Model Output Discussion - Stormy Period Inbound...

[IDO]

You can see from the GEFS at T96 that the Atlantic trigger low has numerous possible outcomes, though the GEM track has now been dismissed:

 

 

So difficult to draw any conclusions till that has been resolved IMO.

Edited January 13, 2015 by i'm dreaming of...

[Kentspur]

Well in reliable timeframe upto T144 its GEM,ECM,UKMO v GFS.Was it the GEM that first showed an Easterly 2/3 days ago before any other models??Would love that GEM to verify at 168 but too far out in FI!!

You beat me to it I remember looking at this forum hearing all bar the GEM had westerlies or at best NWly Could GEM be the new GFS?

And btw great profile name

;-)

Edited January 13, 2015 by Kentspur

[Mucka]

The GFS mean at 72 is slightly more amplified that the 06z.

 

http://modeles.meteociel.fr/modeles/gens/runs/2015011312/gensnh-21-1-72.png

 

In terms of a cold snap from T72- 144 we are more or less home & dry, post that not quite yet.

 

Even the 12z GFS however had solid cold for 5 days....

 

S

 

Yes and we can see where the areas of uncertainty are from the spread with firstly the way energy is modelled to cross the Atlantic and secondly with how it disrupts at Southern tip of Greenland.

 

 

The pattern is not made or broke by the shortwave running SE prior to the ridge as has been suggested by one or two.

Edited January 13, 2015 by Mucka

[IDO]

The control, like the op sends the trigger Low towards N Africa where as in the 06z runs it went to the Bay of Biscay, thus linking up with low heights in the med. We lose that wave of lower heights that help prop up the easterly (later in the run) and this also effects the phasing of the Azores High preventing the Atlantic to slide:

 

06z    12z

 

About 33% of the GEFS send the low to the Bay of Biscay still at T120.

Edited January 13, 2015 by i'm dreaming of...

[Cheshire Freeze]

Yes and we can see where the areas of uncertainty are from the spread with firstly the way energy is modelled to cross the Atlantic and secondly with how it disrupts at Southern tip of Greenland.

 

 

The bad news is the control follows the op....144 hrs...

 

 

As IDO has pointed out, that little SW feature is actually quite important to us.

Edited January 13, 2015 by CreweCold

[ItNeverSnowsInWindsor]

Surely the GFS must be wrong, the PV is raging over Greenland by day 9.....I hope the ECM doesn't follow it as this place will be very depressing if so. GEFS will be eagerly awaited.  The GEM looks good to T108.

Its times like these when it is good to have the METO on board (a little)

This is why the more experienced posters have advised to take the output as far as T120 with a pinch of salt until they come inside T72. Time and time again folk will end up getting disappointed like this.

[Barry12]

GFS day 6 mean looks better

 

[Mucka]

More support among the ensembles for the Op than I would of liked out to 120/144 including the control than I would of liked but plenty of colder runs too forming.

I think p3 sums the uncertainty up really.

 

 

Pick the bones out of that.

[Mucka]

The bad news is the control follows the op....144 hrs...

 

 

As IDO has pointed out, that little SW feature is actually quite important to us.

 

It actually isn't IMO, the upstream flow is much more important.

Tell me what needs to happen with that shortwave to get the proper disruption behind any ridge and I will prove otherwise within the ensembles.

 

Edit

To be clear.

I'm not saying it can't help or hinder or is not a trigger for the ridge behind but small deviations in its track and strength are less important than the upstream

Edited January 13, 2015 by Mucka

[Cheshire Freeze]

It actually isn't IMO, the upstream flow is much more important.

Tell me what needs to happen with that shortwave to get the proper disruption behind any ridge and I will prove otherwise within the ensembles.

 

Well perhaps the positioning of that SW is directly interlinked with the upstream shenanigans; however every run I've seen which places that SW further N goes on to produce a better run in terms of cold thereafter.

[warrenb]

I think what has happened with the GFS and sometimes does I have noticed, is that it looses the signal quite early goes flabby then defaults.

[polar vortex]

I see the Met have forecast a colder week next week with an increasing risk of snow and severe frosts.

They certainly did not see that coming. looking cold to very cold next week and I think we have the 

stratosphere warming to thank for this. Looking forward to the ECM it should be a good one.

[SMU]

Remember shallow features drifting south in the very slack flow with bitter surface temps is a recipe for snow.!!!

 

As expected the GFS ensembles are a mess, the control + 7 + 13 poor. The rest all go varying ways generally pointing towards cold & risk of snow....

 

If you find the bias page the GFS 12z has the biggest eastward bias of all the runs over the atlantic- keep that in mind.

 

PTB is probably one of the best

http://www.meteociel.fr/modeles/gefs_cartes.php?ech=6&code=17&mode=0&carte=1
S
 

[warrenb]

Remember shallow features drifting south in the very slack flow with bitter surface temps is a recipe for snow.!!!

 

As expected the GFS ensembles are a mess, the control + 7 + 13 poor. The rest all go varying ways generally pointing towards cold & risk of snow....

 

If you find the bias page the GFS 12z has the biggest eastward bias of all the runs over the atlantic- keep that in mind.

 

PTB is probably one of the best

http://www.meteociel.fr/modeles/gefs_cartes.php?ech=6&code=17&mode=0&carte=1

S

 

Funnily enough if you look at PTB 17 and the Meto (0z run) at 144 they are almost the same

Edited January 13, 2015 by warrenb

[IDO]

It actually isn't IMO, the upstream flow is much more important.

Tell me what needs to happen with that shortwave to get the proper disruption behind any ridge and I will prove otherwise within the ensembles.

 

Edit

To be clear.

I'm not saying it can't help or hinder or is not a trigger for the ridge behind but small deviations in its track and strength are less important than the upstream

 

I have posted every GEFS that sent the trigger low to the Bay of Biscay or further N, rather than Africa. These are D8 charts:

 

 

 

 

Remember GEM also held it further North as did UKMO. Could just be a coincidence, but any lower heights interacting with the Scandi trough and attracting lower heights from the Atlantic has to be a plus?

[MR EXTREMES]

Remember shallow features drifting south in the very slack flow with bitter surface temps is a recipe for snow.!!!

 

As expected the GFS ensembles are a mess, the control + 7 + 13 poor. The rest all go varying ways generally pointing towards cold & risk of snow....

 

If you find the bias page the GFS 12z has the biggest eastward bias of all the runs over the atlantic- keep that in mind.

 

PTB is probably one of the best

http://www.meteociel.fr/modeles/gefs_cartes.php?ech=6&code=17&mode=0&carte=1

S

 

steve honestly from what ive seen its all a toppler ok we get 5 days of cold but have you seen the later timeframes omg awful 

although if we get any snow down here i be happy but after lastnights runs and this mornings then this evenings are just a downgrade and i wonder how many more are coming     

[mushymanrob]

That is why we have ensembles and other models to cross reference with to determine probability of outcome mushy.

We will have a better idea once the ensembles are out but certainly a prolonged cold spell is very much in the balance.

 

well viewing this chart

 

i wouldnt have thought it supports an easterly as depicted by the gfsp

 

so maybe its the gfsp thats incorrect and the gfs12z op is nearer the mark.

[Ali1977]

Are we getting a GFS P today?

[Mucka]

Well perhaps the positioning of that SW is directly interlinked with the upstream shenanigans; however every run I've seen which places that SW further N goes on to produce a better run in terms of cold thereafter.

 

We could end up splitting hairs here but you would have to give me a time-frame, 96h?

Once it is South of the UK and heading South it has negligible effect, before that it can help enhance the ridge which may or may not aid disruption depending on other forcing such as upstream or even downstream with how the trough develops to our NE which is is more important IMO. If the trough is further West we will get better amplification, especially if it is more vigorous over the UK. If it is weaker and further East the whole pattern will be shunted East and there will be less amplification.

 

Flick through ensembles and do comparisons, I honestly think you will find more consistency of outcome in how the trough behaves and how the upstream pattern behaves than the shortwave.

Of course every ensemble member will be different due to all manner of subtle changes early on and the shortwave is just one of these which after it serves its primary purpose for us) is relatively trivial in the grand scheme of things.

 

We can just beg to differ though since we both want the same outcome but if you want to continue the discussion we can have it in PM as it could be a long one. 

[knocker]

Another little feature that formed north of Scotland in the flow around the main depression on Saturday may be of interest in the north.

Chart courtesy weathebell.

Edited January 13, 2015 by knocker

[Mucka]

I have posted every GEFS that sent the trigger low to the Bay of Biscay or further N, rather than Africa. These are D8 charts:

 

gens-18-1-192.pnggens-16-1-192.pnggens-12-1-192.png

 

gens-11-1-192.pnggens-10-1-192.pnggens-9-1-192.png

 

gens-8-1-192.png

 

Remember GEM also held it further North as did UKMO. Could just be a coincidence, but any lower heights interacting with the Scandi trough and attracting lower heights from the Atlantic has to be a plus?

 

They all look very different? Not sure I get your point. 

Are you still referring to the shortwave/low?

You would need to look at a much earlier time-frame as there so many other developments that impact upon the pattern before day 8.

Happy to discuss it further in PM though. 

[gottolovethisweather]

Personally, whether one thinks the general trend is an upgrade or downgrade, in reality I don't believe we're any further forward knowing the FI outcome than during this time yesterday, see link below for my reasoning.

 

https://forum.netweather.tv/topic/82208-model-output-discussion-stormy-period-inbound/?p=3113748

 

I draw your eyes to my first sentence in the aforementioned post and I seriously believe that any surface synoptic predictions made beyond this weekend's SW/Low Pressure feature (currently forecast anywhere from Southern England to SW Spain) will be futile. Our best guidance will come from the professionals and/or anything that one may be able to decipher from the ensembles past this Sunday, for instance. FI still likely to reside at t+108 hours or thereabouts, simply look for scatter in the perturbations for clarification on this. 

 

With all that said, it is simply could still be a case as to where we were this time yesterday regarding the cold in FI which is something to treasure if you are of that cold-loving persuasion. The here and now in the Southern and South Western section of the UK we are witnessing increasing snowfalls coming off a Westerly flow packing -6/-7 850s, that in itself is very very unusual, I would suggest. 

 

Off to lamp-post watch now and maybe a beverage or two. 

Edited January 13, 2015 by gottolovethisweather

[SE Blizzards]

The bad news is the control follows the op....144 hrs...

 

 

As IDO has pointed out, that little SW feature is actually quite important to us.

 

 

I really hope the GFS is just having a 'wobble' CC.

 

The ENS in FI don't look great i'm afraid. A long way off from what they were Showing this morning that's for sure.

 

Come on ECM, throw out a belter for us cold/snow staved fans, PLEASE!!

Edited January 13, 2015 by SE Blizzards

[johnholmes]

well viewing this chart

814day.03.gif

 

To look in detail at the anomaly chart mushy posted, well my interpretation of it

It shows a small –ve anomaly just north of the UK. This area is often where the 500mb upper low or secondary upper low east of the main Canadian one tends to reside. So only a small anomaly but it MIGHT just be sufficient for lower heights just north of the UK. Remember this is a mean chart so it may be showing what we have been seeing over the past week or so. A series of relatively minor upper troughs within the main ridge-trough set up, assisting or creating, thanks to the temperature difference either side of the jet at about 30,0000ft, rapidly deepening surface systems running under this smallish upper trough and ending up in the area being discussed.

To me it would seem unlikely that a surface flow from an easterly point is likely IF this pattern is correct and I would suggest it has a far higher probability of being correct than a surface flow from somewhere east of the UK.

Is there anything else that might assist or prevent a surface easterly?

Any sign of an upper ridge is most likely somewhere west of 10 west and about 40-45 north I would suggest looking at the contour flow with a suggestion of a ridge NE of the Azores and small +ve heights in similar areas which extends back south of Greenland towards NE Canada, with not much risk I would suggest for this to ridge towards Greenland in any significant way.

So overall the idea of a surface flow from somewhere between NE and SE does seem unlikely.

Finally on this chart and recent previous ones there is little sign, shown at times on the NOAA 6-10 and also the ECMWF-GFS outputs of any upper ridge building south out of this area. It is a possibility but in my view a pretty small one.

Please feel free to disagree but hope this more technical view is easy to understand

Edited January 13, 2015 by johnholmes

[Mucka]

Regardless of the subtleties of pressure patterns over our small Island the actual frigidness of upper air over the UK is remarkably consistent - almost flatlining at -5C