Model Output Discussion 31/07/14 onwards.

[Chris K]

Can anyone give a suggestion why the North Sea lowers the pressure of a storm? Looking at Saturday on the EURO4 and a small shortwave deepens over the North Sea to form quite a potent low pressure system. Now if Bertha follows there could be some unexpected strong winds recorded for the east of the UK:

 

This is just a guess, but I would have thought it may be something to do with the positioning and strength of the Jet as it interacts with the disturbance/Low pressure system?

 

As I said though...a pure guess.

Edited August 7, 2014 by Chris K

[ANYWEATHER]

The NMM-18 12z run shows Bertha quite a nasty storm, heavy rain and strong gusts of winds. So flooding and fallen trees may become an issue on Sunday...

[IDO]

ECM moves a step towards GFS in that it now sees Bertha and deepens it somewhere to the SE of the UK between T72 and T96:

 

 

 

Nothing major and again rainfall may be more relevant.

Edited August 7, 2014 by i'm dreaming of...

[summer blizzard]

All unsettled to some degree out to day 8 before divergence.

 

[ANYWEATHER]

Ecm makes really nothing of Bertha again, gfs does, If I remember correctly the gfs was generally spot on with the prediction of storms during the winter and how that reacted with the jet stream, not so much ecm. Even though we are in a completely different phase of the year, my money is still on the gfs, as this model is great in predicting weather from the west!  After Bertha, the models continue to show unsettled conditions prevailing....    

[knocker]

ECM for end of next week. The anomaly has warm air over Greenland with the trough lying west to east from the UK. This gives a westerly airstream over the UK with the Azores high in it's usual position.

 

Surface wise this has a tendency to translate into a rather familiar scenario of a N/S split over the UK with the low pressure to the N and high to the south again with a westerly flow  and the temps below average.

Edited August 7, 2014 by knocker

[Captain Shortwave]

Snip, missed the area about the day 5-10 mean. My previous post can be ignored. 

 

I might just add as an addendum, no real change next week, looks unsettled and rather cool up to mid week, but conditions should then improve as pressure slowly rises from the west.

Edited August 7, 2014 by Captain shortwave

[IDO]

Hi Captain

That's a five day anomaly chart for days 5-10 where the early part of the period had unseasonably low uppers so even with ECMs typical D9-10 outlier charts the anomaly remains below average. It's a good way of looking at ECM FI output as it smooths out the usual ECM Late just for fun output.

All models are showing a week or so of uppers around 5c below average so I expect much less warm days over week 1.

[legritter]

^ This has been irking me for a while now Knocker, not your posts but the anomaly charts, I find it pretty strange how the average 850 temperature for the south of the UK is nearly 10C. For example the chart you posted does indeed show below average 850s. But

 

This sort of pattern really doesn't translate to below average temperatures at the surface. In fact it would be very warm in the south in any sunny spells (mid twenties at least).

It's rather irrelevant to the discussion as the ECM day 10 won't verify, but it's something that has bothered me for quite a while. But there does seem to be a disconnect between the average temperature at the higher levels and the temperatures at the surface. An explanation on this would be interesting to me.

stand by your beds , no modell no forecaster will get details right for this weekend ,even the Met office as of tonight are struggling with synoptic situation come this sunday .as my next door neighbour who works for the Met says ,Sundays mid day chart could be at least 300 miles eighther way ,current predictions ,wild wet and news worthy [somewhere over the uk ,you may experience some wild weather or you could be sat enjoying a STella under clear sunny skies ,enjoy the weather and remember its not an exact Science ,ok far more precise than 30 yrs ago ,but mother nature is continually foxing us ,a trillion or more segments of data is up there and when tomorrows sun comes up it will change again ,just got a gut feeling that autumn will be  early this year ,as i said a gut feeling ,mother nature as not set out her stall yet so how can we possibly predict any outlook , talk on north american forums of a cold and vortick dominated autumn ,NO WAY OF TELLING   even with modern computers ,enjoy our unsettled and stormy spell coming up, remember what many of us were predicting or hinting at early december last year ,well it finished up Totally different and a real weather freak of this century ,But possibly happened thousands of times before ,Take care all and tune in tomorrow for an update on ex Bertha T48 hrs ,cheers .

[damianslaw]

General theme shown by all models for foreseeable future is a much more unsettled atlantic dominated picture with risk of heavy precipitation for many places and a much cooler spell than recent weeks and much windier.

 

As others have said - difficult to pinpoint how things will pan out on Sunday, but the Jetstream is digging south and with heights ridging north to our west the downstream affect is only one way and that is for the UK to sit on the cool side of the trough.

[knocker]

Just out of interest the ECM ens

Edited August 7, 2014 by knocker

[OldMetMan]

Hi everyone, just dropping in after a long break. I hope the variable summer weather (especially the thunderstorms) has kept everyone entertained.

 

I must confess that I am finding all the forecast dithering over the fate of ex-hurricane Bertha rather baffling. Admittedly, forecasting potential storm tracks this time of year is somewhat difficult, owing to the lower jet speed. Yet, as I see it, the case for Bertha turning into quite a potent storm looks quite compelling.

 

I notice that for at least 5 days, the GFS has consistently shown Bertha developing into an intense LP, keeping fairly close to the same track from run to run. That in itself suggests it is entirely possible that the track will be across England as it has been showing.

 

That apart, the NHC, even when Bertha was still tropical, showed the expected track to be straight out into the Atlantic, south of 50N. The storm is currently very well placed to engage the jet off the E coast of Canada. There is always an abundance of very warm, moist air associated with these ex- tropical storms, which by itself increases the temperature gradient and favours substantial deepening.

 

I think the ambivalence concerns whether Bertha will actually engage the jet or not. Well, as I said, the GFS hasn't had any doubts on that score. The latest MetO thinking gives a 60% probability of Bertha crossing S England, heading NE. Herein lies the greatest risk, I think, with a strong possibility of the storm developing a very tight gradient on its W and SW flank, as pressure rises sharply behind it. Not to mention copious amounts of rainfall, although with the likely speed of the system, that seems to preclude any significant rainfall issues.

 

August storms of this kind are not that unusual, although this is pretty early in the month for one. Personally, I feel this storm could be quite notable, with the wind being the most potentially damaging feature. I shall watch with great interest how the situation develops and how the forecasts change in the next couple of days.

[knocker]

The 12 JOMEC

 

[knocker]

As of 0530 this morning UKMO said Bertha (will be renamed Penbertha if crossing Cornwall) MAY bring strong winds and rain to southern areas on Sunday. The 00 GFS on the other hand is still running with this scenario.

 

0009 Bertha WSW UK, roughly 45n 25w 1002mb

 

0010 Bertha  SWS Ireland 996mb

 

1210 Bertha now over the Isle of Man 992mb. Moderate rain over most of England with strong NW winds in SW.

 

0011 Bertha now just east of Aberdeen 984mb with heavy rain in n. Scotland and strong NW.W winds over the northern Britain.

 

Here endeth the lesson according to the GFS but it must be emphasised this still not a done deal by any means.

Edited August 8, 2014 by knocker

[SteveB]

GFS current thinking on the track of Bertha this morning

 

 

 

 

It stays unsettled into next week as well.

 

 

Looks to stay unsettled into FI as well.

[knocker]

ECM now in agreement regarding Bertha. But UKMO isn't as it has it tracking along the Channel before turning sharp NNE and  not so intense.

Edited August 8, 2014 by knocker

[johnholmes]

I must confess that I am finding all the forecast dithering over the fate of ex-hurricane Bertha rather baffling. Admittedly, forecasting potential storm tracks this time of year is somewhat difficult, owing to the lower jet speed. Yet, as I see it, the case for Bertha turning into quite a potent storm looks quite compelling.

 

For an ex met observer I find this a rather surprising comment. The immense technical problem this kind of thing throws up has yet to be solved in any computer model. So 'dithering' is hardly the right word I would say. Uncertainty, yes, and perfectly understandable. This morning the 3 main models are still no in agreement although returning to basics may be called for if they still have not got very close agreement by the 12z output this afternoon. At least the models now have a good fix on its position since it turned into an ex tropical storm over the last 12 hours, so surface and upper air details should become less problematical from now on.

[knocker]

Oh for a Weather Ship on Ocean Station Juliet.

[Frank Trough]

the latest met office surface pressure (as of 7:30 this morning) charts don't really make much of it:

 

 

 

it's more like the UKMO did on some of it runs earlier this week. Similar to the GEM today as well which has gradually backed away froma  significant event:

 

 

But then there's the ECM at GFS.......

 

This has been really interesting hasn't it? and there's still no consensus in the operational output! 

 

GEM fries the southeast again in FI:

 

[OldMetMan]

For an ex met observer I find this a rather surprising comment. The immense technical problem this kind of thing throws up has yet to be solved in any computer model. So 'dithering' is hardly the right word I would say. Uncertainty, yes, and perfectly understandable. This morning the 3 main models are still no in agreement although returning to basics may be called for if they still have not got very close agreement by the 12z output this afternoon. At least the models now have a good fix on its position since it turned into an ex tropical storm over the last 12 hours, so surface and upper air details should become less problematical from now on.

 

 

Maybe dithering is a bit strong but that's how it seemed to me. I say this mostly because of the run-to-run consistency of the GFS, whereas, apparently, according to the MetO's site, their own models have not shown such consistency. This suggests the ambivalence lies more with the forecasters than the model output; the Met O forecasters are concerned that their own model output has not been doing what the GFS has and have been reluctant to commit to any particular output other than their own. You know more about forecasting processes than I, obviously, when it comes to choosing which model or models to favour.

 

I appreciate the difficulties involved here, but to still be this uncertain so close to the event is somewhat unusual. As I see it, the tropical origins of Bertha, at this point in development, would tend to favour significant development simply because of the presence of the very warm air over the centre - the legacy of an ex-hurricane - and the proximity of the low to the jet entrance, which I would expect all the models to be able to take proper account of. This is the story the GFS has been telling for days so that model at least doesn't have a problem with the low's origins.

 

From a purely historical point of view, ex-tropical storms have caused significant early gales during summer on a number of occasions. so this one does seem, as I said, well placed to do the same. As you say, maybe today's output will clinch it.

[johnholmes]

Oh for a Weather Ship on Ocean Station Juliet.

 

or perhaps Kilo at 45N?

better still - both!

Edited August 8, 2014 by johnholmes

[h2005__uk__]

I'm a relative newbie when it comes to models... what does 'FI' mean? I've come up with a few possibilities but none of them work in context!

[IDO]

Well ECM ensembles are finally seeing the bigger picture and only 10% no longer have Bertha to the SW at T48. Now the main variable is how intense it is and there are breezy members and gale force with ones in between. By T96 Bertha mixes with the core low in the trough and the new low deepens (again variations on that theme). By D5 the new low is filling at different rates according to its members.

 

ECM's track of the low Sunday:

 

6am  noon  6pm 

 

It is in line with GFS, in that again certain parts of the SE will escape the rain.

 

GEFS offer similar variety with regard to Bertha, maybe slightly more have a weakening feature as it approaches the UK.

 

The GEM op also made little of Bertha, but like the rogue GFS run a day or so ago, this was likely to happen at one point as there remains a cluster showing this. Currently about 30% of GEM's 0z support the op, 70% support the GEM control:

 

 

UKMO have struggled with Bertha and this morning the Fax looks like it weakens Bertha as it crosses the Channel/South coast: 

 

Not sure this has much support anymore, yesterday this was showing up as an option, but today most have UK impact around SW crossing NE. Assuming we have reached some sort of consensus (based on ensembles) then UKMO and ECM have been disappointing in their guidance whilst GEM and GFS have been very consistent. Tonights runs should clarify this finally.

 

Afterwards it looks like there is no clear consistent sign of a return to higher pressure. ECM's warm D10 chart last night is now a distant memory. ECM mean at D10:

 

Similar to GEM mean:  and also GFS mean: 

 

I suspect the greater impact Bertha has on our mid latitude location the longer our weather will be sourced from a cooler direction.

Edited August 8, 2014 by i'm dreaming of...

[tempestwatch]

I'm a relative newbie when it comes to models... what does 'FI' mean? I've come up with a few possibilities but none of them work in context!

Fantasy Island!

[OldMetMan]

Here is what the Met O said on 7th regarding the uncertainty over the future of Bertha:

 

"The transition from a tropical to an extra-tropical feature is a particularly hard one to forecast with confidence, so there are still some differences in the location and intensity of the resulting depression, which is expected to pass over, or close to, the UK from early on Sunday."

 

However, this is what the NHC in Florida said in its last advisory on Bertha on Wednesday 6th at 11am:

 

"Satellite images indicate that Bertha has become associated with afrontal system and has acquired extratropical characteristics. Thelow-level center is devoid of deep convection and is on the cold airside of a frontal cloud band or trough extending from Nova Scotiasouthwestward to the Bahamas. In addition, there is a strongwesterly upper-level jet over the system.The low is moving toward the northeast or 055 degrees at 27 knotssteered by the mid-latitude westerlies. Most of the global modelskeep the post-tropical cyclone moving rapidly northeastward andthen eastward over the North Atlantic."

 

So it seems the transition from tropical to extra-tropical had already occurred by the time the Met O decided to discuss it on their website. It looks to me like the NHC's forecasters had a better handle on Bertha's future than our own forecasters did, yet both presumably had access to the same data. It'll be interesting to see how the forecast develops over today and tomorrow