[Model output discussion 11th July onwards]

16 hours ago, DAVID SNOW said:

Yeah, it's the same with using  Teleconnections  to try and see where things may be heading, problem with that methodology  is that there are too many variables, and how they interact, so a lot of guess work needed there.

Just look at what the models (all)  are showing in the near time period, and try to, if one is so inclined, guess their conclusion.

A quite good discussion overall about methodologies and the various proxies at the disposal of the weather observer and all of which provide their own valuable merits

However, posts as over trivialising as the quoted extract, should be challenged for what they are..

In order to even start to consider the 'variables'' behind patterns and pattern changes, there HAS to be a diagnostic assessment of the jet stream itself and which pinpoints where turning forces (as expressed as -ve or +ve  switches of angular momentum) are being exhibited on the jet stream and which implies either lesser (-ve) or greater (+ve) inertia or change of direction/amplitude of the jet stream.

There equally has to also be an understanding, through diagnostic tools, utilising the GSDM plots and phase spaces, of the periodicity ( recurrence timespans) of the tropical  end extra tropical cyclical phenomena that influence wind-flow inertia on cyclical circa 30 to 60 day cycles - and additionally also sub-operate within intra-seasonal repetition wavelengths of up to 90 days.. Used impartiality and by eliminating bias confirmation (that skews suggested outcomes and in turn creates error) the known impacts these make on the jet stream can very reliably be anticipated and factored in to probabilistic outcomes based on the wavelength/timespans they operate within. It is possible therefore, to put together some medium longer term suggestions of the way ahead based on these - which are infinitely more than just guesswork...

Such methodology is scientifically accepted and peer reviewed over many decades by generations of meteorological scientists. Describing therefore' the teleconnections through which these wind-flow cycles are index measured and calculated, and the knowledge and proactive application of the relevant research as being dependant on 'a lot of guesswork' is, frankly, small-minded and dismissively untutored to say the least 

 The upper air pattern modelling of the atmosphere, through which diagnostic assessment gives the forecaster an extra understanding and perception of how the wind-flow budget within the atmosphere operates, is as an accurate representation, numerically, of these wind-flow differentials, as there can be - based on the acceptance of the caveats of longer term numerical model interpretations of global wind-flow.

Without undertaking a diagnosis, or being too parochially sceptical to believe there is need for one, how on earth can any understanding come about of how the science itself works from inception to cause and effects? Its the vital starting point of a systematic process that eliminates mere guesswork..

[Model output discussion 11th July onwards]

Posted a couple of weeks back:

Its a difficult situation judging the further outlook but from the diagnostic point of value, momentum will need to take the GWO out of the Nina phases 1,2 and 3 into Phase 4 to meet the longer range NWP signal for NW European mid latitude high. This can certainly be achieved, but any shortfall or weak eastward propagating orbit, allied to the polar> mid latitude feedbacks mentioned could mean that a retrogressive correction happens subsequently.

----------------------------

 

The GWO has duly orbited into Phase 4 c/o eastward propagating tropical convection increasing westerly momentum within the atmospheric circulation courtesy of torque mechanisms adding inertia within the extra tropics.

 

Hey presto the break from the retrogressed ridge/trough regime that had blighted a few weeks of the summer in NW Europe. Summer down here in SW Europe continuing very warm and sunny but in the absence of any heatwaves (by true definition, not the UK interpretation of a few days of 30C)

The Pacific phase of the high frequency tropical cycle is completing over the coming few days and in turn that is the cue for angular momentum tendency falling right back towards the levels seen from middle of June to the first week or so of July.  Again, much the same  as happened towards the middle of June, dissolving the downstream NW European ridge and retracting the Azores High westwards and southwards and a trough to return to northern and western europe.

Placed so close to its natural home, influence of the Azores High at the same time continues across much of southern and south western europe, Based on its reorientation, enough of an Atlantic flow influence to keep western and northern parts of Iberia relatively cooler - much the same as the summer so far. However, the jet stream still far enough north to maintain traditional summer drought conditions. While the sun and warmth is lovely, a shower or thunderstorm at least, before the sun soon returns once more, would be welcome to give the watering regime a short break and to give some extra weather interest, There has been no rain at all here for the last 4 to 5 weeks and mostly just blue skies  and intense solar power from one day to the next. That is clearly unlikely to change any time soon and keeps a close fire risk watch across the parched land- though the opposite (terrible) extreme of rainfall such as seen recently in Belgium and Germany are wished for by absolutely nobody

Numerical models at this time, a couple of days or so prior to a pattern change such as this are not likely to be able to see past the signal driving it - and extended ensembles are more than likely to extrapolate forward the same thing in the absence of any significant driver within a short enough time period to add sufficient noise to the mix. The noaa charts are upper air interpretations of the main numerical models and as such they are an especially useful guide to accurately deciphering the latest views of NWP. However, numerical models are prone to change the upper air pattern accordingly as and when signals are detected. Which might not be accurately detected or perceived..

Inherent biases and lack of skill from NWP at deciphering tropical and extra tropical evolution more than a week or so ahead can lead to error and over extrapolation of current trends, or, indeed simply jumping on a wrong trend altogether. In this sense the anomaly charts also need to be viewed with this in mind - they might most accurately reflect NWP perception of the weather pattern - but that does not mean that they are not subject to change themselves at any given time more especially within the latter 8 to 14 day period. 

On this particular occasion, a couple of days before this particular pattern change, it is very unlikely a return to summer proper will occur within the 10 day period and probably rather longer. The importance of all of the above though, is that it is overtly unnecessary to be mood driven in making assumptions weeks and weeks ahead but equally at this present same time realistic enough to know that the atmosphere remains defaulted to a falling angular momentum tendency regime, driven by trade wind increases within the tropics and especially Equatorial Pacific .

In high summer this does not usually correspond to sustained warm dry patterns across northern and western europe. With the current 'mini ENSO cycle' aka MJO tropical convection wave waning, summer proper will await the next upturn in the cycle in northern and western europe. For this part of the NH, the shift to an e/QBO regime, within a falling momentum scenario, will also be encouraging some of the ridging towards Greenland as depicted in numerical modelling.

The next window of opportunity most likely to come after the first 10 days of August. Eyes after that time on a possible  (stronger) intra-seasonal response within the tropics to shale-up momentum once again through the middle and second half of the month and which might come on the heels of residual tropical activity in the Atlantic bred from an African wave upcoming as the MJO traverses the Western Hemisphere (and when lack of wind shear is conducive for storm and hurricane development). This could shake-up the Atlantic profile somewhat as often happens in the latter part of the summer. This, while highly credible, is of course somewhat speculative so far out in time - but something to look out for.

[Model output discussion 9th April onwards]

On 24/06/2021 at 14:47, Tamara said:

What is key is that peak summer wavelengths, allied to the lack of any sustained -ve inertia within the atmosphere, and which was covered in a lot of analysis the other day, look set to augment a subtle eastward shift in the pattern, with time, and set up something of a weak -NAO signature in the Atlantic, but crucially disconnected to a mainly +AO polar profile. The main jet stream to the north, as accurately depicted in the quoted summary, having that slight split flow aspect to reinforce the weak troughing close towards the Azores area.

Bom dia

The gist of split flow, as suggested in the quoted post of the other week, proved consistent enough - but equally -ve inertia between the tropics and extra tropics has clearly proved stronger than anticipated and this has resulted in a much more Nina-ish aspect c/o a very -PDO profile upstream which has seen troughs splitting SE'wards into NW Europe  rather than the retention of a downstream ridge more (Nino-esque) that had been previously discussed and shallow troughs stalled/disrupted further west.

This has maintained cooler air advection from a NW vector and kept the lid on summertime heat build over Southern Europe. and any chance of it spreading outwards.  Indeed even in my own locale 1200 miles further S/SW than the UK and other parts of NW Europe, the cooler air advection and Atlantic influences have just about penetrated this far south. Pressure has remained high though and squeezed any residual frontal rain from the main troughs sinking close to S UK and the nearby continent.  A few bands of variable amounts of cloud have been the sole product and temperature have been in a range of 23 to 26C during these cooler air advection incursions and 28 to 32C as the Azores ridge retains its full seasonal control once more. The lower mid banding of these values are cooler than average for the time of year for much of central and southern parts of Portugal.

This weekend repeats that sequence with, this time, a very brief visit of heat from Africa before the next cooler front arrives tomorrow. Values of 35C seen here very locally yesterday, 37 to 41C expected locally> regionally today before back down to 25C by Monday...and then heating back up once again by Weds/Thurs next week

That leads nicely onto the here and now into the outlook period and whether or not this summer cycle keeps rinsing and repeating.

NWP has tried a couple of times to suggest north eastward ridging of the Azores High to more north western parts of Europe, but has subsequently kept the ridge more retracted and allowed another trough to slip south around its perimeter. 

At this point the diagnostic GSDM data closely reflects the Nina-ish NWP pattern and why the numerical models have backtracked to the default pattern since the middle of June: :

Relative total angular momentum capitulated the buoyant levels of early June and has operated a deficit of between -1 and -2 SD (standard deviations) since the middle of June. 

 

Strong trade winds across the Pacific and tropical convection rooted across the Indian Ocean has sustained -ve extra tropical mountain torque across Asia and extended the wavelength of a retrogressive downstream pattern much longer than anticipated in a previous post. Previous activity and strength of eastward propagated tropical convection has not sustained as had been previously discussed.

 

The Global Wind Oscillation, a phase plot depiction of wind-lfow inertia within the atmospheric circulation has orbited into the La Nina attractor phases 1/2/3 at a greater amplitude than previously suggested.

 

This adds up to the stubborn Atlantic ridging and peripheral shallow troughs circulating around the high pressure into north west europe c/o the accented -PDO profile and despite a largely +AO profile. The latter persisting as suggested, the former clearly underestimated.  

NWP ensemble products are more closely congregated around in achieving Azores ridging into more NW parts of Europe in the mid term, but with some retention thereafter of defaulting back to the lower angular momentum regime. Its easy to see why this might be the case and why some caution about longer range numerical products can be understood. It is important, based on AAM falling further than anticipated within the last few weeks, that sufficient momentum builds from upstream to enable this to happen c/o rossby wave propagation from tropics > extra tropics. This is also not made a simple equation due to the stubborness of the -PDO which is aided by the strongly imbalanced polar ice melt and recent extraordinary temperatures at latitudes that should not see such values. 

Its a difficult situation judging the further outlook but from the diagnostic point of value, momentum will need to take the GWO out of the Nina phases 1,2 and 3 into Phase 4 to meet the longer range NWP signal for NW European mid latitude high. This can certainly be achieved, but any shortfall or weak eastward propagating orbit, allied to the polar> mid latitude feedbacks mentioned could mean that a retrogressive correction happens subsequently.

From my own point of view this maintains relatively cooler interludes  (still pleasantly warm) to a generally standard very warm regime (albeit cooler than regional average) and means a good summer is assured -  but for the majority in the UK it is easy to understand why its very important that the present indications are satisfied and so summer proper can be enjoyed

Até breve

 

[Model output discussion 9th April onwards]

 

17 hours ago, Singularity said:

There has been an enormous negative spike to the global sum of mountain torques, which is why AAM has dropped so much. This is the extratropical influence on AAM - but it's not what leads the overall direction of travel. For that, we have to look at the tropics and frictional torques. Those have also been negative but are now heading back toward neutral, a sign that the tropical cycle is ready to move on an start to shift AAM upward.

Despite this, such a big -MT does ease the door open for the scenario that ECM keeps jumping onto and off from, as an Atlantic trough briefly gets shunted in the direction of the UK.

If the cut-off low is still hanging around close enough to our shores, then that low has a shot at moving close enough to interact with it and keep the polar jet across the UK, in which case we'll be having to wait for AAM recovery to lift that trough out and allow the Scandinavian high regime to set up shop (most likely via an Azores high extension then breakaway), some 5-7 days later than was being advertised at longer lead times.

On the other hand, if the cut-off low is far enough east, the door will be shut and the trough is unlikely to make it to us before it stalls out (as the knock-on effects of the huge -MT subside). Without much to move that trough on, a good run of fine, warm weather could result, before the likely destabilisation, possibly via a substantial heat spike akin to what the ECM 12z of yesterday explored.

 

If you'd like a reason to be hopeful, consider what the ECM runs of a few days ago were predicting the cut-off low to get up to this week: Loitering in the Channel until Friday, even into the weekend. Now, that low is set to be clear of us by Wednesday afternoon!

A repeat performance would leave plenty of room for a GFS 06z style 'wall of high pressure' outcome.

A poorer read in here in general than NWP (allegedly) is, but this is another good post from @Singularityand more accurately and specifically pinpoints short term diagnostic departures in momentum tendency c/o extra tropical scrubbing of westerly inertia (based on a natural lull phase in the mini ENSO cycle) - vs the longer term outlook which will continue to be guided by limited sustained mechanisms to perpetuate a low angular momentum regime - such as I have tried to describe in two previous posts. The latter is obscured by overstating and over extrapolation of the former.

RMM high frequency tropical convection plots are equally poor at depicting amplitude of forward momentum beyond about 4/5 days, but during the first 10 days of July the next wave is due to progress eastwards from the Indian Ocean through to the Maritime continent - and then onwards into the Pacific.  There is natural means based on SST arrangements for tropical convergence and deep thunderstorm development to interact with trade winds and reverse momentum tendency in the extra tropics 

This is likely to further spook the numerical modelling as the pendulum of momentum snaps back. Therefore, NWP is heading down a potential cul de sac if it is overly scrambled by short term negative torque impacts in the extra tropics which have a periodicity of a number of days before evolution in the tropics cuts through the noise and forward momentum returns to jolt the pattern. Its worth re-stating once more in this respect that GSDM diagnostic is over simplified by x+y = *insert singular outcome* limited character soundbites via twitter - and which may be overly influenced by bias confirmation processes. Its true purpose is to give an insight into probabilistic ranges of outcomes -  also to give guidance to wavelength (timespans) of these changes and to see where NWP might become overly blindsided by a strong, but time limited signal. Like shoals of fish in midstream they are so often caused to change direction and why it is so bemusing to see so many observers the other other side of the ocean glass slavishly mirror this fickle midstream mentality.

 I am ambivalent of the UK outcome based on my new location, but for what little it is worth despite a natural scepticism towards all numerical model products it is still well worth looking closely at individual members in the GEM suite which rarely gets any attention - as there is a smorgasbord of solutions including quite a few that echo the theme of the ECM operational of today and which have much greater importance of possibilities to the UK than here in the Iberian continent where the outlook is much more assured..  

The lemming mentality to each and every operational output will no doubt continue, but I would continue to believe that the present -ve inertia is a means to re-set the trough in the Atlantic and then as high frequency tropical signal heads eastwards once more, the signal will increase to re-build (or simply just to re-intensify) a downstream ridge with potential for the heat advection processes spoken of previously interplaying with less progressive troughing in the Atlantic. Such heat intensifying processes continuing in earnest down here over the coming week.

 

[Model output discussion 9th April onwards]

9 minutes ago, mushymanrob said:

Well lets have a look at the anomalies, see what they suggest and watch over the next 12 days or so how they perform.

They suggest troughing will be out in the mid atlantic, so not over the UK (but a short lived minor event like a plume breakdown is possible)
They show the jet stream tracking north of the UK and over northern scandinavia
They show a positive pressure anomaly over the UK and to our east.
They show a rather slack mean upper flow from the southwest.

They also suggest troughing over the azores, which when phased with the high to our east would suggest to me anyway, an occassional plume and a more southerly sourced surface flow.

As i see it, and i may be wrong, these charts suggest broadly a warmer and drier summery  settled outlook for this period, possibly even hot at times, so a lot of very pleasant summery weather at least. The only fly in the ointment is a possible thundery spell, short lived, but that could deliver a lot of rain in a short space of time.

Boa tarde

As per the other day, the heat is ratcheting up once more this week here an hour from the Sliver coast in Portugal. A probable 32/33C today and a notch up to 34/35C tomorrow.

Your summary is a very good one - I realise that there is bound to be a lot of micro analysis when it comes to the UK and regional interests, but these other commentaries paint a rather bleaker reality than the bigger macro scale suggests.

I would be encouraged by the recent holding pattern not having gone a step further with the Atlantic ridging pattern of late, which is wholly typical of a lull in the tropical>extra tropical cycle.  The key word here is 'cycle' - and July continues to hold widespread promise for those who like warmth/heat in their summer.

What is key is that peak summer wavelengths, allied to the lack of any sustained -ve inertia within the atmosphere, and which was covered in a lot of analysis the other day, look set to augment a subtle eastward shift in the pattern, with time, and set up something of a weak -NAO signature in the Atlantic, but crucially disconnected to a mainly +AO polar profile. The main jet stream to the north, as accurately depicted in the quoted summary, having that slight split flow aspect to reinforce the weak troughing close towards the Azores area.

Once in place, there should be dalliances between the troughing to the west and south west and the ridging over and to the east. This implies thundery interest from time to time but with a southerly or south easterly vector implied, this is a much more appealing prospect than the short term pattern of downpours within a cooler regime that looks set to cover southern england and the immediate continent across the channel.

The noise from some quarters suggesting cyclonic impacts for UK/NW Europe heading into next month continues to look overstated to me - and requires a wider overview of the GSDM diagnostic than any narrower formulaic perceptions based on AAM levels - without looking at the actual wind-flow plots and seeing where the wind-flow disparities lie. An attempt was made to do this the other day in some detail. .

Vey encouraging that extended range NWP continues to evolve its modelling identifying the suggested diagnostic (as mentioned last time around) - and points to greater Scandinavian influences in the peak summer month to come. Still very much on watch for some significant heat to build northwards through southern and south western europe and expand thereafter northwards. Such an evolving pattern is ideal for such a progression

In the meantime therefore, don't let micro scale details that are shorter term cloud the bigger picture. Enjoy the summer 

[Model output discussion 9th April onwards]

4 hours ago, Uncle_Barty said:

Matt Hugo on Twitter trying to pour cold water on those hoping for much of an improvement going forward...

"Caution required over this signal for high pressure to build into the British Isles from the W through late June...We are still about to see a trend towards a -ve AAM regime. A more changeable/unsettled pattern still remains more likely towards months end/early July..."

Olá a todos

21 to 23C has been the benchmark each day here in Portugal since the second part of last week, and has allowed a lot of outdoor work to be completed without seeking sanctuary in the middle of the day from an inferno in the sky This,, following some heat and spectacular evening thunderstorm activity in the first part of last week. These much cooler levels are very conducive for getting things done throughout the day, but are distinctly below average for Portugal while at the same time they would constitute acceptable levels of warmth for many in the UK - very evidently compared to the parallel cool-off that has happened in the UK over the same period and induced some truly unseasonal coolness along with the rain

The heat is set to ratchet up here again during this week and indeed, following several practice tests over recent weeks, is probably the makings of summer proper to come most likely well into the autumn (as defined by seasonal months).

As far as the UK is concerned, its less straightforward as it often is the case, though that said, the risks of overplaying a changeable/unsettled pattern are at least as large as the converse in my opinion. Why is this the case? Long explanations but quite clear conclusions in essence.

It is correct to state, as for example @Singularityhas done from a read back of recent days posts, that another lull phase of the 'mini ENSO cycle' (aka high frequency tropical phasing) is in progress - but it is also true what he says that it is not as simple as an x+y= fixed formula either when, it comes to -ve AAM = unsettled and cool and +ve AAM =settled and or even thundery and hot warm (in context of summer at least)

The Global Synoptic Dynamical Mode (GSDM), in its most simplistic terms, gives an overview of global wind-flow budgets and an insight, through graph and plot depictions of cross sections of wind-flow, latitudinally and also of longitude - where -ve wind-flows (easterly) and +ve wind-flows (westerly) are occurring at a given time, and on a rolling forward basis.

The aggregate total of these wind-flows tells you whether there is surplus -ve or +ve inertia within the global atmospheric circulation - and as part of a break-down on this wind-flow budget, measures the turning force of torque mechanisms (where changes in flow occur and generate of flow) switches, and express them in terms of angular momentum tendency  (-ve or +ve) according to the overall wind-flow budget within the global circulation.

On this basis the pattern is more likely to retrogress during phases of dominant deceleration of wind-flow as easterly wind inertia is added from the tropics and beefs up sub tropical ridging in the Pacific and then the Atlantic -while at the same time these retrogressions create a downstream trough response. The converse holds true when westerly winds are added from the tropics into the atmospheric circulation and forward momentum adjusts the rossby pattern wavelength poleward and eastwards. This all sounds a bit like the x+y formula though doesn't it?

What is of far more importance is the ongoing tendency of momentum within the atmospheric circulation (not the total -ve or +ve aggregate of momentum. Also, at what latitude and wavelength, and indeed in what hemisphere (which can have stratospheric effects and define the respective annular modes at the poles) momentum is being added or taken away.

To put some context of there here and now,  some GSDM plots will follow in due course to explain the current wind-flow budgets and how they are impacting the numerical modelling. Also some suggestions as to how the diagnostic might evolve NWP in the foreseeable future.

As a prelude to this: the previous post earlier this month suggested that strength and amplitude of the MJO 'mini ENSO cycle would determine tendency of momentum and whether the anticyclonic pattern of the earlier part of the month would tend to hold a similar wavelength or, show an inclination to retrogress. There was also a suggestion that NWP might overdo suggestions of retrogression in the longer range based on the state of the summer polar field (much more stable as predicted since the strong feedbacks of the late winter and much of the Spring) and also based on the fact that trade winds have eased more generally as La Nina has taken more of a backseat and this has been something of a floor on angular momentum tendency (the amount of easterly inertia propagated from across the tropics)

To illustrate both these proxies:

The southern oscillation index (SOI) as a pressure differential sign-poster within the Equatorial Pacific sign posts a sustained neutral trend and points to a cap on the amount of easterly inertia potential generated within the tropics

Another way of representing this modest impact is within the Hovmollers plots which show only sporadic trade wind phases  (easterly inertia shaded blue) across the tropics with pockets of forward momentum (westerly wind convergence zones shaded red) c/o cyclonic impacts across the African continent, Indian Ocean, and the far eastern Equatorial Pacific. 

All said, frictional torque tendency has no doubt still turned negative as tropical convective activity has waned rather quicker than anticipated earlier in the month (Lets express this as a measure of the amount of easterly wind inertia that creates a negative torque response and creates sub tropical high pressure amplification at the inflection point of where easterlies replace westerly/forward momentum.

 

Note however from the plot that a large proportion of -ve tendency is evident within the southern hemisphere and that this means that impacts within the northern hemisphere are muted by proportion.

Notwithstanding that, the effect of modest upstream -ve torque tendency within the tropics, is to inflate and retrogress equatorial ridging into the sub tropics, occurring, as said. at the source of inflection point of -ve torque in the Equatorial Pacific where convective suppression is evident. Frictional torque tendency usually leads mountain torque tendency as these inertia switches propagate between the tropics and extra tropics. The lagged impact of added (but limited) deceleration inertia from tropics> extra tropics in accordance with the laws of conservation of angular momentum is to add (weak) forward momentum strength to the downstream jet from the Pacific (within the extra tropics) across North America into the North Atlantic,

So the spectre of a beefed up sub tropical ridge downstream in the Atlantic, and with a relatively diffuse jet stream riding across the northern flank of the ridging sounds about right with what is being advertised by NWP. Modelling has been consistent with this, but also is struggling with the proportions of this inertia which, as suggested, is not manifest of any full blown summertime La Nina wavelength response. As is/has been well commented on by others, this is producing erratic intra day solutions based on very flabby cut-off low pressure areas breaking off from the diffuse Atlantic jet coming off the US and dropping south around the perimeter of the sub tropical ridging.

The recent -ve inertia switches are represented in wind-flow phase plot depiction form by the Global Wind Oscillation - which is a barometer of how much impact (-ve or +v) the atmospheric circulation is acting co-operatively or 'destructively (a-typical) to the base state. Based on calculated tendency of AAM (which budgets together aggregate global torque contributions to wind-flow) we see, once again, only weak to moderate -ve tendency on the jet stream - producing proportionately weak Nina-esque impact on the pattern

 

As such, the GWO has laddered very slowly down into a quite incoherent and weak Phase 0 signal - which is hard to define in synoptic terms, but erratic and fitful discontinuous retrogression amidst the pockets of equally tatty pockets of cut-off low features is the sum of the parts.

Trying to assess independent parts of the atmospheric budgets through composite matches is fraught with error based on the present scattergun wind-flow inertia budgets that have to be seen as a complete GSDM diagnostic rather than back of a fag packet assumptions about neutral ENSO states and assumptions about MJO modelling. The latter has to be viewed based on periodicity timelines which operate up to 60 to 90 day timescales (with empirical feedback loops within them).

On this basis, and in the absence of taking into account any of the various interlinked factors, it is not possible to predict the GWO with any accuracy without looking to see how much potential bandwidth there is within the atmospheric circulation to release latent Nina-esque forcing (low angular momentum regime) Or indeed any other forcing at any other given time based on torque mechanism strength that can be created within weak GWO forcing as part of a strongly neutral atmospheric response and behaviour network

The resultant dogs breakfast pattern, as expressed in synoptic NWP terms, looks sustainable till the tropics give the pattern a kick as the next high frequency wave likely gears up heading through July.

However, sub tropical Azores ridging based on feedbacks loops assured within a weakly negative/neutral atmospheric and ocean base state, offers lead on the pattern in the period heading into the first part of July. Its hard to see the GWO having a floor limit much below a very weak Phase 0/1/2/3 treading water orbit - and based on the benign state of the polar field, this gives little appetite for poleward amplifying Atlantic/Greenland ridges trapping suppressed low pressure systems across mid latitude such as happened in strongly tanking -AO La Nina summers of 2007 and 2011 etc.

Therefore, all in all, that brings the summary back to the opening gambit. Better to not overstate the -ve inertia potential of this pattern during this 'lull momentum' phase which has evidential limitation as shown through proxies and GSDM diagnostics. I would be watching for resumed eastward progression of quite strong Azores ridging (possibly towards Scandinavia) during July with a continuing stable polar profile to support keeping the jet stream to the north for those in NW Europe (UK) closest to such traffic. This should put something of a lid on any inroads of frontal systems brushing across those further NW in UK and NW Europe. Those of us further south in Mediterranean southern Europe  maybe should keep an eye on true heatwave potential and make the most of getting outdoor work done in the garden and on the land before siesta time and air con take over proceedings

 

 

[Model output discussion 9th April onwards]

On 10/05/2021 at 12:31, Tamara said:

 

,,,,,as far as NW Europe is concerned and specifically the UK from this threads viewpoint, anticipation of the trough re-setting further west in the Atlantic and an erratic evolution to rise in pressure from the south and east is still in the extended period. Still hampered at present by the  long term legacy of the easterly wind zonal wind anomalies at higher latitudes but this should continue to very gradually abate.

The medium term retrogression of the pattern, as momentum slides back c/o increased trade winds across the Pacific (shaded blue on Hovmollers)  c/o convective suppression (shaded orange in the velocity potential forecast) has replaced the recent active passage of a convectively couple kelvin wave (CCKW) - and is the precursor to  upstream amplification backing the trough west before rising momentum then starts to build more of a downstream amplified ridge response in the very extended period. 

 The stubborn long term enduring -AO feedbacks are the fly in the ointment, but continued tropical convective activity should start to strengthen sub tropical ridging as seasonal wavelength changes act to weaken the polar cell as summer rapidly approaches.

 Timing of such a change is rather low confidence at the moment but the end period of May and into June remains consistent with cautious thinking

Bom dia - saudação feliz do ensolarado Portugal

Timing of such change for the better proved highly concordant with the official curtain raiser to summer, and just as I was preparing to leave the UK this week. Sitting looking out over palm, citrus, loquat and olives trees, and the rows of vines shimmering in the sun and heat of the day, its also nice to take up (for now) a very brief perspective of the way forward for the first phase of summer.

As outlined in previous posts, it been a classic situation where seasonal wavelength changes and rising momentum create poleward fluxing of rossby waves which in turn beef up sub tropical ridging and encourage summer-time migration of the jet stream.  

The strength of tropical forcing, and associated poleward migration of jet eddies, set against a much more sanguine and stable polar field profile,  allows the expansive eastward propagating mid latitude ridging and is sufficient feedback to ensure a lot of fine summer weather for a broad spectrum of Europe - warmest/hottest further west and south for much of the coming month..

Its a case of monitoring the tropics for weakening of tropical forcing allied to seasonal trade wind activity which might create retrogression of the pattern and a more widely changeable pattern for NW Europe (still hot and sunny further south), but if it happens at all, this looks quite some way off and worth being cautious of model tendencies to try to be too progressive with such a trend in the medium term, only to re-adjust the pattern back eastwards. Any such signal is more a thought process heading into July, but all a long way off, and with no worthwhile rationale for analysis of any kind at this time

35C expected across much of central and southern Portugal (and Spain) this coming week as the early summer heat builds - which is not unusual for these parts in itself, but it is still quite a change from a distinctly cool Spring (relative to normal), that evident even in this part of the Mediterranean, even if obviously nothing like the UK and NW Europe..

Feliz Domingo

 

 

[Model output discussion 9th April onwards]

24 minutes ago, CreweCold said:

I’ll be shocked if we see HP to our E for any significant amount of time this summer. Pretty much every long range model places a mean HP anomaly just to our west. 
 

Also important to remember that any rising AAM signature is no guarantee of HP settling over or to the E of the UK (which is where heat lovers would want it).

Remember, 2007 was a highly amplified/buckled jet pattern...it didn’t improve until the jet flattened later in summer (towards August)...when AAM went negative?

We’re best off waiting to see where we are come early June. If we’ve settled down then early summer could be useable and decent. If things are still unsettled then I think we could be looking at a cool, wettish summer overall. 

Boa noite

A few things:

There is no prediction in that post for sustained ridging over or to the east of the UK/NW Europe for the summer as a whole - indeed that post was not a  definitive actual forecast at all. Merely an assessment of probabilities that balance the reasonable chances of a mid latitude pattern against any pattern dominated by unstable polar profile and supressed jetstream. The latter being a combination that is perpetuated  by a low angular momentum regime allied to easterly QBO phasing.

The explanation and differences between the regimes were explained in detail and should not leave much ambiguity. Angular momentum collapsed on cue in early summer 2007 allied to rapidly increasing QBO feedbacks assisting downwelling of blocking mechanisms into the troposphere at higher latitudes.  Current indications suggest the opposite trends in the atmosphere for the start of summer and no descent into a significant La Nina event, such as happened in 2007, to drive such a pattern further forward. Rather, the atmosphere is being led by an adjustment a little further eastwards in tropical convergence which should aid a rossby wave pattern that allows sufficient eastward ridging of the Azores high to provide some settled warm summer spells for NW Europe.

An unsettled start to June would mean nothing at all for the greater summer either. Its all about the direction of travel of these wind-flow budgets and how they respond to seasonal wavelengths. Its not anything black and white in terms of x+y =.

This is unlikely to be any typical El Nino led summer pattern where the Azores high actually plays a lesser part, and ridges across Europe and Scandinavia fully dominate and set against thundery trough interplay to the west, but  more a half way house position that is simply aided by convective convergence in the tropics being far enough east to discourage Nina-esque dominant Atlantic blocking and downstream trough. However, once again to balance that out, when talking about seasonal probabilistic, it certainly doesn't rule out plume scenarios either and it would be quite surprising if these didn't crop up at some stage. Especially, as the previous post intimates, if we see active tropical convergence trying to push into the Pacific through the greater part of the summer

At the most 'optimistic' end of the scale, a summer such as 1995 after all benefitted from an eastward displaced convection standing wave arrangement in the tropics within the context of the legacy of a weak La Nina regime. Though this summer may indeed struggle to reach those sorts of levels - at least for NW Europe. However, as stated, this is all about probabilities at range, and not about definitive predictions whether they are, or are not, driven by preference biases.

Obrigada. Cumprimentos.

 

 

[Model output discussion 9th April onwards]

13 minutes ago, Backtrack said:

Dropped a Tweet to Aidan McGivern earlier (Met forecaster). He tells me they are seeing signs of higher pressure dominance towards the beginning of June in the longer range models. 
 

 

Significant that there is increasing confidence in the tropics staying alight as Spring wavelengths switch into Summer.....

Tropical convection modelling is teeing up another substantial MJO event to coincide with this cusp period and that bodes in favour for substantive tropical> extra tropical torque inertia to boost burgeoning sub tropical ridging building to the south.

As soon as the coming week, my newly adopted home country is showing 'summer proper' establishing with pronounced Azores ridging. This coincides nicely for holidaymakers, but also for the likes of me who is not a holiday-maker but is embarking on a one way drive down through France and Spain in time to meet residency requirements for the beginning of June.

This building of summer heat is the first essential piece of the jigsaw for NW Europe who is having to wait and endure another couple of weeks of cool and unsettled conditions.

This brings us back to the switch towards summer wavelengths and the importance of the direction of travel of the atmospheric circulation between the tropics and extra tropics.  Many of the worst summers have seen collapsing momentum budgets within the atmosphere coinciding with these seasonal wavelength switches. This Spring/Summer switch suggests rather more the opposite trend.

Rising angular momentum and corresponding poleward torque inertia  from the tropics into the extra tropical circulation wind-flow should have a profound mitigation and weakening effect on the polar feedbacks that have been perpetuating the Atlantic and Greenland blocking regimes by instead, beefing up sub tropical ridge extensions towards mid latitudes. The initial effect of this process is the strengthening of the temperature gradient as the heat line over lower latitudes seeps northwards to engage the stubborn pools of polar origin air, and feeding yet more lows tracking at the initially supressed latitude relative to more northern parts of europe, and so perpetuating the poor weather across those more central and northern parts of Europe.

However,  as the tropical forcing increasingly engages the extra tropics further, then the amplification of sub tropical ridges become more poleward (rather than  top down from the pole in basic language) and the jet stream eventually gets incrementally kicked and forced northwards with time

Another factor in play behind such a switch is the QBO and angular momentum relationship vs solar forcing. Some of the poorest summers have seen collapsing angular momentum in late May at the same time as the QBO phasing has switched from westerly to easterly, or has at least embarked on a weakening westerly trend.  Low solar forcing in tandem with low momentum tendencies and trending easterly QBO phasing augments the circulation of ozone at higher latitudes - perpetuating blocking in these regions and across the North Atlantic. Seasonal wavelength changes intensifying this regime by sustaining  cyclical retrogression, rinse and repeat of this pattern. Numerical models could become a cropper if they try to persistence factor the deadlock too far into this seasonal switch.

Late Spring 2021 sees robust eastward propagating tropical convection leading to boosted angular momentum at the same time as westerly QBO phasing erratically weakens under a low solar regime......

QBO:

2021  Jan 10.19 Feb 8.92 Mar 9.75 Apr 5.25  

QBO Calculated at NOAA PSL 30mb zonal wind at the equator, zonal average For info https://psl.noaa.gov/data/climateindices/list/ units=ms-1

 

 .......The direction of travel in late Spring 2007 for example saw (rapid) westerly to easterly QBO switch but crucially also saw collapsing angular momentum heading into summer and which sustained downwelling of easterly zonal wind anomalies into the troposphere. With rising momentum however, amplified rossby waves under active tropical convection conditions are more likely to produce amplified mid latitude ridging. Seasonal wavelengths heading into summer acting counter to retrogression of these ridges under more buoyant angular momentum conditions.

This is very much the crossroads.  As long as there is no shortfall or unexpected failure of eastward progression of high frequency tropical convection, then a pattern flip gains parallel momentum and the effect of seasonal wavelengths under this regime is to counter intuitive to cyclical retrogressing Atlantic blocks and adjusts blocking anticyclones eastwards over or to the east of UK and other western european countries. This trend becoming greater through June and into July (assuming the background trends are maintained)  Meantime accumulated seasonal heat in countries such as my new home provide the supply line heat advection pump

[Model output discussion 9th April onwards]

On 09/05/2021 at 09:10, mb018538 said:

 

This AAM forecast doesn’t really tie in with a big trough in NW Europe. I’d expect to see something more settled appearing soon.

 

On 08/05/2021 at 22:01, Mike Poole said:

ECM clusters T192-T240:

 

There’s a lot of them, but picking the bones out of that, seems a tendency to retrogress the trough back west of the UK.  The later 240+ chart:

 

…looks inconclusive so we wait a while more for the first hint of summer proper on the models…

Both these posts compliment each other in terms of the longer range. The detail behind them of which was discussed in a previous post of mine. However changes for the better are outside of the   current 10 day period.

However, as far as NW Europe is concerned and specifically the UK from this threads viewpoint, anticipation of the trough re-setting further west in the Atlantic and an erratic evolution to rise in pressure from the south and east is still in the extended period. Still hampered at present by the  long term legacy of the easterly wind zonal wind anomalies at higher latitudes but this should continue to very gradually abate.

The medium term retrogression of the pattern, as momentum slides back c/o increased trade winds across the Pacific (shaded blue on Hovmollers)  c/o convective suppression (shaded orange in the velocity potential forecast) has replaced the recent active passage of a convectively couple kelvin wave (CCKW) - and is the precursor to  upstream amplification backing the trough west before rising momentum then starts to build more of a downstream amplified ridge response in the very extended period. 

 

The stubborn long term enduring -AO feedbacks are the fly in the ointment, but continued tropical convective activity should start to strengthen sub tropical ridging as seasonal wavelength changes act to weaken the polar cell as summer rapidly approaches.

I am not one at any time to read too much into individual ensemble sets, let alone operational output, ,but purely as an example of the type of evolution that matches the diagnostic thoughts discussed above - the latest GFS 06z operational happens to play out this script. Its not important at all at this time how it sits in ensemble data because too much of NWP will be blindsided by the current suppression of convection across the Pacific allied to the -AO feedbacks. It is though the type of evolution to keep in mind for the very extended period.

 Timing of such a change is rather low confidence at the moment but the end period of May and into June remains consistent with cautious thinking

[Model output discussion 9th April onwards]

17 hours ago, CreweCold said:

I looked at the EC seasonal about 15 minutes back. Striking HP anomaly just to our west...which would suggest mundane summer fayre...pretty bland with the chance of some cooler incursions if troughing becomes stronger to our E and the HP ridges N at times (I suspect Icelandic/Greenland ridging may feature at times)

For those in the UK this summer, I think that is a good enough signal, at that range, based on the increasingly likely potential evolution of tropical and extra tropical forcing driving the atmosphere and the equally increasing likelihood of stratospheric downwelling of the troposphere losing its stubborn grip on the hemispheric pattern. Its very much a mid latitude Azores ridging pattern and not a top down arctic heights ridging pattern - such as has dogged much of Europe for quite some time.

That makes a lot of sense in my view - with every indication of tropical convection remaining active and edging the rossby wavelength a little eastwards and keeping an amplified profile - BUT at the same time as Nina-esque forcing and residual stratospheric instability wane (and by dint of that the former also stops perpetuating the other).

If we see cloudiness and thunderstorm activity increase once again across the Western and central Pacific heading into the latter part of May and into early June, and as the ferrel cell gains its early seasonal supremacy, then look for sub tropical ridge extensions to increasingly drive the jet stream further north and west , displacing the trough somewhat accordingly. Angular momentum is poised quite nicely at present (NB: heading at present into the 'wane' part  of the tropical>extra tropical cycle which means AAM is falling back, temporarily, and retaining the trough solution across NW Europe into the medium term). However, the next upturn c/o renewed eastward propagating tropical convection, should see the extra tropical Global Wind Oscillation, a phase plot depiction of hemispheric wind-flow, re-orbit  towards a higher amplitude Phase 4 (the signal for mid latitude ridging in tandem with a more stable stratosphere than Spring to date)

Again taken at face value and subject to usual caveats as added, but according to plausibility as outlined above - an average. sometimes warm pattern looks indicated from that seasonal outlook for many N and NW parts of Europe with some good fine spells. It doesn't smack of plume generated heat and with relatively low humidity probable - but many would very happily settle for that I would think this summer as restrictions ease and it is quite some improvement on the awful Spring conditions many have been enduring.   

It does look a potentially hot set-up for those of us further south in Europe  on the southern flank of ridging with a lot of heat building in situ - and heatwave territory. Mediterranean heatwave territory takes on another level to UK/NW Europe standards and it is as well, should that scenario verify, that procedures are already in place, as per the the annual calendar, to make sure large clearance of tinder box undergrowth is undertaken ahead of the heat building to reduce fire risks.

[Model output discussion 9th April onwards]

42 minutes ago, Mike Poole said:

ECM clusters T192-T240:

1-4 have some kind of block that might flood certain parts of the country with southerly winds for a while at the earlier timeframe.  Later T264+

1-3 potential for the start of summer maybe, by T360 anyway, a small signal but it should grow I think as AAM rebounds:

Caveat needed, AAM plots are from the same models that are fallible beyond 4 days.  This is why I’m not as sure as some that AAM is the best predictor of future evolution.  It seems to me it is predictable by models that might quite as well be wrong.  The only AAM prediction i get to see is the CFS and we know how that compares to chocolate teapots.  I persist with looking at, and learning about, AAM because I do believe it has some predictive capability but it can be overstated.   I prefer to look at it in the line with seasonal modelling, but giving the seasonal modelling the majority weight in forming my opinions, and conclude from both that a major warm up in mid-May is due, and that it won’t be a direct high pressure hit, so that means some hot humid weather with thunderstorms to come in to summer proper.  

We will see…

 

 

There is a simple answer to that, which is not intended at all to be a clever offering It is simply that a numerical model interpretation of AAM  (atmospheric angular momentum is a representation of the turning force of the jet stream) evolves and changes with time and is prone to bias errors over increasing time scales. It is a forecast interpretation, that evolves and changes according to those biases - but it is not the raw diagnostic.

The diagnostic model leads the numerical model, not the other way around. That is why the Global Synoptic Dynamical Model plots exist (GSDM) . They are totally  independent and separate from numerical model forecasts of AAM that are the derived and sometimes flawed interpretations. The numerical AAM forecasts simply provide insight as the how these models interpret jet stream patterns at a given snapshot of time.

A diagnostic model is divorced from model biases - it is a raw consolidated real time calculation of global wind-flow inertia (i.e the changes of the path and velocity of the jet stream) and intended to be used independently of NWP forecasts as an insight as to how numerical models may evolve (and change according to their biases and misreading of signals).

A constant repetition with no apology - signals lead models, models do not lead signals...

As things stand, and according to analysis given earlier this weekend, the first hints are coming that both the atmospheric circulation pattern and changes in seasonal wavelength patterns are starting to adjust the amplification wavelength across both the Pacific and Atlantic. Some retrogression of the pattern is actually a very good thing at the moment for many part of Western and central europe (including also many western Mediterranean regions) because it starts to allow sub tropical heat to finally advect northwards and repel the incessant polar cold air advection that has dominated for so long.

For NW parts of europe and especially the UK on the maritime edges, this is not likely to be seamless warm up. So wise to not see any step change warming up from such a low base as a linear process to sustained warmth but as a staged transition.

However,  assuming that the direction of travel of both tropical and extra tropical forcing remains buoyant as discussed in detail the other day, and adheres to a non dynamic ushering in of the polar stratospheric summer - then there is a way out of the anomalously cold pattern for Northern Europe and which would also represent the first experience of sustained seasonal heat for someone like me who has not embarked on a holiday, but is permanently relocated in her new home - and will need to adjust a way of life to some lovely siesta time 

[Model output discussion 9th April onwards]

Boa tarde

Its a synoptically intriguing Spring-time situation with the atmospheric circulation, 'c/o tropical and extra tropical wind-flow cycles, still clearly 'remembering' the patterns of mid to late winter; at the same time as seasonal wavelengths in tandem with what *looks* like a standard fading away of the stratospheric vortex start their make their imprint over the weeks to come. However confidence in this needs to further gain traction in the weeks to come.

What is meant by 'remembering' in this context? There are known periodicity timeline recurrences with tropical and extra tropical cycles and when these both combine to produce strong wind-flow signals (high amplitude forcing) they often have a profound amplification response globally - and especially when the winter-time stratospheric feedbacks have been highly unstable as they have been over the winter of 20/21. 

The feedbacks of these tropospheric and stratospheric forcing elements can produce a 'shockwave' response within the broad-scale patterns lasting through extended  intra-seasonal timescales  That has been very much the case in this first quarter of 2021.. Awareness of these cyclical responses can be very useful in terms of anticipating amplification potential - even though it cannot be possible, at distance, to pinpoint more geographical areas in terms of pattern/weather detail. Its very much the case of whether the significantly unstable relationship between the stratosphere and troposphere can evolve through a more seamlessly benign final warming process and then couple with the encouraging adjustment of the rossby standing wave further east within the tropics to reduce retrogressive shifts in blocking and which retain cool air advection process risks - at least for more Northern parts of Europe.

Global atmospheric angular momentum has mirrored the dynamic nature of the atmospheric response to amplitude cycles of the intra-seasonal MJO cycles. A convectively coupled kelvin wave  (CCKW) within the tropics has added westerly wind-flow inertia propagation between the tropics and extra tropics c/o torque responses and the atmosphere has accordingly 'remembered' the similar passage across the Pacific Ocean that occured in February and simulated a further blocking response-  (the one in the first half of February augmented  through the fall-out of the January SSW effects within the troposphere and the strongest downwelling tranches of -ve zonal wind anomalies.

CCKW:    As reflected on the MJO RMM track and forecast  .

= upward movement back to average levels in globally averaged AAM. Notice the much more profound effects c/o the greatest stratospheric/tropospheric instability in Feb 

As the CCKW completes its tropical cycle, and the high frequency signal returns to the Indian Ocean - then this is the signal for a return of greater easterly inertia within the atmospheric circulation and angular momentum tendency easing back again accordingly.  Interestingly, this forcing acts to retrogress the troublesome blocking signatures at mid and higher latitudes sitting to the NW - and in the  short medium term invites a supressed jet stream across more northern parts of europe but also cuts of the ingress southward of polar originated airstreams and restrict them further north than seen for quite some time.  Whether advancing low pressure systems can stall sufficiently and allow warm air advection processes as far west as the UK is debateable, at least to begin with. But it is the first step required to shift the paradigm of blocking away from cold air advection for NW and central Europe. 

Further south,  across many SW parts of Europe a downstream ridge response settling the weather down after recent showers and thunderstorms.

For late Spring/summer interest much depends on continued active tropical>extra tropical forcing at the same time as seasonal wavelength changes act on demise of the seasonal vortex to set a more traditional summer pattern response. If this response is non dynamic, and if tropical convection shows signs of continued trend to want to push convergence (and associated westerly wind inertia) further east across the western/central Pacific, then its conceivable a less Nina like standing wave could lead to greater downstream amplification. rather than innate Atlantic blocking (the latter being La Nina-esque) 

What is key for summer prospects, mainly for Northern Europe including the UK, is that  the relationship between the troposphere and stratosphere is a benign one to assure such ridging at mid latitudes (Western Europe into Scandinavia) - and not persistence of further retrogressing blocks across higher latitudes.  Further south across europe into the Mediterranean ,the implications are more surrounding dryness/wetness and whether more extreme heatwaves are likely relative to usual warm/hot temperature regimes. At least as measured /compared by UK standards.

Latest indications based on tropical>extra tropical forcing adjusting to a less Nina-esque default ,suggest that a more stable mid latitude pattern can still emerge and produce the welcome warm-up that many parts of NW (inc UK) and central Europe are looking forward to with restrictions looking to ease hopefully for the summer. However (there usually is one), May is that pivotal month in the same way as November and into December is in terms of gauging propagated rossby wave extra tropical forcing from the tropics vs seasonal wavelength changes. Time will tell how quickly the atmosphere will be willing to start to evolve away from and to 'forget' the imprinted highly robust dynamics of the stratospheric/tropospheric relationship in the fist quarter of 2021. That is an answer that I expect professional analysts will not have a good answer to at this stage, let alone me or any other interested parties of laypeople

[Spring 2021: Moans, Groans, Ramps and Banter.]

21 hours ago, Scorcher said:

I get wanting snow between November and March...although I'm not keen at any time of of year.

Normally I could tolerate late snow more but with this prolonged lockdown I'm desperate for a long sunny, warm spell as I know the vast majority of the public are.

Many are fascinated by potential damage to plants on this forum which is one of the things I don't understand- that is what concerns me most about Monday and Tuesday.

Yes indeed. It gets forgotten that there are people who view and partake of this site who are actually also ordinary members of the public and not just 'weather enthusiasts'.  Its good to be a weather enthusiast, otherwise why be here? But at the same time  surely retain a grip of the outside world and its outside perceptions and remembering that we all come from such a place - and not some detached idealistic fanaticism time-warp.

Quite apart from having horizons in another country, and a geographical switch of interest, a main reason for distancing from the parochial preference biases within this site is the Neanderthal and tribal attitude towards the subject of meteorology - that would be far better suited to the bearpit of a testosterone fuelled sports bar.  Recent posts on this thread, along with the traditional caveman brawl in the MOD thread, are very good examples of this.

There is, alas,  too little interest in the 'hows and whys' and far too much of a repellent, unsavoury and divisive 'war' over weather preferences. Too often, its a macho club membership/playground, rather then grown up weather discussion.  Objectivity can be a redundant and wasted pursuit within this context. Unless of course it just happens to accord with the tribal preference.

I used to get excited about the prospect of cold weather and snow (at least in winter). But equally always have had (and now to an even greater extent) a large appreciation for sunshine and warm weather - at any time of year but most especially from Spring right through to Autumn  Also, following a period of thunderstorm phobia due to one very severe storm that created a lot of local damage within just a mile away and was a truly frightening experience - a return has come to marvelling at the spectacle of an evening light-show while enjoying some wine on a summer evening (just as an example)  The point is, that any preferences are valid as long as no-one attempts to impose them on anyone. And, as in my own case, its also fine of course to change those preferences at any time.

But here comes one of the main problems, at least in my own experience :

Curiosity has grown about the actual weather patterns over successive years  (the how's and whys) and began overtaking the increasing boredom with just staring at charts waiting for a weather preference which too often than not does not come on its own - and which inevitably then leads to having to wade through pages of emotional tantrums over 'weather failures' and the associated bickering that comes with it.. 

Through the same period of time,  appreciation and reminder of the value of being outdoors more and more - and how Mother Nature better speaks kindly to (just for one example) my own love of plants and the garden has increased appreciation further still of the spring and summer seasons with the long days and warm evenings that are possible - at the same time as long dark days in winter and lack of sunlight overtook and eroded enjoyment of any previous pursuit of the magic of snowfall.   That doesn't mean anyone who thinks differently is wrong - but significantly in this respect, its the tribal 'warlike' attitude, from too many (not all by any means) of the cold weather legions which became a push away from wanting association with it  - and amplified the natural reasons for further increase in appreciation for Spring and Summer.

 Natural enthusiasm for a weather type is fine, but only goes so far - some (not all) try to disguise and at the same time kid themselves that they are not actually instead displaying undue and excessive fanaticism and obsession. Fanaticism and obsession is characteristic of intolerance and apparent contempt of anyone who thinks differently and manifests as wholly unreasonable attempts to dictate and impose manic views ,ideals and preferences. Hence the Neanderthal 'warlike' attitudes that are common-place. 

As I see it, a weather preference coming to reality is a bonus to such a pastime of looking at how's and whys of meteorology. That, rather than a preference bias being the be all and end all - which too often leads to disappointment and frustration if too much dependence is attached to it and there is no stepping way from a computer to break the mindless spell of it all. There is much more to life after all than chasing computer model fantasies.. It is somewhat symbolic of such parochial tribalism though, that such weather preference symbolism has become attached of late with the fairly imminent  re-opening of the pub!  That fulfils the sport bar analogy of earlier. 

You are probably better to sit tight and wait for the weather to change - and then just enjoy it on your own terms and not worry about those who see it as 'boring' or somehow not exciting enough to make you a member of the so called 'enthusiast club'  Its pointless trying to reply to, or reason with, such tribe members  - because, as you and one or two others have observed, there are some quite aggressive primates and they are probably best left to learn basic manners in respect.

[South East, London and East Anglia regional discussion - 8th February onwards]

During the older regional thread days there was a very short period of meetings between a few net weather members which also included Jan-Bromley and one or two others who do not post on this thread anymore. Anyway, during that time I got to meet Antony, who, (most understandably) was not pre-disposed to wanting to meet other people - so it was a compliment to me that this happened. Despite the effects of HD, which already affected his speech and balance and care needed with swallowing food - I was amazed at the mental strength of him and with a sense of humour and strong perception that was admirable in the face of such acute disability. He had apparently also been quite a sportsman before the condition took hold and still had an obvious determination to try to keep active as much as possible. One of the most instantly likeable people one could meet - so after all this time later, this is very, very sad news. RIP Antony x

[Model output discussion 10/02/21]

At the moment, the numerical models are reading diagnostic signals well

Global relative atmospheric angular momentum continues to operate deleteriously to the La Nina base state.

 

However, as suggested was the signal to end last weeks cold spell, extratropical forcing lost the ammunition from the tropics to sustain the upstream forcing to hold that higher latitude blocking in situ as extra polar jet energy forces a more mid latitude downstream ridge and Atlantic fronts are able to make ingress. Meanwhile further south towards 'home to be' some quite delightful Spring-like weather is being enjoyed, and as a very pleasant flavour of the much warmer months to come.

The switch in upstream forcing, as predicted in a previous post, has come about through steeply falling angular momentum tendency as rapidly weakened tropical forcing within the Pacific cuts off the poleward propagating eddies migrating into the extra tropics. This, at the same time as some stability/re-organisation returns within the polar field.

 The Global Wind Oscillation is responding accordingly and, based on two/three day consolidated lag data, is completing an orbit across the El Nina attractor phases on destination towards 'transitional La Nina' Phase 8 -  signifying rapid scrubbing of +AAM anomalies from the atmospheric circulation

 

Putting all this together, and in the face of no real signal for further renewed tropical forcing in the foreseeable future, then a mid latitude pattern has strong medium to longer range support. There should be some pleasant early Spring sunshine likely at times, in between rain-bands - the latter more particularly earlier within the 10 day period.

Hope-casts/avid expectations of renewed ridging to the north and east in the extended period, *should be* set objectively/tempered c/o the lack of tropical forcing and adopting a sanguine approach to long range numerical modelling signalling of a further post SSW downwelling wave twitch - of which the GEFS most particularly can tend to exhibit over enthusiasm.

That doesn't mean such modelling is certain to be inevitably wholly wrong - further cold weather of course cannot be discounted, as perhaps manifested by back door cold air advection on the southern flank of mid latitude ridging (for example) - but while Met Office updates tend to be overly reactive to numerical modelling vicissitudes in respect of  interpreting diagnostic signals, there is some sense to their current expectations that any such possibilities would very highly likely be moderated in comparison to those of early to mid February.  At the very least.

Stronger isolation and longer days one obvious factor - though its known that deep cold air origins can overcome such mitigation for a time yet. With that in mind, the other reason, is because the longer time goes on, then any residual lag (if there is any) from the winter-time weakened stratospheric/tropospheric state fades out. This most especially hastened/mitigated in effects due to the tropics and extra tropics  becoming more hostile than previously towards supporting the mountain torque mechanisms that induce momentum transport of rossby wave packets to assist destabilising the polar profile once again. Such destabilisation clearly has to be proportionately stronger to support sustained cold air advection far enough away from an arctic source, the further time heads into the early new season

There are those who would indeed like that to be the case, and it is not unrealistic that sunshine by day and some frosts by night within calm centres of anticyclonic conditions might be the ultimate outcome, for the UK latitude anyway..

[Model output discussion 10/02/21]

Welcome to (actually from) Portugal

 

 

[Model output discussion 10/02/21]

Posted 6 January 2021

 

*The further wildcard is intraseasonal MJO forcing. In keeping with w/BQO Nina-esque regimes, and linked to known periodicity timelines for high frequency activity - it is worth watching out for signs of an eastward convective parcel progression attempting to negotiate the Pacific later in January or possibly into February.    A further variable that could see a sudden and quite dramatic surge in atmospheric angular momentum, tipping the resultant synoptic patterns even more their head.     Impossible obviously to know where and when these may set up hemispherically at this stage - but high impact synoptics are conceivable with very large temperature boundaries across the mid latitudes.

 

Purely from a diagnostic weather pattern study point of view, its well worth re-visiting this concept of periodicity timelines for high frequency tropical forcing impacting the extra tropics and creating large scale synoptic impacts. That surge in atmospheric angular momentum duly materialised within the envelope of time suggested - the difficult part, knowing how interaction at all levels of the atmosphere (i.e the troposphere and the stratosphere) would translate into synoptic probability solutions. Objectivity usually points to more than one probability outcome - but what the diagnostic can do so well is provide some clues quite some time ahead of potential of high impact weather of one kind or another - when longer range sinewy strength momentum transport exchanges between tropics and extra tropics are identified at that longer distance.

The summary of January discussed the distinctly southward shifted thermal gradient across the Atlantic and into Europe as an expression of the suppressed jet stream pattern of the winter. After all, on the Iberian continent, where I am making my new home this year, such suppressed jet patterns evidenced the record breaking snowfall and intense cold that impacted Madrid and other central parts of the continent, and also provided extremely rare night time frosts and sub zero temperatures at my adopted home an hour from Lisbon in Portugal. Much more typical temperatures and weather conditions have long since returned. Looking forward to ultimately enjoying them myself.

Large scale deposits of poleward propagating momentum have been evident along 30N c/o robust western and central Pacific tropical convection activity convergence. Cue the rigorous surge in AAM tendency as anticipated during the first half of January for this time period. Propagation of these poleward  AAM eddies has been the product of  strong mountain torque mechanisms within the extra tropics, and further perpetuating a weak and disjointed polar profile.

 

Global total relative AAM has adopted a +2 standard deviation countervailing aspect to the La Nina base state. The Global Wind Oscillation, a plot depiction of hemispheric wind-flow inertia, has accordingly also exhibited a marked contra aspect to La Nina , and soared through the transitional phases into El Nino attractor Phase 5. An emphatic wind-flow signal reversal, red flagging a Northern Hemisphere sudden swamping of poleward eddies carving out large scale amplification - and this downstream amplification rooted at higher latitudes due to this seasons inherent instability within the polar field.

The background La Nina state is about to re-claim the wind-flow budgets with scrubbing of this avalanche of westerly inertia, and this is a cue for a drop in angular momentum tendency, polar jet energy to head downstream and pressurise the amplified blocking high and, so through processes of attrition this weekend start to ease the bitterly cold conditions across NW Europe. For a few at least, this respite is to be welcomed - especially any who had originally anticipated being in Southern Europe by this time.

Signals from the tropics look more muted than of late looking ahead - and this influence should gradually tend to shift blocking mechanisms more and more south with time and also as influence from the weakened stratospheric state begins to lose its grip. So the majority on this thread who are waiting on another freeze will have to see how much is left in the stratospheric downwelling reserve as to the appearance, and more especially sustainability of another cold blocking high. There is also a reasonable chance that a more mid latitude anticyclone might persevere which for these particular latitudes implies chilly end of winter & very early Spring conditions but dry at least and pleasant enough with the longer days and strengthening sun 

 

[Model output discussion 24/01/21]

1 hour ago, chionomaniac said:

I had to read your post a couple of times, Tamara and thank you for replying. I do think that the real advance of coming to terms with how tropical responses can affect longer term mid latitude outcomes depends upon being able to make structured forecasts (not punts) on the tropical base states. Otherwise we can become experts at retrospectively analysing tropical events but useless at forecasting based on these events. Surely, the reason in understanding GLAAM, and responses to these events is to give us a stronger capability to forecast further ahead than we would ordinarily be able to, based on them. If we can’t then is there any point? I suspect that it make take some time and a number of years before this is possible, but it would be great for someone who has such great knowledge to be able to move us towards that next stage forward.

And as you know, as you were analysing the Jan 2009 SSW response we were fortunate to get the immediate response from the split vortex but longer term underlying tropical imprints may have overridden the strat in prolonging the response. So much to learn, and I look forward to the day when you feel more confident to predict the mid latitude response to tropical events to a specific outcome.

It was you who asked me to push the boundaries to paraphrase your own words as if it was a life changing decision (which it clearly isn't because it is a discussion with strangers about the weather) and to make 'a punt' - and I did, did I not? Even if the request seemed a little surplus to requirements from what had already been said and it smacked of some kind of fishing expedition - which this latest reply demonstrates it indeed was. You turn around the last chance saloon request of a 'punt' into a volte face and talk about structured answers - which I actually gave.... Even if it wasn't the response you were, self evidently, looking for..

I am not under (your) self appointed examiner rules to 'feel more confident to predict the mid latitude response to tropical events to a specific outcome'.  Perhaps you need to read my post a couple of times more, (and some), and try to respectfully understand the point it was making because I tried to genuinely respond to your own question today of a few days back and took the time to do so when, frankly, I have much better things to concern me than pandering to a chionophile who in essence wants a structured punt to tell him its going to get cold and snow....

I now (equally genuinely) wish I hadn't bothered. Boa noite.

 

[Model output discussion 24/01/21]

Posted by chionomaniac last Saturday:

Just reading through your post, and the one thing that I notice is that despite the drop in GLAAM, and a reduction of the more Nino-ish December response, we have yet to see a traditional Nina H500 pattern to develop. I suspect that we have to grateful for the SSW for that - not only for well recognised polar and mid latitude responses, but also the feedback indirectly to tropical regions. I know that there are those who are far more qualified to put more meat on the bones regarding this than me and there have been a number of papers on this in the last few years, but it is another wild card thrown into the equation.

And, if you had to, and your life depended on it, what would your punt for February be? After all, you have spent years on research of mid latitude responses to tropical forcing, it would be great to see the end product of what you consider more likely. One of the reasons, that I suspect you don’t or can’t ( you are not alone) is the lack of forecast data in this field. This would help a lot. When looking at the data, it is recording what has already occurred and the MJO forecasts are reliably unreliable. This makes commentary on what has happened far easier than being able to predict in the mid range. 

I think that the sooner that we can get more pieces in this jigsaw, the better.

-------------------------------------------------------------------------------------------------------------------------

 

The H500 pattern has been very consistent with a Nina response. The crucial aspect, as you allude to, is that it is a Nina response in tandem with a disrupted stratospheric profile. 

At least a couple of previous posts have commented on the upstream pattern switch to Aleutian heights in response to the GWO moving into the Nina attractor phases heading into the second third of winter. The GWO, phase depiction of global wind-flow within the tropics and extra tropics, being a precise barometer of tropical>extra tropical pattern response on hemispheric levels.

Amplification within the Pacific, very characteristic of La Nina signature, pushes inertia into the downstream polar jet, which is exactly what we have seen. However, the disjointed zonal wind anomaly within the polar field, leading to very weak and erratic flow, has meant that the usual (traditional) downstream response of jet stream flow has been rather blockaded with the result of southward and equally fractured flow rather than the flatter zonal flow across the North Atlantic seen under a more traditional response. Hence the shallow tropospheric 'cold' ridges that have disrupted low pressure systems in the way that has been seen. Nonetheless, there has still been just enough inertia to keep the pattern relatively flat and 'faster' than under a more meridional downstream Nino-esque regime

As the response to a post below also suggests, this diffuse stratospheric>tropospheric response is not new, and was seen to an extent following the SSW of late January 2009 - during February 2009. There were very strident immediate expectations following that particular SSW, but the combination of La Nina and w/QBO at that particular time of the solar cycle provided a much more diffuse tropospheric response than the  subsequent bookend part of the year which saw a classic Nina-esque stratospheric pathway during Dec/Jan/Fed 2009/10. Indeed, the response to the SSW of Jan 2010 was a more 'classic' cold pattern response than that of a year previously. The first part of the season was troposphere>lower stratosphere led (and actually the deepest cold weather of the season) before the upper part of the stratosphere warmed considerably and maintained the unstable (cold pattern) tropospheric pattern of the first part of the winter.

I think for the weather pattern observer those two seasons, a decade back, is a reasonable case study that gives some clues as to the manifestation of this winter (but with further added climate forcing another 10 yrs on - though that is not for this thread) That is the closest I would get to any 'punt' And for good reason, quite apart from not having the same weather preference motivation for specific weather type as most other.

With  all that in mind, and notwithstanding the credible correlations of the comparisons  - one thing that has been learned over years passed -  is there is no one size fits all response and each situation/pattern/set of variables have to be taken on their own merits. That also leaves making 'punts' a little redundant from my point of view. Whilst not a forecaster (and just one of many reasons not to be) is that analogue pattern matching, however unintentionally, tends to be skewed by bias confirmation as well as the added superimposed forcing on the climate which has distorted feedbacks, year on year, across the tropics>extra tropics and at the pole.  However, the GSDM still remains a highly worthwhile aid to diagnosing the vicissitudes of numerical modelling and the inherent biases of these models. What you get with a global wind-flow budget remains a precise measure of inertia within the hemispheres at any given time, which inclusively calculates the superimposed forcing that is almost insidiously being added year on year.

One good reason why so many tropical (MJO) and extra tropical (GWO) phase composites need to be readily updated as a perpetual 'work in progress' to take account of pattern responses according to the ever more volatile wind-flow profiles according to progressive broadscale warming trends.

 

2 hours ago, winterof79 said:

Any thoughts on Matt Hugos comments /gifs and trends? 

Its that stuck record once more but any comments related to trends have to take into account all probabilistic outcomes and not just the one that human intervention would like to steer towards.  As stated above, recent summaries have commented on the diffuse weaker than average westerly gradient of this season and, stripping away all the repeated detail and analysis, the likely outcomes as being a N/S or NE/SW divide. That suggestion has continued to play out and remains well advertised in the further outlook. - if one takes out the usual speculative outputs that tend to catch the eye on this thread and are given maximum exposure  The disjointed and rather unstable polar profile should continue to steer low pressure systems on a more southerly track and invite some cold air advection in their wake, with more northern latitudes seeing these the most. However, the continued expectation for the MJO to be a magic bullet to a definitive  sustained cold block requires greater objectivity as (keeps being repeated) it is not as straightforward as x ingredient = one specific y outcome.

There is no doubt that the La Nina-esque atmospheric profile that has taken over since the end of the first third of this season is assisting the diffused tropospheric response seen similarly on occasions such as February 2009, when the combination of robust tropical forcing lead to equally strong extra tropical +mountain torques inducing a highly significant SSW (when viewed under w/QBO and La Nina profile). There are some similarities, at least, to that time - and the context of the upcoming pattern phase should be viewed with a similar perspective - and that includes the sort of initial blocking responses as seen early in Feb 2009 which, (at least for those disposed to deep freezes) appeared to offer much but actually in terms of longevity fell a long way short. This suggests there certainly IS wintry potential for the UK looking ahead into February, but this is set against a profile that is rather working against the sort of prolonged and sustained very cold spell that might be achieved otherwise.   Equally however there remains other outcomes which will likely not get coverage on this thread.

That is about as off the fence I would, realistically, and equally reluctantly want to move. So, yes, not very much off the fence at all then.....From a (boringly) neutral  and very detached perspective I am far, far more interested in the overview than a specific weather outcome.

 

[Model output discussion - into the last third of January]

12 minutes ago, wellington boot said:

It is true though isn't it? Cold bias informs or influences a lot of thinking and a lot of posts on here - and I've been part of that. I think a degree of sympathy is warranted. If you have so many people all desperately wanting one outcome, this isn't just to be expected but is absolutely inevitable.

But we still ought to aspire to more... In any case, those who watch or post year round will have noticed just how accurately @Tamara - with her marvelously dispassionate, almost robotic style - routinely calls it. 

Thanks - apologies for sounding robotic though. However it is to a large degree, somewhat reluctantly, deliberately written that way to try to emphasise neutrality that has to be adopted in order to provide explanations of what is behind the numerical modelling. Its a self learning exercise more than anything, as there is always so much more to understand. Tweaking such an approach to one outcome is self defeating in as much as it not providing a complete picture when there appears to be more than just that one outcome. Irrespective of what the final outcome ends up being. It is admittedly a good reason why the winter is not the most suitable time to attempt this approach, though sometimes things are written that feel right to put into perspective and that is what some of these posts attempt to do. As for accuracy, it is far more important to try to understand and learn first and foremost - any accuracy is a nice surprise and a bonus and a lot more is actually learnt in truth when things go wrong. And things clearly do not always follow 'a script' by any means.   So it is not something to worry about 

 

20 minutes ago, Radiating Dendrite said:

I usually find she sits on the fence like the pros in all honesty. I don't doubt her knowledge, but I'm all for people sticking their neck on the line and making a big call in plain English

If an assessment is made and there is more than one outcome that is possible, then making a 'big call' as you put it, is not actually 'calling it' at all - if one sticks their neck out for the sake of being seen to come to an emphatic single conclusion and dismisses the other possibilities. Surely it defeats the whole object of doing any assessment in the first place if ALL the conclusions are going to be ignored? Also this is not about competitive forecasting, there is no prize to be correct (and I am not a forecaster anyway) .. Personally its about testing out summaries, and then let time find out the reality and update accordingly. Its not trying to appear to be clever - its simply transparent continuity whether the thinking is right...or wrong.

My own interest is the range of outcomes, not chasing a single one because everyone likes it. I recognise that conflicts with the interests of many on this thread. But so be it - there is a lot more to worry about in the real world, especially at the moment, and its not a day job

[Model output discussion - into the last third of January]

On 22/01/2021 at 14:10, Battleground Snow said:

Perhaps, but it's right on the line between 6 and 7, so maybe a hybrid composite would be most suitable? Also I notice that composite is marked in red for "low reliability. It looks to head into 7 eventually too.

I am not too sure that the composites are even going to be reflective this year, as this year seems to be a very unique one with a la Nina that atmospherically is acting  more like el Nino as @Daniel* has pointed out.

The positive I take from the MJO is it may at least allow blocking in our locale and the Atlantic, which may be able to link to the Arctic high which strat warmings are helping to maintain a long-term -AO

 

 

2 hours ago, Battleground Snow said:

MJO update, now firmly into the Western Pacific (maybe it wasn't a phantom signal after all?)

If it continues on that ECM trajectory, we would likely hit phase 8 eventually. This may support a griceland high

Expect the models to continue to spit out various options in the next few days of scandi highs, greenland highs or maybe even the fabled "sausage" 

 

1 hour ago, IDO said:

We shall have some confidence by Tuesday next week that the MJO is travelling through phase 6. There is a lag of about 7-days so we should not see the phase 7 (ecm) reaction until about the 10th Feb? So what we are seeing now in the models should not yet be a reaction to the NAO-/enso/phase 7 = northern-blocking? As the convection is starting from the low-frequency Maritime Continental then maybe we will get a stronger than normal Hadley response in the W. Pacific?

Fingers crossed that we get the MJO into 7 then 8. Of course, the  Atlantic wave pattern is not necessarily as potent as the Pacific standing wave, and other background signals could mess with that. However, it is better than no signal. Interesting to see if the SSWE interference enhances or disrupts that Rossby wave pattern? I am still fence-sitting but the trend is good.

Attempts to fit the MJO to idealistic blocking scenarios is fraught with error risk because it is just one part of the global wind-flow inertia weighting used to calculate ALL probabilistic outcomes in respect of pattern evolution and change.

One has to look at total global wind-flow inertia which encompasses not just the tropics but also within the extra tropics at different latitudes. That is where the GSDM (modelling) gives diagnostic clues as to where switches in the speed and path of the jet stream are most likely to occur. Simply taking an MJO composite that reflects a tropical phase space element (i.e pinpointing the MJO within one part of the tropics) and without looking at the whole atmospheric circulation - is not a ticket to automatically finding blocking (where it is most desired)  Looking at the broad-scale might not provide only the outcomes that are being sought but will be give a more accurate and objective overview.

Lets briefly look at the here and now and put an overview into practice of latest consolidated data we have of the atmospheric circulation, and which compartmentalises the latest position within the upper atmosphere reflecting a period where the polar vortex remains relatively weak, but is nevertheless undergoing some re-organisation before potential further instability.

Relative global atmospheric angular momentum has sustained its New Year slump and is now wholly reflective of the overall Nina base state. The distinct banding of easterly inertia at 30N c/o enhanced trade winds (shaded blue) is overlaid by compensating westerly inertia driving the extra tropical circulation (shaded deeper orange/red). Good support for the NWP advertised downstream jet pattern driving successive troughs eastward vs the disjointed and relatively weak polar field pressure profile

 

This distinctly Nina-esque wind-flow pattern, following the much more a-typical relationship maintained during late autumn and the first part of the winter. So, since the turn of the year, it is incorrect to try to maintain any position that says that the atmosphere is behaving in any Nino-esque manner. Indices such as the SOI as well as the GWO firmly point to pressure and wind-flow diagnostics well within La Nina territory. the GWO rooted within the low angular momentum La Nina attractor phases, mostly centred around Phase 2.

 

With this in mind, considerable amounts of -ve wind-flow (easterly) inertia remains present across the Equatorial Pacific, at the same time as the high frequency tropical signal (MJO)  propagate into the Western Pacific and add westerlies (forward momentum). Convergence strength of westerlies, as added by tropical convection, has being mitigated by easterly trades ahead of it .

Potential pitfalls lie ahead.

NWP will be somewhat blindsided by the immediate signal from the tropics to ignite active tropical convection phasing in the Pacific - and context of the maximum bandwidth capacity of any westerly wind additions has to be taken from the existing position of low angular momentum inertia within the extra tropics. There is a distinct risk that a rise in angular momentum tendency, as created by (attempted) eastward propagation of high frequency tropical forcing, grinds to a halt - as trade wind inertia resumes after a pause. The effect of this would be for the high frequency tropical signal to beat a retreat and any programmed blocking signals advertised at distance within NWP be prone to correction in both amplitude and duration -  and/or more energy switched to the polar jet as a result of angular momentum tendency being over-egged. Or any such rally programmed to be sustained for too long a time.

Break in trade winds indicated here (ringed in red) :

If the upstream Pacific pattern quickly returns to increased amplification c/o trade winds buffering increased momentum in association with MJO thunderstorm development  (and weakening it due to wind shear) , then sufficient polar jet flow soon returns on a temperature gradient out of the US and Canada to negotiate the weakly disjointed tropopause. Much as discussed as the default in recent summaries.

Putting all this together, if the numerical models get the modelling wrong, and there is shortfall in suggested upturn of wind-flow inertia, this will be registered by the MJO beating a retreat in Phase 7. This will signpost extended ensembles to trend away from some of the coldest downstream solutions . Any element of retained Pacific ridge is likely to continue to assist some polar jet flow in the Atlantic sector and it is not enough, on its own, to just assume, through bias tendencies, that there will be enough weakness within the polar field to stump up a large blocking high.

Extended ensemble suites which might include scenarios of Scandinavian/Arctic high combinations should ideally be viewed objectively within a wider probabilistic field which may tend to create something of a NE/SW split. Colder and drier to the NE and milder and wetter to the W and S.  Without a concerted push, not just from the high frequency MJO signal eastward into the Pacific (that question mark over trade winds sapping its strength) but also with some deficit of momentum to recover within the extra tropics - then the chances of some retrograding high pressure out of the arctic are reduced and while forecasts of further warmings of the stratosphere will no doubt keep the partisan on their toes, it could equally maintain an average to rather cold type of default winter pattern - and as stated, the coldest conditions further north east and with milder conditions continuing to push into southern and western parts.

Meanwhile, my own eyes remain on fortunes across S and SW Europe, where the unprecedented cold weather of early January has been relaxing to something more familiar for the time of year - with warmer temperatures, albeit attendant with some wet weather. Later this coming week there are signs of some lovely Spring-like temperatures into the high teens Celsius. Its a case of remaining patient until it finally becomes very much safer & possible to leave and enjoy such conditions 

 

 

[Model output discussion - into the last third of January]

4 hours ago, mushymanrob said:

Am i the only one who doesnt rate the MJO influence? Is there any corrobrative evidence that the MJO is much of a player? What state was the MJO in when we have had previous Big Freezes?

Seems to me people are grasping at straws for some kind of confirmation of a favoured weather type is likely.

Currently, imho, there is no sign of any developing Easterly, not in the ops nor my favoured NOAA anomaly charts ................................. but then again there wasnt in January 24th 1985 whos synoptic pattern was very close to whats expected by Tuesday next week. And we all know how February 1985 turned out!

There is no doubt that the intra seasonal influence of the MJO has a large scale effect on global weather patterns - but at ALL times of the year and not just in the rabid anticipation and frenzied expectations that so many have for winter.       The diagnostic Global Synoptic Dynamical Model (GSDM) has a framework that encompasses wind-flow inertia changes c/o tropical convection (MJO) and also within extra tropics and presented in a phase plot depiction known as the Global Wind Oscillation (GWO)

If one puts aside all the fancy titles and acronyms, what you have with this diagnostic model, is a measure of total aggregate wind-flow inertia within the total atmospheric circulation to give an highly accurate depiction of the jet stream around the globe, and how this may subsequently evolve and change,  i.e whether it is accelerating (forward momentum) or decelerating (falling momentum) in any given place. In turn it is possible to get an idea of where amplification may occur in any given place (and which creates cold and corresponding warm air advection in different parts of the hemisphere),. It therefore also identifies where faster flow might flatten the pattern and subsequently transfer amplification wavelengths away downstream and in doing so alter where cold and warm air advection re-sets itself .

With that (simplified) overview in mind, the rossby wave changes that occur in the tropics c/o intra-seasonal MJO activity are the catalyst for weather pattern changes in the extra tropics, and indeed potentially at all layers of the atmosphere from the troposphere to the stratosphere. It is just the case that the winter has the added variable of the stratospheric vortex  to consider which makes identifying pattern changes more complex, relatively speaking, than in the summer when rossby wave activity dictates the troposphere much more (though not always exclusively)

The essence of all that analysis and overview is that where your post is correct, is to suggest that the MJO (and any other meteorological driver for that matter) is not some putative golden bullet to delivering to weather preferences, though on this thread in winter one might be forgiven for believing that these intra-seasonal drivers suddenly comes into being as hailed snowmakers (or villains of the peace if they 'don't appear to work'!)  before apparently disappearing into obscurity in tandem with the seasonal audience in March or April

Each season, each set of variables have to be taken on their own merits - and while it might be exciting and entertaining to make believe that MJO Phase x = object y blizzard - a cursory look at the past three winter seasons has seen some different outcomes based around MJO activity involving eastward propagation of tropical activity.  There is neither the time, the place or the space to go into each of them in detail and explain the differences. This has been done exhaustively in many places already, many times.

It would be just as easy to point to the role that tropical and extra tropical wind-flow circulations have played in the different outcomes of those same three summers in those respective years and so on and so forth. Alas, there is nowhere near the same interest between about March and October. It doesn't diminish the true fascination and complexity of the science that underpins it however. And it is very complex with still so much more to learn. But that is, or should be, the purpose and the reward.

In respect of the ongoing outlook : A previous post of mine recently mentioned an array of possibilities, that included the heavily biased solution of the majority in this thread, but it is included through how feasible , on this particular occasion, it is as ONE of the probabilistic outcome - but without intention or any wish whatsoever to pander to bias preferences.  It is wholly counter intuitive (and indeed self defeating) to inextricably try to link or fit MJO phenomenon (and all other variables) to ANY given weather type without  proper diagnostic assessment of ALL probabilities.. Posts such as the one under reply offer the opportunity to provide some realism instead of fantasy -  however it is accepted that is not the primary motivation in any way of this thread

[Model Output Discussion - Snow for some, but what else is in store?]

Falling momentum and weak high frequency MJO activity for the foreseeable future (* above caveat aside ) does weight probabilities towards a more typical sub tropical regime and polar jet flow arcing around this. At the same time and as can be seen, there are very hard to keep tabs of pockets of weak inertia popping op at relatively short notice closer to 60N which quite easily could stall westerly inertia and create subtle eddies within the jet which build very weak 'cold' ridges and derail the movement of troughs from west to east and restrict warm air advection

At present, no outcome is to be discounted or dismissed out of hand, and any discussion should be unclouded by bias preferences and be open minded to the even greater than usual uncertainties. That is not sitting on the fence - its honest objectivity in the face of highly sensitive factors that require a watching brief ,rather than any impetuous call for the sake of wanting to appear confident in appealing to a specific popular outcomes

 

---------------------------------------------------------------------------.

 

Extract from 6th January. As wholly detached as it attempts to be from the strong cold weather biases of this thread which make objectivity tribal and very difficult, the evolution has largely followed the suggestion theme.

Global relative angular momentum has maintained its negative parity trend as depicted by the Global Wind Oscillation, a phase plot depiction of global wind flow, now rooted within the La Nina attractor phases at low amplitude :-

Modest high frequency convective forcing in the Indian Ocean has bumped up trade winds with added easterly wind inertia propagated across the tropics to the Pacific - as manifested by a decelerative jet between 30N and 50N and associated -ve East Asian Mountain torque.  In this respect, note the strong convergence zone of wind-flows c/o the propagating tropical convection (organised thunderstorm development) bumping up against the solid wall of trade winds (shaded blue) at the dateline in the Equatorial Pacific

 

This decelerative upstream wind-flow process, as wind shear creates tropical suppression, is important (if one is interested in the larger scale pattern and not when it next snows) because the inflexion point of -ve torque mechanisms bifurcates the upstream jet across the Pacific - registering a switch from the Aleutian low anomaly that was present up to the first week of January to an amplified NE Pacific ridge - which ridges more and more poleward over the coming 10 days and injects very cold air out of the Canadian arctic to energise a steeper temperature gradient coming out of the eastern seaboard of the US.

This, as hinted at in the previous highlighted post, creates difficulties for numerical models in respect of how this downstream jet flow momentum is partitioned by contrasting weak and disjointed zonal winds at higher latitudes c/o SSW fall-out. The overriding theme nonetheless, which all the numerical models agree on, is for a supressed southward displaced flat jet flow which means that the temperature and pressure gradient remains fixed along a relatively narrow zone - those north of it seeing a wintry variant to the zonal flow, those at, or to the south of it seeing less incursions of polar air and greater influence of moist sub tropical air.  Taking a hemispheric view from this side of the globe, the polar and ferrel cells are impressively delineated by a burgeoning Iberian sub tropical ridge which means some glorious warming winter sunshine to these parts, in contrast to the much more disturbed cyclonic winter mess across Northern parts of Europe

Its is unlikely that stalemate is changed until tropical forcing starts to re-arrange the upstream profile in respect of the Pacific poleward ridging. The low angular momentum regime is juxtaposed with expansive very weak zonal anomalies across the polar field.  The upstream amplification should serve to retrogress the Greenland ridging into Canada as the jet energising process downstream forces sub tropical air along the steep gradient boundary - and quite aside from weather preference wishes of so many others, I think this aspect of the modelling is being handled quite consistently.

A  next pattern re-set where global wind inertia receives a shove of upstream momentum driving angular momentum higher is something to look out for the eagle-eyed. The exact timing of this is still very uncertain - suffice to say that it would result in a rise of pressure downstream and there are tentative signs in some extended numerical modelling (beyond 10 days) of this happening - or at least the cyclonic vorticity backing west into the Atlantic. Such a pressure rise itself is of great interest - to the neutral diagnostic enthusiast eye of myself , as much as to whether it assists (or not) the strong weather preferences that drive NWP opinion and sole purpose of this thread in terms of the imperative to fit these diagnostics to a freeze.

That in itself a loaded dice that creates high risk of error (and major mismatch of expectations based on the seasonal echo chamber)

All that said:....

It *could be* that a northward progression of the Iberian sub tropical ridge occurs as part of downstream European amplification, and at the time that the retrogression of the -ve zonal wind height anomaly is complete across to Canada.. The state of the polar field at this time, in terms of the weakness (or re-strengthening) of the polar vortex will be key to the further movements of such ridging. Continued weakness and instability within the polar field suggests some kind of potential arctic/Scandinavian high link-up - or conversely (should the polar field re-organise sufficiently) then a more mid latitude Sceuro/Euro High arrangement with upper air cold air advection routed into central and SE parts of Europe might be more likely

it *could* also be that a mid latitude high is a transitional arrangement to colder upper air across a greater part of mainland N and NW Europe - but ALL such options are highly speculative at this time. However, intra-seasonal high frequency tropical convection patterns are well worth watching as January comes towards its close and heads into February. They are compelling to my mind, based on the known periodicity (timelines) of  tropical>extra tropical frequency patterns within diagnostic Global Synoptic Dynamical modelling (GSDM).

Intra-seasonal amplitude cycles of such high frequency forcing based on 60 to 90 day periodicity point towards a repeat of the atmospheric processes seen during the late autumn/early winter and it will be interesting to see if the weather patterns replicate similar evolution - BUT based on quite different temperature anomalies across the Northern hemisphere than seen at this time and also lagged effects of stratospheric profile diminution to take into account.

In the meantime, a very unsettled and potentially stormy spell of weather to endure (or enjoy if it is your thing) . Always colder to the north and, generally, milder to the south

[South East and East Anglia Weather Discussion January 2021 onwards]

I am sorry most of you are not getting the snow you are yearning for, but for little it is worth, there is plenty of the winter to go yet and some reasons to look towards the latter part of this month and into February when prospects may be more conducive. But such rationale behind this is for the right place.

For my own part, I am still waiting to leave to get to my new home in Portugal, which has seen unprecedently low temperatures going back many decades since last seen previously. I think that part of this has been down to the Iberian continent effectively generating its own surface cold pool following the, again, unprecedented snowfall over the Spanish interior, and albedo type feedbacks from consolidated snow-pack effectively setting a very low 'fridge' type thermostat across the expanse of the land-mass. In that sense, not too much different to an east or south-easterly drift around winter anticyclones that can bring deceptively low temperatures from the nearby continent into this region.

Following the storm that tracked across Portugal and Spain last weekend, high pressure descended across the land mass and this has created some very intense inversion cold - if one looks at the actual upper air mass it would suggest nothing at all of what the surface conditions have been like.

Over the coming week, that cold air is set to relax and mix out - and as the jet-stream invigorates from upstream as cold air this times spills into the CONUS upstream across the Atlantic, then much warmer air will arrive from across the fetches of the more southern parts of the Atlantic as a western based -NAO profile sets up. With this in mind,  I am personally wanting some sun and warmth on my face, but that will have to keep waiting for, for a longer time yet. At least a couple of the builders at my new home, doing some work on mew piping and plumbing and fitting new bathroom and kitchen units, have contracted COVID, and my Portuguese friend and her little family who live at the annex there, are being tested very shortly this afternoon, and it is of course therefore a worrying time. Suffice to say it precludes me from leaving here any time soon, and with the work on the new house delayed for an unknown time, it looks as though I will be continuing to look at UK and Northern Europe weather maps for the time being!

But here is some Portuguese sun from a pic taken there recently this week - and my friends cats seem happy as well