Model output discussion - Post SSW - Will it turn cold?

[Jason M]

2 minutes ago, Sweetdream said:

The short wave is on the 12z it has featured in the last two gfs runs. Also on the ecm.  Nick did allude to this happening with the depth of cold so that we could all keep track when the models came out.  I would love like every one else for an epic end to winter but we have been here so many times with the models getting into the reliable for it all to go belly up due to a shortwave. I can see this going the same way and watching Europe get the mother load of snow and we are left with dregs.  I would love more then anything to be wrong but these pesky short waves are not going to disappear or evaporate ?

Its a risk and therefore shouldn't be discounted, but a lower risk than usual I suspect. Even if this does happen I think we will still get a punchy cold spell but its the difference between punchy and epic!

[Met4Cast]

Hows this for a mean!

[Ice Day]

Incredible run following an incredible few days of model watching.  I genuinely believe that the best 3 runs I've ever seen have all happened over the last few days.  For those people saying that 'it's always at 240', well it's now at 180 according to this run.  The consistency between the ECM and GFS at 200 hours plus, showing high level blocking bouncing between Greenland and Scandi, is notable and puts us right in the bullseye of a proper long fetch easterly.  

Nothing is nailed and we are due a day of downgrades, also we need to see where this sits in the ensembles (surely right at the bottom), but there's so much going for cold at the moment, surely our time has come?!

Edited February 17, 2018 by Ice Day

[Pixel]

There's something in the water with regard to models reaction to the SSW event... they're clearly not geared up to deal with this particular data scenario and tbh neither are any of us mere mortals.

Certainly going to be interesting and potentially full of surprizes over the next week as they (the model data crunchers) adjust..  

The pro's with the data hidden from us are better placed; ukmo et al' as opposed the flip flop GFS and Brazilian model interpretation  

Edited February 17, 2018 by Pixel
spwellin

[Derecho]

A glance through the 18z ensembles at T102 suggests that support is increasing rapidly for the development of an intense Scandi high. Phase 1 of getting things set up to our NE looks like its going to succeed. 

Next step is to not avoid any awkward shortwaves forming in the cold air to our east like a few other members have mentioned. That stopped the core of the cold air in February 2012 hitting our shores. However with an Azores low instead of a high this time we have less to worry about.
 

Still cautious but belief is increasing this may come off.

Being born in the late 80's I cannot remember a truly cold easterly hitting us. That has to be the best run of the internet era.

[Mike Poole]

So, into the GEFS ensemble, here at T252, this thing is practically  nailed on now, you can tell your mum!

[kold weather]

18z GFS ensembles areif anything faster than the 18z run, many bringing in cold around 144hrs. Those runs are not as cold as the runs that delay the cold (those goto -13/14/15) but they are still by large sub -10C.

Just to put into context, the 2009 Feb snow event came from a small cold pool of around -10/11C which lasted 24hrs...

[nick sussex]

Apparently GFS 18 hrs runs like hanging out at coffee shops in Amsterdam! 

A stupendous run and better in terms of blocking set up.

BA mentioned earlier in the thread the direction of the cold pool and possible shortwaves .

Because there’s a signal for heights to rise to the nw later then it’s better the cold pool doesn’t start off too far north to the east .

Many of the UK cold misses to the south happen because too much energy goes over the high , that wouldnt happen if the height rise to the nw verifies , this would tend to help the cold pool get pulled more nw as it heads into the UK helped by the rise of pressure to the nw.

So for that reason you don’t want the cold too far north at the outset.

Anyway there’s quite a few runs to go before we can be more confident of where the deepest cold will head and we do have to keep an eye on any shortwave development in the flow.

[helen47]

1 minute ago, Mike Poole said:

So, into the GEFS ensemble, here at T252, this thing is practically  nailed on now, you can tell your mum!

Lol ive seen easterlys fail at t48 nothing is nailed with the beast

[Ice Day]

9 minutes ago, Pixel said:

There's something in the water with regard to models reaction to the SSW event... they're clearly not geared up to deal with this particular data scenario and tbh neither are any of us mere mortals.

 

I suppose that makes Chiono and Catacol (among others) not mortal then!?!?!

[Coastal Eddy]

36 minutes ago, SN0W SN0W SN0W said:

We've had a few cold westerlies the past few weeks, only fair to return the favor. 

Canada, Welcome to the beast from the east !

 

[Banbury]

6 minutes ago, Quicksilver1989 said:

A glance through the 18z ensembles at T102 suggests that support is increasing rapidly for the development of an intense Scandi high. Phase 1 of getting things set up to our NE looks like its going to succeed. 

Next step is to not avoid any awkward shortwaves forming in the cold air to our east like a few other members have mentioned. That stopped the core of the cold air in February 2012 hitting our shores. However with an Azores low instead of a high this time we have less to worry about.
 

Still cautious but belief is increasing this may come off.

Being born in the late 80's I cannot remember a truly cold easterly hitting us. That has to be the best run of the internet era.

Late 80’s you’re a boy lol ‘78 , ‘81 and 87 we’re crackers ....you might remember 91 

If this gets anywhere near those we are laughing 

[karlos1983]

So in summary 

wow

wow

wow

gonna be wow

and get back from the stag doo your holyness we need you sober ?

What a day!! I hope @Mucka is getting his beauty sleep for the graveyard shift! 

There really is no better place to be than here when the models are this good! I raise my glass of Gin to Ya’all!!

Edited February 17, 2018 by karlos1983

[metaltron]

7 minutes ago, Quicksilver1989 said:

A glance through the 18z ensembles at T102 suggests that support is increasing rapidly for the development of an intense Scandi high. Phase 1 of getting things set up to our NE looks like its going to succeed. 

Next step is to not avoid any awkward shortwaves forming in the cold air to our east like a few other members have mentioned. That stopped the core of the cold air in February 2012 hitting our shores. However with an Azores low instead of a high this time we have less to worry about.
 

Still cautious but belief is increasing this may come off.

Being born in the late 80's I cannot remember a truly cold easterly hitting us. That has to be the best run of the internet era.

To my eye it doesn't look like the shortwaves are the issue, rather that the high is too far north and the orientation is wrong. The high being too far north is my biggest worry looking at the GEFS ensembles. If we can get the high further south (ie over central Scandi, not the Azores!) and then retrogress it towards Greenland then I think it will drag the cold pool with it.

[Day 10]

So over the last few days we've had a that GFS, that ECM, that ICON, that GEM. It can only mean one thing then surely? RAIN!

 

Seriously though, the chances of an historic cold spell are certainly gathering pace. 

[Jason M]

9 minutes ago, Quicksilver1989 said:

A glance through the 18z ensembles at T102 suggests that support is increasing rapidly for the development of an intense Scandi high. Phase 1 of getting things set up to our NE looks like its going to succeed. 

Next step is to not avoid any awkward shortwaves forming in the cold air to our east like a few other members have mentioned. That stopped the core of the cold air in February 2012 hitting our shores. However with an Azores low instead of a high this time we have less to worry about.
 

Still cautious but belief is increasing this may come off.

Being born in the late 80's I cannot remember a truly cold easterly hitting us. That has to be the best run of the internet era.

Top post! The other variant is the one that forms over the Balkans in response to a deep cold pool and pushes the everything into Greece. 

[Pixel]

7 minutes ago, Ice Day said:

I suppose that makes Chiono and Catacol (among others) not mortal then!?!?!

Yup (-:

[Ice Day]

OK, the short ensembles are in and predictably the Op is just about a cold outlier.  Interestingly, the mean actually rises at days 7-8, which does go to show that nothing is nailed down quite yet.  However, the GEFS really haven't performed at all well over the last couple of weeks, so I wouldn't fret too much, just food for thought!

[blizzard81]

The trend throughout today has been excellent for coldies. My feeling is if we can get through tomorrow and I can say this the same time tomorrow then it will be game on. 

[Catacol]

Oh - I cant resist another stock check. Apologies for sounding like a broken record, but it's a damned good one (think "Great Gig in the Sky" and "Number of the Beast" rolled into one....) Top Ten forecasting signals as follows:

 

1. Azores High. On very extended holiday as the storm track is fired south, and angular momentum at the equator remains positive for a while longer.

2. Vortex. Split and shredded. In reverse gear until March. No frictional downwelling support for any westerly momentum in the north atlantic.

3. Cold air. Spilling out all over the place as temperatures rise in the arctic stratosphere. Cold temps forecast throughout the northern hemisphere as a result, but Eurasian cold particularly noticeable due to total eradication of the Eurasian vortex, consequent swelling of the siberian high, and consequent strong signal for pattern retrogression.

4. Atlantic low pressure conveyor. Fighting a rearguard action as the Canadian vortex survives... but ongoing warming eating away at the foundations of that vortex and consequent trend for residual energy to slide under the growing Scandy block. Battleground scenarios for the West....

5. Ocean moderation of cold. Not significant... oceans in February are approaching coldest period.

6. Sun - growing - but in fact under a very cold airstream the warmth from the sun will promote a lot more shower activity. If 850s are lower than -8 then actually, perversely, we rather like a stronger sun.... (if you like snow that is...) Convective potential for the East.

7. MetO - in line. In fact in line for a while now... and rather than being an irritating voice of reason in the background, suggesting knife edge scenarios are not going to be significant or long lasting (with an even more irritating habit of being proved correct) instead is now sticking to a "very cold" scenario. BFF.

8, Genoa Low. Yep - its in place. Ensemble forecast sees low heights over the med for an extended period of time (see storm track point above) so potential for frontal systems to push SE to NW as per Feb 1991 perfectly in place. Snow for the South.

9. Pressure gradient. Yep - also in place. Scandy High set to get stronger... = slack winds a low risk

10. Cold in the north. Yeah - kinda repetitive this season I suspect... and maybe for once snow potential in the south may eclipse potential in the north.. but we all know its rarely dry in the north!! Snow will fall there too.

 

What have I missed? Doesnt really matter I suppose - all the above point in only one direction... There is a serious chance that Feb/March 2018 will end up in weather folklore.

[NorthYorksWeather]

Just a small spread in the ensembles at day 6 onwards

The 00z OP could be one of those milder runs in the morning so the cold easterly is far from nailed!

[Catacol]

25 minutes ago, Daniel Smith said:

Hows this for a mean!

Never ever seen a mean like that.

[nick sussex]

The thing I like about both the ECM 12 hrs and GFS 18 hrs run is the core of height rises is to the north then edges to the ne.

So the UK isn’t at the flabby end of the block as the cold pool advances .

Think of the core heights as the shepherd and his dog and the deep cold the flock of sheep.

If you have that strong block in a good position  it acts to force the sheep into line!

I must stop with these bizarre analogies! 

 

[skatefan]

3 minutes ago, Quicksilver1989 said:

A glance through the 18z ensembles at T102 suggests that support is increasing rapidly for the development of an intense Scandi high. Phase 1 of getting things set up to our NE looks like its going to succeed. 

Next step is to not avoid any awkward shortwaves forming in the cold air to our east like a few other members have mentioned. That stopped the core of the cold air in February 2012 hitting our shores. However with an Azores low instead of a high this time we have less to worry about.
 

Still cautious but belief is increasing this may come off.

Being born in the late 80's I cannot remember a truly cold easterly hitting us. That has to be the best run of the internet era.

Fantastic runs today!

I don't believe, as I argued earlier, that shortwaves will change the large-scale synoptics caused by the SSW:

- Ridging N/NE of the UK and HP across the pole

- PV energy slowly transferred to the Pacific side

What you see today is that when the models grasp the large-scale developments without to much disturbances from small to medium scale waves, the crossmodel agreement becomes clear. 

Obviously, shortwaves can have a big effect on local development in cold and snow but the big picture is quite clear now....

[karlos1983]

And here’s the ecm ens 

pretty good agreement out to the 25th!! We are making steady progress