Model Output Discussion 29th December - Into mid-Winter.

[shotski]

Just now, bluearmy said:

I checked my diary and it's the 8th Jan 

Well done, give that man a prize 

[bluearmy]

3 minutes ago, Nick F said:

I tend to look at the formation of a Scandi ridge in two layers, a cold surface high formation once the upper trough over Scandi edges away E/SE while aloft a 'warm' ridge builds through strong WAA northeastward due to the strong height gradient / wind on the forward side of the Greenland polar vortex. The combination of these two layers allows the ridge to be thrown quite far northeast.  I imagine in my head that there may also be an empirical rule programmed into the EC computer model that will churn out a Scandi high if the evolution beforehand signals possibility of a ridge NE, 

The shape, intensity and position of the lobes Canadian / Greenland trop vortex IMO seems to be crucial in determining whether we get enough amplification in the flow to get a ridge to build NE towards Scandi and the Scandi trough next week to relax to allow a cold surface high to form to our NE and WAA spread aloft from the SW. 

Given the stubborness of the GFS ops to continually keep the upper flow flat when the EC high res wants to amplify - with not a great deal of ens support for the EC high res easterly, you would have to go for the idea that 12z EC  will model the ridge to still build but further south without the easterly, as per EPS mean.

But, the wildcard for me is: are the models handling the shape of the Canadian/Greenland PV correctly? As this has ramifications for the upper flow over the N Atlantic and potential for amplifications.

You know that isn't actually what happens nick -right ?

[nick sussex]

2 minutes ago, snowice said:

Hi Nick by 96hrs 12z gfs we should know once and for all?

In terms of the easterly no but if it has a chance yes because the knock on effect in the Atlantic either delivers a cleaner picture with less shortwave complications which help moving forward.

The reason the ECM gets to the easterly is that as the PV starts heading south theres a better ridge ahead of that which is forced ne'wards, the better ridge comes about because of that cleaner upstream evolution.

[Captain Shortwave]

To be honest, one ECM operational doing this solution is one thing but.

12z from the 6th and the 7th.

   

00z from the 7th and 8th

   

So the ECM is consistent with the idea, the 00z from the 7th is the only operational to not develop an easterly but is a little flatter with a high over northern Europe with a gentle flow off the continent so surface cold rather than snowy cold.

So to be fair the ECM is either onto something here or is modelling things in the week 2 range consistently wrong. That said I am willing to take a punt that the ECM will at least develop something akin to the 00z from yesterday or better. Of course the one issue is this...

This is the stark difference between the ECM and UKMO this morning. If the UKMO is right then it is likely that the final solution will deviate away from the recent later stage ECM output. So fingers crossed the UKMO will follow something similar to the ECM by day 6 to give a little hope for another good ECM operational later.

 

Edited January 8, 2017 by Captain Shortwave

[Nick F]

32 minutes ago, bluearmy said:

You know that isn't actually what happens nick -right ?

I'm not implying it does happen. But there are old empirical rules of thumb, before NWP advances took away the need so much, that I have seen journal articles or in met papers or books, for particular synoptic evolutions to develop, be it a Spanish Plume, types of cyclogenesis, anticyclone formation in certain areas, etc. The antecedent to a Scandi high is normally a N-S aligned lobe of the PV over Greenland and over Scandi, a ridge forms between the two lobes, eventually the Scandi lobe relaxes and cuts-off S into S/SE Europe. This then allows a cold surface high to form over Scandi supported by a 'warm' ridge aloft. The Scandi high sometimes re-enforced by either an arctic high (think '87) or Russian high (think current EC det).

Edited January 8, 2017 by Nick F

[coldwinter]

1 minute ago, Nick F said:

I'm not implying it does happen. But there are old empirical rules of thumb, before NWP advances took away the need so much, that I have seen journal articles or in met papers or books, for particular synoptic evolutions to develop, be it a Spanish Plume, types of cylogenesis, anticylones formation in certain areas, etc. The antecedent to a Scandi high is normally a N-S aligned lobe of the PV over Greenland and over Scandi, a ridge forms between the two lobes, eventually the Scandi lobe relaxes and cuts-off S into S/SE Europe. This then allows a cold surface high to form over Scandi supported by a 'warm' ridge aloft. The Scandi sometimes re-enforced by either an arctic high (think '87) or Russian high (think current EC det).

Something like this?

[Nick F]

Just now, coldwinter said:

Something like this?

YES! I'm sure John Holmes back in the day, when you couldn't trust NWP past a few days, may have referred to something similar when a UKMO Senior Forecaster.

[damianslaw]

As Nick F has mentioned, I suspect the EC ops are handling the position of the PV differently to GFS, with the influence and forcing of the russian /east asian high elongating it more on a N-S axis, enabling ridge development to its east aided by warm air advection, hence the mid atlantic ridge has a window of opportunity to build NE towards scandi, the other key player driving such force is the north pacific low, anchoring down on the central core of the PV. GFS isn't forecasting the same sort of forcing on the PV, hence it maintains a more rounded shape, which enables shortwave activity to the south of greenland to spawn and quickly kill the window of opportunity.

I can see merits in both evolutions occuring, hence best stick to the reliable i.e. 13 Jan and wait and see how the shape and position of the PV pans out. What we will see in the coming week is some form of forcing to the PV, which I suspect will weaken it, and result in a generally quiet atlantic as we head through the second half of Jan,  the ridge development over E Asia/N Russia could result in warming of the strat which will put major stress on the PV (something that naturally occurs as we enter the second half of winter anyway).

[Geordiesnow]

1 hour ago, Frosty. said:

At the moment I'm more interested in seeing the Arctic Northerly last throughout next weekend as per the Ecm 00z compared to the Gfs 6z which quickly shunts the cold away eastwards, hopefully the slower ecm solution will win out!

Same here, I wont be too fussed if the GFS supports the easterly idea or not as I think that is the outlier at this present time but I do hope it backs away of being over progressive in shifting the projected Northerly and we see something more like the ECM and UKMO which at least means the chances of severe frosts is quite high and keeps the cold for longer.

Going to be an interesting set of runs for sure, I'll be surprised if the ECM goes totally flat on its next run but something like Nick F says that we may get the ridging but the easterly flow being further Southwards. Either way, they are not decesive runs as its still too early to know either way.

Be quite dissapointed though if the the Euro models follows the GFS lead of cutting the Northerly flow rather quickly as a 2-3 day Northerly is on the cards here.

[Tamara]

On ‎05‎/‎01‎/‎2017 at 19:51, Tamara said:

As much tropospheric forcing as possible will be needed to create amplification and also agitate the wQBO assisted vortex (sounds all to familiar).  Hopes maybe rest on further retrogression of the Pacific ridge allowing the vortex position to shift NW,wards. This allowing some height rises to the NE to arrive via the back door courtesy of greater amplification arriving from upstream. Its in this sense that increased amplitude of any convective activity stemming from the Pacific is most required and welcomed

Not quite there yet, but its encouraging to start to see the Pacific pattern changing in a way that gives us a chance of more than temporary Atlantic ridges heading through to the second part of January

Still waiting for the WDT site to update (mainly with regard to EAMT) as mechanism for amplification and vortex destabilisation - but for the first time this winter the ECM at least is finally showing a pattern to cold much less likely to be aborted in consequent suites. Its less important that it precisely leads to a ridge extension at day 10, but more the fact that the Pacific pattern is at last yielding to something that can actually go somewhere - and for me that makes watching NWP finally more interesting to follow more closely

I would look on the end of week cold snap as a bonus...

 

Edited January 8, 2017 by Tamara
Nail slippage on keyboard!

[SMU]

Afternoon all

The GFS is flat for 2 reasons-

* There is no ridging ahead of the low exiting the states @ 108

* The low lifting out of the azores block also @ 108

as a result the 2 systems phase together to produce 1 low pressure migrating East here 

note them coming together at that point-

The ECM at the 96 marker has a ridge up the east coast of the states sending the low NE up the west coast of greenland

Note how far they are apart on the chart- Western greenland coast & the azores low at the bottom left poking up

If the GFS is wrong it will start moving towards the solution today - the worst case scenario is a phase (06z) - the middle ground is a non phase but less amplification ( UKMO 00z ) the best is above the ECM - no phase + amplifcation-

The ECM @ day 5 is about 92% accurate for NH leaving 8% error- lets hope that 8% isnt evident in the 2 locations today!!!

s

 

[Summer Sun]

No change so far from GFS

Main period to watch is t144 to t168 does it follow ECM in remaining cold or does it follow it's 06z in going more westerly

[Ali1977]

Slightly better ridging and higher pressure (surface) over Greeny at T96, may improve the Northerly a bit, which "may" move it slightly toward ECM but we'll see

[Scandinavian High.]

2 minutes ago, Summer Sun said:

No change so far from GFS

Main period to watch is t144 to t168 does it follow ECM in remaining cold or does it follow it's 06z in going more westerly

Has gfs completed yet.

[Jonan92]

Big differences between UKMO and GFS at just 96h

 

[Ali1977]

On 08/01/2017 at 16:04, Jonan92 said:

Big differences between UKMO and GFS at just 96h

 

Yep UKMO looks way better over NE Canada, crazy at only T96

[Mucka]

8 hours ago, Steve Murr said:

Morning All

agreed with all the comments above - absolute crackerjack of an ECM however UKMO not on a par today because of the atlantic low & indeed by 168 appears pretty poor ( athough behind the low there is NE ridging so very difficult to tell )

That makes me uneasy as the ECM doesnt show this profile or evolution

So all in today fantastic charts up to 144 thereafter a lot of divergence - but not without potential- at least its UKMO 144/168 so room for change... ( as is the ECM )- remember the other week 38 ECM ensembles clustered to cold V UKMO... we know who was the winner

Thursday overnight into Friday still sees the biggest window ATM...

S

Hi Steve

One of the rare occasions I don't quite agree with you and others on 00z UKMO not being good and appearing poor at 168. It isn't as good as ECM but you also say in a later post UKMO lifts the low up and through slow. I think it is clear from 120 to 168 that low heads E/SE before phasing with the trough. The Atlantic trough behind is neg tilted and combined with the low moving SE would force a wedge of heights NE which we see to some extent on the 168 you posted. The issue is whether the Atlantic trough and low maintain good separation and the wedge of heights is strong enough to build a ridge. Reality is that 144 is academic but if UKMO goes a similar route this afternoon it could well build a decent ridge. 

Edited January 8, 2017 by Mucka

[radiohead]

2 minutes ago, Ali1977 said:

Yep UKMO looks way better over NE Canada, crazy at only T96

Better over here too.

 

FI is 96 hours.

[Geordiesnow]

3 minutes ago, Jonan92 said:

Big differences between UKMO and GFS at just 96h

 

I would not say its big differences as such but the differences down the line you would imagine could be quite huge. Both models got the same sort of idea but how they will develop later on will probably vary, either way, good start to the UKMO run for coldies.

[SMU]

12 minutes ago, Mucka said:

Hi Steve

One of the rare occasions I don't quite agree with you and others on 00z UKMO not being good and appearing poor at 168. It isn't as good as ECM but you also say in a later post UKMO lifts the low up and through slow. I think it is clear from 120 to 168 that low heads E/SE before phasing with the trough. The Atlantic trough behind is neg tilted and combined with the low moving SE would force a wedge of heights NE which we some to extent on the 168 you posted. The issue is the whether the Atlantic trough and low maintain good separation and the wedge of heights is strong enough to build a ridge. Reality is that 144 is academic but if UKMO goes a similar route this afternoon it could well build a decent ridge. 

Yes I agree perhaps I should have said not quite as good as ECM

UKMO 96 12z has no phasing issues with good seperation

GFS 96 is better but still creeps the low east ...

S

[Man With Beard]

Just a note on precip charts on GFS. For some reason, the amount of precipitation always increases after T84. Don't be surprised to see snow at T102 today be rather less by T78!!

[Jonan92]

I would say that they are big differences, the tilt in those lows are day and night

[Captain Shortwave]

The UKMO still looks keen on that noticeable shallow trough which is exiting Newfoundland, lets see how it affects day 5/6. The GFS still showing a much faster and shallower feature which seems to be worst scenario. That trough will increase the potency of the initial north to north west blast by pushing the Atlantic ridge slightly further north, it is a question of whether it will run towards the UK or whether we see another idea, either could be good or bad, fair to say it is a difference compared to the previous ECM output.

Okay there is your difference, the UKMO sinks the low southwards as opposed to taking it over the top.

Edited January 8, 2017 by Captain Shortwave

[Geordiesnow]

3 minutes ago, Jonan92 said:

I would say that they are big differences, the tilt in those lows are day and night

I mean in the broad pattern they are not different(e.g ridging Atlantic high, deep low over the UK) but the differences that you can see at that range will no doubt make the 2 runs look different by 144 hours and the UKMO you would imagine will look better than the GFS at 144 hours regarding the strength and duration of the cold blast.

[Ice Day]

The GFS at 132 has better uppers over the UK than the 6z

Not much of a shift towards the ECM / UKMO it must be said

Edited January 8, 2017 by Ice Day