensemble charts toying with a greater dig into Europe and suggested height rises to the N and NE. See GFS and ECM 240 hours below Not too dissimilar, with azores high weakened. Some interesting times on the horizon, not for the first time this winter. Relative AAM on the sharp up.... MT spiking. The elastic band is pulling hard right as I type. How hard... and how high will it go??
  9. Good start David. Not quite sure how to angle my posts in this thread - reflective of current output or more broadly educational? I'm going to go for a blend of both and in no particular order pick themes as I go. This one first - basic GWO. I like this slide I found a while back. It helps me visualise what is going on in terms of global winds In essence the GWO is an index of global wind and also the momentum of the atmosphere in relation to the earth. In simple terms if the atmosphere is moving faster than the earth is spinning then we have positive atmospheric angular momentum (AAM). If the atmosphere starts to drag and move slower than the earth is spinning then atmospheric angular momentum is negative. The global measurement of this momentum is sometimes referred to as GLAAM. The key is that the atmosphere and earth do not match speeds in all regions of the earth at the same time. There is regional variation particularly around mountain ranges, and the impact of the interaction between air and earth is affected by these "torques." More about those in another post. Anyway bigger brains than mine (by a long way) explain that relative speed between air and earth is constantly trying to reach a state of equilibrium and that the overall momentum budget is always therefore trending towards 0. Therefore if the atmosphere starts to spin hard and fast at the equator, perhaps inspired by westerly wind bursts via progression of the MJO (more of that in another post again) then the atmosphere at other latitudes will be "dragged" slower to compensate. See net momentum flux in the diagramme. I am not a physicist: I cannot explain it better than that... but know that there is therefore an inverse relationship between momentum at higher latitudes and the equator. Therefore if we get a spike in AAM at the equator we get a reduction at northern latitudes. The jet weakens... buckles... and is more conducive to blocking patterns. Conversely low AAM at the equator, particularly in the pacific, and momentum spikes in higher latitudes blowing away chances of high lat blocks. Final point of note - the diagroam shows that dominant winds at the equator are easterly. These easterly winds from 0 - 30N in latitude serve to prop up sub tropical ridges that in turn help feed the westerly winds in northern latitudes such as ours. Therefore when the trades are blowing hard, the sub tropical ridges are enhanced (eg Azores High) and we get a westerly dominated pattern. When the trades weaken the sub tropical ridges weaken, and lower momentum at higher latitudes helps encourage blocking in winter. A basic concept to grasp as a first step. I'll build more on top another time - but for now it might help explain why we are looking forward to a predicted rise in AAM 0-30N in the nearish future as the atmosphere responds to the current low global value of AAM in an attempt to bring relative momentum back towards 0... and that this process may be enhanced by an active MJO phase causing Momentum to spike above 0. This would be the first stage in encouraging a return of the scandy high in late January. Late night post - apologies for anything that is unclear....
  10. Interesting Stewart. Is this overall skill score - or do you have access to data that is more relevant to a specific scenario compromising convection in the maritimes?
  11. I wouldnt normally bite - but for sake of clarity and accuracy (because I hate it when people start to quote and refer incorrectly) there are precisely 25 hours between my 2 posts. The one yesterday did NOT imply that good charts would be present today. If you think that 25 hours means I am putting the clock back then so be it - though if you wind back to my post on Sunday you will see I'm sticking to the same timeline when I said 20th Jan or maybe a few days later. I've said multiple times that precise timelines are difficult and subject to variation... and we can debate the causes of that variation (eg MJO last week has progressed more slowly to phase 3 than cpc predicted a week back) - but if we have a debate then let's do it on what was actually said rather than a reference to a phantom statement that doesnt exist leading to an unsubstantiated implication that things always get put back and the analysis isnt worth doing. If you want to be sceptical as to the value of signal analysis then that is absolutely your right - but it isnt your place to misquote.
  12. Umm - you've got me. "few days of dross before seeing anything at 10 days" or "a good chance of seeing interesting day 10 charts in the next few days." Call me Mr Picky - but that's the same phrase. Essentially on or around 22nd Jan.
  13. Evening all Model no man's land - and waiting game in full flow. 2 - 3 more days of blah output and then maybe a change to something better gradually appearing at T+240 in NWP. Today's GFS filtered V200 forecast for the MJO is one we want to see come to fruition. Note the current week's situation: MJO in the IO and facing powerful trade winds in the central pacific. Crouch-bind-set.. as the front rows come together and prepare for battle. But 2 weeks on - and the westerly surge from the Indian Ocean has driven the trades back... stolen the ball and the No 8 has picked and gone down the blind side...opposition defenders in scramble mode. That bottom image shows a strong progression and movement towards that crucial 7/8 orbit which is highly desirable and on course for early Feb. In the meantime for Jan the surge in pacific convection on the back of these westerlies at the equator will fire up Rossby action, open the door for additional mountain torque, and provide increased amplification at higher latitudes to get the atlantic trough to dig further south. It is, of course, only another model forecast... but the cpc are in line and current data with logical progression cycles would suggest it is on the money. Nothing is ever 100% certain - remember the disappointing fail at xmas once again (a salient reminder never to get too certain of any particular evolution) - but plenty to look forward to while we work through this current stalemate and flat atlantic trajectory.
  14. Not got time to check back through the thread tonight - but this is a glaring GWO chart if noone else has noted it: For neartime amplification pretty dire (hence atlantic breakthrough coming up) - but for the degree of "stretch" in the atmospheric elastic band this is setting us up for a decent ping-back. Think of atmospheric momentum budgets like a band - constantly stretching out of alignment but then coming back to neutral as the band pulls things together. Here we have an extreme GWO 1 orbit in low AAM tendency... and the elastic band is going to want to bring things back to neutral pronto. End result - bigger chance of a decent spike when it comes. As noted yesterday in posted charts - MJO stalled in phase 2 but CPC predict (again) a move to phase 3 next week. Have to think it will happen this time... in conjunction with rising frictional torques. So not a lot of change from yesterday - but that GWO chart was worth looking at. Timing of amplification and return of scandy high on course. Some interesting charts will start to appear at T+240 in the next few days...
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