Model Output Discussions 12z 03/05/2016

[Tamara]

Following up from the repeated explanations this summer of what has been required to try and edge the default seasonal pattern away from the spot welded Atlantic ridge, flat supressed jet stream and troughing to the north and across into Scandinavia, the simplest representation of why current NWP has been tinkering around with high pressure scenarios that bit further east, is reflected by GLAAM edging into very weak +ve territory for the first time since the start of June - when it first went into -ve territory after El Nino. Which so happened to be the start of summer...

It had nearly achieved the same in July as the graph shows, and no coincidence that the last phased attempt at properly summer-like weather across the nation as a whole was observed fairly soon afterwards, albeit far too briefly. This time, the signal is marginally improved - albeit it still doesn't go the whole way.

Westerly winds added to the atmosphere are propagated northwards and eastwards from the tropics and through mid latitudes, as detailed in previous post 'why's and wherefores', and, if strong enough to overcome easterly inertia present, create those anticipated downstream Rossby waves to inject some amplification and ridging into the pattern in our European sector of the Northern Hemisphere. This provides the important mechanism to attempt to try and swap the Atlantic ridge for a trough, and Scandinavian low replaced with high pressure. John Holmes empirical guidance on formation of Scandinavian High pressure is always a good read (especially in anticipation of winter time easterlies)

The wind westerly additions to the atmosphere are represented here by the orange shadings close to 30 degrees south.

 

It also very well illustrates why the precise relationship that the atmospheric circulation adopts to the base ENSO state, is much more important and relevant than the ENSO state itself when it comes to the specific weather patterns that NWP adopts in accordance to them. Especially in the fuzzy no mans land transitional zone that has dictated the fortunes of the summer and formed the basis of the theme of these posts.

As it happens, we currently have the 'best' coupled relationship of the whole summer - certainly in terms of better weather synoptic. A broadly neutral co-relationship, but currently with total angular momentum fractionally the better side of neutral for the first time rather than existing in a lower more Nina trended type circulation (relative to the base state).

However, the same caveats and uncertainties exist as per the previous post in terms of longevity and extent of this window for a fine weather spell  There remains latent easterly inertia in the atmospheric circulation which is reflected in the modelled ENSO expectations of an overall weak Nina status during autumn.  In accordance with seasonal wavelengths, this acts against the formation of lasting anticyclones for the UK and nearby Europe, and instead the inclination to reverse the pattern to Atlantic ridge and downstream trough

The current more favourable wave trains do not look sustainable heading through later August and into September on this basis. As soon as the current tropical forcing wanes across the Pacific, then in accordance with present indications, the recent westerly additions to the atmosphere (and with them the current ridging suggestions in our sector) will also vanish and the default looks to be restored.  

Composite anomaly charts always need some cautionary interpretation attached to them according to various prevailing factors, but always trust the overall Global Wind Oscillation phase signal which reflects the total atmospheric circulation budget over just the tropical MJO signal in isolation. Extra tropical signals such as frictional and mountain torques have a different and shorter wavelength, or lifeline, to tropical convection feedbacks in terms of their effects on synoptic patterns - but they nevertheless can either augment or offset the direction of travel that the overall atmosphere is heading in. In this way, the reflected circulatory and pattern composites that are suggested as template guidance, can be unreliably skewed.

With all this in mind, I think the well timed GLOSEA signal of height rises over Scandinavia for mid month very appropriately reflects the latest more 'friendly' turn of the atmosphere circulation for UK and parts of NW Europe. Its always been the case though that such a long term seasonal signal for a change in pattern is never a guarantee of sustained change within that season - especially when a cusp ENSO/atmospheric signal still has La Nina tendency to play out.

So I would also suggest this is why the Global Synoptic Dynamic Model (GSDM/GWO) framework does not support a high enough angular momentum phasing through 5/6 to sustain any hot(ter) spell in our sector, and continues to tread water with a weak directional signal in the days to come (ahead of a probable fall in angular momentum as soon as tropical convection ceases and heads back towards the Indian Ocean).

 

That will likely have repercussions for the weather patterns to end the summer and the beginning of autumn

As things stand more immediately however, there is good background support for suggesting that the most recent NWP modelling has been a little too keen, maybe because of climate adjusted biases, to remove the heights building through the UK into Scandinavia next week.

Within those confines of what is 'do-able', as things stand the south of the UK gets a decent length fine spell that extends further northwards into the start of next week to give the rain sodden parts of NW'ern most areas at least a consolation break, and is much less keen to break down as prematurely immediately as overnight Tuesday as face value modelling suggested yesterday.

Latest ECM extended ensembles for London are supportive of comfortable temperatures remaining for a time after the warmest conditions subside later next week. There are plenty of warmer solutions than the continuing rather progressive operational beyond day 7/8

So for the medium term beyond the initial heat spike in the first part of next week, the break down return to changeable conditions may well be slower and more erratic than happened in July.

However, the further we had towards the end of August and official end of summer, the more likely it seems to me that unsettled conditions may establish more widely once more as angular momentum falls, and the pattern upstream retrogresses once more..

Not quite large scale attractive end of summer expectations for everyone, but within the restricted possibilities that this summer offers to the nation as a whole, its better to be glass half full than empty one might suppose

Edit:  @ Gordon - thanks - changed it for you!

 

Edited August 12, 2016 by Tamara

[johnholmes]

Some of the comments above from Tamara, re things looking better than most of the summer but still liable to uncertainty re warmth for all is perhaps why the anomaly charts back tracked a couple of days ago.

Around last weekend, NOAA especially, suggested a sufficiently large upper ridge pretty much over the UK to give, as I erroneously suggested, 6-10 days of 'good' weather for much of the UK. The 3 then showed an eastward or NE'wards movement of the major ridge-trough pattern, leading to the synoptic outputs suggesting the breakdown by about Tuesday (currently looking more like Wednesday from the latest outputs).

The charts today and last evening (NOAA) perhaps are suggestive of a bit of a delay, or maybe more than this in the onward movement of the west to east usual progression of the upper wave pattern and its subsequent mirrored pattern at the surface.

If the NOAA output this evening goes with the idea of a Scandinavian ridge holding, or even retrogressing slightly, then the mostly dry spell with warmth, at least in the SE third of the UK, may be nearer the mark?

 

[Gordon Webb]

looks like summers last hurrah is next week

Thanks Tamara again for an interesting post , I understood a little but got stuck after the word depressed in the first line lol

live and learn well live anyway

[Man With Beard]

The Atlantic is now stalling so far west, it's taken the bit of the plume that reaches the UK through the SW and into Ireland. I wonder if there will be a last minute push east of the pattern as often happens at around T48/72 when a plume is involved. 

Although deep heat looks off the table now, I think the alternative solution now found will please more people as Wednesday increasingly looks sunny and very warm or hot for most, and many GEFS ensembles now have Thursday as very warm and dry too. So several decent T-shirt and evening BBQ days rather than one hot bang if that happens (and things can change very quickly on the models when a Scandi High is in place, of course, even at T72). I still think we'll see a 30C somewhere next week, seeing as 28C was managed today...

...though the ECM tonight has bizarrely put a miniscule cold pool into the pattern over E England for next week. Seems a bit odd! Not in any other output today or all this week. Will have to see if it has any credibility in the morning!

As for the future, I sense the Azores High is going to have another go next week...

Edited August 12, 2016 by Man With Beard

[MP-R]

Fantastic post Tamara, thanks! Always enjoy reading your posts. Correct me if I'm wrong but I take from that that the majority of the rest of August looks fairly settled with varying degrees of warmth (though as today has proven even with high pressure overhead it's been cool and windy), then a descent into a more unsettled and perhaps traditional September.

[knocker]

Quite an interesting evolution on this evening's ecm, not that it will verify. It also slows the front down and at 12z Thursday has it aligned N. Ireland-N.-Wales-Chichester with much activity in the southern portion. The temps behind the front are in the 16C range and in front around 24C in Lincolnshire and East Anglia.

from here it swivels the front with a small low pressure area forming which by 00z Saturday has become a large slack area of low pressure from the UK to Denmark. All of this brings a quite chilly end to the week.

[Matthew.]

I'd take this anti-cyclone starting Sunday from the ECM anyday over the plume:

Edited August 12, 2016 by Matthew Wilson

[knocker]

The 6-10 anomalies tonight are more or less on the same page. Deep low over the Pole with a negatively tilted trough in the Atlantic. High pressure eastern Europe which ridges west over north Scandinavia. This doesn't constitute a Scandinavian high in my book as there is a low pressure area to the south and it isn't a block. This pattern would portend changeable weather, particularly for the north but doesn't of course rule out ridging from the Azores influencing things in the south as is indicated around the 22nd. Temps generally around average but with the usual latitudinal variations.

In the later period there is no strong signal but we still have HP eastern Europe with a weka Atlantic trough s the indications are a westerly upper flow with nothing particularly remarkable about the weather, changeable but pleasant interludes within the Low pressure and high pressure phase changes.

[phil nw.]

Just for info,some off topic posts have been removed-no model discussion.

Just a reminder that general weather chat should go in other threads.

Thanks.

[William Grimsley]

Warm and sunny weather to come according to the ECM and GFS! Could end up with an intense thundery breakdown as well!

Edited August 12, 2016 by William Grimsley

[knocker]

Today

Some sporadic light rain moving south over central England with showers N. Scotland. Marked contrast in temps between NE Scotland and SE England

The GFS this morning is a bit of a dog's breakfast.

Monday sees the anticyclone centred over the North Sea with the frontal systems 300Km to the west of Ireland. The HP proceeds to driftt NE whilst the front tracks east and tends to fragment as it nears the UK but by 06z Weds it's lying N. Ireland to the south west. It continues to track  east, dissipating along the way, bringing thundery outbreaks to places whilst at the same time another low tracks NE to the west with associated fronts straddling the west of the UK by 12z Friday.

Temperatures during this period are quite geographically different. Tuesday perhaps 26C in the far south but 16C-22C north of the Midlands. Wednesday perhaps 28C in parts of England but 14C-22C in Scotland. Thursday 26C in central England, 16C -22C in Scotland.

The week pretty dry with most of the rain in the north west.

All in all not a bad looking week.

Edited August 13, 2016 by knocker

[knocker]

The ecm also has the front crossing the UK during Wednesday, perhaps a little behind the GFS, bringing showery outbreaks perhaps thundery. These continue on Thursday as the convective area drifts east but it tracks the next depression NE over the UK perhaps bring more outbreaks by Saturday. i think the evolution post midweek best put in the pending tray. Temps no great shakes. Struggling to 24C in the Bristol area Tuesday. Better on Weds 24-26C in the Midlands and south  Thursday struggling to 24C in places in the south and 16-20C in the north.

All in all not a bad looking week.

Edited August 13, 2016 by knocker

[Man With Beard]

Fair analysis there from Knocker.

The change to an easterly rather than south-easterly draw on Tuesday has killed off chances of the hottest air reaching us - still might squeeze a 30 somewhere between Bournemouth and Cheltenham but perhaps 28 or 29 the top mark now.

However, the trade-off is good, and that is the prospect of lots of sunshine and not inconsiderable warmth between Monday and Friday (the south coast already in the warmth), with mid-20s a regular occurrence in most of England and perhaps even Wales and parts of Scotland at times. The Atlantic push has almost died off on some runs and I can see it being dry all week for many - Weds/Thurs pose the risk of showers but even that I doubt. However, the easterly draw will peg back temperatures on the east coast.

The UKMO T144 is interesting, as it shows another small depression approaching the SW right at the end of the week - currently well positioned to bring an even stronger draw of southerlies. Eastern areas may hot up even more if that verifies.

So, all in all, not a heatwave that will be remembered for years to come, but possibly the best week of the year for some, and it will feel like a heatwave in the midday sun!

[karyo]

It is worth adding that the nights should be comfortable for sleeping this week which for me is a huge advantage.

[Gordon Webb]

31 minutes ago, karyo said:

It is worth adding that the nights should be comfortable for sleeping this week which for me is a huge advantage.

perfect combination essentially dry and warm by day and comfortable by night

[johnholmes]

If the NOAA output this evening goes with the idea of a Scandinavian ridge holding, or even retrogressing slightly, then the mostly dry spell with warmth, at least in the SE third of the UK, may be nearer the mark?

and it does see below

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

but not the 8-14 so by day 10 we will be seeing a change I would imagine, not looked at this morning for ECMWF-GFS,

so here goes

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

Not unlike what they both showed yesterday with GFS nearer to NOAA.

I still reckon the arrival of the Atlantic will be slower than some of the synoptic models show at times, or rather, have done over the last 48 hours. No major heat but pleasant enough for much of the UK.

[Fourty Point Three Degrees]

the beeb have embarrassed themselves using "30" on their map but yet highlighting only 22 for London on Tuesday. .

[markyo]

25 minutes ago, 40*C said:

the beeb have embarrassed themselves using "30" on their map but yet highlighting only 22 for London on Tuesday. .

No idea where your coming from on that one,the model output has obviously  changed,beeb and the rest can only run on what information they have. They aren't perfect in any way but i suspect a lot better than many at predicting the general trend and picking little points of discrepancy is in my view wrong. No way are they embarrassed.

[Polar Maritime]

Strictly Model Output Discussion only please in here, There is a BBC Weather thread already open, Thanks.

[Summer Sun]

It does look like the Atlantic breakdown will be slower than previously though a good deal of pleasant weather around from tomorrow till mid week and with the nights not too warm it should be a good mix

[Snowyowl9]

Havn`t seen charts like this in august since I can`t remember 1995,although I want the thunderstorms now.

[Singularity]

More and more as we move through the runs, we see the ridge across Scandinavia nosing west and disrupting the Atlantic jet, with an increasingly shallow low to the southwest making ever-less inroads.

Already this looks to have more-or-less secured a retention of dry conditions through Tuesday for all, and through Wednesday away from the far (south?)west. Thursday remains in the balance.
After this, we still have a new area of low pressure looking to wander across Fri-Sun, but the track has been adjusting this way and that and who knows, if trends to strengthen the Scandinavian ridge continue, we might well see that low traversing the likes of France instead. I'm hoping to attend events in the far south on both days of the weekend, for which a track to the north is a safer outcome for dry conditions and warmth - but that'd be wishing more rain on those in the northern half of the UK, which is far from fair - not that the weather actually has anything to do with what I wish for 

[Nouska]

4 minutes ago, Singularity said:

we might well see that low traversing the likes of France instead.

I did raise an eyebrow at the UKMO 168 hour chart last night - almost identical to what the ECM had this morning.

The MF app has a lot of rain at day 7 so maybe their modelling is similar.

00Z runs from ECM and UKMO

     

[knocker]

I keep seeing the Scandinavian ridge mentioned but it's not that apparent on the GFS det.his evening.

Edited August 13, 2016 by knocker

[William Grimsley]

GFS still hinting at a thundery breakdown later on next week!

 

 

Edited August 13, 2016 by William Grimsley