Model Output Discussion - Into the new year

[Penrith Snow]

Just now, Battleground Snow said:

Yes agreed, I remember Matt H showing a graph, which had hardly any precipitation spikes on for the north for this week, and look how many features have popped up at short notice

Absolutely, look how snowy this week is turning out to be after all the fuss about poor uppers and GFS precipitation charts, I haven't seen a flake but many areas have had at least one fall and some parts of the west Midlands and North West have had two 4cms + snowfalls in two days and right down to sea level.

As many on here pointed out last week, get the cold in first and snow will follow and its not all about the uppers!

Andy

[Methuselah]

Not a bad run that -- a good ten days' coldish and at times quite wintry weather, dominated by mostly E/NE winds... But I'm always interested in the fag-end of the run, which always seems to produce either a stonking Northerly (nearly) or a potential barbecue special , or sometimes, both...

    

I'd like to imagine a kind of half-way house, in which umpteen depressions follow each other along the English Channel...? Failing that, the ability to 'pull the plug' for ten seconds, and press [restart]!

 

[kold weather]

5 minutes ago, XtremeUKWeather said:

Wow , are the Arome ensembles public ?

Only two sets of runs, you can see them here:

WWW.METEOCIEL.FR

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Meteociel propose de manière régulière les différents scénarios du modèle à maille fine AROME 0.025x0.025° (2.8km) de Météo-France sur la France, la Belgique, le Luxembourg, les Pays-Bas et la Suisse

 

[Spah1]

59 minutes ago, chionomaniac said:

Here is the wetter view of the UKMO with the next 24 hours suggested. And I don’t think it too far west either.

 

Furthermore, any effects that we are looking for from a SSW is the dramatic fall of trop jet stream to aid blocking. But look already, without the SSW even occurred and downwelled we see 100hPa zonal u winds at the upper trop showing almost record low values forecast. We can’t get much lower than that!

This has to be one of the most amazing mean u wind charts ever seen before an SSW!

The question is then, do we want a SSW considering the set up we have at the moment.

[DogToffee]

6 minutes ago, Mike Poole said:

I disagree, we don’t need the pattern massively changed - we need the trop vortex to remain disturbed until we can home grow or import some proper cold, and that looks set to happen now, with the SSW when it happens part of the evolution.  

End of the GEM, not bad:

All this chat about the probable SSW, and the apparent assumption that it will make cold here even more likely, makes me wonder what the chance is of it spoiling a good cold pattern rather than helping it?

[Frosty.]

I don’t care what anyone says, compared to the absolute mild crap coldies have endured for the last few / several years..this from the GEFS 12z mean is really quite something..it’s making me feel all emotional!!  

 

[tight isobar]

2 minutes ago, kold weather said:

Only two sets of runs, you can see them here:

WWW.METEOCIEL.FR

---

Meteociel propose de manière régulière les différents scénarios du modèle à maille fine AROME 0.025x0.025° (2.8km) de Météo-France sur la France, la Belgique, le Luxembourg, les Pays-Bas et la Suisse

 

The variation between outs on northern extent is ...@VAST. As well as intensity.. I’m walking away from this 1 until tomorrow!!!

[Mike Poole]

4 minutes ago, DogToffee said:

All this chat about the probable SSW, and the apparent assumption that it will make cold here even more likely, makes me wonder what the chance is of it spoiling a good cold pattern rather than helping it?

That has certainly happened with past events.  Thing is all SSWs are not the same, and if the most likely outcome is a split strat vortex (seems to be, what the models are saying) rather than a displacement, and given the mess the trop vortex is in, my thoughts are that it will help a sequence of events that is already in train, re the weather in the troposphere.  

Edited December 29, 2020 by Mike Poole

[kold weather]

3 minutes ago, DogToffee said:

All this chat about the probable SSW, and the apparent assumption that it will make cold here even more likely, makes me wonder what the chance is of it spoiling a good cold pattern rather than helping it?

It could well do so.

However if its a genuine and strong SSW then there will probably multiple attempts at northern ridging over a 30-45 day period.

So what it may end up doing is allowing cold air to flood to our NE even if it means for a week the pattern reverts to something much less interesting.

[kold weather]

So looking at the GFS ensembles later, quite a few are making an attempt to push milder air into the country from the south between 192-216hrs.

Broadly speaking the slower the HP is to move towards Greenland the colder they remain for longer at least at 850hpa.

More progressive and faster runs (and also more northerly) runs bring in a snow-rain event around that timeframe.

So it MAY be better to actually have a slower moving less aggressive upper high at least to start with, which prevents the risk of everything shooting up too fast and not getting the cold air down before we shift into a more classic west based -ve NAO pattern.

[Mike Poole]

Just now, kold weather said:

So looking at the GFS ensembles later, quite a few are making an attempt to push milder air into the country from the south between 192-216hrs.

Broadly speaking the slower the HP is to move towards Greenland the colder they remain for longer at least at 850hpa.

More progressive and faster runs (and also more northerly) runs bring in a snow-rain event around that timeframe.

So it MAY be better to actually have a slower moving less aggressive upper high at least to start with, which prevents the risk of everything shooting up too fast and not getting the cold air down before we shift into a more classic west based -ve NAO pattern.

Yes, I think that is why I was particularly keen on the GEM run.  Rewards, but little risk.  

[sebastiaan1973]

1 hour ago, chionomaniac said:

Sebastiaan. See my post above. Damage to trop is already occurring. It is like you are looking up for a bomb to explode when in reality it has already blown up behind you.....

Yes, but will the impact be there for a long time as by a SSW with European Blocking

[Met4Cast]

A few of the GEFS do bring some precip up into the London area tomorrow/tomorrow night with a few showing something more significant, but the majority have very little to none, so I don't think the mean precipitation charts are telling the whole story. 

[kold weather]

5 minutes ago, Met4Cast said:

A few of the GEFS do bring some precip up into the London area tomorrow/tomorrow night with a few showing something more significant, but the majority have very little to none, so I don't think the mean precipitation charts are telling the whole story. 

Yeah its not going to be a huge event for London unless some of the more extreme solutions were right, and eyeballing most of the ensembles London/M4 is more or less the cut off for the heavier precip in a lot of the runs. There are some that go considerably further north and a few of those runs end up actually being rain further south.

Generally speaking the higher the resolution, the more south their outcomes tend to be.

Given the location of the low is probably just entering their domain of higher resolution its probably time to start putting more weight into them and the more southerly route.

However what the ensembles do show is there is still a *range* of solutions, that it isn't quite clear cut despite decent OP agreement.

 

Edited December 29, 2020 by kold weather

[sheikhy]

3 minutes ago, Met4Cast said:

A few of the GEFS do bring some precip up into the London area tomorrow/tomorrow night with a few showing something more significant, but the majority have very little to none, so I don't think the mean precipitation charts are telling the whole story. 

I think we really are pinning our hopes on this one!!maybe kent might get something out of this but thats about it!!again i hope im wrong!!!i would love to see it smash into wales and give snow more widely!!!

[BlueHedgehog074]

16 minutes ago, kold weather said:

It could well do so.

However if its a genuine and strong SSW then there will probably multiple attempts at northern ridging over a 30-45 day period.

So what it may end up doing is allowing cold air to flood to our NE even if it means for a week the pattern reverts to something much less interesting.

In a way, wouldn’t be surprised should we get a week or two of less cold or milder weather conditions, that we see the pattern reverting more to something supportive of cold and wintry weather again, just like what the models show for the next few days or so. 

What’s been amusing is that we have had two very deep upper Lows drop down over us this month from the North-West. Not something I would say is common at all during Winter. In fact, quite rare I would imagine.

Fingers crossed that the Low tomorrow will just about go far enough North to give many of you in the South or South-East a white treat. No doubt with the models still seemingly unsure of the actual track, then nowcasting will play a part. Would be great to have some of you cold weather enthusiasts further South and East join some of the wintry fun some of us have had further North and West ️

Edited December 29, 2020 by DiagonalRedLine
Typo

[Notty]

46 minutes ago, Penrith Snow said:

Anyone know where I can view historical 850mb temperature charts for the UK?

A link would be great 

Thanks

Andy

http://old.wetterzentrale.de/archive/ra/1982/Rrea00119820108.gif

Just change the year and date. Incidentally this was the best snow of my life.

[feb1991blizzard]

P2 is the '63 redux and then some on top' run. Longest fetch Northerly in history.    Signed A.S Tonker.

 

Edited December 29, 2020 by feb1991blizzard

[Paul]

Trying again, posted the wrong animation first time round. The Netwx-SR (3km) has the prec a bit further north tomorrow/Thurs for southern parts, it also brings a decent area of rain/sleet/snow in across northern England into Thurs.

[Mike Poole]

3 minutes ago, feb1991blizzard said:

P2 is the '63 redux and then some on top' run. 

That is insane!  

[Decemberof2010]

Just had a quick scan of the GEFS. Some serious cold dropping down from the north on some. Here’s a few snapshots

 

[Tim Bland]

12z ensembles still with huge scatter after 5th and op was on the colder side of the pack...

[nick sussex]

Regarding any SSW and its impact . This has been researched and suggests these are correlated with the base state of the AO at onset . So if that’s positive a higher impact and that lessens as you move towards a negative AO which seems quite logical .

 

[Mike Poole]

Just now, Tim Bland said:

12z ensembles still with huge scatter after 5th and op was on the colder side of the pack...

I presume from that, the ones that shoot into positive territory are the ones seeing a west-based -NAO.  Not very many, but would like it to be zero!

[Scott Ingham]

8 minutes ago, Paul said:

Trying again, posted the wrong animation first time round. The Netwx-SR (3km) has the prec a bit further north tomorrow/Thurs for southern parts, it also brings a decent area of rain/sleet/snow in across northern England into Thurs.

Looks a lot less marginal than the met forecast would have you believe with a snow line around 400 metres for the north thursday