Model Output Discussion - Into the new year

[Met4Cast]

The 6th January seems to be the point in which divergence begins within the ensembles. Some members taking things much milder whilst others remain on the colder side. This is mainly because models are trying to resolve exactly where the block is likely to be.

The milder runs blow the low up as it approaches the UK and thus it makes further inroads into the UK, whereas the colder ensembles are keeping this low shallower and more "slidey".

Until models resolve this, anything beyond January 6th is going to wildly differ between runs.

[SMU]

Good Afternoon -

The GFS was never known as a 'high top' model - Its strat resolution was not in the same league as say Gloesea etc, this means even after upgrades at best its resolution through all the layers is course-  With that come lack of clarity & distorted blobs of energy. > 
 

If we examine the past week or so where we morph into a QTR type unusual position models like the GFS / NAVGEM / ICON all become eratic, performance drops & accuracy deteriorates quickly after say 120 - those random blobs of energy suddenly become super mild outcomes or super snowstorms ( hence the comment on the 12z GFS yesterday being fit for the scrapper ) 

If we then load on the usual GFS weakness around split energy in terms of distribution of flows then we quickly remind ourselves of the reasons why it becomes very erratic.

Case in point GFS 00z 27/12 for the 4th of Jan V todays 4th of Jan.

A clear loss of functionality....

With that in mind we should stick with the model of least volatility > Which always brings me round me to the UKMO. Its consistency is metronomic barring the odd 'slight' deviation like yesterdays 12z

If you are a follower of the GEFS ENS then as it stands todays we will get pretty much every scenario thrown at us - Thats because to balance the continual weakness in phasing out blocking we have a signal thats the exact opposite.

This will then manifest in the GEFS ENS at around 192 finding as many possible solitions as possible to remove the block & to move the atlantic East en mass, but there will still be some that despite the bias hang onto the blocking signal long enough to load up those extreme FI runs.

Taking then the UKMO at 144 today which is better than the ECM we see a strengthening of the block with a clear line of site in terms lf regrogression to Greenland & a cutting low to swing SSW through Scandi.

The most positive news also today ( again from UKMO ) less so the ECM is the toning down of the signal which filtered mediterranean air into the flow.

The UKMO makes the angle of flow a lot more acute than the ECM ( which is a gentle bend ) - with such an acute turn the mild airmass cant move North then suddenly take a left turn - so as the cold air & the overall pattern sinks back south so does the mild air

In a nutshell where should be looking next 24 - 48 hours ??

Well around 144 we want to see where that low is going to cut > its the most important trigger to the success of bringing deep cold south, my forecast would be the RED X & the yes track. Not the NO GFS track.

Also the atlantic low > Blue track watch for revisions south on this track set to enforce the easterly... 

Fingers crosses here for tomorrows snow.

 

S

 

Edited December 29, 2020 by Steve Murr

[Paul]

18 minutes ago, Mike Poole said:

According to Meteoceil, the GFS parallel has 127 layers up to 80km - which is one reason why it may have been more consistent re the SSW than the current GFS.

The V16 (which is the current parallel) also starts at around 84km up (current one starts at 55km), which may also help the modelling of the strat and subsequently the upper atmosphere.

Loads of info here:

GFSv16 Official Evaluation

WWW.EMC.NCEP.NOAA.GOV

 

[Hullsnow87]

Guys calm down most winters we would love to see charts like we have now within the reliable time frame. The models will chop and change as there is a lot going on in the strat etc lots just enjoy the ride this is like no winter for the last 10 years, let’s see where we go from here hopefully cold and snowy but we shall see if a few days.

[Stu_London]

23 minutes ago, Steve Murr said:

 

Fingers crosses here for tomorrows snow.

 

S

 

Horrible feeling it's all ending up in the channel - hopefully 12z runs will stop the southerly march

[mountsbaysnow]

5 minutes ago, Stu_London said:

Horrible feeling it's all ending up in the channel - hopefully 12z runs will stop the southerly march

Would that benefit the southerner tho?

 

[MATTWOLVES 3]

Plenty of excitement in the 6z ens folks..looks like quite an upgrade from Exeter in the short term also...mentions snow risks spreading North from the Continent...one to keep an eye on for sure things could get a tad spicy...come onnnn.

 

[saintkip]

15 minutes ago, mountsbaysnow said:

Would that benefit the southerner tho?

 

If you live in Jersey 

[Biggin]

1 hour ago, Met4Cast said:

Turns out this explanation was "dribble on a page" and I had somewhat misunderstood. 

The GFS DOES take every layer of it's forecast into account, however resolution & fewer vertical layers in the model compared with others can give it limited accuracy on modelling tropospheric impacts from SSW's, particularly at the lead times we're currently dealing with. 

ECM/GLOSEA often have a better handle on things.

GLOSEA5 certainly has more levels than GFS

"The vertical resolution, like that of GloSea4, is 85 levels for the atmosphere and 75 levels for the ocean."

[CameronWS]

Some runs yesterday showed the coldest air from the North coming down and missing to the east. Would this potentially be a good/safe thing with a SSW on the way as it decreases the chances of a West-based Nao?

Also, would a West-based Nao affect the potential impacts of the SSW?

 

Apologies if this is all wrong, just trying to learn a bit here as a rookie!

[Ashme]

Can someone tell me or point me in the right direction for info on ssw and qtr? 

When do we know if we're going to have a qtr? Are the models pocking it up now, hence the wobbles in the models?

[Paul_1978]

11 minutes ago, Ashme said:

Can someone tell me or point me in the right direction for info on ssw and qtr? 

When do we know if we're going to have a qtr? Are the models pocking it up now, hence the wobbles in the models?

The Strat thread: https://www.netweather.tv/forum/topic/94538-stratosphere-and-polar-vortex-watch-2020

 

[Battleground Snow]

16 minutes ago, CameronWS said:

Some runs yesterday showed the coldest air from the North coming down and missing to the east. Would this potentially be a good/safe thing with a SSW on the way as it decreases the chances of a West-based Nao?

Also, would a West-based Nao affect the potential impacts of the SSW?

 

Apologies if this is all wrong, just trying to learn a bit here as a rookie!

Potentially, a strong SSW that downwells quickly might push the blocking too far west if it's already in Greenland, but it could also push the blocking over Russia to scandi and link up with Greenland, which may"lock-in"  colder patterns, probably best to PM one of the many knowledgeable strat members for a more detailed breakdown as lots of other factors come into play 

[bluearmy]

12z icon takes tomorrow’s system through n france !

[Battleground Snow]

Icon already vastly better here at 96 v 102 06z run, 

@Steve Murr thanks for the posts over the years showing how small changes in the early timeframe can alter FI. your post earlier was great 

 

 

Edited December 29, 2020 by Battleground Snow

[DEYS(Kent)]

8 minutes ago, bluearmy said:

12z icon takes tomorrow’s system through n france !

Standard, Blue...Standard..

[Scandinavian High.]

8 minutes ago, bluearmy said:

12z icon takes tomorrow’s system through n france !

Do you think that’s a done deal are any more adjustments north.

[Battleground Snow]

The improvement continues at 144,

Decent Easterly feed with colder uppers.

Good start the 12z suites (for cold lovers)

 

[sheikhy]

1 minute ago, Scandinavian High. said:

Do you think that’s a done deal are any more adjustments north.

Done deal in my opinion!!barr a miracle!!!those ridiculous amount by ecm yesterday seem to be over done!!!!

[winterof79]

Thursday mornings snow on its way down the country.

[Scott Ingham]

Well looking through all the high res models i think its increasingly looking likely tomorrows snow is a bust!

[Howie]

2 minutes ago, Scott Ingham said:

Well looking through all the high res models i think its increasingly looking likely tomorrows snow is a bust!

Damn

[Malcolm Edwards]

1 minute ago, Scott Ingham said:

Well looking through all the high res models i think its increasingly looking likely tomorrows snow is a bust!

I'm not terribly gened up on model reading but does this mean rain is more likely? 

 

[Drifter]

22 minutes ago, bluearmy said:

12z icon takes tomorrow’s system through n france !

I’ve always wondered why the Met Office seem to be 12/24 hours behind the curve on these kind of things versus a bunch of enthusiasts on a weather forum. 

We’re all pretty certain now that the snow is heading through the channel, yet they’re pumping out severe weather warnings
 

p.s I hope I’m made to eat my words by 6” of snow falling. 

Edited December 29, 2020 by Drifter

[sheikhy]

If 12z gfs shows the same as 06z up to 192 hours i will be happy!!but i think it will probably show the high closer to the uk and and more energy going over the top!!!still will look good but maybe like the gfs 06 para!!hope im wrong!!