Winter Model Discussion 12Z 15/02/13 onwards.

[legritter]

OK things may evolve a bit different than we were thinking 24/36 hrs ago ,but still finish up good .lets wait till 120fax and tomorrows morning charts ,its going to be a cliffhanger but plenty to be glad about .the end result could be good .

[cooling climate]

The day started off so well with the 0z continuing where the 18z left off with cross model agreement.

18 hours later and synoptics not looking anywhere near as good for convective activity.

It will be interesting to see if the models have overplayed this trend and start to revert back more

towards this mornings outputs.

I do not really see the point though of rolling out the lesser models when the main three do not show

what you want but each to their own I suppose.

[Jason M]

I wonder if were seeing a step change in the output tonight. See the attached chart from the ensembles below. This is the most extreme, but look to our NE at what is going on.

http://www.meteociel...&mode=0&carte=0

This is why were seeing the whole set up move south as the PV threatens to squeeze out the high pressure cell. logic would suggest the heights transfering NW towards Iceland. It will be interesting to see where we head tommorow.

Jason

Edited February 16, 2013 by Jason M

[ZONE 51]

GFS 18z - Thickness 850/1000hpa

168hrs(next Saturday)

180hrs (next Sunday)

Very cold all areas, there would be a lot of cloud down east side of UK.

-

ECM 850s

120hrs(Thurs)

-11C upper temps into SE/EA

-

ECM 850s Central Europe 120hrs this shows where the coldest airmass goes (at this stage)

Edited February 16, 2013 by ElectricSnowStorm

[Jason M]

Really cherrypicking my ensembles now, but to illustrate what i'm saying....

http://www.meteociel.fr/modeles/gefs_cartes.php?code=7&ech=138&mode=0&carte=0

Jason

[london-snow]

If Ian F is about i would be very interested if he can answer to the following :

The bbc weather is information supplied by the meto if i remember.

Just had a quick glance at their 5 day forecast via the teletext service and shows on thursday a heavy snow symbol to the sw of London.

Now i know it is virtually impossible to predict snowfall 5 days out but if its a dry & cold picture like you have been stating then why is it showing different?

Not having a pop or dig at the meto at all i am just interested in the answer as to why.

Cheers.

L~S

[mountain shadow]

It cannot be argued that the latest model trend is for high pressure to fail to gain enough latitude to bring in the colder unstable air. Yes, extreme south eastern areas may do well but the trend is for this to go South of the UK. I concur that this may change.

Looking past 8 days and we signs of retrogression to Greenland and the PV dropping into Scandanavia but with a west based -NAO we are in danger of the Atlanic pushing in from the South West before the Arctic air can arrive.

[Liam J]

I think that is the key, we do not know how clear the flow will be, it could be a cloudy flow. It could end up being largely cloudy, little snow, limited frosts and chilly days. Shelter western areas would be best favoured for breaks in this set up. I get the feeling that is what is going to end up as.

Yes, if it's a cloudy slate grey type flow then one good thing about living west of the Pennines is their ability to break up cloud sheets in an easterly flow which would otherwise lead to grey and depressing skies! In such set ups it can be well below freezing overnight here under clear skies whilst further east under cloud the temps hover around the 0c mark or just above.

I'm sure that further changes will occur across the outputs in coming days, this is far from set in stone and the crucial element and deciding factor will be the position of the high pressure cell. I'd absolutely love to have retrogression towards Greenland then we'd be really talking, some serious cold lurking not far away.

Edited February 16, 2013 by Liam J

[fergieweather]

OK... Let's look at the Thurs-Fri period and offer some explanatIon re how the rather changeable precip fields are playing this. THURS first: the forecast profiles show how any convection is capped firmly beneath a low inversion and thus cloud tops probably up only to circa 850-900 HPa. The net result in this sort of set-up is a veil of stratocumulus advancing west, i.e. as any convection across the N Sea then flattens-off under the inversion. Now, clearly wIth any such shallow cloud depth, the likely ppn will only be light snow flurries and/or snow grains, with these more probable across windward coasts and (E facing) hills.

Let's then look later into THURS PM towards FRI. The crucial change is the injection of a low-level cold pool of air, whilst coincidentally, it gets overridden aloft by an upper trough. Result? A greater degree of destabilisation - albeit not spectacular - and lo, suddenly the profiles want to offer more towered cumulus with tops running up above the 800 HPa level and reachIng into territory of circa -13C.

So.... start walloping these together in any semblance of alignment through any coherent process, such as 'classic' Thames Estuary convergence, and quickly we might develop a local situation where snow accumulations might become a bother from moderate PPN rates.

Thus, devil in the detail and frankly (a) the raw PPN fields are far too 'raw' so don't take serIously; (B) I continue beating the "look-at-the-profiles" drum; © the regional snow issues are far from conclusive at this juncture so less depression please, especially you folk in E/SE.

[Barry12]

A week of cold and dry weather followed by Westerlys to bring winter to an end is what I'm expecting.

[Continental Climate]

I think its game over for the easterly and probably for winter as well!! Lets just put it all behind us and look forward to a (hopefully) warm spring and nice hot summer with ridging azores highs, euro highs and bartletts aplenty

I dont want to see another greenie or scandi high for nine months thank you very much

Edited February 16, 2013 by Continental Climate

[Jason M]

OK... Let's look at the Thurs-Fri period and offer some explanatIon re how the rather changeable precip fields are playing this. THURS first: the forecast profiles show how any convection is capped firmly beneath a low inversion and thus cloud tops probably up only to circa 850-900 HPa. The net result in this sort of set-up is a veil of stratocumulus advancing west, i.e. as any convection across the N Sea then flattens-off under the inversion. Now, clearly wIth any such shallow cloud depth, the likely ppn will only be light snow flurries and/or snow grains, with these more probable across windward coasts and (E facing) hills.

Let's then look later into THURS PM towards FRI. The crucial change is the injection of a low-level cold pool of air, whilst coincidentally, it gets overridden aloft by an upper trough. Result? A greater degree of destabilisation - albeit not spectacular - and lo, suddenly the profiles want to offer more towered cumulus with tops running up above the 800 HPa level and reachIng into territory of circa -13C.

So.... start walloping these together in any semblance of alignment through any coherent process, such as 'classic' Thames Estuary convergence, and quickly we might develop a local situation where snow accumulations might become a bother from moderate PPN rates.

Thus, devil in the detail and frankly (a) the raw PPN fields are far too 'raw' so don't take serIously; ( I continue beating the "look-at-the-profiles" drum; © the regional snow issues are far from conclusive at this juncture so less depression please, especially you folk in E/SE.

What do you think re the PV dropping down and the heights moving towards Iceland? Early signs tonight IMO.

[mountain shadow]

A week of cold and dry weather followed by Westerlys to bring winter to an end is what I'm expecting.

Apart from the extreme South East that is. But the trend is to push even that into the continent.

[london-snow]

OK... Let's look at the Thurs-Fri period and offer some explanatIon re how the rather changeable precip fields are playing this. THURS first: the forecast profiles show how any convection is capped firmly beneath a low inversion and thus cloud tops probably up only to circa 850-900 HPa. The net result in this sort of set-up is a veil of stratocumulus advancing west, i.e. as any convection across the N Sea then flattens-off under the inversion. Now, clearly wIth any such shallow cloud depth, the likely ppn will only be light snow flurries and/or snow grains, with these more probable across windward coasts and (E facing) hills.

Let's then look later into THURS PM towards FRI. The crucial change is the injection of a low-level cold pool of air, whilst coincidentally, it gets overridden aloft by an upper trough. Result? A greater degree of destabilisation - albeit not spectacular - and lo, suddenly the profiles want to offer more towered cumulus with tops running up above the 800 HPa level and reachIng into territory of circa -13C.

So.... start walloping these together in any semblance of alignment through any coherent process, such as 'classic' Thames Estuary convergence, and quickly we might develop a local situation where snow accumulations might become a bother from moderate PPN rates.

Thus, devil in the detail and frankly (a) the raw PPN fields are far too 'raw' so don't take serIously; (B) I continue beating the "look-at-the-profiles" drum; © the regional snow issues are far from conclusive at this juncture so less depression please, especially you folk in E/SE.

Thanks Ian for that great explanation.

[Argyle1980]

I wonder if were seeing a step change in the output tonight. See the attached chart from the ensembles below. This is the most extreme, but look to our NE at what is going on.also keeping a close eye on that Pv .

I think it's going to move the high into a favourable position for all of us in the uk.

Give it a couple of days. :-)

http://www.meteociel...&mode=0&carte=0

This is why were seeing the whole set up move south as the PV threatens to squeeze out the high pressure cell. logic would suggest the heights transfering NW towards Iceland. It will be interesting to see where we head tommorow.

Jason

[london-snow]

I think its game over for the easterly and probably for winter as well!! Lets just put it all behind us and look forward to a (hopefully) warm spring and nice hot summer with ridging azores highs and bartletts aplenty

LOL Just LOL!

[SMU]

Indeed- As pointed out- higher cloud tops & heavier snow is in prospect...

the much maligned GFS has suddenly become the model of choice-

In favour of the top performing ECM

which with a gentle goodnight I will remind everyone of the day 6 chart - MEAN

http://www.meteociel.fr/modeles/ecmwf/runs/2013021612/EDM1-144.GIF?16-0

S

Edited February 16, 2013 by Steve Murr

[london-snow]

Indeed- As pointed out- higher cloud tops & heavier snow is in prospect...

the much maligned GFS has suddenly become the model of choice-

In favour of the top performing ECM

which with a gentle goodnight I will remind everyone of the day 6 chart - MEAN

http://www.meteociel.fr/modeles/ecmwf/runs/2013021612/EDM1-144.GIF?16-0

S

Thank you steve,

Finally someone who can understand my thoughts also & read between the lines.

I do also hope the 00z push the high a tad further north to bring more of the forum into play. As things stand it is great however if you're in the south east of england but nothing is nailed on as yet.

Edited February 16, 2013 by london-snow

[Weather-history]

I'd absolutely love to have retrogression towards Greenland then we'd be really talking, some serious cold lurking not far away.

The problem is that low that sits south of Greenland and east of Newfoundland. I can't see how favourable retrogression can occur whilst that low sits there.

[Panayiotis]

So another day of model watching, so where do we stand? All models show the cold weather starting from Wednesday night all the (and possibly beyond depending on which model you pick) to 192hrs (Thursday 28th) at least. Models at 192hrs:

Above is the GFS,ECM,JMA,BOM,CMA, and CFS, as you can see all the models still showing a cold flow, be that from the E or NE, again note the PV has moved from Canada/Arctic to Russia/NW Europe, this one thing that I have been on about for quite some time, with the movement of enegy from Canada/Arctic should allow heights to build into Greenland, if we get the retrogression of heights towards Greenland we are in the colder pattern for longer and snow would be likely if we get the polar low.

However when the PV moves the GFS, and CMA want to move the high SE, this is because of the energy around the southern tip of Greenland, notice that those models have part of the PV just south of Greenland with that being there IMO we wont get the retrogressing heights. Like the ECm,JMA, and CFS which have the low 300/400miles south of Greenland, this shunts the heights behind it therefore moving them into Greenland, this also allows for an undercut and with the PV over NW Europe the isobars will link up bringing the part of the PV towards us.

To me I think the JMA is a bit progressive at 192hrs but it is surprisingly similar to the CFS.

I also want to note on how far the PV goes; We want part of it to drop into Norway like the BOM, JMA and CFS have it as this gives us the opportunity for the deeper uppers and possibly a polar low. The further east and north it moves the worst our possibility of getting the cold to last.

These are some of my points and things that I will be looking out for in the next couple of days.

Edited February 16, 2013 by Panayiotis

[Barry12]

I'd trade this Easterly for another warm spell in March like last year, got to 21C here

[BM4PM]

LOL Just LOL!

I think its game over for the easterly and probably for winter as well!! Lets just put it all behind us and look forward to a (hopefully) warm spring and nice hot summer with ridging azores highs, euro highs and bartletts aplenty

I dont want to see another greenie or scandi high for nine months thank you very much

Sorry I now it's off subject.but do people put posts like this up in the summer telling people it's gona rain when the forecast is for warm weather .

[fergieweather]

I'd trade this Easterly for another warm spell in March like last year, got to 21C here

I concur. Brave post on this forum, incidentally ;-)

[Nick F]

So.... start walloping these together in any semblance of alignment through any coherent process, such as 'classic' Thames Estuary convergence, and quickly we might develop a local situation where snow accumulations might become a bother from moderate PPN rates.

Thus, devil in the detail and frankly (a) the raw PPN fields are far too 'raw' so don't take serIously; ( I continue beating the "look-at-the-profiles" drum; © the regional snow issues are far from conclusive at this juncture so less depression please, especially you folk in E/SE.

Yes, the raw model data - particularly the GFS and UKMO GM that don't have the resolution of the mesoscale models will not pick up enhanced snowfall developments, particularly where we see convergence along coastlines, Thames Streamer as an example. Such locally enhanced snowfalls most likely Thurs/Fri for the SE/E Anglia when it catches the edge of the 500mb cold pool moving SW over the near continent - which will allow cloud heights to gain better depth.

But for many, it's looking like dry or snow flurries at best.

Edited February 16, 2013 by Nick F

[swfc]

I'd trade this Easterly for another warm spell in March like last year, got to 21C here

Id agree.It looks quite lame in regards to any snowfall and i for one dont want cold frosty weather at this stage of winter.