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phil nw.

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

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The Gfs 18z op run is showing spells of rather wintry weather for the northern third of the uk, especially for n.ireland & n and w scotland with snow showers at times, mostly at elevation but sometimes lower down, stormy at times with severe gales and heavy rain / hill and mountain snow in scotland with northern uk seeing very little of anything mild, the colder air also digs further southeast at times with a risk of the showers turning wintry on hills but with occasional milder days for southern uk, but the north looks borderline wintry.

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Edited by Frosty.

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I knew what you meant but what about those trying to learn?

 

they've learned that even the 'experts' can make mistakes john...... Posted Image

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Again a nice FI all due to the developing + PNA sending heights to the pole, consequently shifting the PV...

Posted ImagePosted Image

Edited by Panayiotis

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Again a nice FI all due to the developing + PNA sending heights to the pole, consequently shifting the PV...

Posted ImagePosted Image

Agreed. The jet coming south , along with the polar vortex itself !! We actually are in quite a wintry set up toward the end of the run . Cold northwesterly winds with sleet and snow at times. Unsettled and wintry fi tonight is how I would sum up the 18z Edited by Severe Siberian icy blast

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Let's keep watching FI to see if there are continuing hints of high pressure pushing into the pole and PV could be shunted away. Obviously caveats apply strongly as it's FI but trends would be very interesting as we see a dominated spell of zonal weather with low pressures cutting across and though us after a benign spell of chilly weather. All interesting.

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Putting aside just how unreliable the GFS lower resolution output is, taken at face value you can see just how resilient the PV is, that Alaskan Ridge sends wave after wave of attack and the PV troops finally give in but its hard going!

 

I think going forward we're going to need some help from that region to disrupt the PV,

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For the newer model-watchers, you'll now witness a phase where all manner of output solutions appear from especially mid-late next week onwards. Just very minor ripples or perturbations (almost imperceptible at times) in the strong jet / baroclinic breeding-ground out west across the Atlantic will herald considerable variation in outcomes; e.g. witness how the last 00z runs ushered a bothersome-looking dartboard low right across the UK later next week with some rather sporting gust strengths (a potential yet to be reliably discounted) whereas by 12z, deterministic models effectively lost it or tempered it. An inevitable oscillation in such solutions - some more extreme than others - makes for some difficulties in the medium-range forecasting pondering the period later next week, let alone the downstream knock-on's that cascade further along model timelines beyond circa T+168. Fascinating times, after what feels like innumerable recent days of chasing boundary layer detail and stratocu gunk around the charts with likes of EURO4 and UKV, just to stay awake at work... (!)[/quote

The british at is best coming up. No wonder we are a nation obsessed with it. Cold coming in the New Year?

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Yep it must have been hideously boring describing different layers of cloud in a stagnant rather mild pattern, thank gowd that limpet euro high will not scupper the first month of winter.

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For the newer model-watchers, you'll now witness a phase where all manner of output solutions appear from especially mid-late next week onwards. Just very minor ripples or perturbations (almost imperceptible at times) in the strong jet / baroclinic breeding-ground out west across the Atlantic will herald considerable variation in outcomes; e.g. witness how the last 00z runs ushered a bothersome-looking dartboard low right across the UK later next week with some rather sporting gust strengths (a potential yet to be reliably discounted) whereas by 12z, deterministic models effectively lost it or tempered it. An inevitable oscillation in such solutions - some more extreme than others - makes for some difficulties in the medium-range forecasting pondering the period later next week, let alone the downstream knock-on's that cascade further along model timelines beyond circa T+168. Fascinating times, after what feels like innumerable recent days of chasing boundary layer detail and stratocu gunk around the charts with likes of EURO4 and UKV, just to stay awake at work... (!)

 

What about the sudden development of a 'third' low for this weekend which has cropped into a fair % of GEFS 18z members.

 

It is often the case that the severest storms come out of the blue.

 

The transfer of energy in these situations can change from run to run, often the focus of energy can move ahead of the expected intense low and develop a feature that was initially expected to be benign. This has historically occurred, i am not read up about it enough but it has something to do with group velocity.

 

Posted Image

Edited by Matty M

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For the newer model-watchers, you'll now witness a phase where all manner of output solutions appear from especially mid-late next week onwards. Just very minor ripples or perturbations (almost imperceptible at times) in the strong jet / baroclinic breeding-ground out west across the Atlantic will herald considerable variation in outcomes; e.g. witness how the last 00z runs ushered a bothersome-looking dartboard low right across the UK later next week with some rather sporting gust strengths (a potential yet to be reliably discounted) whereas by 12z, deterministic models effectively lost it or tempered it. An inevitable oscillation in such solutions - some more extreme than others - makes for some difficulties in the medium-range forecasting pondering the period later next week, let alone the downstream knock-on's that cascade further along model timelines beyond circa T+168. Fascinating times, after what feels like innumerable recent days of chasing boundary layer detail and stratocu gunk around the charts with likes of EURO4 and UKV, just to stay awake at work... (!)

Recent conditions get the hearts of aviation forecasters beating rapidly; no problems staying awake there! The sort of action weather shown by some models can sometimes be less troublesome by comparison...

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Recent conditions get the hearts of aviation forecasters beating rapidly; no problems staying awake there! The sort of action weather shown by some models can sometimes be less troublesome by comparison...

Yup the fog issues have been decidedly tricky!! Tomorrow equally so with that wave running up the occlusion into SW/Wales. Difficult detail.

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For the newer model-watchers, you'll now witness a phase where all manner of output solutions appear from especially mid-late next week onwards. Just very minor ripples or perturbations (almost imperceptible at times) in the strong jet / baroclinic breeding-ground out west across the Atlantic will herald considerable variation in outcomes; e.g. witness how the last 00z runs ushered a bothersome-looking dartboard low right across the UK later next week with some rather sporting gust strengths (a potential yet to be reliably discounted) whereas by 12z, deterministic models effectively lost it or tempered it. An inevitable oscillation in such solutions - some more extreme than others - makes for some difficulties in the medium-range forecasting pondering the period later next week, let alone the downstream knock-on's that cascade further along model timelines beyond circa T+168. Fascinating times, after what feels like innumerable recent days of chasing boundary layer detail and stratocu gunk around the charts with likes of EURO4 and UKV, just to stay awake at work... (!)

In other words, in my simple (and very unprofessional capacityPosted Image ) this from earlier:

 

The deep depression on the ECM from this morning is not indicated on tonights output at day 7, but we should continue to watch for secondary developments spawning on the south western perimeter of the vortex gyre, where the temperature gradient is very steep, and then tracking eastwards towards the UK. Before then, NW Scotland in particular is threatened by very strong winds as soon as the latter part of this weekend

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In other words, in my simple (and very unprofessional capacityPosted Image ) this from earlier:

The deep depression on the ECM from this morning is not indicated on tonights output at day 7, but we should continue to watch for secondary developments spawning on the south western perimeter of the vortex gyre, where the temperature gradient is very steep, and then tracking eastwards towards the UK. Before then, NW Scotland in particular is threatened by very strong winds as soon as the latter part of this weekend

Exactly. Continuity/inter-model agreement broadly ok up to around Weds. By then, UKMO-GM has widespread 45kt gusts across UK. Blowy for sure. Beyond that, it's a ripe cookpot for small-scale lows to deepen rapidly and models will presently struggle with such detail. Edited by fergieweather

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well glad i popped the computer on looking at recent very interesting posts ,woken up by wind knocking blind ,yes certainly in current and medium range forecast a LOT happening and a lot of changes as systems develope in a mix of air in the north atlantic .so looking at the period of past 168 hrs on the models i would expect many changes over the course of just one day in the models . some very interesting times ahead and a fair possibility now that we could be seeing something wintry turn up in what will be a very turbulent atmosphere .Posted Image just a DE Cafe as going back up now .

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Boxing Day looking potentially snowey in a fairly Northerly flow. Trend continues to show interest in FI

I think some excitement might build in here this morning.

Edited by Ali1977

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The GFS op looks an extreme run compared to the ensembles, in outlier territory on various indices, including 500hPa temps, from about Christmas week:

 

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In fact there are only 7 instances of only 5% snow risk from the ensembles, the lowest on recent runs, so the outlook on the ground  barring a more interesting op is no better. The Christmas day 850 mean shows limited (average) cold uppers for most:

 

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Looking at the GEFS postage stamps, although the majority have us in a zonal flow, there is now a shuffling of the long wave pattern with the Euro/Russian high showing its hand again with attempts at ridging north in the late FI: http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=6&ech=384

 

Still no sign of real cold but cooler would be a fair assessment, with potential if this trend is maintained. The op was the only one as progressive with the vortex split so an outlier at the moment.

 

Upto D10 little change with dry days followed by weather fronts or lows; the north suffering the greater rain amounts. Most of the GEFS are different so FI for surface conditions starts very early at the moment. ECM has the whole country under the zonal flow between D5-6 and is another variety of the GEFS. Good synoptic cross model support.

Edited by i'm dreaming of...

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Very interesting run from the GFS, with storms, potential snow, a split vortex at the end with a section of the polar vortex's lobe slumping down on us which would be very snowy and windy for sure and it's not something you see very much of, but it would be cold enough for widespread, 'proper' blizzards.

 

Lovely to see the run of dull weather being upgraded to 'something for everyone' weather :-)

 

 

All I have to decide now is whether to fix my fence this weekend or wait until next? I only got the panels 2 days ago becaue of the shortage caused by the last storm?     What do you guys think?

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P20...GEFS 00z snowfest please Posted Image

 

Looking at the GEFS 00z mean, the PFJ is generally to the south of the uk and the weather continues very disturbed with frequent bouts of heavy rain and severe gales interspersed by clearer, colder showery weather and generally cold enough for snow across northern hills and occasionally on higher ground further south, there is also a chance of it being cold enough during christmas for snow showers as arctic air digs south/se.

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Edited by Frosty.

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Well after overnight minima between 8-12c for the majority of the country, anything other than a cooling trend would be a major surprise to be fair. All the main models are now singing from the same very unsettled, locally stormy hymnsheet up to and across the Christmas period, but any hope of snow on the big day remains very much a timing issue for now and as such a long shot. Looking at the 00 GFS London ensembles the Op was one of the coldest runs in FI, particularly around Christmas itself, with the mean around +3c rather than -3c.

 

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Edited by shedhead

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We're still an eternity away from Christmas day in meteorological terms, but snow on the big day is a distinct possibility for Scotland, N.Ireland and northern England in such set ups and can't be ruled out for areas further south - one to keep an eye on I think and the Bartlett fest promised by many is looking almost certain not to occur.

 

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Spot on.  Bartlett did not happen, and there is no way of knowing what Pattern we are going to really go into.  Maybe this Zonal spell will be another week long affair rather than protracted spell.  More runs needed 

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