Model Output Discussion - Colder but how cold and for how long?

[Midlands Ice Age]

7 hours ago, claret047 said:

I like the cold and snow, but it is not just that which enthrals me as far as the weather is concerned. Like you BFTP I like to see how the charts develop from one frame to the next and from 0Z to OZ, 06 to 06 and so on. How the change happens will be fascinating to watch.

Computer technology,  I believe,  can only go so far in determining what the weather will be like to any degree of accuracy much more than 5 days ahead. Perhaps the computers read too much information and the tiniest nuances magnify/distort the final conclusions. Perhaps MIA and other software experts may care to comment on this.

In the meantime we have about a week of cold weather in my neck of the woods with little chance of snow as things currently stand. At least the sun is out now and we have lost the North Sea clag that we have been enduring. 

Looking at the ECMClaret chart someone posted a few moments ago it looks like a very windy and possibly wet spell is in the offing. I very much hope not as that is the last thing we want!
I intend to go out this afternoon and enjoy the weather we have and not lament what we could have had, and suggest my fellow southerners do the same. Me I am watching the mighty Chelmsford City play Wealdstone inn the 4th Round of the FA Trophy. Perhaps @Ice Day and other nearby posters might wish to come along and support their local team.

Claret047 (Dave)

I hadn't forgot your query above, but waited until it was quieter to respond.  

In general more data is good news.

However, if you have more data (assuming a normal distribution)  you also introduce more 'out of range' data.

Generally models use various techniques  for handling the threat.  Within the models you can check the data against other data for the immediate locality.   (If there is one - could be difficult to apply in the Arctic or Antarctic),  and this generally is quite effective. 

Another method that was employed a few years back was by using a pre-edit stage. This will check for data being within certain ranges.

It was employed by BOM and led to complaints that some data had been omitted.

It  is quite difficult to use ranges in the world models as they have ranges of from -80c to +60c, and the same goes for pressure,  rainfall,  etc.

I do not know what method is adopted for each model.         Perhaps some else can help?

These days most data is produced automatically and normally will not have errors. When something goes wrong it is fairly easy to see.

MIA  

Edited January 13 by Midlands Ice Age

[Tamara]

6 minutes ago, Eagle Eye said:

Still a while away from the next?+VE EAMT event w/tangible results. Not in the GFS 5 day forecast yet. 

Double rise to a significant AAM rise by early February which is what Tamara was talking about w/MJO phase 5/6. That would result in tangible results by mid month. CFS has been insistent on this for the last 3 runs. General support is for a high rise GLAAM response which should be enough to re-invigorate momentum distribution in the Northern Hemisphere to displace the zonal pattern if it did happen. Winter is far from over. It's not all doom and gloom. This would be the strongest rise in a while with it moving towards a 2 S.D rise where GLAAM has spent most of my time in this forum very close to the COD. GLAAM forecasts are rarely that accurate but gloom posters are trying to invoke a response if they're saying Winter is over in January. Im not even going to bother deep diving into the potential responses when looking at the MJO propagation, clearly it's not worth it. Just kidding of course I will. 

MJO Nino Phase 6-7 response to have high latitudal blocking and combined with tropical forcing, there should be a constructive interaction signal. Wouldn't get overly confident of x+y = x again, the GLAAM will intefer with the RWT signal either favourably or unfavourably depending on the strength of the GLAAM input into the total distribution. However, a high rise GLAAM + MJO + weak vortex suggests either a wave reflection of the 6-7 state or a total Strat buster and double major SSW technically possible given the Arctic and lower Strat vortex basing of the current one meaning that it should recover well despite the slowest recovery occurring in the lower Strat, it just doesn't really do much damage the major warming though it may cut off momentum feed vertically for a bit post SSWE (appearing likely). Either way, February or maybe March if delays occur are looking good. 

Easy to lose momentum and MJO strength and the vortex can recover properly but for now general synoptics are favouring that high tropical forcing. The ENSO support for active MJO phases should probably get some work done soon otherwise we'll have been really unlucky. 

While indeed unlikely to show for 5 days based on timetable for eastward propagation of tropical forcing through Maritimes, I would add that those GFS forecasts have never been overly reliable based on a -ve tropical forcing bias that underplays +ve momentum transport.

In respect of potential impacts moving forward, the MJO forcing is better permed with the extra tropical GWO.  As @Singularitynoted, global angular momentum levels are still above parity overall during this "lull period" following the easterly inertia added c/o Indian Ocean forcing. Rapid convective suppression will follow in this area and that will be in tandem with the engagement of +ve torques as the MJO cuts through the Maritimes.

Based on existing relatively buoyant levels of AAM in the atmospheric circulation, the GWO is primed for a high amplitude Nino attractor Phase rebound.

Additionally e/QBO shear stress is likely to augment the effects of Rossby wave action on the vortex within enhanced Brewer Dobson transport between the tropical > polar stratosphere at the same time as ensure that the intraseasonal MJO wave itself, based on the periodicity of amplitude waves, does not weaken from forecasted status & via convective velocity potential indicators

For those predisposed to cold outcomes in NW Europe I still see relatively earlier in Feb rather than beyond midmonth for arrival of maximum potential impacts.

But first much to continue to monitor in respect of the next momentum uptick.

[Jeremy Shockey]

11 minutes ago, Scott Ingham said:

Tentative signs on the eps of scandi euro ridge which should in my view push into scandi when we get the movement into high amplitude western pacific phases. 
 

Very encouraging!

yes indeed Scott and would very much tie into the wording of the MetO 28th Jan - 11th Feb long range forecast where they suggest an increased likelihood of high pressure forming and winds from the north or east leading to an increased chance compared to normal of cold spells. 

[Methuselah]

2 minutes ago, Tamara said:

While indeed unlikely to show for 5 days based on timetable for eastward propagation of tropical forcing through Maritimes, I would add that those GFS forecasts have never been overly reliable based on a -ve tropical forcing bias that underplays +ve momentum transport.

In respect of potential impacts moving forward, the MJO forcing is better permed with the extra tropical GWO.  As @Singularitynoted, global angular momentum levels are still above parity overall during this "lull period" following the easterly inertia added c/o Indian Ocean forcing. Rapid convective suppression will follow in this area and that will be in tandem with the engagement of +ve torques as the MJO cuts through the Maritimes.

Based on existing relatively buoyant levels of AAM in the atmospheric circulation, the GWO is primed for a high amplitude Nino attractor Phase rebound.

Additionally e/QBO shear stress is likely to augment the effects of Rossby wave action on the vortex within enhanced Brewer Dobson transport between the tropical > polar stratosphere at the same time as ensure that the intraseasonal MJO wave itself, based on the periodicity of amplitude waves, does not weaken from forecasted status & via convective velocity potential indicators

For those predisposed to cold outcomes in NW Europe I still see relatively earlier in Feb rather than beyond midmonth for arrival of maximum potential impacts.

But first much to continue to monitor in respect of the next momentum uptick.

And if all that doesn't 'deliver', there must be something else that's coming into play. All we can do is learn. 

[Eagle Eye]

3 minutes ago, Tamara said:

While indeed unlikely to show for 5 days based on timetable for eastward propagation of tropical forcing through Maritimes, I would add that those GFS forecasts have never been overly reliable based on a -ve tropical forcing bias that underplays +ve momentum transport.

In respect of potential impacts moving forward, the MJO forcing is better permed with the extra tropical GWO.  As @Singularitynoted, global angular momentum levels are still above parity overall during this "lull period" following the easterly inertia added c/o Indian Ocean forcing. Rapid convective suppression will follow in this area and that will be in tandem with the engagement of +ve torques as the MJO cuts through the Maritimes.

Based on existing relatively buoyant levels of AAM in the atmospheric circulation, the GWO is primed for a high amplitude Nino attractor Phase rebound.

Additionally e/QBO shear stress is likely to augment the effects of Rossby wave action on the vortex within enhanced Brewer Dobson transport between the tropical > polar stratosphere at the same time as ensure that the intraseasonal MJO wave itself, based on the periodicity of amplitude waves, does not weaken from forecasted status & via convective velocity potential indicators

For those predisposed to cold outcomes in NW Europe I still see relatively earlier in Feb rather than beyond midmonth for arrival of maximum potential impacts.

But first much to continue to monitor in respect of the next momentum uptick.

Yes, I think I probably should have elaborated on the it not starting it 5 days bit. What I meant is that we aren't near seeing the response in the NWP forecast yet. It was meant to ask people to be patient. 

Agreed with all of that. Timing can be argued, I just tend to see later response times than excepted because of delays. 

[damianslaw]

Looking longer term, just hints and signs from the ECM and GFS, that as we move into latter stages of January, heights may build up from the south and either ridge into scandi, or ridge through mid atlantic bringing the atlantic to a halt - in tandem with a movement of the PV back to Siberia scrubbing low heights over Canada.. 

A week of cold blocked conditions, followed by a week of atlantic conditions and then increasingly back to blocked.. where the block sets up is unclear.. Certainly January 2024 will probably go down as a very mixed month compared to many recent ones.

Edited January 13 by damianslaw

[Mcconnor8]

ICON 18z looking slightly more North than the 12z did, should hit the South Coast again and a bit further inland too.

 

Edited January 13 by Mcconnor8

[Ali1977]

2 minutes ago, Mcconnor8 said:

ICON 18z looking slightly more North than the 12z did, should hit the South Coast again.

Nearly up to the M4

[Ali1977]

Quite a covering down south 

[Battleground Snow]

It looks a bit more ridgy in the Atlantic too

[Ali1977]

Just now, Battleground Snow said:

It looks a bit more ridgy in the Atlantic too

Much more ridgey at such a short time frame - hopefully the pub run follow suite 

[tight isobar]

5 minutes ago, Ali1977 said:

Nearly up to the M4

Safice to say- a classic under /upper maybe?!! The energy it will have gained… if she hits @ 150/200 miles on bedrock!! It’s snow chaos!! “ once again “ - this is a truly evolutionary if- but- or maybe.. keep watching

Edited January 13 by tight isobar

[Mcconnor8]

This run also has snow in the midlands as the low moves away.

[tight isobar]

4 minutes ago, Mcconnor8 said:

This run also has snow in the midlands as the low moves away.

That’s a watcher!- I had a feeling not only an inland extension.. but a bow..n, pivot under the flow….. That “would be something “!!

Edited January 13 by tight isobar

[nick sussex]

This Atlantic low has certainly caused a lot of frustration for coldies especially in the south .

It’s determined to wring every last vestige of drama out of the occasion! 

The ICON after the very progressive 00 hrs run seems to have edged the pattern a bit further west during subsequent runs .

 

 

[Tim Bland]

Certainly looking like the far south is back in the game midweek

[Met4Cast]

59 minutes ago, Mike Poole said:

I am increasingly coming to the conclusion that, regardless of what signals there are, naff all decent tends to come off!

Really? 

This week has been largely below average with blocking. High pressure is now shifting NW towards Greenland ushering in much colder air for this coming week. That’s 2 weeks of below average & blocked conditions which has been well advertised within the GSDM/teleconnections. 

Is it widespread snow? No, perhaps but, but that wasn’t really advertised or promised. What was advertised is an increased likelihood of blocking & colder weather and in fairness that’s exactly what we’ve seen. 

Teleconnections can give a broad sense of the larger patterns but will never be able to tell you if X will see snow. 

[BLAST FROM THE PAST]

 

wow.  Already we see potential changes afoot.  As I said this Atlantic influence unlikely to be a trans continental express.

BFTP

[Garthvader]

1 minute ago, BLAST FROM THE PAST said:

 

wow.  Already we see potential changes afoot.  As I said this Atlantic influence unlikely to be a trans continental express.

BFTP

The 0z runs will be quite interesting  

[Jayfromcardiff]

30 minutes ago, Ali1977 said:

Nearly up to the M4

Any chance of another 50 miles push North do you think?

[Tim Bland]

Just now, Jayfromcardiff said:

Any chance of another 50 miles push North do you think?

It’s possible … but so Is a shift south again

[BLAST FROM THE PAST]

1 minute ago, Garthvader said:

The 0z runs will be quite interesting  

RE the LP coming from SW yes!   Maybe not that soon for beyond….but looking forward to midweek!!

 

BFTP 

2 minutes ago, Jayfromcardiff said:

Any chance of another 50 miles push North do you think?

No.  Caerphilly like the Gobi Desert…sorry

BFTP

[steveinsussex]

6 minutes ago, Jayfromcardiff said:

Any chance of another 50 miles push North do you think?

I’d say more likely to trend south again 

[Tim Bland]

Here’s another view of icon for midweek. Gets above m4 in the east and covers London and Essex up to beds and just scraping south cambs ..

Edited January 13 by Tim Bland

[BLAST FROM THE PAST]

deep cold, make no bones about that. No short term down grade

 BFTP