Sorry if this is the wrong thread for this,However a post from Ian F on NW

met office keeping an eye on a small feature which looks like it could produce some snow

for southern/central areas Thursday afternoon/Evening

C.S

Just posted the midnight 25th Dec GFS pressure chart on my site and frankly, it's dangerously stupid. If that come soff we're looking at 2005 again. 

It's bad enough now sat here writing this post with it blowing storm force 10 (62mph) and gusts getting on for 80mph. And it looks to just keep right on through Christmas. As someone said, these wind speeds are dangerous....

http://modeles.meteociel.fr/modeles/gfs/runs/2013121718/gfsnh-0-168.png?18

All seems a bit further North on the 18z

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2013/12/17/basis18/ukuk/rart/13121918_2_1718.gif

Highest parts maybe

http://modeles.meteociel.fr/modeles/gfs/runs/2013121718/gfsnh-0-192.png?18

Xmas day looking awful

A very unsettled spell for sure but also much cooler

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2013/12/17/basis18/ukuk/rart/13122412_2_1718.gif

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2013/12/17/basis18/ukuk/rart/13122418_2_1718.gif

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2013/12/17/basis18/ukuk/rart/13122500_2_1718.gif

JFF JFF JFF

Don't get too excited but a white Xmas for some could be on the cards

Sometimes you just need a pic to tell the story. 

http://www.wetterzentrale.de/pics/Rtavn3601.png

http://www.wetterzentrale.de/pics/Rtavn36017.png

A cold start to 2014

That would be the safe bet - and the key indicators from the airmass do look marginal:

850-1,000hPa thickness: http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/17/basis18/ukuk/th85/13121918_1718.gif

950hPa temp: http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/17/basis18/ukuk/t925/13121918_1718.gif

2m Temp: http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/17/basis18/ukuk/tmp2/13121918_1718.gif

As often in marginal situations, the intensity could well be the key:

http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/17/basis18/ukuk/prec/13121918_1718.gif

That chart gives you two measures, the surface level pressure (SLP) and the 500hPa temperatures.  500hPa is approximately 18,000 feet up.

As you will know, I think, air expands as it warms, so warmer air equates to higher pressure.  When you see orange colours on the 500hPa chart it tells you there is, in effect, an 'upper high'.  On that chart at the surface (SLP) there is also a high pressure cell.  When you read people commenting on 'false highs' over Greenland it is because the SLP indicates a high pressure cell but there is no support for it at 500hPa, with only cold air.  For an effective block you want both an upper and a surface high - the upper one acts as the block, "the boulder in the stream" that blocks and diverts the jet and LP systems.

That chart doesn't tell you much about what's going on at the surface, other than some clues from wind direction. Ideally you want to look at the 850hPa chart for temperatures (that's about 5,000 feet) and thickness values.  If you want to check whether there is a chance of snow you look at the 500-1,000hPa thickness and want values generally below 525dam.  For better guidance look also at how cold the lowest layer of the atmosphere is, 850-1,000hPa (effectively 5,000 feet down to near the surface).  In that lowest layer you need values below 130dam.

On that chart for 19th January:

500-1,000hPa thickness: http://modeles.meteociel.fr/modeles/reana/1963/archives-1963-1-19-0-2.png

850hPa temp: http://modeles.meteociel.fr/modeles/reana/1963/archives-1963-1-19-0-1.png

That's sub-zero at the surface but the relationship between the airmass above and surface temperature depends on lots of factors.

Hope this helps

ECM 00z gives us a cooler Xmas day, with snow possible in some favoured locations

http://www.wetterzentrale.de/pics/Recm1682.gif

...before a nasty looking low piles through the south on Boxing Day.

http://www.wetterzentrale.de/pics/Recm1922.gif

Even this far out, there seems to be some consolidation on the timing of the potential Christmas storm (I shall avoid the term 'Rao') and brings it in overnight into Boxing Day. All a long way out but something could be brewing.

In the meantime it's kitchen sink stuff with an active CF tonight, very strong winds especially in the far NW, an interesting system running W to E Thurs pm with some steep vertical gradients posing the risk of 'cold drag' and transient snowfall, more wind on Friday and then it goes downhill into Christmas week.

No freeze-up, but plenty to keep forecaster's heads-up LOL.

A remarkably large area of Europe (everywhere except Iberia) with above average temperatures for the next week, and even milder, not to say warmer, in the following period.

http://www.wxmaps.org/pix/temp4.html

Even if we got a raging easterly out of nowhere, we'd still be above freezing! Cold lovers need to cross their fingers and look for signs of a northerly spell of weather.

It's very rare we are below freezing lets be honest, but certainly cooler weather on the way , places will see some wintry ppn during the next 10 days and not exclusively the North

Yep a fair bit of interest thats for sure.

When was the last time the pv migrated to sit on top of us?

Exciting times ahead, but also potentially quite dangerous

Indeed, it could make it quite miserable for many

Hurricane Bawbag part II Xmas eve according to GFS

http://www.wetterzentrale.de/pics/Rtavn1621.png

Good morning. Here is the morning report on the NWP output for midnight Wednesday December 18th 2013.

All models show a strengthening SW flow across the UK this morning as a rapidly deepening depression moves NE towards NW Scotland. This is shown to swing an active front across the UK later today with severe gale force winds and heavy rain ahead of it. In the NW storm force winds could give rise to damaging gusts for a time tonight when colder and clearer conditions with squally heavy showers on a colder Westerly gale arrives later, lasting through tomorrow and into Friday. Later on Friday all models show winds backing SW and remaining very strong as milder and wet wet weather spreads back across the UK from the SW. This then slowly clears from the North over the weekend, last from the South as a wave delays any clearance here and gives rise to more heavy rain on Saturday down here. By Sunday all areas look to be in a broad and chilly Westerly flow with sunshine and squally showers.

GFS then shows yet more mild, wet and windy weather at times in the run up to Christmas with further gales, especially in the North and West. Over Christmas itself the weather looks like reaching it's peak potential for storminess as very intense Low pressure crosses on Boxing Day with Christmas Day having been already wet and windy Boxing Day looks like it could be very stormy with severe gales and damaging gusts of wind across England and Wales coupled with heavy rain and blustery showers following. After Christmas and in the run up to the New Year little overall change is shown though things look likely to turn somewhat colder with some wintry showers on all hills and the chance of night frosts where winds fall light enough. By the New Year celebrations though the stormy and windy weather returns with gales and heavy rain sweeping East over the UK once more.

UKMO shows Christmas Eve with deep Low pressure out to the NW with a gale force SW flow over the UK delivering mild and wet weather through the day. On Christmas Even night it looks like a vigorous trough would spread East across the UK with very heavy rain followed by squally showers and colder air.

GEM today shows intense Low pressure near and over the UK on the approach to Christmas and Christmas itself with strong winds and heavy rain never far away from anywhere though this run does lessen the impact of damaging wind risk.

NAVGEM today maintains a low pressure belt all the way from Scandinavia across to Newfoundland with strong winds and rain rushing across the Atlantic and over the UK frequently with a mix of showery weather with brighter intervals in between. There is also less impact of damaging winds from this model either this morning.

ECM today shows a very unsettled run up to Christmas with rain and wind featuring for all. Over Christmas the weather looks very volatile with Boxing Day looking particularly troubling as a vigorous Low is shown to sweep across England and Wales with potential storm force winds bringing damage in places and coupled with heavy and persistent rain before squally wintry showers take over late in the day and in the days that follow.

The GFS Ensembles show a continuation of average value temperatures but accompanied by very wet and windy conditions throughout the output this morning with the peak of the worst of the weather likely over the Christmas period.

The Jet Stream shows the flow roaring over the Atlantic and the UK in the run up to Christmas before sinking South temporarily over the Christmas period itself before returning North over the UK towards the New Year.

In Summary the weather will remain very unsettled over the entire period. Dry days will be at a premium with fast moving weather systems making for fast changing conditions in any one place with the basic ingredients of mild and wet weather alternating with colder and more showery conditions when some snow may fall over the hills, especially but not exclusively in the North. Of most concern is the potential for damaging winds to accompany these weather systems as they are extremely deep even by Winter standards and could give rise to some damaging gusts over the Christmas period itself. Longer term there seems little evidence of signs of a pattern shift even into the New Year with the Jet Stream crossing WSW to ENE across the UK at that point with High pressure remaining over Southern Europe and low to the North and NW.