Model Output Discussion - 12th December Onward

[Weather-history]

The ECM is very progressive and the consistent thing is the deep PV over Greenland - the GFS is the very best outcome from the cards we have to play with.

It has to be said that ECM 12z is not exactly one long mild fest. Infact extrapolating, some areas in the far north could even something wintry out of it Christmas Day if it was run exactly as such

[Jhonny Peter Carson]

No doubt now, we are on. Models are all saying the same thing now and about time too. All you snow vampires, it is time to feed.

[jonnybradley]

GFS wed 12z t66

GFS having a go at push some of that Siberian high towards the pole. Not really any heights in the high pressure (is that right?) and gets pushed back south into Siberia towards the end of the run.

Could the PV be weakening going into the new year?

Jon

p.s sorry if thats wrong about the heights need to read up on it me thinks!

[TEITS]

Looking at the NAE I would advise some caution before getting too excited. In my experience of these marginal set ups the NAE has a tendancy of overdoing the possible snow and as +0 nears the pink area tends to shrink. Might not happen in this case but it is something i've noticed over the years.

As for beyond this LP system and like I said last night the best that we can hope for over xmas is dry, cold, settled due to HP i.e GFS 12Z.

[Duane S.]

To be honest i'm amazed the GFS 12z is not being ramped more. It's only one run of course but this is the biggest showing so far from the Siberian/Scandi high and whilst hardly being a BFTE I would bank that run in the blink of an eye. The ens for my area show support for it as well.

More good signs from the Stratosphere today as well. Quite possibly he beginning of the end for the early winter strong PV, question is how long and protracted will the transition be?

[feb1991blizzard]

Looking at the NAE I would advise some caution before getting too excited. In my experience of these marginal set ups the NAE has a tendancy of overdoing the possible snow and as +0 nears the pink area tends to shrink. Might not happen in this case but it is something i've noticed over the years.

As for beyond this LP system and like I said last night the best that we can hope for over xmas is dry, cold, settled due to HP i.e GFS 12Z.

Totally agree regarding the NAE, and sometimes it doesnt shrink and it even gets modelled wrong at T6, im certainly not holding my breath here, the other models dont seem to show as much Northwards progression and i would say the Northward limit will be Derby but hope to be proved wrong, one positive is Laura Tobin had the snow area even bigger than the NAE so you never know i suppose.

[Downburst]

The ECM run ends exactly where it starts. So this is a very stubborn pattern. Cold winds, W to NW, polar maritime, snow on hills and if you like snow you might be lucky in the north and west over the next two weeks. One thing I have noticed that the -5 isotherm doesn't have to be overhead, just out west a little and you can get snow the way the air is moving so fast.

Now the 12z GFS I am not so sure about, let's see if it shows again on the next couple of runs.

[feb1991blizzard]

It has to be said that ECM 12z is not exactly one long mild fest. Infact extrapolating, some areas in the far north could even something wintry out of it Christmas Day if it was run exactly as such

Agreed, as time goes by any SW / NE jet alignment keeps getting put back and now looking like a more West to East.jet is possible over the Xmas - New year week.

[shedhead]

ECM 240hr is worlds apart from GFS at that time and to my mind represents a far more plausible outcome. Any Xmas easterly looks a very long shot, probably 10/1+ as things currently stand. I'd offer similar odds that it's not there in a couple of hours time too, even the pub run is unlikely to follow it in my opinion.

[Downburst]

ECM 240hr is worlds apart from GFS at that time and to my mind represents a far more plausible outcome. Any Xmas easterly looks a very long shot, probably 10/1+ as things currently stand. I'd offer similar odds that it's not there in a couple of hours time too, even the pub run is unlikely to follow it in my opinion.

Exactly, ECM is exactly the same at 240 as it is at 0 hrs. Nothing changing, so remaining cold. max temp here today was 3 C in a stiff breeze, so that is wintery enough and I'd settle for that. ECM will be ignored though due to that certain GFS easterly now nailed on at 240 hours with it's snow showers falling on christmas eve as it does every year.

Edited December 14, 2011 by chionomaniac
Baiting

[damianslaw]

Meto forecast for the run up to christmas suggests more of the same - it appears to be more in line with ECM than GFS. So some temporary ridge development over the weekend from the west this being quickly pushed back southwards early next week by the jet and stubborn strong PV.. No signs of heights moving south and east - as the jet takes a west-east path rather than SW-NE path.. this is important as it would mean polar maritime air would continue to plague northern parts and every chance of a decent NW shot by christmas day itself.

Longer term - watch developments to our east and signs of a weakening PV, January and February show lots of snow and cold promise! (bit of a ramp it has to be said..).

[Robbie Garrett]

http://www.metoffice.gov.uk/weather/uk/se/london_forecast_weather.html

Snow for London this Friday, hmmm!

[Thundery wintry showers]

In my view if we're to see a cold snowy spell into January it will help if the jet maintains a NW-SE tendency, as anything SW-NE will tend to restrict any European pressure rises to no further N and W than southern Scandinavia. A NW-SE jet, as well as allowing some more shots at cold zonality, would be more favourable for allowing high pressure to develop over Scandinavia with troughing undercutting it into Europe, a setup which quite often leads to continental air extending its way towards the British Isles.

[ANYWEATHER]

Ecm ,goes for a more Zonal outlook, right at the end of its run, this is more to what Im thinking, I really dont see any Blocked patten in the near future. Models keep suggesting a blocked pattern we have already had this scenario during the previous months, but the Jet as Ive mentioned earlier is to strong for any high to develop.... Xmas day, Im not sure of the weather but I will put my Money on some Cold Zonal Atlatic weather having some influence across the Uk......

[WhiteFox]

Siberian high showing its hand early this year. As always worth a note of caution... Many times over the years I, and many other model-junkies have watched a siberian high come perilously close, only to be pushed back at the last minute. The problem is that we need so many things to fall into place for it to push far enough west and far enough north to deliver. This is why we so often see one or two very cold runs on the Ensembles showing upper temps at -10 with others showing average or above. Anyway, don't count on the siberian high delivering unless it's t+48 and all models are in agreement. You're relying on the jet being aligned perfectly unlike last December when northern blocking was prevalent and we had a much safer route to cold.

[phil nw.]

I thought that with all the changing scenarios created in the daily runs for the medium term i thought i would try and link some output from a wider view.

First the 12z mean hts for days 8-10(ECM +GFS)

http://www.meteo.psu...F_12z/test8.gif

and the latest 500hPa forecast

http://www.cpc.ncep....y/610day.03.gif

The constistent pattern being suggested is of mid-latitude high pressure near the UK just to our West or South West with further hts away to the East and low heights to our North.

The daily runs are toying with different placements and shape of the surface features and this will not be fiirmed up for a few days yet.

If we look for example at the thumbnails of the 12z GFS run-all 20 show the main Azores high and low hts to our north but they have different shapes to the surface features.

http://www.wetterzen...nspanel2401.gif

Of course things can and do change but looking at every run can be confusing,especially for newer members, and this sort of information can help to keep perspective in conjuction with the daily 2-4 times a day model runs.

John H`s updates looking at the bigger picture are well worth following for this reason.

I would say based on current and recent output an Easterly would be a rank outsider by Xmas --the energy over the top looks to strong to allow our High pressure to build far enough north at present.

The best we could hope for is to keep heights close by or over the UK to allow a cold surface setup,which would result in frosts and maybe fog--seasonal at least.

[Frosty.]

The Ecm 12z looks similar to the canadian ensemble 00z run this morning and the Gfs 12z has delayed the return of milder weather by a day compared to the 06z and then from later next week completely changed from the 6z. It will be good if the gfs can build on the 12z run which was cold and settled in FI but with no risk of snow as the bitter cold air can't find a route to the uk but that could change if the idea on 12z wasn't just a mirage. Snow risk even for london on friday then a cold and fine weekend with sharp frosts.

[nick sussex]

The mystery of the NAE continues, its 18hrs run is a mirror image of the earlier 12hrs at the same timeframes.

Theres no way every detail would be exactly the same if this was using the latest data.

Check the 42hrs and then put the run back to the 12hrs at 48hrs, identical!

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&CONT=ukuk&MODELL=nae&MODELLTYP=1&VAR=prty&WMO=&ZOOM=0&PERIOD=&PANEL=0&ARCHIV=0&BASE=201112141800%26HH%3D42

[SP1986]

The NAE of recent has been poor, even to the shortest time frame - there's definitely something up with that model recently!!

[snowking]

The mystery of the NAE continues, its 18hrs run is a mirror image of the earlier 12hrs at the same timeframes.

Theres no way every detail would be exactly the same if this was using the latest data.

Check the 42hrs and then put the run back to the 12hrs at 48hrs, identical!

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&CONT=ukuk&MODELL=nae&MODELLTYP=1&VAR=prty&WMO=&ZOOM=0&PERIOD=&PANEL=0&ARCHIV=0&BASE=201112141800%26HH%3D42

I had noticed this too nick - it's not updated fully yet!

Take a look at the bottom right of each chart - that's gives the init. time (eg 12, 18 etc.). For some reason the WO system is showing the 18z out to 42 hours, but in reality it is only out to about 9 hours at present, with the other timeframes shown still currently the 12z run. But it's coming out slowly!

I had to take a step back and look though, I thought that was remarkable consistency!

Kind regards

SK

Edited December 14, 2011 by snowking

[scotto]

The 6hrs is the only one which has been updated atm. The rest soon!!!

[Isolated Frost]

The 18z rolling out, massive run in terms of storm-track, only the 0z/6z and 12z after this so it's the last 'pub run' before tomorrow's potential event. All I can say right now is that 6 hours ago the 12z got 6pm tonight's scenario spot on!

[feb1991blizzard]

The mystery of the NAE continues, its 18hrs run is a mirror image of the earlier 12hrs at the same timeframes.

Theres no way every detail would be exactly the same if this was using the latest data.

Check the 42hrs and then put the run back to the 12hrs at 48hrs, identical!

http://www.weatheron...41800%26HH%3D42

That is the 12z still Nick.

[nick sussex]

I had noticed this too nick - it's not updated fully yet!

Take a look at the bottom right of each chart - that's gives the init. time (eg 12, 18 etc.). For some reason the WO system is showing the 18z out to 42 hours, but in reality it is only out to about 9 hours at present, with the other timeframes shown still currently the 12z run. But it's coming out slowly!

I had to take a step back and look though, I thought that was remarkable consistency!

Kind regards

SK

Thanks, I never even thought to check the botton right hand corner!

It's nice to see at least chances for some snow for more areas, I suspect every slight shift in track of that low will either be greeted with cheers or dismay depending where people live!

Still room for more changes even tomorrow but we're at that timeframe where we should be able to narrow the snow risk areas after the latest outputs.

[Frosty.]

There could be heavy snow as far north as northern england through the early hours of friday before the system drags the wintry weather away southeastwards, i know the gfs 12z doesn't show that but it's still possible according to the bbc forecasts.