Model Output Discussion: 12Z (02/12/12) And On...

[chris55]

Cheshire?

Cotswolds lol

[Rob K]

In my experience it turns out that in reality if it shows cold it's wrong, if it shows mild at 144 it's more likely to come off.

That's the crux of the matter, for any model.

[chris55]

Yup and then down to gather more especially through E Wales across to uplands of Glos by around Weds AM rush-hour; quite a strong signal now for this outcome, with modified NAE leaning towards the GM prog and tweaked in this direction somewhat, but an inevitably complex and awkward forecast at sub-regional level at this range, not least given diurnal cooling into the mix as this phases with progression S'ward of the occlusion.

Quite frankly, the threat of heavy showers tomorrow for parts of W Country sensitive to more rain is of greater focus for us presently, but we'll see what UKV makes of the Tues night-Weds AM story in due course.

Oh nice update Ian.

Just looked at the NAE for this period, interesting. Although hills favoured as you say. PPN looks well defined though, ie heavyish.

http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2012/12/03/basis12/ukuk/prty/12120512_0312.gif

Edited December 3, 2012 by chris55

[Timmytour]

The UKMO is terrible. But I'm feeling generous so I'm prepared to give it a couple of more runs before dismissing it to see if it can come up with the kind of modelled outcome I wish to see!

[Weathizard]

A sense of anticipation but DREAD about the ECM because far too often we see 1 step taken (GFS getting on board with similar ideas) only for 2 steps to be taken backwards. (ECM pulling out a terrible run)

Let us ask the weather gods to be kind.

[Ian Brown]

http://modeles.meteo...21-1-192.png?12

Followed up by a great mean at 192...

Another 72 hours of this come to become clear what flow we get in week 2 of December...

*IF* the GFS lands it will cold & snowy all the way out to th 20th & beyond....

S

Yes, the coming days will be very interesting. We know from past experience that easterlies at T168 and T192 rarely end up coming to fruition. T120 to T144 has a better record though not bombproof....

What we have though is a significant block to the NE that IMO is not going to be brushed aside by the Northern arm of the jet. I would say the worst outcome we could get in 8-12 days is a High on top of us.

[Geordiesnow]

In my experience it turns out that in reality if it shows cold it's wrong, if it shows mild at 144 it's more likely to come off. How often has the UKMO stuck a spanner in the works!

Save that 144 hour chart CC and lets see in 144 hours if that UKMO chart is close to being correct or not. The point I'm making, people only get that assumption because they chase down the cold charts(somehow people expect a cold chart expect to last 144 hours with perfection) whilst the mild charts don't get the same attention, the outlook will vary but normally the trends don't in the medium range and the trend appears to be a hint of ridging into Greenland but a more stronger trend is for a Scandi high to develop, orientation, positioning of all these features are yet to be decided.

Anyways, some cold in the short range to look forward to, its just typical that the flow will be off shore for the most part in Eastern areas otherwise those showers would be falling as snow with those low thicknesses and upper air temps!

The weather front for Thursday has got the potential to deliver some fun and games for Scotland and the central belt in particular, hilly areas of Northern England could get a pasting also, it will depend on the strength, timing, angle the low arrives in the UK at and how stubborn the cold air will be which will determine whether we see a more widespread snow event or not but its something to keep an eye on and perhaps look forward too hopefully.

[Harsh Climate]

Don't know why some people think the Gfs run isn't so plausible, to me it isn't that great anyway. At no point do we really get uppers colder than -7, yes there will be some cold surface air drifting in from the continent, but I do not see this conductive to the formation of heavy frequent snow showers, which is what we want for good accumulations.

What we really need for a memorable easterly is a pool of -10/-15 uppers coinciding with tightening isobars.

This gfs run is more than plausible even in FI, the problem is when the truly frigid air moves towards the UK, if the high pressure is just too far south, mainland europe get clobbered with blizzards and brutal cold while we just stay cold and dry.. Thats always the worry with a scandi high, I'm hoping the models continue pointing towards a greenland high in the near future as that is certainly the safer option!

Edited December 3, 2012 by Harsh Climate

[Grimsby Snow Lover]

The UKMO is terrible. But I'm feeling generous so I'm prepared to give it a couple of more runs before dismissing it to see if it can come up with the kind of modelled outcome I wish to see!

I know where you are coming from but lets not be misleading. The UKMO run is pretty good for cold in the reliable time frame. Yes the 144 chart is no screaming easterly but where it goes from there is anyones guess.

[Ian Brown]

Modified NAE - two key frames attached - tells current thinking (dynamic rain as '0's; snow / sleet signal as 'x', etc - usual stuff applies re this and colour scales)

Thanks Ian, do you think a November 28 2005 type development is possible, which rather caught the METO out ?

[fergieweather]

Thanks Ian, do you think a November 28 2005 type development is possible, which rather caught the METO out ?

Nah - ahead of the game on this one. Chief et al considering warnings etc in discussions tonight. Tricky forecast but we'll worry about detail tomorrow. No point hyperventilating over it at this range. Nuances outside scope of reliable forecast at this juncture.

[kold weather]

UKMO showing the logical evolution from yesterdays 12z run, to build an area of high pressure over W.Europe and shutting the door for another 3-5 days at least for any meaningful cold. Terrible run from it.

Though to be fair, for the south there would still be the surface cold lingering on.

As great as the GFS run is, the UKMO is bad....leave it at that!

[Cheshire Freeze]

Don't know why some people think the Gfs run isn't so plausible, to me it isn't that great anyway. At no point do we really get uppers colder than -7, yes there will be some cold surface air drifting in from the continent, but I do not see this conductive to the formation of heavy frequent snow showers, which is what we want for good accumulations.

What we really need for a memorable easterly is a pool of -10/-15 uppers coinciding with tightening isobars.

This gfs run is more than plausible even in FI, the problem is when the truly frigid air moves towards the UK, the high pressure is just too far south and mainland europe get clobbered with blizzards and brutal cold while we just stay cold and dry.. Thats always the worry with a scandi high, I'm hoping the models continue pointing towards a greenland high in the near future as that is certainly the safer option!

Whilst what you say has some merit, the initial easterly would be more than enough to freeze the ground solid.....low dew points, low surface temps- it would be bitter. Then we wait for the undercut......with the ground frozen through, any snow that falls sticks in its entirity and only serves to accentuate the cold overnight periods. '62-'63 had long periods of 'dryish' easterlys but when snow did fall it stuck around due to no melting of the snow from underneath- even on the few ocassions where uppers ventured above -5 on transfer of heights from Scandi to Greenland.

[SMU]

http://www.meteociel.fr/ukmo/runs/2012120312/UN144-21.GIF?03-18

I think people are misinterpreting the UKMO at 1440

The low sliding east at 1000MB south of Iceland will help tug that low 1010 MB east of of iceland - it will all move south at 168 with the atlantic building-

S

[Weather-history]

The UKMO 12z 144hrs reminds me a little of how the December 1997 easterly came about.

[The Northern Ramper]

Nah - ahead of the game on this one. Chief et al considering warnings etc in discussions tonight. Tricky forecast but we'll worry about detail tomorrow. No point hyperventilating over it at this range. Nuances outside scope of reliable forecast at this juncture.

It's great having your input in this thread Ian

[Cheshire Freeze]

It's great having your input in this thread Ian

I'll second that

[Mucka]

People banging on about potential up north this week and nothing for the South but 12z ensembles have a higher snow risk for the SE of England than the NW of England for Wednesday morning.

Edited December 3, 2012 by Mucka

[Glacier Point]

12z GEFS suite is very strong on blocking to our N and NE, with an equally strong (if not stronger) signature for block to retrogress towards Greenland in the extended frames as the pv is transferred towards Siberia (which has been a consistent signal now for a few days).

Get set. It's coming.

Edited December 3, 2012 by Glacier Point

[chris55]

Thanks Ian, do you think a November 28 2005 type development is possible, which rather caught the METO out ?

That one sticks in my head rather well. Back then (in the dry days, regarding snowfall) I came home from work expecting nothing only to watch the forecast for a period of heavy snow, didn't amount to that much on the ground, a few cms, but was a surprise.

Edited December 3, 2012 by chris55

[The Northern Ramper]

http://www.meteociel...44-21.GIF?03-18

I think people are misinterpreting the UKMO at 1440

The low sliding east at 1000MB south of Iceland will help tug that low 1010 MB east of of iceland - it will all move south at 168 with the atlantic building-

S

Look at the gfs around 120 , it seems similar to me just a day earlier.

[weather is fun]

I dont understand why everyone is getting so worked up over the gfs run we all know it has about 0% of happening. Expect a horror show from ecm now. Then end up with a half way house between ukmo and ecm perhaps. But in my opnion that gfs run has little chance of verifing.

[kold weather]

http://www.meteociel...44-21.GIF?03-18

I think people are misinterpreting the UKMO at 1440

The low sliding east at 1000MB south of Iceland will help tug that low 1010 MB east of of iceland - it will all move south at 168 with the atlantic building-

S

I think its going to ride over the top Steve, look at the angle of the low tha is developing, its putting pressure on our high, its also being tugged around that PV core over Canada. Eventually it may well get to our east but by that time we'd have wasted probably 3-4 days of prime time northern blocking.

The whole lot is CLEARLY getting tugged NE, you only need to go between 120-144hrs to see that is happening and its trying to flatten the developing high near our neck of the woods. The connection beyween our high and the Siebrian high is going to mean pressure will probably remain firm for at least the SE but its going to look ugly for a few days if that evolution came to pass. Best case solution for the medium term there is a HP builds strongly enough so it doesn't bring in milder air...at least that will put us in place fr when the more favourable northern blocking forms down the line a little.

Edited December 3, 2012 by kold weather

[MKN]

12z GEFS suite is very strong on blocking to our N and NE, with an equally strong (if not stronger) signature for block to retrogress towards Greenland in the extended frames as the pv is transferred towards Siberia (which has been a consistent signal now for a few days).

Get set. It's coming.

I thought this was Steve posting for a minute. Good to hear you be so confident about what's coming.

[kold weather]

12z GEFS suite is very strong on blocking to our N and NE, with an equally strong (if not stronger) signature for block to retrogress towards Greenland in the extended frames as the pv is transferred towards Siberia (which has been a consistent signal now for a few days).

Get set. It's coming.

Good signal, I think the end game will eventually be the same no matter what, its just do we take the LONG way round (like UKMO) with less cold pooling to tap into, or do we take the easier and probably colder method of getting into the great set-up.

Either way, its going to take a real botch job not to get very cold at some point this month!!