Winter Model Discussion 18Z 19/2/13 onwards.

[No Balls Like Snow Balls]

GFS wants to continue to sink the high SE - if it gets this one right then it will be the first time it has lead the way for a long long time.

[frosty ground]

look more like sleet showers as the rain and snow symbols are showing on that chart

The light blue AKA very light PPN will always be light blue regardless of temp, just the way the output works for those charts.

[No Balls Like Snow Balls]

http://www.wetterzen...cs/Rtavn001.png

Evidence showing heights over Greenland! Right now.....

The issue being the core of the high is over Canada AKA to far west.

Not sure what you T+384 comment is regarding, clearly it can’t be about the 33% of GFS Ensembles that fall below -10 for large parts of the UK within the 240 hour time frame.

or the flip side 66% don't

[snowmadchrisuk]

This wide spread light Snow from the SE on Monday has been showing up on quite a few runs now .. Can't comment on the Models but have some seen some Heavy Snow from an Easterly even though only light PPN is being detected on the radar ...

Just to add rain today is already detecting Showers building in the North Sea and heading SW , I would not be surprised to see that the shower potential has been under estimated.

Edited February 20, 2013 by snowmadchrisuk

[Methuselah]

http://www.wetterzen...cs/Rtavn001.png

Evidence showing heights over Greenland! Right now.....

The issue being the core of the high is over Canada AKA to far west.

Not sure what you T+384 comment is regarding, clearly it can’t be about the 33% of GFS Ensembles that fall below -10 for large parts of the UK within the 240 hour time frame.

But, as has been the case throughout this winter, no evidence (yet) that it'll have the desired effect on our weather, any time soon??

Guessing the 'unkown' is never easy!

[Thundery wintry showers]

I think there will indeed be a build of pressure over Greenland and a surge of northerlies from the Arctic, but the question mark is whether or not the northerly catches the British Isles. Quite often we end up with a slow-moving trough developing in the eastern North Atlantic in these situations which results in mild moist south-westerlies over the British Isles and the northerlies being shunted away into Scandinavia.

The easterly doesn't look set to bring much in the way of convection. The skew-t forecast for London for T+84 highlights the main issue:

http://cdn.nwstatic.co.uk/gfsimages/gfs.20130220/06/84/sound-London-84.png

There is a layer of dry, stable air starting at around the 850hPa level- convective clouds over the North Sea are likely to keep hitting that capping layer and spread into stratocumulus, resulting in grey skies and just occasional sleet or snow flurries near the east coast. Much of Scotland and the western side of Britain are likely to see sunshine at times thanks to the high pressure (in the case of Scotland) and shelter (in the case of the west).

[Methuselah]

Of course it's 'worthy of discussion', fg...Since when is disagreeing, or reporting what's true, synonymous with 'mocking'?

Edited February 20, 2013 by Rybris Ponce

[shaky]

Good to see some snow showers finally appearing into E Anglia on the NAE.

http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/02/20/basis06/ukuk/prty/13022206_2006.gif

have you seen the uppers mate there was always something bound to develop!!and fingers crosses it looks like there might be a washer streamer setting up aswelll!!

[Jason H]

The easterly doesn't look set to bring much in the way of convection. The skew-t forecast for London for T+84 highlights the main issue:

http://cdn.nwstatic....d-London-84.png

There is a layer of dry, stable air starting at around the 850hPa level- convective clouds over the North Sea are likely to keep hitting that capping layer and spread into stratocumulus, resulting in grey skies and just occasional sleet or snow flurries near the east coast.

Thanks for that link. It would seem the logical reason as to why the forecast for convection is inhibited. A shame that with cold 850's and a favourable wind direction the convection is going to be killed. Still some falling snow seems likely for the South East.

[SomeLikeItHot]

GFS wants to continue to sink the high SE - if it gets this one right then it will be the first time it has lead the way for a long long time.

It will be its also interesting to note that it keeps the high in place just north of scotland for basically the entire Hi res part of the run then shifts it relatively rapidly as soon as it hits the low res.

[Cloud 10]

thats the op cloud ! the mean is similar but more diluted re the strength of that anomoly.

Yeah,i know its the operational run,but a black hole is a black hole,lol!

As you say,buckle up!

[nick sussex]

The will it or won't it possible northerly is still more won't this morning. The core of those heights are far too west and then you have a race between low to the sw and troughing to the ne, I think you can make a small case for the far north seeing something but its really a long haul to get the Arctic air much further south.

It's for this reason that I intensely dislike west based negative NAO's because they look good on the chart but rarely deliver, however because of the upstream profile with still energy being ejected se then I wouldn't completely rule out the chance of an early spring shock but we'd need to see a very large correction east in the pattern.

In terms of the easterly if people put aside the uncertainties re snow potential its been quite a surprise to actually see the 850's upgraded rather than downgraded, the cold pool isn't the problem at all its really just the set up isn't condusive to delivering those hefty snow showers, however I think we should reserve judgement till after the event and not before because there might be a few surprises.

I think the problem with easterlies is that people often get heightened expectations at the mere mention of them when in fact they all have very different characteristics, sometimes they deliver lots of snow to more favoured areas and others its more the flurry type outcome. For this reason I don't understand the comments re downgrade if something wasn't being shown to begin with, I don't remember any of the big 3 ever showing some classic easterly set up, as for the smaller cannon fodder models well thats exactly why they're not at the top table.

We'll see over the next few days what exactly this easterly delivers, it might surprise or disappoint or just be close to what the models currently show.

[No Balls Like Snow Balls]

It will be its also interesting to note that it keeps the high in place just north of scotland for basically the entire Hi res part of the run then shifts it relatively rapidly as soon as it hits the low res.

Yes I noticed this to - it is currently in line with meto thoughts though - of course meteo thoughts can change as rapidly as the models though.

[BLAST FROM THE PAST]

As we approach the equinox, it might actually happen: this winter's ever-present 'retrogression signal' might actually lead to something...A 1975-like Spring, perhaps?

You mean the one that's verifying?

Cold has upgraded over last day or so and some very low daytime maxima coming up and I wouldn't be surprised to see a vast improvent on 1cm of snow predicted. For anyone that thinks this spell won't be in bitterly cold category [particularly for the southern half] they'll will be way off the mark. Further signs now of the models picking up on the HP moving west and finally we see HP develop to our NW and a potential prolonging of this cold spell well into March. The SW flow developing in 7days time [tweeted recently wasn't it? Although I'm no fan of twitter as not much can be said on it] seems off the mark looking at the models as that would make the SW flow arriving in 5/6 days time?

All to play for in a last hoorah of winter

BFTP

Edited February 20, 2013 by BLAST FROM THE PAST

[Methuselah]

So chipping in with "Aye, it's been a winter of potential: potential being, that one-or-more perturbations usually show some sort of retrogression, by T+384?"

Added to the discussion did it or was it simply a one liner in response to this?

"Is there actually any real evidence that heights will rise over Greenland?, all I see at this minute is speculation and 1 chart showing heights going to Greenland @ 10 days away"

A post that is in reality not any way near factual. Just the one chart showing heights going to Greenland? Pretty sure more than one of the Ensembles show this as an outcome, but let’s not deal in facts, lets trivialise any discussion regarding this outcome because,

"Aye, it's been a winter of potential: potential being, that one-or-more perturbations usually show some sort of retrogression, by T+384?""

Lets not forget heights are already high over Greenland with the core of the heights over Canada, which as I have said is not great for UK cold.

It's a discussion fg. And where there's discussion, there's disagreement...But, yes, elevated heights are indeed shown around Greenland; but will they affect our weather the way we all want? I don't know; but, whatever, with successive model-runs suggesting often vastly differing outlooks, guessing the unknown is, as I said before, difficult...

Just don't confuse 'disagreement' with 'mockery'?

Edited February 20, 2013 by Rybris Ponce

[No Balls Like Snow Balls]

I see height's over Greenland both on ECM and GFS, but mostly blue's and Purple's which means it is only surface pressure and can quite easily be shifted by any LP's heading that way (this is what the more knowledgeable told me last year when i commented on exact same thing). It is only way out in FI on the ECM that you see the proper greens and Yellows pushing into Greenland

Edited February 20, 2013 by No balls like Snow Balls

[snowmadchrisuk]

Not very much Dry air showing over the UK currently , will have to keep an eye on the water vaper charts as we head into the weekend .

[Coast]

The posts seem to be drifting off topic here more than the hoped for snow at the weekend. Could we try and keep to model output discussion and less about personal comments at other members and bickering please?

Thanks

Edited February 20, 2013 by Coast

[Tim Bland]

Some great new terminology today, faveriouts are the "Maddenology" "Cobynolgy" and "sussex Slider"

To be honest I think we are clutching at straws to get anything of note out of the rest of winter. If there was a nice Low around the med stretching across southern europe then the Greenland high would be of interest. Maybe something for scotland as Nick says but cant see it being widespread.

Would also like to say another great result for GP looks on the cards. He predicted an west based Neggative NAO for the end of winter back in November... God he is good!

[shaky]

Not very much Dry air showing over the UK currently , will have to keep an eye on the water vaper charts as we head into the weekend .

Is that a positive for snow shower development?

[snowmadchrisuk]

Is that a positive for snow shower development?

You would have to ask Ian or someone , as I am not sure how well shallow layers of dry air are picked up on water vapor images . Also remember that chart is for right now not Fri/Sat.

[Coast]

The closest to the weekend that shows you water vapour transport currently is Friday early evening and it's dry as a bone over the UK at that time on this run:

Edited February 20, 2013 by Coast

[fergieweather]

You would have to ask Ian or someone , as I am not sure how well shallow layers of dry air are picked up on water vapor images . Also remember that chart is for right now not Fri/Sat.

Story consistent with previous updates. By Friday, Dartmoor continues to be an area singled out for a little more focused snow given ripe conditions for Channel shower banding. Flurries elsewhere in E. Saturday offers somewhat deeper convective depth but really relies on convergence to offer more meaningful snow showers, as per UK4 prognosis I posted last night. Some localised impacts possible so being watched. By Sunday we're back to skinnier depths and lighter showers; Monday more awkward given frontal/pseudo-frontal feature from E rotating W around top of continental vortex. Likely to offer a trickier forecast hybrid of wintry PPN into E Anglia and SE with potential for a leading area of snow to low levels across Midlands. However, amounts not looking too bothersome at this juncture but it's a dynamic PPN feature so perhaps a more widespread snow potential versus weekend story. Beyond that, MOGREPS-15 retains anticyclonic influence well into trend period, versus the shift to more cyclonic EC members. Latter somewhat favoured, ie to less cold SW regime eventually, but a fine balance of choice frankly and hence UKMO not yet nailing colours to either mast given low confidence.

[johnholmes]

Thanks for that link. It would seem the logical reason as to why the forecast for convection is inhibited. A shame that with cold 850's and a favourable wind direction the convection is going to be killed. Still some falling snow seems likely for the South East.

limited convection showing on the skew-t diagrams is something that has been evident on about 80% of the runs for the same date. Hence as you say why anyone trying to be objective about snowfall chances have mostly played this down.

The other thing is the skew-t is no more accurate really than the predicted amounts falling from the sky of whatever type. One is dependent on the other.

As T+00 approaches then more reliable assessments of snow or whatever will be possible. Max=48 hours, more probably 12-24 hours then watch the temperature/dewpoint values and the radar for a quick guide to what/when/where/how much?

Edited February 20, 2013 by johnholmes

[shaky]

Story consistent with previous updates. By Friday, Dartmoor continues to be an area singled out for a little more focused snow given ripe conditions for Channel shower banding. Flurries elsewhere in E. Saturday offers somewhat deeper convective depth but really relies on convergence to offer more meaningful snow showers, as per UK4 prognosis I posted last night. Some localised impacts possible so being watched. By Sunday we're back to skinnier depths and lighter showers; Monday more awkward given frontal/pseudo-frontal feature from E rotating W around top of continental vortex. Likely to offer a trickier forecast hybrid of wintry PPN into E Anglia and SE with potential for a leading area of snow to low levels across Midlands. However, amounts not looking too bothersome at this juncture but it's a dynamic PPN feature so perhaps a more widespread snow potential versus weekend story. Beyond that, MOGREPS-15 retains anticyclonic influence well into trend period, versus the shift to more cyclonic EC members. Latter somewhat favoured, ie to less cold SW regime eventually, but a fine balance of choice frankly and hence UKMO not yet nailing colours to either mast given low confidence.

Thanks for that ian!!looks like anywhere could see a few snow showers then across eastern england!!