Model Output Discussion - Stormy Period Inbound...

[IDO]

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. 

 

Not to worry Mucka but the short wave low by D4 is already in Africa or the Bay of Biscay region so I would not thought that at D4 the upstream would be the trigger as they are pretty much the same (GEFS). I was suggesting that with that low further north it acts as a gateway for the Atlantic sliders to slide SE, where as when the low goes to Africa it allows the Azores to ridge within the phasing of the Atlantic slider. The charts I posted (Bay of Biscay SW) all showed at D8 relatively colder potential than the op and control who sent the short wave to Africa. You can see from the FI of the op and Control the pattern flattens and IMO that is due to the short wave spoiler.

[Tamara]

A fairly short update - pending some longer term atmospheric uncertainties which will determine whether a colder trend becomes something of greater significance in the longer term or not

 

Positive frictional torques are indeed increasing - signalled by the GWO in Phase 4 (and still signalled thereafter to head to Phase 5 and re-orbit to phases 8/1).

 

Increase in frictional torques is favourable for weakening the current intensity of the Azores High and on the basis of orbit back through Phases 8/1 this is also support for the current modelled indications for the ridge to shift north westwards.

 

Retrogression of the pattern is therefore coming into modelling focus as previously suggested, and leads credibility for a growing impetus for air masses of polar origin

 

<The question still remains as to how sustained this trend might be?>  <The MJO might yet provide some modest assistance>  and then fresh impetus towards Phases 7/8 are followed up.

 

<With this possibility in mind, repeated retrogression of the pattern and more frequent North Westerly and Northerly influence as per current ECM and GEM trends are well underpinned>

 

 

<At the very least, a steady colder trend is supported through the second half of January, with lower heights better sustained into Europe>.

 

There is an impetus just beginning, which I think will be much harder to reverse than we have seen so far

 

 Cautious optimism instead of despicable shameful ramping can be rewarding those pending uncertainties are playing out a more favourable hand.

 

We still have to remain cautious in expectations, but can reasonably identify:

 

1) We have the benefit of a better amplification signal courtesy of improved MJO progression signal - with the UKMO and ECM both in agreement for a Phase 7 towards 8 orbit, and at a better amplitude than seen in late December.

 

 

 

2) A slight positive shift in AAM tendency as the GWO modestly orbits Phases 5 to 8 has helped in respect of 1) and the consequent induced twin MT torques set to add some wave breaking and amplification of the pattern quite helpfully just when we need them

 

3) Both 1) and 2) look set to occur in tandem with a little stratospheric help from the recent 'wannabe SSW'. This underpins both the weak height anomaly modelled to our N/NE around day 6 and then Phase 8/1 GWO orbit favours assisting the Atlantic pattern to provide amplification and trough disruption thereafter which *should* prevent the pattern flattening. This retrogression phase of the Pacific pattern and the slowing of westerly wind momentum occurring close together add up to reduced and buckled jet flows in our sector and so are supportive of the increasingly colder and more wintry outlook.

 

On this basis, the Azores High *should* not be too much of a spoiler as it is withdrawn further west into the Atlantic - with troughing sliding SE just ahead and against its more amplified shape and engaging resident cold air.

 

Much will depend on how bell-weather a height anomaly to the N and NE we can secure.

 

I realise that it might be naughtily premature of me, but in certain respects, this type of scenario *might* be somewhat akin to what was seen in February 2012. Achieved without any really notable HLB block - just a modest height anomaly to the NE and a good block of cold upper and surface air over the nearby continent.

 

Back then in the modelling run up to that weekend snow event, it looked as if the Azores High would be a bigger spoiler - but it kept sufficient south to north amplitude ridging for the cold air over the UK to not be displaced eastwards to any degree

 

The 'warm sector' to the west clearly indicated moving SE here against the cold air to the east and north

 

http://modeles.meteociel.fr/modeles/reana/2012/archivesnh-2012-2-4-12-2.png

 

The cold air holds firm after snow event. Not everyone benefitted as usually is the case - but it was decent enough in an otherwise very unremarkable winter up to this time

 

http://modeles.meteociel.fr/modeles/reana/2012/archivesnh-2012-2-5-12-0.png

 

http://modeles.meteociel.fr/modeles/reana/2012/archivesnh-2012-2-5-12-2.png

 

January 2013 is another example of just a fairly modest anomaly to the N/NE and a slider snow event. The Azores High here, displaced further westwards this time in the Atlantic and trough disruption again occurring NW-SE. A more definitive and stronger easterly results and cold air and low dewpoints undercut the trough disruption

 

http://modeles.meteociel.fr/modeles/reana/2013/archivesnh-2013-1-18-12-0.png

 

Tonight's UKMO nicely advertises the way ahead well enough I think and hence not cherry picked at all in this regard

 

http://www.meteociel.com/ukmo/runs/2015011312/UN144-21.GIF

 

Usual caveats apply to intra day model watching in general of course, and not paying too much face value knee jerk to them obviously as always - but I think this especially applies to reacting to 4 X daily GFS suite.

 

The lines, as always with these scenarios, will be drawn in the sand how far SW these trough disruptions can occur (and thus keep larger areas of the UK the right side of the polar front). However, northern and eastern parts especially (but not exclusively) look well positioned to see snowfall chances next week.

 

We just have an awful impending storm to get past first, which is a worry.... Hopefully all intact afterwards - and better relaxed to watch and enjoy what looks to be the best synoptics of the winter so far unfolding

Edited January 13, 2015 by Tamara תָּמָר

[Captain Shortwave]

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

 

To me its a case of either a cool/cold west/north-westerly or a much colder easterly as the two solutions. Depending on location will determine how happy will be with the output.

I for one are hoping for the easterly solution

[gottolovethisweather]

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

 

 

Greatest amount of scatter (looking at SLP in particular) on that shows up from around the 17th onwards, so t+96 to t+108 hours is where FI begins then. Now we watch the ECM to see how it handles and more importantly evolves the surface features, post that timeframe. 

Edited January 13, 2015 by gottolovethisweather

[Nick F]

IMO, wouldn't get too hung up on the 12z GFS op, it can often be too progressive with Atlantic energy pushing east and given the quite large differences between it, GEM and UKMO by t+144, would think Shannon Entropy would increasing beyond the weekend ...

[terrier]

Regarding the gfs. Isn't it know that the 06z doesn't have as much info and balloon data input. So perhaps those eye candy runs this morning were on thin ice so to speak. Now I've heard on here many times that the 12z is a more reliable output. So perhaps it is nearer the money. To me it looks abit like a northerly toppler showing this evening. This would bring us around 5 days of cold. So much better than we saw last year. As ever Easterleys are so difficult to achive in the uk. I have seen these disappear at t48. Anyway onto the ECM see what it thinks.

[Mucka]

Not to worry Mucka but the short wave low by D4 is already in Africa or the Bay of Biscay region so I would not thought that at D4 the upstream would be the trigger as they are pretty much the same (GEFS). I was suggesting that with that low further north it acts as a gateway for the Atlantic sliders to slide SE, where as when the low goes to Africa it allows the Azores to ridge within the phasing of the Atlantic slider. The charts I posted (Bay of Biscay SW) all showed at D8 relatively colder potential than the op and control who sent the short wave to Africa. You can see from the FI of the op and Control the pattern flattens and IMO that is due to the short wave spoiler.

 

Yeah I'm not trying to be pedantic and we can have different opinions no worries but I will try one last time to make my case here so any noobies wanting to understand can understand at what we look at when analising charts - as I say this could go back and forth and I don't want to clog up the thread with it but I am happy to discuss it in PM if you have an alternative take.

I will use most recent output that had contrasting fortune from GFS Op 6z and 12z as that seems best.

 

96h comparison. Forget about the shortwave for now and look at other aspects that directly affect the flow over the UK such as the trough, the ridge and the upstream pattern.

 

 

The ridge if anything is slightly stronger on the 12z. The trough though is further West on the 06z. The upstream pattern is pretty close match.

 

120h.

 

 

We can see now that the ridge is better aligned and stronger on the 06z but why? Is it the track of the shortwave that long since departed or is it that the pattern is further West due to the trough and that the upstream on the 12z is faster and flatter than the 06z?

 

140h

 

 

We see a cut off high on the 06z with just weak heights there on the 12z.

Also we can see that this is because the 06z had better disruption more S/SE aligned than GFS 12z which was slightly more E/SE aligned due to less effective disruption against the ridge which in turn was due to strength of ridge and upstream forcing which in turn... etc.

 

That doesn't mean the shortwave doesn't play a part earlier but the mainly subtle differences we see being modelled from run to run will not determine whether we get a more prolonged blocked cold spell IMO.

I accept you and others are entitled to a different opinion and to disagree. 

Sorry for the derail people but I don't think anyone is reading but us model geeks, especially as the "crucial" ECM roles out. 

[Mucka]

To me its a case of either a cool/cold west/north-westerly or a much colder easterly as the two solutions. Depending on location will determine how happy will be with the output.

I for one are hoping for the easterly solution

 

You and me both. A comparison between the 06 suite and 12z with 2m temps shows an alarming lurch back away from cold spell proper but we often see this sort of flip flopping when a cold spell is in the offing. 

 

Edited January 13, 2015 by Mucka

[SMU]

the ECM @ 96 has the alignment of the low out of the states bang on the alignment of the UKMO - where as the GFS has it facing ESE ( UKMO + ECM SSE)

 

therefor the 120 below is pretty much expected !!!!

 

http://www.meteociel.fr/modeles/ecmwf/runs/2015011312/ECH1-120.GIF?13-07

For those in Scotland & NI & the NW + Wales its a snowfest from T 72 onwards.... ( also transferring to the NE of Scotland @ 120)

 

-9c with EMBEDDED TROUGHS

http://www.meteociel.fr/modeles/ecmwf/runs/2015011312/ECU0-120.GIF?13-0

 

SNOW SHOWERS

http://www.meteociel.fr/modeles/ecmwf/runs/2015011312/ECU1-120.GIF?13-0

 

S

Edited January 13, 2015 by Steve Murr

[Hotspur62]

As usual another fantastic calming post by Tamara!!.Lets not get fixated with just one run.I know it is frustrating but as others have said it is what it is when the vast majority on here are after the Holy Grail of snow and cold. Sit back, grab a beer and enjoy the evening !!.The general trends are good and the best we have seen for 2 winters!! 

[Mucka]

 

Snowfest alert! Not an Easterly (yet) but cold and likely snowy away from the SW.

[egret]

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

 

Simply stunning chart, I don't recall one quite that impressive - well spotted. ( If only.......!)

Time to check where PV is really heading

[Captain Shortwave]

ECM day 6

A mess sums it up.

A cold mess mind you. Snow should definitely be falling in places.

That area of warming over Eastern Greenland should aid to slide low pressure towards the UK and keep us in the colder air.

Edited January 13, 2015 by Captain shortwave

[SMU]

 

 

ECM identical as the UKMO 144

 

 

http://www.meteociel.fr/modeles/ecmwf/runs/2015011312/ECH1-144.GIF?13-0

 

But importantly the 850's

http://www.meteociel.fr/modeles/ecmwf/runs/2015011312/ECU0-144.GIF?13-0

 

 

We now need to see ridging NW out of the azores at 168 - although even if it doesnt because the pattern is so far backed west the UK may be under its own snowfest with the azores warmth well to the west of Ireland.....

 

 

S

Edited January 13, 2015 by Steve Murr

[Smiler1709]

As usual another fantastic calming post by Tamara!!.Lets not get fixated with just one run.I know it is frustrating but as others have said it is what it is when the vast majority on here are after the Holy Grail of snow and cold. Sit back, grab a beer and enjoy the evening !!.The general trends are good and the best we have seen for 2 winters!!

Completely agree, maybe the old gfs wants to go out on a sour note and let us down just one last time

[Mair Snaw]

is it me or does the GFS do this every time we have a cold spell being modelled?? it did every time in 2013... and im sure it did just in the run up to xmas 2014?? if its upto its tricks again 3-6 runs time it will be back in line with ECM/UKMO etc.....

[IDO]

GFS P just rolling out

[bluearmy]

at day 6, upstream offshore nova scotia the 12z ecm very different to the 00z with a much deeper depression. that should affect the latter part of teh run as it will either draw the azores further west with some WAA or it will deepen further and perhaps push it further east. the wedge from the 00z run is less impressive on the 12z and further west. will be interesting to see if days 8 to 10 are still wintry, given these differences with the earlier run.

[nick sussex]

Quite unusual set of charts from both the ECM and UKMO at T144hrs, good luck though to anyone trying to forecast where snow might fall at that range.

 

A very complex set up but interesting.

[johnholmes]

 

hi Tamara

I am utterly lost as to what this means?

Much will depend on how bell-weather a height anomaly to the N and NE we can secure.

 

Can you explain it to me please?

thanks

john

[Frosty.]

GEFS 12z mean becomes very impressive for cold lovers, gone is the Atlantic dross and the UK heads into the freezer, with the met office now backing a colder more wintry outlook...all roads are leading to cold.

Edited January 13, 2015 by Frosty.

[Captain Shortwave]

GFS parallel at day 6

Cold again with heights to our north.

The outlook does look complex with low pressure close by. It really depends at the moment on the direction of the flow to determine whether we get rain or snow. 

Edited January 13, 2015 by Captain shortwave

[SMU]

ECM would be a total snow fest for large swathes of England barring the EXTREME SE of the UK.....

 

Also GFS p still singing the easterly

 

http://modeles.meteociel.fr/modeles/gfsp/runs/2015011312/gfsnh-0-156.png?12

[bluearmy]

ECM would be a total snow fest for large swathes of England barring the EXTREME SE of the UK.....

 

Also GFS p still singing the easterly

 

http://modeles.meteociel.fr/modeles/gfsp/runs/2015011312/gfsnh-0-156.png?12

 

the ecm snow map confirms that. only the south coast and se corner (inc london) without cover.  note that this is a useless tool at more than a few days range

[TSNWK]

ECM would be a total snow fest for large swathes of England barring the EXTREME SE of the UK.....

 

Also GFS p still singing the easterly

 

http://modeles.meteociel.fr/modeles/gfsp/runs/2015011312/gfsnh-0-156.png?12

Why.not the south east Steve..? South west I would get, but not sure why you say south east.. But you know what! It's great to have these types of niggles.. It has been a long two years..