In Depth Model Discussion, Analysis and Summaries

[Zenarcher]

Happy new year everyone

Model comparison using the GFS, ECM, UKMO, GEM, JMA and NOGAPS,

Next 72 hours to Friday - All the models show high pressure over the UK we can expect this to give us cloudy conditions with plenty of mist and fog around, winds will be generally light overall although Northern parts will see gales at times.

96 hours Saturday - All models show high pressure sticking over the UK at this time and out in the Atlantic we still have disagreement on the low entering the Atlantic, all models apart from JMA and UKMO form a low, I've marked out on the image where the center of the low is,

They all are close to each other although the depth of it ranges from 980mb to 995mb so still uncertain about it and we even have two models not showing it.

120 hours Sunday - Looks like it's 3 models against another 3, the GFS, ECM and NOGAPS show a very deep low to the South of Greenland, GEM has two lows in the Atlantic although none of them are too deep and the JMA and UKMO have a low sitting out in the Atlantic. Over at the UK the models still show high pressure in control.

144 hours Monday - Most of the models end up showing Atlantic depressions moving over our North giving unsettled weather for most of the UK although the far South of England hangs onto high pressure.

168 hours and ahead - General picture from them is the Atlantic staying in charge but the ECM builds up high pressure over the UK again and the end of the GFS run shows some wintry weather arriving.

Overall - The models are still in disagreement but do show high pressure staying with us for at least a week. Western and Northern parts will be unsettled at times as well. For those new to model watching or a reminder to everyone about why the models struggle in the long range take the GFS for example even in the high res part of the run it can get things wrong that happens all the time once we get to the low res part of the run 192 hours onwards that's where little faith is. Something like a SSW will take a bit of time for the models to catch onto but once we get closer to the time the models will become capable of picking it up. That being said the GFS for a while now has shown constantly a warm up in the Northern Hemisphere even in the low res.

Edited January 1, 2013 by weathermaster

[Gibby]

Good morning. Here is the report from the 00zs from GFS, UKMO, GEM and ECM for today Wednesday January 2nd 2013.

All models show a warm front crossing East over the UK today. A mostly cloudy day with a spell of rain can be expected, heaviest in the North and very light and patchy in the South. After a chilly start it will become milder through the day with hill and coastal fog developing. From tomorrow until Sunday a very mild westerly flow is shown around a strong Anticyclone just to the South of the UK with a lot of cloud and hill and coastal drizzle to parts of the Western hills and coasts.

GFS then shows High pressure losing its grip slowly next week with some weak troughs moving East across the UK with further cloud and light rain or drizzle on occasion with a more active trough by Thursday bringing a spell of more noticeable rain through from the West in temperatures somewhat lower but well up to the seasonal normal still. Through FI the weather remains High pressure based with a new High developing over and then just to the West of the UK with a temporary burst of colder air with frost and a possible wintry shower before rather cloudy skies topple over the High and down over the UK late in the run. Right at the end High pressure looks to be slipping SE in a confused and complex Atmospheric state as Low pressure sinks South over the Atlantic.

The GFS Ensembles show 850's well above normal for 4-5 days to come before they fall back to levels much nearer the normal in the following period out to the end of the run. After a dry week it looks like the return of some rain seems likely for all areas as Low presure trends to regain some control of the UK weather. The operational was a cold outlier for a while in the final third of the run in the South with little indication of a trend to anything colder than normal shown from today's ensembles.

The Jet Stream shows the flow ridging over the UK in the coming days before trending to relax back slowly South next week albeit, in a slack and weaker state.

UKMO for midnight on Tuesday shows High pressure and ridge moving away SE as a trough of Low pressure preceded by an increase in the SW breeze bring a return to rain from the West overnight. It will remain fairly mild.

GEM shows a Westerly flow at that time with High to the South and Low to the North with rain at times in the North before colder and dry conditions return under slack High pressure though with a trapped shallow Low drifting across the South dull and misty conditions would probably allow for a little rain here for a time.

ECM shows a fairly flat pattern for a few days with a SW flow as High pressure slips away to the SE. A cold front would meander slowly East across the UK with some rain followed by High pressure rebuilding across it towards the end of the run with rather colder conditions with frost and fog patches steadily developing later.

In Summary the models are agreed on a very mild few days to come up to and including the weekend. With the High to the South Sunshine will be limited with large amounts of cloud cover so little chance of any widespread fog and frost. Next week the models diverge to some degree, all showing differing views of bringing the UK into somewhat colder conditions with at least a little rain at times and perhaps more in the way of frost and fog. The ensembles from GFS still fail to show anything remarkable in their later stages to suggest anything wintry developing though High pressure late in some of this output does put itself in a better position to evolve later into something which could progress to colder conditions with time.

[Gibby]

Good morning. Here is a look at the 00z output from GFS, UKMO, GEM and ECM for today Thursday January 3rd 2013.

All models show High pressure close to Southern Britain with a broad and moist Westerly flow over the UK carrying a lot of cloud and some drizzle to west facing coasts and hills. Little change is expected over the coming few days as the basic setup as now remains in place. Early next week a weak trough does move East bringing some rain acoss from the West on Monday or Tuesday and again on Thursday with the remainder of the week seeing High pressure remain relatively close to the South with any rainfall restricted to more Northern parts as Low pressure to the North continues to push troughs East over the North at times.

GFS then through FI shows similar conditions for a while before a Southerly flow freshens due to a more meaningful depression in the Atlantic. This spreads cloud and rain across all areas later with all areas becoming unsettled and chillier by the end of the run with rain at times and snow possible on Northern hills. After a very mild start to the run temperatures gradually fall back to more average conditions later.

The GFS Ensembles show that the operational was on the milder side of the pack in the second half of the run with the majority showing cooling rather more prominent to levels slightly below the seasonal normal with the control run taking us into the freezer in the final week. Rainfall amounts do increase somehat in Week 2 but there remains quite a lot of dry weather shown in most places.

The Jet Stream shows a continuation of the flow arching over the UK in response to High pressure close to the South of Britain before it slips further South in a very much weakened state towards the end of next week.

UKMO for midnight on Wednesday shows the trough that crossed East on Tuesday having moved away East returning the UK into dry and settled conditions again as High pressure re-establishes itself close to Southern Britain with dry and fine weather in temperatures well up to normal.

GEM shows a High pressure cell drifting slowly East from Southern Britain to Europe as a light Southerly flow develops with some bright or sunny spells and the chance of some overnight frost and fog patches developing overnight.

ECM shows a trough moving East on Thursday with some rain for many for a while before a return to High pressure conditions develop as height's to the South of Britain remain in place. Temperatures remain very much up to normal or above at Day 10.

In Summary this morning the UK weather will be dominated with High pressure to the South or East of the UK for the next 10-14 days. This means there will be a lot of dry weather around, especially in the South. There will be some rain at times in the North and this may filter South and East at times. Temperatures will be on the mild side especially early in the period before temperatures decline to levels nearer to the seasonal normal during the second half of the run.

[Zenarcher]

Evening everyone some interesting model outputs today and things certainly looking more promising than they have been lately,

Using the GFS, ECM, UKMO, GEM, JMA and NOGAPS for comparisons.

Friday to Sunday 72 hours - The models show all of the UK can expect cloudy and misty conditions, temperatures will be on the mild side and it will be a lot more drier. Gale force winds are likely at times in the North and West and elsewhere will be breezy.

Monday 96 hours - It seems like the UKMO and NOGAPS are the odd one's out with the Atlantic low we have they form it differently,

Here is a close up comparison of the ECM and UKMO,

More models show something similar to the ECM and the UKMO seems to have it further East.

Tuesday 120 hours - The GFS, ECM and GEM all show either one or two low pressure systems form in the South of Greenland, the UKMO and JMA do look similar here they have things just slightly more East and then NOGAPS as usual showing something on it's own.

Here are what they show side by side,

I've also made up this other image of the situation over Iceland notice how the UKMO and NOGAPS are the only ones here that look the odd ones out.

144 hours Wednesday - All the models show a deep low to the South of Greenland but again its the UKMO and NOGAPS showing something different I explain in the image below,

Overall - The models I believe are slowly picking up on something interesting but it will take a bit more time for things to start to show up. As for the models today most seem to have agreement between them but the UKMO and NOGAPS seem to have little support at the moment on their outputs when you compare them to the other models.

Edited January 3, 2013 by weathermaster

[Gibby]

Good evening. Here is the report on the 12z Output from GFS, UKMO and ECM for today Thursday January 3rd 2013.

All models tonight show a mild and moist WSW airflow over the UK around a strong Anticyclone just to the South of the UK. occasional light drizzle will continue to affect many Western and Northern coasts and hills with any brightness in the day restricted to sheltered Eastern areas where high ground lies to the West. By early next week a weak trough crosses from the west with the chance of at least a little rain for many in continuing rather mild and benign conditions.

GFS then shows further quiet weather if less mild as winds back slowly Southerly later in the week as Low pressure drifts slowly SE to the West. The West of the UK could see some rain from this as the pattern becomes complex as High pressure tries to build to the North and East. On this occasion it fails with the rest of FI showing unsettled weather returning from the West as the Jet Stream migrates South with some rather cold conditions in the North especially where some snow could fall with time especially over the higher ground.

The GFS Ensembles show a decline in uppers after this weekend with the return to nearer normal values when taken as a whole. However, this paints just half of the story as there are a notable number of members who dip to much lower values than has been seen for some time in the second half of the output. The incidence of precipitation increases somewhat too as we move through the run.

The Jet Stream shows a continuation of the Arching of the flow over the UK around the Northern periphery of the High to the South of the UK in varying degrees for the coming week or so.

UKMO for midday on Wednesday shows a large slack area of High pressure over Western Europe with a SW flow over Northern and Western parts of the UK. A continuation of the rather mild and rather cloudy weather seems likely at that point with the chance of some rain and drizzle in the North and West.

ECM shows a similar pattern at that point moving forward to show a couple of weak fronts crossing East over the UK in the broad Westerly flow with some rain and drizzle for most as they pass. At the end of the run the pattern remains quite flat with High to the South and lower pressure towards the North and Northwest.

In Summary there is still not too much to talk about for our cold loving friends tonight, at least not what's likely to be felt at the surface in the period of the output. There will be a lot of dry and rather cloudy weather still to come with a little rain at times. GFS does show the embryonic signs of a pattern wanting to change and their ensembles do show some interesting options tonight between some of their members but the ECM operational remains very uninspiring out to 10 days with the same pattern of High to the South and lower uppers to the North at the end of it's run. So all in all it's a case of waiting to see if the models respond to the SSW event over the coming days and wondering what implications that may have on the output and eventually our weather later in the month.

[lorenzo]

I key consideration thereafter will be whether the MJO can migrate eastwards towards phases 7-8 (currently a strong pulse of east winds ahead of the MJO which it will need to negotiate) and the response of the middle and high latitudes, which a stratospheric warming would favour.

Stewart do you have any thoughts on how this is progressing had a look at the TAO/Triton page but unfamiliar with how to decode the data and place in context.

My thinking would be if the ECM 32 is led by the MJO set up post 240 then it will be may be very slow to come on board with GFS?

[Gibby]

Good morning. Here is the report of the 00z output from GFS, UKMO, GEM and ECM for today Friday January 4th 2013.

All models show a mild and moist westerly flow over the UK under the influence of a strong High to the South. Through the following few days changes to this overall pattern will be slow with just the mildest of the uppers leaking away somewhat with time. Secondly as we approach the new working week and probably most likely on Tuesday the High gives ground sufficiently to allow a weak front to cross over the UK with a band of rain though amounts in general will be small. By midweek the trough has passed and High pressure regains control close to the South, though in less mild air than recently.

GFS then shows High pressure ridging North through Britain to form a closed centre to the North of Scotland allowing a slack Easterly flow to develop over England and Wales with progressively colder conditions developing with frost and fog patches overnight though it would likely stay dry. In FI this morning the Jet Stream pulls South in the Atlantic and a very cold pool develops over Europe. The combination of the two engage late in the output to raise pressure to the North and Northwest pulling increasingly cold and eventually bitter air West from Europe over the UK as Low pressures are steered with the Jet flow well to the South. As shown this would make for a spell of sub zero temperatures day and night for many with frequent snow showers or longer spells of snow moving in from the East.

The GFS Ensembles show the operational only an outlier right at the end while the control run shows a major severe cold outbreak in its second half. There is still plenty of scatter between members in the second half of the run with plenty of mild options still shown but the trend towards colder scenarios developing over subsequent runs is increasing.

The Jet Stream shows a continuation of the current flow up and over the UK before the flow decomes disrupted and blocked in a week or so with a returning flow SW from Northern Europe hinted at late next weekend with a compensatory Northward drift high to the Arctic in the Eastern Atlantic.

UKMO for midnight on Thursday shows High pressure close to SE England with a ridge North over the East of the UK. A SW flow is blowing over the NW. A lot of dry weather is still shown over the UK at this stage with perhaps some rain and drizzle from weak troughs in the NW. It would be less mild than recently with perhaps some frost and patchy fog towards the South and East.

GEM shows a High pressure ridge over the UK at the same time pulling away slowly East over Europe in the following days leaving a slack South or SW flow over Britain with fairly benign if less mild conditions continuing.

ECM finally shows a trough crossing East next Thursday with some rain followed by more High pressure close to the South bringing a return to dry, less mild conditions with patchy frost and fog later. On Day 10 the Jet flow is shown to be more disrupted with cold air establishing over Europe. In the days that follow Day 10 the likelihood of colder weather for the UK looks like increasing as High pressure builds over Scandinavia and falls to the West.

In Summary there is still a lot of quiet, benign type weather to come over the next 7 days or so. Thereafter, there are signs of developments turning conditions rather colder and more interesting for those looking for cold as High pressure starts to build in more favourable locations. If the GFS Control run and to a lesser degree the operational run at the end would have us believe we will be well and truly in the freezer in two weeks time but support is still too sketchy to get too concerned at this range. Nervertheless, if its trends we are looking for at that range there is a definitive trend towards a more wintry look to things slowly taking shape, especially given the rumblings of the Professionals who are quite openly talking about the chances of a marked change towards late January on the media. It will be interesting to see how things develop on the models over the coming week or so as that time comes nearer.

[johnholmes]

An in depth but simple guide to what I think the upper air and surface may show in the 6-15 day time frame

7-weekly update on anomaly charts-fri 4 jan 12.pdf

[MattH]

An in depth but simple guide to what I think the upper air and surface may show in the 6-15 day time frame

7-weekly update on anomaly charts-fri 4 jan 12.pdf

Excellent discussion John for all to read and get some info from.

M.

[Gibby]

Good evening. Here is the report on the 12z Output from GFS, UKMO and ECM for today Friday January 4th 2013.

All models tonight show a mild and moist WSW airflow over the UK around a strong Anticyclone just to the South of the UK. There will be a lot of cloud over the UK with some occasional light drizzle along with hill fog over Northern and Western coasts and hills. There could well be a few brighter spells for the lucky few, most likely in the sheltered Eastern parts of the UK. Temperatures will remain above normal over the weekend with any frost restricted to the North behind a very weak cold front edging South tomorrow night. Early next week all models show little change until Tuesday when a more active trough crosses East from the West bringing some more appreciable rainfall for a time. By Wednesday a return to dry and rather colder fresher conditions look likely with a better chance of seeing some sunshine.

GFS then moves into the later end of next week with High pressure gradually transferring to Scandinavia with a resultant Easterly flow developing over Britain, especially in the South. Things would start to turn rather cold though still with a lot of dry weather. Through FI tonight the operational model shows High pressure steadily retrogressing West towards Iceland and Greenland with the Easterly flow maintained over Southern Britain where overnight frosts and the odd wintry shower becomes likely. Late in the run the High sinks SE over the UK declining as it goes with frost and fog widespread overnight over the UK.

The GFS Ensembles show a lowering in uppers from early next week to values closer to the seasonal normal. The Control run is again well on the low side of the pack in the second half of the run with other members varying between very mild members to very cold members in the second half of the run. Occasional rainfall, though never substantial occurs on occasion throughout the run after this weekend. There is a large spread between the members from the mid point.

The Jet stream shows the flow ridging strongly over the UK gradually weakening as the Jet flow becomes disorganized and weak as we move through next weekend.

UKMO for midday on Thursday shows a ridge having moved East over the UK moving away East as a trough approaches the West with rain crossing east over the UK through the day.

ECM shows a similar setup to UKMO with several spells of rain crossing West to East before High pressure builds over the North and to the NE of Britain delivering colder and still mostly settled weather to the UK in 10 days time.

In Summary there are signs of a change to come after the middle of next week. Progressively colder weather looks likely to develop over the UK in a week or so time with synoptics unimportant as shown tonight as I'm sure there will be many different evolutions thrown at us over the coming days as the pattern develops.

[snowking]

Right well a lot of very high quality information and discussion has passed through these forums today, so I thought it might be useful to try and summarise some of this information.

Before I go ahead, one should bear in mind that most of this data is all based upon NWP, and as such, given the current stratospheric events, it should be taken with a large pinch of salt.

OK, lets start from the top....

Our very consistently and very well forecast warming at 10mb has made it all the way to T+0, and over the next couple of days, this breaks the 'surf zone':

And delivers us a technical SSW

As time develops, and further warming potentially occurs:

We see a resultant displacement and splitting of the Polar Vortex over the Arctic:

This forms two distinct segments of the vortex, one based around Western Siberia, and the other just to the west of Greenland.

Over time, these segments become more and more displaced by the further forecast warmings, along with strong wave 2 activity:

Until we arrive at this at day 10 on the GFS:

Backed up by the ECMWF:

The biggest change at 10mb over the last 24 hours has been the difference in energy between the two stratospheric vortices. This is a result of difference in placement of the secondary warming, with the GFS having been toying with various scenarios in the last few days, but both the GFS and the ECMWF today go with warming the Siberian vortex more initially (though hints of attack on the Greenland vortex offered by the ECMWF). The net effect of this is to maintain a slightly stronger western vortex (though it should be noted this is displaced into Canada as opposed to Greenland) with a weaker Siberian/Scandi vortex. This is the most likely reason for the modelled Scandinavian based tropospheric heights (as opposed to more Greenland based as per yesterdays hints). Whether this stays a consistent theme is of course very much up in the air.

All of this said, whilst its all well and good having this up at 10mb, if it doesn't downwell then its next to useless for us, so lets take a look at the lower stratosphere:

Fortunately, whilst not quite as amplified as at 10mb, still a similar picture, with a ridge evident across and to the north of the UK (though slightly further east than modelled yesterday) with a stronger Western vortex.

Further down the line, the GFS keeps the Greenland/Canadian vortex heading west:

And moves the ridging more towards Greenland - again a theme of the troposphere there.

So, from a stratospheric standpoint whilst there is still some subtle variation of the pattern, the theme remains two vortices, one Canadian based, the other Siberian based, with the longer term outlook transferring the wavelengths slightly westwards (a sign of the times)

Down we go to the troposphere then.

The biggest thing to take from our ensemble means (though i'm not a great lover of these in situations such as this because of a pretty obvious risk of dilution of a given pattern) is the movement of the PV lobes following very closely those showing in the stratosphere.

GFS:

ECMWF:

The other thing to be noted is that the Ensemble mean low modelled across the North Pacific (our much mentioned Aleutian Low) will help to drive further Wave 1 activity (which keeps the vortex displaced away from the pole), whilst any potential Scandinavian Height Rises would drive Wave 2 Activity (which keeps the vortex split). Whilst the signal for Scandinavian height rises is much more muted in the ensemble means, when you look at mean height anomalies such as this at day 7:

That risk becomes more apparent.

Incidentally, the ECMWF mean height anomalies show very well the tropospheric response to the westward longwave shift in the stratosphere:

With the height anomalies transferring from W Scandinavia to Greenland through the run, and the two main vortices following suit.

Hopefully from this you can see that any recent fears of a disconnect between the Stratosphere and Troposphere are quickly becoming quashed, with the stratosphere seemingly leading the pattern in the next 10 days or so at least

It is for this reason that great caution has been urged when viewing NWP output, with an initial disconnect between the two (and plenty more twists and turns to come undoubtedly)

But even if there are any remaining fears about a need for a separate tropospheric response, here comes the MJO:

RAW:

For anyone unsure, thats the GFS, UKMO, GEM, ECMWF and ECMWF 32 day raw output. Heres the bias corrected equivalents:

Without any shadow of a doubt the best MJO forecasts of the season, taking us through into phases 7 and potentially 8

Heres where 7 and 8 leave us for January:

YES PLEASE

By the time we head towards February, most likely phase 8:

So, where are we likely headed? In all honesty, as suggested at the start, all of this is very open to the frailties of NWP at present, HOWEVER. We can see that the suggested Scandi becoming Greenland HP scenario is not that farfetched from the point of view of Tropospheric/Stratospheric coupling, and at the moment, IF the modelling is even anywhere close to correct, this is where I see us heading.

The stratosphere really could not be much better primed for the UK in terms of long term cold, and should this (as currently suggested) downwell to the troposphere - with the MJO looking to come onside too (argue the relationship there until your hearts are content) - then winter will be arriving for the UK, and potentially within the next 10-15 days.

When I issued some early winter thoughts on another forum back in November, I suggested the risk of February being one of the coldest 10 in the last 100 years....after looking at all this, I'm reluctant to back away from that.

SK

Edited January 4, 2013 by snowking

[chionomaniac]

Fantastic post SK.

[bluearmy]

here here SK !!

are the effects of the SSW leading the MJO forecast? without the SSW, the MJO forecasts (and the amplitude is fair) lead us to the wintry output we are now seeing in the models. so is this a situation where both drivers will force the pattern? does one reinforce the other? i hope its not a 'double negative' scenario !!

[Coast]

Right well a lot of very high quality information and discussion has passed through these forums today, so I thought it might be useful to try and summarise some of this information.

Thank you for the summary SK, a lot of information has flowed here in the last couple of days and I believe even the main media has picked up on it afterwards!

[chionomaniac]

here here SK !!

are the effects of the SSW leading the MJO forecast? without the SSW, the MJO forecasts (and the amplitude is fair) lead us to the wintry output we are now seeing in the models. so is this a situation where both drivers will force the pattern? does one reinforce the other? i hope its not a 'double negative' scenario !!

They are like the ballroom dancers that I have suggested. They don't step on each other toes but dance together.

[lorenzo]

Top Notch post SK, great work, enjoyed reading that.

[phil nw.]

Yes i must add my appreciation for that very thorough and well constructed post S.K.

Nice work.

[Tamara]

I would like to add my thanks for that post from SK as I have no quota of 'likes' left for usual silent appreciation. Explained very logically, very thoroughly and in simple understandable terms for us ordinary folk

[damianslaw]

Excellent post from snowking - very easy for us non-meteorologists to understand. As ever the route to cold in this country is never easy, our weather is like a jigsaw, and requires all jigsaw pieces to slot into the right place for sustained cold and warm weather- the NWP output certainly shows the pieces could very quickly fall into the right place for a sustained very cold outlook.

[syed2878]

nice1 sk its posts like that makes people like my self don't fiel left out.

[Gibby]

Good morning. Here is the report on the 00z outputs from GFS, UKMO, GEM and ECM for today Saturday January 5th 2013.

All models continue to show a very mild and fairly cloudy couple of days to come before falling pressure early in the week brings a more meaningful band of rain Eastwards on Tuesday. Once cleared High pressure re-establishes itself close to Britain in rather colder air with frost and fog at night in places but some sunshine by day. The models then diverge in a slow route towards rather cold conditions.

GFS shows another band of rain moving slowly into the UK from the West late next week which dies in situ over the start of the weekend as a strong Scandinavian High builds a ridge across it. After cloud from the front breaks up frost and fog would develop under a cold drift from Europe. Through FI this morning the High slowly pulls west to the UK before retrogressing NW to Greenland with a cold and potentially wintry situation developing with some snowfall in places, chiefly towards the North.

The GFS Ensembles show a general cooling over the next two weeks. The operational is on the warm side of the pack right from the start with a rather colder outlook than the output I have described above more likely. A couple of the members take the UK right into the freezer with more unsettled conditions with time, especially in the North with precipitation likely to be of snow at times.

The Jet Stream shows a strong ridging of the flow North around the UK and down over Europe. With time the flow weakens as well as become disorganized before taking a more Southerly route late in the period in response to building pressure to the North of the UK.

UKMO for midnight on Friday shows a Low pressure over the Baltic sea and the Atlantic with high pressure to the South and North of the UK. A weak ridge in association with the High to the South slowly crosses the South of Britain in a Jet stream that is sinking South of Britain. The weather will likely be dry and much colder with a frost likely for many with a few showers in the East, perhaps wintry over the hills for a time.

GEM shows High pressure remaining in close proximity to the UK in the latter stages of its run before a Low pressure to the North and a rise in pressure over Grenland forces cold Arctic Northerly winds down over the UK by Day 10 with rain followed by snow showers from the North.

ECM also shows High pressure more in dominance close to the UK with a different outcome to GEM, bringing lower temperatures, quite settled conditions with overnight frost and fog after a little rain from a trapped and small Low pressure gets squeezed out next Sunday. the run ends with a strong UK anticyclone with frost and fog widespread night and morning.

In Summary today there is firm agreement on a route to colder conditions from Tuesday onwards. The route is slow and complicated and doesn't result in anything particularly wintry for many as shown today. Nevertheless, these details are unimportant at this stage and will in no doubt change from subsequent runs. The GFS Ensembles are very notable this morning with a strong trend to colder weather shown. In more general terms a change to colder weather will be welcome to many people as it more or less guarantees no return to the wet and mild disruptive so much of the Winter this far has delivered for many with the drying process able to continue over the up and coming two weeks.

[J10]

Latest Ski Blog out now.

http://forum.netweat...h-january-2013/

Synoptic Extract here

Synoptic Charts

The weather pattern starts with low Pressure over Greenland and the Western Atlantic, High Pressure ridging from Iberia through the UK to Western Scandinavia and much of Western mainland Europe, with a mild South Westerly flow here. Low Pressure over Eastern Europe with Northerly winds keeping it cold here.

Little change over the weekend, but the pattern moving slightly further east, putting more of Europe into the mild air, with the cold in Eastern Europe pushing away further east.

By Tuesday and Wednesday, the High Pressure covering most of mainland Europe, so the cold restricted to Far East and into Greece. Largely mild over the UK and the Alps during this time, however always colder to the East, with cold air fringing eastern parts of Austria and very cold for Bulgaria further East.

Towards the end of the week a change in the pattern with Low Pressure over Scandinavia introducing a cold NE flow over Scandinavia and into the UK, and over Northern parts of mainland Europe Possibly turning very cold over NE mainland Europe, and generally turning cooler over the Alps and the UK

[Gibby]

Good evening. Here is tonights look at the 12z output from GFS, UKMO and ECM for today Saturday January 5th 2013.

All models support a period of benign conditions continuing between now and this time next week. High pressure currently to the South of the UK will dominate conditions over the UK for some time yet wafting mild Atlantic air across the UK. A few weak troughs could bring some occasional drizzle as well as some transient clearer spells here and there. On Tuesday and again on Thursday it looks as though some troughs moving in from the West could bring some more noticeable rain, heralding rather colder conditions too as the rain clears with temperatures returning to near normal or a little below for some by next weekend.

The GFS operational then has nothing to do with this morning's cold theories and maintains heights down near NW Spain preventing any cold reaching our shores. Instead a run of West or NW winds brings rain at times from Low pressure as they run SE and weaken through Scotland and the North Sea as High pressure builds across them. Eventually in FI High pressure does develop strongly over the UK with some fog and frost problems likely, slow to clear for a few days in places. Late in FI the High slips SW and a mild NW flow develops with a situation not dissimilar to where we are now with benign and relatively mild conditions in a fresh and strengthening westerly flow. Some rain would affect Northern and some Eastern parts towards the end of the run.

The GFS Ensembles look pretty ordinary this evening after some encouraging output of late for cold lovers. Instead we have a set that average near to the long term mean with some very mild options and a share of cold options too with precipitation, though present not substantial by any means.

The Jet Stream shows the current setup in place for a few more days before the ridging flow to the north of the UK collapses and a confused and flabby nature to the flow develops late next week and weekend with weak flows all over the place over the Atlantic and Europe.

UKMO for midday next Friday shows a more unsettled look to things than of late with a Westerly flow over the UK with one rain bearing trough having cleared the East Coast while another waits just to the West. Temperatures would continue to leak away under colder uppers filtering down from the North.

ECM shows a trough moving into the SW next Friday which develops a closed 'low' centre close to Southern Britain next weekend with cold rain and maybe some sleet over the hills as winds back East and freshen. High pressure has built quite strongly between Scandinavia and Greenland with the North likely to be drier with some frost should skies clear overnight. Later in the run a cold spell is well and truly setting up as the exiting Low pressure leaves behind a legacy of cold easterly winds and some wintry showers in the East before a strong height rise over Greenland brings very cold frosty weather on Day 9 under a ridge while Day 10 sees a strong Greenland block with Low pressure over Scandinavia and NW Russia steering bitter NNE winds and snow showers into Scotland and the NE later.

In summary the models are still jockeying around various scenarios as they continue to factor in the SSW event. GFS will be a disappointment to many but don't be surprised if it doesn't flip back to cold in the following day or so. Perhaps the more worrying scenario from the GFS camp though is that there is still too many members in the Ensemble pack not wanting to develop any cold near our shores over the period. Nevertheless, ECM is much more on the case as the weather from as early as the latter half of next week is shown to become colder and not without interest from precipitation either in the ever colder air accentuating itself by next weekend with cold Arctic winds and snow showers pulling down from the North. As usual in these developing situations the lesson should be not to take each run literally and sit back and enjoy the ride as the UK could be on the cusp of another cold wintry spell but hold on tight because we know what happened in early December.

[TonyH]

A look at the coming week for west Wales and the Midlands:

http://forum.netweather.tv/blog/309/entry-4541-weather-prospects-for-the-midlands-and-west-wales-monday-7th-to-sunday-13th-january-2013/

[johnholmes]

copied from model thread before it gets buried!

Looking back at the 500mb anomaly charts-7 jan 12.pdf