Winter Model Discussion - Cold Hunting - 20th Dec

[Thundery wintry showers]

The main issue with the current projected setup, as often happens in these situations, is that while we have a lot of cold air flooding out of the Arctic into the eastern North Atlantic, the strong jet stream just to the north of the British Isles is set to send a rapid succession of weather systems in off the Atlantic. This forces the cold air to travel a long distance over the Atlantic before it eventually reaches us as polar maritime or returning polar maritime air (as opposed to a colder arctic maritime version) and those incursions are brief and interspersed with tropical maritime incursions, especially the further south you are. Parts of Scotland, especially to the north of the Lowlands, may get some marginal snow events out of this setup though.

Christmas Day itself looks like being one of the brightest days of the spell for most of us, and probably dry away from southern and western coastal areas, though there is the chance of a disturbance giving more general rain over southern England. Wet spells will include Christmas Eve and possibly the period 27-29th for N and W areas as we get a burst of mild and moist tropical maritime air.

I'm not convinced about this pattern lasting 4-6 weeks, given the teleconnection support for a colder and more blocked spell towards mid-January, but I think we are unlikely to get out of this essentially zonal pattern until after the first week of January.

Edited December 23, 2012 by Thundery wintry showers

[nick sussex]

These are from an American site and are from the 00z outputs Nick the ops and ensls,

Not great for cold lovers it must be said.

Link here http://raleighwx.ame...onnections.html

Just a note they don`t include the ECM on some of those Nick.

Thanks Phil

What does seem strange is that the latest outputs go completely against what NOAA suggested only two days ago.

Could there really have been that much of a change in such a short space of time?

[Thundery wintry showers]

The current NOAA 8-14 day outlook suggests continued west to south-westerlies over the UK but with blocking around the North Pole and eastern Canada/western North Atlantic:

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

Potential for a pattern change from that setup I think, but certainly a recession of the northern blocking compared with recently.

[snow1975]

The main issue with the current projected setup, as often happens in these situations, is that while we have a lot of cold air flooding out of the Arctic into the eastern North Atlantic, the strong jet stream just to the north of the British Isles is set to send a rapid succession of weather systems in off the Atlantic. This forces the cold air to travel a long distance over the Atlantic before it eventually reaches us as polar maritime or returning polar maritime air (as opposed to a colder arctic maritime version) and those incursions are brief and interspersed with tropical maritime incursions, especially the further south you are. Parts of Scotland, especially to the north of the Lowlands, may get some marginal snow events out of this setup though.

Christmas Day itself looks like being one of the brightest days of the spell for most of us, and probably dry away from southern and western coastal areas, though there is the chance of a disturbance giving more general rain over southern England. Wet spells will include Christmas Eve and possibly the period 27-29th for N and W areas as we get a burst of mild and moist tropical maritime air.

I'm not convinced about this pattern lasting 4-6 weeks, given the teleconnection support for a colder and more blocked spell towards mid-January, but I think we are unlikely to get out of this essentially zonal pattern until after the first week of January.

Perhaps this chart shows the first signs of a pattern change to a more blocked one as you suggest?

[Frosty.]

Latest GEFS 6z mean, the period out to T+144 there is a tendancy for the jet to be more sw/ne orientated but thereafter it becomes more of a westerly or even hinting at marginally north of west which suggests some polar maritime influence in the mid range after the early tropical maritime domination, however, beyond that ray of hope, the jet buckles more sw/ne again before finally veering westerly again but the gefs shows high pressure generally to the south of the uk and low to the northwest and north, just occasionally the pressure over southern britain rises slightly which would suggest some drier, brighter spells but mild or very mild for the time of year, cold zonal looks in short supply and mainly for the far north of the uk in the mid range. So, a very unsettled pattern is set to continue with frequent spells of mild, wet and windy weather tracking north and east across the uk in the next 2½ weeks or so.

[itsnowjoke]

Off topic i know but i would like to wish you all a merry christmas.

[Summer Sun]

Some positive signs from GFS 06z with high pressure shown to build during the first few days of January bringing with it some drier and milder weather giving the flood hit areas a welcome break

[itsnowjoke]

Some positive signs from GFS 06z with high pressure shown to build during the first few days of January bringing with it some drier and milder weather giving the flood hit areas a welcome break

Those charts look like bbq charts to me oranges and reds blues thats what i like.

[Frosty.]

Those charts look like bbq charts to me oranges and reds blues thats what i like.

EWW they are horrible charts for winter, lovely in july and august.

[Methuselah]

I'm not convinced about this pattern lasting 4-6 weeks, given the teleconnection support for a colder and more blocked spell towards mid-January, but I think we are unlikely to get out of this essentially zonal pattern until after the first week of January.

Agreed Ian...Not very scientific I know, but if this were 2004 I'd have disagreed!

[Frosty.]

Off topic i know but i would like to wish you all a merry christmas.

Merry christmas to you too, shame the models don't look remotely festive but perhaps with extra strong beer goggles they will look gorgeous.

[bluearmy]

Indeed, Phil. But how can models make computations, utilising equations that may not have been formalized yet?

We all know that there gaps in understanding somewhere; the recent BFTE no-show was, I think, a perfect example of this?

Of course I may be typing bullocks!

Last comment on this: I assume the horizontal layers in the models are spread out all the way to the top of the strat on both gfs and ECM. I have no idea re ukmo GM. Maybe IF could help here. I believe, having read a couple of papers, that the layers in the strat are spaced much further apart than in the trop. That would mean the lattice of grids above us in the 3D model representation of the atmosphere are not all the same shape but become stretched vertically as we head higher up. I wonder if the lower strat is modelled with the same vertical resolution as the upper strat?

[Timmytour]

Temps for Boxing Day don't look too different for Eastern side of UK than they do for Warsaw.

Hard to imagine from a couple of weeks ago that the reason for that is the influence of the Atlantic and not a Russian high!

[Summer Sun]

The GFS operational and mean support a rise in pressure as 2013 begins going from a low of 990mb on the 26th around 1018mb from the 3rd to 5th of Jan the operational takes it even higher to just over 1032mb around the 4th of Jan

The Aberdeenshire ensemble has a lot more scatter the London one has but again the operational takes pressure well above 1010mb during the opening week of 2013

There is also very good support for Cornwall to remain mild for the foreseeable future with a range from 8c to 13c most likely

The GEFS mean shows rain totals becoming lower as well from boxing day onwards

Maybe the Atlantic train of low pressure systems one after the other is running out of steam giving people and rivers time to recover from mid week

Edited December 23, 2012 by Gavin.

[Frosty.]

Just before the latest gfs winter horror show rolls out, the latest Ecm 00z ensemble mean looks broadly similar to the Gefs 6z mean with predominantly swly flow bringing spells of mild, very wet and sometimes windy weather to our shores on a regular basis, there are signs that as the main trough to the northwest edges further east, the airflow will then veer to a cooler westerly north atlantic type flow or even something more polar in nature which would bring the risk of snow back to northern hills but really the pattern shown on the gefs and ecm mean suggests a continuation of the torrential rain risk with more flooding into the new year, perhaps pressure rising to the south and southeast will bring some respite from the very unsettled pattern but also bring the chance of even milder air from southern europe in the process. Looking further ahead, we can only hope for a change in fortunes from mid january onwards, surely the current nasty pattern won't persist for the next four weeks or more?

[Timmytour]

Here's a mild looking chart.....how different from those we are currently seeing modelled is it?

[mountain shadow]

Very similar to where we are now, unfortunately pattern matching is up there with astrology.

[phil nw.]

Closing this one in a few minutes folks ready for the 12s

[phil nw.]

OK closing this one now-new thread here.