General Model Output Discussion Tuesday December 22Nd:

[Guest North Sea Snow Convection]

Agreed Tamara.

Another difference this year, is that a cold pattern is progged to evolve from an already cold pattern? IMO, unlike most of the recent winter situations - we already have most (if not all) of the ingredients already in place...Judging from (straw clutching) last summer's self-reloading patterns, it's always easier for the existing situation to remain, than for an entirely new one to develop? Inertia anyone?

That said, today's 06Z can only be described by that esoterically scientic term: a stonker!!

What - you mean 'sod the science its go to snow!?

I'm not 100% sure about this, but I think that after the initial Greenland blocking at the end of Dec 78 into the start of 1979, the stratosphere was not especially warm in the winter of 78/79 and the cold set-up was perpetuated by a very southerly tracking jet stream with a lot of resident cold air to the north of the polar front across the NH. A bit like the situation we have atm. That kind of highlights the very good point you have made about 'cold leading into more cold'

[Thundery wintry showers]

Flicking through some of the charts for both January and February 1979, indeed, it's remarkable how we kept evolving from one cold setup to another- especially so around 8 January 1979 when it looked like the Atlantic was coming back in with the polar vortex setting up close to Greenland. But the recurring themes of southerly tracking jet and blocking to the N and NW kept us in a regime of repeated outbreaks of polar air.

[Frosty.]

Hi Frosty,

I was referring more to the GFS as regards, no severe cold, but I agree the ECM has does show great potential at around 192H.

If it continues to repeat these current projection for a couple more days, then some very interesting times ahead.

Hi Polar,

Great to see the GFS 06z is now more in line with the mega wintry ecm 00z run although the gfs 00z wasn't too shabby, I have a feeling we will have a massive cold reload after a few less cold days across the southern half of the uk. Christmas day looks messy with a lot of low grey cloud, some mist and drizzle and a few snow flakes in eastern england. Fingers crossed the trend for next week continues.

Edited December 23, 2009 by Frosty039

[kold weather]

By the way this is likely to be very similar to the way this cold spell was modelled, in that the Op runs will lead the ensembles towards the probable evolution. The GFS ensembles still ultra keen on reducing heights and merging the PV....which is not likely to happen so quickly given what we have progged for the AO over the last 2 weeks, such patterns are rarely shifted in a few days like the ensembles seem to be keen on doing.

The danger period where it could all go wrong for any reload is between 96-144hrs, its not the easiest pattern to get into but even failing it I'd imagine we'd still end up with a HP over us...

[Thundery wintry showers]

The main issue would be if that low to the S fails to get east or spawns shortwaves behind it, keeping the polar air to the north and leaving most of Britain with a modified easterly flow bringing rather dull damp conditions. The eventual outcome would be a HP over us and no snow. However the current trend appears to be away from that possibility.

Interesting parallel with January 1982 (though I doubt it will be quite as extreme as that). Earlier in the month I was making parallels between the current setup and that of December 1981, and suggesting that if the Atlantic gets in it could subsequently be forced to buckle south again like it did in early January 1982. The operational runs of GFS and ECMWF are currently showing what looks like a speeded-up version of that.

[Nick B]

Potentially record breaking blizzards for the northern half of the country next week with 3-4 feet of lying snow and drifts of up to 30ft if those charts for next week come off, crap down here but Scotland, Cumbria, Midlands, Yorkshire, Tyneside will be getting heavier snowfalls than the eastern seaboard of the USA got the other day if there is no downgrades

Maybe plenty of snow (I think you may be overstating it just a tad!), but there is no point at all looking at precipitation until a day or two beforehand because the actual underlying pattern is going to be different from what is shown. Those in the W Midlands feeling a bit down at the moment will recognize this fact, particularly with cold and no snow to show for it. The route to cold if it comes may be this way, but in this timeframe it may well be another, meaning some may get more white stuff than others. It is looking much more likely to head towards cold / very cold for everyone in the mid-long term outlook. Snow may be widespread if/when this happens but it wasn't for this particular spell we are in now. Caution needed for a few days, and watching how the synoptics pan out. AO and NAO looking like trending particularly favourably, would be good to read input from GP in not too distant future - he has called it very well all the way. Edited December 23, 2009 by Nick B

[Cecil Hogmanay Melchett]

Looking good this morning.

Still very complicated short term and the behaviour of the lp's around our shores will play a significant part as far as the long term synoptics are concerned.

I'd say 50/50 for a reload next week,but the next 48 hours will give us a grand diea of where all this is heading.

fascinating times though,i hope those who have missed out this week get their share next time round!

[rbw]

I posted this in this forum a while ago and it got moved to the "will it snow thread" but that is not what I am asking. I am trying to understand why the forecasts don't seem to be showing what people are suggesting here

Widespread snow is being talked about if next weeks models come off but the Netweather Forecasts show +3C and sleet for me at least. Are the forecast not keeping up or are the indications that this is an event that will be for the north of the country only?

[sandstorm2]

Well after a slightly less cold day or to the GFS 0600 is showing a return to cold and then very cold conditions in FI with temps of -14 in central England.

SS2

[karyo]

The MetOffice further outlook mentions the word snow (in the form of showers) and also getting colder. However, they are not going with the ECM as they expect the weather to become more settled and less cold in the end.

Actually, the last sentence made me laugh 'The further outlook should continue much the same, but indications are that it will become more settled and less perhaps cold.'

How can it be much the same if it will turn drier and less cold??? :lol:

Karyo

Edited December 23, 2009 by karyo

[Frosty.]

To avoid disappointment we should assume that the projected wintry spell which evolves next week will end with the high toppling in and cutting off the arctic flow, we may get lucky and see a more prolonged outbreak but at this range it could all go wrong despite the wonderful wintry charts.

[mushymanrob]

interesting possible developments next week being shown on the gfs 06z, (and on the 00z)

... that channel low next week could give a huge dumping across the country before the bitter cold wins out from the north... the temperature gradient between central uk and northern france is 10c , surely that would give huge precipitation amounts, and on the northern side of the fronts will be snow...

its been a very long time since sypotics like this were around in winter...

[kold weather]

The main issue would be if that low to the S fails to get east or spawns shortwaves behind it, keeping the polar air to the north and leaving most of Britain with a modified easterly flow bringing rather dull damp conditions. The eventual outcome would be a HP over us and no snow. However the current trend appears to be away from that possibility.

Interesting parallel with January 1982 (though I doubt it will be quite as extreme as that). Earlier in the month I was making parallels between the current setup and that of December 1981, and suggesting that if the Atlantic gets in it could subsequently be forced to buckle south again like it did in early January 1982. The operational runs of GFS and ECMWF are currently showing what looks like a speeded-up version of that.

Even that first option would probably be cold and could well eventually evolve into another colder pattern down the line...

I think you make a good point about the speeded up version, the models tend to be overprogressive generally in these set-ups so the evolution IMO would be a little slower. Its very interesting to see the mess the ensembles arein but the key point is they keep suggesting a mid-Atlantic ridge will try and form...usually we have to try and evolve from a less then decent pattern however this time we have a split PV, a severely negative AO. Of course one very poorly placed shortwave could be an issue, of course without even knowing it the key timeframe is nearly already in 96hrs!

[Snowyowl9]

Looks like this milder mini SW-ly breakdown is getting pushed back today.

http://www2.wetter3.de/Animation_00_UTC/24_30.gif

http://www2.wetter3.de/Animation_00_UTC/36_30.gif

http://www2.wetter3.de/Animation_00_UTC/66_30.gif

Christmas day could even see some snow fallling now.

http://91.121.93.17/pics/brack0a.gif

http://91.121.93.17/pics/brack1a.gif

Could air still hangs on midlands northwards and here,there will be freezing rain too,

already has been in the south.

http://91.121.93.17/pics/Rtavn6017.png

Fantastic models after showing undercut cold NE-ly surface winds coming back in.

Blizzards potential Mid Wales northwards, havn`t seen charts as good as this over christmas.

http://91.121.93.17/pics/Recm1681.gif

http://91.121.93.17/pics/Rtavn1681.png

Everything seems to be getting pushed further south.

[492]

Even that first option would probably be cold and could well eventually evolve into another colder pattern down the line...

I think you make a good point about the speeded up version, the models tend to be overprogressive generally in these set-ups so the evolution IMO would be a little slower. Its very interesting to see the mess the ensembles arein but the key point is they keep suggesting a mid-Atlantic ridge will try and form...usually we have to try and evolve from a less then decent pattern however this time we have a split PV, a severely negative AO. Of course one very poorly placed shortwave could be an issue, of course without even knowing it the key timeframe is nearly already in 96hrs!

The shortwave currently south of Greenland developing in the cold air needs watching. If it over develops and hangs around to the west there is a danger of it throwing up a ridge from the SW and putting us in mild SW flow. However if it fails to develop much and runs southeast we will be back in cold air much sooner.

[Guest North Sea Snow Convection]

The MetOffice further outlook mentions the word snow (in the form of showers) and also getting colder. However, they are not going with the ECM as they expect the weather to become more settled and less cold in the end.

Actually, the last sentence made me laugh 'The further outlook should continue much the same, but indications are that it will become more settled and less perhaps cold.'

How can it be much the same if it will turn drier and less cold???

Karyo

In a confuddled way it sounds as though they think the ridge will topple into the UK rather than reload near Greenland as the models are suggesting this morning

[kold weather]

Yeah or a upper high to our west feeding down probably anticyclonic gloom I'd imagine NCS, esp given under that sort of high you'd probably be as cold as presently (as we saw quite nicely in early Jan 09) however the ECM ensembles are looking much better then what the Met office suggest and so I suspect they are simply hedging thier bets at the moment.

For now there is agreement on at least some sort of cold shot for the last day of December/Early Jan. The ECM is slower and more realisitic with the pace of the incursion IMO. the biggest question is do we get a new Greenland high form or does the Arctic become more unfavorable and high pressure is forced to form further SE?

[bluearmy]

the NAEFS show a rise in pressure over iberia (also the omerga block south greenland and troughing scandi into e europe). maybe the ecm ens mean pressure chart makes more of this rise in pressure over iberia which is what the meto 15 dayer is responding to. would have thought any settling down early jan couldn't be described as less cold though ??

[Guest North Sea Snow Convection]

If the models haven't got the detail agreed upon (and they won't at this range) then I don't think that one can start to regionalise the UK pattern at this stage either. But FWIW, any scenario where LP gets east of the UK, whether that be over the continent or Scandinavia - with pressure high to the W and NW then it is inevitable for however long a duration that a N flow, perhaps NE flow will follow to all parts as pressure rises from the west in the wake of the low pressure. The only scenario where a Uk split would occur is where a longwave trough gets stuck over the UK and there is no support anywhere for that to happen.

But the detail is total conjecture atm

Edited December 23, 2009 by North Sea Snow Convection

[kold weather]

the NAEFS show a rise in pressure over iberia (also the omerga block south greenland and troughing scandi into e europe). maybe the ecm ens mean pressure chart makes more of this rise in pressure over iberia which is what the meto 15 dayer is responding to. would have thought any settling down early jan couldn't be described as less cold though ??

I'm not sure thats the case, I think instead the UKMO are mentioning the chance that the high pressure doesn't quite latch upto Greenland and instead the high pressure sets up to our west instead (think somewhat like the 12z ECM last night) where we have a weak northerly flow but settled conditions thanks to the high pressure to our west, but not the coldest of flows and prone to gloom I'd have thought.

Still thats a long way away yet, just about anything could happen still, for now there has to be some confidence in at least some sort of NE/N flow.

[tinybill]

well good afternoon merry xmas all well looking at the gfs and looking deep in fantasy land its looking very wintry next week good job the u.k. on holiday what i can see we going to get some very low temps next week and plenty of the white stuff as well

[Eugene]

Wow the ensembles are very impressive today, i mean last time i looked there was a possibility of a mild breakdown just after christmas day now it looks cold almost all the way, too busy enjoying the present cold spell to do any model watching i`m afraid, it's great to just to go away and not worry about any possible breakdown

http://www.wetterzentrale.de/pics/MT8_Manchester_ens.png

[stewfox]

Looks like this milder mini SW-ly breakdown is getting pushed back today.

http://www2.wetter3....0_UTC/24_30.gif

http://www2.wetter3....0_UTC/36_30.gif

http://www2.wetter3....0_UTC/66_30.gif

Christmas day could even see some snow fallling now.

http://91.121.93.17/pics/brack0a.gif

http://91.121.93.17/pics/brack1a.gif

Could air still hangs on midlands northwards and here,there will be freezing rain too,

already has been in the south.

http://91.121.93.17/pics/Rtavn6017.png

Fantastic models after showing undercut cold NE-ly surface winds coming back in.

Blizzards potential Mid Wales northwards, havn`t seen charts as good as this over christmas.

http://91.121.93.17/pics/Recm1681.gif

http://91.121.93.17/pics/Rtavn1681.png

Everything seems to be getting pushed further south.

Very good summary, still think T168 a bit of F1 but for T48 (Xmas day !) the prospect for snow for a good half of the country remains.

We have light rain now in reading but given the temps I can see a lot of places 'down south' holding onto at least 50% snow covering for the day itself.

I posted this in this forum a while ago and it got moved to the "will it snow thread" but that is not what I am asking. I am trying to understand why the forecasts don't seem to be showing what people are suggesting here

Widespread snow is being talked about if next weeks models come off but the Netweather Forecasts show +3C and sleet for me at least. Are the forecast not keeping up or are the indications that this is an event that will be for the north of the country only?

If your on tele would you say

GFS is showing 12ft snow drifts and blizzards next week with a set up like Jan 1987 and just look at this T384 chart amazing

or Snow and rain showers for some.

I think you have to take the middle ground

Some 'suggestions' are here are a bit OTT

Edited December 23, 2009 by stewfox

[cheeky_monkey]

i think it has been said elsewhere..but the models are showing something similar to what happened in the last week of Dec 1978..short milder interlude never quite making it north of the border before the cold sinks back south with possible heavy snow events in many areas around the end of the month.

it will be intersing to see how cold or mild it becomes in the next few days and how far north or east this reaches?

[kev238]

After days of model confusion, I feel there is a broad pattern emerging. Remaining cold in the North, becoming very wet and a touch milder from the Midlands Southwards up until the 30th or so, then a battle being drawn somewhere across the UK with the cold air winning (probably). After that, it is all up for grabs. I think it is impossibe to suggest where battle lines are drawn at this stage but somewhere next week will more than likely get a lot of snow!