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Model Output Discussion - 18z - 25th Nov onward


Paul

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Posted
  • Location: Lytchett Matravers - 301 ft ASL
  • Weather Preferences: Snowy Winters, Torrential Storm Summers
  • Location: Lytchett Matravers - 301 ft ASL

15.30 till 16.45

Cheers, could be an important Run IMO, waiting with baited breath!!! clapping.gif

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Posted
  • Location: Cheshire
  • Location: Cheshire

I suppose that people will soon be swiftly turning their attentions towards a cool zonal period of weather and the general interest that bring which funnily enough is exactly what started of last December, says it all really.

Edited by Anonymous21
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Posted
  • Location: St Albans, 95m asl
  • Location: St Albans, 95m asl

People are talking about plenty of Northern Blocking, I can't see much sign of that on the ECM 00z mean

Day 10:

EDH1-240.GIF?26-12

At least there's ensemble P2 to provide some fun in deep FI

gens-2-1-384_jbo1.png

gens-2-0-384_pzb5.png

Overall, putting everything together, my opinion is that this first attempt at a proper cold spell will now fail to deliver, with the Atlantic returning for a time. It was always looking dodgy with the consistent lack of ensemble support and swinging OP runs. There's certainly a possibility of another attempt later down the line but the only thing certain at the moment is that things are uncertain.

NAEFS lends supports the Atlantic making a move in around +168/+192

naefs-0-0-192_vcq1.png

Whilst I agree to an extend Barb, you might want to take a look at the ECM ensemble mean again RE: no northern blocking

I can point out two areas of high pressure at northern latitudes, one pushing down through Greenland and the other huge one across the arctic edging in to NE Siberia.

But I completely agree, the current medium term prognosis based upon Ensemble means is cool down (how cold is questionable), followed by a little atlantic influence, and then looking likely to see northern block re-assert itself afterwards

The issue here, as chio has pointed out, is differentiating between a full blown atlantic attack, and areas of LP from the north atlantic heading SE and undercutting the blocks to the north - any such scenario will only further aid northern blocking.

Very tricky forecast period for the next couple of weeks

SK

Edited by snowking
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Posted
  • Location: Huddersfield, West Yorkshire (170m ASL)
  • Weather Preferences: Snow
  • Location: Huddersfield, West Yorkshire (170m ASL)

So basically reading between the lines we have three options? -

A -

A battleground where milder weather tries to push in from the west and colder air is established to our eastern half the two join together and we have a snowfall event on the eastern side and sleet to rain on the western side. Colder air to win out and re establish in a few days after while the east stays cold throughout.

B -

A battleground where milder weather tries to push in from the west and colder air is established to our eastern half the two join together and we have a snowfall event on the eastern side and sleet to rain on the western side. Milder air to win out on that occasion however this is just very temporary as a renewed push of cold establishes in the uk.

C -

That low out to the west is forced north and west and does not make any inroads east thus allowing the cold to spread further west and the Atlantic not firing up and keeping the uk in a cold spell throughout.

Is that a fair assessment of options on the table at present?

One of the most sensible posts I've seen for a while, nice one!! Going to be interesting in the next few model runs to see where that Los goes near Greenland.

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Whilst I agree to an extend Barb, you might want to take a look at the ECM ensemble mean again RE: no northern blocking

I can point out two areas of high pressure at northern latitudes, one pushing down through Greenland and the other huge one across the arctic edging in to NE Siberia.

For a blocking high though you need heights to be high as well not just high pressure (greens and yellows vs blues and purples). There's a bit of height rising towards Svalbard way but much else.

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Posted
  • Location: St Albans, 95m asl
  • Location: St Albans, 95m asl

For a blocking high though you need heights to be high as well not just high pressure (greens and yellows vs blues and purples). There's a bit of height rising towards Svalbard way but much else.

I know but believe me, on ensemble charts at day 10 on meteociel, they are never orange/red over the polar regions given the spread of solutions by that range

WZ shows this slightly better:

Reem2401.gif

Though unfortunately there is no NH view on there

But you can see even from the euro chart that the 'blues' you see on Meteociel are actually even lighter greens on WZ (dont let the colouration bias on various models fool you)

SK

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Posted
  • Location: Aviemore
  • Location: Aviemore

I know but believe me, on ensemble charts at day 10 on meteociel, they are never orange/red over the polar regions given the spread of solutions by that range

WZ shows this slightly better:

Reem2401.gif

Though unfortunately there is no NH view on there

But you can see even from the euro chart that the 'blues' you see on Meteociel are actually even lighter greens on WZ (dont let the colouration bias on various models fool you)

SK

npsh500.png

http://www.netweather.tv/index.cgi?action=nwdc;sess=

:)

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Posted
  • Location: Morden, Surrey.
  • Location: Morden, Surrey.

I suppose that people will soon be swiftly turning their attentions towards a cool zonal period of weather and the general interest that brings, says it all really.

What draws you to that conclusion & care to show some chats to back up your statement because your statement does not match with the charts on offer atm.

At the moment any transition to the Atlantic breaking through will be temporary if at all. Not only does the pros state this but background signals also back that up further.

As i said previously in another thread i dont particularly put any blame to the models and output it has been churning out over the previous days. Today it has become a lot more clearer in my mind that the situation going forward is so delicate its ridiculously hard to get right and forecast.

I do feel for those lusting consistency with the models and as such wanting to be put out of there misery for either the good or bad. However i dont think we will see this for a little while yet such as the nature of the emerging pattern.

One thing i will say it is model watching at its very best.

Edited by london-snow
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Posted
  • Location: St Albans, 95m asl
  • Location: St Albans, 95m asl

Thanks Paul - would be great if we can get the Ensemble means with something closer to resembling WZ type colouration

You can hopefully see from that Barb that we're not talking about 'faux' highs here, the reason you still see some of the 'blue' colours close to these ridges is merely down to the large scatter of current ensemble solutions

Unless all 50 ECM ensemble members agree on a given area of heights, they are likely to end up looking red nearer the equator, and blue near the poles

But the mean pressure anomalies still suggest HLB with LP undercutting smile.png

SK

Of course this should be disclaimer-ed, the example of the ECM mean is merely one run!

Edited by snowking
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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

that's the problem with relying too much on mean charts far out, they can still change suddenly.

In fact, the trend since last Tue/Wed has been for a weaker ridge to our west. The ridge we are going to get later this week is much weaker and less expnasive than what the ensembles and the NOAA charts were showing during most of last week

still far more reiable and closer to what happens than the synoptic 4x or 2x daily outputs in my view of watching for 6 years or so

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Posted
  • Location: Morecambe
  • Location: Morecambe

I think the ecm has backtracked slightly from what it was showing from last night, more amplified but far from perfect. UKMO is still looks the best if albeit the any easterly flow is not as strong as it once was, the GFS is frustrating, it has the trough place where the UKMO has been placing it for a long time but theres no amplified ridge!

All the models still show blocking of some sorts, but little minor details is making all the difference sadly. I really hope we don't get left to rue the lack of cold pool available at the start of this blocking set up.

12Z runs will be interesting for sure, one is hoping for further backtrack from the ECM and more consistency from the UKMO but we must remember, it only takes one minor change for the UKMO to change and all its consistency will mean very little sadly.

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

Does anyone know if the Fax charts have any human input from proffessional forecasters? I know they have stuck with the UKMO for the last few days so surely the boffins in exeter must think that is the likely outcome? Or is the fax done by computers?

short answer=always human input

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Posted
  • Location: Basque Country - Northern Spain
  • Location: Basque Country - Northern Spain

In 20 minutes the GME will be out, it will be interesting to see how it shows the atlantic low

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Posted
  • Location: Enfield | Reading
  • Weather Preferences: Snow; Thunderstorms; Heat Waves
  • Location: Enfield | Reading

What draws you to that conclusion & care to show some chats to back up your statement because your statement does not match with the charts on offer atm.

At the moment any transition to the Atlantic breaking through will be temporary if at all. Not only does the pros state this but background signals also back that up further.

As i said previously in another thread i dont particularly put any blame to the models and output it has been churning out over the previous days. Today it has become a lot more clearer in my mind that the situation going forward is so delicate its ridiculously hard to get right and forecast.

I do feel for those lusting consistency with the models and as such wanting to be put out of there misery for either the good or bad. However i dont think we will see this for a little while yet such as the nature of the emerging pattern.

One thing i will say it is model watching at its very best.

To a degree - and I accept it takes a leap - there is a flavour of consistency in the fact that the output isn't consistent. You can imply from that, that there is significant disagreement owing to a determining factor. We all know that factor rests on the exit of energy off the Eastern seaboard, and specifically its transit thereafter; different models favouring different evolutions, which then propagate further divergence throughout the rest of the run.

So being consistent isn't always about having a clean evolution or transition to an agreed phase. The over-arching consistency which we've all witnessed in the operationals is one of - in some instances - black/white disagreement. Some like it to be more absolute than that, but it's not to say that you cannot extract information from variable outputs - it's just a bit more subtle, intangible but yes - accepted - also tenuous.

I have to say, reading this mornings' musings on here didn't make for fun; statements like "...may this be a lesson to you..." are just so unnecessary, not to mention premature. At the end of the day, everyone is trying to learn - and everyone is at different stages of building their knowledge up - so, unless you know it all - and I've yet to read anyone on here who does - then statements like that are disappointing to read.

Very interesting to see Stewart's observations, and I implore you all to view the outputs to come with those underlying thoughts in-mind. Also, quite sagacious of John to refrain from committing to a forecast until such time as more confidence is available, lending to a stronger foundation. These are your pointmen in complex situations like this.

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Posted
  • Location: Tunbridge Wells
  • Weather Preferences: Warm dry summers and cold snowy winters
  • Location: Tunbridge Wells

So basically reading between the lines we have three options? -

A -

A battleground where milder weather tries to push in from the west and colder air is established to our eastern half the two join together and we have a snowfall event on the eastern side and sleet to rain on the western side. Colder air to win out and re establish in a few days after while the east stays cold throughout.

B -

A battleground where milder weather tries to push in from the west and colder air is established to our eastern half the two join together and we have a snowfall event on the eastern side and sleet to rain on the western side. Milder air to win out on that occasion however this is just very temporary as a renewed push of cold establishes in the uk.

C -

That low out to the west is forced north and west and does not make any inroads east thus allowing the cold to spread further west and the Atlantic not firing up and keeping the uk in a cold spell throughout.

Is that a fair assessment of options on the table at present?

Seems good to me and I have to say none of those options are too disastrous.

The posting today has (on the whole) been really helpful and constructive - wouldn't want to go through this sort of stress too often but it's been a valuable experience - thanks all!

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Posted
  • Location: Near Keele, North Staffs
  • Location: Near Keele, North Staffs

So basically reading between the lines we have three options? -

A -

A battleground where milder weather tries to push in from the west and colder air is established to our eastern half the two join together and we have a snowfall event on the eastern side and sleet to rain on the western side. Colder air to win out and re establish in a few days after while the east stays cold throughout.

B -

A battleground where milder weather tries to push in from the west and colder air is established to our eastern half the two join together and we have a snowfall event on the eastern side and sleet to rain on the western side. Milder air to win out on that occasion however this is just very temporary as a renewed push of cold establishes in the uk.

C -

That low out to the west is forced north and west and does not make any inroads east thus allowing the cold to spread further west and the Atlantic not firing up and keeping the uk in a cold spell throughout.

Is that a fair assessment of options on the table at present?

LS, the weather has made mugs of supposed teleconnection signals many times before. The NAO particularly is a complicated driver so I would add a fourth zonal option, which is shown by both of todays GFS runs and the ECM later frames.

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Posted
  • Location: Cheshire
  • Location: Cheshire

What draws you to that conclusion & care to show some chats to back up your statement because your statement does not match with the charts on offer atm.

Oh don't get me wrong it would foolish to rule out another shot at cold at this juncture, it's just that it's now looking like we could well be back to chasing decent looking synoptics deeper into FI with nothing more than average conditions in reliable bar an unlikely sudden turn around from the 12z's which is a really bitter pill to swallow after all the build up over the last week or so.

Edited by Anonymous21
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Posted
  • Location: Liphook
  • Location: Liphook

The GFS is living in lala land, to develop a powerful PV vortex is not going to happen. I could buy a more flatter zonal set-up for a time, but there is way too much going against the PV for it to strengthen in the manner the GFS op run does.

Ensembles by in large are much more realistic on that front, the ECM pretty much doesn't have a vortex and instead keeps a really flat height gradiant.

ECM at 240 barely has a PV left and the deepest low is at 995mbs in the whole atlantic, the GFS has a PV starting to pull itself together again and a rapidly depeening low in the atlantic at 240hrs.

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Posted
  • Location: Aviemore
  • Location: Aviemore

LS, the weather has made mugs of supposed teleconnection signals many times before. The NAO particularly is a complicated driver so I would add a fourth zonal option, which is shown by both of todays GFS runs and the ECM later frames.

The NAO is not a driver, it's a measure of air pressure difference.

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Posted
  • Location: Lincoln, Lincolnshire
  • Weather Preferences: Sunshine, convective precipitation, snow, thunderstorms, "episodic" months.
  • Location: Lincoln, Lincolnshire

I think there is indeed the possibility of a fourth option along the lines of what today's GFS 00Z/06Z and yesterday's ECMWF 12Z showed, involving a stronger Atlantic influence with low pressure to the north, but it doesn't look like classic zonality to me- we keep high pressure at high latitudes with little sign of the reformation of an organised polar vortex. Even the relatively zonal-looking outputs, such as the GFS 06Z, have temperatures generally near or below average with the jet tracking NW-SE.

Also, the last few frames of this morning's ECMWF 00Z run are far from "zonal"- we get an increased Atlantic influence but the high pressure to the north and west of the UK is still a prominent feature.

Edited by Thundery wintry showers
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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

Exeter lean towards the block being a temporary phase ahead of an equally temporary return to mobility, albeit their detailed 6-10d prognosis (not copied below, but abstracted version of their latest (00z run) analysis is shown here, incl to trend period) expresses obvious uncertainties (including as emphasised in some posts here already):

"4. Trend for Days 10-15 : Still much greater than average level of uncertainty through this period. Most likely scenario is for rather cold unsettled cyclonic W to NW to displace the cold/blocked type at least for time but with an increasing probably that blocking becomes re-established with the UK within the cyclonic limb of the block.

5. Discussion : Slightly better agreement between MOGREPS and EC ENS to break down the block and allow more atlantic mobility by around day 8-9 and EC still supports this breakdown longer into the trend period but still a big spread in degree of cyclonicity in terms of track, depth and orientation of fronts. No major change of story suggested for the 6-10 day period From as early as this weekend a major divergence of weather types is present in the ensembles. The majority of MOGREPS and NCEP members retain the cold block over the UK, with any breakdown only partial and only affecting the far W/SW. EC deterministic, along with about 50 % of the EC ensemble have a full return to Atlantic mobility and much milder conditions by as early as Sunday. Interestingly, the zonal spell may only be temporary with EC deterministic trending colder again by day 10. Clearly a good deal of uncertainty is present in this period and a compromise has been made in allowing a partial breakdown of the block to take place later in the weekend and early into next week. Such a scenario brings a risk of heavy rain to the SW and a risk of sleet and snow along the leading edge..."

I fully agree with this its an excellent summary and totally realistic and I have to agree just using the anomaly charts that some kind of temporary change to a coldish unsettled westerly looks the form horse to me at the moment. Again I agree that a return to a more blocked pattern is probably the most likely consequence of this.

thanks as always Ian for these inputs-they are an area of calm reasoned science in what is often a rather frantic and somewhat ill informed area of posts.

Edited by johnholmes
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Posted
  • Location: St Albans, 95m asl
  • Location: St Albans, 95m asl

LS, the weather has made mugs of supposed teleconnection signals many times before. The NAO particularly is a complicated driver so I would add a fourth zonal option, which is shown by both of todays GFS runs and the ECM later frames.

Ian i'm sorry but your suggestion of the GFS showing a 'positive NAO" just does not bear fruit. If you were to say Neutral then I would agree, and indeed the ensemble NAO output (presumably from the 0z) backs that up:

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/new.nao_index_ensm.html

Even the 6z op itself suggests such an occurrence for no more than 24 hours here:

gfsnh-0-168.png

Followed by our atlantic HP ridging north again and leaving things more neutral once again:

gfsnh-0-192.png

Im not suggesting neutral is going to give us extreme cold, but its factually incorrect to call this a positive NAO situation...not to mention the NAO is not a driver (as suggested in the quoted post) but merely a measurement of pressure gradient and type.

However, that is simply one model run. So lets take a look at another that i've used plenty in the past and found really rather more accurate, the NAO outlook from the PSD of the NOAA:

http://www.esrl.noaa.gov/psd/forecasts/teleconn/images/nao.png

A very different outlook there.

I don't think its right to suggest either way at this stage the likely outcome because we simply don't know. I can't say that you're definitely going to be wrong with your ongoing milder, zonal thoughts eventually, nor can you suggest that cold won't become entrenched within the next couple of weeks, it really is that uncertain.

But it would probably be helpful to be a little more factual if you are going to religiously follow NWP output at the moment (and please don't take that as a dig - thats a perfectly reasonable route to follow if it works for you :) )

SK

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