[Focussed Model Discussion]

41 minutes ago, Catacol said:

Agree 100%. Only Jan 20th and half of winter still to go. Very disrupted hemispheric pattern, strat reversal still ongoing and downwelling, and MJO coming back towards favourable phases. Much uncertainty on specifics, but overall pattern of Euro trough very much still the feature of the ensembles. Waiting a day or two while the atlantic blows itself out thanks to the storm over in the US wont alter the direction of travel. 

Clearly the models are still struggling to resolve the downwelling. Looking at the GFS zonal winds forecast (apologies, I know it's out of date, but having difficulty finding a new chart using the phone!) you have got to think that those negative anomalies will touchdown at some point. 

 

[Focussed Model Discussion]

15 minutes ago, Roger J Smith said:

However, this shift over the past 2-3 days illustrates that the models are only approximately catching the full reality of the here and now part of the run, which means the medium term and longer term portions are almost certain to bust badly.

 Would lay a bet that either the 00z or 12z model suite swings back to the cold end of the spectrum and the cold will then be closer to reliable time frame. We'll see about that one. 

I think you may be right. Looking at previous MJO forecasts, we were originally looking at an emergence into late phase 4 then quickly through to phase 6. One of the things that has happened over recent days is that it is now forecast to emerge towards the start of phase 4. This then delays the extra kick towards blocking that may have provided what we needed to land the blocking required. 

With the SSW the signal is there for blocking in northern latitudes, but the key for us is getting it in the right place. The (probable) failed easterly required threading through the eye of a needle and, as so often, this didn't work out.

But, background drivers are moving more in our favour, so it may be that we are looking at threading the eye of the needle to not get a colder outcome going forward. This may not be picked up on the models quite so clearly well in advance as there are clearly struggles with a pattern of background signals which have rarely been modelled before.

Plenty of interest, and I definitely feel that we won't have to wait too long. In the meantime there is still plenty of interest in the pattern over the next few days.

[Model output discussion - cold proper on the way?]

8 minutes ago, Spah1 said:

Bored. 

Been reading, hoping and anticipating since November. 

Can’t be bothered anymore.

Amazing how those cold charts have just disappeared. 

Back to square 1 at 216hrs on the ECM. 

Looks like Feb when we might feel the full effects of the SSW. 

Depends what you call square one! ECM shows NW to N bursts and hints of blocking which is what we would expect given SSW downwelling and MJO.

Square one, to me, is the horrible dirty UK high bringing endless gloom. The pattern has changed to colder, don't let the failure of ultra rare, ultra cold charts cloud your judgememt on a pattern that has definitely changed for the better!

[Model output discussion - cold proper on the way?]

56 minutes ago, FiftyShadesofSnow said:

Would be nice if certain posters explain the change in Synoptics.......Good to see the before and after.....Was it Mjo forcing....poor modeling of the Arctic....Nao not going negative...lack of downwelling from the Strat...etc etc

MJO and Arctic I would say. There's a real struggle with modelling the downwelling and I think that models seem to be suggesting that MJO is overriding the SSW for now. Given the shortish range pickup of micro details it seems likely that something similar may happen at short range either way. Not saying it would resurrect next week's Narnia, but could pickup a short range feature which does deliver more than the coldish pattern that is evident from upper level charts.

[Model output discussion - cold proper on the way?]

6 minutes ago, Broadmayne blizzard said:

For those bemoaning our current chart output am I not right in Thinking that the guys with greatest knowledge. GP etc were going with a start date of around the 21st for snow prospects then a possibility of needing a few bites of the cherry before the severest of the weather arrived for the first half of February.  As far as I can see that is still the picture. 

Indeed. But clearly people have to go through their catharsis first! Perhaps we do have to wait until the MJO phase plays its hand and rise on GLAAM shows through. But, SSW effect is still there and as the recent model upsets have shown, it is very difficult to model.

[Model output discussion - cold proper on the way?]

3 minutes ago, kold weather said:

 

ps, the UKMO also has gone. Well done on the ICON as well, first saw the change and the others have really followed its lead.

I disagree. The ICON has flipped since yesterday. All it tells us is that it was a finely balanced situation. All the models showed it at one point or another.

[Model output discussion - cold proper on the way?]

2 minutes ago, Chris101 said:

Cool cheers, i would have thought being Saturday, that a Tuesday snow chart would not be so much FI

When it comes to exact PPN type in this sort of situation we cannot be sure until much closer to the time. The high resolution models will give us a much better idea. It's a complex situation and there are many variables involved which can affect PPN either way within a small area of just a few hundred miles; far too small a scale for the model runs we have at the moment.

[Model output discussion - cold proper on the way?]

26 minutes ago, nick sussex said:

Is the output terrible ? No but after seeing some great charts these mostly have bitten the dust and we’re left trying to salvage something from the wreckage of another easterly fiasco .

Expectation management is probably the real problem. There are some snow chances but the easterly signal has weakened .

That’s where we’re at . So that’s our baseline . Let’s see if we can squeeze out just a bit more . 

There’s still a chance there’s been some over reaction by the models to a new signal.

Lets see what the models do this evening , still a chance we could see some better changes .

Almost certainly. No one model will ever get the situation spot on at a 7 day range; ablend is almost always the likely solution.

And things still remain positive. I suppose it's natural to feel disappointed that Narnia is not on the cards, but we are still in a cold pattern and will likely remain so for the foreseeable future.

For those who tie in so much emotion to each run, the @nick sussexhelpline is always available...

[Model output discussion - cold proper on the way?]

18 minutes ago, Steve Murr said:

 

My form horse is the UKMO with others falling into line this eve... A 3/4 way house to the amplified solution & the energy will split in the atlantic with the shortwave spoiler heading towards Portugal..

I think some people are disappointed that Narnia seems to be disappearing from many of the models this morning. Nothing wrong with that as many would love to see the conditions those sorts of charts would bring.

But feet need to be planted on the ground again and emotions untethered from each run.

What Steve says is true; it is unusual for an actual outcome to fully reflect one model's output if there are wide differences at a specific timescale. The most likely outcome would be some sort of blended solution which, it seems to me, has cold written on it albeit not in hundred foot high letters portrayed by all models yesterday for a brief few hours before the ECM came out.

Signals are still there: GFS still says cold. UKMO still says cold. ECM less so. But this is where @johnholmes ever excellent insights into the upper charts provide guidance. The pattern is still cold and there is, currently, no signal in the medium range for that to change.

In conjunction with the unchanged background signal of the SSW and the MJO heading for phase 6, the position will only become more favourable, not less, even if the ECM is correct on its own (which I don't think it is for now).

It is possible that the MJO phase 5 signal is, for now, overriding the SSW effect on blocking to our north. On the other hand, there could be issues with the models handling the SSW impact and the counter-effect of a phase 5 MJO. This is not a position they will have modelled frequently, so there is extra room for uncertainty.

For now, position remains largely the same which is not to let individual runs cloud judgement on the overall pattern which, at the microscale, is certain. To be uncertain .

.

[Model output discussion - 7th January onwards]

8 minutes ago, warrenb said:

I still think if it happens next week it is a bonus, the fun and games will be in February..

Don't think so. For what seems like ages we have been looking at around 21st January for the change to cold. Anything before that is a bonus, but after is now coming into the realms of the expected. 

All signals are now green, with the exception of a single amber light for NE US storm over the weekend, and even if that amber light is correct, it is a slowdown in the charge towards cold rather than a turnaround. 

The background signals have been signposting this for some time, and now we are on the cusp. I'm looking forward to @nick sussex musings on irritating shortwaves that may be the difference between heavy snow and slightly less snow rather than the more normal knife-edge situations we usually find ourselves in.

[Model output discussion - 7th January onwards]

3 minutes ago, PersianPaladin said:

Yes, the trends continue in much the same way but as I said yesterday - the set-up is precarious and highly changeable within a short time-frame. I don't know about how the different models resolve the resolution of the upper-troughing west of Greenland or over N.Canada, but I'm suspect of this pattern. I think given the record in these situations, the extent of that cold air will end up producing sufficient cyclogenesis in the N.Atlantic to erode heights over Scandi, where quite frankly we need them if we are to have any snow except the SOUTH of the country. Too many a time have we ended up with a weak block collapsing over the UK with shortwaves over the top, flurries for the far SE and the main LOW heading off south towards Italy and Greece. I predict the same to happen in this scenario.

Only if that signal for the Euro trough disappears. The ECM almost takes it too far south, but this is no ordinary setup which we've seen in that past.

[Model output discussion - 7th January onwards]

10 minutes ago, Steve Murr said:

Every picture tells a story

It's a cracker whichever way you look at it. We don't often get to see a cold slack flow over ground that may already have snow cover. Could be some very cold overnight minima if that did verify. The words "penetrating frost" spring to mind...

[Model output discussion - 7th January onwards]

11 minutes ago, kold weather said:

Not totally but fair to say what we have is more of a cold UK/Euro high rather than a scandi by 240hrs due to the pressure from the NW by the vortex.

I'd love to see where it goes from 240hrs.

Yes, it's one option and precarious at points, but it's such a complex setup that it seems unlikely. Having said that, the Low pressure is still diving towards the south, so other opportunities for snow and it seems that the Euro trough remains a strong signal!

Any other time we'd love to have a chart like that. Only thing remaining now is to get more ensembles onside and it's looking good. 

[Model output discussion - 7th January onwards]

4 minutes ago, feb1991blizzard said:

Yes - that's the point - where there are massive uncertainties in the short range, thats more crucial, Where as the Greeny high in FI potential, really could not show for another 10 runs of all models and it would still have a chance, if this slider is too far East and the ridge behind it is flatter and no decent Easterly is showing by the end of tomorrow, it is game over for that particular Easterly, with the persistent trough to the south yes im sure more chances will come as GP said, but that one will have gone - indisputable fact.

There are no indisputable facts which is why statements like "downgrade" or "upgrade" in are meaningless in isolation. It's all probability on deterministic models, and although probability increases as you get closer to T0, it doesn't always increase at the same rate. That is why you cannot say that one run or another will definitely "nail a pattern".

[Model output discussion - 7th January onwards]

1 minute ago, Skullzrulerz said:

Personally I see a VERY important ECM tonight 

It needs to stay on track but it's starts going off track I think its best to say that this so called beast from the east will be just a cold spell

It's no more and no less important than the 0z run.  It could easily show a GFS style evolution tonight and then revert back to the 0z tomorrow morning. We will not know for sure until the energy moving into the US on the STJ phases  with the energy coming from the PFJ and even then  there will still be small variance.

Background signals consistently favour the Euro trough as highlighted by @Glacier Point, so it is meaningless to write off any cold solution at this stage especially as the signals for northern blocking actually increase as we go forward.

[Model output discussion - 7th January onwards]

17 minutes ago, nick sussex said:

Tonights outputs so far show why a low dropping se and ridge building over the top are rare .

Its always that last hurdle that’s the hardest . However the track of the low will continue to change and there’s another one after that we’ll have to watch .

There is a little bit of insurance because originally the models weren’t that keen on much going on to the ne . The high pressure wedge there will help to disrupt energy away from low pressure near the UK and force a more se jet track .

So certainly things haven’t got off to a flying start this evening but there’s time for changes.

Upstream is important of course. I think for the first attempt we are reliant on the upstream flow playing ball. However, with MJO forecast to go into phase 6 by around 23rd I think that we will be less reliant on tiny differences upstream.

In short, probability of much colder air increases with each subsequent system dropping SE. At the moment we are totally reliant on SSW overriding MJO signal and the correct phasing of energy over the US. With MJO onside,  we should start to see more outcomes favour better variations no matter what happens upstream (although of course there is still linkage).

[Model output discussion - 7th January onwards]

2 minutes ago, Skullzrulerz said:

Man it's so confusing in here it's unbelievable ? Is this a downgrade/upgrade ????

Don't get drawn in is the answer. People post a chart and proclaim downgrade as if that is the end of it. 

The truth is that the atmosphere is highly dynamic and no prediction by a deterministic numerical weather prediction model can be taken as the truth at any point ahead of T0. Model output is a function of the input data and the algorithms. Both are far from perfect so a slight error at a point in time increases exponentially as you progress through the run, hence the seemingly big differences. 

No amount of statements saying "the 12z runs are really important" changes the basic fact that we are feeding imperfect information into an imperfect model.

 

That is why we should wait until we see the ensemble runs which give us a good idea of where the greatest uncertainty begins, and compare to previous runs; doing so enables us to pinpoint where models are struggling to handle particular permutations and where we should hold our patience for further information.. Comparing one point in time chart from one operational run to another is a route to madness but is, I freely admit, incredibly compelling in situations such as these.

 

 

[Model output discussion - 7th January onwards]

8 minutes ago, Buzz said:

I've been pondering that too - surely if it's the most accurate then it's now showing the most favoured outcome?

Or is that only when it shows what people want to see?

It's one solution amongst others. ECM and cluster, current GFS plus ensembles and UKMO (so far as we can see) largely back the colder solution.

It may be that the GFSp has the correct outcome, but we can only go on probabilities dictated by the models we have and, at the moment, it favours the colder outcome.

[Model output discussion - 7th January onwards]

27 minutes ago, Skyraker said:

Yeah it is (day 6+), probably expected given those charts, that said, it takes a couple of members with it.

Mind you, on a plus note, those means are fabulous.

Based on those ensembles only, it's in a sizeable cluster right through to day 7, after which there is no clear signal. Scatter becomes too random after day 7 to be able to discern a favoured trend. 

But, the background pattern is unchanged. For now, ensembles give reasonable guidance to day 7, after which it is pointless trying to figure out what happens at the detailed level. 

[Model output discussion - 7th January onwards]

1 minute ago, Ed Stone said:

That's some cold pool out east. There don't seem to be any of those pesky wee 'mild' bits, either:

Nope. Deep midwinter cold with very little solar energy. An easterly has the potential to be very potent at this time of year! 

@s4lancia called it just about right with his probabilities earlier on I think. About 65% in favour of an easterly right now, but details to be defined. 

If easterly sets up a shown by Wednesday/Thursday as shown in GFS 6z then you would expect to see disturbances travelling East to West towards the UK. 

[Model output discussion - 7th January onwards]

16 minutes ago, pureasthedriven said:

Agreed, all roads point to promise on this morning’s models. Checking in on the MetO extended then, underwhelmed to read the output. Doesn’t seem to correlate with what we’re seeing here, especially for the south. Suggests a different pattern to that long fetch easterly. Irritating. 

Nothing is yet certain.

For some time it's been looking like around 21st was the date for a real change and that doesn't seem to be too far out. Slight delay as MJO passes through unfavourable phases but think this is a signal being largely overriden by the SSW downwelling. As the MJO moves towards phase 6 we see the signal for northern blocking to increase.

This is not the place to talk about Met Office forecasts, but given the uncertainty and their public duty, it is not surprising they do not ramp up prospects for cold, choosing instead to mention the possibility. Those who need to know will have been briefed of likelihoods and will plan accordingly. FWIW, if you are interested in seeing what goes through a forecaster's mind when looking at events, Google "nws discussion NY" and you can read their description of how they out together the forecast for the upcoming potential storm.

[Model output discussion - 7th January onwards]

2 minutes ago, AWD said:

It shows the UK in Atlantic winds with the Scandinavian ridge too far east?

It shows a building Scandinavian high with a negatively tilted trough approaching. That low to the West would slide SSE and the Scandinavian high ridge west. 

Would the high sink? Don't think so looking at the shape of the pattern.

[Model output discussion - 7th January onwards]

1 minute ago, Froze were the Days said:

Not sure what to make of that upstream after 240 - a bit flat

Classic battleground situation. The alignment of the low to the west suggests pushback to me.

Far too distant to look at in detail of course, but good signs 

[Model output discussion - 7th January onwards]

20 minutes ago, knocker said:

This is still a major player in the ext period as part of the highly amplified upstream ridge/trough complex

 

Yes, and indeed the ECM is trending towards that outcome towards the end of the 0z run. 

[Model output discussion - 7th January onwards]

1 hour ago, Leo97t said:

I think that this is a blip, however i think that a deep cold spell can be taken off the table, but it will certainly stay cold. However the last thing we want is for high pressure to return for europe which is looking increasingly likely... 

Which neither the GFS or ECM show. Both models still support troughing into Europe which is the opposite of the high pressure which we saw over the past month. At 240 hours (beyond any sort of reliable timeframe given the uncertainty over exact details), the ECM shows this:

The kink in the isobars to the West of Ireland suggests trough disruption which would prevent high pressure establishing to our South. To further muddy the smaller scale details, there is another storm exiting NE US/Canada, so again amplification would depend on the track of that storm. Given that we still don't know how the energy will phase for the storm forecast for early next week, it is pointless speculating on exactly how any further storms will affect the pattern downstream. For now, the high remains in the mid-Atlantic with ridging attempts. The MJO is forecast to move towards phase 6 by around the 23rd, which is much more conducive to blocking towards the north, so chances should increase after this point.

A further spanner in the works is the handling of the Pacific pattern; yesterday showed a strong push of heights from Alaska towards the Pole. This is much less pronounced today which also suggests that we await further resolution in that area: