Model Output Discussion 18z 28/07/13

[Frosty.]

The Ecm 00z is a peach of a run once the weekend low is out of the way, high pressure builds strongly from the south and intensifies, then becomes centred to the east, beyond T+240 hours it would turn hot & sultry from the continent but with an increasing threat of storms, but most of the run is settled, warm and sunny with temps in the mid to high 20's celsius...BANK 

[Frosty.]

The GEFS 00z mean is another peach of a run once the weekend low is out of the way, becoming very warm and anticyclonic across the whole of the BI during the course of next week, the PFJ is forced to retreat well to the northwest and the atlantic looks very benign which would bode well for a prolonged settled spell stretching into september.

Edited August 14, 2013 by Frosty039

[forecaster]

Although the EC deterministic and ensemble are in good agreement synoptically for much of the period, towards the end of the 10 days there is a stark difference in the 500hPa heights, and this is why the ensemble mean does not have surface pressures rising to our east. Although it's happy about the ridge extending from the west and giving us a spell of settled weather.

 

 

 

See above, with the ensemble mean giving a very flat W/NW 500hPa flow whereas the deterministic is trying to develop an Omega type pattern. The lack of agreement from within the ensemble itself suggests that the surface pressures rising to the east - with potential blocking pattern - is not yet highly predictable from the current atmospheric conditions. 

[Nick F]

Although the EC deterministic and ensemble are in good agreement synoptically for much of the period, towards the end of the 10 days there is a stark difference in the 500hPa heights, and this is why the ensemble mean does not have surface pressures rising to our east. Although it's happy about the ridge extending from the west and giving us a spell of settled weather.

 

 

 

See above, with the ensemble mean giving a very flat W/NW 500hPa flow whereas the deterministic is trying to develop an Omega type pattern. The lack of agreement from within the ensemble itself suggests that the surface pressures rising to the east - with potential blocking pattern - is not yet highly predictable from the current atmospheric conditions. 

 

Looking at those H500 ens mean and deterministic charts, it looks as if the fortunes of any omega-type ridge building over the UK/Nern Europe will fall on whether the trough digging S/SE over Scandi disrupts into a cut-off low or not. The EC ens mean and 00z GFS op doesn't disrupt properly, but the deterministic charts on the right clearly show a cut-off low forming over SE Europe - which allows heights to build NE through the gap over UK and France.

Edited August 14, 2013 by Nick F

[Captain Shortwave]

Very little confidence this morning on where we go, that little low is a real pain for forecasting.

GFS - flattens the first ridging attempt with the shortwave, high pressure builds but in the high resolution part of the run its pretty cool with the shortwave aiding to dig troughing into Scandinavia. Overall pretty poor in comparison to previous runs.

UKMO - Don't know what to think, it doesn't make much of the shortwave but the pattern is pretty similar to the GFS at T144, trouble is it's probably got the pattern too far south as usual.

ECM - absolute peach of a run, doesn't make much of the shortwave, last frames are pretty much perfect for widespread sunny conditions (maybe rain in northwest Scotland at day10)

GEM - Settled spell, what settled spell? Just continues the mixed conditions, high pressure builds like the GFS but a lot later (note this is 3 runs in a row the GEM has done this)

The way I see it is the chance of a drier spell of weather is pretty high but we could have;

1) A heatwave starting as early as the 21st/22nd August if things go in our favour.

2) The settled spell could turn into a non event if models shift towards the GEM.

 

Oh GFS 06Z, the shortwave isn't even there at T120,

edit - it's there now, but it develops a lot slower than previous runs and has a better track to it

Edited August 14, 2013 by Captain shortwave

[Tamara]

It looks to me as if the initial ridge that positions itself close by over north east France and towards the south of England effectively dissolves into a more dominant cell from the atlantic behind the weak indeterminate shortwave feature that ripples along ahead of it. It is probably this which is creating 'noise' in the ensembles as to where exactly the final High pressure cell sets up. And being slightly east, slightly west or central to the UK can have subtle implications for weather on the ground in terms of temperature and cloud cover etc etc.

 

The EPS members this morning illustrate the full range of High pressure options developing by day 7 i.e midweek next week. So as the previous post suggests, there is some uncertainty at this time regarding the exact position and orientation of the pressure rise, even though some kind of settled spell is looking more and more likely to verfiy, and as has been constant in the modelling on approach for some days already Otherwise essentially it is as you were...an unsettled weekend, leading to the improvement though next week

 

Edited August 14, 2013 by Tamara Road

[Frosty.]

The GEFS 00z control run becomes hotter and more humid than the mean but has a brief unsettled and cooler blip before the azores/atlantic anticyclone builds in strongly again, but for a while later next week it would deliver temps well into the 80's F and perhaps low 90's F for the south/se.

[Frosty.]

The Ecm 00z ensemble mean looks absolutely rock solid fine to me, high pressure builds gradually northeastwards across the whole of the uk and temperatures rise daily next week, by the second half of next week it would be very warm in the south with temps in the mid to high 20's celsius, nearer low to mid 20's for northern britain but it's an excellent trend, there is a chance of a few heavy thundery showers eventually for southern britain as the humidity increases with quite a stagnant pattern setting in with no end in sight to it either once established.

[Tamara]

As stated last night the broadscale pattern is simple enough to see in terms of weekend low pressure giving way to anticyclonic conditions, but the shortwave is a fly in the ointment which could bring cloud into the mix even in areas where no rain is produced.The north west of the UK looks most prone atm to this possible shortwave in terms of precipitation.

 

For this reason and due to the way the pattern evolves, I'm not sure that initially the High pressure pattern will be a straightforward clear and sunny one. If the High sets up or migrates slightly further east then this might be the case, or become the case with time along with those increasingly very warm temperatures as posted

 

The latest METO update sums up this process of the fine weather gradually extending north for most of us to enjoy through the B.H and beyond after the shortwave(s) clear from the north west.

Edited August 14, 2013 by Tamara Road

[Captain Shortwave]

Positive GFS ens, perhaps showing that the ECM might be the closest to the mark

Just need the high to be a little further north

Edited August 14, 2013 by Captain shortwave

[Summer Sun]

The latest met office outlook today hints at some "very warm conditions developing across parts of southern Britain" towards the end of next week and into the following

 

Edited August 14, 2013 by Summer Sun

[Frosty.]

The first thing to say about the Gfs 06z is that it's much better than yesterday's, especially for the southern half of the uk which hots up during the second half of next week with the 564 dam line making good inroads at times into the south, there is just a brief blip where the anticyclone becomes centred to the west and this allows cooler/fresher atlantic air to push down the eastern side of the high for a day or so but aside from that, southern britain has lots of very warm and hot settled weather with temperatures generally in the mid to high 20's celsius, perhaps even nudging into the low 30's celsuis at times in FI. Across northern britain (cumbria, northumberland, n.ireland & scotland it's not as straight forward on this run, there is a fly in the ointment later next week in the form of a small feature pushing northeastwards across the northwest corner of the uk and then at the end of next week, low pressure has another swipe at the far north of britain before pressure begins to rise again, so it's a bit more mixed the further north you are on this run and during FI the anticyclone sinks a little further to the south allowing a more broadly zonal atlantic westerly flow to spread across n.ireland and scotland but continuing hot and sunny further south with increasing humidity and the likelihood of a few isolated thunderstorms being triggered by the heat. I have a feeling the upcoming pattern will draw comparisons with July with the prospect of a hot spell developing later next week into the end of august, if not, then at least a warm or very warm anticyclonic spell.

[Captain Shortwave]

The latest met office outlook today hints at some "very warm conditions developing across parts of southern Britain" towards the end of next week and into the following

 

 

Couldn't help myself.

Good times for the tourist industry if we do get a warm and sunny bank holiday. 

[shedhead]

It looks to me as if the initial ridge that positions itself close by over north east France and towards the south of England effectively dissolves into a more dominant cell from the atlantic behind the weak indeterminate shortwave feature that ripples along ahead of it. It is probably this which is creating 'noise' in the ensembles as to where exactly the final High pressure cell sets up. And being slightly east, slightly west or central to the UK can have subtle implications for weather on the ground in terms of temperature and cloud cover etc etc.

 

The EPS members this morning illustrate the full range of High pressure options developing by day 7 i.e midweek next week. So as the previous post suggests, there is some uncertainty at this time regarding the exact position and orientation of the pressure rise, even though some kind of settled spell is looking more and more likely to verfiy, and as has been constant in the modelling on approach for some days already Otherwise essentially it is as you were...an unsettled weekend, leading to the improvement though next week

 

Agree with this....a quiet, settled spell starting in the south and slowly pushing north now looks fairly certain next week, but imo that is about as much as can currently be said with any degree of confidence.  I'd suggest the chance of a nationwide heatwave is pretty similar to that of a nationwide spell of cooler, unsettled weather, i.e c.10%, but a period of drier than average weather is now 90% likely.  Whether we can add sunnier and much warmer than average to the 'drier' is still 50/50 for me, primarily because the margin for error regarding the eventual placement of the high at this kind of range....even 300 miles can make a huge difference to what we see at the surface across our small island. 

Edited August 14, 2013 by shedhead

[Frosty.]

Here we go, hot off the press, the Gefs 06z mean shows the south hotting up during the second half of next week with temperatures into the mid to high 20's celsius, high 70's to low 80's F, not as warm across northern uk but pleasant enough in the low 20's celsius range. The azores/atlantic anticyclone builds in strongly and looks set to dominate for some time once it's established, which is great news for the august bank holiday weekend and also promises a fine and very warm start to september..BRING IT ON

Edited August 14, 2013 by Frosty039

[Frosty.]

Just to round off the 6z output, the Gefs 06z control run looks fantastic next week with the weather turning warmer and sunnier from the south as high pressure takes control, the second half of next week hotting up across the southern half of the uk and even the north hots up by the end of next week, there is then the suggestion of a thundery breakdown possibly by the end of next week or early the following week before high pressure regains control, at least across the southern half of the BI, the north, n.ireland, the northern half of northern england and scotland ends up with a mixture of warm and fine and pockets of cooler more unsettled weather with small shallow trough disruption, the pattern through low res becomes messy but the high res and early low res is a superb trend, and having read the latest met office update, the overall trend the models are showing today looks about right, things are going to become a lot lot better from early next week once this weekends spoiler low clears off.

Edited August 14, 2013 by Frosty039

[mushymanrob]

interesting times ahead...

 

its now looking like that pesky shortwave might delay the arrival of the settled/sunny spell proper. once it was progged for as early as monday, that shortwave interferrance looks like spoiling it for some of us.

 

however..

 

i was concerned about johns post last night regarding the anomaly charts, because they have not fully supported nor agreed with eachother, the nature of the expected pressure rise.

 

but today...

 

 

these are looking much more promising... IF they continue to suggest this type of chart..

 

i claim to be no expert on these, still learning, but isnt that red line over the uk a good thing for heat?

 

it would also support a pressure build, but slower then at first expected, possibly because of that pesky shortwave, so the settled/warm weather is still on the cards, but looks like being delayed... of course the cynical, or those who take pleasure in raining on ones parade, could legitimately suggest that the warmth is always being put back... but now the anomaly charts are moving in the right direction, the ensembles are, all three main op runs are.... its gotta be 'on' hasnt it?

[johnholmes]

Yes the ECMWF-GFS versions show signs of an actual ridge but NOAA so far has not done so either on its 6-10 or its 8-14 version, NAEFS of course simply shows the anomalies making it hard to see what the 500mb pattern might be from them. You are right about the 5760dm line, (somewhere amongst my early forecasting notes is a bit about relationships between 1000-500mb thickness and surface temperatures, though not quite the same as the 500mb contour height, but I cannot find them), but yes 5760dm does suggest fairly warm air at 500mb and thus also at the surface. If the NOAA outputs start to show ridging close to the UK then it would be not that different to how the 3 shaped up towards the end of June for the change to our weather in July-but so far NOAA keeps a flattish 500mb flow over the UK. This would suggest any surface high would be temporary in nature.

Edited August 14, 2013 by johnholmes

[Captain Shortwave]

Yes the ECMWF-GFS versions show signs of an actual ridge but NOAA so far has not done so either on its 6-10 or its 8-14 version, NAEFS of course simply shows the anomalies making it hard to see what the 500mb pattern might be from them. You are right about the 5760dm line, (somewhere amongst my early forecasting notes is a bit about relationships between 1000-500mb thickness and surface temperatures, though not quite the same as the 500mb contour height, but I cannot find them), but yes 5760dm does suggest fairly warm air at 500mb and thus also at the surface. If the NOAA outputs start to show ridging close to the UK then it would be not that different to how the 3 shaped up towards the end of June for the change to our weather in July-but so far NOAA keeps a flattish 500mb flow over the UK. This would suggest any surface high would be temporary in nature.

If I'm correct the NOAA use a blend of the model forecasts to make their climate predictions for the coming 7-15 days or so. I notice that their blend is using the GEM model forecast for about 20% of their prediction. the GEM has consistently been rather cold towards any sustained pressure rise over the UK (operational and ens) which may explain why the NOAA output has not been as good as the anomalies more based around the GFS/ECM output.

[johnholmes]

If I'm correct the NOAA use a blend of the model forecasts to make their climate predictions for the coming 7-15 days or so. I notice that their blend is using the GEM model forecast for about 20% of their prediction. the GEM has consistently been rather cold towards any sustained pressure rise over the UK (operational and ens) which may explain why the NOAA output has not been as good as the anomalies more based around the GFS/ECM output.

you may be right about that, I admit to never delving too deeply into what any particular weather centre uses and why. It is too easy to perhaps become sidetracked by these differences, well my view anyway. Keeping to the overall output from each centre does USUALLY give a decent idea of what that centre believes, human or model output, is suggesting, and will throw up differences between centre ouputs. Perhaps that is what is the case just now with the anomaly charts, I confess I don't know.

 

There is just so much data available on the web that it is quite difficult knowing which to follow. The 500mb anomaly charts do seem the most reliable in the 6-15 day period for the best idea of the major upper air patterns so I'll stick with them. That is not to say other methods are not going to give similar results. For me to accept another method that gives 70% results as the anomaly method does then I would want someone to do a similar length study to mine. That is 2 years of routine posting with the data and results, not something most folk will undertake understandably. Most of you work or at school, college/Uni and have less time than me.

Edited August 14, 2013 by johnholmes

[Captain Shortwave]

I guess in the end it's finding what you feel most comfortable with, I think with a 70% success rate in getting the broad pattern correct is pretty decent. You can look at all the data in the world and then be way off in forecast, especially if there is little cross model agreement.

Anyway mr shortwave makes an earlier return on this run.

Edited August 14, 2013 by Captain shortwave

[draztik]

MetO becoming more GEM like this evening...

pressure not building in as quickly, certainly when compared with gfs at same timeframe.

[Summer Sun]

UKMO is getting there slowly with the south seeing the settled weather first before the high should slowly move north wards from mid week

 

Edited August 14, 2013 by Summer Sun

[draztik]

Gfs 12z showing a return to heatwave conditions! Think ill wait for the ensembles, as the op has been on a run of warm outliers recently.

[Captain Shortwave]

Gfs 12z showing a return to heatwave conditions! Think ill wait for the ensembles, as the op has been on a run of warm outliers recently.

 

Gfs 18z looking less settled and less warm tonight in fi, compared to earlier runs..

support for a hot spell, seems to be slipping! Edit : tho if you ask me, that support was limited in any case. 

Edited by draztik, Yesterday, 22:48.

 

Yep, GFS sure has had a spell of warm outliers, like your post last night which contradicts everything you just said  

GFS fi like the high resolution part is fantastic. Again caution must be used due to that shortwave

GEM coming out and it looks better than previous runs

Edited August 14, 2013 by Captain shortwave