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phil nw.

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

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Not sure if this is in the right place, but with regards to the models, are they organic, or are they rigidly programmed so that when for example A does something and B does something the outcome is always C?? which as we know doesn't always happen [sorry no specific example] or do they learn as they go along?

 

Thanks..delete if in wrong place mods.

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There are certainly been some signs of the jet easing south around Christmas which would bring some polar air into the mix.

A chance of some highland snow and perhaps for the north but only for brief periods in this very mobile flow.

We have to be realistic wrt to any prolonged and widespread cold though.

We are now into the period where without any forecasted warmings the vortex is at it's coldest so it will continue to dominate the Atlantic pattern for now.

The 00z mean charts underline the expected pattern

post-2026-0-33112000-1386932986_thumb.pnpost-2026-0-08049600-1386932994_thumb.pn

 

There will be plenty of interest for followers of cyclonic weather but for now it's a waiting game for snow lovers.

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For what it's worth the gfs again moves the jet south as we head toward Xmas , surely this is a trend now?

It also gives a notable snow event Xmas eve

post-9095-0-30445200-1386931980_thumb.jppost-9095-0-98327300-1386931998_thumb.jp

Marginal but heavy .

Again showing the AO going negative with high pressure taking control over the polar regions .

post-9095-0-68584300-1386932084_thumb.jp

The last 2/3 days we finally have signs to look toward a change , all fi at the minute but consistently modelled .

With wave 2 activity picking up over the next 7 days .

As for the ECM 32 dayer , it's always nice to have it showing a wintry outlook but going from my experience last year, if it was right about the Greenland high pressure taking hold just 50% of the time then we would of had a very severe winter but it constantly failed in its attempts . Only to have a completely different outlook 2 weeks later .I have noticed even this year so far it's been way out . 2 weeks ago we was looking at the potential of a record breaking dry spell. Now we have the Atlantic taking control with what looks to be a very stormy spell. So can we trust any long range models?

In my eyes the only long range trends that's worth looking at is the stratosphere developments , it absolutely never fails . All of our weather is controlled by what going on up there , if the vortex is vigorous , expect low pressure above us . High pressure south of us . If it gets disrupted/blown to shreds for what ever reason (ie SSW , wave activity etc , ) then the chances of cold and snowy weather are improved , but not guaranteed .

The major player in our winter time is the vortex /stratosphere . Look to that for guidelines , if there is rumblings of strong -/+ mountain torques / strong wave 1/2 activity events / and if we're really lucky , a Sudden Stratosphere Warming event then chances are as this propagates down the lower levels of the strat , we will see a tropospheric response , which will show its hand in the models , first in fi , then more in the reliable time frames.

So for me , we have the first signs of a major pattern change into the new year , but as ever , time will tell. ;)

Edited by Severe Siberian icy blast

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For what it's worth the gfs again moves the jet south as we head toward Xmas , surely this is a trend now?

It also gives a notable snow event Xmas eve

Posted Imageimage.jpgPosted Imageimage.jpg

Marginal but heavy .

Again showing the AO going negative with high pressure taking control over the polar regions .

Posted Imageimage.jpg

The last 2/3 days we finally have signs to look toward a change , all fi at the minute but consistently modelled .

With wave 2 activity picking up over the next 7 days .

As for the ECM 32 dayer , it's always nice to have it showing a wintry outlook but going from my experience last year, if it was right about the Greenland high pressure taking hold just 50% of the time then we would of had a very severe winter but it constantly failed in its attempts . Only to have a completely different outlook 2 weeks later .I have noticed even this year so far it's been way out . 2 weeks ago we was looking at the potential of a record breaking dry spell. Now we have the Atlantic taking control with what looks to be a very stormy spell. So can we trust any long range models?

In my eyes the only long range trends that's worth looking at is the stratosphere developments , it absolutely never fails . All of our weather is controlled by what going on up there , if the vortex is vigorous , expect low pressure above us . High pressure south of us . If it gets disrupted/blown to shreds for what ever reason (ie SSW , wave activity etc , ) then the chances of cold and snowy weather are improved , but not guaranteed .

The major player in our winter time is the vortex /stratosphere . Look to that for guidelines , if there is rumblings of strong -/+ mountain torques / strong wave 1/2 activity events / and if we're really lucky , a Sudden Stratosphere Warming event then chances are as this propagates down the lower levels of the strat , we will see a tropospheric response , which will show its hand in the models , first in fi , then more in the reliable time frames.

So for me , we have the first signs of a major pattern change into the new year , but as ever , time will tell. Posted Image

 

Well, that really would be something if that came off on Xmas Eve - I would give a lot for it to come true, but sadly, we can but hope... Posted Image Posted Image

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Until the next EC32 update that is Ian.

Hmmm. It's been solid on broad continuity for period up to Xmas over past 3 runs (ditto DECIDER, but in both cases the rapidity and extent of how the Euro high faded were initially unclear). But it's less bullish after New Year, so jury out. Edited by fergieweather

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Very much so Nick, there is definately a feeling of deja vu developing for me at the moment, with the vortex currently looking very robust....almost with a 'come and ave a go if you think your ard enuff' look about it. Certainly not ready to chuck in the towel yet on my much colder 2nd half of Winter, but Ian's latest post combined with what I'm seeing is pushing me ever further towards Feb now being the best chance for some sustainable HLB.

Maybe, I still believe roger will be closer to the mark even the CFS supports his hypothesis. You have to remember things was looking a lot different a few days ago with the main theme being settled and mild looking different now with it likely to be very stormy who knows what things will look like by new year. If the weather was as simple as you described it wouldn't be nearly as fun.

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Hmmm. It's been solid on broad continuity for period up to Xmas over past 3 runs (ditto DECIDER, but in both cases the rapidity and extent of how the Euro high faded were initially unclear). But it's less bullish after New Year, so jury out.

I agree so far so good, but it's constant chopping and changing in the latter stages of its updates kind of renders it's long term use a little redundant. I much prefer the John Holmes way of looking at the 7-10 day as being more often than not right and everything else beyond is a case of looking for trends. The trend I see is one where the jet sinks further and further south over time, what happens next who knows.

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GFS has snow on XMAS day, this isn't in the deep FI, and not following the EC32...........Is the GFS wrong then

GFS has snow on XMAS day, this isn't in the deep FI, and not following the EC32...........Is the GFS wrong then

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Hmmm. It's been solid on broad continuity for period up to Xmas over past 3 runs (ditto DECIDER, but in both cases the rapidity and extent of how the Euro high faded were initially unclear). But it's less bullish after New Year, so jury out.

Looking at the 06 GFS 10 day postage stamps the Euro high remains very much a feature.  OK the main core might have drifted 11 or 12 miles farther E, but it looks as equally robust as the badly located PV does.

 

it's not until the low res part of the run that it's shown to loosen it's grip, so until that trend starts to get modelled consistently inside T+180hrs I'd personally view even this with a fair degree of scepicism.

 

 

Posted Image

Edited by shedhead

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Looking at the 06 GFS 10 day postage stamps the Euro high remains very much a feature. OK the main core might have drifted 11 or 12 miles farther E, but it looks as equally robust as the badly located PV does.

it's not until the low res part of the run that is't shown to loosen it's grip, so until that trend starts to get modelled consistently inside T+180hrs I'd personally view even this with a fair degree of scepicism.

Posted Image

Agree and by the same token And for balance i believe it's also reasonable to treat these EC32 updates with caution beyond day 10. Edited by TSNWK

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Agree and by the same token And for balance i believe it's also reasonable to treat these EC32 updates with caution beyond day 10.

Yes, I must say I am not a huge fan of the ECM32, to my mind it has a penchant for modelling the kind of pattern that we're heading into and then locking it in for to long.

 

That said tho I've never heard anyone say they rely on it soley and have absolute, un-questionable faith in it....it's one weapon in the overall armoury, not any kind of 'golden bullet'

Edited by shedhead

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The short answer is that they're rigidly programmed. 

 

However, members here tend to anthromorphise the models somewhat, or at least treat them differently to how they really are. My experience is that forecasters also don't think of models in their truest sense. This is all understandable, because at their core, it is just a set of equations which are integrated forwards in time. 

 

Models are pretty much just a massive equation solver. That is hard to picture. It's also pretty dull (unless you're really into that sort of thing).

 

Decades ago, the equations used were the primitive equations:

 

http://en.wikipedia.org/wiki/Primitive_equations

 

Most (or all?) of these do not have "analytic solutions". That's a way of saying that they don't have solutions that can be precisely written by another formula. For an example of the converse:

 

Posted Image

 

That's the form of a quadratic equation, familiar to anyone who's done GCSE maths.

 

What is x? The answer is always:

 

Posted Image

 

That's an analytic solution. 

 

None of the primitive equations have solutions that can be written in such a way. All the solutions are numerically produced approximations (though they are very good approximations). If anyone has ever done "trial and improvement" solutions at school, it's a similar thing. 

This is part of the reason we need supercomputers. 

 

The reality is that the primitive equations are only approximations themselves. I don't know what goes into modern models, but the equations will be more complicated than that. 

 

Other issues that arise are how to deal with things that cannot be explicitly modelled. These are many. Convection being the classic example, and all the components of that. 

 

Models don't go around thinking "I'll have a high there, and a jet there, and a nice low there, and we'll stick a front there" even though that's the output we see. The gritty reality is that it's an unfathomably vast solver of ugly looking equations.

Everything we see is produced through masses of equation solving; it's just that these equations are rather good at approximating the state of the atmosphere, and how the parts link together. So when we see a low, everything within the model has contributed towards making that low, and there is a lot of stuff going on there.

 

I'm no modeller, but hopefully the above is approximately true enough.

 

a nice summary of what happens there f without getting too deeply into what the euqations actually look like-frightening on your first forecast course is what I remember and going to sleep with them stuck on the walls of my bedroom study. Yuk, best not think too much about them as it could bring back nightmares.

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I have very little confidence in the "cold zonality" shown by the GFS 06Z for the Christmas period.  Particularly as we get into the low resolution part of the model runs, there is often a tendency in zonal setups to overdeepen lows, send polar air too far south, and underestimate secondary low development, and secondary low development tends to force the polar air to "return" a longer distance over the Atlantic Ocean before reaching us, as well as restricting the length of any polar maritime incursions.

 

However, I can see northern parts of the country potentially having a shot at some wintry showers next Thursday associated with a polar maritime incursion behind a vicious midweek low.  At this range, even that is prone to being toned down, but it's something that has been showing on the model outputs for quite a while.  A bookies' white Christmas can't be entirely ruled out because we might get a similar shot coinciding with Christmas Day, similar to what happened for Christmas 1999, though I don't expect any polar maritime incursions to be as potent as the Christmas Day 2004 one.

 

In the short term there will be rather more "weather" going on than we've been seeing recently, with some quite active frontal systems and strong winds.  Tomorrow, and Wednesday of next week, look set to be the days most likely to see damaging gusts of wind, while next Monday/Tuesday will generally see the quietest weather, with a rdge of high pressure moving up from the south, and probably somewhat sunnier conditions for most than we've generally seen during the recent quiet spell.

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I agree so far so good, but it's constant chopping and changing in the latter stages of its updates kind of renders it's long term use a little redundant. I much prefer the John Holmes way of looking at the 7-10 day as being more often than not right and everything else beyond is a case of looking for trends. The trend I see is one where the jet sinks further and further south over time, what happens next who knows.

 

If you look at those postage stamps, which I find very hard to follow sometimes but then that is just my old brain, but the overall impression in those shown is how at the surface the high is being split into two with a trough between the two. This is I assume the synoptic models trying to show what the upper air (using the 500mb anomaly charts is BEGINNING TO SHOW-nothing more, with more meridionality being suggested). Currently this is restricted to the western half of North Ameica and west of there.

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The short answer is that they're rigidly programmed. 

 

However, members here tend to anthromorphise the models somewhat, or at least treat them differently to how they really are. My experience is that forecasters also don't think of models in their truest sense. This is all understandable, because at their core, it is just a set of equations which are integrated forwards in time. 

 

Models are pretty much just a massive equation solver. That is hard to picture. It's also pretty dull (unless you're really into that sort of thing).

 

Decades ago, the equations used were the primitive equations:

 

http://en.wikipedia.org/wiki/Primitive_equations

 

Most (or all?) of these do not have "analytic solutions". That's a way of saying that they don't have solutions that can be precisely written by another formula. For an example of the converse:

 

Posted Image

 

That's the form of a quadratic equation, familiar to anyone who's done GCSE maths.

 

What is x? The answer is always:

 

Posted Image

 

That's an analytic solution. 

 

None of the primitive equations have solutions that can be written in such a way. All the solutions are numerically produced approximations (though they are very good approximations). If anyone has ever done "trial and improvement" solutions at school, it's a similar thing. 

This is part of the reason we need supercomputers. 

 

The reality is that the primitive equations are only approximations themselves. I don't know what goes into modern models, but the equations will be more complicated than that. 

 

Other issues that arise are how to deal with things that cannot be explicitly modelled. These are many. Convection being the classic example, and all the components of that. 

 

Models don't go around thinking "I'll have a high there, and a jet there, and a nice low there, and we'll stick a front there" even though that's the output we see. The gritty reality is that it's an unfathomably vast solver of ugly looking equations.

Everything we see is produced through masses of equation solving; it's just that these equations are rather good at approximating the state of the atmosphere, and how the parts link together. So when we see a low, everything within the model has contributed towards making that low, and there is a lot of stuff going on there.

 

I'm no modeller, but hopefully the above is approximately true enough.

Hello,

 Not sure where you are coming from regarding this information but looks impressive. Respective matching spatial resolutions have come along way since my day and are almost 100% accurate in the short term range (0 -72hours ) forecast period, however less so in the post 14 day model forecast ranges with about 50 % success. So, since the first super computer  installations at Bracknell I would say not a lot has changed in the success rate post 7 days relative to the short term forcasts.

The best forecast charts generated in my view are the METO fax charts to 120 hours. Beyond that modelling is still in the lap of the gods.

C

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I agree so far so good, but it's constant chopping and changing in the latter stages of its updates kind of renders it's long term use a little redundant. I much prefer the John Holmes way of looking at the 7-10 day as being more often than not right and everything else beyond is a case of looking for trends. The trend I see is one where the jet sinks further and further south over time, what happens next who knows.

I stress that posting the EC32 solutions here in abstracted descriptive sense is not a vouchsafe for outcome matching prognosis. Nonetheless, it paints a clear signal until & through festive period, albeit a minority of members offer 850 temps to -10C into early Jan for Reading ENS plume. Whether this signal is bolstered in further runs next week, we shall see. Either way, I'm uncertain how many folk who readily dismiss EC32 actually have access to the full suite of products to offer informed judgement, but of course we can't reproduce it all freely which I do appreciate is a frustration for those keen to compare it with likes of CFS or into tail-end timeframes of main model DET runs.

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Once again the 06 GFS Op is a clear outlier in the low res part of the run and unlike the 00 is the coldest member of all, highlighting the dangers of expecting the kind of charts previously posted for the big day.  That said at least the mean sits pretty close to average after the 23rd, but whether that will still be the case in 6hrs time remains to be seen.

 

Posted Image

Edited by shedhead

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I stress that posting the EC32 solutions here in abstracted descriptive sense is not a vouchsafe for outcome matching prognosis. Nonetheless, it paints a clear signal until & through festive period, albeit a minority of members offer 850 temps to -10C into early Jan for Reading ENS plume. Whether this signal is bolstered in further runs next week, we shall see. Either way, I'm uncertain how many folk who readily dismiss EC32 actually have access to the full suite of products to offer informed judgement, but of course we can't reproduce it all freely which I do appreciate is a frustration for those keen to compare it with likes of CFS or into tail-end timeframes of main model DET runs.

My point being though Ian is that come the next update we could be looking at a completely differing signal to  the one being presently shown, even the xmas period is at the latter stages of reliability. I would say the only certainty is that it will remain unsettled, but with regards to the jet alignment  there's plenty of options available.

Edited by Sceptical Inquirer

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My point being though Ian is that come the next update we could be looking at a completely differing signal to  the one being presently shown, even the xmas period is at the latter stages of reliability. I would say the only certainty is that it will remain unsettled, but with regards to the jet alignment  there's plenty of options available.

Of course we could.... as with ANY other NWP product! That sort of possibility is always a given. Nonetheless: as I stressed earlier, last 3 runs have offered good continuity on *broad* expectations into Xmas period. The latest DET models into same time frame offer similar story. Nuances such as depth of cyclonicity; transient chillier spells of Pm or rPm flow etc are obviously beyond the realm or raison d'etre of EC32. Anyway... we move on.

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My point being though Ian is that come the next update we could be looking at a completely differing signal to  the one being presently shown, even the xmas period is at the latter stages of reliability. I would say the only certainty is that it will remain unsettled, but with regards to the jet alignment  there's plenty of options available.

Indeed SI, even flatter being one of them....there will of course be changes, but at this juncture we can no more assume they'll be for the better/colder, than the worst/milder. 

Edited by shedhead

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Ho Ho Ho...Brrr Posted Image ..Look at these festive charts from the Gfs 06z op run, untold riches compared to the prolonged stagnant mild outlook the models were showing recently, it looks like there could be a more pronounced wintry spell within the overall structure of the upcoming very unsettled pattern with some snow events as we reach christmas week..we were told it would take a long time to get back to anything remotely wintry, well it might be sooner than that.Posted Image

post-4783-0-81840600-1386940299_thumb.pn

post-4783-0-12987600-1386940314_thumb.pn

post-4783-0-88129800-1386940334_thumb.pn

post-4783-0-34823300-1386940350_thumb.pn

post-4783-0-76264900-1386940361_thumb.pn

post-4783-0-94576800-1386940373_thumb.pn

Edited by Frosty.

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No doubt about it Christmas day currently looks like it will be unsettled, whether its cold enough for snow away from high ground remains to be seen the GFS ensemble

 

Posted ImagePosted Image

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