Model Output Discussion - Into the new year

[DanDorsetUK]

Great Tweets from Marco Petagna just now. Regarding SSW. And Glosea 

[moochops]

2 minutes ago, Faronstream said:

I mean for really wintry wise conditions, not about what you need for snowfall.

You mean how cold do the 850s need to be to get the deepest/best convection?  The lowers the better

[Kasim Awan]

Just now, MJB said:

Agreed , we are fixated with -10's and below for some reason

I don't agree 100% with the easterly = lower upper requirements, in a moderate easterly wind there will be maritime layer & you will need good uppers. Fronts / inversions (inland) are different.

[Stu_London]

2 minutes ago, Weathizard said:

When the wind direction is East 850’s don’t even need to be -5 to deliver widespread snowfall, in fact some of the biggest snow events in recorded history have been with uppers that are only just below freezing, air sourced from the east means it’s drier, lower dewpoints and less modification.

Not every easterly is a beast however. Longevity, uppers, size and shape of high all are factors. 1986, 1991 and 2018, the only true beasts in the last 35 years, in my opinion. 

[winterof79]

Death by snow if you like breakdowns

[That ECM]

Anyone questioning cold will find it hard to argue with these.

377DF0E8-0996-42D6-A287-B056FEA4AB99.webp A040064F-1CB1-4611-B584-A5CB0C7D45CC.webp

[kold weather]

1 minute ago, MJB said:

Agreed , we are fixated with -10's and below for some reason

Depends on he EXACT wind direction, ENE typically need lower than -5c because the water temperatures tend to warm up the surface flow somewhat and this makes things increasingly marginal the warmer the air is in the lower atmosphere to begin with. Of course the colder the SSTs the less modification there is, but also tends to lead to weaker precipitation.

Now if you can get more of an ESE then typically the air travels less time over water and typically will be colder at the surface, therefore you get away with having higher temperatures at 850hpa, in exceptional circumstance over snow fields right upto 0c in theory.

[MJB]

1 minute ago, Kasim Awan said:

I don't agree 100% with the easterly = lower upper requirements, in a moderate easterly wind there will be maritime layer & you will need good uppers. Fronts / inversions (inland) are different.

As Weathizard says -5 will even do the job , yes of course -45 would be brilliant but we have had cracking falls of snow , below the -10 mark

[radiohead]

8 minutes ago, Penrith Snow said:

Just out of interest how cold does it have to be before we can call an easterly a BFTE, daft question I know but surely some of the output today would be borderline at least?

From my own memory, once uppers of -7/-8 sweep in then the showers popping up off the coast will usually turn to snow. That's the BFTE "feel".

But with very intense frontal precipitation like the storm on the GFS around Day 10 you can get snow with uppers just barely below freezing. 

 

 

[rug]

8 minutes ago, weathertoski said:

Dartmoor anyone?

On my way!

[MATTWOLVES 3]

5 minutes ago, Rapodo said:

Great Tweets from Marco Petagna just now. Regarding SSW. And Glosea 

It looks like significant warming in the strat above North Pole.. fairly strong signal for it to be a major event also...thats the Marco thoughts currently....wow thats music to my ears,just that little bit if luck,and we could be staring down the barrel of something very note worthy.

Edited December 27, 2020 by MATTWOLVES

[Mucka]

Of 30 GFS 12z ensemble members and the Op not one shows anything like this mornings GFS 00z Op.

[iceman1991]

5 minutes ago, Rapodo said:

Great Tweets from Marco Petagna just now. Regarding SSW. And Glosea 

What they saying Rapodo ? 

[Battleground Snow]

This showing on the para for the 4th of Jan too.

I'll let the more knowledgeable than me decide if this will split or not

 

[MJB]

2 minutes ago, kold weather said:

Depends on he EXACT wind direction, ENE typically need lower than -5c because the water temperatures tend to warm up the surface flow somewhat and this makes things increasingly marginal the warmer the air is in the lower atmosphere to begin with. Of course the colder the SSTs the less modification there is, but also tends to lead to weaker precipitation.

Now if you can get more of an ESE then typically the air travels less time over water and typically will be colder at the surface, therefore you get away with having higher temperatures at 850hpa, in exceptional circumstance over snow fields right upto 0c in theory.

Yes indeed , well explained 

[Ali1977]

Day 9 mean from the ENS, WOW a GFS ZERO to HERO episode today  
 

HUGE UPGRADE for coldies, if ECM follows this will be awesome 

[Scott Ingham]

It all seems to good to be true what we are watching.

BUT. 

Its literally bang on time for a rise in AAM

The vortex is displaced to the siberian side which is forecast

It matches the mean charts to the letter 

It matches the EPS weeklies

It seems crazy to say but it was forecastable 10 days ago when you chuck all these factors together so in my opinion its realistic.

Now off and back for a very important ecm!

[Fozfoster]

10 minutes ago, Allseasons-si said:

WOW WOW WOW!!!

look at the mean so far

186

       

BANK.............BOOOOOMM...........WTF..........

[Battleground Snow]

1 minute ago, Ali1977 said:

Day 9 mean from the ENS, WOW a GFS ZERO to HERO episode today  
 

HUGE UPGRADE for coldies, if ECM follows this will be awesome 

Tbf it looks alot like the EPS from this morning.

[kold weather]

Just now, Scott Ingham said:

It all seems to good to be true what we are watching.

BUT. 

Its literally bang on time for a rise in AAM

The vortex is displaced to the siberian side which is forecast

It matches the mean charts to the letter 

It matches the EPS weeklies

It seems crazy to say but it was forecastable 10 days ago when you chuck all these factors together so in my opinion its realistic.

Now off and back for a very important ecm!

Yeah I was surprised yesterday when the models totally backed off, these runs have somewhat moved back to where the base background factors would suggest we should be.

I'm always very wary when I see models flip flop around with drastically different solutions, in my experience it doesn't tend to bode well. However you are right that this time there are alot of factors out there which auger well for our current cold spell to intensify further.

Could end up becoming the longest cold spell since Mar 2013.

[Met4Cast]

GEM broadly similar to the 12z GFS, if a little messy..

HUGE upgrade on the GEFS mean too, cannot wait to see the entire ensemble suite, I suspect there will be a few very cold runs in there. 12z plays out pretty much how I'm expecting, albeit on a slightly faster timescale.

Brief relax of the pattern early January (albeit staying blocked in this case) before a resurgence of heights into the 2nd week as the +EAMT event kicks into action. Cold > getting colder > into the freezer. 

That's before any potential SSW..

[Anthony Burden]

Continuation of some very wintery conditions,GFS returns to some sanity with strong blocking 

to the west/northwest/ north/northeast.Playing with the idea of low pressure pushing up

from the south all of course in fantasy island.Colder and colder is the theme snow in the short

term.

[Scott Ingham]

1 minute ago, Met4Cast said:

GEM broadly similar to the 12z GFS, if a little messy..

HUGE upgrade on the GEFS mean too, cannot wait to see the entire ensemble suite, I suspect there will be a few very cold runs in there. 12z plays out pretty much how I'm expecting, albeit on a slightly faster timescale.

Brief relax of the pattern early January (albeit staying blocked in this case) before a resurgence of heights into the 2nd week as the +EAMT event kicks into action. Cold > getting colder > into the freezer. 

That's before any potential SSW..

Really tremendous potential.

Its been the most enjoyable month tp forecast and watch as different bits of the jigsaw come together.

You were right with the initial placement of high level blocking

[Weathizard]

Let’s be careful, fantastic GFS 12z but DO NOT go and tell your families snow and cold is coming  

The way that 4 runs in a row have been so significantly different suggests we should be very careful, those height rises around Iceland are notoriously troublesome. 
 

When I woke up this morning and saw the laughable difference between the 0z and last nights 18z I said to be very wary with the GFS and I’d stand by that for now until we see some consistency.

[Valleyboy]

15 minutes ago, weathertoski said:

Dartmoor anyone?

That’s a big snow event for southern and southwestern England and South Wales.  Depending on speed of low and whether the low stalls, you can be looking at snow depths any where between 15cm and 40cm.