Model Output Discussion - cold spell to end Autumn

[fromey]

Just now, Man With Beard said:

Michael's tweet in no way contradicts my take on the means:

When there is a large anomoly on a mean chart, it is very useful. It could indicate an even more extreme median, since any outlier ensemble members closer to the norm will take the edge off the anomaly

When anomalies are small, it is less useful as ensembles could be clustering more tightly, or there could be a large split either way.

I’ve just posted that in the strat thread, could you explain what it means and the implications 

 

cheers

[bobbydog]

9 minutes ago, RAIN RAIN RAIN said:

Examples and steps are lower than winter first ... So I think there is a chance to have another goal during the month. Gefs and Eps are updating the stratosphere related to the second part of November 3 and good ideas from Wave 1 are rising briefly in the next few days. This underscores weakened weaknesses and causes stratosphere near Alaska. These include sunflower model and red polar. At the same time, we have a large hole in the North Pacific Ocean and north of the North Atlantic to prepare. Miracles of miraculous use are the finest appearance found in late September and October (ie restoration) and slow movement (second sign, big sign). It is important to look at the amount of cold fever that can be shattered in the northwest.

(Translated from North Korean)

[Man With Beard]

1 minute ago, fromey said:

I’ve just posted that in the strat thread, could you explain what it means and the implications 

 

cheers

With regards to Michael's tweet, I am absolutely not the best person to answer this but I guess it means the normal volatile cold, stormy weather associated with northern latitudes in winter getting pushed further south??

[weirpig]

I think people are turning mad in this thread.  Anyway  Met still seem to be pushing the colder regime next week infact its quite a update with snow and heavy mentioned in the same sentence.   hopefully over the next day or so we will start to see some agreement with this evolution within the various models.  Much better than last year already   and its still only Autumn.

[Frosty.]

Although later on Friday and especially this weekend will see a weak warm front from the northwest introducing slightly milder air brushing around the top of atlantic high pressure and down across the uk, it looks like we will see another cold / arctic plunge / meridional flow returning during next week as was shown on the Gfs 00z / 6z...with snow showers, frosty / icy nights and high windchill factor..Fingers crossed!

[knocker]

17 minutes ago, Man With Beard said:

Michael's tweet in no way contradicts my take on the means:

When there is a large anomoly on a mean chart, it is very useful. It could indicate an even more extreme median, since any outlier ensemble members closer to the norm will take the edge off the anomaly

When anomalies are small, it is less useful as ensembles could be clustering more tightly, or there could be a large split either way.

Quite but that in no way contradicts my main point on all of this which is that the means, clusters, teleconnections, the Strat and the retrograde orbit of Mars are all tools in the box and if used correctly and in context are all useful in attempting to unravel the complexities of the atmosphere. .Definitive and categorical statements about any one of the these along the lines of. "as much use as a choc olate fireguard", have no place in a scientific forum

Edited November 29, 2017 by knocker

[fromey]

6 minutes ago, Frosty. said:

Although later on Friday and especially this weekend will see a weak warm front from the northwest introducing slightly milder air brushing around the top of atlantic high pressure and down across the uk, it looks like we will see another cold / arctic plunge / meridional flow returning during next week as was shown on the Gfs 00z / 6z...with snow showers, frosty / icy nights and high windchill factor..Fingers crossed!

Which model does this go with???

[knocker]

13 minutes ago, fromey said:

I’ve just posted that in the strat thread, could you explain what it means and the implications 

 

cheers

I assume he is saying that this could plunge arctic air south in cold troughs in similar fashion to the one illustrated over eastern North America in other areas such as north west Europe.

[Luke Best]

23 minutes ago, Cloud 10 said:

 

The GFS op and control run are run at a higher resolution than the other GEFS members,so in theory they should verify better.

I don't believe that this is correct.

As I understand it, the op is run at a high resolution and the control at a lower resolution.

The 'GEFS members' are run with slightly adjusted starting data (and also at a lower resolution).

[weirpig]

3 minutes ago, Luke Best said:

I don't believe that this is correct.

As I understand it, the op is run at a high resolution and the control at a lower resolution.

The 'GEFS members' are run with slightly adjusted starting data (and also at a lower resolution).

yep as follows

Operational run = high resolution model, no change to initial conditions

Control run = as operational model but a lower resolution model (i.e. less horizontal and vertical grid points)

Ensemble runs = the lower resolution model (same as control run) but with small changes to initial condtions

 

[russell k]

7 minutes ago, fromey said:

Which model does this go with???

Probably the 12z suite, which we don't see until 3.30

Maybe the pros see it roll out at the time it is run??

[mountain shadow]

15 minutes ago, Frosty. said:

Although later on Friday and especially this weekend will see a weak warm front from the northwest introducing slightly milder air brushing around the top of atlantic high pressure and down across the uk, it looks like we will see another cold / arctic plunge / meridional flow returning during next week as was shown on the Gfs 00z / 6z...with snow showers, frosty / icy nights and high windchill factor..Fingers crossed!

Given the UK is roughly only 250 miles wide it doesn't take much for us to miss out.

Another crucial set of runs beckon.

[Gavin Hannah]

1 minute ago, russell k said:

Probably the 12z suite, which we don't see until 3.30

Maybe the pros see it roll out at the time it is run??

I believe they do see as it rolls out. We will see if it is the12Z in a couple of hours.

[Gavin Hannah]

1 minute ago, mountain shadow said:

Given the UK is roughly only 250 miles wide it doesn't take much for us to miss out.

Another crucial set of runs beckon.

This is why we should tow the UK 100 miles further north and nudge it east a tad.

[comet]

I think most posters on here know where our weather is heading from the middle of next week and that is into the freezer. It could be for quite some time as well.

should be an excellent afternoon and evenings model watching.

[winterof79]

11 minutes ago, fromey said:

Which model does this go with???

UKMO168 Chart previously posted hinted at this

[Summer Sun]

7 minutes ago, russell k said:

Probably the 12z suite, which we don't see until 3.30

Maybe the pros see it roll out at the time it is run??

To avoid any confusion that image Frosty posted is from yesterday's weekly forecast from the beeb it is not based on model data from today

Edited November 29, 2017 by Summer Sun

[russell k]

5 minutes ago, Summer Sun said:

To avoid any confusion that image Frosty posted is from yesterday's weekly forecast from the beeb it is not based on model data from today

Seems a bit selective nevertheless to delete my post!

 

[Frosty.]

10 minutes ago, mountain shadow said:

Given the UK is roughly only 250 miles wide it doesn't take much for us to miss out.

Another crucial set of runs beckon.

Well it's just a snapshot of what could happen but I do think another cold plunge will return next week similar to earlier Gfs and which has just been reinforced by the latest update from Exeter which is going for cold / blocked pattern with increasingly snow showers, frosts and ice..lovely jubbly!☺???

[Tamara]

 

This slow/stationary orbit underpins the modelling over the coming days in terms of the very big signal for a very amplified holding Atlantic ridge - and certainly favouring a cold pattern sustaining into the medium term as the vacuum occurring upstream slams on the brakes with  jet flow rapidly decelerating

 In terms of the stratospheric feedbacks though, the question mark in my mind is the extended hints of the Pacific pattern starting to show the first signs that La Nina is going to tighten its control from upstream with the building of the Alaskan ridge. On that basis a highly anticipated two week stratospheric forecast is just that, and on the basis of potential upstream changes that ultimately spell return of the jet, it cannot be wholly assumed it will automatically favour this side of the pole as the Pacific pattern starts to take control.

So I don't personally agree with some of the views being expressed that this is a "good thing" for downstream prospects in terms of sustaining a cold weather pattern beyond the early to (possibly?) mid December period. Its a typical La Nina development that often happens as wavelength cycles occur with the change of month and season and has the effect of increasing Canadian cold and re-booting the energy into the downstream polar jet. Such inications are minority model solutions at the moment that show increased upstream flow in FI, but I think its not a case that they are automatically wrong, simply maybe on the progressive side.

And I would be highly cautious of 100% confident assumptions then return energy will automatically split and encourage trough disruption under the Atlantic ridge

On that basis I'm not sure that any equal assumption (however valid) can be made that the present amplified pattern has a sustainable feedback. Or at least not sustainable without a further eastwards moving MJO catalyst, to engineer further tropics>extra tropical rossby wave train and set up further downstream amplification via +ve MT and then, just as importantly in turn externally pressurise the polar stratosphere.

Even the freeze of 2010 ended on the basis that no follow up occurred to the high amplitude MJO event of October and that led to the rapid taking of control of the default La Nina Pacific ridge and return of polar jet flow after Christmas

So the La Nina default will not favour any undercut of -NAO automatically. The upcoming pattern is a traditional (extra amplified) mid latitude ridge pattern. 

The stratospheric pathway can certainly override the tropospheric winter La Nina effects

------------------------------------------------------------------------------------------------------------------------------

 

Highlighted extracts from last weeks post simply intended as helpful to assist continuity of analysis of progress.  

The thoughts expressed regarding the current and nearer term amplified pattern still hold very true in terms of increasing likelihood of tendency, with time, of the amplified Atlantic pattern to come under pressure from the polar jet. This, as part of the advancement of the advertising of developing an Alaskan ridge in modelling as consistent with seasonal La Nina, and as discussed in the highlighted post and again as part of some latest very interesting discussion on the current thread.

We have seen in various winters where low angular momentum patterns are evident, that there is something of a juxtaposition of the persistence of the La Nina Atlantic/Azores ridge with height rises to the NE as the winter progresses. In this sense its true that how the stratospheric pathway plays out in the coming weeks will have quite a bearing how the Atlantic pattern duels with any developing cold pool to the NE. 

If La Nina consolidates to any greater extent then attempted rises in atmospheric angular momentum tendency are logically supressed. As a consequence, this implies a dearth of +ve torque forcing c/o poleward rossby wave development from tropics to extra tropics and then to polar stratosphere via +MT to develop the Eurasian cold equation as a means of cold air advection from the NE.

In such circumstances, with the vortex more organised this side of the pole, the outcome would favour the Pacific/Atlantic ridge combination and too much overriding polar jet energy to enable sufficient trough disruption of lows heading downstream and in turn allowing height rises from the NE to ride over and cut off low heights to the south.   If La Nina forcing is too strong then this favours increased strength to the sub tropical Azores ridge which would override too weak any -AO signal.

On the other hand, especially if MJO propagation can be strong enough to propagate eastwards to influence the Pacific (not helped by seasonal wavelength cycle changes) and induce sufficient westerly wind inertia to keep the lid on La Nina easterlies that bolster the Pacific and also the Atlantic/Azores mid latitude ridge, then the polar stratospheric pathway is enhanced and the Eurasian heights signal could be bolstered in such a way to provide some deeper cold air advection south westwards with time.

In this sense a restricted or preferably waning La Nina signal would imply only a small amount of polar jet - but just enough to enable the classic horseshoe orbit to carve out an extension of the Eurasian cold anticyclone into Scandinavia with the reverse jet flow looping around the High and advecting cold air south-westwards across the North Sea.

All a very way off, but I think that the nearer December time modelling period in both the troposphere and the stratosphere is highly relevant in starting to shape up the crossroads options of the main winter season patterns one way or the other 

 

 

[bluearmy]

25 minutes ago, Luke Best said:

I don't believe that this is correct.

As I understand it, the op is run at a high resolution and the control at a lower resolution.

The 'GEFS members' are run with slightly adjusted starting data (and also at a lower resolution).

The control runs at the same res throughout - the other 19 members drop resolution after T192. The op is high res till day 10 and lower thereafter - I have a funny feeling it drops to the same level as the control at that point 

[Paul]

10 minutes ago, russell k said:

Seems a bit selective nevertheless to delete my post!

 

Your post hasn't been deleted. 

 

[Dacyfo]

25 minutes ago, bluearmy said:

The control runs at the same res throughout - the other 19 members drop resolution after T192. The op is high res till day 10 and lower thereafter - I have a funny feeling it drops to the same level as the control at that point 

This may seem a daft question (I'm still but a novice at this) but why aren't all members just run at high Resolution.

[Nick L]

3 minutes ago, Dacyfo said:

This may seem a daft question (I'm still but a novice at this) but why aren't all members just run at high Resolution.

I suspect due to the huge amount of computing power required to do so.

[ACCOUNT DELETED]

Latest CFS model brings the high pressure over southern & central UK next week stopping the cold returning and instead bringing milder weather across the whole of the UK & Ireland. 

All a case of wait and see, although it's very likely the weather will turn less cold this weekend but we lose the sunshine and wintry showers and replace it with a lot of cloud and some patchy rain from weak weather fronts.