In Depth Model Discussion, Analysis and Summaries

[Gibby]

Good morning. Here is the latest report of the 00z output from GFS, UKMO, GEM and ECM for this morning Tuesday December 4th 2012.

All models show a similar pattern now up to and including the weekend and Monday of next week. A rather cold NW flow covers the UK currently. Through tomorrow a trough moves South over England and winds turn Northerly dragging even colder air South behind a weakening band of rain and snow tomorrow. Thursday sees a cold day after a frosty night as a ridge becomes replaced by a strengthening Westerly wind and rain and sleet spreading down from the NW as a deepening depression is shown to move SE across Scotland and down the North Sea by Friday. The rain and snow clears the SE with a cold and strong Northerly flow for a day or so with frequent sleet and snow showers to the North and East. Frosts will then become widespread and hard overnight through the weekend as pressure rises strongly with High pressure close to Southern Britain late in the weekend and start of next week.

GFS then shows a ridge over the UK drift slowly East and become absorbed by a large Northern European High with a cold SSE wind developing over the UK in dry conditions away from the far West. Through FI this morning the trend shows winds backing slowly and surely towards the East with cold continental winds taking hold. There would be a lot of dry and cold weather around with some wintry flurries near the East coast and the threat of more substantial snow to the SW at times as milder air approaches Southern areas turning the snow to rain on this occasion later.

The GFS Ensembles are not quite as good for cold lovers this morning with a huge spread of uppers between +5C & -10C. The colder options still have the upper hand though with the prospect of at least a rather cold or cold spell to come, especially in the South. Precipitation is more prevalent for the North where the operational was a cold outlier. The South looks like seeing a fair amount of dry weather under higher pressure conditions.

The Jet Stream continues to be shown to flow East or SE over or to the SW of the UK and down towards Southern Europe. Later next week the flow ridges High over the Atlantic and disrupts almost entirely around the UK leaving a weak flow high up in the Arctic and another over Southern Europe. A new stronger arm begins to head East over the Atlantic at 50N latitude at the end of the reliable prediction range.

UKMO for midnight on Monday shows High pressure over NW Europe and a larger one over Northern Russia. Low pressure is held well out in the Atlantic making for a an anticyclonic South or SW flow over Britain giving typical early winter conditions of chilly bright weather by day with frost and fog patches night and mornings, at this point particularly in the South.

GEM this morning shows a similar pattern but with a small Low over Denmark encouraging a pressure rise to the NW which links to the Scandinavian High bringing a cold ENE flow across the UK under a ridge with the end of the run showing High pressure close to NW Scotland to Scandinavia and a slack and cold North to Northeast flow over the UK bringing cold and frosty weather with just the chance of a wintry shower near South-Eastern coasts.

ECM shows a similar pattern to the UKMO model on Monday before a stubborn Low pressure over Denmark and Germany slows the advection West of cold air West to the UK from Europe. Nevertheless, in time it does and by the end of the run high pressure has taken a stranglehold over NW Europe with a cold NE flow bringing the risk of wintry showers of sleet or snow into the SE while all others stay dry, cold and frosty under a ridge of High pressure from the NE.

In Summary it still looks like a colder spell is on the way. How much colder is yet to be decided and is entirely dependent on how the building blocks fall in favour of the British Isles or not. After this weeks taste of snow for some there looks little on offer thereafter as High pressure looks like being in control though if the East or Northeasterly materializes then some wintry interest is likely for Eastern coastal counties. It's a rocky road of model watching which is going to keep rolling until the end of this week before things become clear one way or the other.

[lorenzo]

Another positive I found this morning, although perhaps I should say another negative.. In respect of the AO. Fits well with the trend in the Winter forecast, that Greenland high features strongly again within the analogues presented.

the ensembles were in good agreement that the Arctic Oscillation is forecast to drop to severely negative levels (-3.000 or below).

[johnholmes]

another input from Ian f from UK Met

Latest from Ops Centre:

" 4. Trend for Days 10-15 : Best estimate is to remain colder than average with frost more widespread than normal and some wintry ppn likely, especially in the N and E. Highest probs of milder, but wetter interludes are towards the W/SW.

5. Discussion : There are major differences between EC and MOGREPS through this period. Initially these differences are not too great, with both ensemble suites having a signal for a brief milder interlude early next week, especially across northern Britain. Thereafter a blocked pattern is expected to develop, but there are large differences between MOGREPS and EC with the detail of the block, with EC ensemble having a strong signal for an E’ly, whilst MOGREPS has a S’ly. NCEP ensemble appears to be roughly split 50/50 E’ly and S’ly. The EC solution has been favoured at the moment, with slightly more support, but with the caveat of occasional frontal incursions into at least in W’ern parts of the UK."

I have to say, in a short post, that for the first time in over 2 weeks, the anomaly charts are not showing complete agreement.

more on Thursday as promised above-maybe it will be clearer by then?

Edited December 4, 2012 by johnholmes

[Gibby]

Good evening. Here is the evening report on the 12z outputs from GFS, UKMO, GEM and ECM for tonight Tuesday December 4th 2012.

All models continue to show an agreed pattern to the course of events between now and Monday. An occlusion moving steadily South over the UK will bring a mix of rain, sleet and hill snow overnight, reaching Southern England by morning. Following on behind a slack North flow will push the occlusion away South tomorrow morning and give many areas a dry cold end to the day with some snow showers near Eastern coasts as a ridge of High pressure brings a very cold night with a severe frost tomorrow night. On Thursday Low pressure will slip SE over Scotland and down the North Sea towards the SE on Friday. Rain and hill snow spreads SE through all areas on Thursday followed by a cold and windy day on Friday with rain and sleet clearing South to leave snow showers for many Northern and Eastern areas through Friday. The weekend then sees High pressure building rapidly from the West bringing cold, crisp weather with frosty nights with some increase of cloud over the extreme West and North later as the High pulls away slowly SE.

GFS then shows the early part of next week with the UK under slack and relatively high pressure. The weather would be relatively dry with frost and fog by night, chiefly in the South. Through the week the trend is for progressively colder air to drift West from Europe with dry conditions still with broken cloud and some weak wiintry sunshine, especially in the West. Later in the week the breeze increases with a bitter feel and the trend for some wintry showers of sleet and snow or snow grains increases towards the East and South. A breakdown is shown in the latter part of FI with a messy transition of snow and sleet followed by rain and much milder conditions pushing up from the South.

The GFS Ensembles show good prospects for cold lovers this evening with uppers well below the long term mean throughout over the UK. Some very cold members are being shown tonight with -10C breached by several members later on. With very few mild options shown it is a big step back from the somewhat disapponting sets we were seeing earlier. There is some precipitation about too at times with no doubt some of that falling as snow in places.

The Jet Stream shows that the UK lies as the target for the South-eastwards moving flow for some considerable time as it moves down to Southern Europe where it continues East. later next week it ridge High over the Atlantic and crosses East to the North of the UK before turning SW from Scandinavia to the UK and South to Spain.

UKMO for Midday on Monday shows High pressure over Northern France with slack Low pressure over Scandinavia, moving SE slowly. Fine and dry weather would be likely for many with cloud and drizzle to the far West and NW. It would be rather cold in the South with some frost and fog at night.

ECM shows not such a pretty picture for those wanting snow but shows a messy transition from rather cold and dry conditions early next week into what would be a rapid change into a cold Easterly flow were it not for a stubborn small but significant Low cell near Denmark preventing a quick link from the UK High to the Northern European High. Nevertheless, it does show a dveloping and cold SE flow towards the end of its run before the cold is thwarted by a large and powerful depression out to the NW pushing warmer Atlantic winds in towards Southern and Western Britain.

In Summary things have taken an upturn for cold lovers this evening. GFS has returned to its former opinions of bringing a cold East flow into the UK in a week or so. However, as always there is a fly in the ointment in the shape of ECM tonight where it refuses to show the Low to the East slipping SE which in turn prevents the vital feed from the East to the UK. Consequently the Atlantic power horse looks very active late in its run and will attempt at least to break the block down around the UK with the usual messy mix of snow and rain. We will need to see where this solution lies in the ensembles later with the GFS ones very favourable tonight. So the period of fascinating model watching continues with many more instalments of upgrades and downgrades to be endured over the days to come.

[johnholmes]

dropping this in here as it will soon be lost in the model thread

They ( the 500mb anomaly charts) are at the moment not quite at 6 and 7's but close to it although the overall trend is still to show a cold and certainly not a mild spell of weather at the surface into the 3rd week of December.

As always the hiccup, if that is what it is, over the past 24 hours will be revealed as a hiccup or a trend after they revert back to showing a pretty similar pattern between the main 3 and also the NAEFS version in about 3 days time when they have settled into whatever they think it is going to do. My own personal punt would be back to cold. Whether that is NW based as the current cold is or more NE based I'm not sure.

My 500mb update will get done, I hope, during Thursday.

I hope this may help some newer folk to get a grasp of upper air patterns and that they are, in my view, more reliable at 6-16 days range, than the 4x or 2x daily synoptic outputs. I stress that is my view and others will disagree. However the 'success rate of these charts at these time scales is about 70% which I think is quite impressive.

Edited December 4, 2012 by johnholmes

[johnholmes]

Just to add the 30mb link below-it crossed the average line 1 December and is still climbing. In my very amateur view this sufficient in most cases to have an effect in the Troposphere. The earliest this effect of causing/increasing any blocking already occurring is 15 days more probably 25 days. I'll leave you to do the arithmetic and I will do a full update using various links/ drivers etc during tomorrow. No specifics that is impossible beyond 2-4/5 days in my view in 99% of cases, but an overall view of the type of upper air pattern be it SW NW or NE.

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/html_e/pole30_n.html

[Gibby]

Good morning. Here is todays report on the 00zs from GFS, UKMO, GEM and ECM for today Wednesday December 5th 2012.

All models show a consistent pattern between theirselves on the course of events between now and Monday inclusive. The current slack Northerly flow will give way to a ridge of High pressure moving in from the NW later today bringing a sharp overnight frost to all replacing the early snow in the SE and wintry showers near the East coast. Tomorrow shows Low pressure moving SE across Scotland and down over the North Sea to NW Europe in the following 24 hours. A band of rain and snow will move down across the UK quickly with the snow on Northern hills. Later clearer and colder conditions follow a cold front South by Friday with a return to very cold weather and snow showers, especially in the East for the rest of the day. Over the weekend High pressure builds quickly over the UK with a fine and frosty spell likely with some freezing fog patches too likely in the South at the start of next week.

GFS though broadly similar has the High a little further SW with a NW flow over the late weekend and start of next week turning NE by Tuesday as a new High pressure belt extends from Northern Scandinavia to Scotland. For the rest of the week progressively colder and unstable air makes its way West from Europe with snow showers becoming prevalent over Southern and Eastern areas by the end of the week. There would be widespread night time frosts. Through FI the pattern remains cold or very cold as High pressure migrates slowly West from Scandinavia to Greenland with Low pressure to the South. There would plenty of opportunity for snow with the risk of disruptive snowfall over Southern and Southwestern England as mild air tries to encroach. Late in FI a Arctic blast reinvigorates the cold with snow showers relocating to Northern and Eastern coasts.

The GFS Ensembles continue to show a cold spell coming. The depth and longevity of cold is open to debate with the operational a colder member for part of the run. There is some precipitation shown to be around so some snow is likely for some. There is a slow recovery in uppers later in the run and the Norrthern pack looks less encouraging overall.

The Jet Stream shows a SE flow over or near the UK for a few more days before it ridges High over the Atlantic and up to Greenland and well North of Iceland before travelling East over the Arctic. A Southern arm is maintained over Northern Africa and the Med.

UKMO for midnight on Tuesday shows Low pressure over the Baltic Sea and High pressure over Northern France with a ridge North over the UK. Fine and dry conditions would be likely for most with frost and fog overnight, especially in the South. Slightly milder and cloudier conditions would prevail in the far NW.

GEM today shows an inverted ridge over the UK on Tuesday with a colder NE flow developing. Thiss flow intensifies over the coming days with snow showers developing with time, especially in the East. Frost at night would be widespread.

ECM also shows an inverted ridge over the UK from a strong High to the North and NE next Tuesday which moves forward to show a strengthening and cold NE flow with sleet or snow showers in the east and South later next week. The run closes with a strong 1045mb High ideally placed over Scandinavia as a block to the Atlantic and maintaining a prolonged cold spell for the UK.

In Summary there is a strong coming together of the models today. They all show a large High developing over Scandinavia next week with an Easterly flow developing with sufficient instability to give some showery snowfall especially in the East. Frosts would be widespread at night with some sunshine too, chiefly in the NW. GFS goes on to show the High moving West to greenland late in its run with a Northerly flow maintaining the wintry feel.

PLEASE NOTE. There will be no report from me tonight but should be OK for the 00zs tomorrow morning. Lets hope I'm looking at a similar pattern this time tomorrow.

[nick sussex]

An interesting day in the models with the ECM delivering a simply wonderful output which delivers on all levels.

The UKMO continues to drag its heels but for the moment its solution is very unlikely to verify. Over recent days it has really been slow to react.

The ensembles, and the majority of operational output disagree with the UKMO with its only support from the lowly NOGAPS.

Back to the ECM, its very rare to get this set up and hence we should be somewhat cautious in getting too excited, its always difficult to maintain that almost perfect orientation to the high. Towards the end of its output we see the PV moving back to Siberia, this is in line with the strat forecasts and looks a reasonable assumption.

You can see that here:

If this movement of the PV does happen then I certainly would be wary of reading too much into the operational output in terms of detail, this is likely to add some volatility to the situation.

I suppose the big question is can the UK maintain the cold during the changeover?

This is possible as long as you maintain lower pressure to the south, if we do see retrogression then expect to see the blocking transfer to the nw near Greenland with a possible northerly thereafter.

In terms of the GFS its similar in overall trend but doesn't quite deliver the wow factor of the ECM, I would certainly expect to see more changes with the orientation of the high over the coming days, in terms of what cold pooling will be available to the east, again this is likely to change between runs, we won't be able to firm up on this until nearer the time.

I think for the timebeing we should just concentrate on getting cross model agreement, hopefully the UKMO comes in line tomorrow.

We're almost there with the trigger shortwave coming into the reliable timeframe, but being cautious I'd like to see the big 3 all in line tomorrow morning before cracking open the champagne.

Edited December 5, 2012 by nick sussex

[johnholmes]

from Ian F late Wed evening

Latest GM modifications into d4-5 versus raw output, for info:

"3. Modifications : Frontal link over the UK moved south a little faster to clear the SW later Monday. Low pressure centre maintained near Denmark at T+120 and over German/Poland borders at T+132 in line with ECMWF and close to the central spread of the Ensemble. This maintains cyclonic N’ly flow and the risk of snow showers over eastern areas into Monday. Dynamic ppn maintained in weak frontal link moving south over the UK. Wintry showers added to cyclonic flow pattern on the western flank of the modified low pressure centre east of the UK. Increases the risk of wintry showers over eastern areas into Monday."

[Gibby]

Good morning. Here is todays report on the 00zs from GFS, UKMO, GEM and ECM for today Thursday December 6th 2012.

All models show the pattern as before for the period today until midweek next week. Today sees a Low pressure area moving SE over Scotland and down the North Sea in the next 24-36 hours. A band of rain and snow will move steadily SE clearing away tonight to leave a cold Northerly flow with wintry showers across the UK by dawn tomorrow. After a windy and cold day wintry showers will die out from the West as winds sie out as a ridge of High pressure builds in from the West for the weekend. This would mean a dry and cold weekend with frost and freezing for overnight, especially in the South. By Monday a new Low passes SE to the NE declining the ridge North as a NE flow develops on the back side of the Low pressure as it moves SE over Europe. The cold flow will begin to pull wintry showers in from the NE early next week intensifying by midweek with widespread night time frosts.

GFS then shows High pressure to the North with Low pressure close to the South with a cold and unstable East or NE flow over the UK. There will be snow showers or snow at times with some appreciable falls possible over the hills. In FI details are unimportant at this range but the trend of the operational is for a change to slightly less cold conditions with rain or sleet at times in cyclonic winds.

The GFS Ensembles show a cold spell to come with the operational a milder outlier at the end. Rain and snow is shown to occur at times thought as usual in cold spells no huge amounts are indicated.

The Jet Stream shows a SE moving flow over the UK and on down over the Med where it turns East over Southern Europe. Later next week the flow ridges High over the Atlantic with a flow moving East over the Arctic Circle while another arm travels East over Southern Europe. The UK sees Scotland see a returning if weak Westwards moving flow from Scandinavia later and an equally weak Easterly moving flow over Southern England indicating a complex Wintry Low pressure system near Southern Britain.

UKMO for midnight on Wednesday shows High pressure from Iceland to Northern Russia with Low pressure over the Baltic and the SW approaches. A cold and wintry look to the weather would be had with sleet and snow in places most likely in the east and SW.

GEM shows a complex area of Low pressure over or close to the UK, trendding down towards the SW. An increasingly wintry picture would develops with outbreaks of sleet and snow expected for many at times.

ECM today shows an unstable cold pool developing over the British Isles as an Easterly flow pulls it in from the East. Low pressure develops over and around the UK with sleet and snow a common feature of the weather over the UK later next week. The pattern does show sign of moderating later as the block to the NE weakens.

In Summary things look very wintry this morning. The longevity of the cold is open to debate and we need the Low pressure areas mixed in the cold pool to locate in the right place to allow the risk of sleet and snow to continue but the theme even far out is for cold weather to be still in place and though details will change I think we can safely say that a week or two of cold and wintry weather looks likely from early next week when there is a more than evens chance we will all see some snow.

[Catacol]

As this is a thread about thoughts... I must say (keeping away from all the mad stuff on the model thread for a minute and trying to be objective and analytical about it) I think the prognosis for winter this year is now really very severe. I have taken to looking at the models and charts the other way around... ie instead of looking for cold as so many of us do and hoping to see it, I am now looking for mild and trying to see it.

I cant find very much solace from this angle at all. The obvious potential for atlantic air from the SW is a gimme in this scenario, but where do we see any sign of the vortex regaining its form and strength when it is currently under such attack, and where therefore can a westerly dominated regime come from? Low heights over Europe look to be the form horse as a very negative AO squeezes high pressure toward mid latitudes and therefore keeps low pressure dominant to our south. The lag effect in any vortex recovery is putting a return to a westerly regime further and further back as medium term NWP output suggest more and more pressure on the vortex itself. In this scenario the jet looks fixed to the south and the northern arm of the jet too weak to break down the block.

Any SW attack looks transient - and loaded with snow potential as ground temperatures entrench on the cold side. Movement of the block will lead to an alternating northerly or easterly regime with the odd milder patch as the wind direction moves and I guess a trough that anchors over Ireland might raise temperatures a bit... but I am struggling to see any sign that things are going to change substantially now before February at the earliest. That obviously doesnt preclude the odd day where westerly or southerly air enters the pattern - I mean more in terms of the bigger picture.

Is there anyone out there with more teleconnective and pattern knowledge than I (not difficult!) who believes that a change in this pattern is possible overall inside the next 5 - 6 weeks? I freely admit that I lack the ability at the moment to make an effective link between the patterns on the pacific side.

Edited December 6, 2012 by Catacol_Highlander

[johnholmes]

as promised No 5 of the weekly outlooks

5-Another look at 500mb charts and what type of upper air pattern they are predicting 6.pdf

[weather eater]

as promised No 5 of the weekly outlooks

5-Another look at 500mb charts and what type of upper air pattern they are predicting 6.pdf

Excellent John and I have to say far more informative than those attempting to put over much flesh on the bones of the synoptic guess work made by model projections post 120hrs. Whether mild and wet, cold and dry or cold and snowy the 18z will be out in three hours time it will show another evolution and another round hype vs despair bickering will ensue . I’ve found the trick is to skim read.

[phil nw.]

Thanks John.Keep up the good work.

These outputs are a very useful and far less volatile collection of medium range forecasting tools.

[If Wishes made Weather]

Perhaps this post belongs in this thread, more than in the model discussion where I think I might get a one line answer or snapped at. Perhaps one or other of the experts can assist on a coule of questions? -

Yesterday (12z) the ECM and I beleive the GFS showed a long draw easterly that circled roughly half the globe from Asia over Europe, the UK into the Atlantic and dissipating around Greenland. Today there is non of it. Not even in a watered down version. So my questions are:

a) how can the models, at what is now a semi-reliable time frame, be so very wrong? This isnt finer tweaking, or even more sort of broader tweaking (say just over the last 500 miles of Atlantic. Its a feature that has dissapeared from accross a vast part of the NH.

B) Seeing as the models apparently can no longer show - or at least in their operational version - this feature as 'most likely', can they, within 24 hrs suddenly re-find such a feature, or would it be the case, at least in such an easterly scenario, that it must be something that can only be built over time, large scale points such as broken PV etc taken as a given?

Many thanks

[johnholmes]

I really do find it utterly impossible to understand the hype that goes on in the model thread. Detail will always be hard to pin down at T+120 down but some of the comments are hard to believe.

Folk even worrying about the end of the cold spell!

In spite of the 12z Fax being quite different to what was shown at T+120, it happens at times and is simply a measure of what the latest output into UK Met shows the Fax charts are the most likely to be nearest the mark out to T+120 and always update each day so check the time of issue for the senior man's latest thoughts from T+84 down.

The cold is here to stay other than the odd day now and then, nothing in the upper air suggests anything else. Will it be a NW based cold or a NE based cold, no one if they are honest can say more than 96-144 hours ahead. The form horse for next week looks like the NE being the area the ridge will be. How much snow and how cold=watch the models at T+48 and below for a better idea. Compare the different models at the same time to see what variances if any are showing.

Edited December 6, 2012 by johnholmes

[Rocheydub]

There were even several people asking would it snow at +240 IMBY... Jesus H!!!

Anyway, just to add, love your 500mb charts John and the comparisons... Very easy to understand, even for a dummy like me. Please keep up the good work!

[johnholmes]

Model thread seems to have got even more unfriendly overnight, ya boo type comments and apparently UK Met forecast, whatever it says as not seen it, is incorrect for next week.

When I get time I will have a look and see if its possible to find out how far apart the 00z set of runs are out to T+120.

[Methuselah]

Cheers John...Common sense is always useful...

[johnholmes]

Left to my draconian attitude I would close the model tread, re open it and EVERY off topic post or moaning type, one liner etc I would simply bin after warning what was to happen.

Still like I say at times really I am too old for this place.

[NL]

Totally agree there, some folk should get some sleep instead of being first to post 'downgrade/upgrade'..!!! I'm really getting fed-up with the childish repertoire in there.

[Glacier Point]

Ensemble mean projections look reasonably in line with the overall trend in the 10 day timeframe.

The blocking centred north of the UK (not suprised that we see the main core of this centred around Iceland) forecast to remain until at least day 10. The shifting pv leaves enough residual energy to phase with a strong jet streak over the eastern US coast as the sub-tropical ridge strengthens over Bermuda. That brings us into slider territory and the potential for snow. Although note that the movement of the pv and how much residual energy is still yet to be resolved - which will have ramifications on how much energy is sent south-east, which will have an impact on the longevity of the deep cold, which will have established by this time.

The GEFS mean temperature anomalies depict nicely where I think we stand in the next 2 weeks, which maybe understand the persistence of surface cold:

Day 10 GEFS H5 anomaly also a good representation of where we stand at the edge of the mid range:

Where we go after that ? Some waning of the cold pattern is inevitable but note the position of the jet modelled in any format well into the future - well south of the UK and low heights associated in the Atlantic and over Europe. That still probably translates to below average temperature for the UK and much of Europe (continuation week 2 GEFS). Proibaly a 10 day peridiocity to the cold waxing and waning.

Longer term, the extended GFS continues to advertise a building stratospheric ridge into Alaska and Canada. That is the precursor to a major mid winter warming which still looks very much on for very late December.

So December already running around 2C below average no prospect of any milder weather and the likelihood of further dropping temperatures and some snow. Happy with that.

[Gibby]

Good morning. Here is the report from the 00zs from GFS, UKMO, GEM and ECM for today Friday December 7th 2012.

All models are clear cut on the weekend pattern but beyond that differences quickly emerge between the models. A cold Northerly flow over the UK today gives way to lighter winds tonight as a ridge of High pressure crosses the UK from the West. A slight frost will develop overnight tonight away from the coasts. Tomorrow will see a Westerly flow develop with cloud and rain and drizzle developing over Scotland through the day. The South holds on to drier and brighter conditions through the day. Sinday is a rather cloudy day for all with occasional light rain through Central Britain with drier and potentially brighter weather further South and North of this zone. There will be less frost and fog over the weekend than previously thought as winds remain rather stronger from the West and NW.

GFS then moves us into next week with a Low pressure near Denmark moving East and South into Germany with a chilly North wind over the UK giving way to light winds and calm conditions with frost and fog under High pressure midweek. Later in the week very cold air over Europe will seep West to the UK as a freshening SE flow develops with rain bearing fronts approaching Western Britain later. Into FI the South and West are at risk from rain and snow as fronts buffer up against the cold air while a SE flow over the North and East bring some wintry showers towards North Sea coasts. Through the FI period this morning the block to the NE holds firm and Low pressure becomes a cut off feature to the South while the High re-orientates its axis to favour a NE or East flow to develop over the South. The weather would be dry, cold and frosty for all with some freezing fog possible in the North.

The GFS Ensembles still show a cold spell to come although the longevity and severity of it seems to be tempered in more recent output. It also appears to become more unsettled after the coldest phase as rain and wind from the Atlantic breaks through the block by some members. there is huge scatter between the members though from the mid point of the run.

The Jet Stream shows the flow running SE or South over the UK over the coming days having ridge High up over the Atlantic before re-aligning to a point West to East well South of the UK later next week.

UKMO for midnight on Thursday shows Low pressure to the East and High pressure North of Scotland with an inverted ridge over the UK in cold air. The weather would be basically dry and bright with some wintry showers near the SE.

GEM shows a slack SW flow over the UK at the same time point, strengthening in the following days with cloud and rain preceded by snow sweeping the cold air away NE in the latter days of the run.

ECM shows a slack and increasingly cold airflow over the UK through the midweek days before an increasing SE flow develops ahead of Low pressure to the West brings a messy breakdown of snow followed by rain steadily across the UK late in its run.

In Summary this morning the cold weather is still on the way. However, it may not last long before it becomes under attack from an attack from Low pressure to the West. The spoiler Low which prevents the Easterly flow proper to reach our shores is also reponsible for allowing the Atlantic to get a foothold at least into the West of the UK later. Evenso, there is likely to be more twists and turns in this story over the coming days with cold weather never far away but conversely a period of deep cold and widespread long lasting snowfall looks somewhat less likely today.

[johnholmes]

I've posted this in the model thread but it will be lost very soon, partly so I can find it easily if I want to add other comments I will drop it in here.

hi

This is an attempt having struggled through the past 4-5 pages of unfair posts both to one another and for new folk trying to make head or tail of what the models show.

below is an attempt by me to be as objective as I can from T+24 out to T+120 using the 00z output from UK Met, ECMWF and GFS.

I hope it helps some of you.

T+24=all 3 have Iceland low same place and ridge sw of UK similar again

T+48=slight differences in position of the low, 60-90 miles perhaps

T+72=and all 3 have it within about 1 degree of each other, and each has a 1015mb isobar within 30 miles of each other across the east of the UK, identical direction

T+96=identical positions for the low and the developing high to the NW of the UK

T+120=UK Met has a more definite ridge than GFS giving a flow north of east with ECMWF tending to more like UK Met.

So the charts for 00z are about as identical as you could reasonably expect 3 different models to be.

The T+120 Met Fax produced last evening is, in my view, as close as anyone this far out is likely to be with the surface set up bearing in mind what the models all show at T+120 00z this morning.

So some of the posts, comments in the model thread really are not that good at giving overall guidance to new folk in my view.

Can I also add regarding some posts commenting on the input from Ian F. PLEASE read the actual post or the copy made of it by Lorenzo, read it carefully, don't skim and see what you want PLEASE?

Edited by johnholmes, 19 minutes ago.

[johnholmes]

adding to the above regarding the 500mb anomaly charts

They keep values above average from Greenland-Iceland to Scandinavia/Russia/northern Europe with lower than average values showing more in an east-west alignment than the WSW-ENE they have been shoing.

Whether this is a change that will occur or another hiccup is not yet clear. They may be showing the so called battleground set up. I'd prefer to see at least another day or 2 of outputs before I make any judgement.

What seems highly unlikely is that a mild Atlantic is being shown over the next 2 weeks. On top of that the 30mb temperature suggests further blocking by about the 3rd week onwards this month?