HERE IS MY LATEST ANALYSIS FROM THE OUTPUTS OF THE WEATHER COMPUTER PREDICTION MODELS FOR TWO WEEKS FROM 8AM TODAY TUESDAY DECEMBER 23RD 2014.

NEXT UPDATE WEDNESDAY DECEMBER 24TH 08:00

THE CURRENT GENERAL SITUATION A cold front across Southern Scotland and Northern England will move SE tonight and tomorrow replacing the mild SW flow in the South with colder NW winds for all tomorrow.

MODELS-2 WEEK HEADLINE Continuing changeable with some dry and fine rather cold days and some rain at times in milder temperatures at other times. A brief much colder period could occur for a time post Christmas.

THE JET STREAM ENSEMBLE FORECAST The Jet Stream Forecast is for the flow long term to maintain a fairly brisk West to East flow in the vicinity of the British Isles lying between Low pressure to the NW and High over the Azores and parts of Europe.

GFS OPERATIONAL The GFS operational this morning shows the deep Low post Christmas sinking SE over Europe late this week taking it's cold Northerly flow with it and it's attendant innitial rain and strong winds then wintry showers. Thereafter the flow backs Westerly under a toppling ridge scenario with mild SW winds and rain at times through the New Year. Incursions of High pressure continue to affect principally the South at times and a build of pressure over Europe is also shown later, but too far South to bring the UK any signifiacant cold conditions as the Jet continues flowing North of the UK in balmy South or SW winds at times.

THE GFS PARALLEL RUN The Parallel run sings the same song overall with only small differences in specifics but maintaining the trend of a brief cold shot under Northerly winds and some snow showers before High pressure to the NE collapses under the weight of a powerful jet stream riding over it and returning mild SW and rain at times for all later with some powerful storm systems crossing East to the North of the UK by the end of the run.

THE GFS CONTROL The GFS control run doesn't need going into detail with today as it replicates the theme of the other partner runs in a broad sweep colder then milder theme.

THE GEFS ENSEMBLES The GFS Ensembles do show the temporary chance of cold weather from quite a few members post Christmas with the overlying trend thereafter for the cold to lift out in preference to milder Westerly winds between High to the South and Low to the North into the New Year.

UKMO UKMO shows the quiet Christmas weather giving way to Low pressure sliding SSE down across the UK and the North Sea bringing a short shot of cold North or NE winds on it's back edge with the chance of some wintriness in places before the run ends next Monday with a large and strong UK anticyclone delivering bitter cold conditions with severe frost by night and no doubt some persistent freezing fog patches for a few.

THE FAX CHARTS The Fax Charts today keep the story of the operational run with High pressure keeping Christmas dry and crisp for many before a Low moves across the North of the UK deepening rapidly with rain and strong winds likely for many next weekend.

GEM GEM today shows the post Christmas storm sinking South across the UK post Christmas with rain and strong winds followed by colder air with a few wintry showers to exposure briefly before all areas fall back into a mobile Westerly flow with rain and strong winds at times in average temperatures.

NAVGEM NAVGEM looks much like UKMO this morning with it's modelling of events which take us out of the Post Christmas storm. After a chilly but fine Christmas for many a period of very wet and windy weather will be sewpt away by a brief cold interlude with some wintry showers for almost anywhere before High pressure takes control later over the UK with widespread sharp frosts and freezing fog as we approach the New Year.

ECM ECM this morning also shows a UKMO and NAVGEM type evolution bringing a sharp rise of pressure following the storm as it slips South away from the UK. There is a period when some snow could affect any part of the UK on it''s back edge as it slips away South, this quickly quashed by High pressure developing strongly over the UK for the remainder of the run with severe frosts and freezing fog a major issue especially in the South.

ECM 10 DAY MEAN The ECM 10 Day Mean Chart is made up of a varity of options but with an increasing trend to develop higher pressure over Europe than over Greenland where pressure is likely to stay quite low. The positioning of such a European rise of pressure is instrumental in surface conditions over the UK and in that resolve the jury is still out.

NOTABLE TREND CHANGES FROM PREVIOUS RUNS The trend this morning has been to extend the length of cold across the UK somewhat as High pressure becomes established over us or close by. The path towards mild SW winds to return though towards the New Year remains a possibility.

MY THOUGHTS  While there is some unison over the path of the post Christmas depression event moving SE the exact positioning remains uncertain with the Americans wanting to push the Low SE over Europe and giving no more than a glancing blow from a cold North or NW flow before a flattening pattern behind a toppling ridge reverts the UK back to default mode of West winds, average temperatures and rain or showers at times. On our side of the pond the UKMO and ECM both drop the Low South across the UK quite quickly filling it as it does. In this period there is a strong possibility of a spell of snow on a short sharp and strong East or NE wind which could occur almost anywhere before rapidly rising pressure clears this away South to leave the UK under very cold clear air where surface temperatures under High pressure could drop very low overnight. Areas of freezing fog could also become an issue, failing to clear in places under the light anticyclonic winds. Within the ensembles the GFS group are not supportive of much in the way of persistence to this High pressure block preferring to sink everything South and set us up on what could be another prolonged Westerly phase of wind and rain and average temperatures. However, within the ECM pack are much more resilience to this theme in holding High pressure over Europe. Although this is a dangerous game for the UK as we could end up on the mild side of a Euro High it could provide dividends if it is allowed to ridge North to Scandinavia and allow at least some continental cold to seep into at least Southern areas with a more seasonal mix of frost and fog patches by night. However, for those looking for any significant amounts of the white stuff outside of a 12 hr window somewhen post christmas the charts longer term don't paint a very Christmas card type scene this morning I'm afraid. Still the interest values are high at the moment and I'm sure we'll see more twists and turns over the coming days output as the situation which involves the rapid development of the post Christmas Low comes nearer.

A  fascinating range of opinion available to the casual lurker this morning.  Take your pick

FWIW I am now strongly favouring a cold outlook with some limited snow possibilities around in populated areas (see UKMO 120)

WI

They're box and whisker plots.

They show where the majority of runs are clustered, as well as the median (which is in the middle - as in half the runs are milder, half the runs are colder). Note that the median is not always the same as the mean! The long "whiskers" show the absolute warmest and coldest runs.

As an example, for the 1st Jan:

The median is 3C. The absolute wamest run shows a high of 12C and the absolute coldest run shows a high of -4.

The wider cyan box means that 50% of the runs were between +1C and +7C, with a further 15% of the runs being between +7 and +9C. Another 15% of the runs were between -1C and +1C. Finally 10% of the runs showed a high between +9C and +12C, the same number showed a high between -4C and -1C.

The longer the boxes and whiskers, the more variance there is. You'll see they gradually lengthen over the course of the run, with the early time periods showing very short boxes and whiskers - much higher confidence here!

Thanks Darren. In other words more runs needed!

I'm very much hoping that the ECM and UKMO are nearer the mark with this. Their solution would at least allow river levels to drop a bit after all the rain recently, especially Sunday's deluge which is still affecting parts of NW England right now I think.

Lol! Really sums up the model output thread this winter . As fast as one says something like "looking better", another says "not so good today"

I really feel sorry for those who have yet to master reading the charts for themselves, and who have to rely on information posted here - there's so much inconsistency about output interpretation, it must be bewildering  (<--- don't know what that emoticon is meant to be, so I thought I'd post it anyway :-D)

Cheers Darren! You learn something new every day 

PS - The last 'box and whiskers' I encountered, was related to a dodgy woman I met in Amsterdam 

Thanks Retron,  sparkingly clear explanation!

I'm beginning to wonder that if there is to be a change to a predominantly colder pattern in the New Year, it may come about in a similar way to the colder pattern that developed from early January 2013 onwards. That came after a very unsettled second half to December 2012 which continued through the festive season. Here is a chart for 5th Jan 2013:

http://www.wetterzentrale.de/archive/ra/2013/Rrea00120130105.gif

Note a fairly strong Azores High over France and Spain and a strong polar vortex over Canada. On the face of it, that didn't look wonderful for cold, but a few days later it turned into this:

http://www.wetterzentrale.de/archive/ra/2013/Rrea00120130110.gif

A bit more clarity in the short to medium term now with a UK high developing after the weekends low moves out of the way, so at least we'll see some frosty landscapes fro much of next week. Thereafter the form horse IMO is for the Atlantic to regain the upper hand with something similar to this months setup with alternating TM and PM air masses. Absolutely no signs of any Northern blocking occurring on any model output this morning and all eyes are now on developments on a SSW, though to me anything happening there always seems to be at day 10 and beyond and is a case of more jam tomorrow.

Can't recall for sure, but I think it was in a similar way to what is happening right now. Some runs showed atlantic zonality continuing well into January and other went for a more HP dominated set-up.

There hasn't, as far as I'm aware, been an SSW modelled this winter season. What has been shown is a push of warm air right at the top. And that, at least, is actually happening right now. Whether it downwells and causes the vortex to split in due course (rather than just shove it out of the way) is another matter...

Current situation:

http://www.instantweathermaps.com/GFS-php/showmap-strat.php?run=2014122300&var=TMP&lev=1mb&hour=000

As modelled a week ago:

http://www.instantweathermaps.com/GFS-php/showmap-strat.php?run=2014121618&var=TMP&lev=1mb&hour=156

The Op draws some pretty cold air down with it, so the low gives a period of snow.  The Parallel draws in much less cold air, so it's all rain.

And that's only within the GFS itself. If you factor in the ECM & UKMO just about anything is possible. 

Well the 06Z GFS has moved back towards the ECM and UKM with the low vector now more SE than E, and the GFSP looks like getting some high pressure in further N into Scandinavia again.

Is it too early for a rum?

Where? The op looks like rain.

http://www.theweatheroutlook.com/charts/gfs/06_99_preciptype.png

Snow on favoured coasts later though?

http://www.theweatheroutlook.com/charts/gfs/06_126_preciptype.png