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phil nw.

Model Output Discussions 18z 31/01/2016

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Not wanting to come across as a kill-joy.. But can we please try and only discuss 'Model Output' in here. There are Winter ramp/moan/BBC/METO threads already open for other discussion.

That aside.. I hope your all enjoying Valentines day :D 

Many thanks, PM

Edited by Polar Maritime

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The 6z snow risk for Thursday.

a.pngb.pngc.png

Edited by Polar Maritime

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40 minutes ago, johnholmes said:

re Thomas S on BBC and being a mild ramper, with the Fax chart we see showing atlantic air over the country by Wednesday, what on earth do you expect him to say having had his brief from the senior man that drew that chart up?

get real some of you.

Pretty much all the model output shows milder Atlantic air is going to move in during Wednesday, on current timing. The anomaly charts have been signalling this perhaps for a couple of days at about day 6 which initially suggested about 19th, but now looks more like Wednesday into Thursday.

links below

http://www.weathercharts.org/ukmomslp.htm#t120

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

http://www.cpc.noaa.gov/products/predictions/610day/500mb.php

 

Over the past 3-4 days the heights at 500mb over the far south of the UK have been predicted to rise quite steadily, from about 540DM 6-7 days ago to closer to 552DM ir a bit higher on the latest NOAA 6-10.

I'm sorry to disagree but the fax chart does not show mild Atlantic air over the UK. The air coming in behind the front is PM and not some blowtorch sw'erly. The fax chart shows the mild sector being squeezed out and theres still cold at the surface ahead of it. If that was not the case then how on earth would the UKMO text forecasts suggest a chance of snow if the cold had already been mixed out? Or was the UKMO text forecast written by a junior on work experience? Midweek is still complicated and could go either way. The issue is Wednesday, its of course likely to turn milder later in the week but the point of debate is Wednesday.

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The 6z shows a more progressive colder N/W flow by the weekend with more heavy snowfall over the Highlands as -7/8 850's push S/E over the UK. There's some excellent skiing conditions to be had up there as we speak.

a.pngb.pngc.png

Edited by Polar Maritime

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To clarify the fax charts to show the progression of milder air:

The area circled red is the milder air, you can see between T60 and T84hrs this gets squeezed out:

fax60s.thumb.gif.883da8f77129d62eca9f97c

fax72s.thumb.gif.97481d4bfd128d791f8d7cc

fax84s.thumb.gif.58e9e16abb8221c745ec2ee

You can see just how slow the progression of fronts is between T72hrs and T84hrs. Models often find these sets ups difficult especially in terms of milder sectors and how quickly the fronts might occlude.

I've just used the 546 dam as that's the easiest to highlight, the fax charts might well change in terms of the speed of those fronts. We'll probably have a better idea tonight or tomorrow morning but theres still a lot of uncertainty for Wednesday.

 

 

Edited by nick sussex

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Part of the problem for next week is that the deep low that was projected to be over Italy has been downgraded to a much shallower feature. That low was helping to keep the high to the north of it in a favourable position for keeping some cold ahead of the Atlantic front.

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Good morning ,The cold is in [hooray] so something to be happy with .

looking at all current charts and Data we will i feel be having an interesting and nail biting Model output Discussion and i,m sure plenty of twists and turns .

Next weeks action currently shown tues/wed will probably go down near to the wire ,Fax charts eagerly awaited for finer detail .

Very briefely [if only weather presenters had more air time ,i,m pretty sure that would save a lot of confusion for many ]question ,at what time frame was tonights tomorrows snow showers pushing in from the east forecast ,i,m pretty sure it wasnt that long ago ,my point the weather later next week may be totally different to what we currently expect .

great forum ,chins up gang  its not over yet cheers :yahoo:

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1 hour ago, nick sussex said:

To clarify the fax charts to show the progression of milder air:

The area circled red is the milder air, you can see between T60 and T84hrs this gets squeezed out:

fax60s.thumb.gif.883da8f77129d62eca9f97c

fax72s.thumb.gif.97481d4bfd128d791f8d7cc

fax84s.thumb.gif.58e9e16abb8221c745ec2ee

You can see just how slow the progression of fronts is between T72hrs and T84hrs. Models often find these sets ups difficult especially in terms of milder sectors and how quickly the fronts might occlude.

I've just used the 546 dam as that's the easiest to highlight, the fax charts might well change in terms of the speed of those fronts. We'll probably have a better idea tonight or tomorrow morning but theres still a lot of uncertainty for Wednesday.

 

 

 
 
 
 
 

Yes, from the media forecasts I've watched so far, they are expecting back edge snow (most likely from central to Eastern regions based on current thinking) on Wednesday through to Thursday. We shouldn't get too hung up on the specifics as the timeframes of said event are moving and if the cold fronts move in at a pace and catch up with the warm front an occlusion(!) occurs and snow will likely fall more widely. Questions then will be, how much can settle on already saturated ground, the heaviness of the precipitation, where and when and how fast the mixing out of air masses might assist in boosting the snow-making potential. Yep, far too complex and complicated right now to second guess anything with regards to the snow and it'll be a wait and watch until Tuesday for me. The colder that Northerly airflow is beforehand the better. Exciting times ahead, whatever. :friends:

Edited by gottolovethisweather

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Nice to see the reports and photos of snow in the NE today, the sleet and snow showers transfering further south tonight and through Monday morning, as high pressure begins to build across Scotland, some showers perhaps getting inland across the eastern half of England, but probably not amouting to much for most.

The frontal system passing through mid-week dragging its heels more and more over recent few runs as it reaches SE England and E Anglia, big 3 GFS, UKMO and ECMWF not clearing the precip here until at least Thursday lunchtime, 00z GFS not from the far SE until Thursday evening.

What's happening is that there is an increasingly amplified diffluent upper trough behind this frontal system, where jet winds are strongest going into the western side of the trough and weakest coming out of the eastern side allowing divergence aloft and one or two waves to develop along the frontal boundary - slowing its progress after moving through more swiftly across northern and western areas.

gfs_jet_300_natl_18.thumb.png.e8e8b0b789

Unfortunately,  the way things are going this winter, surface dew points and temperatures shown by the models are for now a few degrees the wrong side of marginal for snow on the front for most away from higher ground due mixing out ahead of the front, so unless the colder air and sufficiently low dew points catch up from the NW and undercuts, the less cold air occludes out quicker than modelled and/or, we see stronger advection of cold and dry air off the near continent ahead of the front - then it looks nothing to get excited about. Still a chance, that lowland areas may see some wet snow out of this front, particularly if the precip is heavy enough to allow evaporative cooling and coincides after dark (Weds night) with the added cooling that brings. 

But it really is slim pickings from this cold snap for most, I will at least enjoy the frosty mornings while they last ...

Edited by Nick F

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On ‎07‎/‎02‎/‎2016 at 11:11 PM, bigdog1 said:

How many times this winter have we been here with these models and then two days later a complete downgrade happens 

was not far out when I posted this seven days ago

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46 minutes ago, ajpoolshark said:

Well, I have to say, all the models are bang on for today and the next few days!..........lets see now....

  1. wind from an easterly quadrant.................................check
  2. Cold T850's....................................................................check
  3. dew points below 0c....................................................check
  4. Thickness values low...................................................check
  5. ...and then big mild sector spoiler on wednesday...check
  6. white flakey things on wednesday.............................uncheck

Lord Poolshark's search for his snowy apprentice continues......................... :80:

When I was a boy I used to draw synoptic charts which showed immense amounts of cold and snow. Six checks would be no problem at all  :D

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7 minutes ago, Weathervane said:

When I was a boy I used to draw synoptic charts which showed immense amounts of cold and snow. Six checks would be no problem at all  :D

I'm glad I'm not only one!:D

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Lack of posts somes up the mood in here this evening!!!12z i assume aint any different!!!

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Two rain events for the week ahead. Wednesday a cold front but the GFS now shows a total rain event , then a warm front on Friday to herald a mild weekend with 12-14 possible:

Sat:gfs-9-144.thumb.png.5650adbd4e9dd1ac38ccgfs-15-144.thumb.png.cb6196aeb97590c5242 Sun: gfs-9-168.thumb.png.3a3322e95ce0b1555097

Hopefully the models will firm up on a nice weekend, being half term at least a few mild dry days in the mix.

Edited by IDO

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IDO is wrong.

The front stalls over SE/EA with some back-edge snow being offered.

image.thumb.gif.287b88b3a8ef931d14d1b13e

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All change next weekend with much milder air sweeping across large parts of the UK

144-778UK.GIF?14-12168-778UK.GIF?14-12

144-574UK.GIF?14-12168-574UK.GIF?14-12

This then moves away with temps back closer to average as we start the final full week of winter

192-778UK.GIF?14-12

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GFS 12z take on Wednesday/Thursday snow risk.

a.thumb.png.ec933d8340eef820badb10abaa57b.thumb.png.5bffdfb0f448c70a038faf0c3c72c.thumb.png.10fcb62123df1bc378c13c5313af

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