Model output discussion - summer rolls on

[Cheshire Freeze]

Interesting, looking back on previous postings...From the 14th and 17th July respectively-

*I've been looking at the longer range today. To me it looks like next weekend may be a flash in the pan for more northern areas with a more NW/SE divide appearing thereafter as the PFJ sinks further S.

Regardless, the background pattern is now slowly shifting, this may be in fits and starts at present but it is evident that ridging from the SW is having a tougher and tougher time becoming as dominant than it has done over the past couple of months

**longer range modelling looks fairly set on a westerly dominated August now

***I did say it looked increasingly like the background pattern was changing. When you rely on surface features to prolong the heat rather than upper features which are more entrenched like the large HP we saw earlier on in the summer, the whole pattern lies on shaky ground.

In general there has been an overall decline in pressure (though in no way linear) for the past couple of weeks. 

To me it looks as though the Azores HP is having more and more issue with ridging in sufficiently.

Sometimes it is possible to simply monitor the modelling, along with the general synoptic trend and get a grasp on where we are headed in the longer term. The modelling did fairly well in this instance in the longer term.

Edited August 15, 2018 by CreweCold

[mb018538]

Not much to add again today - warmer for a couple of days mid next week before we perhaps get a mid Atlantic high and a northerly of sorts. Certainly no return to high summer that we had through June and July. ECM looks very isolated with its prognosis this morning.

[Man With Beard]

OK... I'm officially on bank holiday heatwave "watch" - not forecast, I must stress. This morning's ECM op was the first to follow a growing trend on the ensembles - only about 30% so far (clusters 3/4), but some of the other clusters shown below (for 26 Aug) have potential to develop in a similar way

Edited August 15, 2018 by Man With Beard

[Djdazzle]

18 minutes ago, mb018538 said:

Not much to add again today - warmer for a couple of days mid next week before we perhaps get a mid Atlantic high and a northerly of sorts. Certainly no return to high summer that we had through June and July. ECM looks very isolated with its prognosis this morning.

The mid Atlantic high won’t happen though according to the teleconnections. So not to worry.

[danm]

It’s the ECM vs GFS &  possibly the UKMO this morning. UKMO only goes out to Tuesday but follows the GFS in building heights out west, with low pressure looking primed to dive south across the UK bringing cooler, NW’erly winds. The GFS develops this idea later next week with high pressure out west and troughing over Scandi = cool N/NW winds. 

The ECM on the other hand is the complete opposite late next week. It develops that low to the north on Tuesday, but then pressure tends to build over and then to the east of the UK, drawing up hot continental air. 

Is the ECM out on it’s own or has it picked up on a new trend? We’re being shown two completely different outcomes by the models as we head towards the bank holiday weekend - cool north-westerly or hot south-easterly.

Edited August 15, 2018 by danm

[Frosty.]

A perfick end to summer this would be from the Ecm 00z operational.☺

Edited August 15, 2018 by Frosty.

[summer blizzard]

GFS and Euro very much at odds today with regards to how they handle a shortwave exiting Newfoundland around day 5. Euro strengthens this quickly while GFS and UKMO (at day 6) keep this weak. The difference being that the GFS (and probably UKMO) allow the Azores High to retrogress while the Euro does not. 

The result down the line being more substantial. 

 

[Man With Beard]

We also now have 5 days in a row with the 12C 850s line over the south of the UK on the latest ECM mean, from Saturday until Wednesday. That's a pretty warm spell coming up? 

[Singularity]

   

We've been working with very fine margins since the 2nd week of this month. Just look at how yesterday was modelled 8 and 7 days in advance by ECM compared to the actual outcome. At the time I said the runs looked too Nina-like with the mid-Atlantic ridge build and while this has proved correct, the difference has only been fairly small in the grand scheme of things. Yet still enough to make the difference between quite cool and warm conditions for the S half of the UK.

This continues to be the case through the weekend and into next week.

 

See here how we've seen, as a anticipated a similar move away from a Nina-like mid-Atlantic ridge build to an outcome which, while flatter, is closer to the Nino-like UK-Scandi ridge build scenario. Basically, you can see how that pattern wants to emerge, but is unable to due to the unhelpfully timed (for that) arrival of the CCKW traversing the tropical Pacific then Atlantic.

 

ECM's newly added LP development out NW of the Azores is of some interest as a possible kick-start to the more Nino-like setup, but as already reported by others, GFS keeps it very weak - and traps it west of yet another attempted mid-Atlantic ridge, of all things - while UKMO straddles an uncertain middle ground; the low is there, more developed than GFS, but enough to travel as ECM has shown us? Anyone's guess!

MWB is right to go onto BH heatwave watch though; the ingredients are there. We just need the head chef in the tropical Pacific to be in the right mood!

[mushymanrob]

1 hour ago, Man With Beard said:

We also now have 5 days in a row with the 12C 850s line over the south of the UK on the latest ECM mean, from Saturday until Wednesday. That's a pretty warm spell coming up? 

muggy, humid, cloudy, with some rain id have thought. of course IF the sun gets out it could be very warm/hot in the south.

[Frosty.]

1 hour ago, Man With Beard said:

We also now have 5 days in a row with the 12C 850s line over the south of the UK on the latest ECM mean, from Saturday until Wednesday. That's a pretty warm spell coming up? 

Indeed, the Ecm 00z ensemble mean makes for pleasant viewing with a strong azores ridge extending across southern england from the weekend and well into next week with predominantly fine and warmer weather..fingers crossed for some decent sunshine, with uppers (850's) like that it would become very warm further south!☺

Edited August 15, 2018 by Frosty.

[Singularity]

Here's the weekend troublemaker.

 

As for that next possible system of similar nature, 06z GFS got closer to the 00z ECM but still trapped the low west of a ridge in the end. I expect that either the trend of GFS will continue all the way to a solution very close to the 00z ECM, or ECM will meet it somewhere in the middle (the most uncertain outcome in terms of effects on the UK).

[Frosty.]

Most of the Gfs 6z operational looks pretty good for southern uk, especially this weekend bar a few splashes of rain here and there and the first half of next week also looks predominantly fine with some strong ridging and warmth with mid 20's celsius and plenty of fine and sunny weather further s / e and then again towards the end of the run when it becomes more anticyclonic and warmer again.

Further north across n.ireland and scotland it looks generally cooler and more changeable and later next week it becomes cooler and more unsettled nationwide due to another brief dip in the jet stream but then followed by a marked improvement as these charts show.☺

Edited August 15, 2018 by Frosty.

[Jo Farrow]

Quite a variation for Sunday forecast . Distinct deepening low on GFS or flatter solution on MR 

[Singularity]

One of those 'to engage or not to engage' situations for the ex-tropical remnants of SD 5 (or STS/TS Ernesto if it intensifies enough) with respect to the upper troughs in the jet stream, which itself has a wide range of solutions in the modelling output in terms of location, wavelength and depth.

Oh, what fun .

[Frosty.]

Longer term the GEFS 6z mean shows that the warm anticyclonic later stages of the 6z operational (charts i posted above) has plenty of support..hopefully a very good end to the meteorological summer for the uk.☺

[Tamara]

45 minutes ago, Singularity said:

   

We've been working with very fine margins since the 2nd week of this month. Just look at how yesterday was modelled 8 and 7 days in advance by ECM compared to the actual outcome. At the time I said the runs looked too Nina-like with the mid-Atlantic ridge build and while this has proved correct, the difference has only been fairly small in the grand scheme of things. Yet still enough to make the difference between quite cool and warm conditions for the S half of the UK.

This continues to be the case through the weekend and into next week.

 

See here how we've seen, as a anticipated a similar move away from a Nina-like mid-Atlantic ridge build to an outcome which, while flatter, is closer to the Nino-like UK-Scandi ridge build scenario. Basically, you can see how that pattern wants to emerge, but is unable to due to the unhelpfully timed (for that) arrival of the CCKW traversing the tropical Pacific then Atlantic.

 

ECM's newly added LP development out NW of the Azores is of some interest as a possible kick-start to the more Nino-like setup, but as already reported by others, GFS keeps it very weak - and traps it west of yet another attempted mid-Atlantic ridge, of all things - while UKMO straddles an uncertain middle ground; the low is there, more developed than GFS, but enough to travel as ECM has shown us? Anyone's guess!

MWB is right to go onto BH heatwave watch though; the ingredients are there. We just need the head chef in the tropical Pacific to be in the right mood!

The ECM difference you illustrate as measured by the Global Wind Oscillation in reality being in "transitional" Phase 8 as of yesterday 14 August....

 

 

.....rather than heading through low angular momentum La Nina Phases 1  into 2, (as suggested at face value by those operational outputs a week out) which models a sharper Atlantic ridge and hence greater cool air advection from the NW than has been the reality  The reasoning as so often discussed in these posts being the degree of upstream amplification in the Pacific which serves to retrogress the high that is downstream from this in the Atlantic - and with the polar jet pulling troughs around the top of the high c/o of a more NW/SE axis. If the model overcooks the upstream amplification, then it overcooks the polar flow and looped jet axis

Looking at the Pacific we see an increase in trade winds (covered in last post) following the passage of westerly winds c/o tropical activity which is now in end/re-start cycle - simply a natural pause in the tropical cycle and coinciding with CCKW towards the Western Hemisphere. Its this that modelling is jumping on and gunning for as pattern evolution to Atlantic ridge.

 

This actually mirrors the sequence during the first half of July - the difference being that the trade wind increase is set to be weaker this time (albeit seasonal wavelength changes since then mean that the polar Jetstream is rather naturally adjusted further south according to this latest global wind-flow position than earlier summer). Notwithstanding that, the significance of the trade wind increase being weaker compared to back then is that in related terms, global atmospheric angular momentum is significantly higher than it was in early-mid July -

 

- so extrapolating an establishing mid Atlantic ridge ahead on this basis needs some care and caution and none of the usual MOD discussion premature declarations in terms of an early autumn (beyond a possible transitory cooler interlude)

This isn't 'teleconnections' saying "No" to an Atlantic ridge either - its an attempted diagnosis as to how likely a wind-flow pattern is to assist it developing and lasting for any meaningful time.

Compare current AAM establishing closer to parity to the  more -ve longer term establishing pattern of August/September last year c/o the persistent easterly trades and La Nina standing wave. N.B Its seasonal wavelength changes that are the essential importance here which heighten the Atlantic ridge synoptic response to -ve AAM conditions from mid summer increasingly into autumn

 

This on the other hand looks very much like a transitory phase and certainly not a shift regime phase such as was seen during late July and August 2017 where a persistent signal for a mid Atlantic ridge in late summer and early autumn was well supported.  The summaries since May have been covering this aspect and fully anticipating it and stressed the differential as to mid summer crossroads *should* a La Nina type signal persist (which it hasn't) and force the first half of summer Azores ridge eastwards extension to retrogress and force a homogeneously distinctly cooler, showery and unsettled second half of summer countrywide - such as seen in 2017.

This clearly has not happened and instead we have seen a more traditional UK summer pattern emerge, still largely warm or very warm at times further SE and most changeable and average conditions further NW. The jet axis favouring tropical maritime, mostly, rather than mostly dominating polar maritime influences

Compare a one year snapshot of  tropical activity imprint of summer 2017 to summer 2018

A stark difference - and emphatic evidence of the role that tropical>extra tropical momentum transport has played in sustaining programmes of amplified late spring/summer ridges, whilst the standing wave regime of last year and associated lack of activity allowed a much more repressed Azores ridge to take over semi-permanently the closer high summer approached and Atlantic/polar maritime regimes increasingly prevalent

Its also clear from this year how the mid to late July low frequency signal has transferred to the Pacific rather than defaulting back to the I/O and the relevance in that sense as to where we are in the current tropical cycle to early-mid July this year is very similar.

Its this benchmark that the remainder of the summer and heading through September is best assessed in my opinion. This means that, overall, we should expect an Atlantic trough (not ridge) to prevail) and a case of looking for signs of the next Pacific low frequency engagement to re-emphasise a sharper trough to the west and south west and downstream European/Scandinavian ridge

CFS vs 2 seasonal modelling identifies the next Nino standing wave engagement with associated surge in angular momentum tendency and tropical momentum transport beginning around the last week of the month and especially into September. 

 

Such a surge sharply reversing any interim easterly trade wind burst, and with it, any intuitive reason for mid Atlantic amplification to prevail too long

Anticipating ahead comments about CFS capabilities here - these daily updated angular momentum forecasts have been consistently flagging this next upturn - and proving highly reliable and useful guides since becoming available c/o Victor Gensini maproom. Dr Gensini is co-working on developing further this maproom faciility to include further and larger data-sets with Ed Berry (former NOAA scientist and co author of the GSDM)

Based on NWP behaviour since mid summer, then confidence in picking up extended signals in good time and then carrying them forward consistently is pretty low to say the least. Much as the mid July period, the models were as suggested at the time blind-sided and over pre-occupied by the tropical phase lull and were programming a mid Atlantic ridge and downstream trough to take over from the sustained heat of early to mid summer. This clearly didn't happen and instead over the ensuing days the path to a  plume c/o Atlantic trough and Scandinavian ridge and a reload of heat into early August came into focus instead.

In conclusion, in my opinion anyway, best to perceive any Atlantic ridge programme as a temporary blind-side to the bigger developing picture and no permanent feature- should it evolve to any extent in the medium term. Focus looks very much on an extensive ridge adjusting east with time (if it doesn't evolve more quickly from within the circa 10 day modelling) ahead of a defined Atlantic trough.

As so many recent updates have suggested, this keeps prospects of further plume scenarios very much alive if nothing for a pinpoint micro scale island such as this can be guaranteed by anybody But as late winter 2018 starkly showed, it makes little difference to the weather if a season changes, it will do what it sees fit regardless

 

 

[Man With Beard]

So the latest EC clusters not really seeing eye to eye with the OP run

But clusters 1 and 4 provide a pattern that could play with a plume shortly after. That takes us over 50%. But sure, significant clusters remain that would tip things into the unsettled, autumnal category. 

Potential is there, but clarity awaits. 

[danm]

GFS still keen on a NW’erly airflow later next week (Weds-Thurs) with the high out west, however by the time we get to Friday the high is pushing east and building over the UK. Small improvement from the 0z which kept troughing out to the east at this time frame with N/NW winds. 

 

Edited August 15, 2018 by danm

[Frosty.]

In a nutshell, the Gfs 12z operational shows a north / south split for most of the run, most of the rain and cooler temps further north, the best of the fine weather and warmer temps further south but even the south has a few cooler unsettled days too..but then, as we have seen with recent gfs runs, high pressure becomes dominant towards the end of August and this run, as with the 6z shows a lovely end to summer.☺

Edited August 15, 2018 by Frosty.

[Man With Beard]

UKMO looking set to pump up a ridge at T144. Could be the end of the Atlantic train for a while. 

[claret047]

4 hours ago, Tamara said:

As so many recent updates have suggested, this keeps prospects of further plume scenarios very much alive if nothing for a pinpoint micro scale island such as this can be guaranteed by anybody But as late winter 2018 starkly showed, it makes little difference to the weather if a season changes, it will do what it sees fit regardless

Good evening Tamara.

Another excellent, informative and very readable posting as per usual, and even a weather illiterate ;like me could understand the majority of it. This is what makes this site so great. It is for all of us, whether we have a great knowledge on this fascinating subject or not, there is always someone on this thread who is able to inform us if we have a particular question.

At first I thought you meant late winter 2017 but I now realise what you mean and you was not ahead of yourself

Kind Regards

Dave

[mb018538]

51 minutes ago, Man With Beard said:

UKMO looking set to pump up a ridge at T144. Could be the end of the Atlantic train for a while. 

If that low sticks around to the SW...then every chance. GFS is great and goes warm again, GEM goes cold with an arctic northerly. Worlds apart!

[Mike Poole]

I think the key timescale is T144, with this low out to the southwest.  Here's ECM, UKMO, GFS and GEM:

The first three hold it well out west giving the potential to pump up a ridge ahead of it, but the GEM runs it straight through and we end up later with an Atlantic ridge.  ECM looking good so far for the settled and very warm option.

[Djdazzle]

17 minutes ago, mb018538 said:

If that low sticks around to the SW...then every chance. GFS is great and goes warm again, GEM goes cold with an arctic northerly. Worlds apart!

I’ve come to the conclusion that beyond 144, GEM is particularly useless. Just seems to flip between more extreme solutions, from hot to cold then back again!