Model output discussion - Winter has arrived and the hunt for cold is on

[IDO]

2 minutes ago, swfc said:

wonder when that will show on the output if at all 

It is already showing up on the GFS and has done for some runs. The problem is the AO is just a measurement of the Arctic pressure and if we look at the charts, its basically a wedge of heights spat out by the Pacific Ridge. It is not a classic Arctic High and ATM GFS has the wedge unfavourably placed and the net result of the direction of travel for the cold uppers are as per the 06z:

The two vortices over the US and Eurasia. with the Euro arm well to the east of the UK. So not going to get excited by a negative AO until we get a reset of the HP cell train. With the experts downplaying any tropical forcing for the medium term then maybe the best we will get are scraps from the NW or a northerly from a passing LP system?

[Mucka]

2 minutes ago, booferking said:

Gfs 12z v 06z trending.

Slowly getting to grips with Arctic high pressure, only because it is already there and developing, so not so much modelling as having the data force fed.

[Mucka]

14 minutes ago, booferking said:

Sliding under?

Decent chart for sure. Strong Arctic blocking and almost vertical ridge about to push up just West of Britain.

 

GFS today 12z V Yesterday V day before 162 hrs, still correcting it seems.

Edited December 12, 2019 by Mucka

[northwestsnow]

Still differences between UKMO/GFS at 144

[Ali1977]

Where is that WAA going near Scandy can it link with Arctic heights 

[Mucka]

GFS modelling splitting energy in the Atlantic for the first time. Not quite there this run but definitely  moving in the right direction. Will it keep heading that way though?

For those worried about cold uppers if we hit the jackpot then just to reiterate that the further West and more vertical and strong the ridge the closer the cold air will be before we begin to draw in a NE/E flow

Example below today's 12z V 6z re how far W 850's are at start of any pattern change.

Edited December 12, 2019 by Mucka

[Ali1977]

5 minutes ago, Ali1977 said:

Where is that WAA going near Scandy can it link with Arctic heights 

It’s certainly trying

[SLEETY]

More evidence as has been mentioned how poor GFS is at modeling high pressure in the Arctic expect more changes in future runs too.

[northwestsnow]

GFS 12 looks completely different compared to 6z by day 8

[frosty ground]

Jet is playing ball more with the curve back over Scandi (at least an attempt too)

[booferking]

16 minutes ago, TSNWK said:

Not so sure! - would the trough to our West / South west not bump into, be slowed down by the High-pressure over Greece ( if anything the trough might pump it up a little ) for balance it would certainly ramp up the interest if it did with what is a promising profile to our north.

 

 

Yes on the balance put an improving picture with each run.

[northwestsnow]

12Z looks much drier generally than the 6z ..

My baseline is now so low for Dec i'm delighted to see this, hope the trend continues..

[frosty ground]

Differences are start to our south east,

[Mucka]

5 minutes ago, frosty ground said:

Differences are start to our south east,

Symptom of the split energy earlier which itself is caused by a more vertical stronger ridge resisting the Atlantic low. We need more corrections upto the 19th to get that ridge further W and have the Atlantic lows disrupt SE with some proper undercut.

Worth noting the UKMO is in a better position for this by 144 than the GFS.

GFS has nearly caught up now on the changes in the Arctic so worth taking a little more seriously from tomorrow.

Edited December 12, 2019 by Mucka

[booferking]

96hr is outside the reliable at the minute the gfs is that bad..

[TSNWK]

2 minutes ago, frosty ground said:

Differences are start to our south east,

Yes! big differences there, nice leaking away of heights to our south-east - another couple of similar changes ( not unreasonable at that time-frame ) and we might, just might be looking at some festive Christmas week weather - defo trend in the right direction.... can it be maintained?

[mountain shadow]

1 minute ago, booferking said:

96hr is outside the reliable at the minute the gfs is that bad..

True. A GFS OP run is never going to get this kind of energy split correct.

[northwestsnow]

3 minutes ago, Mucka said:

Symptom of the split energy earlier which itself is caused by a more vertical stronger ridge resisting the Atlantic low. We need more corrections upto the 19th to get that ridge further W and have the Atlantic lows disrupt SE with some proper undercut.

Worth noting the UKMO is in a better position for this by 144 than the GFS.

GFS has nearly caught up now on the changes in the Arctic so worth taking a little more seriously from tomorrow.

Nice post mate, i posted the UKMO/GFS 144 and UKMO looks better to me too..

[tight isobar]

Today's by-notes.

@slidingsliding @blockingblocking..

12zgfs offering up decent transition. @blocking format.

Here's hoping for an ecm similar evo..this evening...

Things ramping up !!!

 

[northwestsnow]

GFS low res goes AWOL - not bothered by that as it so different to the 6z prior to day 10..

[Tony Beets]

Anyone got any snow charts for this weekend? Thanks 

[chris55]

Lots of potential beginning to unfold as we head into the Xmas period. The models are starting to see the disrupted flow and aren’t really sure where everything will eventually end up. 
 

UKMO was first to spot the Newfoundland low not just barrelling through. Nice to have something to watch in the run up to Xmas

UKMO 120 ! 

 

[IDO]

There appears to be a small window of opportunity to get some cold to the UK at around D8:

As others have said, better split flow for undercutting of the nascent Scandi wedge. A step towards it on this run but probably need the Arctic wedge to dock with that ridge to enable the cold to spread from the east. There is no way it is coming from the north if a status quo, and any NW'ly is going to be washed out. 

Unless something unforeseen pops up pre-D10 this is a hit or miss chance for cold around Christmas. The mechanics of the NH profile are just not working for us with an entrenched latent background state that is keeping the bitter cold well away from us despite multiple cold spells in the NH since November.

[swfc]

well im not over impressed with the 12z output tbh.ukmo looks to have a lobe of pv towards the nw waiting to pounce.gfs looks very at odds with itself.im trying to be optimistic but I think gp comments earlier kind of sum things up.see what ec brings but it could show limp heighths at day 10 which really wont cut it.onwards and upwards either way

[swfc]

4 minutes ago, IDO said:

There appears to be a small window of opportunity to get some cold to the UK at around D8:

As others have said, better split flow for undercutting of the nascent Scandi wedge. A step towards it on this run but probably need the Arctic wedge to dock with that ridge to enable the cold to spread from the east. There is no way it is coming from the north if a status quo, and any NW'ly is going to be washed out. 

Unless something unforeseen pops up pre-D10 this is a hit or miss chance for cold around Christmas. The mechanics of the NH profile are just not working for us with an entrenched latent background state that is keeping the bitter cold well away from us despite multiple cold spells in the NH since November.

I think the pv to the east of the low will merge with the low and blow up imo stopping the low sliding. hope to be very wrong tho