Hunt For Cold: Model Discussion - Heading Into Christmas

[gottolovethisweather]

2 hours ago, nick sussex said:

This is the latest from the NCEP discussion for NY State:

The Thursday through Friday time frame continues to feature a low
confidence forecast, as model guidance showing considerable
disagreement with regards to timing and track of a potential
significant storm system approaching from the west. Main challenge
is how models are handling potential phasing of northern/southern
stream energy. It appears the ECMWF continues to be most consistent,
indicating a progressive upper level low tracking east into the
southern Appalachians by Thursday night, then phasing with a
northern stream trough on Friday inducing cyclogenesis near the
southern New England coast. The GFS and CMC are also now indicating
phasing and coastal development, although have this occurring much
earlier (Thursday night as opposed to Friday). The GFS is depicting
a more southerly track and thus lighter QPF in our area, while the
CMC has a track closer to the ECMWF (although much earlier).

Will lean towards the ECMWF due to better consistency.

What they're talking about can be seen here, the southern jet in red and northern arm in black:

 

Both these jets phase over the ne USA helping to develop the deeper low pressure shown in red below.

This is important as this effects the movement of the PV lobe, generaly in these situations as the low then phases with that it causes  a pivot action which helps to pull that lobe further to the nw. The amplification ahead of the low develops that little high in black. Ideally we want the low even more amplified than the ECM but its a start.

 

It all points to week two being a good one, as hinted at by most runs, aside from a rogue one here an there as to be expected. Before all that we at least have a day or two of Northerly influence as we hit 2019.

[Johnp]

55 minutes ago, BARRY said:

As there is a shut down of American government services has this any effect on the GFs output

I wish they would shut the GFS down for a week or two.

I think it would do a world of good for the forum's collective sanity!

[Methuselah]

Just a wee look at the GEFS T850 ensembles... 

All but one of the runs for Aberdeenshire now finish below 0C: 

And, for Northamptonshire, it's all but three: 

[Frosty.]

Now that mid January is in range of the models, I must say it's looking potentially very interesting from a cold / snow lovers perspective according to the GEFS 6z postage stamps!....I have a feeling there will be plenty of wonderful output for coldies as we go further into the new year.

[northwestsnow]

Lift - off?

Edited December 30, 2018 by northwestsnow

[seabreeze86]

1 minute ago, northwestsnow said:

Lift - off?

Beginning to look that way northwestsnow by New years day some real eye candy will be showing I think. The ECM will lead the way as your chart illustrates. The high slowly but surely edging northwards everything is in place we just await the trigger 

[Frosty.]

P7 (GEFS 6z) pretty please with a cherry on top!!!

Edited December 30, 2018 by Frosty.

[ArHu3]

1 minute ago, seabreeze86 said:

Beginning to look that way northwestsnow by New years day some real eye candy will be showing I think. The ECM will lead the way as your chart illustrates. The high slowly but surely edging northwards everything is in place we just await the trigger 

We need @Man With Beard to explain the Icelandic clusters but seems 40% continue boring, 20% Scandinavian blocking 28% Greenland blocking 12% with the block just misplaced for me in the Netherlands

 

[E17boy]

Good afternoon peeps

Hope you all are ok and having a relaxing Sunday afternoon. Can't believe it's the last day of this year tomorrow, how quickly has the year whizzed past. I was going to post yesterday but to be honest I just had a sinking feeling in my heart from all the outputs that I went away to refresh.

so here we are still search for our snow. Rather s from day here in Walthamstow today not a glimmer of the sun. I must admit from what I am seeing from today's posts looks like a glimmer of hope is beginning to show, are we on the cusp of something special. Having said this we are still in the unknown and what the weather is about to do in the coming weeks is anyone's guess. The big question mark that is making me scratch my head is what is this high going to do. It could either be our sincere saviour and help the weather deliver our goods or it could be a heartbreaker and herald a pattern that we don't want to see going further into January.

i think we have only started moving on this rollercoaster the coming week is going to be tense and at times it's going to have us at the edge. Let's just now think positively and hope everything is on our side and hold our heads up. 

On s finishing note back in Feb/March it's the ECM that led the way and the others followed persuitr can it happen s second time. We live in hope 

our search for our winter wonderland continues 

take care for now all stay safe

kind regards

[bluearmy]

26 minutes ago, northwestsnow said:

Lift - off?

Am I missing somethng NWS?  Isn’t this the ec operational from 8 hours ago ? 

[northwestsnow]

Just now, bluearmy said:

Am I missing somethng NWS?  Isn’t this the ec operational from 8 hours ago ? 

Its this mornings Blue yes

[northwestsnow]

ICON better again compared to 6z-

[Mucka]

Plenty of changes to come. This is a big difference in the ICON from 00 to 12z at just 120 hrs

Strange, it doesn't show the right image on the thumbnail until you click it.

Edited December 30, 2018 by Mucka

[ArHu3]

7 minutes ago, Mucka said:

Plenty of changes to come. This is a big difference in the ICON from 00 to 12z at just 120 hrs

That could be because of the 12h time difference 

 

Edit:you probably copied the wrong links both are from 12z

 

 

Edited December 30, 2018 by ArHu3

[damianslaw]

Models holding the high pressure firmly in place - rather a sinking high, it looks like it will stay in situ for quite some time, meaning low level cold surface air, plenty of frost, sunshine and possible freezing fog, so feeling more like winter to start 2019. 

I said yesterday GFS has a habit at sniffing out a northerly first, and the 6Z is showing one with heights advecting westwards into the mid atlantic - this is very plausible evolution, provided we maintain heights over or slightly to the north of the UK - as indicated by ECM today.

Whilst I doubt it will be a rapid trigger to an eventual much colder set up, what it will allow is for the jet to align on a more NW-SE path, bringing bouts of wind and rain, and wintry precipitation in the north (goes with the Met Office prediction), the trigger will though no doubt come from heights ridging sufficiently through the mid atlantic just when we see the PV shot to bits, heights over the Pole quickly linking hands, and the jet forced well to the south.

I won't be surprised to see the GFS 12z sink heights again, and dispel the northerly, only to serve up the 6Z scenario today in future runs, it will keep dropping the northerly idea, but then come back to it eventually and hold onto it.

Edited December 30, 2018 by damianslaw

[Mucka]

7 minutes ago, ArHu3 said:

That could be because of the 12h time difference 

 

Edit:you probably copied the wrong links both are from 12z

 

 

 

No the links are correct with correlating times and the one on the right shows 00z when you click it for me, does it show 12z for you when clicked?

Edited December 30, 2018 by Mucka

[ArHu3]

1 minute ago, Mucka said:

 

No the links are correct and the one on the right shows 00z when you click it for me, does it show 12z for you when clicked?

I see January 4th 1300 and January 5th 0100 both from today's 12z when I click on them 

[damianslaw]

40 minutes ago, Frosty. said:

P7 (GEFS 6z) pretty please with a cherry on top!!!

The above could well be the eventual pattern - but might take a slight while longer to get there -- a matter of days.. 

[steveinsussex]

2 minutes ago, ArHu3 said:

I see January 4th 1300 and January 5th 0100 both from today's 12z when I click on them 

this

[Mucka]

3 minutes ago, ArHu3 said:

I see January 4th 1300 and January 5th 0100 both from today's 12z when I click on them 

LOL that has me doubly stumped then. They both show 4th Jan 1300 for me. Must be a browser cache thing or something.

I suppose I should use the archive from 00z instead like thus.

Edited December 30, 2018 by Mucka

[Spah1]

26 minutes ago, northwestsnow said:

ICON better again compared to 6z-

Better in what way? 

I thought this ridge was just going to sit there until the proper amplification post ssw. 

[SMU]

Afternoon so 2 hours on the train should be plenty of time for a post-

The last 2 weeks the projected SSW has gradually worked through the models & is now 'imminent' ~ 30hours away is when we go negative on the zonal wind @10HPA/ 60N.

But I guess many onlookers will be wondering why the distain for the GFS V the Euros, is it really that bad.

Well sadly yes it is. The failure of the GFS is going to be 2 fold here.

1) Identity of type of SSW - Split or displacement.

2) Non propergating ENSEMBLES.

So going by the first point, this refers to a models ability to 'see' what that Stratospheric energy & warming looks like at the height of the strat, you have 'high top' models - highest being Glosea then ECM, you also have non High top - GFS which IIRC is 64km V Glosea ~80KM. IIRC ECM vertical resolution is closer to the Glosea.

The GFS being poor resolution & the ENS being even lower resolution means that the ability to resolve / locate & then split energy is much inferior to the Euro model, as a result the model will see a 'blob' of warming however wont be able to see the warming plus energy splitting, thats above its means.

So the GFS can be scored reasonable for the 'identification' of a warmer- even taking into consideration the errors in actual timings - however its score rapidly decreases if you want resolution to a Split V Displacement-

NB here is the GFS elipses about 10 days ago-

You will see the GFS ENS green & operational orange not being able to pinpoint a split - ( which the sparked masses of debate on twitter from people who should know better than to use the GFS )

If we compare this to the high top ECM, whilst similar to the GFS in timing errors the actual resolution of the SSW was pretty much bang on.

Why is this important

- What we are currently seeing is a QTR to the split as the Troposhere mirrors the stratosphere split, however why did it take days for the GFS to see the first ridge & cutting trough over Scandi- Why was it always East!????

Simple- The 'Eastward' (E) energy from the zonal wind was incorrectly modelled -

NB GFS model 'E' v ECM (E)

* remember take the Eastward component *

The poor modelling of the (E) component for about 5 days up until about Fri Eve / Sat AM drove a fairly uniform Eastward motion around our part of the globe, hence with the scandi tough there was a fairly amplitude inflection point meaning its bend & southerly element was low -GFS catapulting it Eastward-

Then slowly as the warming proergated down from 1HPA to lower 5HPA & into the GFS comfort zone so the GFS picks up the split-

We now look at todays elipses - for day 4/5

Its finally caught up 96/120 & hey presto its on the same page as the Euros now.... ( At least for the time being )

So onto point 2 - GFS propergation issues.

The modelling of the strat is generally difficult especially the coupling of a downward propergating SSW to the troposhere, so again only the highest resolved models will pick it up- it appears the GFS has coupling issues as the its ENS suites for the past 5 days have stopped it fully propergating ( again creating much speculation on here & twitter ) all again annoyingly GFS based-

Here is the NAM index which shows how the SSW is progressing with negative vales indicating propergation

NB GFS ENS 3 - 7 days ago = Non propergation. 100HPA is where we want it to reach !

Notice it stops short - So the ensemble suite from maybe Weds onwards up to around Yesterday wasnt seeing that wave come down - hence a lot of people were looking 10/12/14 days out in the ENS for high lattitude blocking when infact it was never going to appear-

Whilst the ECM had already picked up the deceleration at 100HPA for day 10 ( 26/12 ) day 1 & day 10 char

So again, ECM was already factoring in a decelerating jet - hence the operational model runs showing a maintained blocked response out to day 10 with higher & higher potential.

The GFS has cottoned on now though-

Todays ENS @100HPA show the GFS dropping nicely ( NB how poor the operational is though in orange )

Pic 1 ENS from 5 days ago flatlining the 100HPA wind V todays dropping it from 10 to around 4 M/S

The main dip comes down around the 8-10th & guess what thats why we are seeing High lattitude blocking now appearing in the GFS ENS - its not a coincidence !!!!

Now that the split is in range & the GFS is picking up on the correct outcome in terms of deceleration so the gulf between the GFS v the EUROs should reduce this week as they are working on the same stratospheric & zonal wind speed data now -But never forget how bias the GFS is in terms of powering up that jet....

Propergation is alligned to the 10th Jan - ( which is about 2-3 days later than initially progged ) 

Dates for propensity of lowest -AO values 10-20th Jan....

Cheers

S

 

 

 

 

 

 

 

Edited December 30, 2018 by Steve Murr

[The Eagle]

UKMO is not the greatest this afternoon. 

[Weather-history]

Christmas Day 12z for 5th Jan

Today's 12z for 5th Jan

[Weathizard]

ICON pretty poor, even if it is a chocolate teapot. (IMO)

 

Always look on the bright side of life do do do do.

Edited December 30, 2018 by Weathizard