Model output discussion - The run up to Christmas

[georgiedre]

17 minutes ago, Vikos said:

So which is then? 2m temps? Snow at +5°C? Serious?

2m temps will be about 2-3c maximum so probably between 0-2c on average 

[northwestsnow]

That Russian high can be positive in relation to the vortex, but we need it  to sod off in the next week or two.

Edited December 22, 2020 by northwestsnow

[Leon1]

It's not annoying having a few posts talking about the 850 temps being too hot. Having entire pages filled up with people complaining is what is annoying. @snowking did an amazing post earlier and I wish people could leave it with that. These charts are not bad (it snowed in essex earlier in the month with uppers higher than currently forecast) and we should be much more confident than last year. 

 

[BlueHedgehog074]

The 12Z ECMWF ensemble mean between days 7 to 10 shows the Low Pressure over and just to the East of the UK gradually shifting away further East. Not agreeing with the operational model of it staying sellotaped over the UK. Although the operational model couldn’t be discounted, the outlook the mean shows seems to make a bit more sense. The ridging, while it does lose some of its amplitude, is maintained in the Atlantic and so is some troughing South into mainland Europe. With that troughing over Europe along with a lack of a raging Vortex over Greenland, the Atlantic ridge would likely struggle to ridge over to our South-East pulling in a milder South-Westerly flow. Should be noted as well there is some blocking maintained over the Russia area. Chilly overall with some rain, though some sleet or snow could be possible too, particularly over high ground. 

[Weathizard]

4 minutes ago, Jason M said:

Its the squeeze between the Russian high and the low. It just pumps the warm air up into NW Europe. Comes back to the 'airmass' point I made yesterday. Effectively were sucking in a rTC airmass (returning tropical continental) around a closed off low. That Russian high has been a killer for recent winters as it just pumps warmth north and leaves us with no cold pool. Then add on 1.5c of background AGW and its a one way ticket to Mildsville (bit OTT but you get my point!).

Don't know about 'follow the yellow brick road' its a case of 'follow the isobars'.

Here here, I hate the Russian high. I see some people saying it’s a precursor and an ingredient in a U.K. cold spell but it’s killed so many winters.

Even now when we have a dead Atlantic and massive ridges being thrown north we still can’t get cold enough air far west enough because of it. The worse winter in recent memory I can’t remember what year it was but maybe 3/4 years ago it seemed to persist for the entirety of winter.

[Vikos]

3 minutes ago, georgiedre said:

2m temps will be about 2-3c maximum so probably between 0-2c on average 

Allrighty then, happy Narnia to you!

[Jason M]

Just now, clark3r said:

Global warming 

In fairness its probably 95% synoptics and 5% background warming. That last little 5% can be crucial in our climate though.

This is far from over either way though so no doubt this debate will rage for a few days yet (and that's not a bad thing if its done respectfully).

 

[Catacol]

28 minutes ago, Weathizard said:

Shall we all just be happy clappy and pretend that the 850’s are cold enough for widespread laying snow?

I think for the majority at the moment the 850’s are not cold enough, nobody is trying to be annoying by saying that it’s just the truth.

It also depends what some people define as snow because I define snow as snowing AND laying, not Snowing and melting.

People are getting frustrated by comments like this, but it is important to keep feet on the ground and there is validity to this view. Whatever occurs over the weekend and into the start of next week is going to be marginal away from high ground. Now - this isn’t to say that marginal cannot develop into something special. I’ve lived through a marginal event many years ago that turned into much less than marginal and gave a big dump of snow - but that’s once in a lifetime. Conditions next week are not ideal (yet) for the blizzard many of us would love to see. If you get lucky next week then grin from ear to ear, make a chain of snow angels and count your lucky stars - but it won’t get away from the fact that this early turn to cold is not going to create ice days immediately.

I am getting more and more confident that conditions will turn genuinely cold, but it will be a slow process. The trough in situ would appear to be staying with us for the foreseeable, and while it is possible that the gfs NE solution might come to pass and pull colder conditions in more quickly it is equally possible that we might sit under a stagnant trough and live with on/off marginality out to the New Year and beyond. However.....and it’s a big However - renewed blocking from a significant +EAMT is looking likely in the longer term, meaning stronger heights and a bigger easterly draw. Add downwelling impacts from a split SSW and the direction of travel at the moment is only in one direction. Cool becoming cold becoming colder.

So - sit tight. Ride your luck next week and fingers crossed some folk get some snow, even if wet and relatively temporary. But be aware that this is just the beginning...........

[Joe Bloggs]

3 minutes ago, CreweCold said:

Given the low drops from Greenland, you'd expect more cold in its circulation than what is shown. You'd think it was travelling over a lava bed the way those 850s warm up.

It doesn't help that the low is currently wrapped up in very mild air moving up the eastern seaboard as we speak. Check out a t+0 850 hPa chart and you’ll see all those horrible orange colours.  Yes it gets much colder as it moves through the Greenland region but our starting position isn’t great. 

In terms of the GFS 2m temps & dewpoint projections - personally I’d urge significant caution with those in the medium range. They’re far more useful when forecasting within 48 hours. I suspect they’re a bit sketchy in the longer term. 

[Dancerwithwings]

Just out of interest the para GFS that supposedly is coming into play in the forthcoming new year is showing the biggest black hole anomaly I've ever seen 

[booferking]

P30 get that system south east as quickly as possible and elongated then it increases are margins for snaw.

[Frosty.]

I actually found the end of the GEFS 12z mean to give a rather misleading impression, sure there is a scattering of mild members but there are more in the way of colder options for sure!...anyway, that’s the lowest of low res and there’s plenty of wintry potential ( excitement ) in the pipeline during the next few weeks..and hopefully well beyond!    

 

Edited December 22, 2020 by Jon Snow

[Jeremy Shockey]

ECM 12z ensemble mean

Op was not an outlier.  Still not bad , plenty to excited about

[Scott Ingham]

5 minutes ago, Catacol said:

People are getting frustrated by comments like this, but it is important to keep feet on the ground and there is validity to this view. Whatever occurs over the weekend and into the start of next week is going to be marginal away from high ground. Now - this isn’t to say that marginal cannot develop into something special. I’ve lived through a marginal event many years ago that turned into much less than marginal and gave a big dump of snow - but that’s once in a lifetime. Conditions next week are not ideal (yet) for the blizzard many of us would love to see. If you get lucky next week then grin from ear to ear, make a chain of snow angels and count your lucky stars - but it won’t get away from the fact that this early turn to cold is not going to create ice days immediately.

I am getting more and more confident that conditions will turn genuinely cold, but it will be a slow process. The trough in situ would appear to be staying with us for the foreseeable, and while it is possible that the gfs NE solution might come to pass and pull colder conditions in more quickly it is equally possible that we might sit under a stagnant trough and live with on/off marginality out to the New Year and beyond. However.....and it’s a big However - renewed blocking from a significant +EAMT is looking likely in the longer term, meaning stronger heights and a bigger easterly draw. Add downwelling impacts from a split SSW and the direction of travel at the moment is only in one direction. Cool becoming cold becoming colder.

So - sit tight. Ride your luck next week and fingers crossed some folk get some snow, even if wet and relatively temporary. But be aware that this is just the beginning...........

Amazing post.

Im an agreement next week is just a starter.

Its only going to get progressively colder as first the EAMT kicks in and then the SSW starts and is the validity behind a sustained period of below average temperatures that could create that top 10 winter 

[fromey]

30 minutes ago, feb1991blizzard said:

Its not, its 2m Dew points.

Bloody google translate!!  

[Mike Poole]

ECM mean v GEFS mean:

ECM mean seeing a bit more uncertainty but the positioning is good.  I’m struck on both by the lack of anything vortexy anywhere near us!

[Zak M]

Evening all, I just saw a snapshot of the UKV on Twitter - chance of sleet/snow for inland parts of EA on Christmas Eve if this was to come off:

Also, there's some pretty interesting feature on the day 10 ECM chart for eastern Europe - a sudden cold pool develops out of nowhere. Does this feature have a specific name?

   

Edited December 22, 2020 by Zak M

[Tim Bland]

7 minutes ago, Dancerwithwings said:

Just out of interest the para GFS that supposedly is coming into play in the forthcoming new year is showing the biggest black hole anomaly I've ever seen 

It’s a great run! A lot of snow and even the south coast gets in on the action!

[MATTWOLVES 3]

ECM mean not bad,and the ens follow suite...im not sure i can take much more of this....Will it won't it....to me to you scenario..The chuckle brothers would be proud of this...RIP... I think I'm gonna stick my head through a wall just to unwind..

[Mucka]

After Snowkings wonderfully informative post it seems though that some people may have misinterpreted it that 850's aren't that important when they are the most important initial indicator when attempting to gauge snowfall possibilities days out, not only  because most of the other important factors in marginal conditions can only be accurately gauged much nearer the time, often on the day, but because they show the initial expected starting point for cold air aloft. 

What Snowking was saying is that different conditions need to be taken account of as to how much that air will be modified down to the surface and eloquently pointing out some of those variables including those that will likely exist in our expected set up late Dec which will mean the 850 temp values may not need to be as low as traditionally expected from a NW flow.

So for newbies taking the -5 850hpa value is still a nice basic guide for other setups along with the concise info snowking gave before learning about all the other factors that contribute as to whether you will see rain, sleet or snow on the day and remember even in present day professional forecasters can be caught out on the day. 

[stodge]

Evening all

On and on and on we go, where it stops, no one knows - well, presumably the destruction of the planet might cause the PV some disruption but that's a shade drastic. As a work colleague reminded me today , midsummer is only 6 months away so that's winter done with (apparently). 

Back to the here and now and a very mild day in downtown East London but the output last night suggested a colder evolution for the post-Christmas period through to New Year after which confusion reigned supreme. Let's see if tonight's output provides any clarity - I suspect not.

12Z GEM: - the LP which develops over Iceland starts sinking toward the British Isles and by T+120 is a significant feature just off the north west of Scotland. The last of any less cold air is being chased out of south-east England as the colder uppers move down.  By T+180, the LP has slipped further south and east to be centred over northern France and on its northern flank a NNE'ly flow has set up dragging in -4 850s widely across the British Isles. The mid-Atlantic HP remains in situ with a new LP developing to the north of Iceland. By T+240 this has developed into a complex feature and moved a little south but the Atlantic HP has thrown a ridge across southern Britain and the airflow is now coming off the Atlantic but heights remain over Greenland and LP dominates the Mediterranean so the longer-term evolution not clear. It's become less cold by this time for most but whether this is just a temporary state remains to be seen.

 

12Z GFS OP - a slightly underwhelming GEM with a 4 day cold spell. Let's see where GFS OP takes us. As it has been the last few days, it's more progressive than GEM at T+120 and makes more of the polar heights to the far NE. The LP is directly over the British Isles with -4 850s spreading in though as nothing compared to the -20 850s over northern Finland. By T+180 it's not too far removed from GEM with the LP in the North Sea, heights to the NW and a cold NNE'ly across the British Isles. The new trough developing off east Greenland is more pronounced. The cold airmass over the British Isles is more pronounced. The LP develops further and it's almost a rinse-and-repeat as it sinks south and by T+240 it's right over the British Isles with strong heights to the north-west. For those who follow 850s, still below zero though I'd expect a warm sector of sorts with the second LP as well. The Greenland heights help push the jet well to the south of the British Isles. The next Atlantic troughs phases with the trough over the British isles and the new LP runs to the south along the Channel at T+312 (yes, I know). Heights are -4 in southern counties at that time so you'd be thinking snow, wouldn't you off a Channel low in January? At the far edge of FI, a lobe of the PV sets up directly to the north of the British isles and that does enough to re-align the trough positively and bring back milder air but it continues very unsettled with a lot of rain.

12Z ECM - well, the GFS run was wonderful for the most part for cold fans and there's certainly plenty going on. As for ECM, will it be the belle of the ball or a party pooper? Let's see. By T+120, the LP is, if anything, slightly deeper than either GEM or GFS OP so plenty of rain and snow in the circulation you'd think by Sunday. 850s not terrible inspiring in contrast to the cold air for Christmas Eve and Christmas Day. By T+192 it's all looking a bit messy - the LP came south and has returned north to sit over NE Scotland but with the British Isles still very much in its circulation but not as cold an airmass as both GEM and GFS at this time. By T+240, a new LP from Greenland has started to move SE having phased into the initial trough.  It is pulling in a colder airmass and if it slips down across the British isles you'd think it would keep things cold.

Looking elsewhere, as I like to, 12Z Control ends with the PV over the Pole and a weak ridge across southern Britain after an extended colder period. The GFS 12Z OP splits the PV at 10 HPA once again which continues to be a positive even though not all the GEFS achieve quite as dramatic an outcome.

Conclusion: - lots to be positive for cold fans tonight. The GEM evolution is a shade underwhelming but both GFS and ECM extend the cold out to at least 5 days if not more. The question now is longevity as much as severity. We aren't as yet looking at -20 uppers and a storm force E'ly but the longer we stay on the cold side of the trough the greater the prospect for a colder airmass and there was an excellent contribution from @Kentspur yesterday evening as to how 850s are a long way from the whole story. I'd be surprised if the GFS and ECM evolutions didn't produce widespread snow for many to greet 2021. As always, it's going to be one for the lamp-post watchers and those with altitude are going to have the best prospects but the initial cool-down on Christmas Eve and Christmas Day is going to help in the medium term.   

 

[jules216]

34 minutes ago, booferking said:

If your talking about Germany and that particular run from ecm your right to be frustrated as your not even in -4 category your bathing in +2 to +4 for the majority of it, while uk sits in the coldest uppers the whole run so understand your frustration nightmare run for @jules216 also.

i have given up on trying to put my point across.Ever since november I have been mentioning here tíme and tíme again to look east as well not only NAO/AO "fetish" This winter has proven me right 100%.Appart from north of Scandinavia and Alps above 1000m there has Been no Snow in any major European Capital. EC 12Z run is perhaps the best example of blocking with very little cold- poor pattern to the east. 

[northwestsnow]

9 minutes ago, Mike Poole said:

ECM mean v GEFS mean:

ECM mean seeing a bit more uncertainty but the positioning is good.  I’m struck on both by the lack of anything vortexy anywhere near us!

GEFS much more palatable, I'm looking SE wards in particular   

[Allseasons-Si]

Evening everyone,had lots to read up and catch up on in here

Firstly i would just like to thank @snowking for pulling out a right ol Christmas cracker of a post,what a great detailed explanation,it learnt me a thing or two,i bet his notifications have been plonking away like a pinball machine and he will have another one after this post lol,but i bet he loves it with all the reactions he's got,197

secondly i would like to welcome back @Severe Siberian icy blast and i am glad that you have pulled through a tough time

now onto the models:-

as Ed said( @chionomaniac),that ECM run looks a little suspect like a lost dog without a bone but on the face of it,it looks quackers

still a nice NH pattern overall  though with plenty of amplification

Oh! and did anyone check this mornings gfs/p out!...

heights in the right place,troughs undercutting,cold "UPPERS" all through the run,massive black hole anomaly over Greenland,...now that's a bobby dazzler.

 

 

[Griff]

11 minutes ago, Tim Bland said:

It’s a great run! A lot of snow and even the south coast gets in on the action!

Apparently it acquitted itself well last week with precipitation totals for the North East USA snow storm...