Model Output Discussion - 31/8/14 Onwards.

[Captain Shortwave]

No real sign of the Atlantic returning, the low to our south west does try to approach the UK, but without any help it simply fills to the south west of the UK, it could destabilise the atmosphere enough for a few showers, but that is about it.

Even out to day 10, it still looks like drier than normal conditions will prevail from the GFS ens

Day 6 charts from the GFS/UKMO/GEM

Very warm and humid cyclonic south easterly flow with the 12C isotherm getting into the south of the UK. Possibly heavy and thundery showers could develop in this pattern.

[Polar Maritime]

The GFS this morning is showing the Atlantic making inroads around the 25th from a cool N/W flow..

 

Edited September 12, 2014 by Polar Maritime

[mushymanrob]

It's interesting you mentioning the warmth because the latest met office update isn't hinting any unusual warmth next week, indeed, they say the settled spell will fade out later next week with unsettled weather spreading from the southwest by 2nd half of next week, it's another case of some modelling showing potential hot and humid weather and then the met office saying temperatures just above average..there is a big low down to the southwest and it appears to be heading our way and impacting on the uk by midweek onwards.

 

do they?... oh well ill argue with them then

 

i guess how warm itll be depends upon cloud cover, which will increase as pressure drops as that low becomes dominant. the inceased humidity too will help it feel warm too. but im sure that if they are right, and temps are 'just above' average, itll feel warm in the humid air. and of course theres time yet for changes in the detail either way.

i remember mid sept '73 when we had similar synoptics, it wasnt so much the heat but the humidity that was notable.

[IDO]

The GFS this morning is showing the Atlantic making inroads around the 25th from a cool N/W flow..

 

 

 

Then again it could play out like the GFS Control:

 

 

 

HP in charge from D8-16. FI remains uncertain with around 50:50 settled or more unsettled: 

 

It seems sensible to assume the status quo till there is a stronger signal pointing elsewhere. In any case with ex Tropical Storms possibly entering stage left around D8-D10, we have a trigger for a pattern change either way. GEM handles this different from GFS in timing and track:

 

GEM:   GFS: 

 

Good support now for week 1 with declining pressure and rising temps for the south with convective showers possible but no washout:

 

Then things get messy as the trough/cut off upper low towards the Bay of Biscay is squeezed out by it's flanking Atlantic and Euro ridges. Models then have subtle differences as to how this goes down though a general rise in pressure for the south is the likely outcome. More runs needed.

Edited September 12, 2014 by i'm dreaming of...

[knocker]

Knife edge?

 

[Frosty.]

We need to keep an eye on that large area of low pressure near the azores, the Gfs 00z op run shows it slowly heading our way and just after midweek it brings a potentially very showery and increasingly hot and humid thundery spell. Anticyclonic conditions are set to persist up to the middle of next week, then we import continental heat with storms cracking off, peaking next friday night, then pressure rises again bringing fine, warm and sunny weather to most of the uk but towards the end of the run we are into a more undulating pattern with ridge, low, ridge & the jet tilts more to a nw / se alignment with vigorous depressions racing our way and the first shot of very cool air of the autumn takes a swipe at scotland to end the run.

Edited September 12, 2014 by Frosty.

[johnholmes]

IF that run turns out as predicted then the current Tropical Storm is the main feature behind the marked change at the end on those charts frosty shows

 

current position and predicted track for the next few days see link below

http://www.nhc.noaa.gov/

 

Neither of the 2 main models at that stage agree, EC below at 192h shows no major low

http://www.wetterzentrale.de/topkarten/fsecmeur.html

whilst GFS at the same time does

http://www.wetterzentrale.de/topkarten/fsavneur.html

 

so an awful long time to go before we can see just what effect, if any, the latest tropical storm may have on the UK.

As always NO model deals well with these features so best wait until T+xx is down to no more than 120-144 hours I would suggest.

 

But remember how the last one more or less ended the heat of summer! Summer being 1 June-31 August in meteorological terms before some start to argue about the last week or so.

Edited September 12, 2014 by johnholmes

[knocker]

The GFS tropical runs it thus

 

[Frosty.]

No comments on the Gfs 06z? get the BBQ ready

 

It shows a hot and humid spell for southern uk later next week, thurs, fri and saturday..it could be a mid  /  late september sizzler with temperatures into the mid to high 20's celsius..not bad huh   it also shows an increasing risk of heavy showers and thunderstorms breaking out and also spreading up from the scorching near continent, The 6z then shows the atlantic breaking through and forcing the block further east, turning much cooler and fresher from the west with heavy rain pushing east to all areas but the anticyclonic block fights back with help from the azores, however, vigorous atlantic depressions are a significant feature later in low res with much more autumnal conditions later in the month.

 

Sooo..anticyclonic until almost midweek then hot, humid and thundery for 3 days

[mushymanrob]

No comments on the Gfs 06z? get the BBQ ready

 

It shows a hot and humid spell for southern uk later next week, thurs, fri and saturday..it could be a mid  /  late september sizzler with temperatures into the mid to high 20's celsius..not bad huh

 

have the met office updated their temp prediction yet, from 'just above average' to 'warm' or 'hot'?..

[Frosty.]

have the met office updated their temp prediction yet, from 'just above average' to 'warm' or 'hot'?..

Not really mushy man rob..same as although reading between the lines, a little warmer than yesterdays summary.. initially anticyclonic and on the warm side, I suspect on the warm side could mean well into the 20s celsius, something to firm up on as the timeframe approaches. Rain and showers spreading from the southwest beyond midweek, then temperatures dropping a little at the end of next week, then a very unsettled further outlook, cooler and more atlantic driven by the sound of it    

Edited September 12, 2014 by Frosty.

[Spikecollie]

As I said in the convective thread, this seems to be a very similar setup to September 2006 when warm thundery weather came up from France. I've been watching this all week on the French weather sites and they have been getting more and more committed to it. I think come about Wednesday the alerts will start to be issued over there. They are very clear on the warm, unstable air coming up from the Iberian peninsula. Temperatures progged over there up to 30c. I'll be your roving reporter!

[phil nw.]

The heat plume still showing on the 12z GFS Operational for the end of next week.

Temps well into the the 20'sC and a risk of storms still being shown on this run.

 

Not sure that it will play out like this though with mean outputs indicating something less dramatic.

Signs that our semi-resident block will be pushed away eastwards as we go through next week but the uncertainty lies in the behaviour of that Iberian low.

Longer term things do look like changing eventually into a more  Atlantic driven pattern.

Edited September 12, 2014 by phil nw.

[Scorcher]

Not really mushy man rob..same as although reading between the lines, a little warmer than yesterdays summary.. initially anticyclonic and on the warm side, I suspect on the warm side could mean well into the 20s celsius, something to firm up on as the timeframe approaches. Rain and showers spreading from the southwest beyond midweek, then temperatures dropping a little at the end of next week, then a very unsettled further outlook, cooler and more atlantic driven by the sound of it    

 

Can't see any evidence of this Atlantic driven weather in the models tonight Frosty, if anything the predominant airflow is from the east/southeast. If the 12Z GFS is to be believed it will actually get warmer towards the end of the week. 

[Frosty.]

Can't see any evidence of this Atlantic driven weather in the models tonight Frosty, if anything the predominant airflow is from the east/southeast. If the 12Z GFS is to be believed it will actually get warmer towards the end of the week. 

Hi Scorcher, Gfs in FI today, (0z and 6z at least) shows the atlantic firing up and more importantly, the met office expect unsettled weather to become more dominant further ahead.

[Captain Shortwave]

Hi Scorcher, Gfs in FI today, (0z and 6z at least) shows the atlantic firing up and more importantly, the met office expect unsettled weather to become more dominant further ahead.

I think anything properly Atlantic driven is a long way off at the moment, we will see some rain or showers beyond this weekend as pressure falls and low pressure to the west of Portugal threatens the UK. Looks warmer than average and any rainfall isn't guaranteed to be honest.

As ensembles go, there is agreement on the ridge to our east declining somewhat, though the jet still looks to be taking a more northerly path than usual so more of a north/south split with the south becoming drier than average whilst the north sees more mixed conditions.

A long way off, this Scandi high/ Iberian low combo could continue on for much longer than we currently think. 

[Scorcher]

 

This looks like a superb chart for the time of year if you're after more warmth- I think I'm right in saying the airflow would be south of east which tends to be a good direction for sunshine with such a short sea track, even without particularly high pressure.

Edited September 12, 2014 by Scorcher

[phil nw.]

I think anything properly Atlantic driven is a long way off at the moment, we will see some rain or showers beyond this weekend as pressure falls and low pressure to the west of Portugal threatens the UK. Looks warmer than average and any rainfall isn't guaranteed to be honest.

As ensembles go, there is agreement on the ridge to our east declining somewhat, though the jet still looks to be taking a more northerly path than usual so more of a north/south split with the south becoming drier than average whilst the north sees more mixed conditions.

A long way off, this Scandi high/ Iberian low combo could continue on for much longer than we currently think. 

 

I guess Atlantic driven wrt the outlook beyond the plume can be interpreted in different ways Captain.

We are certainly not looking at raging zonality perhaps a westerly pattern would be a better term in this instance.

 

A change to that outlook is now being modelled beyond any plume around next week end, as opposed to the current east/south east setup.

Thicknesses still look reasonably high into week 2 further south and with the lowest heights to our north west it looks like our typical north/south split perhaps.

 

Days 5 and 10 mean Atlantic flow

 

Still some decent Autumn days would result from that i would think with the Atlantic jet still not yet fully awake.

[Frosty.]

I think anything properly Atlantic driven is a long way off at the moment, we will see some rain or showers beyond this weekend as pressure falls and low pressure to the west of Portugal threatens the UK. Looks warmer than average and any rainfall isn't guaranteed to be honest.

As ensembles go, there is agreement on the ridge to our east declining somewhat, though the jet still looks to be taking a more northerly path than usual so more of a north/south split with the south becoming drier than average whilst the north sees more mixed conditions.

A long way off, this Scandi high/ Iberian low combo could continue on for much longer than we currently think. 

I wish Fergieweather or Gibby were here to give their opinions on late september, however, I have seen a lot of charts which suggest a more typical autumn pattern will eventually win out against the stubborn block in a few weeks time. I think most crucially the met office are currently going for a generally more unsettled further outlook with atlantic depressions eventually peppering the uk, especially northwestern uk.

 

Just to clarify..I have lots of respect for captain shortwave's opinions too...and many others, too many to name..keep up the GREAT WORK Guys

Edited September 12, 2014 by Frosty.

[knocker]

I guess Atlantic driven wrt the outlook beyond the plume can be interpreted in different ways Captain.

We are certainly not looking at raging zonality perhaps a westerly pattern would be a better term in this instance.

 

A change to that outlook is now being modelled beyond any plume around next week end, as opposed to the current east/south east setup.

Thicknesses still look reasonably high into week 2 further south and with the lowest heights to our north west it looks like our typical north/south split perhaps.

 

Days 5 and 10 mean Atlantic flow

1.pngviewimage (3).png

 

Still some decent Autumn days would result from that i would think with the Atlantic jet still not yet fully awake.

 

Looking at the difference between the 6-10 and 8-14 NOAA anom. I'll settle for a westerly pattern. There is major change with the block weakening and moving east and a very weak trough south of Greenland.

Edited September 12, 2014 by knocker

[johnholmes]

Looking at the difference between the 6-10 and 8-14 NOAA anom. I'll settle for a westerly pattern. There is major change with the block weakening and moving east and a very weak trough south of Greenland.

 

 

The 8-14 rarely does anything more than smooth out the 6-10 pattern and anomalies be they + or -. Only once in perhaps 20 issues maybe even more, does it keep the same intensities as the 6-10 or even rarer go for a definite change in pattern, so nothing unusual in what the above charts suggest.

[knocker]

Okay thanks John.

 

So looking at the ECM and GFS anomalies and they are very similar with the HP to the north east and the Spanish low to the south west.

 

On the surface the HP is further to the east with both and the shallow area of low pressure encroaches the UK particularly the south introducing some moister air and with the general southerly flow, some quite warm temps.

 

[Frosty.]

John Hammond just said turning pretty warm indeed later next week, the biggest hint yet that mid to upper 20's celsius could be on the way for southern parts of the uk as per the gfs has been showing today. Also mentioned Tropical Storm Edouard which could develop into a hurricane and it's track, although nowhere near the uk, could have significant implications for the uk weather longer term..such as a brief unsettled blip later next week and then high pressure returning.

[phil nw.]

The 8-14 rarely does anything more than smooth out the 6-10 pattern and anomalies be they + or -. Only once in perhaps 20 issues maybe even more, does it keep the same intensities as the 6-10 or even rarer go for a definite change in pattern, so nothing unusual in what the above charts suggest.

Just a thought about those NOAA anomaly forecasts.

On those anomaly charts the signal for change in week 2  is less obvious .The second image is after all only an average spread of the pattern through days 8-14.

If we refer again to the daily mean charts from around day 9/10 onwards it's much clearer that the Scandinavian ridge moves away as the pattern changes further on to a westerly.

Just one of the reasons to best view those anomalies in conjuction with the daily mean charts to clarify the general trend towards any changes. 

Sometimes there are only subtle changes to those wavelengths and positioning(green Contours) from one to the other, especially when the anomaly differences are small as they are currently.

[damianslaw]

Lots of uncertainty in the longer term thanks to the development of further ex-tropical storm activity coming into the mix - it seems we are at the mercy of these features at the moment - they have certainly been the big player and there track appears to be crucial as to how things pan out here, hence BBC mentioning a northerly tracking feature which I suspect would mean a strong ridge anchoring itself over the country, but its all conjecture at this stage.

 

In the reliable - the high pressure looks like declining slowly eastwards allowing low heights over Iberia to edge NE towards our SW shores producing greater instability. Indeed before then we have a very weak warm front moving westwards into eastern Britain meaning much cloudier damp conditions by Sunday and into the start of the week for much of the east and north east.

 

As we move towards the latter part of the month -you would expect the atlantic to start to fire into gear, its rare for it to go into sustained slumber at this time of year for any great length of time - the odds quickly start to stack in the favour of the atlantic, very much a case of waiting for the inevitable, but an unusually long wait it seems this year..