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

[Backtrack]

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.

My face in real life when you said that:

[SMU]

Kold look at the bump of high building at 144- where that low is 1005 + 1010- moves North, 1000 MB low moves East then SE

S

[Frosty.]

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.

Yes but NE Scotland has the highest risk of heavy snow showers on tues night and wednesday, quite a blast of arctic air being drawn south by the end of tomorrow, shame it can't be sustained really but the pattern is moving very quickly this week.

[Ice BIast]

The BOM could be a useful tool tonight. It looks similar to the UKMO at T144, so it will be interesting to see where it goes beyond this.

[Harsh Climate]

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.

You make some good points their but what I mean is, I doubt in any part of the gfs 12z run would there be heavy snow accumulations from north sea convection? We would be relying on an undercut further on or a reload.

[The Northern Ramper]

I like the way GP is ramping things up but seems confident that January is going to be better still.

[nick sussex]

If the ECM comes out with a similar output to the UKMO then at least we have a 168hrs chart to see where that might go.

In terms of the UKMO its 96hrs chart does have some snow potential so thats a positive.

[phil nw.]

The GFS Easterly is shown on the control run too within the High resolution period.

I notice too the the GFS mean is now suggesting the link up of heights in week 2

This adds more confidence and with the vortex easing towards the Canadian side of the pole this would encourage such a development.

The mean run also looks like going from an easterly towards a northerly-(Greenland high) in week 3.

[weatherguy]

I like the way GP is ramping things up but seems confident that January is going to be better still.

As I understand it, the real positive effects of the stratospheric conditions won't be felt until late December...so the fact that we already have extensive northern blocking can only be a good thing

[ITSY]

For those wondering about UKMO, this is the BOM at 180 - after having been very similar to UKMet at 144:

NElies in the offing, atlantic backing away, scandi/siberian pressure building and low over southern europe. I'd take that even without GFS!

The real difference is the time it will take to get the cold IMO. If this represents the 'worst' of the lot so far today, then it's been a goodun!

Edited December 3, 2012 by ITSY

[Cheshire Freeze]

The GFS Easterly is shown on the control run too within the High resolution period.

I notice too the the GFS mean is now suggesting the link up of heights in week 2

http://modeles.meteo...21-1-216.png?12

This adds more confidence and with the vortex easing towards the Canadian side of the pole this would encourage such a development.

The mean run also looks like going from an easterly towards a northerly-(Greenland high) in week 3.

If we do get that Scandi to Greenland transition, we'll be facing a rare commodity in terms of synoptics.

[swilliam]

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!!

I really do think people should stop guessng what will come after the UKMO 144. Looking at it those small LPs they could move in a variety of ways and we will never know who is right/wrong as it is extremely unlikley to verify exactly like this anyway. None of the models are showing the link up at this juncture so I do not know why people think the UKMO should. Also remember that IF said last night that the UKMet do not use their GM beyond day 5 anyway.

Edited December 3, 2012 by swilliam

[phil nw.]

If we do get that Scandi to Greenland transition, we'll be facing a rare commodity in terms of synoptics.

Yes easterly/northerly as the fragmented vortex moves around with heights filling the gaps to our north Crewe.The way to go for a prolonged cold spell-such as 62/3 when this switch between one or the other happened more than once.

[Panayiotis]

Sorry to be a nuisance but can anyone give me the link, where it shows snow as a snowflake (3 if heavy) and rain as a green circle? On precipitation charts.

Edited December 3, 2012 by panayiotis

[MattH]

Evening all...

Just bit of a one-off post from me in the model output thread and whilst this may not go down well, I want to air caution regarding the synoptic evolution, the reason being is experience and the amount of model divergence at medium and long term.

As GC pointed out there is GFS ENS mean support for the 12Z GFS Det model, however, lets get real, the synoptics at the end of the GFS Det run are akin to that of 63 for example, extreme blocking in all it's sense. Granted, you could equally argue the point that it could be right as much as it could be wrong because of the time frames involved, so I'll leave that "chicken and the egg" scenario for discussion.

However, I've been on shift for 6 days now and I have been struggling to forecast synoptic changes at days 5 and 6, let alone out to next week and beyond. I have quite publicaly discussed the potential changes long term thanks to stratospheric conditions, but as ever the information is just that, information on a forecast chart. Until it actually happens it is nothing more than a 'prediction', which isn't a certainty.

The amount of spread evident within the 12Z GFS ENS longer term highlights the model uncertainties over the synoptic evolution. As is often the case the models, for the UK, struggle so much in this kind of synoptic pattern. Throw up a zonal pattern, like last December, and the ensembles never vary very much as it is such an 'easy' pattern to forecast. The 'behind closed doors' ECMWF ENS information also throws up some major divergences in synoptic evolution towards and beyond T+300hrs, to the point where the 51 ECMWF ensemble members, of late, have been split 5 or 6 different ways.

I recommend caution regarding the up coming synoptic pattern. The stratospheric conditions are indeed conducive to blocking patterns and clearly the longer term stratospheric conditions may well enhance that risk, but this isn't the be all and end all. There's a lot more to forecasting and these E or NE'ly solutions long term are still very much in the balance for now until far more model consistency in particular develops.

One thing's for sure, despite the uncertainties and potential outcomes, it makes for a far more interesting model analysis than for example the zonal dross of last December which anyone could forecast with their eyes closed!.

Let's see what happens.

Cheers, Matt.

*crawls back to the forecasting cupboard*

[fergieweather]

I recommend caution regarding the up coming synoptic pattern. The stratospheric conditions are indeed conducive to blocking patterns and clearly the longer term stratospheric conditions may well enhance that risk, but this isn't the be all and end all. There's a lot more to forecasting and these E or NE'ly solutions long term are still very much in the balance for now until far more model consistency in particular develops.

Hoo-rah

[Stu_London]

If we do get that Scandi to Greenland transition, we'll be facing a rare commodity in terms of synoptics.

Probably only 1 of 2 ways to get a sub-zero month in winter (like Dec 2010). The other being a siberian high (like Feb 1986). Even then you need to be a bit lucky for it to be exactly in line a calender month.

Steve M did a superb video and chart animation of how to achieve the holy grail sub zero month a few years ago - maybe he still has it somewhere.

Btw, I don't think December 2012 will be sub zero, but it's starting to look like it might be in the severe category (below 2C)

[on the coast]

Very sensible post Matt. Shame your not in here more often. Have learnt the hardway and never look past 96 hours now from any model.

[TEITS]

As some are disappointed with the UKMO I think its a good idea to remind you of my post this morning.

Despite the differences between the GFS/UKMO if we use the BOM as an example because its output is similiar to the UKMO then the end result is the same i.e E,ly. The UKMO is a longer route to an E,ly with added complications. However the overwhelming signal is an E,ly despite the differences at +144.

[Tom Jarvis]

what is the ECM like??

[Geordiesnow]

Again, between 96 hours - 120 hours, there is a small snow showers risk for some Eastern areas as the low pulls away before high pressure starts to perhaps topple in, this could still upgrade so still keep an eye on it although the Northerly for mid-week does look to have more potential except for sods law to dictate that for most parts in the East, the winds will be off shore for the most part.

I also prefer the ECM/UKMO's orientation of the high over Russia, better than the GFS therefore more cold air should flood down into Scandinavia hopefully. Shame about the low pressure system in Iceland though.

[Weathizard]

UKMO

ECM

[SMU]

As expected that would be the evolution, now watch that low swing south at 168-

S

[Snowy Liverpool]

what is the ECM like??

A return to southwesterlies. No doubt this is just another "delay" and we'll eventually see our easterlies in April.

[swilliam]

Well ECM is very similar to the UKMO at t14 so I guess we will get to see it might evolve from here.

Edited December 3, 2012 by swilliam