Model Output Discussion - cold spell to end Autumn

[nick sussex]

Just now, chris55 said:

  Is it cause or effect?

Can a shortwave 3000 miles away really have that much influence alone on the downstream pattern?? Or does the longwave synoptic forcing allow such features to grow and develop?

 

Both are of course connected however if you look at the outputs this evening the main key features haven't changed within T144hrs, as in the longwave pattern is similar to this morning but amongst that these small features can play a role.

Take for example the spoiler shortwave this morning.  Lorenzs original view of the butterfly effect, yes one effects the other but the initial small change can manifest itself into bigger changes down the line.

 

 

[tight isobar]

Incidently..-GEM- 

has v-similar synoptics to ecm 12z...

Azores influence' mild south/south-westerlys(of sort)..

@latter frames.

Edit:

Just to add not to say this will be the pattern of fruition..

Just a comparable suite!!!

Edited November 28, 2017 by tight isobar

[Summer Sun]

Looking further north temperatures in Greenland will be over 20c above average for a time later this week before a rapid fall next week

[bobbydog]

32 minutes ago, nick sussex said:

Heres the aforementioned subject of my irritation:

This stops better ridging into Greenland, it also then puts on its shades and relaxes in its sun lounger waiting to complicate the phasing action of the upstream lows one over the ne USA and the other further upstream.

The damn thing is still sitting there at T168hrs!

 

 

you seem to have a shortwave obsession nick...

[feb1991blizzard]

10 minutes ago, nick sussex said:

Both are of course connected however if you look at the outputs this evening the main key features haven't changed within T144hrs, as in the longwave pattern is similar to this morning but amongst that these small features can play a role.

Take for example the spoiler shortwave this morning.  Lorenzs original view of the butterfly effect, yes one effects the other but the initial small change can manifest itself into bigger changes down the line.

 

 

Nick I think the shortwave spoilers occur because the longwave pattern isn't conducive, so the shortwaves will then appear at the wrong time / take the wrong track to deliver UK cold, I think all the pro's say this anyway, that the longwave pattern drives the shortwave pattern, however, please don't change your analytical style as its brilliant - its the best and simplest way to read the charts and understand what needs to happen to deliver UK setups that deliver cold IMO.

Edited November 28, 2017 by feb1991blizzard

[LRD]

5 minutes ago, Summer Sun said:

Looking further north temperatures in Greenland will be over 20c above average for a time later this week before a rapid fall next week

Yes, Nuuk, Rekyavik and Oslo are the ensembles to look at but more for pressure trends. Obviously, for those locations, the higher the better

[knocker]

When thinking of last night's anomalies this isn't a million miles away. and the 850mb  contours and anomaly

[nick sussex]

Just now, feb1991blizzard said:

Nick I think the shortwave spoilers occur because the longwave pattern isn't conducive, so the shortwaves will then appear at the wrong time / take the wrong track to deliver UK cold, I think all the pro's say this anyway, that the longwave pattern drives the shortwave pattern, however, please don't change your analytical style as its brilliant - its the best and simples way to read the charts and understand what needs to happen to deliver UK setups that deliver cold IMO.

Thanks , yes of course without a good longwave pattern you’ve got no chance but here we’re talking of a tiny difference in terms of angle upstream within T144 hrs . 

The longwave patterns of the big 3 are very close , so we can see here at T144hrs hrs that the butterfly might be playing a role .

This mornings spoiler shortwave highlights how sensitive the evolution is.

I think I’m going to coin a new term Longwave Sensitivity.

 

[LRD]

10 minutes ago, feb1991blizzard said:

Nick I think the shortwave spoilers occur because the longwave pattern isn't conducive, so the shortwaves will then appear at the wrong time / take the wrong track to deliver UK cold, I think all the pro's say this anyway, that the longwave pattern drives the shortwave pattern, however, please don't change your analytical style as its brilliant - its the best and simplest way to read the charts and understand what needs to happen to deliver UK setups that deliver cold IMO.

Agreed. Nick's analysis is still really valuable because we may not truly know what the atmosphere is set up to do (despite clues like QBO, solar activity, etc) until we look at and understand the smaller stuff... and then observe the reality.

Edited November 28, 2017 by LRD

[LRD]

6 minutes ago, FiftyShadesofWine said:

Not forgetting the well noted point by Recretos of the gefs bias for reversal of zonal winds until nearer the time, hence some over the top fantasy island GFS forecast charts....A reversal is I doubt about to come to fruition, hence the Mets mid December change to a mobile pattern...Maybe....

 

 

Nice first post. Yes, the Met Office and, therefore presumably GLOSEA, are clearly seeing a stratospheric driver to enable mobility by mid December. What I would say, though, is that the predicted period of mobiity seems to be getting every so gradually pushed further back...

[Derecho]

Evening, here is my interpretation of the 12z GFS, ECM and UKMO.

Only interpretations up to T240 are made.

So we can breathe a sigh of relief that ECM is backing off from developing that shortwave! (I hope). At T144 we have all the big 3 looking well placed to send some WAA to the NW North Atlantic. SLP over Greenland is already shooting up at this point which would be useful if that occurs.

GFS                                                         UKMO                                                      ECM

What happens from here is really difficult to pin down at this point but its likely a strong Greenland High will develop, indeed we see this  from both the GFS and ECM. Though a few subtle issues can stop us from getting bitterly cold sustained northerlies:

- Further shortwaves develop later on leading to problems with the Greenland high.
- High Pressure sinks towards Spain

At T192 the GFS does sink part of the high over Spain but because the Greenland high is so strong the northerly put the high over Spain under a lot of pressure. A weaker Greenland high risks the cold air not getting far south at all but that isn't seen here.

ECM meanwhile develops a shortwave near Newfoundland that rapidly develops and causes the Greenland high to collapse… now I am a coldie but that doesn’t seem realistic.

GFS                                                          ECM

At T192 and T240 we therefore have some large differences in output again. The GFS sees the northerly eventually progress south shifting the high over Spain eastwards in the process. Snow events would be frequent in this pattern  and the GFS has a superb late run, until pressure increases to the south... but no need to worry at this point about that.

The ECM well… doesn’t warm up till T240 but by then everything falls into the worst place and the jet over N America looks set to awaken from its slumber. I just don’t see something like that happening so quickly.

GFS                                                         ECM

The most important thing is to get the building blocks in place for retrogression and that seems to be very likely now, quite a turnaround from this morning! Lets see what transpires from there.

UKMO 8/10 snowflakes – Looks primed for retrogression, shame later frames can’t be seen
GFS     8.5/10 snowflakes – Gets towards a great setup in the end, great run!
ECM   5/10 snowflakes – We get a period of cold weather but urgh… the ending looks grim.
 

[nick sussex]

9 minutes ago, LRD said:

Agreed. Nick's analysis is still really valuable because we may not truly know what the long wave pattern is (despite clues like QBO, solar activity, etc) until we look at and understand the smaller stuff... and then observe the reality.

Thanks. The longwave gives us the bigger picture but as we know in the UK it’s often at the periphery of the cold , small changes have often bigger effects .

When we see for example a Scandi trough and high to the west the big picture doesn’t show whether the UK had a direct hit of cold or whether it’s too far east.

Globally a few hundred miles isn’t much in terms of the longwave pattern but has huge effects on the weather on the ground for the UK.

Edited November 28, 2017 by nick sussex

[LRD]

5 minutes ago, nick sussex said:

Thanks. The longwave gives us the bigger picture but as we know in the UK it’s often at the periphery of the cold , small changes have often bigger effects .

When we see for example a Scandi trough and high to the west the big picture doesn’t show whether the UK had a direct hit of cold or whether it’s too far east.

Globally a few hundred miles isn’t much in terms of the longwave pattern but has huge effects on the weather on the ground for the UK.

Agreed. I suppose if the amosphere is particularly well primed to help UK cold then the marginality can be taken out of it and it's comfortable to get the cold in as it seemed to be during the period from Feb 09 to Mar 13. Today, the atmosphere is obviously in a state where it's more knife edge for the UK, making your analysis even more valuable 

Edited November 28, 2017 by LRD

[mountain shadow]

38 minutes ago, LRD said:

Exactly what I was thinking Chris. It's not really a case of the shortwaves destroying anything. It would be the general long wave pattern that allows those 'little' lows to break through or over ride northern blocking. 

I don't think we have proper Northerly blocking though, only ridges. There is no Greenland upper high, without that, the jet pushes through and flattens the pattern.

It's the same problem most Winters as progged decent Northerlies become blink and you'll miss it affairs.

[Methuselah]

38 minutes ago, bobbydog said:

you seem to have a shortwave obsession nick...

He takes after the queen mum.

[Frosty.]

Following the increasingly cold showery spell from the north this working week with night frosts and icy patches, the weekend becomes less cold / milder and fairly benign from the west but then the GEFS 12z mean indicates another cold plunge from the arctic gradually spreading south as we go through next week with a return of wintry ppn , frosts and ice with a good chance of snow for some of us, especially further north...so, potential for early December cold this evening.

Edited November 28, 2017 by Frosty.

[LRD]

1 minute ago, mountain shadow said:

I don't think we have proper Northerly blocking though, only ridges. There is no Greenland upper high, without that, the jet pushes through and flattens the pattern.

It's the same problem most Winters as progged decent Northerlies become blink and you'll miss it affairs.

Indeed. That's because the long wave pattern obviously isn't quite right. It might be selective memory playing tricks but I'm sure those colder periods between 2009 and 2013 were seen by the models and then didn't really wobble much. Because the atmopshere was in a particular state during those years. This year it's obviously more ambiguous so the models are struggling a bit more

[snowbunting]

Can someone  please tell me what is meant by shortwave and longwave is met terms?

 

I must say the GFS looks awesome. Very potent Nly. Wonder which model will prove right next week.  Part of me thinks the ECM as the GFS would cause havoc in the NW. 

[Northwest NI]

2 minutes ago, snowbunting said:

Can someone  please tell me what is meant by shortwave and longwave is met terms?

 

I must say the GFS looks awesome. Very potent Nly. Wonder which model will prove right next week.  Part of me thinks the ECM as the GFS would cause havoc in the NW. 

I’ll happily take the havoc ?

[Penrith Snow]

1 hour ago, LRD said:

Exactly what I was thinking Chris. It's not really a case of the shortwaves destroying anything. It would be the general long wave pattern that allows those 'little' lows to break through or over ride northern blocking. In cold winters those areas of low pressure still exist but the overall pattern is more conducive to cold so they don't mess anything up. So, if things aren't properly set up then the shortwave pattern will be allowed to develop in a way that kicks northern blocking into touch. However, to be fair, we will only know if the pattern was ever conducive by observing the behaviour of the shortwave synoptics and seeing the reality unravel! Sfort of chicken and egg but it's the long wave atmopsheric pattern that's the true driver

First class post well said.

Its the long wave dog that says the short wave rail not the other way round.

The obsession some people have with short wave behaviour is daft, its the long wave pattern that magtsds.

Andy I 

[blizzard81]

Ecm ext ens showing an upward trend in temps as we approach mid Dec along with increased precipitation. In line with meto thoughts. A sobering prospect. 

[knocker]

looking just at the GEFS 8-13 anomaly this evening, to my rather simplistic mind the uncertainties going forward still revolve around how the downstream reacts to the amplification increase over North America This was evident with last night's anomalies and is still there  Essentially the structure of the Atlantic ridge and the orientation of the trough to the east  With the gefs we still have the split flow and no obvious route to tap into any sustainable cold.with positive anomalies and ridging into southern Greenland. Actually looking at this evening's NOAA is not a straight comparison obviously but taking in both charts we are I think in the same ball park as  the GEFS. Helps if I post the correct chart

Edited November 28, 2017 by knocker

[northwestsnow]

2 minutes ago, blizzard81 said:

Ecm ext ens showing an upward trend in temps as we approach mid Dec along with increased precipitation. In line with meto thoughts. A sobering prospect. 

Im not concerning myself with mid Dec ...im not convinced the models have next week sorted yet...:)

[Paul_1978]

5 minutes ago, blizzard81 said:

Ecm ext ens showing an upward trend in temps as we approach mid Dec along with increased precipitation. In line with meto thoughts. A sobering prospect. 

Are you allowed to post graphs of that?

[feb1991blizzard]

 

 

5 minutes ago, blizzard81 said:

Ecm ext ens showing an upward trend in temps as we approach mid Dec along with increased precipitation. In line with meto thoughts. A sobering prospect. 

So after 240, the ridge never gets any higher / more defined than the 240 mean?