Winter Model Discussion - Cold Hunting - 20th Dec

[phil nw.]

A very wet and mobile picture painted by the 12z models.Never mild with brief incursions of polar air around Christmas and Boxing day where some further snowfall looks likely for the Scottish Highlands.

If we can get some upstream amplification in the jet we could see the cold further south but otherwise the flat jet and those heights around the Azores will limit any real cold moving south.

The main concern is the successive rain bands due to move NE across the UK in the next few days.

[nick sussex]

Tonights horror show is brought to you by the ECM miserable scrooge model!

Thoroughly miserable and wet throughout, it did have that ne USA storm which may have lead to a temporary ridge agead of it but sadly it bloats up that troughing in the Atlantic so that comes to nothing.

There are differences within 144hrs, the UKMO looks best of the big 3 for something resembling festive weather but sadly is never the shepherd but the sheep!

The PV is at least in pieces but one piece decides to limpet itself to the north.

I suspect we'll probably still see a cluster of colder solutions on the ECM ensembles but its operational output to be blunt sucks big time!

[LomondSnowstorm]

Pretty cold for Scotland, with upper temps passing 0c for only a 24-36hr interlude in the 240hr run, and plenty of -4c and below incursions. On a W/NW flow with plentiful Am/Pm incursions, there is a lot of snow to be had on high ground, and at times on lower ground as well. Expect some sunshine to come of it as well under a more showery regime than the current one.

Just because there is not notable blocking around Greenland---Scandi, doesn't mean we can't have some cold and snowy weather, this time though, Scotland and the north mostly enjoy it, maybe that's why it's so glum around here!

Once again, the offer to come to mine for the holidays remains for any snowless sassenachs, the ECM was probably the worst run but even it had some decent cold spells and certainly a lot of hill snow. GEFS looks almost identical to yesterday for here, which is something that hasn't happened in a while:

[Frosty.]

Tonight's Ecm 12z demonstrates how we cannot assume we will have a cold northerly pattern next week, it's a sobering run for the southern half of the uk with mild swly winds but at least the run ends with colder polar maritime air rushing in from the west around the low, at this range i'm not too concerned though, it just highlights how we will need the trough to the north of scotland to push further east and open the arctic floodgates or else it will be a non event.

I'm fairly sure the ecm 12z will be a mild outlier for most of next week.

Edited December 20, 2012 by Frosty039

[mountain shadow]

Well tonights ECM was better for cold than the 0z so a small step in the right direction.

The GFS normally handles northerlies better, we will know soon enough.

[nick sussex]

Tonight's Ecm 12z demonstrates how we cannot assume we will have a cold northerly pattern next week, it's a sobering run for the southern half of the uk with mild swly winds but at least the run ends with colder polar maritime air rushing in from the west around the low, at this range i'm not too concerned though, it just highlights how we will need the trough to the north of scotland to push further east and open the arctic floodgates or else it will be a non event.

I think the ECM is basically pants for everywhere and theres little time to advect cold air south.

The UKMO still hardly screams winter but the next low approaching at 144hrs could run more se'wards, ordinarily the UKMO would get a flatline on my excitement monitor but given the rest on show its positively hysteria inducing!

Sadly I've yet to see a colder 144hrs UKMO output verify against the rest in my time on the net, you can rely on it to harpoon a cold spell at 144hrs but never the other way round.

I wait with baited breath to be shocked tomorrow! Overall theres no blocking, not even a much maligned northerly toppler on offer and here we are trying to make a Michelin starred dinner out of spam and microwave chips!

When we had a few decent ingredients the models managed to deliver pretty much nothing so lets hope spam blossoms into something better on the ground!

[Isolated Frost]

vortex has had a tooth or two knocked out... no sub 500 air at 240- a very 'blocky' arctic profile as we enter a new year- plenty of cold bubbling just to the north, but not quite the substantial cold on our shores just yet

[UV-RAY]

Tonights horror show is brought to you by the ECM miserable scrooge model!

Thoroughly miserable and wet throughout, it did have that ne USA storm which may have lead to a temporary ridge agead of it but sadly it bloats up that troughing in the Atlantic so that comes to nothing.

There are differences within 144hrs, the UKMO looks best of the big 3 for something resembling festive weather but sadly is never the shepherd but the sheep!

The PV is at least in pieces but one piece decides to limpet itself to the north.

I suspect we'll probably still see a cluster of colder solutions on the ECM ensembles but its operational output to be blunt sucks big time!

Sounds much like how this month panned out Nick with regards to the PV, surely we couldn't be that unlucky twice.

[IDO]

Pretty cold for Scotland, with upper temps passing 0c for only a 24-36hr interlude in the 240hr run, and plenty of -4c and below incursions. On a W/NW flow with plentiful Am/Pm incursions, there is a lot of snow to be had on high ground, and at times on lower ground as well. Expect some sunshine to come of it as well under a more showery regime than the current one.

Just because there is not notable blocking around Greenland---Scandi, doesn't mean we can't have some cold and snowy weather, this time though, Scotland and the north mostly enjoy it, maybe that's why it's so glum around here!

I would expect nothing less from a cool zonal setup.

Who would have bet that from the much hyped blocked pattern of December that we would experience one of the wettest (expect around 135mm for month IMBY) I can remember with zero mm of snow and a handful of frosts. Based on projected highs for the next 10 days I expect the average high in my area to be +0.4 above the average.

No it is a poor December for cold for those south of the Midlands and really its been all about the rain and unfortunately rain will remain the watchword for the foreseeable. Especially this weekend and early next week: http://www.meteociel...ax72s.gif?20-12

ECM is poor for cold IMBY: http://www.meteociel...M1-240.GIF?20-0 and little potential.

GEFS mean after the toppler is zonal end to end:

http://modeles.meteo...21-1-240.png?12

http://modeles.meteo...21-1-384.png?12

The only blocking I can see from late December to the end of FI (5th Jan) is the Azores High:

http://cdn.nwstatic....384/npsh500.png

Until we get rid of this feature, Winter will be very poor for most in the south. The LRF's picked this out some weeks ago so it must be a very strong indicator for the UK in the coming months. This may change with a reset from a strat event, but even then I am not getting my hopes up.

Edited December 20, 2012 by i'm dreaming of...

[nick sussex]

Sounds much like how this month panned out Nick with regards to the PV, surely we couldn't be that unlucky twice.

Lol! its the UK remember if the PV can split and find the worst location to set up it will!

December I would sum up as having a few opportunities with some good synoptics but we missed penalty after penalty. The good thing after the ECM is that it can only get better!

We have to hope that we get a SSW and any blocking sets up in the right place, it still could happen so even though I sound a bit grumpy tonight theres still lots of winter yet.

[cold snap]

I think the ECM is basically pants for everywhere and theres little time to advect cold air south.

The UKMO still hardly screams winter but the next low approaching at 144hrs could run more se'wards, ordinarily the UKMO would get a flatline on my excitement monitor but given the rest on show its positively hysteria inducing!

Sadly I've yet to see a colder 144hrs UKMO output verify against the rest in my time on the net, you can rely on it to harpoon a cold spell at 144hrs but never the other way round.

I wait with baited breath to be shocked tomorrow! Overall theres no blocking, not even a much maligned northerly toppler on offer and here we are trying to make a Michelin starred dinner out of spam and microwave chips!

When we had a few decent ingredients the models managed to deliver pretty much nothing so lets hope spam blossoms into something better on the ground!

Great post

Yes with out any kind of block ,it's just quick hits of pm air ,even though the 850s get going its just to short notice before the next front comes in

The angle of jet might look slightly favorable but it doesn't cut the mustard

Look the showers may turn wintry for about 5 minutes before the next shortwave ,it wouldn't be a place you would like to be stuck in for to long ,unless you see Greenland blocking but that Seams not on the agenda at present time,

Ecm 2 out of 10

Gfs 5 out of 10

Ukmo 6 out of 10

To conclude Scottish mountains won't mind this set up best others can hope for I suppose is a possible dusting but they may be pushing it, further south and east you are the chances of even that would be nearly zero

[Froze were the Days]

ECM hasn't shown anything to make us optimistic for days now, obviously nice and consistent when it comes to Atlantic conditions

[Summer Sun]

The Aberdeen ensemble has almost full agreement now for a cold period starting on or just after the 25th just about all members are trending below zero and with precipitation also increasing this could fall as snow

London's ensemble has more scatter but they are still trending to a colder period just after Christmas and lasting to around the new year 2013 starts with some members trending close to +5

Edited December 20, 2012 by Gavin.

[cold snap]

No - I can assure you it wouldn't. Potential (stress 'potential') for key broadscale pattern change has been hinted at into Jan but not in any formal sense - more importantly, the zonal train continues into the forseeable.

Ian can I ask please is the phrase zonal train a phrase one would use at ukmo hq?

Thanks in advance

[phil nw.]

vortex has had a tooth or two knocked out... no sub 500 air at 240- a very 'blocky' arctic profile as we enter a new year- plenty of cold bubbling just to the north, but not quite the substantial cold on our shores just yet

Yes plenty of evidence to show a weakened vortex IF.

Unfortunately with the current polar profile it shows it doesn`t always mean cold for the UK.

The main area of vortex energy modelled from Siberia across to our north

http://www.meteociel...CH1-96.GIF?20-0

keeps us in an unsettled Atlantic pattern-some polar maritime air around but no deep cold getting south without Arctic blocking closer to home.

Edited December 20, 2012 by phil n.warks.

[Ian Brown]

Ian can I ask please is the phrase zonal train a phrase one would use at ukmo hq?

Thanks in advance

It's one that I would use !

Anyway, just variations on a theme tonight whichever model you look at, no blocking at High latitude, the possibilities for colder air to filter into Northern parts especially at times, but nothing sustainable and the longer that this goes on the more likelihood of more permanent heights raising over Europe in response to the upper forcing.

[Frosty.]

ECM hasn't shown anything to make us optimistic for days now, obviously nice and consistent when it comes to Atlantic conditions

I would go as far as to say tonight's ecm is pretty much what todays meto update looked like for next week, but a little bit worse. In other words, unless you live on a scottish mountain, it is indeed pants.

[Gibby]

Good evening. Here is the latest report on the 12z output from GFS, UKMO and ECM for tonight Thursday December 20th 2012.

All models show a continuing spell of unsettled and rainy weather all the way through Christmas and to the New Year. Details between now and Christmas are fairly clear with some further spells of heavy rain on Saturday, probably Sunday and again on Christmas Eve. The rain will be heavy and disruptive at times with the continuing risk of flooding in various areas. In between there will be some brief drier spells. Temperatures will remain well up to the seasonal average with some mild weather at times in the South while temperatures will slowly recover from the rather lower levels than normal in the NE.

GFS then takes us out of Christmas with slightly cooler weather as winds turn more towards the West and a more showery period develops though this in itself is also brief as a further slide into deep Low territory in the vicinity of the British Isles as we move towards the New Year. The rest of FI shows somewhat drier conditions in the South with winds from the SW it could become on the mild side though rain at times will continue, especially in the North, though not as heavy as recently.

The GFS Ensembles shows a very wet spell still to come with copious rainfall for many. Later in the run the Ensembles show less disruptive rainfall totals as we move towards the New year. 850's peak in the next few days before they taper off to levels much closer to the long term mean as winds turn more Westerly through Christmas and beyond.

The Jet Stream shows a continuation of the flow pumping strongly East over the Atlantic to the vicinity of the British isles as we move through Christmas week.

UKMO for midday on Boxing Day shows a ridge of High pressure crossing East over the UK with showers clearing in the East. Elsewhere will be dry and somewhat cooler than of late with new Low pressure likely to affect the UK on Thursday.

ECM shows a ridge over the UK too on Boxing Day followed by a West, backing SW strong flow developing later in the week with troughs bringing further rain east over the UK, heaviest in the NW. Towards New Year the weather looks decidedly disturbed again as Low pressure winds it's way into UK airspace once more with heavy rain and squally winds in near normal temperatures for all.

In Summary there is very little change in the output from earlier that will be felt on the surface with wind and rain frequently battering the UK for the foreseeable future. The very mild conditions at times in the South will subside somewhat as a more Westerly flow brings a drop in uppers over the UK towards the long term mean. It will make little difference to the actual weather with further Low pressure off the North Atlantic bringing rather colder rain for many towards the New Year.

[mountain shadow]

Gibby, the GEFS clearly Show good potential for snow in the North and West just not cold rain.

[Duane S.]

Last few days I checked the 00z and 12z suites looking for a hint of proper pattern change, even in FI. Nothing showing. With this set up the jet has to dig south and there is absolutely no indication of that, or we need some decent upstream amplification which just isn't showing. I can see there are windows of opportunity for Atlantic ridging but nothing that won't get flattened out shortly afterwards.

NW incursions best hope for the next 7 - 10 days. Thereafter much more hopeful we will be back on the rollercoaster when strat warming starts to show its hand.

Edited December 20, 2012 by s4lancia

[nick sussex]

Just a few quotes from the NOAA extended discussion:

THE AO INDEX IS FORECAST TO REMAIN NEGATIVE OVER THE NEXT COUPLE OF WEEKS,

WHILE THE PNA IS FORECAST TO RETURN TO NEUTRAL OR EVEN SLIGHTLY POSITIVE AFTER

A PROLONGED NEGATIVE PERIOD. THIS IS EVIDENT ON THE OFFICIAL HEIGHT BLEND AS

NEGATIVE ANOMALIES ENCROACH ON THE ALEUTIANS AND HEIGHTS RISE DOWNSTREAM OVER

WESTERN AND CENTRAL CANADA.

For the 8 to 14 day period:

WITH THE AO

BEING PERSISTENTLY NEGATIVE, WE MIGHT NOW BEGIN SEEING THE CANONICAL IMPACTS

MORE SO THAN EARLY IN THE WINTER, ASSUMING OTHER FACTORS DO NOT INTERFERE. ONE

COMPLICATING FACTOR, THE MJO, SEEMS LESS LIKELY TO IMPACT THE EXTRATROPICS THAN

IT DID YESTERDAY. INDEED, THE HEMISPHERIC PATTERN SEEMS DOMINATED BY THE

MIDDLE AND HIGH LATITUDES.

In summary for us in Europe, a negative AO is a positive although looking at the outputs they're not listening. The PNA going neutral or even better positive may add a bit more amplification upstream.

Unfortunately it doesn't look like we're going to get much help from the MJO although their mention of that canonical AO negative pattern means we may see blocking edge further east.

That phrase canonical was the subject of digging around to find a chart last night, its on the strat thread under my post of yesterday evening in that link.

It certainly looks better than whats currently on offer but best not to get too excited, theres really no sign of that in the current operationals.

The ECM postage stamps whilst not that exciting in terms of cold/snow potential at least offer some better solutions. Its a mixed bag but enough there to hope that the ECM operational outputs may pick something less horrific tomorrow!

http://www.ecmwf.int...t!2009112700!!/

The short ensembles show the operational run close to the mildest solution, nothing terribly cold in those members but given the expected pattern things could still be a bit more interesting for especially northern areas of the UK.

http://www.knmi.nl/e...M_06260_NWT.png

Edited December 20, 2012 by nick sussex

[tinybill]

http://www.meteociel.fr/modeles/gfse_cartes.php?mode=2&ech=204

just looked into fantasy world i can see huge problems coming looks like a lot of heavy rain coming to the uk

[IDO]

Gibby, the GEFS clearly Show good potential for snow in the North and West just not cold rain.

I went through the GEFS mean:

http://www.meteociel.fr/modeles/gefs_cartes.php?code=21&ech=6&carte=&mode=2

Very little snow apart from Scottish mountains.

[cheeky_monkey]

Looks like a filthy drive home from Heathrow on Saturday..i forgotten what it is like to drive in the rain!

[LomondSnowstorm]

I went through the GEFS mean:

http://www.meteociel...6&carte=&mode=2

Very little snow apart from Scottish mountains.

Well call me a mountain goat:

-5C is good enough for low ground snowfall inland off a northwesterly. It may not last more than 24-36 hours on many runs but any showers in that period would fall as snow.