Model output discussion - summer rolls on

[Badgers01]

23 minutes ago, shaky said:

As a result is it warmer for the uk?!!

Nope high pressure forms much further west and we are left in cool and I would suggest cloudy North Westerly - a jittery run if we are to get the extension of summer into September!!

[MR EXTREMES]

interesting charts if it been dec or jan coldies would be getting excited.

interesting  from end of winter to now heights have been dominant to our northeast.

there plenty of heights around in the model runs over the last few days, so id expect this theme to continue for sometime yet although dry looks likely thundrey breakdowns could show up soon.

very slow sluggish out to our west although there is a chance the latest tropical storm developement might throw the models into chaos.

but in regards to temps theres possibilty as cooler air plunges down into eastern europe it could deflect our direction around scandinavia from either northeast or east.

although touch and go for a return to some late summer heat as well,

its possible we could pull in warmer or hotter temps from either southeast or a southerly although nothing mega is in the short term across all models.

but the atmospheric conditions are certainly not screaming stormy wet windy just yet.

 

so far 2018 would suggest not identical to 09/10 but certainly closer this year.

 

 

number of options on the table but predominantly from south, southeast east, or from the northeast .

must apologies for the charts mixed up the the ecm 192 shows chillier chance but by 240 we have a spanish plume so not the worst outlook by far.

the rest are similar but last nights later jma run was showing more cooler air making inroads.

but most models support plenty of heights around and as you all know!

this summer is proven to be pretty resilient so not much atlantic influence at all really.  

[Mike Poole]

Not many posts in here, understandable as now the settled high pressure dominated spell of weather is nailed on, and things will only change slightly from run to run.  The position of the high, and therefore the direction of winds will have a big influence on potential maximum temperatures.  

GFS 12z has an enormous high (for the time of year) at T240 drawing some warm uppers in as well, something to watch for in subsequent runs:

[SMU]

ECM continues to tout a fair old swing in pattern towards a solid -AO base state 

Cold air filtering into mid lattitudes may include the UK - but more so Central / Northern Scandi

[Frosty.]

That's a settled blocked and pleasantly warm looking Ecm 12z ensemble mean tonight as we go deeper into september.☺

[Man With Beard]

Well it's a good job this isn't January. A bit of northern blocking and modeling is suddenly going haywire. Gone is the benign endless high to our east - this morning we have high pressure staggering around northern latitudes like a drunkard. I don't even know where this morning's ECM fits in with last night's ensembles - it's not even close to any! 

[Frosty.]

The Ecm 00z ensemble mean is dominated by high pressure / strong ridging,  ergo I would expect largely settled / pleasant surface conditions with variable amounts of cloud and sunny spells, feeling warm in the sunshine but with clear periods overnight I would think some chilly nights with a risk of patchy fog forming.☺

[The PIT]

lala land is doing what it always does but the trend to take note of is the domination by High pressure. Interesting last night that the metogroup preferred the GFS outcome to the ECM. 

The main worrying issue still is the lack of rainfall though.

[Frosty.]

The Gfs 6z operational looks very benign throughout high res under high pressure / strong ridging bringing pleasantly warm fine days with sunny spells but with some chilly nights into the mid / upper single digits celsius and a risk of fog patches forming. Through low res (post T+192 hours) the settled spell crumbles (rather like England's batting!) and it becomes cooler and increasingly unsettled for a time before high pressure gradually returns towards the end of the run.☺

PS..tropical storm (s) to keep an eye on throughout this month  as the 6z operational shows!

Edited September 1, 2018 by Frosty.

[Tamara]

On ‎08‎/‎08‎/‎2018 at 16:01, Tamara said:

This ultimate destination of the low frequency tropical convection signal in later month involves, downstream, the re-implementation of a substantive ridge to the NE, likely overspreading an amplified upper trough that is perhaps more likely to dig southwards and become slow moving to the SW as opposed to the more progressive west>east solution in late July. The ramifications of this are highly interesting indeed for those of us who want summer extension to take us through to conclusion and beyond : 

More settled, but most especially the further north once heads and always a good chance of mid level convection and thundery potential showing up due to destabilisation c/o of the stalling trough to the SW spiralling up some embedded features in the humid airflow from the south 

The initial estimates, have proved to be a little on the extended end of the envelope ( and hence the fate of the last week or so of Augusts prospects less inspirational than hoped).

But overall the pattern has progressed reasonably well in terms of expectations as expressed initially some 3 weeks back. The one part of the jigsaw remaining, and which has been proving slower still to appear ( up to now) than envisaged is an upper trough showing signs of diffusing energy underneath any of the blocking.

This element is actually now materialising in NWP, however the suggested difference to the early analysis is that it might manifest itself amidst more of a -AO regime rather than the long prevailing +AO regime.

Taken at face value, this implies quite a possible difference in surface conditions to those envisaged in the captured quote because a less  +ve NAO set against a still prevailing +AO infers a mid latitude Sceuro block with upper trough in Atlantic disrupting to the SW to provide late season influx of humid air northwards (as per early August assessment)

On the other hand, and purely at face value (which is an important thought to retain) a -ve AO profile suggests the type of smorgasboard on offer from elements of latest NWP - with cooler upper air seeping around the blocking re-positioned at higher latitudes and a hard to pinpoint array of shallow troughs appearing in the upper cold pools of these troughs, at the same time as the direction of approach from troughs approaching from the Atlantic suggests possible fusion with these shallow features to erode the higher pressure regime further and further northwards.

But, as implied, this is getting way too far ahead in detail at a range that is still open to question in terms of why the broadscale changes are being suggested - and of course how likely and to what extent might they might verify.

On that basis, probably best to do some analysis of events since early-mid August. to try to make sense of it all moving forward

This period has been frustrated by some contradictory signals between the tropics and the extra tropics. The former attempting to resurrect something of a Nina flow with increase in easterly trade winds amplifying the pattern upstream (Atlantic/more supressed ridge and greater trough influence) and the extra tropics which have retained much of the westerly wind inertia of the tropical signal in late July (with the Scandinavian ridge and Atlantic trough that concluded the final days of that month) 

The tropical>extra tropical cycle is looking to set to resurrect this sequence again through September (as stated at the beginning, slightly later than first thought a few weeks back) and its no surprise to see the Scandinavian heights programmed accordingly.

Total global angular momentum is currently broadly neutral...

 

..., despite the on-going lull in the low frequency tropical>extra tropical cycle and has been largely dictated by micro scale tropical activity to a small degree in the Atlantic but more especially the Pacific as one might expect with an El Nino standing wave erratically implementing itself.

This balance of activity has helped support westerly wind inertia in the extra tropics whilst the easterly trade wind inertia in the tropics c/o  -ve South Pacific Oscillation influence (SPO) and also weak phase of the low frequency signal since the start of August has been represented by -ve frictional torque tendency which is now starting to trend more +ve (ahead of likely changes upwards in angular momentum tendency through September as discussed later)

 

The propagation of those -ve easterly winds in the tropics and subsequent degree of amplification in the Pacific has been negated of late in the extra tropics through the continued presence of the developing Nino standing wave and high levels of accumulated cyclonic energy (ACE) in the Pacific.

 

Hence any -ve Asian MT tendency, which serves to help decelerate the jet in the Pacific in response to the lead set by -ve frictional torque tendency from the tropics, has shown a much more muted response to the previous (much greater) trade wind response that propagated to the extra tropics in early summer

 

and prevented total global angular momentum from repeating the falls to the low point indicated of 8 to 12 weeks previously...

...and which at this time of year would be manifested as a very different outcome not just to the conditions of early summer, but to what we presently see nowcast synoptically according to the growing shift in seasonal wavelengths since then

 

Kind courtesy of @Snowy Hibbo if we look at an ECM plot of forecasted angular momentum tendency,the advertised rise through September as mentioned earlier on, is in evidence.

 

Backing up the CFS seasonal expectations (of which has proved a little progressive with the Nino standing wave) Note that both of these plots are overall tendency plot forecasts which have to be set against where total global AAM currently sits close to parity.

 

The upward trend in tendency imminently commencing from the current 'low point' (and as indicated by the rising frictional torque tendency plot as above) helps bring about the re-set return of extended heights to the NE and the suggested approaching trough from the west to replay the sort of sequence seen late July.

So this leads to the question of the suggested difference to late July in terms of the switch of heights from mid latitude orientation to progress to higher latitudes.

A large part of the complex global blocking picture is the effects of a northwards recurvature of super typhoon Jebi through the North Pacific (with ominous threat to Japan), as part of a tropical>extra tropical interaction creating a knock-on anticyclonic wave breaking pattern which shakes up the NWP picture in term of trying to fit the precise positioning of these blocks set against the broadscale factors already outlined.

 

There has been uncertainty as to the speed of downwelling westerly phase of QBO looking ahead through autumn (and then into implications for winter). This appears, to be now rapidly advancing through 30mb as is often the case when phase switches are becoming increasingly imminent

 

Much the same principle as stratospheric vortex switch regimes, the advancement of +ve westerly winds starts flushing out the existing -ve easterly phase winds to the surface and these manifest themselves as they exit into the tropospheric surface level as +ve height anomalies.

So on the basis of so many factors in play, then a lot of caution is needed in terms of NWP and how all the cards in the air fall to the deck. The background trend in angular momentum tendency to be rising through September well supports the overall continued evolution to an Atlantic trough and one which looks increasingly likely to undercut where the blocking mechanisms ultimately position themselves. The higher AAM potentially climbs through autumn then the more sub tropical jet energy seems likely.

In terms of detail this is obviously almost impossible to gauge, but suffice to say and as per some previous analysis during August, the more unsettled conditions perhaps further south and south west and more settled the further north one heads.  But with the suggested changes in latitude orientation of the high, this makes interpretation less reliable than was envisaged with a more mid latitude block. Nonetheless, with residual summer heat to the south, the track of any meandering troughs could have big local impacts in terms of boundaries of temperature and rainfall anomalies from one place to another.

But I suspect based on the presence of troughs appearing more and more to the west and south west that any cool air filtering around these large ridges further north and north east is going to have a hard time this early advecting far south and west enough to the greater part of the UK and the potential remains for very warm unstable and humid air, (especially with SST's still close to peak from the summer) to be some influence furthest south.

[Leo97t]

Colossal upgrade medium term on the Gfs 12z. Next week looks lovely and possibly thundery start

Below is out to +240

[Frosty.]

To call the Gfs 12z a colossal upgrade is very misleading, there is a much cooler unsettled spell later next week across northern uk in particular and the ukmo 12z becomes quite autumnal next week with cool unsettled conditions.

 

Edited September 1, 2018 by Frosty.

[Captain Shortwave]

37 minutes ago, Scorcher said:

How deflating...you really couldn't make the British weather up at times.

What just a couple of days ago like a nailed on settled spell has suddenly turned into a potentially awful spell.

Hard to believe that cut off low can just drop down from the north and then actually move westwards directly over us! Worst type of scenario in my opinion.

It may end up okay in the end, that low allows the jetstream to push east acrosd the north of the UK and into Scandinavia so by week 2 we now are looking at a strong area of high pressure centred over northern france and southern England so possibly a chance of warmer conditions developing than probably possible under a slack easterly feed which looked most likely a couple of days ago.

Still a slightly bizarre set up developing late this coming week.

[mb018538]

Very disappointing from my view too - you just know that upper low is going to be a pain in the backside and spoil things, when it looked nailed on for a good week across the UK. Hopefully it’ll move out quickly and pressure can rebuild.

[SMU]

6 minutes ago, mb018538 said:

Very disappointing from my view too - you just know that upper low is going to be a pain in the backside and spoil things, when it looked nailed on for a good week across the UK. Hopefully it’ll move out quickly and pressure can rebuild.

All to be expected in afraid...

If you look at the Sep / Oct NH patterns thread - We should be expecting a quasi stationary high to the NE & another blocking high towards the Kara / laptev seas 

This means that whilst we can get 'generally' a warm S/SE flow - There is also risk of high rainfalls in short periods of time due to stationary lows- 

All the HP anomalies that we are seeing to the NE & over the Northern Russian coast are low sea ice driven > Nothing more. Nothing less.

Edited September 1, 2018 by Steve Murr

[Frosty.]

Looking at tonight's Ecm 12z ensemble mean, there could be some cool unsettled weather, especially for the E / NE for a time later next week but there is considerable uncertainty about it which was highlighted on the 21.55 forecast on BBC News 24 and it could well be that next week is quite pleasant / benign with sunny spells and light winds under high pressure / strong ridging but also some chilly nights with a risk of patchy fog forming where skies clear. The mean ends nicely with warm fine weather further s / e but more changeable and cooler atlantic conditions for the far nw / n.

Edited September 1, 2018 by Frosty.

[Froze were the Days]

ECM reverts back to good old HP close to the south in 8/9 days time backed up by GFS 12z and a warm to very warm Tm air mass after what looked like a cooler period with blocking to the north and fairly settled, so now only a cooler period country wide for a few days after about Monday/Tuesday but as others have mentioned could be rainy for a couple of days or so after that.

Edited September 1, 2018 by Froze were the Days

[LightningLover]

why hello there, CFS...

[Midlands Ice Age]

4 minutes ago, LightningLover said:

why hello there, CFS...

Hasn't it just changed the dates from this year?.

MIA

[MP-R]

38 minutes ago, LightningLover said:

why hello there, CFS...

Two months late but nice to look at!

[SMU]

This mornings ECM chart would bring some incredible weather to the UK at day 8/9/10

Long may that continue....

 

[Man With Beard]

3 hours ago, Steve Murr said:

This mornings ECM chart would bring some incredible weather to the UK at day 8/9/10

Long may that continue....

 

Ironically this interruption next weekend could lead to something even more summery down the line - rather than an easterly, we end up with a southerly flow.

That strong south to north movement evident in the clusters

but hard to have confidence given the recent turnaround

[ANYWEATHER]

Evening! After a Projected high pressure scenario for September certainly for the first half its all change ....Low pressure developing across the nation....umm ummm aghh

[Scorcher]

A bizarre state of affairs coming up this week- one of the strangest evolutions I've ever seen with the UK seemingly a magnet to that tiny trough. How often do you see a trough moving westwards, this strange setup is likely to lead to something even warmer than was previously shown for this week. True autumn is still a fair way off.

Edited September 3, 2018 by Polar Maritime
To move discussion on.

[Frosty.]

Longer term that's a great looking Ecm 12z ensemble mean tonight if you like settled and warm weather, especially if you're further south.☺