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phil nw.

Model Output Discussion 4th Dec.2013-12z onwards.

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It would be quite ironic if some places manage a White Xmas given the overall NH pattern. I think the technical version used by the UKMO for snow falling is possible further north, in terms of accumulations I think realistically only higher ground at the moment.

 

By and large theres very good model agreement out to day ten for the overall NH pattern, the ECM towards day ten is however less amplified upstream and you can see it makes less of that ridging than the GFS does. You should in these situations go for the flatter solution unless this appears closer to the more reliable timeframe as the upstream pattern isn't really condusive to the more amplified solution.

 

The models are still toying with moving the main PV chunk east but unfortunately they want to leave some remnants behind in Arctic Canada, this will preclude any sustained ridge to the west, any ridging even if does manage to develop will be flattened.

 

After this brief eastwards movement the suggestion is that the PV reforms once again to the nw, essentially here the bellwether to look at is what happens over the northern part of Greenland because the weak pressure rises here helped to some degree by the Siberian ridge is what helps to drive the jet further south.

 

Essentially here for coldies you're trying to squeeze as much interest out of a relatively poor NH set up, we've lost the more amplified east Pacific Ridge and  with less amplification upstream its not really condusive to delivering anything of note for western Europe especially with the PV reluctant to clear away from the north.

 

Until we see changes in the PV and more amplification upstream I'm afraid we're going to have to be dining at the Little Chef rather than the Ritz!

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snow in the north and on hills,whatever does that mean>

I take it to mean that snow could fall to any level in the North and on hills in the South at times.

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I have seen many charts like these, showing 'dart board' lows, dismissed by experienced posters as being unlikely to verify, and even as being almost impossible in terms of the depth of the low pressures depicted. I am still unable to understand why those who program the models should have set parameters which are outside the limits of probability - surely the models should err on the side of caution and then ramp up their predictions as the indications of extreme weather become more certain nearer to the actual event? What seems to happen is the reverse - they regularly predict Armageddon at 192+ only to back off rapidly at the last possible moment. If I didn't know better I would have to guess that the models are deliberately programmed to continuously get our hopes up and then pull the rug out.

 

Anyway, if either of these scenarios occurs I won't be walking the dogs that day.....

 

Posted Image

 

Posted Image

 

 

Looks to me like strong winds and rain almost everywhere throughout the Christmas period.

 

 

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I take it to mean that snow could fall to any level in the North and on hills in the South at times.

Exactly. Higher depth temps in S should generally prevent any bothersome degree of settling (plus patchy distribution in any case).

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Anyway, if either of these scenarios occurs I won't be walking the dogs that day..... 

 

 

Looks to me like strong winds and rain almost everywhere throughout the Christmas period.

I'm sure they would love it!

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I think this is where the problems / negative comments about the models are coming from. The mountains here had a dusting too, which wasnt expected.

 

I woke to a harsh frost too.

 

It's mainly a North/South divide thing, as in for the South it's looking quite poor, but for the North we have things to shout about.

 

Just check out Metcheck forecast for Buxton, or take a look at the charts = lots of snow.

I think some people's expectations need to be managed re a 'typical' UK winter, especially for us Southerners.

North/South divide in winter re cold and snow - to all those in the South that's pretty normal for the UK.

What we experienced in 09/10, End November/December 2010 to name two recent cold, snowy winter spells is not that normal for The South.

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Sky Full, I believe the models show extremes which they then back off from because it is similar to when you swing a pendulum.

In general when something is trying to find the correct solution to a given event it will go to both extremes i.e an extreme storm then the next model may show a weaker storm

then the actual solution will be somewhere down the middle. It is all to do with the forecast mathematics evening out to find the mean solution (in general)

However that always has the possibility to be proved wrong and occassionally go for the most extreme out put, but this is not common.

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snow in the north and on hills,whatever does that mean>

 

It means there is unlikely to any settling of snow at low levels here in Newbury whilst I can get my snow fix just five miles away to my SW by visiting the local downs, bring it on I say. Posted Image

Edited by gottolovethisweather

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No change in today's NAO update with it remaining positive as we see out 2013

 

Posted Image

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GEM remains very unsettled over the Christmas period

 

Posted ImagePosted ImagePosted Image

 

Its looking more likely now that It'll be the strength of the winds which grab the headlines over Christmas

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Well looking at current model output, Christmas day boxing day period which is still 8/9 days in the future could produce almost a surprise for many at this range .plenty of very active weather to come before this period with some uncertain outcomes .Fax charts very usefull and Reading met office updates Daily .Certainly not boring as new features every day are likely to be picked up bringing us interesting outcomes .So at this range possibilitys for all ,so lets enjoy .Posted Image

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snow in the north and on hills,whatever does that mean>

It means they're covering all bases....and it also means that Frosty will be hyperventilating.  

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No change in today's NAO update with it remaining positive as we see out 2013

 

Posted Image

 

 

But, the AO moving to neutral from the last few days outputs showing raging positive values

 

post-5114-0-24685000-1387289500_thumb.gi

 

Perhaps the slightly improved AO forecast not overly surprising seeing some of the output of late with the increased pole heights (although far from anything worth raising your eyebrows for yet). The grim fact is that the NH profile is simply not conduicive in any way to a prolonged cold spell, certainly not in the South at least. It is worth remembering that Scotland can though have memorable cold spells with the right tilt on the jet, going from one severe blizzard to another one, insterspersed by mild(er) periods but never mild. That is always a possibilty

As often happens in these situations the vortex could well move away from Greenland after a week or so and this will allow ridging to edge in behind it but with little amplification on tap it is only likely to be fairly weak and transient and will then be easily brushed aside as the vortex will meanders back west again. There appears little forcing on tap right now for it to do otherwise.

What the charts haven't done for a while, and I am talking about the GFS here as it goes out the furthest, is pick up a new signal for cold for quite a while. It doesn't mean that makes the GEFS correct by any means but it doesn't bode well either IMO.  I use the Dorset ensembles as a good guide to this (although most places in the South will do). For over a week now consistently out in the far reaches of FI rarely has -5 been breached for the 850 temps. Once you start see members hitting i.e. -8s and below, generally it will be as a result (whether accurate or not) of the models having picked up a different signal to that over a vortex raging away on our side of the pole. Until we see that, most of us can forget it  for a decent cold SPELL.

Also watching Bern / Rome air pressure trends is a one way to see if the models are picking up on a signal for more of a southerly jet, which would possibly be the precursor to the eventual pattern change.

 

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snow in the north and on hills,whatever does that mean>

I think they were hoping that the word 'elsewhere' would be redundant? It's a very common scenario, when all the models point towards marginality...Posted Image

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