Model Output Discussion - Christmas and New Year

[Djdazzle]

Not going to get drawn into these short term snow discussions - it will be different again on the next runs.

Looking to see whether the 18z GFS goes down the easterly route.

 

[kold weather]

7 minutes ago, danm said:

Ah this old chestnut again. Hear it every winter (apparent SE bias). 
 

One thing I’ve learned over the years is that the track will continually change and end up becoming a nowcasting event. We’ll get an envelope of possible tracks, within a few hundred miles, and it won’t be firmed up until 12-18 hours beforehand, but even then things will change. 

Its interesting to see the models shift north it has to be said, it probably only happens on the models 1/2 out of 10, but the models are coming towards agreement so that does strengthen the case that this is what will now happen, and it was within the range of possibilities that both the ECM/GFS ensembles had in their respective suites even yesterday.

However it is also true there is time for it to shift around further.

Edited December 26, 2020 by kold weather

[Mike Poole]

7 minutes ago, Kasim Awan said:

M4 north with gfs 18z. Model consistency equillibrium pretty much hit. Amounts varing with precip longevity latitude & elevation. 

I don’t know what it is with the M4!  On GFS I’m sure it is just a row of grid points...but on 10/12/17 it was absolutely the snow/rain divider, fortunately I was on the right side and got 5 inches of snow, but 10 miles south....just rain.  

[kold weather]

2 minutes ago, Mike Poole said:

I don’t know what it is with the M4!  On GFS I’m sure it is just a row of grid points...but on 10/12/17 it was absolutely the snow/rain divider, fortunately I was on the right side and got 5 inches of snow, but 10 miles south....just rain.  

Interestingly I'm a decent way south of the M4 yet also got snow on that event, I was quite surprised as well, though not in the same quantities mind you! I do have a modest elevation mind you thanks to the downs.

I suspect 28th may well be a wintry slop down my way if it comes off as planned, but the downs maybe worthy a little trip being reasonably local (thus not breaking rules lol!) 

 

[Kasim Awan]

2 minutes ago, Mike Poole said:

I don’t know what it is with the M4!  On GFS I’m sure it is just a row of grid points...but on 10/12/17 it was absolutely the snow/rain divider, fortunately I was on the right side and got 5 inches of snow, but 10 miles south....just rain.  

The M4 divide is only applicable for the initial band which has a channel originated maritime layer. Pivotting will introduce an offshore breeze & change these dynamics. 

[Methuselah]

1 minute ago, danm said:

Ah this old chestnut again. Hear it every winter (apparent SE bias). 
 

One thing I’ve learned over the years is that the track will continually change and end up becoming a nowcasting event. We’ll get an envelope of possible tracks, within a few hundred miles, and it won’t be firmed up until 12-18 hours beforehand, but even then things will change. 

It's cobblers, Dan... When I first joined NW (way back in the Middle Ages) I was living in the Northwest Highlands of Scotland, and that irritating accusation of 'SE bias' irked me even then... More folk live in the southeast of England than anywhere else... Get over it, peeps!

And, will it snow? Yes... and all the usual hotspots will benefit, IMO: Scottish Highland, Southern Uplands, Pennines, Welsh mountains, Dartmoor and Exmoor, Cotswolds, Chilterns, Downs...

But, from looking at the models, Beccles will almost certainly miss out... But, give us a BFTE and we're buried! It's just the way the cookie crumbles?

[Windysun1]

Bit off topic but what is the greatest snow depth recorded in UK after a snowstorm or roughly in a 24hr period? Cheers.

[Ice Day]

At 114 and there's quite an upgrade on the 850's on the pub run vs the 12z

  

Lovely looking 120 chart

Great day's reading on here today.  As others have stated, do not get wrapped up in snow charts for Monday at this point, it will be another 24 hours until we can really narrow things down.  Some of us are going to be in luck though, of that there is no doubt!

 

[dragan]

1 minute ago, Windysun1 said:

Bit off topic but what is the greatest snow depth recorded in UK after a snowstorm or roughly in a 24hr period? Cheers.

i believe it was very deep in places 

[Snowman.]

GFS improving heights N/NE. More amplfied by Greenland too.

 

[Tim Bland]

15 minutes ago, Allseasons-si said:

The ICON in the latter stages(low res)has another feature coming down from the NE coast and running through Yorkshire and down through the the midlands then down into the SE,speculation at this stage but at least it is showing another snow event.

Oh!,and a possible channel runner too.

Good stuff, especially for this in the east who miss out on Monday. GFS also has a feature coming south albeit more marginal.

Re the M4 don’t forget this is also the rough line of the South Downs and Chilterns so on the higher ground (just north of the m4) it’s usually snow, then often rain on lower ground along / just south of M4

Edited December 26, 2020 by Tim Bland

[sheikhy]

Well well wheres the gfs goin at 138 hours!!looks an upgrade

[Battleground Snow]

GFS doing its slow creep to other models again here at 135..

[ALL ABOARD]

Huge difference 

GFS climbing towards the euro as early as 120. 

 

[TSNWK]

Much better with the heights sharper to the north and spreading east towards scandi.. should help with the topple..

[Mike Poole]

GFS pub run (what is a pub, I hear you ask) has a much better angle for the cold than the 12z, T138 compared with T144 on 12z:

[Snowman.]

GFS climbdown has begun, looking very UKMOish now.

[Weathizard]

Backtrack from the GFS, the wedge is going up, perfect Icelandic positioning as well.

Edited December 26, 2020 by Weathizard

[Allseasons-Si]

That's more like it,colder uppers,better angle of attack,could we get a closed off Atlantic ridge?

[Snowman.]

Wedge alert!

[sheikhy]

Ahhh i said i said it earlier!!!!!all the years of model watching i knew this was gona happen!!!its not just clawed back to the euros but its gone the full whack and beyond!!!!

[Weathizard]

Lol @ The GFS

This wedge is about as perfectly positioned as it can get.

 

 

[Ice Day]

Pick of the bunch now at 168!!!  GFS is full back-track mode.

  

Cut off high over Iceland 

 

[Allseasons-Si]

Just look at the difference...

18z 168 v's 12z 174

which one would you believe in?,i would say the 18z as it is more in line with the other models.

Edit:in fact,it's taking the 12z gfs/p route.

 

 

Edited December 26, 2020 by Allseasons-si
typo

[Weathizard]