Model Output Discussion - Into Summer 2020.

[Tamara]

20 hours ago, offerman said:

23 hours ago, Tamara said:

So this is duly playing out once more in the modelling - with the Azores ridge advertised to return eastwards into the second full week of July. Assuming that the high frequency tropical forcing aiding this shift plays out sufficiently to diffuse the low frequency tropical signal as it propagates eastward across the tropics, then the risk of the ridging being adjusted back into the Atlantic at this timeframe is reduced. During the next few days it will be possible to monitor this and report back on progress - but at this time it looks promising for summer weather to make a return, at least for a time, during the following week

That means I agree with @bluearmycomment, on the basis of the above analysis, that chances of extended country-wide heatwaves are unlikely - but if one is prepared to be sanguine over a mixed pattern of relatively shorter warm spells, potentially thundery breakdowns of interest (such as end of last week) back into cooler more changeable spells when the low frequency tropical signal re-dominates, then it is a reasonable seasonal outlook

 

Can I ask , was the PV in part to blame ( in a good way if you like long dry periods)  for the unprecedented dry sunny weather as soon as lockdown started right up to latter June bar two rainy days in April.  What enable such huge high pressures almost encircling the globe at mid latitudes especially towards and over the UK for Such a long period of time ? 

Another question which I have always pondered, do you think there is any correlation between the inner workings regarding metals under the core and certain large strong high pressure cells ( Hadley I think ) that make them tremendously difficulty to shift at times ?  One of note often seems one off the Portuguese coast and extends over Spain although this year Spain doesn't appear to have this but instead a constant slack low pressure producing many thunderstorms over the country this year.

 

These are good questions, and they relate completely to how and why there has been pattern shift since the summer began. . The excerpt taken above from yesterdays post gives some answers in terms of the relocation of the low frequency tropical signal further upstream to Africa and the Indian Ocean - which essentially also re-configures the rossby wavelength further upstream as negative torque mechanisms increase easterly trade wind inertia -  and amplification in our part of the Northern Hemisphere takes place across the Atlantic, more often than NW Europe - which was the case during the Spring.

As far as the PV is concerned, this was very strongly influenced by the westerly QBO phase during winter, and a strong lag effect persisted through the Spring - also aided by the fact that there has been no progressive transition to the easterly phase which would assist stratospheric downwelling of negative zonal wind anomalies and increase pressure over the pole.

What we are seeing is the increased La Nina forcing c/o the relocated tropical signal steering the pattern away from the persistent downstream ridging of the Spring to the more retracted ridging seen under much lower angular momentum conditions than up to just a month back in time. This type of regime often favours countries like Portugal and Spain - at that latitude clearly on the opposite flank of the Azores ridge and immune to the cold fronts and incursions of much cooler maritime air that cut short  fine and very warm spells in our part of NW Europe. One aspect someone like me has in her dreams for the future...

This 90 day plot tells the story in  terms of the changes between spring and summer for this part of the world however:

Momentum fell below average on cue at the start of June and summer. It is no coincidence we have seen much more mixed conditions since then

My own view though is that, taken in the round, we have actually done better than might have been anticipated - thanks to the off equator diffusing of the effects of the relocation of the low frequency forcing and kelvin way characteristic high frequency tropical forcing providing some further temporary ridging as we have seen. Also the enigmatic QBO transition has prevented a much worse outcome developing c/o higher latitude blocking. As suggested, attempts to switch the Annular Mode have proved to reverse due to countervailing westerly inertia playing peek a boo in the stratospheric echelons.

As long as something of a disparate relationship persists between the tropics and the extra tropics, and the polar field doesn't tank negative, then the story is the same one. Next week is a test of the off equator forcing helping a more eastward displaced ridge and further high frequency tropical forcing assistance. Much as discussed at length in recent posts.

This is why I continue to recommend not being too reactionary to each and every operational model suite. There is some bandwidth in solutions here according to how the upstream wind-flow inertia plays out. In simple terms this translates to timing and extent of Azores ridging eastwards - meaning there is an envelope of a few days for its arrival and there is also room for either reduction OR increase in extent of this ridging.

That sounds like covering all bases to be proved correct whatever happens. However, being correct is secondary to monitoring a very interesting fine margins as far as I am concerned and the truth is that a favourable or rather less favourable outcome are both highly conceivable at this time. We are simply under an different overall regime to that of the Spring and whilst we readily saw prospects for ridges upgraded in nearer timeframes , the re-configuration of the pattern since then simply makes it harder to achieve that favourable outcome each and every time

However, we are (relatively) fortunate to still have the real chance to see some shorter warm spells amidst the more changeable and cooler periods. It really could be considerably worse than that as a perspective for those who continue to be underwhelmed by how the summer is panning out so far

Edited June 29, 2020 by Tamara

[johnholmes]

Many thanks for that MWB, very interesting to read and also pretty helpful

[MATTWOLVES 3]

No worries folks.. EC46 runs this evening, hopefully I will be bringing positive news, unfortunately I'm still only learning how to read it, so don't shoot the messanger...

Amazing Tams.. And just goes to show how your always willing to anwser many posters questions with such high detailed and alot of time consuming posts. 

Gr8 stuff..

Edited June 29, 2020 by MATT☀️

[Guest]

What a woeful ten days being forecast with nearly all coastal areas approaching gale force winds for the foreseeable!

Utterly disappointing for mid summer.

[Downburst]

"That sounds like covering all bases to be proved correct whatever happens. However, being correct is secondary to monitoring a very interesting fine margins as far as I am concerned and the truth is that a favourable or rather less favourable outcome are both highly conceivable at this time. "

Tamara. I just want to thank you for the courage to keep doing what you are doing in posting on a thread for us all to learn, a thread that doesn't often allow time or space for such detailed analysis of the complexities that form our global weather system. I do have some difficulty with your expressions sometimes, but I try hard to and I'm increasingly getting to grips with understanding your analysis but a long way to go, or rather perhaps more effort needed my end. I am sure I speak for many when I say bravo and many thanks and have no fear.

 

 

[Fourty Point Three Degrees]

GFS 6z looks like standard mixed weather up to the middle of July. Rainy days from time to time mixed with some dryer interludes. No big heat or toasty 850s coming our way for the foreseeable. 
 

[MATTWOLVES 3]

8 minutes ago, 38.7°C said:

GFS 6z looks like standard mixed weather up to the middle of July. Rainy days from time to time mixed with some dryer interludes. No big heat or toasty 850s coming our way for the foreseeable. 
 

The more settled conditions seem to have been put back a few days, perhaps towards the backend of next week we see the real improvements.. This backed up by the latest Exeter update also and still a fair amount of fine conditions are being called for July... Always a concern for some when nice conditions get put further back! But I myself are not to concerned about it.. If it was a winter yes.. When cold snaps being put back seem to always mean one thing and one thing only.. Buy at least with Summers we can literally be guaranteed fine and hot conditions at some stages during the Summer, even when seasonal conditions are only remotely average. 

The 6Z mean does highlight the change to more settled conditions during the 2nd week of the new month.. So i feel its never so much of a... If it can go wrong... It will go wrong.... Not in Summer anyway. We just need to ride the next 10 day's out.. No real dramas. 

. 

[Fourty Point Three Degrees]

Some interesting weather being hinted at from mid July with an Azores / Scandi link up. One to keep an eye on but I remain sceptical 

[Guest]

1 minute ago, 38.7°C said:

Some interesting weather being hinted at from mid July with an Azores / Scandi link up. One to keep an eye on but I remain sceptical 

Would be very interesting to see this sort of thing come off as I believe it goes the grain with it comes to La Nina? 

But wrt to the pressure rises next week I think I mentioned last night they rarely come at the first attempt when modelled so it could well be that we have to wait until the second tercile of the month to get any real improve. If so down here that would make it pretty poor first half of summer, only 4 days above 25C along with a 3weeks unsettled interlude followed by a 2week unsettled interlude. Still that could all change and we could still end up a great August with has been absent for nearly 20years now. 

[Methuselah]

Well I'd be lying if I said the GFS 12Z's latest prediction for Sunday isn't a bit meh!

    

[Singularity]

 

A bit of northward adjustment from GFS with the LP position on Saturday. Good to see.

This is still a long way from the latest UKMO run, though (UKMO +120 & +144, then GFS +144):

    

So, that's thrown everything up in the air!

Ah, just scrolled up a bit and saw that Tamara's been active again - off to read now .

[MATTWOLVES 3]

Well UKMO raised a few eyebrows... Wasn't expecting that... Was we Jim...

[mb018538]

A slight tweak and the UKMO is nice on Sunday. Fine margins!

[mb018538]

1 hour ago, 38.7°C said:

Some interesting weather being hinted at from mid July with an Azores / Scandi link up. One to keep an eye on but I remain sceptical 

This is an oddity to me - I don’t see any evidence for a stonking UK-Scandi high setting up towards mid month. Neither do the ECM ensembles. Will watch carefully!

[Methuselah]

Sundy 12 looks mighty 'interesting'...I do, however, expect (or rather hope!) that the GFS 12Z is 'pushing the envelope' in the wrong direction... Lots of scatter in the ens?

    

[Guest]

12 minutes ago, General Cluster said:

Sundy 12 looks mighty 'interesting'...I do, however, expect (or rather hope!) that the GFS 12Z is 'pushing the envelope' in the wrong direction... Lots of scatter in the ens?

    

Its an awful, awful chart. Just look where the Jet is 

[Guest]

Ugh the GFS ensembles make grim reading post the 6th July.....A run for the bin.....The Ops is something of an outlier towards the weekend of the 11th/12th however there is worse.....

[Andy Bown]

All that incredible weather during the full lockdown and how predictable was it being so bad once everything begins to open up!

We’re into a pattern where even the better days are iffy, like in West Wiltshire today with a strong wind, minimal sunshine and drizzly showers.

[Methuselah]

Well, I have seens many ensembles worse than these GEFS 12Zs...T850s drop from 11 to around 5C, so not really as catastrophic as I'd first feared:

    

    

In fact, having had time to reflect, I reckon things are not looking nearly as potentially gruesome, as they did at the start of June...?

NH profiles:

    

    

Is that a menagerie of cartoon animals I see circling around the Pole!

Edited June 29, 2020 by General Cluster

[Zak M]

12z ECM @144 does show something warmer, mainly for southern areas but it doesn't last for long.

I would happily take this though...

   

Edited June 29, 2020 by Zak M

[Djdazzle]

Apart from a brief nice day in the south, ECM is pretty foul. Hoping to God it’s an outlier. You just can’t keep on getting unlucky, surely? Somehow, it parks a trough over us?

Not writing summer off, but this promised AAM is having little impact on settling our weather down.

Edited June 29, 2020 by Djdazzle

[northwestsnow]

5 minutes ago, Djdazzle said:

Apart from a brief nice day in the south, ECM is pretty foul. Hoping to God it’s an outlier. You just can’t keep on getting unlucky, surely? Somehow, it parks a trough over us?

Not writing summer off, but this promised AAM is having little impact on settling our weather down.

Not the greatest EC det,i agree.

Clusters will reveal more.

[Djdazzle]

The fact is, we need some oomph from the Azores high. Maybe this will happen as we move towards mid July and August. I have a feeling that this summer will almost be the opposite of what some have been expecting I.e. front loaded.

[mb018538]

Apparently the EC46 today is in sync with the CFS and shows strong scandi/UK heights setting up towards mid July....doesn’t look like it at the moment, but keep an eye out!

[Djdazzle]

Just now, mb018538 said:

Apparently the EC46 today is in sync with the CFS and shows strong scandi/UK heights setting up towards mid July....doesn’t look like it at the moment, but keep an eye out!

CFS - now we are doomed!