Model Output Discussions 12z 03/05/2016

[carinthian]

On ‎31‎/‎05‎/‎2016 at 10:45, carinthian said:

Well the sun shone for most of the Holiday weekend here in Skipton with the rain reserved for the Southeast from early today . Looks like a full spin reversal in fortunes to start this summer season compared with last year with the North West doing well near the high pressure. The  East fairly cold with persistent winds from the North Sea  (sst around 8c brr ) A feature so far is the dominance of the European trough which continues with its vaporous weather to the SE. However, many folk in the NW would like it to stay this way, especially after the horrible dullness and low temps of last summer . Still fascinated to see how the models develop over the coming 10 days. Could be locked in this pattern for a while yet with more unsettled weather to develop this weekend to the south with the added ingredients of heat plumes in development for Southern Iberia and noticeable cold pool into Northern Scandinavia thrown into the equation. Great for forecast watching or trying to predict. As reported earlier ,never trust NEly flows in early summer ,they also provide a surprise to bite back at the forecasters!

 C

Well there we have it. This picture below paints a very interesting scenario for the middle of next week. Heat plume over Iberia, cold plunge into Northern Scandinavia, note the 30c differential 850mb upper temps between the far SW of Euroland and the  North Cape. Looks like we will loose the cold surface winds that have affected much of SE Britain with a gradual rise in warmth with a more sub tropical /continent feed . How long will it last ?, hopefully for a while, but not much point in looking beyond 144 hours. At least vapourous conditions to improve after this weekend in parts of mainland Europe. Great weather watching at the moment as the early summer synoptics reaveal their hand, cetrtainly different to last year when the Euro drought started and the NW of Britian endured countless days of dullness.

 C

Edited June 2, 2016 by carinthian

[johnholmes]

As usual my guide are the anomaly charts for 6-10 days ahead, 2 versions, the EC and NOAA or GFS. The two former are probably more likely to be nearer the mark based on a good many years experience using them. see below for the outputs.

http://www.cpc.noaa.gov/products/predictions/610day/500mb.php

how changeable or unsettled is far from clear but at least the awful N Sea flow would be gone. Here it is more like early March than early June

The alternative idea from the GFS output is below, of course it may turn out that it is nearer the mark with ridging the main feature. It too would have no surface easterly flow thank goodness.

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

Edited June 2, 2016 by johnholmes

[northwestsnow]

Lovely 0z GFS this morning wth the Atlantic really toiling to get in.

Unfortunately UKMO looks more like ECM at 144 so the favourite has to be the more progressive Euro models, in my opinion of course.

Hoping it will be one of the rare occasions GFS trumps the euos

And there we have it from John, GFS 10 day mean looks good, ECM looks poor.

Edited June 2, 2016 by northwestsnow

[Man With Beard]

Yes really quite substantial differences between GFS and ECM means, which mean confidence cannot be too high. I think it can be agreed that Monday to Thursday next week will be settled and increasingly warm:

  

By Saturday, the ECM is fairly autumnal, whilst the GFS is more of a NW/SE split:

  

It must be said there are still a number of GEFS members that keep the heat into the weekend, including this little beauty:

  

 

 

[northwestsnow]

Im really hoping GFS is right here, 6z looks another good run at 120 with a ridge in control and while there may well be thundery showers its into the low 20's widely, heart says gfs, head says ecm/ukmo and metoffice...

[Convective]

06Z GFS following a similar pattern to the 00Z, with the low remaining slightly further west before being pulled away into Iceland

[northwestsnow]

Goodness me GFS is like a dog with a bone here, absolutely a million times better than ecm/ukmo, looks a very warm week acc to the Americano model..

[Tamara]

The usual rules apply as always in terms of NWP that involve assessment of the height anomaly charts and ensemble means ahead of intra daily model output variances.

However, we still need to assess how these front line numerical tools are reading the global and hemispheric atmospheric circulation in order to assess the direction of travel as to how the height anomaly charts, and ensemble means, might keep evolving from where they are, or change away to a different pattern suggestion 

This is particularly no easy task as we start this summer. It is with this type of scenario especially in mind, that these little periodic updates are attempted to be constructed as (hopefully) helpful, if (just a tad!) complex to unravel into simple English and explain in less than a book of writing.  

The last review continued to track the transition of the Pacific ocean ENSO signal and its major influence on the overall weighted budget of atmospheric angular momentum (AAM).

This, and the effects of other ever changing global torque mechanisms. That refers here, in simplest terms, to earth and mountain induced turning forces on the global jet stream ribbon that cascade a butterfly effect on the far and wide upper and surface pressure patterns.

In tandem with tropical convection, which also majorally affects torque tendencies via the ocean,  these forcings help comprise the total atmospheric forcing budget on the atmosphere. This total budget and its associated endless state of flux, is measured and reflected by the use of the Global Wind Oscillation, and in turn evaluated by the constant updating, each day, of the numerical computer models as discussed on this thread

We should always be mindful that transitioning ENSO is never automatically seamless in terms of atmospheric/ocean coupling of a given, or changing signal.  Many transitional seasons through the years have been littered with forecasting minefields in terms of weather pattern evolution expectations over a given season, against what at face value might appear as unforeseen developments in terms of the atmospheric circulation angular momentum budget.

Timelines of intra seasonal factors are very much a driving force in terms of managing forecast expectations. Tropical convection (MJO) timelines have intra seasonal boundaries - between 30 and 60 days. Earth/Mountain induced torques usually have much shorter timelines - often 5/6 days out to maybe 12 to 14 in terms of some strong mountain torque episodes and the effect that they might have on upper troposphere circulation (especially in winter time as directed downwards from disruption to the seasonal stratospheric polar vortex if the torque is strong enough).

All this means in very basic and simple terms, is that Mother Nature abhors a vacuum, and continually adjusts the atmospheric circulation to the suddenly changed momentum budget caused by sudden buckling or change of direction of travel to the jet, as air driven momentum forces meet solid objects. This has the effect of decreasing or increasing AAM, according to whether the associated torque is negative (easterly) or positive (westerly). These changes in jet stream trajectory and velocity in turn carve out changes to prevailing weather patterns - first in the upper height circulation, and then the surface features. These changes systematically being affected further and further downstream form their source - and that can take more and more days at a time to take effect the further way one is from their source.

The anomaly charts and ensemble data sets can be assisted in their monitoring, rolling forward, through the anticipation of these atmospheric interactions and help forecasters decide whether the models are following the right path, or not as the case may be.

The previous updates have discussed in simplistic terms how an El Nino influenced atmospheric circulation adds increased westerly momentum to the atmospheric circulation - as represented through the GWO in a category of repeated orbit Phases 5,6 and 7 that are a graphical measure of the currently prevailing state of the atmospheric circulation. If the GWO repeatedly orbits these particular phases, then you can be sure that the atmospheric circulation continues to embrace an El Nino signature

We see that as Spring bowed out,, this is firmly the case with the GWO completing yet another Phase  5,6,7 cycle. Much as suggested would occur in the last update. This is indicating that westerly additions to the atmospheric circulation have been still, on balance, prevailing over the attempts of increasing easterly momentum developing in the sub tropics and trying to propagate to mid latitudes and slow down and scrub out that westerly momentum.  On that basis, whatever representation we might see of emerging Nina in the Pacific Ocean SST's - the atmosphere is still representing the legacy of the very strong imprint of the potent 15/16 Nino. This is important in terms of possible implications for weather patterns in Summer 2016.

So we should not underestimate the stubbornness of this signal and that the momentum budget might well take some sustained easterly momentum, *possibly* over two or more cycles before a change of imprint finally (sustainably) occurs that defines a switch of impetus that recognises an officially Nina globally influenced weather pattern. The GWO breaking through the transitional Phase 8/0 zone, eventually, into Phase 1 will tell us when this happens

The effect of the latest swathe of westerly additions to the atmosphere has been a further bubble up of AAM, and over the last 10 days we have seen blocking manifested as a function of that atmospheric forcing, as those westerly additions are propagated northwards and eastwards though to the mid latitudes. However, here we have to factor in the continued legacy of the highly potent final warming of the stratosphere which has manifested our blocking signal as adjusted to a higher latitude due to the legacy of easterly upper zonal winds persisting across the Northern most extent of the Atlantic.    These polar easterlies, having been downwelled into the troposphere as a Spring time lag of recurring swathes of warm stratospheric anomalies since the final warming in March.

Further augmenting the higher latitude amplification signal has been the ever escalating instability and fragility of the Arctic ice meltdown  - the unknowns of this phenomena, and where it takes the state of one of our earth's natural refridgerators, adds further uncertainty to any attempted medium and longer term predictions

Its only if that GWO progression, mentioned just now, heads into Phase 1 as a reflection of the atmospheric circulation becoming overwhelmed with easterly momentum over westerly, that persistent retrogression of the ridge/trough anomalies from upstream in the Pacific will end up in the Atlantic/European sector manifested as a Scandinavian/UK trough and westward displaced Atlantic/Azores high. In other words, a full reversal of the Atlantic trough and European/Scandinavian High symmetry of summer warmth. This reversal being the full hallmarks of an emerging classic UK Nina type summer.

What of the here and now and what the models show in respect of all this information?

Modelling of the MJO is reasonably agreed on the remaining present cycle as it decays from the reasonable eastward moving amplitude discussed in the last update, and as a consequence starts suppressing AAM a little ahead of the new cycle later in June.

 

At present, another GWO Phase 7 (borderline eight) to Phase 0 cycle, such as we saw earlier in May, seems to beckon. Its too soon to have higher confidence yet, but should this once again represent the bottom of the angular momentum cycle as fresh convection in the Indian Oceans starts another MJO wave through June, then the portents for further into summer are more and more positive beyond the first half of June 10 to 15 period. This would confirm that the atmosphere remains for further time in Nino territory and heaps evidence that a de-coupling to ENSO is in progress as SST's more and more embrace the developing Nina signature in the Pacific. Especially if we assume the persisting 30 to 60 day feedback lags discussed above.

 We know that the currently changing seasonal wavelengths from Spring to Summer will do us a favour in respect of continued delay to Nina territory. *Should we achieve this*  The longer that the status quo prevails through the first weeks of summer, then the stronger the signal for an Atlantic trough and European Scandinavian High becomes and persists. Even the transitional zone of GWO 8/0, with its very slight loss of jet momentum, increasingly helps default the trough back into the Atlantic and encourage warm southerlies rather than unseasonally cool northerlies such as many E areas away from the high to the NW of the UK are experiencing at the moment. We also know that the easterly anomalies c/o the final stratospheric warming will become overwhelmed by seasonal changes to the traditional Summer ascendency of the Ferrel (tropical) cell in our Northern Hemisphere - which implies in itself strengthened sub tropical ridges to mid latitudes and the jet forced north.

So we get the idea of what type of patterns to look out for in the model output in order to give us some idea of whether Jetstream push, or pull, is either formerly keeping parity, or, latterly gaining the ascendancy instead.

At present the models are playing with this exact trough/ridge scenario. The slight fall back in momentum, as suggested above, is re-setting the trough in the Atlantic and in tandem with the amplified downstream ridge, is set to pump up warmth next week. The models are in full agreement of this and fully advertise the pattern between days 4 to 6.

                    

 The importance of where we go from here is how the pattern continues to ebb and flow with momentum. The modelling suggestions of the Atlantic trough coming further towards the UK are not necessarily anything to worry about. What matters is whether atmospheric momentum continues to fall, or whether it finds a floor (much as it did in May) and attempts to rise again thereafter. 

Stabilisation and rise suggests that the Azores ridge will follow the trough and attempt to bump up mid latitude ridges once again. (The GFS 0z this morning was hinting at this). Any suppression of momentum, or worse, further falls, will start to put in place the mechanism for the summer time jet to stay south and for retrogression of the Azores High to allow the UK trough to cement in place.

Modelling can often be over progressive with trough/ridge scenarios. Interestingly, the GEM model especially has been playing in the last couple of days with an extended stall scenario and, to a degree, has led the other models so far. Hinting at the trough holding west and the downstream ridge sticking longer. This would give a little further band-with of an extra day or so to the suggested plume next week.

The GEM ensemble mean gives indications of the attempted plume perhaps lasting to end next week. A blended mean, with likely at that distance scope for greater warm air advection.

   

 

Whatever happens with the trough in the days 8 to 10 period and associated cold front with increasing likelihood of attendant widespread thunderstorms with it - its how the pattern re-cycles thereafter that matters.

The current weakening of tropical MJO activity in its latest orbit from the Indian Ocean through the Maritimes on its way to the Western Pacific is reflected in the present fall in global torques (black line) from a high level (and subsequent probable move of the GWO through to Phases 8/0)

Easterly wind anomalies being added to the atmosphere from the tropics is represented by a negative (falling) influence on global torques and consequent slowing down of the jet stream. The further that torques fall, and the more sustained that fall is, the greater and more sustained is the downward pull on AAM. Hence the GWO entering Phase 8/0 transitional zones from the prevailing Nino orbit phases, as proposed above, tells us that the atmosphere is attempting to add easterly momentum to the atmosphere and scrub out the westerlies. This in turn causes that loss of impetus to jet flow as described earlier, and a retrogression of the upper air patterns as a consequence of this loss of momentum

So, in terms of current modelling - a little retrogression of the NH long wave pattern? Yes, as indicated presently - to re-set the trough. Further loss of momentum? - No. This will amplify the pattern from upstream and set a ridge in place to our west and keep the trough ahead of it in place, over the UK and perhaps extending towards Scandinavia.

That takes us back to sentences one and two of this very long explanatory post - and the relevance of understanding these sequences in terms of how the upper air pattern anomalies might evolve and change. That is, whether increases with westerly momentum evolve downstream ridges ahead of troughs as created by an accelerated jet stream, or whether troughs fall into place ahead of retrogressed ridges, as jet velocity is receded.

The outlook is therefore continuing to be dominated in both the short, medium and longer terms by these push and pull momentums on the jet. We also have to factor in how changing seasonal wavelengths impact these ebbs and flows and create subtle differences of placement of the upper (and in turn surface features) at all latitudes, including our own Atlantic sector, as one month and season turns towards another month and new season

There lies the upcoming litmus tests of the lagged strong 15/16 Nino imprint - and how long might the atmospheric circulation reflect this and increasingly as a consequence become more and more disconnected from the progressively changing ENSO ocean signal, which in itself manifests the less favourable possibilities to our Summer.

The procedure, in question, happened, in reverse in Summer 2011 - when La Nina was transitioning to El Nino. Anticipated summer warmth courtesy of increasing westerly momentum propagation on the atmosphere to puff up mid-latitude ridges, instead stayed stubbornly disconnected through the summer to a default UK trough and displaced Atlantic High - with the jet looping south over us and keeping the weather disappointingly relatively cool and unsettled. It wasn't till the autumn that the changes in the atmosphere (that had been anticipated in the summer) finally occurred, and led to a classic Indian Summer period of weather in Sept into October

So, can such anecdotal reverse psychology, splashed on top of the basis of some attempts at interpreting some well founded ocean/atmosphere science dynamics, do us a compensating favour this summer?

Edit: The latest GFS is very much playing with the ultimate pumped up ridge scenario as discussed above and takes the preferred jet route north. Whether correct or not, its an illustration of how even transitional ocean/atmosphere patterns evolving with seasonal wavelengths can produce attractive seasonal weather patterns *if the dice falls right*. Echoes of years like 1995 in that respect.

Edited June 2, 2016 by Tamara

[Frosty.]

Great post as usual Tamara..Echoes of 1995 would be very welcome as August of that year in particular was filled with high pressure and very warm / hot conditions nationwide!

[Matthew.]

Thankyou for that amazing post Tamara. May have to read a few more times but I really hope 'the dice falls right.' It really is a game of chance! Nice pictures Frosty also..they remind me of 76 aswell

[Man With Beard]

Very nice 06Z from GFS. A reasonable mean too:

  

The outside horse, but never discount the GFS!!

Edited June 2, 2016 by Man With Beard

[MR EXTREMES]

4 hours ago, mb018538 said:

ECM is still very keep to steamroller the Atlantic through by the weeks end. UKMO looks like it could evolve in a similar fashion. GFS has a more preferable evolution, but is a bit of a warm outlier In the ensemble cluster, so I would expect something closer to the ECM picture to emerge, though details will be hard to pin down. Either way, it looks warm!!

interesting you say this there is a very strong signal in fi to do exactly what your suggesting 

although fi and this could be the ecm getting hyped and removing heights very rapidly .....

but im not convinced and neither is the gfs gefs even the gem in fi has very long drawn sw flow from the azores

so the only model to reduce temps to average or slightly below would be the ecm.

 

[northwestsnow]

Well thanks to T for a very detailed and at times over my head post lol, but i guess the message is all to play for.

Would love GFS to trump the ecm today, the 12z's will be very interesting to say the least, wouldn;t it be superb to have euro 2016 and hot sun here and France, and a good England performance!!

[Scorcher]

It's certainly looking very good until Thursday at the very least going by the models this morning. Temperatures are looking nothing particularly notable but I imagine low to mid 20s will be widespread across the UK, although I wouldn't be surprised to see some higher temperatures locally as we get closer to the time.

Let's hope the ECM backtracks on that breakdown for the end of next week- it's still outside the reliable time frame so is subject to change. 

[wishingforsnow]

6 hours ago, Tamara said:

 

Superb analysis Tamara. Encouraging to see the signs of a reverse pattern of years like 2011 where the opposite pattern was happening to give us the unseasonably cool and wet Autumnal summer weather 

As for the more recent timeframe, this is one of the rare occasions recently where I hope that the GFS is right over the ECM. If it isn't well I think that any Atlantic steam train won't last for more than a week tops anyway. At least it's finally getting warmer from next week  

Edited June 2, 2016 by Polar Maritime
To remove long quote

[Singularity]

Fantastic post as usual Tamara!

I have watched with some amusement as GFS has displayed all-too-obvious forcing from its seemingly outrageous GLAAM projections, causing an attempted ridge back in from the southwest days 9-10 to suddenly be thwarted by a trough dropping in from the NW as the pattern retrogresses.

That GWO plot has to be seen to be believed. Going off the scale according to the GEFS mean... if this is indeed well wide of the mark, it gives cause to wonder how it is that this error has not at least been reduced following the two updates to the model that have taken place over the past year or so.

I have noticed from looking at analogues that July is the most sensitive month to what the GLAAM gets up to. There have been some tragic ones during La Nina onset but, as Tamara implies, there's room for a much finer month if GLAAM stays in positive orbit.

Curiously enough, CFSv2 has been outputting week 2, 3 and 4 500 mb anomaly charts that are more in line with an avoidance of the GLAAM cascade. It seems strange that one American model has been handling things so differently to the other (GFS). Other long-range models seem to offer general support for CFSv2, though with the usual variation in details.

 

That 06z GFS is looking pretty toasty for my time in the Balearic Isles; I'll be there for two weeks starting the Monday after next. The charts from +300 onward are close to what CFSv2 is indicating. This later-on heat comes at the expense of some quite exceptional heat from around 9th to 11th, which GFS has dropped, but ECM continues to advertise without even blinking. This model is persistent in drawing the Atlantic trough east as a consequence of a better defined Greenland ridge + Svalbard trough combination in the mid-range, which brings cold air from the north closer to the UK, resulting in the jet stream waking up across the UK rather than to the NW. Is ECM being too tidy and/or amplified with the pattern N of the UK? We ought to have a clear enough picture before too long. By tomorrow evening, with any luck.

[Summer Sun]

This afternoons UKMO shows high pressure lasting to at least mid next week with the flow from the NE getting cut off we'll see a significant improvement in the east though right on the coast cloud and or mist could still be an issue but it certainly won't be as widespread nor stubborn as this week

Edited June 2, 2016 by Summer Sun

[northwestsnow]

Looks like we might squeeze thursday out of the ukmo before the trough gets in, GFS similar so a mainly warm and dry 5 or 6 days for many with the odd thundery shower popping up tues onwards.

Not bad, not bad...

[Scorcher]

50 minutes ago, northwestsnow said:

Looks like we might squeeze thursday out of the ukmo before the trough gets in, GFS similar so a mainly warm and dry 5 or 6 days for many with the odd thundery shower popping up tues onwards.

Not bad, not bad...

I'd say at least Thursday, the arrival of the trough could yet be delayed- it's still out in FI. The GFS 12Z would give a very nice day on Friday for most as well, with possibly the highest temperature of the year so far in the SE if that run comes off.

[northwestsnow]

ECM at 96 looks to have edged the trough back just a tad meaning the UK is under slightly warmer 850's.

http://www.wetterzentrale.de/pics/Recm961.html

http://www.wetterzentrale.de/pics/Recm962.html

Slightly more influence from the high pressure cell over Scandy than the 0z run - probably, hopefully will mean a slight delay in the breakdown..

[Summer Sun]

ECM has the high holding on nicely during mid next week better than UKMO as well

UKMO at the same time

[mountain shadow]

Ukmet and ECM move towards the GFS ops with holding the trough in the Atlantic,  will it even get in at all as the ridge ahead of the trough pushes the low North.  

 

[ANYWEATHER]

Evening all, A mixture of just about everything depending on where you live . Thunderstorms may well be prevalent in the week ahead especially for southern Britain. After that , it looks as though the long wave trough in the Atlantic will have some influence later during next week...

[joggs]

15 minutes ago, ANYWEATHER said:

Evening all, A mixture of just about everything depending on where you live . Thunderstorms may well be prevalent in the week ahead especially for southern Britain. After that , it looks as though the long wave trough in the Atlantic will have some influence later during next week...

But winds coming from a southerly direction.Hope the trough stalls in the Atlantic.

[northwestsnow]

ECM has delayed the breakdown for a good 36 hours this evening.

Atrend i would like to continue..