Model Output Discussion - 19th - 25th December

[Frosty.]

ridge to the west implies a possible northerly, that would be a bonus if we could see another cold snap after christmas.

[nick sussex]

ridge to the west implies a possible northerly, that would be a bonus if we could see another cold snap after christmas.

Unfortunately Frosty I don't think within the next ten days we can see any ridge hold the jet off for long enough to get a northerly, any amplification is likely to be brief, its really how the ridge topples thats a bit more uncertain.

Theres IMO more chance of a continental flow than anything from the north. To get the ridge at least far enough north for a more favourable topple we definitely need some help from troughing in the eastern USA.

[Frosty.]

Unfortunately Frosty I don't think within the next ten days we can see any ridge hold the jet off for long enough to get a northerly, any amplification is likely to be brief, its really how the ridge topples thats a bit more uncertain. Theres IMO more chance of a continental flow than anything from the north. To get the ridge at least far enough north for a more favourable topple we definitely need some help from troughing in the eastern USA.

we could end up with neither and just have a mix of average and mild weather alternating until the end of the year. The southeast would only benefit from a continental flow as I suspect most of the north will remain influenced by low pressure to the north of the uk with a nw/se split. I still feel a bit encouraged by the meto update which was not suggesting endless swlies as IB keeps hammering on about. All we can do is hope for something good to pop out of nowhere during the christmas period of model watching.

[Jhonny Peter Carson]

Looks like this High Pressure to the South will do what it has all Autumn and give us some nice mild weather. I do not think with the set up looking like this that we will not have any snow until late February, early March.

[phil nw.]

Looks like this High Pressure to the South will do what it has all Autumn and give us some nice mild weather. I do not think with the set up looking like this that we will not have any snow until late February, early March.

As the models only extend their charts to a maximum of 15 days Jhonny how do you come to that conclusion?.

[Grimsby Snow Lover]

Looks like this High Pressure to the South will do what it has all Autumn and give us some nice mild weather. I do not think with the set up looking like this that we will not have any snow until late February, early March.

Thats a brave call JPC, it wasn't that long ago that people were saying the same about December and here we are having had 3 weeks of below average temperatures and snow across most western parts of the British Isles. The charts do look dire at the moment for cold and snow I admit, but having read the Strat thread earlier, things could be on the move - the only problems with any strat warming is that it takes time to filter through the atmosphere and the models rarely pick up on this until much later. A reason to be a little more cheerful I feel.

Edited December 20, 2011 by Grimsby Snow Lover

[Thundery wintry showers]

Just to give one counterexample, 15th December 1985:

http://www.wetterzen...00119851215.gif

...led, eventually, to this chart on the 28th December 1985:

http://www.wetterzen...00119851228.gif

I think we can be fairly safe in ruling out anything snowy this side of the New Year, though a colder anticyclonic type is possible towards the end of the month if we get a bit of amplification around the 28th allowing high pressure to extend further north. But after the New Year it's still anybody's guess.

[lorenzo]

Am thinking along the lines of the ridge being flattened in the short term and a return to the Bartlett output so many on here dislike..

Unfortunately models show just what is modelled, with no pre-requisite to cold / mild/ bbq/ zonal/ meridional/ Bartlett / Blocked !

Witht he majority of ens illuminating long trail Swerlies this is not to be discounted as the current 'pattern'.

What is important is that in lower ens. there are hints of the blocked 'trend'.

[johnholmes]

Looks like this High Pressure to the South will do what it has all Autumn and give us some nice mild weather. I do not think with the set up looking like this that we will not have any snow until late February, early March.

I do like these 1 and 2 line posts that tell us all what the weather has been-wrongly as it happens, and then proceeds to suggest it will stay the same, 'nice mild weather' until February or early March, how about some charts to back up your post please?

[bluearmy]

Just to give one counterexample, 15th December 1985:

http://www.wetterzen...00119851215.gif

...led, eventually, to this chart on the 28th December 1985:

http://www.wetterzen...00119851228.gif

but ian - thats a completely different set up to our north. there are people that view this website less clued up than yourself that may take your post as evidence we could see something cold happening within a fortnight. (which we wont unless its an inversion under high pressure)

Edited December 20, 2011 by bluearmy

[Liam J]

Looks like this High Pressure to the South will do what it has all Autumn and give us some nice mild weather. I do not think with the set up looking like this that we will not have any snow until late February, early March.

How did you reach that verdict? We can only rely on model outputs up to a week ahead and even that is sometimes pushing it!

Plus many areas have already seen snow very recently, and we weren't supposed to be expecting snowfall until 2012

Edited December 20, 2011 by Paul

[mountain shadow]

Just to give one counterexample, 15th December 1985:

http://www.wetterzen...00119851215.gif

...led, eventually, to this chart on the 28th December 1985:

http://www.wetterzen...00119851228.gif

I think we can be fairly safe in ruling out anything snowy this side of the New Year, though a colder anticyclonic type is possible towards the end of the month if we get a bit of amplification around the 28th allowing high pressure to extend further north. But after the New Year it's still anybody's guess.

There is already northerly blocking evident on the first chart though with a nose of arctic high ridging into Greenland, and the PV is not as deep.

[phil nw.]

but ian - thats a completely different set up to our north. there are people that view this website less clued up than yourself that may take your post as evidence we could see something cold happening within a fortnight. (which we wont unless its an inversion under high pressure)

Yes i noticed that cheeky little Arctic High at the top of the charts--a sign probably of a less cold strato.than we have now.

In fairness i think it was just an illustration of how quickly patterns can change--given the right trigger.

[Thundery wintry showers]

It was more an illustration of the fact that persistent high pressure to the SE at a given time doesn't necessarily mean weeks on end of the same weather type. A closer match might be the second week of December 1994:

http://www.wetterzen...00119941211.gif

...which led shortly to this:

http://www.wetterzen...00119941214.gif

OK, nothing particularly snowy resulted from that, but it turned generally colder with a couple of frosty anticyclonic spells and a few wintry showers from a NW'ly incursion in between them, before mild wet weather resumed around Christmas.

I don't think it's beyond the realms of possibility that we could end up with something happening within the next fortnight, though it looks very unlikely within the next 10 days. In addition it is very difficult to find past analogues where the pattern was exactly the same as it is now (e.g. the Dec '94 pattern had a stronger high over eastern Europe, not that it made any difference to our weather which remained dominated by the Atlantic).

[johnholmes]

I hope you will bear with me admin/mods as it may seem a touch off topic-it isn't but I will post a comment about the possible changes that can and do occur, seemingly out of the blue.

Some talk about things cannot change for xyz days or weeks! Why not?

December 1946 was certainly colder than this month is going to turn out, it also had a +ve NAO 8.4 and January also turned in 1.4, February showed up at -34.4. One could hardly get a larger or quicker turn round?

I have no idea what the Stratosphere was doing at the same time scale-perhaps someone could post that data in here.

Equally I am not totally convinced, although those like chio, philw and GP are much more clued up than me, that an SSW is required to give 'cold' by Met O definition spells of several days, possibly a week, without any such help. Be it SSW or a simple warming event that leads to blocking of the Atlantic flow.

I am neither for or against the arguments being put forward why it will/will not change, I'm just showing that rapid changes do occur. How many predicted the coldish zonality of this month? I know its hardly snowed in the 'soft underbelly' of England (!) but it has over fairly low areas of NW England and Scotland.

Enjoy the green Christmas 99% of you.

Edited December 20, 2011 by johnholmes

[BLAST FROM THE PAST]

Fairly mild Blast?? 850Hpa temps of between 5-7c for most tomorrow, so 11-12c looks like being widely available and 13, perhaps 14c locally. I'd call that very mild, with a repeat performance possible on Thursday too, albeit perhaps not quite so warm overall.

Yes fairly mild, and two days before dipping again....hardly lengthy mild to very mild spell Shed. So mixed is a better/more accurate description IMO.

BFTP

Edited December 20, 2011 by BLAST FROM THE PAST

[PubliusEnigma]

FIrst signs of a long term barltett High setting up shop at 1035 - 1040 Mb over the near continent.

These features, typically can be very stubborn things to shift. GFS and ECM out to the end of FI,

keep the HP there almost as a permanent feature. It can bring some dull foggy dank weather to

the south east with lower temps, however towards the NW half of the UK, perpetual rain and mild

can last for weeks, even months in a worst case scenario. The other thing this set up does is to

pump an endless train of very mild and wet weather into Scandinavia, and even much further east

temps in western Russia tend not to fall much below freezing as opposed to -10 to -20 which is

more seasonal. With the bartlet in place and seemingly taking root, and a mildish near continent as

well as Northern Europe its difficult to see where any cold is likely to come from. Days begin to draw

out slowly from tomorrow as we pass the mid winter soltice.

[mountain shadow]

The pub run appears to have frozen just as it was getting interesting?

[Duane S.]

Nothing special showing up on the 18z so far, let's hope the Ens continue to hint.

It has been for a while that the 28th (ish) is a windowfor a push of WAA northwards but it is very difficult to see it not being flattened almost immediately. I suspect it may be a recurring (and increasing in intensity) theme for a while before finally we get heights into the right place and energy is diverted southwards.

Edited December 20, 2011 by Paul

[damianslaw]

Some subtle changes in the medium term outlook with signs of heights ridging north across southern parts of the country once we get past christmas, suggesting a weakening in the zonal flow - certainly not suggesting a significant pattern change, but the atlantic does look like it is weakening somewhat compared to the last 3-4 weeks enabling generally more settled anticylonic conditions to set in as we run towards New Year. Whether this would be a temporary feature remains to be seen..

I am expecting the models to start to pick up on upstream shifts in the overall pattern as we head towards New Year - a pattern which will be much more conducive to 'northern blocking'.. courtesy of a shift in the position of the PV and more importantly a weakening PV but realistically it may not be until mid Jan before this change begins to 'bed itself' in, but the overall trend is colder and colder as we head through January.

Edited December 20, 2011 by damianslaw

[stewfox]

I have no idea what the Stratosphere was doing at the same time scale-perhaps someone could post that data in here.

Equally I am not totally convinced, although those like chio, philw and GP are much more clued up than me, that an SSW is required to give 'cold' by Met O definition spells of several days, possibly a week, without any such help. Be it SSW or a simple warming event that leads to blocking of the Atlantic flow.

I am neither for or against the arguments being put forward why it will/will not change, I'm just showing that rapid changes do occur. How many predicted the coldish zonality of this month? I know its hardly snowed in the 'soft underbelly' of England (!) but it has over fairly low areas of NW England and Scotland.

Enjoy the green Christmas 99% of you.

Why do you think that is ?

I mean we have the usual wind-up merchants without any model support state ie no cold now till end of February

But many knowledgable members who suggest no established sustained period of cold can occur for at least 4 weeks because cold strat or what ever.

Or others saying no chance of a cold day or two in next 3 weeks because...

Seems far more frequent this winter ?, has FI been shifted to T900 ?

Edited December 20, 2011 by stewfox

[SP1986]

Personally I find it interesting a potential 'Bartlett' is setting up, it's somethign we haven't seen for a while, and in a synoptic sense it's quite impressive to see long fetch southwesterlies moving into Russia (although once they reach Russia they are more westerlies or northwesterlies).

As for what will happen, well at current we can only really go on the models, and for most it's suggestive that until New Year it will remain mostly mild, but with odd cooler periods just before Christmas in particular. Looking beyond this is fraught with difficulty, but the suggestion at the moment is southwesterlies or westerlies continuing..

Edit: 18z ensembles show absolutely nothing in the way in terms of trends, again it's just a mess. The average line shows slightly above but it really is pointless trying to find agreement. Even the pressure ensembles struggle to find any common ground (albeit than a loosely declining trend)

[karyo]

The 18z looks like a re-run of November to me! Not a month I'd like to experience again but hey ho.

The winds are projected to come from the southwest for almost the entire run!

Karyo

[damianslaw]

The 18z looks like a re-run of November to me! Not a month I'd like to experience again but hey ho.

The winds are projected to come from the southwest for almost the entire run!

Karyo

When there are no obvious upstream signals of a pattern change i.e weakening of PV etc.. (which the models don't tend to prog very well), then the default position will always be more of the same - in these set ups take what they are showing 2 weeks + with a pinch of salt, we should have learnt lessons 3 weeks ago when they were all suggesting falt zonal southwesterlies all the way, but in the end we saw sustained period of cool and in the north cold zonality at times.. do we ever learn I wonder?

[lorenzo]

Personally I find it interesting a potential 'Bartlett' is setting up, it's somethign we haven't seen for a while, and in a synoptic sense it's quite impressive to see long fetch southwesterlies moving into Russia (although once they reach Russia they are more westerlies or northwesterlies).

Edit: 18z ensembles show absolutely nothing in the way in terms of trends, again it's just a mess. The average line shows slightly above but it really is pointless trying to find agreement. Even the pressure ensembles struggle to find any common ground (albeit than a loosely declining trend)

This bit in bold SP I love, whre there is so much nailed on this and nailed on that, this is the true picture - divergence.