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06z model discussions - wet and windy soon?!


Paul

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

you had best read the output regarding models by TWS. I don't think the remarks you make about the models are all that accurate.

ECMWF has generally done quite well as have both GFS and Met O.

John

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

Interesting that John Holmes's blog points out that the main three models are all well-aligned in their predictions come Saturday; it seems to be how we get there from Wednesday through Friday that brings massive disagreement.

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Posted
  • Location: Ayton, Berwickshire
  • Weather Preferences: Ice and snow, heat and sun!
  • Location: Ayton, Berwickshire

I'm afraid that it's very poignant that the low progged by 6Z GFS over S. England at T120 is the shape of a pear! I would expect UKMO and ECM to fall in line at some stage today. 2-4" max over 300m from pennines northwards IMO, followed by rapid thaw.

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Posted
  • Location: Peterborough N.Cambridgeshire
  • Location: Peterborough N.Cambridgeshire
What is 'ramping' ??? All I have seen over the last few days is people discussing the model output as it has looked at that time, and it is only human nature to respond to that output accordingly. I haven't seen many posts talking about how much snow we were definitely all going to get at any specific time or location - in fact generally speaking it has all been very circumspect.

The fact the models are now showing a different outcome does not make the discussions of the past three days invalid. If individuals have chosen to build up their own hopes too much then that is their own look-out !

Very well said PFTD.

You know I feel some members would be better off not just using the models but using their own experiences of such synoptics in the past to assist in helping what might happen.

As an example let me use some members posts whose location is the S coast who seemed disappointed with todays outputs. If I lived on the S coast then I wouldn't be disappointed with todays runs because I wouldn't of expected much out of this anyway. The S coast requires alot of luck in achieving a snow event and what you basically need is a cold feed off the continent and then the LP tracking along N france. This is where the luck comes in because if that LP tracks just further N you remain in the warm sector i.e S of the LP system. Now the models haven't really suggested a cold feed off the continent because our cold supply is via the current N,ly and the current tracks of the LP system have been to far N for thee locations.

So what we need to establish is how will the atlantic approach our shores. Will the GFS be right with a classic scenario of rain preceeded by snow before milder weather moves in or will the UKMO be right with a channel LP bringing snowfall to the locations I mentioned. What could also happen is the Scandi HP remains firm and as the LP tracks SE we then start pulling a colder feed from the continent so you could then have a case of snow/rain then turning back to snow.

So IMO don't just use the models use your experience of following the weather in your location and don't make the mistake of assuming just because the wind is from the E you will have snow look at the wider picture.

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Posted
  • Location: Kippax (Leeds) 63m
  • Location: Kippax (Leeds) 63m
A little bit disingenuious, I feel, and certainly a bit unfair.

A cold/mild battle happens whenever there is a frontal boundary I think that the likelihood for snow happening this week is what is in the balance. Even if that's not what has been said, that is certainly what is meant.

Incidentally, snow shower forecasts (those being caused by convective activity alone from an unstable surface boundary) are always well forecast by the models, and their human counterparts. That is, of course, their existence: the problem in those situations is the distribution of such showers leading to the 'Will it snow in?' Which has it's summer counter-part: 'Will I see lightning in?'

Snow caused by frontal systems is always going to be marginal because a front marks the difference between cold and warm air masses so you are always going to have warm(er) air around. These setups are notoriously hard to to predict; and, as I understand it, there is no notion of numerical certainty that can supply a method to produce a good forecast in marginal situations. I read, somewhere, that the existence of showers is forecast with an accuracy of 75%, and frontal snow, currently stands at 20%.

It may indeed be a case of watch the big picture, let the cold air come in, and see what happens on the day.

In fact, I'm almost certain of it.

A nicely put post there :lol:

I agree with many things you say there, but the major concern is that once the progged frontal systems push through, the floodgates for mild south westerlies get smashed open! (according to latest gfs/esembles that have performed pretty well this winter..) I feel that the battle might be won before it even happens! (i.e no battle at all means the iresistable force has won every time ;) )

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Posted
  • Location: Eastbourne and Larnaca,Cyprus .
  • Location: Eastbourne and Larnaca,Cyprus .

You have to love the gfs! from more snow than you can shake a stick at to a complete implosion all within 2 runs, even by the gfs standards thats going some!

Heres the ukmo 48hrs chart from its latest 06hrs run.

http://moe.met.fsu.edu/cgi-bin/ukmtc2.cgi?...&hour=048hr

And heres the gfs for the same time.

http://moe.met.fsu.edu/cgi-bin/gfstc2.cgi?...&hour=048hr

For only 48hrs ahead thats quite a difference, the fly in the ointment is that shallow feature in the north sea which forces the ridge from scandi too far north, as ever in the uk theres always something to pop up and throw things into turmoil!

Paragraphs 2 and 3 here suggests why the models are all over the place. Until the models get to grips with the energy coming off the PV then you can just view all output with alot of caution and given the difference between the ukmo 06hrs and gfs of the same time F1 starts at 48hrs!

http://www.hpc.ncep.noaa.gov/discussions/pmdepd.html

Edited by nick sussex
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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks
Interesting that John Holmes's blog points out that the main three models are all well-aligned in their predictions come Saturday; it seems to be how we get there from Wednesday through Friday that brings massive disagreement.

yep I think they have it and my attempt at a forecast I hope explains how it will happen. Always happy to explain if anyone has any questions.

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Posted
  • Location: West Sussex/Surrey border
  • Location: West Sussex/Surrey border
You have to love the gfs! from more snow than you can shake a stick at to a complete implosion all within 2 runs, even by the gfs standards thats going some!

Heres the ukmo 48hrs chart from its latest 06hrs run.

http://moe.met.fsu.edu/cgi-bin/ukmtc2.cgi?...&hour=048hr

And heres the gfs for the same time.

http://moe.met.fsu.edu/cgi-bin/gfstc2.cgi?...&hour=048hr

For only 48hrs ahead thats quite a difference, the fly in the ointment is that shallow feature in the north sea which forces the ridge from scandi too far north, as ever in the uk theres always something to pop up and throw things into turmoil!

Paragraphs 2 and 3 here suggests why the models are all over the place. Until the models get to grips with the energy coming off the PV then you can just view all output with alot of caution and given the difference between the ukmo 06hrs and gfs of the same time F1 starts at 48hrs!

http://www.hpc.ncep.noaa.gov/discussions/pmdepd.html

Blimey, this is the biggest disagrement with all the models I have ever seen. What the hell is going on?

And to think it's 48 hours. I could use pine cones to predict the forecast better than the models.

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Posted
  • Location: Weston Super Mare , North Somerset
  • Location: Weston Super Mare , North Somerset

Lets hope the essembles throw some light. all we can hope for is that the majority of them go for the ukmo sollution. it is not unusual for a gfs operational run to be a complete outlier.

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Posted
  • Location: Co Dublin, Ireland
  • Location: Co Dublin, Ireland
You have to love the gfs! from more snow than you can shake a stick at to a complete implosion all within 2 runs, even by the gfs standards thats going some!

Heres the ukmo 48hrs chart from its latest 06hrs run.

http://moe.met.fsu.edu/cgi-bin/ukmtc2.cgi?...&hour=048hr

And heres the gfs for the same time.

http://moe.met.fsu.edu/cgi-bin/gfstc2.cgi?...&hour=048hr

For only 48hrs ahead thats quite a difference, the fly in the ointment is that shallow feature in the north sea which forces the ridge from scandi too far north, as ever in the uk theres always something to pop up and throw things into turmoil!

Paragraphs 2 and 3 here suggests why the models are all over the place. Until the models get to grips with the energy coming off the PV then you can just view all output with alot of caution and given the difference between the ukmo 06hrs and gfs of the same time F1 starts at 48hrs!

http://www.hpc.ncep.noaa.gov/discussions/pmdepd.html

Why do people keep saying 'F1' instead of 'FI' ;)

Anyway I agree with that. Huge differences there I would argue even less then 48hrs out!

You would have to say thats a little attrocious to say the least :lol:

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Posted
  • Location: Macclesfield
  • Location: Macclesfield
Why do people keep saying 'F1' instead of 'FI' ;)

Anyway I agree with that. Huge differences there I would argue even less then 48hrs out!

You would have to say thats a little attrocious to say the least :lol:

F1 hybrid like seeds maybe?

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Posted
  • Location: Upper Tweeddale, Scottish Borders 240m ASL
  • Location: Upper Tweeddale, Scottish Borders 240m ASL

After the weekend outputs suggesting the south coast, then the south Midlands and a proggessive movement north of the atlantic front hitting the colder air - somebody somewhere is going to get a dumping?:

prectypeuktopo.png

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Posted
  • Location: Kippax (Leeds) 63m
  • Location: Kippax (Leeds) 63m

''After the weekend outputs suggesting the south coast, then the south Midlands and a proggessive movement north of the atlantic front hitting the colder air - somebody somewhere is going to get a dumping?:''

Hmm.. places like eskdalmuir and Glasgow allways seem to do really well from these scenerios!

Edited by Jed Bickerdike
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Posted
  • Location: Eastbourne and Larnaca,Cyprus .
  • Location: Eastbourne and Larnaca,Cyprus .
Why do people keep saying 'F1' instead of 'FI' ;)

Anyway I agree with that. Huge differences there I would argue even less then 48hrs out!

You would have to say thats a little attrocious to say the least :lol:

That link I provided was from last nights discussions at NOAA, but the problem for the models is deciding how much energy gets thrown off the PV over canada and how quickly east it travels and then deciding what happens to that ridge from scandi, that shallow feature in the north sea is a real pain as it stops the ridge from scandi backing west further south and this then changes the surface flow ahead of the shortwaves. In a marginal situation small changes make a huge difference as one can see from those two differing views from the ukmo and gfs.

On top of this the models are desperate to breakdown the pacific ridge driving more energy into the atlantic but they've been trying to break this down for the last few weeks and have failed so far, there is intense cold across most of the east usa and canada and the models IMO are being too progressive in trying to get rid of this so at this moment in time all the output is likely to be very unstable and for the longer term completely all at sea.

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

for the south of UK, England, IF the models are anywhere near correct, then apart from transient snow on the higher hills, Briefly, the main concern must be wind strengths into the weekend.

Edited by johnholmes
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Posted
  • Location: Irlam
  • Location: Irlam
for the south of UK, England, IF the models are anywhere near correct, then apart from transient snow on the higher hills, Briefly, the main concern must be wind strengths into the weekend.

Depends on what model. Not much wind on the latest FAX chart for Saturday

http://85.214.49.20/pics/brack4a.gif

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Posted
  • Location: Rochester, Kent
  • Location: Rochester, Kent
for the south of UK, England, IF the models are anywhere near correct, then apart from transient snow on the higher hills, Briefly, the main concern must be wind strengths into the weekend.

Yes, John, I quite agree.

However, I don't think it's all over for the far S/E though, in terms of seeing some of the white stuff - just highly marginalised. I was hoping to get some showers drifting off the N Sea; but, according to GFS, that's about the time the winds curl up and turn into a westerly as the low disspates slightly when it heads into Scandinavia. After all the air source for much of the UK (for the next two days) is Arctic Maritime - unstable surface, and long (unmodified) sea tracks can often spring a suprise or too!

Anyway, enough hopecasting, by me

;)

Depends on what model. Not much wind on the latest FAX chart for Saturday

http://85.214.49.20/pics/brack4a.gif

Shame that the air will already be well-mixed before it hits Kent, though :lol:

Edited by VillagePlank
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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks
Depends on what model. Not much wind on the latest FAX chart for Saturday

http://85.214.49.20/pics/brack4a.gif

it does indeed depend on which chart you use.

I based my comments on the fact that all 3 main models have a deep depression heading into or already over the south of England at the start of the weekend.

I've always said as a forecaster, sit, watch, wait, ponder, but sooner rather than later you have to grasp the nettle and issue a forecast. That is what blog 8 is about. I'm quite prepared to issue blog 9 later today, or more likely tomorrow, with a different slant if the models indicate it. I doubt they will change overmuch for their predict of the cold spell ending, probably with a short rather windy interlude, as it does so.

Edited by johnholmes
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Posted
  • Location: Eastbourne and Larnaca,Cyprus .
  • Location: Eastbourne and Larnaca,Cyprus .
Not one single ensemble member is like the UKMO. All very transient stuff from every run expect for the far north of Scotland. :lol:

Theres no point looking at the GEFS ensembles for the shorter term detail which is so crucial. The GEFS is run at a lower resolution than the gfs operational run upto 180hrs, after 180hrs its resolution is better than the gfs. For crucial small detail in a knife edge situation the gefs ensembles wont tell you a great detail because we're dealing with tiny margins here, by far the best in this situation is the ukmo for within 72hrs.

Edited by nick sussex
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Posted
  • Location: Co Dublin, Ireland
  • Location: Co Dublin, Ireland
Theres no point looking at the GEFS ensembles for the shorter term detail which is so crucial. The GEFS is run at a lower resolution than the gfs operational run upto 180hrs, after 180hrs its resolution is better than the gfs. For crucial small detail in a knife edge situation the gefs ensembles wont tell you a great detail because we're dealing with tiny margins here, by far the best in this situation is the ukmo for within 72hrs.

I think im right in saying that the fronts are located slightly further north on the 6z UKMO for 48hrs? This makes sense considering the ECM output. Still that is a cracking chart IMO. :lol:

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Posted
  • Location: Aviemore
  • Location: Aviemore
Theres no point looking at the GEFS ensembles for the shorter term detail which is so crucial. The GEFS is run at a lower resolution than the gfs operational run upto 180hrs, after 180hrs its resolution is better than the gfs. For crucial small detail in a knife edge situation the gefs ensembles wont tell you a great detail because we're dealing with tiny margins here, by far the best in this situation is the ukmo for within 72hrs.

While you're right in terms of the resolution Nick, the ensembles still provide a very useful tool at closer range as the different members can show subtle differences which can be key in working out the outcome.

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