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

[bradymk]

well they're not from the ecm 12z op run gavin. that tells a different tale re a white xmas. however, likely it will be a different story tomorrow.

Yes, interestingly, ECM forecast data shows snow late xmas day for birmingham. Its only a very rough guide on "yr.no" site but that was a cold xmas day chart on ECM this evening for sure.

Edited December 16, 2013 by bradythemole

[mountain shadow]

Polar profile none to shabby there surely? Certainly a chance the PV could split around Greenland sending a segment towards Scandi bringing in colder air just in time for Christmas?

http://cdn.nwstatic.co.uk/gfsimages/gfs.20131216/18/129/npsh500.png

[stodge]

Evening all

 

The 18Z Operational output keeps the very stormy theme going over Christmas but this time it's the south in the firing line;

 

http://modeles.meteociel.fr/modeles/gfs/runs/2013121618/gfs-0-204.png?18

[mountain shadow]

Well the PV did shift across the Atlantic..

http://cdn.nwstatic.co.uk/gfsimages/gfs.20131216/18/216/h500slp.png

Unfortunately only in this country can we have the PV overhead and its still to warm for snow..

http://cdn.nwstatic.co.uk/gfsimages/gfs.20131216/18/216/h850t850eu.png

[TSNWK]

Well I actually enjoyed that 18z. From Christmas Eve onwards the vortex shifts towards us, then scandi, then ends with the bulk over Siberia with shallow heights over greenie. Looks ok at 1st glance, seen far worse.

Night all

[SMU]

Well, to be honest- things look better- but inferring that its good is probably being over optimistic-

 

I think due to the fact that things have been SO bad this month ( I saw a +4 AO index mentioned in another thread) reminds me of the 90's when westerly zonality lasted forever & any blocking highs made very short appearances-

 

Whilst we can get out of it, sustained + AO index tends to set the 'tone' for winters- & the current prognosis for no blocking signal out to day 12 puts us 1/3 down of Winter.

 

If your in the south forget snow for now- maybe even to Jan 1- a SLIM slither of hope would be from 'lucking in' from a low swinging around the base of the parent low-

 

The only meaningful snow looks north of the border as the jet straddling the south of the UK intercepts some of the cold air feeding in from the NW.

Places like the North midlands & wales could get into the fray, but mostly transient.

 

Its a poor picture, only brightened by some excitement around the big day itself- but that's only really if your at elevation in the North.

 

 

So long December- Roll on the new year.

[nick sussex]

Shame that a chunk of the PV decides to remain in Canada whilst the rest moves east, always a bit dubious of cold advection south with heights dropping to the north in the lower resolution, earlier at least the higher resolution edges the jet south. A lot of uncertainty though with these fast moving lows running east, somewhere could get lucky around Xmas if one of these encounters enough cold air ahead.

 

Because of the marginality the type of feature shown on the ECM is preferable as some evaporative cooling in slacker winds on the northern flank could help any rain to snow, its a very difficult forecast because we're not dealing with deeper cold.

 

These possible lows could pop up at anytime upto Xmas, given the strong thermal gradient off the ne USA, theres a lot going on but at the moment I think the best chance of a White Xmas is further north, however if you're further south I think something like the ECM could deliver a temporary fall of snow depending on the track, its unlikely to last long but given the set up I would still class that as doing well out of the current pattern.

[MP-R]

Just wow:

 

I think that's possibly the lowest I've seen pressure be forecast for so far south over the UK. If that chart verified, even with higher pressure than that, I would be absolutely gobsmacked if the south didn't get snow. Normally I wouldn't post a chart as apocalyptic as that but rapidly deepening air pressure and cold uppers has been a constant trend for Christmas now and the days beyond look cold too. The GFS 18Z even sends a channel low eastwards on the 27th. 

 

Of course, that is all outside the reliable. First we must get through a very unsettled week (after a quieter day tomorrow) with high winds, longer spells of rain and heavy showers. Wouldn't be surprised for some wintriness to feature in the heaviest showers on Thursday either.

[Mucka]

Something afoot in ECM London ensembles.

 

 

That colder snap just after Xmas is likely the PV moving close to the UK so remaining unsettled. Now if we can just move that forward and prolong it a little.

[phil nw.]

In this very cyclonic pattern we will see frequent changes in the air masses as each low moves across from the Atlantic.

As Nick and Steve have said some snow chances in the cold sectors further north over higher ground but nothing sustainable or widespread in such a mobile pattern.

The one trend that's being hinted at are that those wave depressions or short waves if you like developing on a more southerly track in later output.

Both ECM/GFS T240 hrs means show the jet to the south of the UK.

http://www.meteociel.fr/modeles/ecmwf/runs/2013121612/EDM0-240.GIF?16-0

http://modeles.meteociel.fr/modeles/gens/run/gens-21-0-240.png?12

This would reduce any real mild incursions or warm sectors but we still need some heights further north to force the real deep cold Arctic air this way.

In summary for coldies not great but a step away from the mild Atlantic pattern that was modeled a few days back-near average or slightly on the cold side especially the northern half of the UK.

[fergieweather]

Latest EC32 follows it's predecessor in suggesting a gradual but very slow wane of LP anomalies to N/NW by or into 2nd week Jan; temps back to average by New Year onwards. No pronounced cold anomaly (yet) over UK or Europe: but it's exclusively & widely over Atlantic W of UK fringes. Examination of clusters and individual members introduces some, albeit still a minority, with signal for height rises to either NW or N/NE. Representative ENS plumes for southern England continue towing a path of 850 temps settling circa -2 to -5C; v gradual rise in 500mb heights post New Year onwards. Dry PPN anomalies by 2nd week Jan over e.g. Iceland also suggestive of some MSLP rises to N albeit no anomaly signal for such (effectlively an unbiased MSLP signal across all N Europe & contiguous boreal zone; HP signal to SW). So, as earlier noted, perhaps some *tentative* signs of pattern change underway but certainly not bullishly so, at least until few days on into 2014. Crucially, the wider mean 500mb heights summarised by 12 Jan retain a lower signal above Iceland, with no bias towards northern blocking; wInds predominantly from a W/WNW quarter BUT with distinctive cold anomaly to W it sure won't be mild.

Edited December 17, 2013 by fergieweather

[Panayiotis]

CMA has different ideas for Christmas! 

^^Thanks Ian for the insight!

Edited December 17, 2013 by Panayiotis

[Chris W]

Christmas Eve, midnight from the GFS 00z - little time to analyse but certainly an interesting Christmas morning!

 

[That ECM]

http://images.meteociel.fr/im/8765/ECH1-192_lxj2.GIF

http://images.meteociel.fr/im/8673/ECH1-216_sss3.GIF

The detail will change I am sure but the trend is the same. With nh looking like this none of the lows can get far enough south to drag some sustained cold air to us. Fore sure northern areas may well see some snow for short periods and the winds associated with these lows may well become news worthy.

http://images.meteociel.fr/im/414/ECH1-240_wkl8.GIF

This is of interest with PV moving east and less energy coming from the nw which maybe gives a small window of opportunity to build some heights but we have seen the ECM do this before.

Edited December 17, 2013 by That ECM

[Frosty.]

Ecm 00z op run shows a very turbulent pattern with potent lows regularly sweeping severe gales and heavy rain in off the atlantic followed by a backwash of colder polar maritime air, cold enough at times for a wintry mix of sleet and wet snow on hills and occasionally to lower levels. This run shows some low thicknesses at times with 528 dam sometimes covering the uk in rather deeper colder air and even 522 dam makes an impression. Christmas looks like a stormy period and as the main trough to the north west pushes further east into scandinavia and a ridge begins to build in mid-atlantic we would tap into much colder arctic air between christmas and new year with snow showers and sharp frosts, as things stand, the ecm shows the weather briefly milder on christmas eve but turning colder and showery by xmas day with the showers turning wintry..so there is a realistic chance of some parts of the uk seeing snow on the big day with cold and strong westerly winds funneling across the uk, especially strong across and to the east of the pennines and then an increasingly wintry run up to the new year with a more amplified pattern.

Edited December 17, 2013 by Frosty.

[Gibby]

Good morning everyone. Here is my take on the midnight outputs of the NWP (Numerical Westher Prediction) from the midnight outputs today Tuesday December 17th 2013.

 

All models show a period of potentially stormy weather with the exception of today where the weather is rather quieter as a brief ridge of high pressure crosses from the West. Later tonight and from tomorrow everywhere the winds will become strong for all from the SW and very strong for some with severe gale or even storm force gusts for a time in the NW later tomorrow as a vicious Low is shown to sweep NE across NW Scotland. Rain, very heavy for a time will sweep East followed by a 36-48 window of colder weather with strong West winds and showers, wintry on all hills even in the South and giving accumulations over Northern elevations. Then on Friday and the weekend the weather becomes milder again with spells of rain and gale force SW winds though the colder and showery variety of weather could spill back across at least Northern areas for a time again over the weekend.

 

The GFS operational run shows the run up to Christmas simply put as wet and windy with strong to gale SW winds and mild weather particularly in the South. Over Christmas itself the weather turns colder and there will be plenty of showers around for all areas, especially in the West driven in by gale force winds with snow on all high ground of the North and maybe in the South too at times. The very volatile pattern of rain followed by showers continues then up to and including the New Year with rain and strong winds alternating with colder and brighter spells with showers, wintry in the North.

 

UKMO shows next Monday as a windy and wet affair as another wave disturbance runs quickly East in the near gale WSW flow bringing further heavy rain across Southern areas through the day followed by righter colder and more showery weather in the north and West later.

 

GEM shows unsettled weather throughout next week, becoming deeply unsettled by Christmas with very low pressure values over the UK, strong Westerly winds and heavy rain and showers at times, increasingly falling as sleet and wet snow at times over high ground, especially over the Christmas period itself and in the North.

 

NAVGEM also shows a wet and relatively mild start to next week before things become more alternating over Christmas itself between wet and windy weather to rather colder and showery conditions with strong winds continuing unabated throughout.

 

ECM today shows a wet and windy run up to Christmas followed by a rather chilly and very windy Christmas with squally showers of rain and hail with sleet and snow over the hills.

 

The GFS Ensembles continue to show no let up in the powerful Westerly flow across the Atlantic aided by a Jet Stream rushing East across the British Isles from the Atlantic. Hence periods of wet and windy weather is indicated from all members with an overall trend of maintaining average temperatures but very wet conditions at times for all.

 

The Jet Stream is shown to continue in it's powerful state crossing the Atlantic and over the UK in the period up until Christmas. Beyond that it sinks somewhat South at times bringing much of the UK on the cold side of the flow with the increased threat of wintriness in the showers for the UK later in the period.

 

In Summary the weather looks like remaining and becoming even more deeply unsettled throughout the forecast period this morning. All models show the potential of quite a wild Christmas with cold Westerly winds and wintry showers from which some places could indeed see a white Christmas though wide scale snowfall is not expected with the higher ground favoured for any settling snow albeit briefly. At other times severe gales could occur giving their own brand of travel disruption and when coupled with the likelihood of heavy rain with attendant flooding issues there looks to be plenty to talk about over the UK in the next few weeks weatherwise to distract observers from the family festive activities.

[Mucka]

Nothing new in the output today really other than a firming up on the idea that the Christmas period is likely to be cold and blustery in W/NW winds with perhaps some wintriness for the North, especially to high ground.

Otherwise GFS continues toying with the idea of having rapidly developing low pressure systems crossing the UK from further South which would put much of Ireland, Wales and England in the firing line for increased storminess while ECM is still modelling these low pressure systems to track further North.

 

In the longer term there is a weak signal for height rises to our East as we head toward New Year perhaps aided by the Russian high moving West and/or ridging West from a Siberian high, all this in conjunction with a slightly less mobile Atlantic pattern.

Given Ian's summary this morning it may well be that GFS ensemble suit is overplaying this (Or at least I am overplaying what is a weak  signal) and it will be well into the New Year before we see any real signs of blocking taking hold if it develops at all.

Edited December 17, 2013 by Mucka

[shedhead]

http://images.meteociel.fr/im/8765/ECH1-192_lxj2.GIF

http://images.meteociel.fr/im/8673/ECH1-216_sss3.GIF

The detail will change I am sure but the trend is the same. With nh looking like this none of the lows can get far enough south to drag some sustained cold air to us. Fore sure northern areas may well see some snow for short periods and the winds associated with these lows may well become news worthy.

http://images.meteociel.fr/im/414/ECH1-240_wkl8.GIF

This is of interest with PV moving east and less energy coming from the nw which maybe gives a small window of opportunity to build some heights but we have seen the ECM do this before.

Agreed, therein continues to lie the main problem. The Euro high still looks very robust until early next week, but at least on the face of it the colder air does appear to make in roads by Xmas Day. 

 

 

However at the range involved this transition should still not be considered a given imo, with far more spoiler systems likely to be modelled in the overall flow when inside c. T+120hrs. Until we see some proper height rises to the north that not only look feasible, but also sustainable, any 'colder' shots are likely to remain fleeting affairs - especially in the south.

Edited December 17, 2013 by shedhead

[Summer Sun]

ECM once again shows a nasty low crossing north of Scotland for Christmas day

 

 

The ensemble has it at 960mb

 

 

GFS continues to show an unsettled day although mild for the south

 

 

The GFS ensemble has the low at 955mb

 

Edited December 17, 2013 by Summer Sun

[carinthian]

Interesting chat with the team this morning. The December prediction going to plan with the rather mild conditions prevailing (ie ) westerly mobile flow to the north and solid high zone further south over mainland Europe. Signs now taking place of a shift southwards of the polar front over the Christmas to New Year period. Prior to this period a lot of rain expected over Southern England on the boundary of the front if not already happening. Increasing confidence of a wider change to colder conditions over January, which I assume would be a marked rise of pressure over the Arctic zone . In the meantime cannot see much snowfall over here on the run up to Christmas.

 C

Edited December 17, 2013 by carinthian

[Cecil Hogmanay Melchett]

Interesting chat with the team this morning. The December prediction going to plan with the rather mild conditions prevailing (ie ) westerly mobile flow to the north and solid high zone further south over mainland Europe. Signs now taking place of a shift southwards of the polar front over the Christmas to New Year period. Prior to this period a lot of rain expected over Southern England on the boundary of the front if not already happening. Increasing confidence of a wider change to colder conditions over January, which I assume would be a marked rise of pressure over the Arctic zone . In the meantime cannot see much snowfall over here on the run up to Christmas.

 C

We need to see the back of the huge swathe of High pressure stretching from the Azores right across Europe to the Ukraine C,there seems to be no end to it,even warsaw is struggling to get below freezing at the moment!

[carinthian]

We need to see the back of the huge swathe of High pressure stretching from the Azores right across Europe to the Ukraine C,there seems to be no end to it,even warsaw is struggling to get below freezing at the moment!

Yep HP, better now here in the early season. Some in roads expected before the end of this month and prospects for cold increases in January. A high zone over middle Europe in the middle of January would also prolong a mild damp winter over the British Isles and probably snow starved Alps. Confidence now 60 % of some form of blocking further north during January.

c

[knocker]

Quite meaningless but the complete GFS  run to 2nd Jan. Just picked the 27nd as the most interesting.

 

http://www.weathercharts.org/wetterzentrale-t120-t384.htm#384

 

 

[Cecil Hogmanay Melchett]

GFS suggesting a frost to start christmas Eve before the next onslaught from the West.

[Ali1977]

Snow for most of the uk on xmas day according to the latest GFS :-)