Winter Model Discussion 12Z 15/1/13 onwards.

[nick sussex]

It's important to look upstream to see which model is calling the pattern correctly there because the energy leaving the ne USA will impact the jet track into the UK.

I'll just pick out the most important parts of last nights NOAA extended discussion:

BY THE END OF THE MEDIUM RANGE PERIOD THE RIDGE/TROUGH PATTERN

ACROSS THE CONUS MAY START TO BREAK DOWN. THE UPPER VORTEX OVER

HUDSON BAY IS FORECAST TO LIFT TO THE NORTHEAST WHICH ALLOWS

NORTHERN ENERGY TO RIDE THE NORTHWEST FLOW OUT OF CANADA THROUGH

THE GREAT LAKES AND NORTHEAST...

BY MON/D5 THE NORTHERN ENERGY SHOULD FORM AN ARCTIC

FRONT THROUGH THE UPPER MIDWEST INTO THE GREAT LAKES THAT SHOULD

PUSH STEADILY SOUTHEASTWARD WITH STRONG HIGH PRESSURE IN ITS WAKE.

FRONT SHOULD CLEAR THE COAST AND POSSIBLY SPIN UP A STRONGER AREA

OF LOW PRESSURE BUT THE MODELS ARE ALL OVER THE PLACE FROM THE

SOUTHEAST COAST UP TO NOVA SCOTIA.

If you compare the ECM and GFS for 144hrs you can see the huge differences in what they do with that northern stream energy, also with the PV possibly lifting ne 'wards out of Hudson Bay this will impact the pattern in Europe.

What I would say is you must have a separation of the energy coming out of the ne USA before this happens. Just to show you the importance heres the ECM at 144hrs:

I've circled the key area in red with that black arrow showing that the low near the UK has removed itself from the energy in the ne USA.

If you don't get a clean break and have phasing of energy the low is less likely to be able to head se under the ridge to the ne.

Once you get that clearing through the ridge to the north can back sw'wards over the top.

If that happens then even with the PV edging ne out of Hudson Bay you can maintain a decent ridge to the n/ne which can help disrupt the energy se'wards.

[TEITS]

Looking at the ECM mean from the N Hemisphere and whilst im not an expert like GP, CH it does appear as though the lobe of Vortex over Canada begins to weaken.

So the potential for our cold spell to change its characteristics. What I mean by this is at the moment the upper temps haven't really dropped below around -8C and our snowfall potential is coming from the W. What could happen is we pull in much colder NE,lys with upper temps below -10C and snowfall coming from the NE instead. I would go as far to say that the potential is even greater than the classic cold spells of Dec 2009, 2010.

Probably getting overexcited but I can't help myself.

[Glacier Point]

Good agreement between ECM and GFS ensemble means at day 10 pattern. Remaining cold throughout that period with high risk of snowfall.

Thereafter, the modelling remains keen on the draining of the pv lobe over Hudson Bay within a general eastward moving longwave trough exiting the North American seaboard. So the question is posed, where does that energy go ? South-east into Europe where there is an existing trough and block of cold air to the north, or more NE allowing for a pressure rise over Europe ?

Given we already have a trough in place and cold block, allied to the 2nd wave of downwelling into the troposphere from this major midwinter warming of the stratosphere, I suspect cold intensifying is the favoured solution. Look NE.

[MKN]

Doing a quick comparison at +45 06z NAE to +51 00z gfs. NAE pushes everything roughly 50miles further east. Good news if like me not convinced precip will push this far east

[TEITS]

Latest NAE.

http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/01/16/basis06/ukuk/prty/13011806_1606.gif

Light patchy snow spreading E during Thurs night followed by main band approaching into Wales.

[Matty23]

look good cant wait maybe a day off work friday

[Ali1977]

Snow right down into east Cornwall on latest NAE Fri morning...

[mountain shadow]

Very poor NAE for Ireland, North and South. The front doesnt appear to be pivoting as much meaning the Atlantic wins out quickly.

Still different from the overnight ECM, UKMET and GFS which brings snow to NI at least.

Still time for change.

[swfc]

cant find model update times!sorry mods

[Cloud 10]

Good agreement between ECM and GFS ensemble means at day 10 pattern. Remaining cold throughout that period with high risk of snowfall.

Thereafter, the modelling remains keen on the draining of the pv lobe over Hudson Bay within a general eastward moving longwave trough exiting the North American seaboard. So the question is posed, where does that energy go ? South-east into Europe where there is an existing trough and block of cold air to the north, or more NE allowing for a pressure rise over Europe ?

Given we already have a trough in place and cold block, allied to the 2nd wave of downwelling into the troposphere from this major midwinter warming of the stratosphere, I suspect cold intensifying is the favoured solution. Look NE.

ECM mean looks tastier?

ecm.. gfs..

Excellent long range ensembles from the 00z ECM as well.

[Severe Siberian icy blast]

The 06z is further easy already than the 0z , quite progressive at t50 even

Edited January 16, 2013 by Severe Siberian icy blast

[Wayneywoo]

As usual, 06z exhibiting it's "let's push everything slightly further East" bias of late. So this is the "worst that can happen" scenario.

[Cheese Rice]

The 6Z from an IMBY perspective is good it pushes the front further east, stalling it across the spine of the country. The NAE is very much inline with the GFS too although it only goes out to 48 hours.

Edited January 16, 2013 by Cheese Rice

[NO LONGER POSTING]

06z is a cracking run... I expect it to be a bit west - east - west with the runs right up till the day..

[Severe Siberian icy blast]

But once the undercut begins which is as soon as the ppn arrives really the temps come tumbling down again and the areas in the far southwest that did turn to rain turns to snow again and looks to intensify through Friday night.

Getting really excited now.

[TEITS]

As usual, 06z exhibiting it's "let's push everything slightly further East" bias of late. So this is the "worst that can happen" scenario.

Well for a change I hope its right. Like the UKMO this does bring the front into our region.

http://www.wetterzen...cs/Rtavn724.png

Edited January 16, 2013 by THE EYE IN THE SKY

[Ian Brown]

06z is a cracking run... I expect it to be a bit west - east - west with the runs right up till the day..

Excellent to see the 06z take the PPN further East.

[Wayneywoo]

Well for a change I hope its right. Like the UKMO this does bring the front into our region.

http://www.wetterzen...cs/Rtavn724.png

I was going to say, on this occasion at this short time frame, the worst that can happen might be the best that can happen for some

Hopefully the rest of the run doesn't follow the trend of the 06z though and push the block away East. Of course if it does, all other runs/models suggest otherwise...

Edited January 16, 2013 by Wayneywoo

[chris55]

But once the undercut begins which is as soon as the ppn arrives really the temps come tumbling down again and the areas in the far southwest that did turn to rain turns to snow again and looks to intensify through Friday night.

Getting really excited now.

Undercut clear on the high res GFS, all such fine margins for some, 6z more like the euros with a slight eastward shift of the main band.

Thank god for the regional threads as its very hard to post unbiased thoughts in the general thread as everyone is (rightly so) concentrating on there back yard!!!

For us SSIB we seem to be in a pretty decent position!!! Kind of in the middle, slight shifts east or west should still keep us under the snow, often the way in these situations that the Cotswolds end up doing quite well.

[MKN]

Well for a change I hope its right. Like the UKMO this does bring the front into our region.

http://www.wetterzen...cs/Rtavn724.png

That's about as perfect imo as it could be if you want as large an area as possible seeing snow fri/sat.

[SandraD77]

Very poor NAE for Ireland, North and South. The front doesnt appear to be pivoting as much meaning the Atlantic wins out quickly.

Still different from the overnight ECM, UKMET and GFS which brings snow to NI at least.

Still time for change.

GFS is only model with any snow potential for Eire, but it's not being backed up by any other models right now! Oh well, I think this will very much be a Feb 2012 situ all over again with Ireland missing out on any significant cold! Met Eireann no longer even mentioning sleet in their forecast. NI may see something, but I think right now the atlantic has too much of an influence over our small island and after months of model watching with any potential always getting pushed further and further out into FI, I'm calling it a day for this winter! Mind you I'm happy for all our UK friends and the posters on here who'll hopefully finally get some proper snow this weekend! No sour grapes on my behalf!

[chris55]

Very cold for most!

[mountain shadow]

Excellent to see the 06z take the PPN further East.

Not excellent to see the PPN further East for many.

[Methuselah]

Not wanting to, in any way, come across as ramping...But the 06Z appears to have the word STONKER written all over it???

[TEITS]

I was going to say, on this occasion at this short time frame, the worst that can happen might be the best that can happen for some

Hopefully the rest of the run doesn't follow the trend of the 06z though and push the block away East. Of course if it does, all other runs/models suggest otherwise...

Forgive me for sayng but I think you're misreading this run.

The 06Z isn't pushing block away E and so far this is a better run than the 0Z. Our locations can afford a correction east but what we cannot afford with regards to Fridays snow is a correction too far W.

Also worth adding surface temps, dewpoints are much better than Mondays snowfall. This would certainly help with accumulations.