Model Output Discussion - the cold has arrived

[TSNWK]

 an agreeable UKM  - un settled from the north east and looking nicely primed for next weekend, as the over spain is movin eastward.

[Cold Winter Night]

6 minutes ago, Cold Winter Night said:

GEM will have to spend the evening in the naughty chair, that's for sure.

That same GEM takes many of you from -12c on Friday morning to + 12c  Sunday afternoon.
At least it's not boring!

[jamesgold]

Just now, Downburst said:

How can we go from this

To this

In 24 hours?

 

I expect FI is well and truly about 180 to 190 hrs on the GFS 12Z

These are runs from different days, the top pic is yesterdays…

[Mark wheeler]

1 minute ago, Mike Poole said:

UKMO very good tonight, and actually a bit of consistency here, not dissimilar at all to its 0z run, here T168:

Add to that a very snowy ICON run for the south, and all is peachy.  GFS is a mess but largely stays cold.

Just don’t mention the GEM…

Yes Mike , the UKMO seems to have been quite consistent on its last few runs , the question is , is it right ? I certainly hope so .

[Theresnoway]

4 minutes ago, Wivenswold said:

At which day are we calling "Shannon's Entropy"? 
I'd venture there's enough variance between the models at Day 4. The rest is FI. 

I guess the ensembles will help to answer this question, but I would guess around 4 to 5 days.

[MATTWOLVES 3]

11 minutes ago, Cold Winter Night said:

GEM will have to spend the evening in the naughty chair, that's for sure.

Somebody frame this for good reference keeping...for all those who wonder about what scuppers our cold chances..take a look at this and be reminded its a pure Winter killer!

Use it for throwing darts at or being sick over...but never wish for it and only hope GEM is having a laugh.

[Bricriu]

How can we go from -12 on a Friday to +12 by Sunday. I suppose it's possible. If the GEM starts to show this consistently, i suppose you would have to pay some heed to it.

[Catacol]

AAM rebound underway - will begin to neutralise the retrograde signal that has helped ease the Greenland High towards the west

We are not yet in a low momentum base state with the GWO holding a pretty neutral orbit

and so there is not currently a signal for a flat atlantic. If the MJO can get its act together and recover some amplitude then renewed amplification is still on the table. Timescale? Well - all rather tricky. AAM is pinging back already, MJO has yet to engage. I would say that we get our next 10 days of cold and then we hit a crossroads moment - as signalled in ensembles and on John's 8-14 day charts and as flagged by a few more experienced folk - that will set the tone for the rest of the month. By that time some might not care because they may have had their fill of cold and some snow after 10 action packed days....but others may still be chomping to get in on the action!

My thoughts have been anchored on the belief that the last third of the month would see the peak of cold for December. This was based on observations of early December cold usually not delivering, of the timing of the next phase of the MJO and on the belief that, by this point in the month, the column of westerlies better known as the vortex would be sufficiently distressed that, instead of gathering pace and cohesion, the opposite would occur. Now....one of these assumptions are already up in smoke. It is properly cold outside right now - the arctic air that has landed is the coldest I can remember in early December since 2010 and that was the coldest since....well - 1981? I couldnt be happier to be proved pessimistic. So the early phase of winter is delivering as we speak. The MJO heading back towards 7/8 I await patiently - and what about the strat?

A lot - at least for the way I see things - rests on the strat. This current cold hit has arrived because of a trop led dagger pushed straight through the layers over Greenland. This itself was a product of the Nino-esque setsup of the atmosphere in November which intially brought us a very strong Ural ridge stopping atlantic systems dead in their tracks over the UK, hence a mild and wet month, but then pulled west over Greenland as the amplification signal fell away. If we are to prevent a Nina grip on winter, and further falling momentum which is the trademark of a Nina winter, from sucking the amplification out of the system entirely we need something else to boss the pattern. EITHER we get a major bump up in the momentum profile again as we head into late December and on into January (and while we can't rule this out I can't quite believe we will roll a double 6 again, having rolled it in November, and see a trop led amplification signal big enough to maintain ongoing high lat blocking) OR we get significant assistance from the strat. Late November was full of good precursors - we had that very strong Ural ridge and we had low pressure over the Aleutians. This is your ideal strat stress precursor pattern and it was clearly visible. So - can we see the strat wobble, tilt and fall apart?

Too early to tell. If it happens then this winter could become a big one. If it doesnt then we may look back at a winter that started in great style but then gradually fell away. I am musing and not offering much of a forecast here, other than to suggest that we enjoy the next 10 days, expect at that point to arrive at a crossroads, and then peer with purpose into the mists of stratospheric forecasts as we hope to get the added boost to turn this winter into a properly long term cold one. We can still get the cold Xmas period from current pieces in play enhanced by the MJO and current bounce back of AAM. But to get more than that then a strat meltdown would be very very welcome.

On this note I'll close with this vertical profile. I bow, nose on the floor, to Chio's expertise in this area, but I get a sense of things when I put my head at the top of the vortex column and look down from on high - just what this tool gives us.

I see a vortex that looks to be very misshapen and showing signs of tilting. Notice the clear pressure on the upper vortex from the Asian side as demonstrated in Chio's recent warming charts - squeezing that upper vortex into the atlantic sector and threatening to setup a damaging wobble. Get a bit more tilt - take the centre of the upper vortex far enough away from the centre of the lower vortex and it might just be game on for a December SSW event, maybe early January. We can hope.

[Ali1977]

T156 control and mean look great , better northerly than the op 

[bluearmy]

Ukmo day 7 with the Norwegian shortwave too 

assuming that ec 12z will also do so, be interesting to see how it evolves compared to the 00z run 

[Notty]

16 minutes ago, Mike Poole said:

UKMO very good tonight, and actually a bit of consistency here, not dissimilar at all to its 0z run, here T168:

Add to that a decent ICON run for the south, and all is peachy.  GFS is a mess but largely stays cold.

Just don’t mention the GEM…

Yes - good consistency

[Dbarb]

Although the icon doesn't show any precipitation there certainly would be snow piling into the south east with the strong onshore flow cold uppers and still warm water. 

[TSNWK]

Just now, bluearmy said:

Ukmo day 7 with the Norwegian shortwave too 

assuming that ec 12z will also do so, be interesting to see how it evolves compared to the 00z run 

is this Norwegian a postive or negative for coldies - without doubt in my it has been an issue - but we are not in normal times and wondering.................

[claret047]

Can someone explain to me how the actual charts are arrived at. Is the data collected for each run used on to coin a better phrase "a blank canvas" or is it inputted into the previous run and the results spewed out therefrom. On the other hand is the data from say today's 12Z inputted into yesterday's 12Z for todays 12Z model. Alternatively is it a combination of 2 of these with perhaps some human input thrown in for good measure. Sorry for the ramble, but I would be intrigued to know.

[Skullzrulerz]

17 minutes ago, Mike Poole said:

Just don’t mention the GEM

Hang on, i thought it had the hero's welcome just a few hours ago.

Still, we really need some consistency with the models.

[Notty]

17 minutes ago, Downburst said:

How can we go from this

To this

In 24 hours?

 

I expect FI is well and truly about 180 to 190 hrs on the GFS 12Z

FI is usually at T+72 in my view

Just now, Skullzrulerz said:

Hang on, i thought it had the hero's welcome just a few hours ago.

Still, we really need some consistency with the models.

The proof of the pudding will be in the eating next week …

[Johnp]

2 minutes ago, TSNWK said:

is this Norwegian a postive or negative for coldies - without doubt in my it has been an issue - but we are not in normal times and wondering.................

I think the key is to make sure it doesn’t link up with the lower pressure out west in the Atlantic.  We need some kind of mid Atlantic ridge to Greenland. 

[phil nw.]

Just outside the reliable but i like the way the UKMO is going .

Starting to see the low extended further east up the channel as it disrupts. which helps to draw the colder air from the NE.

A way to prolong the cold.Nice trend.

 

 

 

 

[CSC]

Sunday evening Met Office website is suggesting a snow event for South East UK..

[northwestsnow]

UKMO ❤❤

[E17boy]

Just now, CSC said:

Sunday evening Met Office website is suggesting a snow event for South East UK..

Damm that misses London 

[northwestsnow]

1 minute ago, CSC said:

Sunday evening Met Office website is suggesting a snow event for South East UK..

Looking good guys ..

Countdown is progressing

[Paul_1978]

53 minutes ago, Mark wheeler said:

UKMO 144 

Looks like grazing the south coast again . Going to be interesting next 2 frames later .

One thing I can never work out is how do you know where the front will lie - is there and easy/foolproof way to tell from a chart like this?

[Guest]

 We've peaked too soon!...A week later, would have been a Xmas eve to remember!....(If it happens, that is!!)

 

[Singularity]

I've been refraining from looking past however the middle stages of next week unfold, but will drop this note: Judging by the MJO & Kelvin Wave analysis on Mike Ventrice's site, it seems to me that the cold surge out of East Asia is being predicted to kickstart more of a fast-moving Kelvin Wave than a traditional MJO event.

Those tend to have shorter-lived impacts on AAM etc, but it can be a pretty sharp kick, which might be just what's needed to set up a high near or over Scandinavia (a possibility that several others have rightly been noting for a while now). No telling at this stage what orientation it would have though or where cold pooling would have occurred prior to its establishment, which makes all the difference in terms of how cold received airmasses are, especially aloft (850 hPa level).

Modelling, mainly GFS/GEFS, is having a hard time picking out that signal against the near-term lagged effects of the recent AAM drop.

Incidentally, the GEM 12z might not actually be in the same camp as GFS - looks to me that a happenstance merger of two lows in the North Atlantic had much to do with the sudden, strong push from the west. Without that, it might well have looked more of  a 'Scandinavia high precursor' come day 10.