[quote=White Meadows;555508]An interesting shift in NAO taking shape?

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/new.nao_index_ensm.html[/quote]

Always bare in mind though that they are individual GEFS members, that loan ranger towards the end has to be perturbation 6 me thinks!!!

http://www.meteociel.fr/modeles/gefs_cartes.php?code=6&ech=384&mode=0&carte=0

I will probably jinx it but i am for the first time this winter, really starting to get interested now, only a minor upgrade on the de bilt ens but they keep trending slightly colder each run.

http://www.knmi.nl/exp/pluim/vijftiendaagse/Data/15DAAGSE_06260_NWT.png

Some of those really fridgid now, the sort where massive instability could occur.

Ecm at the bottom of page as it always is with mine

Speaks for its self

http://www.jp2webdesign.co.uk/two/ensembles/

.

Cheer up Beast have you not read Brians winter forecast, Its going all ok

please can you link me to Brians forecast, thanks.

Wind direction for coast on the Dutch/Belgium border.

http://i.imgur.com/RTzbO8n.png

T2m for same location.

http://i.imgur.com/cWYxo2s.png

I think that might offer me some guidance.

Must admit I'm always pretty skeptical about the models getting easterlies right - the current sort of Northerly is a much more reliable pattern for them to get right. Okay corrections east can mean we end up missing the cold but the broad pattern is usually pretty good.

Easterlies though just seem much more likely to all go wrong either before the reliable frame or once you get to T120 or so. Once it does go wrong it's usually because the jet rides over the top and sinks it and you get a massive contrast from the cold that was progged to the mild south westerlies you end up with

All that said the current evolution does at least seem quite plausible to me and even the GFS op doesn't blast the block away despite an awful lot of energy in the Atlantic. Given the tendency for GFS (and all models at range I guess) to overplay the Atlantic then it's certainly interesting even if not something I'll give much confidence to for a while. I guess what needs to happen and what the ECM (and some of the other models) has been showing is for the jet to sink south after the initial shots of warm air riding over the nascent block. Coupled with what looks like a reasonable PV, most of which is far enough west to indicate scandi blocking then some sort of easterly influence is the result.

Bit of a high risk way to get cold but almost always better IMBY than a 'standard' Northerly. Now if we could get a cold easterly initially and then the HP transfers to somewhere near Greenland........

Edit: Turned in to a bit of a ramp that, which is a little bit daft given how unlikely the charts are to verify 

During the last 3 or 4 years we have seen some changes where the jet doesn't (always) win the way you describe. This is related, imo, to the way the Azores high manifests itself, which is somehow affected by the changing UV output of the sun. (Jo Haigh)

http://forum.netweather.tv/topic/78631-model-output-discussion-30th-november-onwards/page-64#entry2852232

Post 1277- Ive tried 3 times to paste it rather than link it but it doesnt work :(

S

Better amplification already on the 18z

EDIT : thanks and thanks to Steve for another enlightening post.

When I logged on and noted how many posts there was on the Model Output thread I thought there must have been a massive pattern change!

Alas, nothing of the sort, more anticyclonic gloom and a 'potential' mild easterly at day 10 on ECM.

Oh dear, if that gets TWO members so excited things really must be bad

I will stick to the MetO MRF which basically says more of the same (anticyclonic gloom) till Christmas.

Andy

Anyway - guaranteed pattern change will come after Friday as that's when I disappear for a few weeks watching England getting a good hiding in The Ashes.

Here is Steve's post.

Evening All-

Ive not replied to anything today- so sorry if ive missed anything important.

A juicy post to get your teeth into before the 18z.- An honest evaluation of the model performance this week.

So we are there now ( all but) - but the wide variations between the models have been removed & finally we have some unity with the best of it seemingly here at T84.

http://www.meteociel...84-21.GIF?02-12

http://www.meteociel...N84-7.GIF?02-12 into 96.

Within this short window of 18-24 hours there is the prospect of storm force Northerly winds & heavy snow showers packing into Northern Scotland, western Scotland, NI & possibly NE Scotland-

Im sure we will see a line of snow showers glancing the extreme east coast- but all staying offshore.

Perhaps now we have allignment of sorts - todays a day to reflect on the Rollercoaster that has been the model output of the last few days.

ECM-

Very very strong consistency from the ECM, showing the Northerly pattern - in-fact the ECM has had the correct pattern type on Nov 26 @ 00z & 12z - but really got its act together on the 27th-

Here are the ECMs for the last 5 days running 216 - 192 - 168 - 144 - 120

00z + 12z 216 chart 27th

http://www.meteociel...ECH1-216.GIF?00   SPOT ON

http://www.meteociel...ECH1-240.GIF?12  VERY GOOD

00z + 12z 192 Chart 28th

http://www.meteociel...ECH1-192.GIF?00  SPOT ON ( 100 miles to far west though) possibly slightly over amplified

http://www.meteociel...ECH1-192.GIF?12  EXCELLENT

00z + 12z 168 Chart 29th

http://www.meteociel...ECH1-168.GIF?00 V Close but to amplified at the SW Greenland tip

http://www.meteociel...ECH1-168.GIF?12 V Close but to amplified at the SW Greenland tip & to far west.

00z + 12z 144 chart 30th

http://www.meteociel...ECH1-144.GIF?00 V Close but as above- slightly to amplified & to far west 200 Miles.

http://www.meteociel...ECH1-144.GIF?12 V Close but eastward correction 100 miles - still to amplified.

00z + 12z 120 01st

http://www.meteociel...ECH1-120.GIF?00  Spot on barring the over amplification

http://www.meteociel...ECH1-120.GIF?12  Correction East, angle of amplification more NE instead of North-                 Looks to be spot on.

00z + 12z 96   2nd today

http://www.meteociel.../ECH1-96.GIF?00   SPOT ON

http://www.meteociel.../ECH1-96.GIF?12   12 hours later spot on....

ECM Summary :

If you look at the GLOBAL Picture- back across the last 12 runs you will see it nailed it on the 26th - some 9 days out at 216.- that's the ridge in the Atlantic, Deep low digging south over the North sea,

Aleutian Ridge moving SE downstream & a split flow over the states with a low in the Midwest.

PART 2 OF STEVE MURR'S POST.

The ONLY area of fault on the NEW updated ECM has come from the area around the SW tip of Greenland & the speed of the solution- being slow & amplified, in-fact its not 'quite' been there & that subsequent swing to a faster solution has taken the amplification past the point when it no longer goes North, but ENE traversing the coast of southern Greenland.

HERE

What we are talking is an UNDER estimation of the Jet by a maybe a FEW M/S -

The net correction is a 'slightly flatter pattern, a slightly eastward jog (200 miles is nothing in weather terms- but Massive for the UK) & of course 1 full less day of cold as there is no high pressure to traverse around the high but through it.

We need to be clear though the ECM has never promised sustained HLB, just over amplified the ridge towards Greenland.

Incidentally the ECM made a similar mistake the other week, that is- totally lick the GFS in the overall pattern but mistake the over amplification- which again has big repercussions for the UK-

this was the model output ECM

http://www.meteociel...ECH1-144.GIF?12 

Notice ridging into Greenland

ACTUAL Varification:

http://www.meteociel.../ECH1-48.GIF?12 -

Notice the flatter upstream pattern- right in the place it hurts for us.

What to take away from the ECM for the rest of Winter,  ECM is the leading model over the GFS, it licked the 500 MB pattern 9 days in advance & has stuck with it run after run all the way through, however around the Iceland region it 'sees' more ridging than perhaps is going to happen-

there's not many places in the globe that the extra amplification matters, however at the southern tip of Greenland there comes a cut off where systems all of sudden STOP going North & suddenly start going East- this through an angle of 90 degrees.- so a SMALL error / bias which would normally swing from say 10 degrees to a ever so slightly flatter 20 degrees to the North is suddenly swung from 0 degrees North to nearly 90 degrees East.

This pattern change has a direct impact on the sustainability on UK cold as it shortens the cold & reduces the westerly penetration of cold-

This small error is some peoples eyes is a huge error- hence the calls for the ECM being trounced / its failed its followed the GFS etc etc-

No the model error is small but the visible impact to the UK is huge.- so the perception is skewed towards a thought process that the model is rubbish.

Its not- its king with a bias just like nearly all the models.

In terms of the rest of the Winter wit the ECM I will generally STILL run with this model - why? because the Hemispheric pattern for the last 4 years has been heavily loaded towards Northern blocking so fortunately the ECM bias hasn't been visible due the conditions actually supporting the bias, however this winter thus far that bias has made it look a little foolish - when actually its performed superb.

So for Future budding cold spells look towards Southern Greenland to see if there is any low pressure or shortwave action that is the key trigger - as this may be to slow & to far west in the ECMS eyes- then as it corrects east the low slips east of the tip rather than South.

SW GREENLAND = CRUCIAL TO THE UK COLD.

The GFS model... ( Links are the 12z & 00z model only)

What can I say about the GFS  ..... well in the name of balance when the ECM at 216 was picking up the pattern for spot on the GFS was here-

216 00z & 12z

http://modeles.meteo...700-0-216.png?0   Very good but to flat with the US pattern

http://modeles.meteo...12-0-216.png?12   VERY GOOD

192 00z & 12z

http://modeles.meteo...800-0-192.png?0  Pretty good but upstream Midwest low very fast ejecting out to pole

http://modeles.meteo...12-0-192.png?12   AWFUL AWFUL

look at the eastward bias in all its glory our northerly it over into Germany

168 00z & 12z

http://modeles.meteo...900-0-168.png?0  Not bad- pretty close upstream

http://modeles.meteo...12-0-168.png?12  POOR AGAIN- look at that bowling ball low to the NE- but like all the other runs to Greenland ridging

144 00z & 12z

http://modeles.meteo...000-0-144.png?0   V Poor but very flat- +4c isotherm across England some 14 degrees to warm @ 850.

http://modeles.meteo...12-0-144.png?12  Poor again- to far EAST - England has zero cold air. - Eastward bias evident again.

120 00z & 12z

http://modeles.meteo...100-0-120.png?0 Pretty good ticks all the right boxes.

http://modeles.meteo...12-0-120.png?12 Slightly to far east again but catching up & westward correcting.

96 00z & 12z

http://modeles.meteo...0200-0-96.png?0 SPOT ON

http://modeles.meteo...212-0-90.png?12 SPOT ON.

GFS SUMMARY

Why do I personally Hate the GFS- because its always playing catch up to the EUROS, Its always flat when the Euros show an amplified pattern so is wrong nearly every time we get a Scandi or Greenland high.

We get 4 runs a day- which If I overlaid all the other 12 runs would show a multitude of scenarios, some at the extreme eastern end of the range, some over amplified ( looks like the 18z is usually the pub run) & some just on some wild tangent- usually the 06z.

Should I dismiss it- well I'm going to change my tact on GFS, what the faster flat pattern helps to show is usually the opposite of the pendulum, If the ECM is at the slowest amplified end then you can bet your bottom dollar that the GFS will be the flattest, with this in mind quite often the final solution is a blend of each- the halfway house- but normally not quite halfway to the GFS, more like 1 third to the GFS & 2 thirds of the EUROS-

From this you could generate a predicted forecast, but with one very difficult element & that is does the 2 third house create any pinch points that could change the final pattern so drastically for the UK-

2 main areas arise from this- ( For UK cold)-  Southern tip of Greenland energy is 1 & the other is when we are setting up Easterlies & low pressures are projected to move south then SW whilst the ridge builds above.-

The fast solution ( GFS ) will throw the low pressure further into Europe - but the bigger impact on the long-wave pattern is instead of a Scandi High you see a 'Sceuro' high, with the UK in a southerly or SE flow & the jet to flat on top.

Then as the Easterly approaches its how far does the GFS move to ECM where the Sceuro is suddenly a Scandi high again because the solution was in-fact slower.

This example is VERY evident tonight.

GFS SCEURO HIGH- http://modeles.meteo...nh-0-192.png?12

JMA Scandi high       -http://www.meteociel...92-21.GIF?02-12

This all comes from FAST v SLOW solutions.

Anyway, what to take away from the GFS-

12z Eastward bias. IGNORE- if its significantly FLATTER or EAST than the ECM.

6z/18z                   . IGNORE - if its significantly different to the ECM.

00z-                       do not discount- I cannot find to many faults with the 00z GFS- not biased in many ways & generally the most consistent.

What we can also take away is the GFS will find the weaknesses in the blocking first ( usually) because its primed for a faster solution- so that can support us going forward with comparisons with the ECM.

The model that's come out best again is the UKMO- resilient & Smooth, seemless & minimal fuss.

In this case it started at 144 with the 2 thirds house & has never changed since.

The Scandi High..........

I'm pleased that I presented this idea first ( even Mr Holmes questioned the 500 heights not following ANY ridging to Scandi)

The forecast was driven by the angle of the jet coming out of Canada & the subsequent split flow-

It is now appearing in the models-

So what would be tonights forecast- based on the ABOVE model inconsistencies.

GFS- 12z 240- Slight amplification -

http://modeles.meteo...nh-0-240.png?12 

But a Euro high- 

Mild SW winds for the UK.

ECM 240 12z Much better amplification

http://www.meteociel...H1-240.GIF?02-0  KEEN ESE wind & very cold at the surface, -

JMA 192-        Run of the day

http://www.meteociel...92-21.GIF?02-12  Easterly @ 216

GEM 240 - AWSOME

http://modeles.meteo...nh-0-240.png?12 

But... the Best suite of the day is the ECM 15 day.

00z Chilly

http://www.knmi.nl/l...0.png&width=692   day 11/12 mean around 4c.

12z very much colder

http://www.knmi.nl/l...0.png&width=692 ( swop to 12z) Day 11/12 mean now down to 2.5c & the control + op very cold.

Therefor the updated forecast based apon the model bias today is-

Northerly toppler, for 24 hours, high pressure ridging over the top but contrary to the GFS no WAA getting into the UK barring the extreme NW -

The SE staying cold-

day 8 -9 look for Energy dropping south into scandi in the form of a shallow low- with rapid pressure building NE, the UK sitting at the extreme western end of blocking for day 9/10.- light Southerly or SE tug.

Then energy getting underneath tugging the winds easterly & increasing day 12.

Look out for the Maps for 13/14 December.

best regards

Steve

In 2 parts as it wont let you post that long a post in one go.

Underwhelming end to the 18z but a cracking days entertainment model wise, the trend is there.

Cast your mind back the last few days, ok the Northerly plunge was progged to last longer by other models but never the GFS, but24-48 hours ago it was zonality in FI or a MLH, today we have seen undercutting taking place and in the case of some model output, being on the cusp of an 09 Easterly, possibly even a 91/87 Easterly, yes of course completely FI timescale but you want it trending that way surely???,   PV getting smashed right up the middle which can only help us long term, even if we are not on the right side of blocking, surely some sort of stratospheric feedback on the cards with charts like that, yes a potent cold spell still odds against before xmas, but was looking a near impossibility not so long ago.