Model Output Discussions 12z 03/05/2016

[Frosty.]

The Gfs 6z op run shows us entering a cooler n / nwly sunshine and showers regime later this week and throughout the weekend into the start of next week and some of the showers will be heavy with hail and thunder but the good news about this run is it has some warm / very warm spells in it too with occasional high pressure / ridging and even some thundery humid days but the overall pattern remains changeable / unsettled with some cool breezy and rainy days too but as I said, there is warmth, especially further south..I've seen worse!

[Frosty.]

I've used 8th August as my template to give an idea of what the GEFS 6z mean and perturbations are generally indicating for that period and it does look encouraging with a more robust Azores ridge in place over most of the uk. The 6z perturbations around that date show quite a few anticyclonic scenarios, some centred slap bang over the uk. In no way am I saying this will happen, there are some unsettled runs too but there continues to be a trend for some type of warm settled spell within that period which may be stronger than shown or may be just a transient ridge but it's one to watch as most of us are hoping for a decent August!

[Man With Beard]

ECM extended ensembles: A reasonable cluster going for a slightly warmer patch 4-8th August (and, to be fair, a number that don't).

(note this chart will be out of date by tomorrow morning)

[phil nw.]

Yes i was just looking at those MWB.

Really no signs yet of any real change into the new month to our typical UK Summer outlook-better further south and east as usual in this pattern.

The Azores high again shown to occasionally poke his nose this way but the omni-present Icelandic trough continues to suppress any prolonged settled conditions from extending north for too long.

The day 10 mean jet and surface pressure pattern still shows it's influence-GFS 06z illustrates this quite well, and the 00z ECM mean chart with the heights at 500hPa and surface underlining the expected picture.

As we have seen so far there will be some decent weather about with sufficient warmth to enjoy outdoor activities but in this broadly westerly pattern expect some fronts- sometimes weakening as they come south east- to move across the country. 

[Frosty.]

1 hour ago, phil nw. said:

Yes i was just looking at those MWB.

Really no signs yet of any real change into the new month to our typical UK Summer outlook-better further south and east as usual in this pattern.

The Azores high again shown to occasionally poke his nose this way but the omni-present Icelandic trough continues to suppress any prolonged settled conditions from extending north for too long.

The day 10 mean jet and surface pressure pattern still shows it's influence-GFS 06z illustrates this quite well, and the 00z ECM mean chart with the heights at 500hPa and surface underlining the expected picture.

As we have seen so far there will be some decent weather about with sufficient warmth to enjoy outdoor activities but in this broadly westerly pattern expect some fronts- sometimes weakening as they come south east- to move across the country. 

I honestly think the GEFS is on to something for the early to mid August period, the reason I say that is Exeter have again mentioned the chance of a fine and increasingly warm spell by the end of next week (the first August weekend) they are very cautious about it, and rightly so, duration is unclear but they don't expect a lengthy settled spell but mogreps / Ec32 must be indicating something better in that timeframe and the extended outlook further into August sounds decent by this summers standards...fingers crossed. :- )

Edited July 27, 2016 by Karl.

[mb018538]

UKMO looks slightly different this evening, low pressure making inroads at 144 hours. In fact it's so different to GFS at the same timeframe, I don't know what to believe! There's a 10mb pressure difference in the south (1025mb on the GFS, 1015mb on the UKMO) so I think it's safe to say the models aren't handling this especially well again...

[Frosty.]

19 minutes ago, mb018538 said:

UKMO looks slightly different this evening, low pressure making inroads at 144 hours. In fact it's so different to GFS at the same timeframe, I don't know what to believe! There's a 10mb pressure difference in the south (1025mb on the GFS, 1015mb on the UKMO) so I think it's safe to say the models aren't handling this especially well again...

I just thought I should add the charts you mentioned for the benefit of folk who for any reason can't access them.

Edited July 27, 2016 by Karl.

[knocker]

Those charts can be a little deceptive. The last one for example

[Frosty.]

2 minutes ago, knocker said:

Those charts can be a little deceptive. The last one for example

Indeed knocker, I should have checked that before I posted it.

[mb018538]

I'd say those charts can be just as deceptive - as the pressure increments are 2mb instead of the standard 5mb, they make it look like it's going to be blowing a gale!

[knocker]

6 minutes ago, mb018538 said:

I'd say those charts can be just as deceptive - as the pressure increments are 2mb instead of the standard 5mb, they make it look like it's going to be blowing a gale!

I just meant they do not show the full picture. I'm sure people can take into account pressure increments when looking at charts, particularly on a weather forum. And where did you get the standard 5mbs from as the METO use 4mb.?

Edited July 27, 2016 by knocker

[Frosty.]

The Gfs 12z op run shows some settled and warm weather between unsettled spells. the end of next week shows a window of more pleasant weather for the s /se especially and then later in the run there is a general improvement with the jetstream pushed further north..much better ending than the 6z op which finished very unsettled and cool.

Edited July 27, 2016 by Karl.

[Frosty.]

The GEFS 12z mean is showing a considerable improvement by the first August weekend which lasts into the following week with a stronger Azores ridge bringing increasingly settled and warmer weather to most areas. Hopefully this trend will continue to firm up and upgrade in duration but for now, it's a light at the end of the tunnel, early next week looks briefly better for the s / se as a weak ridge pushes east but my hopes are on what happens towards the end of next week which is a period the met office also indicate the possibility of a fine and warmer period commencing.

[knocker]

no significant change in the overall pattern with the GEFs anomalies this evening. The usual caveat applies that the phasing of the LP and HP could easily initiate, when in the HP more influential phase, more Azores ridging and thus warmer and drier weather for a time, more particularly in the south. But in this mobile pattern it does throw up a new scenario tonight with height rises in the western Atlantic in the 10-15 day period. This would not be good news as it would bring the weak trough more into play and certainly keep the temp around average. Fortunately the pattern is quite fluid so a very good chance this evolution will not be maintained.

Edited July 27, 2016 by knocker

[markyo]

42 minutes ago, Karl. said:

The GEFS 12z mean is showing a considerable improvement by the first August weekend which lasts into the following week with a stronger Azores ridge bringing increasingly settled and warmer weather to most areas. Hopefully this trend will continue to firm up and upgrade in duration but for now, it's a light at the end of the tunnel, early next week looks briefly better for the s / se as a weak ridge pushes east but my hopes are on what happens towards the end of next week which is a period the met office also indicate the possibility of a fine and warmer period commencing.

Agree,possible trend,others have also commented,think next 48/72hrs should firm it up if it is true.

[Frosty.]

15 minutes ago, markyo said:

Agree,possible trend,others have also commented,think next 48/72hrs should firm it up if it is true.

Fingers crossed markyo, day after day the GEFS is showing it x 3 so hopefully it's going to keep firming up. I and I'm sure most of us want a good August.

[Tamara]

Alignment of easterly winds across the tropics, courtesy of low atmospheric angular momentum (AAM) La Nina type forcing, is generating further Pacific sector amplification as discussed in previous posts.

This upstream amplification is manifested as a northward displacement of sub tropical ridges which fuel gradients as the jet stream crosses the inferno heat of the US and consequently adds some extra velocity as it enters the Atlantic sector.

This is a return to the conditions we saw often during the first half of the summer, until that mid season temporary rise in angular momentum adjusted the jet northwards across our Atlantic sector and allowed our temporary Western European ridge to deflect low pressure further to the NW of the UK.

But this week we are back to the all too familiar supressed flat pattern and procession of low pressure systems and unfortunately this looks set to continue next week after the cool polar maritime incursion this weekend.

The Global Wind Oscillation continues to be fixated especially around low AAM Phase 2  - with brief attempts at orbit into Phases 3/4 as tropical forcing wax and wanes as discussed below

This regime fully supports the advertised Atlantic Ridge and UK/Scandinavian trough alternating with the brief eastward ridging of the Azores High to the south of the UK. 

The next attempt at the start of next week, as the weekend NW flow eases out, is not likely to be successful beyond a drier warmer day or two, perhaps, for SE UK - but, fingers crossed, there are some better hopes as we arrive at the following weekend.

The previous updates in the last week or two suggested that a further uptick in AAM would occur (courtesy of amplified tropical convective forcing during late June/early July and which has a 30 to 60 day recurrence feedback lag on Rossby wavelengths).  The upshot of this in simple terms is that a more decisive attempt of the Azores ridge to edge the Atlantic jet northwards is still on target to hopefully occur as we head towards the second week of August.

The NWP hints of this therefore are well underpinned in the suggestions of more general improvement around the weekend of 6/7 August. However, as previously stressed, we should still see this as a feedback legacy response of temporary nature - and therefore not indications of any sustained settled spell.

The overall downward drift trend of GLAAM through the summer is very apparent, with just that short spike earlier this month to generate our recent glimpse of proper summer

In the absence of any renewed further amplified eastward moving tropical convection in the pipeline, such as seen in the first half of the summer, the concern is that there is nothing further to re-boot angular momentum and hence promote UK/West European ridging (beyond the upcoming feedback response). This implies further increased downward AAM tendency pressure heading through the last month of summer -  allowing easterly winds to keep persisting across the tropics, propping up the Pacific ridge, and perpetuating the downstream response that has frustrated the potential of much of the summer

.

It is no surprise that the METO updates appear a cut and paste out to 30 days. The mid Atlantic Ridge and Iceland/Scandinavian trough looks set as the default pattern in the remaining summer.  Further brief proper summer warmth obviously can't be ruled out, and there is nothing yet to suggest the pattern will worsen further from what we have been used to - but best make the most of those more settled interludes which will come along from time to time.

Edit: Next Morning in response to some latest post. Little joy is going to be found within the 10 day period. Any ridging, which would still likely be temporary, is more likely second week of August

Edited July 28, 2016 by Tamara

[Frosty.]

A promising end to a changeable / unsettled Ecm 12z run with high pressure to the southwest gradually building in across the uk by T+240.

[knocker]

After the influence of the showery north westerly from the low pressure to the NE over the weekend wanes the ecm has brief ridging until Wednesday when a low zooms in from the west bringing wet and windy weather to all. This quite rapidly clears reintroducing the ridge which hangs on, particularly in the south, as the next system tracks more to the north and by the end of the run the later is over Oslo with a ridge just to the west of the UK. Temps a little below average becoming average.

Edited July 27, 2016 by knocker

[Man With Beard]

I commented yesterday how there were some encouraging signs for the D10-D15 period - here's the graph for the past 4 GEFS runs for London:

Still signs of promise but a tad weaker than at this stage yesterday. Yes, still that potential for that super-hot run, with a number of runs topping 15C at 850Hpa and even a few above 20C - always notable when appearing at that range - but I'd say slightly fewer runs in the 10-15C range compared with last night, and the mean is a little down. 

The general thrust of a height rise in our part of the Atlantic is still on, and many ensemble members are still crackers (thanks Karl for highlighting this) - but the main reason for the very slight downturn is a few more naughty runs which manage to squeeze a trough in between height rises immediately to our west and to our east. Having said that, these are precisely the patterns that bring the mega-heat our way when slightly to our west. So a bit of a "risk/reward" board as we see things for D10 onwards tonight. But looking likely that the flat pattern will be mixed-up by the weekend after next.

To be continued!

EDIT - I see Meteociel has a new feature (or at least I hadn't spotted it before) - probabilities of a scenario happening - have a scroll through the timeframes after T192 and you can see how the warmer air infiltrates the UK (link: http://www.meteociel.fr/modeles/gefs_cartes.php?ech=192&code=0&mode=31&carte=&proba=1). Below are charts for T192 and T252 - you can see how the warmer air has [potentially!] encroached northwards:

 

 

Edited July 27, 2016 by Man With Beard

[Frosty.]

12 minutes ago, Tamara said:

best make the most of those more settled interludes which will come along from time to time.

Agreed Tamara, lovely post again by the way.

I think it's clear that this summer isn't going to become wonderful, e.g.. not expecting an August like 1995 but your last sentence sums it up in a nutshell really.

[Matthew.]

Great post Tamara looking longer term can't wait till this Azores high weakens after Summer, splits off and hopefully crosses the Uk's region, maybe September onwards as the Siberian High strengthens.

[markyo]

24 minutes ago, Karl. said:

Fingers crossed markyo, day after day the GEFS is showing it x 3 so hopefully it's going to keep firming up. I and I'm sure most of us want a good August.

Yep totally agree,i dislike hot weather but August is the most important month of the whole year for so many,holidays and trade associated,much more so than in the winter. Me thinks many eyes will be watching forecasts in the next week or so. Just myself hope that the humidity stays low,that's the part i hate!

[Frosty.]

13 minutes ago, Man With Beard said:

The general thrust of a height rise in our part of the Atlantic is still on, and many ensemble members are still crackers (thanks Karl for highlighting this) 

 

 

 

No problem

[Matthew.]

9 minutes ago, markyo said:

Yep totally agree,i dislike hot weather but August is the most important month of the whole year for so many,holidays and trade associated,much more so than in the winter. Me thinks many eyes will be watching forecasts in the next week or so. Just myself hope that the humidity stays low,that's the part i hate!

Yes for a pleasant warm spell we need this for August 7/8 instead of the hot/ possibly humid Spanish plume. 

Edited July 27, 2016 by Matthew Wilson