[Hunt For Cold: Model Discussion - Heading Into Christmas]

Admittedly this is at 30mb, but a proper view of the FV3 stratosphere:

A complete split evident there with a minor geopotential wave coming in through the Atlantic sector to aid the Wave 1 displacement from the Pacific

Whilst you could argue that one of the daughter vortices being that close to Greenland is not ideal (were that pattern to impress itself on the troposphere too), assuming any ridging followed suit, then you're getting into high risk high reward scenarios with some blocking likely around the GIN corridor somewhere and a likely southerly-displaced but still potentially active jet stream roaring just underneath it if everything falls into place....a la 2013

Still, this is only a single run from an experimental output which has had lower anomaly correlation out at day 10 than the model it is supposed to replace....I would recommend for now sticking with the EPS guidance as I suspect this will (eventually....not yet while everything is still chaotic) give us the first glimpse of what effect the impending stratospheric shenanigans will have on the troposphere through the second 2/3rds of January

[Stratosphere and Polar Vortex Watch]

5 minutes ago, Altostratus said:

Yes I’m curious as to why strat forecasts at such range would be any more reliable than typical tropospheric forecasts? After all, the cause of the SSW is as a direct result of goings on within the troposphere if my understanding is correct. We all know not to trust the models beyond 120-144hrs so can’t help but be circumspect of these long range stratospheric forecasts.

Question for the experts, assuming we get a SSW, what impacts length of time for effects to filter down into the troposphere? Lots of nervous people in the cold hunt thread but surely eye candy charts won’t even be shown yet as they are out of reach. I’ve read various sources that suggest it typically takes a week or two for the effects to filter down into the troposphere. Based on that, and assuming PV split around Boxing Day (as per tweet above), realistically, we should expect to see less Atlantic influence and more HL blocking being picked up by the models from around 7^th Jan?

I don’t have the time for a full reply right now - and we should still be cautious of any model output at such a range without some ensemble consensus (which fortunately we do have to a large extent at the moment). But the primary reason that stratospheric modelling should in theory be more accurate is that it is an easier environment to model - you don’t have large geographic features like bodies of water and big mountains in the way, you’re essentially dealing with a flat “surface”. Of course, there is always the argument that as tropospheric behaviour can affect the stratosphere, it is still open to the same flaws, but generally the physics of the situation should be easier to handle

[The hunt for cold - Model discussion (late November)]

3 minutes ago, bluearmy said:

I like the general pattern - displace it a few hundred miles south and you have a seventies winter! 

Ditto the EC46 really 

I commented the other day about the GLOSEA anomaly potentially being a little far north with the low heights for comfort - it’s one of two things for me. Either, it will be a relaxation/delaxation (no idea if that is an acceptable word but I stand by it) of a more west based -NAO.....or its the perfect recipe for some very big snow events with the perfect mix between just enough polar sourced air and Atlantic moisture

January is going to be a really properly fascinating month on so many levels (that is an intentional stratospheric pun....I make no apologies...)

[The hunt for cold - Model discussion (late November)]

The other encouraging thing in recent runs of the FV3 has been the tendency towards another warming phase through Western Siberia towards the end of the run - yet another shot at the vortex. We have below the peak of the first wave of warming

Then this secondary bout of warming (also visible on the 0z):

[Stratosphere and Polar Vortex Watch]

Some timely tweets from Ventrice - how is this for a 51-member ensemble MEAN warming - temperatures in the -15 to -10 range out at day 15 as an average. The reality could be much much warmer

 

EDIT: Just adding the anomaly view in, in case anyone missed just how significant a projected warming this really is

[The hunt for cold - Model discussion (late November)]

50 minutes ago, Daniel Smith said:

GLOSEA update continues the blocked theme Jan-March

If I'm going to be purposely picky and a little bit obnoxious towards the models.....the only thing I would comment on is that the low MSLP anomaly is a little further North than one would like in an absolutely perfect world. Some would argue that this throws plenty of opportunity for precipitation into the mix....others would argue that it has just the faintest of tinges of the risk of a more west-based -NAO pattern to it....

But I caveat all of the above with the fact that this is a three month average anomaly, and with that sort of pattern, should it prove to be correct, there will be more than enough opportunity for the UK to join in the fun - and this is actually more in line with my thoughts for the coming months than the ECM seasonal projection in terms of where the core of the higher anomalies may sit

[Stratosphere and Polar Vortex Watch]

31 minutes ago, feb1991blizzard said:

What we need to see next (and this is a concern because the warming is moderating at 384 at 1mb on the 6z GFS) is those zonal winds to flatline for a significant amount of time at 0 or preferably below 0 m/s, im hoping for a split soon afterwards which would do this hopefully, my concern is with a displacement SSW, we might only have limited opportunity before the vortex returns to the pole.

Possibly....although looking at the images posted in here this morning (unlike the meteociel temperature only ones which always do the rounds in the model thread) the warming wave from Asia (presumably from an EAMT) is riding around the surf zone of the beaten-up and displaced vortex and is starting to take on that shape where it looks primed to break into the heart of the vortex in the following few days - if, and it’s a big if, that does happen, then it shouldn’t matter too much where the displacement ends up....because there probably won’t be too much of a vortex left to be displaced.

I need to do some further digging in to this but timing wise, and looking at the shape of the temperature wave, this feels fairly similar to 2013 - I will caveat that though but saying I have had no time to analyse this yet.

[The hunt for cold - Model discussion (late November)]

29 minutes ago, Catacol said:

I’m cautiously optimistic on that, but not at the stage yet that I’d put any money on it. I’m convinced of the benefits we are going to get from the Pacific pattern...but want to see more over the next couple of weeks on just how the vortex responds. The longer we keep an east based scandy high and aleutian low the better....though for many on this thread this is a source of great frustration because it means short term Atlantic pain. I’m not enjoying the wet and windy right now...but my internal smile is widening because it is all money in the bank for January.

It’s a difficult one to ask for really, for people to be patient whilst the current tropospheric pattern, frustratingly close to cold as it is, delivers not much to the UK but does put on its steel toe-capped boots and gives the stratospheric vortex some Vinnie Jones tackle treatment - of course this doesn’t guarantee cold for the UK, but I’m of very similar mind to you in terms of where the gaps are likely to be left in the vortex in the longer term

If anyone needs a reminder of why this is - think December 2012....then think January (and March) 2013. This sort of tropospheric pattern puts us right in the mix in the longer term.

Hang on in there

[The hunt for cold - Model discussion (late November)]

17 minutes ago, IDO said:

 

This current stalemate of a flat NH profile is bad for wave propagation and bad for any short-term meridional Atlantic building blocks. We really need wave attacks to finish off the strat and the forecast setup is not going to help long-term?

 

If helpful tropospheric precursor patterns are what you are looking for (and eventual wave propagation), in combination with the Aleutian low, then there are not many positions better to be in than having a Scandinavian high there...

[The hunt for cold - Model discussion (late November)]

7 minutes ago, ICE COLD said:

This is now getting closer , it’s starting around day 12 . 

The PV is in a right old state. 

That is one hell of an Aleutian low too - combine that with the resilient Scandinavia/Siberian high, and what do you get?

The atmosphere is cooking up something tasty, it’s in the prep stages at the moment, but it’s getting ready to turn the oven on....

[The hunt for cold - Model discussion (late November)]

1 minute ago, Daniel Smith said:

Screw it..

204hr we see energy heading SE, perhaps a little more than what the Op shows but I suspect the Atlantic will be coming in by day 10/11 on the EPS judging from this chart

Which I don’t think is unreasonable given the shifting around of the vortex towards our part of the hemisphere, though with the usual caveats in terms of NWP tendency to blast away blocking to our east

What follows after that could be far more interesting....

[The hunt for cold - Model discussion (late November)]

17 minutes ago, ArHu3 said:

You're right, I was in a hurry. Anyway, not that discussing this changes anything but I think that displacements are more often than not unfavorable for us and we need an actual split. In the stratosphere thread catacol explains why displacements often can be unfavorable 

 

 

It depends entirely upon where the displacement pushes the vortex to - and often the ‘angle’ of the displacement too.

What we see with the current/forecast Wave 1 action is the core of the vortex pushed from over the arctic/Greenland/Canada across to Siberia and Asia.

There’s a lot of ifs, buts and maybes, but if you are eventually looking for a draining of the low heights to our NW (and assuming that the tropospheric response is near identical to the stratospheric one) then this is good news in the longer term - and especially in association with the later (I suspect East Asian Mountain Torque led, but I have not checked this yet) more significant warming in the Asian sector, which in recent stratospheric history has been one of the more exciting warming locations in terms of cold tropospheric consequences

But what we should bear in mind is that with this westerly push of the vortex (and again assuming the tropospheric pattern follows the stratospheric one quite closely) is that it is likely to mean we get some more momentum in the Atlantic at some point in December. That is not to necessarily say a return to raging zonality is on the cards, but I suspect the forecast potential height rises to our north-east may be somewhat short lived (unless we get very lucky) for now - but a) the continued tendency towards Scandinavian/Siberian blocking in the short term will continue to damage the already wobbly vortex, and b) I really do think this would be short lived whilst we see the vortex shift above our heads take place. And what happens the other side of this could be something quite welcome for most members on here

In summary - it’s all very complicated, but there’s no magic formula to say that Wave 1 = this and Wave 2 = that - but observations of this season so far look really rather positive to me

[The hunt for cold - Model discussion (late November)]

26 minutes ago, northwestsnow said:

Well GFS 12z might not be the eye candy at ground level but up in the strat its consistency is noteworthy..

Absolutely and that is why we should be taking any tropospheric output beyond a few days with some caution right now

The Wave 1 displacement, if coupled in the troposphere, would, you would think, give a period of stronger westerlies across the Atlantic in the 10-15 day period. But we'll see how that plays out.

Either way, as we head towards the second half of December, this looks pretty exciting....especially if we can get a secondary warming into the core of the vortex while (if!) it resides in the asian sector, as has been hinted at at 10mb in several recent runs

[SE and East Anglia general weather discussion 07/11/2018]

2 hours ago, LightningLover said:

So much rain has fallen this morning, that local surface water flooding has occured... Really makes me wonder how much snow we may have had by now via this streamer, if conditions were just that little  bit more favorable...

Unfortunately sods laws dictates that if conditions had been favourable for lowland snow, the flow would not have aligned this perfectly for this long to allow the streamers to form....

[Model output discussion - The Hunt For Cold]

Three observations from me tonight:

1) Still in line with my thoughts from the other night, im not convinced on Greenland height rises just yet - GIN corridor seems more realistic at this early stage, and that’s partially because....

2) I don’t really want Greenland height rises at this stage given such a mild 2018 across Europe so far. I fully expect synoptic evolution towards 2010 type scenarios as we progress into winter (and late 2010 has been a favourite for me in terms of analogues for some time, albeit I think we approach this with a slightly delayed timeline - but for the first time in a long time, I think long range NWP with its emphasis on northern blocking is not far from the mark)

3) Everyone needs to start appreciating how valuable the contributions of @bluearmy are in this thread. Nick has consistently through the years, whilst always being a cold seeker like most of us, offered an incredibly balanced view of what’s going on in NWP, and we should all count ourselves lucky that he continues to post his thoughts for us. (I promise I was paid no fee for this...)

There has, as always, been a lot of conflict in this thread in the last 24 hours - and sadly that has just become a matter of fact in this thread as we get to this time of year. And I would hope that we can maybe move beyond that this year - we are blessed with some ridiculously knowledgable people in this thread and I would like to hope that nobody, no matter how experienced, is scared away (or frustrated away) from offering their thoughts this year. Each and every thought contributed is just as valuable as any other, given that for the overwhelming majority of us this is just a far too obsessive hobby and we are all looking for one thing - a happy snowy ending.

—————

To return to my thoughts from the other night, and returning to point 1) - the reason I am not concerned about whether we get cold/snow in the coming week is that, as per my post earlier this week, the upcoming pattern (near record breaking Scandinavian high and, as GP aluded to earlier, Aleutian low to tow), the damage to the fledgling vortex will be near irreversible, and the longer term results across the northern hemisphere should be beneficial to the cold and snow enthusiasts among us. This is clasic wave 2 precursor stuff, and regardless of a rebounding QBO, given the current disconnect between the stratosphere and the troposphere, should play havoc with attempts from the polar vortex to set up its usual happy shop across the arctic.

In short - I’ve not been this excited about a winter since 2009/10 - and this is just the beginning...

[Model output discussion - The Hunt For Cold]

For what it’s worth -

Obviously the major scandi high looks pretty well fixed right about now, and that is good news in terms of longer term prospects from a stratospheric standpoint

In the longer term, the retrogression signal to Greenland I remain dubious of. We’ve been here too many times before in recent winters and what has generally spoiled things is how much of the tropospheric vortex is left residually over Greenland as we get closer and closer to T+0. Generally speaking, all modelling has been too keen to drain low heights away from Greenland and across to the Asian sector at longer timeframes, only generally to downgrade prospects with just a bit too much vortex energy left over Greenland.

However, this early in the season before the big bad spinning plate of the vortex has had a chance to get its balance, such disruptive tropospheric patterns are hugely comforting to see

 

[Model output discussion 14/04/18]

1 hour ago, Alex said:

Interesting model watching for the London marathon runners on Sunday. Interestingly the models have slowly been revising the pattern more east. Earlier in the week a ridge was expected to be sitting over the south and now it’s quite far East. I wonder if this continues whether the cooler air will reach all areas earlier than thought and give some welcome relief to us runners.

I really hope so for anyone running the marathon on Sunday, let's get it back under 20c for you all otherwise it's going to be just that bit tougher than it already is for so many people doing something I am in awe of for charity - very best of luck to everyone running! 

I have to say today has been just the perfect temperature for me in central London, up to 25c, just perfect for wandering around in (should read: wandering to the park for a beer in). Tomorrow will probably be a little bit unbearable for so early in the season with 28c likely to be hit I would think looking at high res modelling. Back down a few degrees it looks like again by Friday and into the weekend so something a bit more comfortable.

What an incredible couple of months of weather we have had

[Model output discussion - after the beast, what next?]

20 minutes ago, cheese said:

Considering it reached 22C in early April last year here, it certainly could happen.. though I don't think it will. 20C in April is really not that uncommon.

Ohhh I'm not suggesting that it's impossible to reach 20c in April, far from it. Just that it's not in the current scope of forecast modelling 

[Model output discussion - after the beast, what next?]

9 minutes ago, Summer Sun said:

 

As for the 7-day trend chart, next weekend is it quite simply sensational more than 10c above average for some parts

I'm not sure that's quite how those charts work Gavin, they're a temperature trend chart - so it's the difference between the temperatures at day 1 (which in those regions under cloud and rain/sleet/snow tomorrow will probably be rather depressed) and those at day 7 - so a very good trend and nice to see some warmer temperatures on the way, but 10c above average would be a bit extreme - that would put those parts of Northern England under the most extreme trend anomaly there at around 20-21c (which will not be happening we can quite safely say!).

They instead show that the temperature will be 10c warmer in a week's time, which will be pretty welcomed for many 

[SE and East Anglia general weather discussion 03/03/2018 onwards]

So today I've been from Greenwich across to Clapham, down to Wandsworth then to Tooting and then back across via Westminster, Elephant & Castle, through Peckham and now back in Greenwich. Pretty similar conditions all the way across to be honest. Roofs, grass and cars covered, patchy coverings across the pavements - around 2-3cms of snow throughout.

Just now it's that really fine powdery snow which hurts your eyes a bit to walk through. Not bad all in all for March. The Met Office warning were a little out of kilter it must be said, but this episode goes to show once again that no matter how far we humble homosapiens like to think we have come with NWP, dynamic situations such as this can still catch us all out. I did suggest on Friday that realistically we could expect 2-5cms for those on lower ground and that looks to be just about right.

But again - this is March. All of this is a bonus and we have a good few winters yet to come

[SE and East Anglia general weather discussion 03/03/2018 onwards]

Well I had just left a pack of Peroni out in the garden to cool down and it did the trick

I did have to clear about 1cm of snow off the top though

[SE and East Anglia general weather discussion 03/03/2018 onwards]

5 minutes ago, Nick F said:

Moderate fall of big flakes now in SE25; starting to settle on grass now, as well as roofs, cars and fences but not on pavement and roads.

00z EC keeps much of the SE under snow for much of the day and through the night, radar shows more to come off the E Anglia coast.

Indeed a much improved ECM run after a little wobble yesterday

I suspect that might be the start of the convergence zone showing its hand off the coast of EA

[SE and East Anglia general weather discussion 03/03/2018 onwards]

Really horrible out there in London at the moment on the way home - chilly with driving rain

Thank goodness it will be driving snow by the morning 

[SE and East Anglia general weather discussion 03/03/2018 onwards]

Probably time to set some realistic expectations (without some surprises cropping up which are currently unmodelled)

Certainly the risk of 2-5cms across the region, more especially around the estuary, with perhaps 10+cms over the downs.

If you want more than that, you need to hope the HIRLAM is correct

 

[SE and East Anglia general weather discussion 03/03/2018 onwards]

44 minutes ago, kold weather said:

Just to note someone on TWO has posted a great link to a 1km WRF model, which is very high resolution. It shows some good looking streamer action (maybe that is what the UKV is seeing as well, hence the warning?)but this eventually becomes engulfed in an area of light-moderate snow which is on-off pretty much all day Sunday. Widespread 10cms, but with a local amountof 25cms near say Croydon. VERY interesting stuff, this kind of goes along with the HIRLAM as well fwiw...

It looks awesome

The only thing I would caution is that it looks as though it was initialised from Thursday 18z GFS, so it may be a little out of date by now