full_frontal_occlusion

Hi Lorenzo, yes it woud be good to get GP's thoughts on this. John Holmes wrote an excellent blog entry from first principles which is hard to argue with. I'm assuming all of your obeservations are based on ensemble forecasts given the MJO space you attached? Reading from the actuals one could get a different interpretation: mountain and frictional torques are toying with the idea or have weakly returned +ve again. AAM rate of change has decayed but still remains significantly +ve. The highly -ve AO (-5 SD) shows no signs of abating. NAO remains significantly -ve at around -4/5 and anti-correlating +ve PNA at this time is around +1 SD. SST's north and north eastwards of Panama in the Mexican Gulf, around the Florida peninsula as far out as the central North Atlantic belt are all below long term average. Whereas in contrast, SST's into the Norwegian Sea and into the far North Atlantic are anomalously +ve. Closer to our shores, Atlantic attacks would need destabilising the standing Rossby wave with subsequent shortwave propagation. In that respect the ENSO ocean/atmosphere coupling needs to be weakened. I may be reading too much into it but there is evidence of Pacific warming in the ocean immediately west of the central Americas which could possibly herald a weakening of the ENSO signal but at this time, that's pure conjecture on my part. In any case the coupled energy and inertia dictates a significant lag (several weeks) before effects are felt downstream but that process may already be underway. The difficulty in extrapolation of the teleconnection indexes is a function of the time integral over which the first order EOF is calculated. i.e. no different to any other statistical average only that the harmonic in question is more difficult to extract (needs the eigenvectors in the co-variance matrix algebra set) and is always a post event analysis. In that respect, teleconnection indexes extrapolated from ensembles which are themselves dependent on the skill of NWP ocean/atmosphere coupling models are a bit like a circular reinforced argument in justifying each other to lead us up the garden path. ffO.

A top quality read John and thank you for spending the time to produce it. Sets the benchmark for us all. ffO.

Agree with most everything you say. I'm not disputing your synopsis but am very interested in how you arrived at the MMW resulting in Scandi blocking? ffO.

For what it's worth and IMHO: Looking at the teleconnections for some guidance, mountain and frictional torques are toying with going +ve again. AAM seems fairly static and still significantly +ve. The highly -ve AO (-5 SD) shows no signs of abating. NAO remains significantly -ve at around -4/5 and anti-correlating +ve PNA at this time, all suggest no change in the reverse zonal winds. Looking to the now locked in ENSO pattern eastwards of Panama, SST's in the Mexican Gulf, around the Florida peninsula as far out as the central North Atlantic belt are all below long term average. Whereas in contrast, SST's into the Norwegian Sea and into the far North Atlantic are anomalously +ve. The consequential Rossby wave thereofore looks solid for the forseeable (at least out to early/mid March) with the implication of a suppressed Atlantic with no significant short wave features to introduce S/SW incursions of milder air. Further cyclogenesis appears more likely from the North tracking south with continued building of high pressure over Greenland. All of this suggests the models in FI are very much over cooking Atlantic attacks. NEasterlies sourced from Scandinavia are a distinct possibility, however those cold air incursions may well end up continuing with returning Polar Maritime air mixing with SW continental air as repeated Arctic sourced lows meander around our western shores and over us. Track is all important. Further cold and snow events a distinct possibility with short lived less cold air thrown in. Favours snow the further north one gets, but those cold front battlegrounds will keep us on our toes. Exciting times and plenty of learning opportunities with continued unusual synoptics. The models will continue to struggle into FI. ffO.

Interesting new developments showing up. Mountain torques are on the up, MJO flipped back into phase 8 after briefly intruding into phase 1 with frictional torques looking like going +ve shortly. So the reverse zonals at this time look rather indeterminate one way or the other. This is still in accordance with GP's observation that ocean/atmosphere coupling is consistent and locked in with the El Nino (or could that be the effect of a Kelvin wave?). With that forcing symmetry established, one assumes that the current patterns in our locale look locked for the forseeable. However there's the little issue of the MMW to factor downstream. ffO.

One of the first things in the modelling process is to mathematically interpolate grid point data (used to initialise the models) from the available raw data. By inspection alone, this process introduces some inaccuracy as blocking features cover large swathes of area with little to differentiate between grid points. Solutions are then at the mercy of small scale features just above the noise floor (point at which a discernable signal is measured and not random) and thus affects outcomes as in the trajectory of weather systems. This is akin to say correctly decoding deep space communications from probes, where the wanted signal needs to be transmitted many times in order that ground systems can differentiate it from the all swamping background noise. Hope this helps. ffO.

Snowray, you answered your own question: Nowhere in Great Britain is more than 70 miles from the sea. The North Atlantic Drift also plays a big role. Then think about where streamers form and in which direction? There are few places where streamers form in the UK since the topology is right in but few places. And there you have it. Smallish land mass on the extreme western edge of a continental land mass, with a warm sea current across our western and northern approaches and few topological features to induce such favourable snow conditions. Continental Europe in winter is cold but mainly dry and when a snow event happens (don't forget Europe covers a large numebr of big compared to ours countries) wherever those weather systems meander, somwhere in Europe will get pounded. So many more factors need to be in place for us than on the continent, that the probability of a major snow event dumping feet of snow is a twice a century occurrence for the British Isles. Viola - marginality screams from the rooftops. So yes it is down to luck when it finally happens. But then that's why we're so transfixed with snow as a nation. ffO.

Why not share those methods with us and why widespread snow is your conclusion? ffO.

Looking at todays output, I'm not convinced that the evolutions offered are showing the final outcome and not simply by how much the patterns have changed since last weekend from widespread snow to cold damp squibs and everything in between. The Meto adding the widespread snow warning for next Tuesday sounds like an insurance for the possibility of an event. Too long range to be accurate given the current state of the models - better to be downgraded/removed than be caught out with all the ramificatios that would entail re' their credibility. ffO

Hello peeps, Originally posted on the general model thread but I guess better suited to be answered here. Going to stick my neck out and probably get it shot off however the resident teleconnection and GWO experts may like to comment on the current set of data wrt AAM, Mountain torques and flux convergence wrt next weeks synoptics currently showing n the models: 1) Relative AAM seems to have peaked although still very +ve: 2) Mountain torques have dropped to zero or are now -ve: 3) Frictional torque has gone -ve: The torques generating the high AAM and hence reverse zonal winds would therefore suggest the westward retrogression of that low pressure system should soon be arrested. That bodes well for the models to begin picking up on a a more favourable South Easterly track?: 4) NAO indexes still show -ve deviation but is that not a function of the ensemble members which perhaps have not picked up on the AAM developments? A better indicator is the copuling between the MJO and the NAO: 5) MJO is phase 8 transition to phase 1 imminent: and could move to phase 3/4 within 7 - 10 days with it coupling to the NAO which should show signs of a returning to a less -ve index according to the current crop of mixed ensembles. This is just my amateur interpretation but to me heralds a pattern change where the reverse zonal winds influence is diminished and we start to see more of an Atlantic feel once again but perhaps some fun times during the transition period starting wrt to that progged low next week, tantalising us with various trajectories depending on which model one cares to view. Would welcome your expert comments. Thanks. ffO

I've always looked at the NAO and AO as being a represenatation of the deviation from the long term average or dominant pressure patterns. As such significant deviations point to changes in large scale synoptics such as the dominant Atlantic vs blocking-highs etc. ffO.

Going to stick my neck out and probably get it shot off but..... Seems to me that the postioning and track of the low out to the west next week, is dividing snow-potential opinion on the boards wrt marginalty or major event. It also seems clear that a South Westwards trajectory improves the prospect for Polar Maritime rather than returning Polar Maritime air? The resident teleconnection and GWO experts may like to comment on the current set of data wrt AAM, Mountain torques and flux convergence but: 1) Relative AAM seems to have peaked although still very +ve: 2) Mountain torques have dropped to zero or are now -ve: 3) Frictional torque has gone -ve: The torques generating the AAM anomaly and hence reverse zonal winds would therefore suggest the westward retrogression of that low pressure system should soon be arrested. That bodes well for the models to begin picking up on a a more favourable South easterly track for the low? 4) NAO indexes still show -ve deviation but is that not a function of the ensemble members which perhaps have not picked up on the AAM developments? A better indicator is the copuling between the MJO and the NAO: 5) MJO is phase 8 transition to phase 1: and could move to phase 3/4 within 7 - 10 days with it coupling to the NAO which should show signs of a returning to a more +ve index. This is just my amateur interpretation but to me heralds a pattern change where the reverse zonal winds influence is diminished and we start to see more of an Atlantic feel once again but perhaps some fun times during the transition period starting wrt to that low tantalising us to the west next week. Would welcome the resident experts comments. :blink: ffO

Make an analogy with say a leaf carried downstream by the current, then look to the Jetstream and notice where all the analogous current energy is? There is nothing to force a southerly track. The Coriolis effect is negated by high pressure blocking to the east and once each systems angular momentum is in phase with the earths rotation,viola, stationary low pressure. The high pressure continues filling the low with the effect of shunting the centre of mass of the low westwards. ffO.

Hey diddle diddle the cat and the fiddle Nessie jumped over the moon but sadly burned up on re-entry.

This is where the Kalman filters in the models will influence trajectory of larger scale dynamic features such as those lows - increasing rates of change in position resulting in overshoot then undershoot and finally stable between runs. If I'm right, expect the lows to progressively appear further E/SE before back-tracking and finally settling somwhere between the two. But as NS mentions, it remains to be seen how much the reverse zonals modify the evolution. ffO.

GFS 12z 150+ has a very flattened Jet over North Africa / Southern Europe, pressure rises over Greenland and Siberian Block holding but gradually drifting east. The options for snow in the medium term depend on the positioning and depth of any developing low in the GIN/Arctic region whose track will be defined by the Siberian block to the east and the latency between cyclogenesis events off the US eastern Seaboard. Lack of any real dynamic features (at least large enough for the models to get a grip) is producing this rather benign North Atlantic picture. As GP suggests AAM is off the scale, the 12z looks like its a good facsimile. A waiting game springs to mind. ffO.

Not quite right Pinball. The models are modular with very specific parameters passed between the physics packages (ie. the mathematical descriptors for the gas laws, etc), the main partial differential equation solutions (conservation of energy, momentum etc), the main sequencer (resolution, stochastic iteration etc) and then finally the GUI (Graphical User Interface, houskeeping, diagnostics etc). Point is, all of these items can be developed in parallel and integrated into the final model as and when they reach a level of test compliance independent of other modules. Software development goes through very definitive stages from Analysis, Specification and Definition through to Coding, Testing, Integration and Qualificaton. Each of these stages can be estimated with increaing accuracy as each stage of development is completed. The final delivery date can be quite accurately predicted once the definition phase is completed. If the development lifecycle goes through successive iterations of testing and modification as you suggest, then this is a sign that not enough risk analysis and/or risk reduction was included in the early phases. Software development at thus scale is incredibly expensive and mistakes made at the start just get compounded eponentially if they are not found early on. Giving 'provisional' dates for release is a way of managing expectations and does not reflect the fact that the Met does not know when - any other way and serious questions would be asked about how much the whole thing was going to cost with quite a few heads rolling as a result! ffO.

(Originally posted on the Model output thread) It may have escaped some folks notice (but by no means all) that this thread is in serious danger of becoming an exclusive club for sycophants and cliques. Should we not forget that the rules for posting should be adhered and applied fairly to all, lest the moderators could be accused of at best favouritism and at worst fascism. We're discussing the model output and interpretation for upcoming weather for goodness sake. Perspective people, perspective. Moderators. If you decide to delete this post (which I'm sure you will) please look at a few of the other posts on this thread and decide if they are sticking to the rules - whoever happens to have posted it? Thank You. ffO.

For those of us who lived through it, the Gemini/Apollo era stoked the dreams and imagination of a generation still believing that science was the magic genie that would set us free from the confines of our miserably small planet. Well it hasn't quite lived up to the expectation - Recruiting Vulcans into the UFP will take a little longer than the average 9 year olds chidhood. The Apollo programme produced awe of biblical proportion. Mere mortals could scarcely comprehend the science or feel the shiver of wonder at the iconic images beyond anything our imagination had prepared us for. Little wonder then of the regard we almost subconsciously invoke every time someone uses the phrase 'it ain't rocket science' or 'I'm not a nuclear physicist / brain surgeon'. Children today are far more sophisticated and demand so much more from their entertainment - courtesy of CGI, Lucas, Spielberg, Scott, Cameron et al. Technology has moved apace. Every kid can explore the universe from the safety of his X-box. Mobile Phones make Jim's communicator look antiquated. Talking computers confound you every time you try to get through to your bank. An answer to every conceivable question one could ask is but a few button presses away, automatic language translation is no longer the distant dream it once was. Moonbase? Humbug! They want Warp Drive, Transpoters, Vipers, Phasers, Light Sabres. So whose childhood would going back to the moon inspire? Perhaps only those whose dreams were not quite delivered in the 1960's. Going back to the moon would galvanise and inspire the planet the second time around barely more than a Space Shuttle launch does now. Pragmatism recognises the need for technological leadership in the face of rapidly growing competition from China, India, Europe, Japan, Russia etc. The best way to do this is not re-invent the wheel, but to focus innovation to expand capability and sustainable infrastructure whilst the others are forced to continuously play catch up. Building a commercial LEO capability frees up NASA for the long haul. New propulsion technologies (VASIMR for instance) will significantly reduce the size of the solar system just as steam ships followed by the aeroplane did for our planet. Autonomous robots strategically servicing significant parts of the infrastructure needed to support Human exploration of the solar system are just the vanguard. I think history will look back and see the global financial crisis as the turning point that was not the end for NASA. If it pays off, Obamas decision will be viewed as visionary and the catalyst needed to take the next steps in our evolution to leave this planet. 'The needs of the many outweigh the needs of the few or the one.' ffO.

:lol:

Mr Tattum, you do realise there are probably impressionable young persons reading this thread? Naughty boy.

Solar pole reversal is linked to the sunspot cycle which is averaged at 11 years with the next maximum due around 2012 - 2014. However the sun has only just begun to emerge from solar minimum after the longest minimum period for the last 100 years. So it's still a guess when the next flip will happen. The earth also goes through magnetic pole reversal but since the last one was estimated at 750,000 years ago, nobody (not even NASA) can possibly know when the next one will happen. Then there are the popular doomsday rumours that predict death and destruction. Again it does not take too much effort to realise the earth (therefore all life) has survived probably several thousand of these events with no apparent ill effects, so its safe to assume humans will survive also when it finally does happen. As for modern infrastructure? Again a rudimentary knowledge of physics (GCSE) is all that's needed to allay fear: Most will know that a chamging magnetic field induces both physical force and electric current in a conductor. Both force and current depend on a. the strength of the magnetic field and b. the rate at which that field changes. The earths magnetic field is physically very weak at the earths surface - barely capable of deflecting a compass needle. It does however extend over great distances out into space and can deflect (atomic scale) cosmic particles because of this scale. It's effect on even small sized objects (say a pin resting on a table) are utterly ignored. If however, the earths magnetic field changed rapidly say within a few seconds, large currents can be induced in large scale conductors - the national grid comes to mind. In this case global electricity distribution could be disrupted and power surges may affect anything connected to it. Akin to a lightning strike for instance. There is no evidence to suggest that reversal has ever happened with such rapidity, the most likely being decades or centuries. On this tiemscale, the reversal will be utterly imperceptible. Aside from all this, one can't take everything read at face value. Choose your sources of scientific reading wisely - general science monthlies (Scientific American, National Geographic etc.) are excellent sources for fact based science. Treat science-fiction type magazines with a very healthy dose of scepticism (Fortean Times, lads mags etc.) Don't believe websites that focus on conspiracy, armageddon, Mayan calandars, UFO's, x-files, area 51 etc. Remember that the tabloid press tends to sensationalise headlines using fear and misconception to generate sales. A good starting point for finding out genuine fact based science is listed here: List of popular science scources Above all, don't worry. ffO.

Interesting you mention Buchan - we very often forget (or at least most do not know) of 'rules of thumb' postulates with some surprising statistics for the British Isles, long before NWP;Brookes C.E.P (1889 - 1940) weather 'singularities'(rates of change = 0 in other words static) which accordingly predict: mid Jan (18 -24th) anticyclonic high pressure 87% probablity late January (25 - 31st) cyclonic stormy 85% early Feb (8 - 16th) anticyclonic 56% late Feb (21 - 25th) cold spell 42% late Feb early March (26 - 9th) stormy 88% Lamb Hubert (1913 - 1997) natural seasons: LATE WINTER (20 Jan - 29 March) lengthy spells but no preference between zonal-mild-windy & blocked/cold. i.e. 50% either Coldest winters when persistent blocking highs Scandinavia/Iceland. Polar Continental / Arctic Maritime ... cold. northerly types 5 days max. 20th - 23rd January Anticyclonic EUROPE + S. & E. Britain 27th January - 3rd February renewed storminess gales and rain or snow Lows pass into North & Central Europe from Atlantic. The first lows of the series commonly approach England from the South-West (N.B. liability for freezing rain with advance of mild air after some days of frost). Anticyclonic type rare. 8th - 13th February Anticyclones Record frosts in cold winters. Fogs common inland. Southerly & Easterly types common in Britain. 26th February - 9th March Cold Stormy period Northerly outbreak from Norwegian Sea and cyclonic weather over N. Sea and surrounding lands. Cyclonic type maximum 26th February - 2nd March; Northerly type maximum 28th February - 3rd March. Buchan Alexander (1829 - 1907) Spells: 7th - 14th February: COLD 11th - 14 April: COLD Barry & Perry: 20 - 23rd January - Precipitation minimum in central / Southern England >70%. So, combining these rules we should expect: Mid - late Jan; Anticyclonic dry and frosty. Late Jan - Early Feb; A stormy Atlantic period with lows approaching from the southwest and passing into north and central Europe with a liability for freezing rain. Early - Mid Feb; Anticyclonic (Southerlies and Easterlies) with potential for record frosts. Late Feb - Cold Spell with northerly outbreak from Norwegian Sea. Interesting indeed. ffO.

Models huh?....a graphical representation of the solution for an immensely complex set of partial-differential equations. The thing is, there is always more than one solution. Ensembles? As a previous poster suggested, sheep in wolves clothing - 'ya cannay change the laws of physics captain.' Continuity between runs is also no guarantee of a correct solution especially in a blocked synoptic where the entrance and track of dynamic features can significantly alter an outcome with even minor deviations between runs. For instance, ECM suggest 15-30% of the kinetic energy of transient eddies on all scales are underestimated with a tendency to zonality. The recent heavy snowfall over the last few days in central and eastern Europe may also play into reinvigorating the blocking pattern and extending the uncertainty of this period. Teleconnection indexes are but statistial representations of semi-permanent pressure patterns - retropspectively accurate but constrained by the same limitations that govern synoptic evolution models. As such they are are also sheep taking their lead from the potentially flawed ensemble members. In this situation experimental (and the traditional old school seagull) techniques may offer the only path for guidance. Methinks more upgrades, downgrades and also ran grades will be on offer before the week os out. ffO.

Surely the model evolution within the nearfield is a direct consequence of realtime data accuracy? Each new timestep compounds the errors but from your example - given the positioning of all the high and low centres, 850 distribution, heights etc - the limited error differences between those charts is pretty impressive. ffO.