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In Depth Model Discussion, Analysis and Summaries


Paul

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

This is a pdf in which I try to answer the query raised by TEITS and to show how upper and surface patterns/features are inextricably linked. They cannot be separated and used one used without the other but it is the upper pattern which governs what the surface pattern does.

surface-upper air re 10 march on 4 march 13.pdf

Edited by johnholmes
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Posted
  • Location: Beccles, Suffolk.
  • Weather Preferences: Thunder, snow, heat, sunshine...
  • Location: Beccles, Suffolk.

Thanks for that, John. Informative and erudite, as always...

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Posted
  • Location: Peterborough N.Cambridgeshire
  • Location: Peterborough N.Cambridgeshire

You are perfectly entitled to that view Dave but your argument is flawed. By that I mean unless you understand how the upper air and surface features intereact then you will not truly understand why any model, such as the two you mention, arrive at the chart(s) you are discussing.

I am happy to set up a separate thread to try and explain this in more detail if you or any others wish?

If my argument is flawed then which option out of the two I mentioned do you think is more likely based on the charts you posted. Im perfectly aware of how the upper air and surface features interact. My point is you won't find the answer to which option is more likely on the charts you posted, which is all im saying.

Thanks for that, John. Informative and erudite, as always...

At the rate you're going you will start suffering from cherry blossom poisioning.laugh.png

Edited by THE EYE IN THE SKY
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Posted
  • Location: Peterborough N.Cambridgeshire
  • Location: Peterborough N.Cambridgeshire

If members want to know whether its going to become cold and wintry or cool instead then I would follow every operational run including the ensembles. Im saying this because at +144 we are seeing quiet a difference between the models.

12Z UKMO with its annoying SW near Iceland.

UW144-21.GIF?04-06

Far more promising GFS if you're after a cold, wintry spell.

http://www.wetterzentrale.de/pics/Rtavn1441.png

Now look at the excellent +168 GFS.

http://www.wetterzentrale.de/pics/Rtavn1681.png

Would the UKMO be similar at +168? Answer no chance because of that annoying SW near Iceland.

For the UK to see a cold, wintry spell ideally we want the GFS to be right because of the quick, smooth transition of the LP going under the block to our S. This then allows the block to our N to push further S introducing the much colder air. This is unlikely to occur with the UKMO. If a SW did develop near Iceland then ideally we would need to see this become detached and back W.

GEFS ensembles are very keen on a very cold outlook!

http://modeles.meteociel.fr/modeles/gens/graphe_ens3.php?x=314&ext=1&y=88&run=12&runpara=0

Now we anxiously await the ECM.

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Posted
  • Location: Kilmersdon Radstock Somerset
  • Weather Preferences: None Really but a snow lover deep down
  • Location: Kilmersdon Radstock Somerset

Good morning. Here is todays look at the 00z outputs from GFS, UKMO, GEM and ECM for today Tuesday March 5th 2013.

All models show Low pressure gathering control down to the SW of Britain as it edges NE towards SW England pushing trough slowly North and East across the UK from tomorrow. Winds will be from a relatively mild Southerly or South-easterly source in the South for much of the next 4-5 days while further North Easterly winds will develop and strengthen pulling much colder air across from Scandinavia with time with snow developing over the hills in a relatively dull, wet and cold regime.

GFS then shows cold NE then lighter Northerly ones as we move through the first half of next week with things becoming very chilly though drier everywhere with scattered wintry showers in the East especially. High pressure then builds SE across the UK with sunny spells and frosts at night before milder SW winds quickly spread wind and rain across the UK from the Atlantic in what becomes a more mobile and unsettled Westerly winds when things may become quite mild in the South and East for a time.

The GFS Ensembles show a much colder plunge as we move into next week with rain at times turning to snow showers for a time with frost returning at night. The operational was a much milder option and more progressive in its return to milder conditions which occurs much more steadily from most members.

The Jet Stream shows the flow continuing on a more Southerly course than average before ridging slowly North over the Eastern Atlantic later next week.

UKMO for early next week shows Low pressure out in the Atlantic and another filling centre over Southern Britain. Colder ESE then East winds are shown developing over the North. Rain at times would occur for all areas changing to sleet or snow over the hills of the North later.

GEM shows a similar path to GFS in bringing cold air South over Britain next week with sleet and snow showers developing in the East for a time following the rain clearance from the South. Unsettled conditions from the West are returning off the Atlantic at the end of its run with a South wind and cold rain to end the run.

ECM shows a full blooded return to cold next week with NE then Northerly winds quickly becoming established with snow showers flooding down in the Northerly flow with frost at night but some sunny spells between the showers. Milder air does look like it could start to encroach from the SW very late in the run.

In Summary the milder interlude developing currently looks like being a short-lived one as colder weather returns from the North later in the weekend and into next week. Frosts look like returning widely at night with a heady mix of sunshine and wintry showers likely for many areas next week before a hint of a return to something slightly milder begins to appear towards the end of the outputs as the Jet Stream drifts slowly North at last.

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

These are my ideas this morning using the 500mb anomaly charts as a guide to the type of weather pattern after the shortish milder spell .

And no I give no detail for the surface as that is not what they are for; they do give a good idea of the weather type though, cold not mild with the flow from the north not the south. The proximity of the upper trough will govern the degree of dryness or not. The height of the 500mb contour will give a guide to both the surface temperature and what falls from the sky.

Cold compared to the mid March average with precipitation likely to be wintry at low level and snow with heights of very modest level and quite possibly at very low level at times. The synoptic charts, when they start to converge on detail accuracy will give the fine detail on both temperature and rain/snow. Think in terms of T+96 as the outer marker.

Tue 5 march

Ec-gfs

Both show a block with trough to east of it, gfs mostly with ec having block w/nw of Iceland whilst gfs shows it from e atlantic north into Iceland and main centre about Greenland

Both show marked trough to east, ec is closer to uk

Ec is a colder chart than the one it showed yesterday

Over the last 3 days the gfs charts are more consistent than the ec version, its often the other way round

Noaa 6-10 and 8-14 have both been quite consistent and have slowly gone to a more n of west flow, not that much similar in positioning of the main +ve area nor to a degree the suggestion of where any upper ridge will be.

Overall this morning I would suggest that some kind of block or at least a 500mb flow from north of west looks the most likely in the period 10 about 18 March but there must be some slight reservations about just what surface pattern will turn up under this. It does seem very unlikely that we have either a mobile atlantic north of 50 north or a mild flow from the south west in that period at 500mb.

The links to NOAA and ECMWF-GFS charts are below

http://www.cpc.ncep....14day/500mb.php

http://www.meteo.psu...0z/hgtcomp.html

Edited by johnholmes
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Posted
  • Location: Lincoln, Lincolnshire
  • Weather Preferences: Sunshine, convective precipitation, snow, thunderstorms, "episodic" months.
  • Location: Lincoln, Lincolnshire

We are in for a spell of cloudy, damp and increasingly cold weather over the next few days, with an east to south-easterly flow bringing moderately cold air in off the continent, but nothing major.

The main divergence point comes at T+96, for we have the GFS showing extensive high pressure to the north, the ECMWF is quite similar to the GFS while the UKMO has a stronger low pressure area to the W and SW:

http://www.wetterzen...cs/Rtavn961.png

http://www.wetterzen...ics/Recm961.gif

http://www.wetterzen...ics/Rukm961.gif

The GFS is proving remarkably consistent with its potent but short-lived north-easterly, which would bring notably low temperatures but, due to the proximity of high pressure, just a scattering of snow showers for eastern areas. The ECMWF has moved a bit in the direction of GFS this evening IMHO, bringing in the cold blast next Monday, but it then keeps a cold north to north-easterly regime going through to T+240 which would most likely mean sunshine and snow showers, and the relatively low heights that develop around the British Isles would probably help re. the relatively strong March sun generating some limited convection inland as well as the usual snow showers over the North Sea. Having said that, I imagine that if those charts were to verify, many western areas would be mostly sunny and dry.

I've seen these north-easterly types showing on the ECMWF's extended timeframe a fair number of times during the 2012/13 season and they have never come off so while I think the evolution to the north-easterly is plausible, I doubt that the wintry weather will end up anything like as prolonged as the ECMWF is showing.

There isn't much support for the UKMO evolution at the moment, but I'm reluctant to "bin" the UKMO raw output as it does have quite a good track record these days. Given that the jet stays to the south at T+120-144, I feel that the UKMO evolution would give us an extended spell of grey, fairly cold and damp weather with slow-moving frontal systems, rather than a push of warmth from the south, and of course it would throw a lot more hurdles in the direction of anything snowy.

Edited by Thundery wintry showers
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Posted
  • Location: Kilmersdon Radstock Somerset
  • Weather Preferences: None Really but a snow lover deep down
  • Location: Kilmersdon Radstock Somerset

Good morning. Here is the report of the 00z output from GFS, UKMO, GEM and ECM for today Wednesday March 6th 2013.

All models show Low pressure down to the SW of the UK with a slack SSE flow over the UK with occasional rain and cloudy conditions extending North and East to all areas. Temperatures will stay close to average over the coming days. Over the weekend as Low pressure generally inches in close to Southern Britain cold Easterly winds develop over the North and begin to extend South to other areas by the start of next week with rain turning to snow in the North.

GFS then shows a strong and cold NE flow over the South on Monday with rain turning to snow here too while drier conditions reach the North. These drier conditions extend South to other areas next week in association with High pressure slipping South just to the West of the UK through the week with frost developing again by night. Late in the week new Low pressure moving South to the North of the UK brings rain and sleet down into Northern Britain which through FI sweeps South and renews the surge of cold air from the North with spells of rain, sleet and snow over all areas to end the run in temperatures well below average.

The GFS Ensembles indicate the operational as a slightly colder option of the pack through the second half of the run. However, there is universal support for temperatures to fall off a cliff through the 10th as the cold Arctic air sweeps South to all of the UK. The general trend is for uppers to gradually recover to closer the seasonal average though there is plenty of spread between milder and colder options late in the run under unsettled conditions.

The Jet Stream shows the flow continuing to blow across Southern Europe well South of it's average. The flow does weaken in a weeks time and ridges North over the Atlantic just to the West of the UK.

UKMO early next week shows Low pressure moving slowly East along the English Channel with colder Easterly winds propagating slowly South from Scotland through the period. Largely cloudy skies will predominate with rain, especially in the South potentially turning to snow before drier air filters South from Scotland later.

GEM has Low pressure a little further South over france early next week moving away East. A cold NE flow with rain or sleet clears away as High pressure moves down from the NW later in the week. A few snow or sleet showers near Northern and Eastern coasts would be the exception to cold and bright conditions in light winds and sharp overnight frosts.

ECM shows cold and unsettled conditions next week with High pressure over Greenland and with deep cold air over Scandinavia Northerly or Northeasterly winds will pull this down over the UK with sleet and snow showers developing widely through the week with the chance of more persistent rain or snow later as Low pressure tracks East close to Southern Britain. Widespread unwelcome sharp night time frosts would occur again next week under these synoptics.

In Summary the weather will take a sharp turn colder early next week as High pressure over Greenland pulls very cold Arctic winds South over the UK. With Low pressure close by to the UK there looks to be plentiful opportunities for snowfall, more especially but not exclusively to Northern and Eastern Britain but maybe in the South and SW too should Low pressure close to the SW push troughs up into the cold air from the South. Frosts will be widespread and sharp so Gardeners beware the last few days of mild Spring weather was a false dawn and we will have to wait quite a while for anything remotely Springlike temperature wise looking at this morning's output and Jet Stream profile.

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Posted
  • Location: Kilmersdon Radstock Somerset
  • Weather Preferences: None Really but a snow lover deep down
  • Location: Kilmersdon Radstock Somerset

Good morning. Here is the report of the 00z output from GFS, UKMO, GEM and ECM for this morning Thursday march 7th 2013.

All models show a change to colder conditions next week. Currently a SE flow blows across the UK in association with Low pressure down to the SW of the British Isles. Over the coming days this moves slowly East continuing to push troughs of Low pressure slowly North over the UK at the same time as backing winds off towards the East over the weekend and NE by Monday with cold air near Scandinavia flooding SW across all of the UK at this time.

GFS shows the flow backing slowly towards the North through the working days of next week as High pressure slips slowly South to the west of the UK. The bitter winds of Monday will decrease with the cold moderating somewhat from then on. Nevertheless, in the Northerly flow there will be bright spells and showers or hail, sleet and snow, especially near North and East Coasts but inland elsewhere through the afternoons. Frosts will be widespread and sharp at night. Through next weekend and onward the flow backs more Westerly bringing milder winds in from the Atlantic with any showers, chiefly in the North only at this stage turning back to rain. Later in the run the weather becomes more akin to where we should be at this time of year with High pressure to the SE and mild SW winds wafting across the UK with some rain, chiefly in the NW.

The GFS Ensembles show a four or five day cold spell starting from Sunday and lasting through the working week before most members bring rather less cold weather across the UK from the West accompanied by rain at times as High pressure to the NW collapses and allows the Jet to move North.

The Jet Stream forecast itself continues it to blow West to East well South of it's regular March position before a portion of it ridges North into the UK later next week flowing NW to SE over the UK then. The main punch of it though remains well South.running East across Northern Africa.

UKMO shows Low pressure over Europe and a direct Northerly feed over the UK with an inverted ridge of High pressure to the West of the UK from High pressure centred to the NW. A typical Spring mix of sunshine and scattered but locally heavy snow showers would occur with widespread and sharp overnight frosts with some accumulating snow in places over the hills and temporarily overnight in other areas too.

GEM shows a complex and slack cold Northerly flow over the UK later next week before winds fall light and back West with low pressure to the West bringing milder air across the UK later with rain preceded by snow in places.

ECM has watered down the cold this morning with it too showing just a slack Northerly flow next week with snow showers here and there before high pressure kills these off and eventually brings in rather milder air courtesy of Low pressure moving in at more Northern latiudes. feeding in milder and rainier SW winds across Southern areas at least towards the end of the run.

In Summary a cold spell is on the way. On comparison with previous output the cold is quickly modified as we go through next week and it may well be that Monday is the coldest day in the strong NE flow following the exit of the depression from the South. Through the week daytime's may not feel too bad in the South though bright and sunny intervals could be punctuated by some scattered but potentially heavy snow showers especially towards the middle of the week. Longer term it does now look that milder air makes inroads back into the UK from the West next weekend with a return to more average conditions again later in the period.

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

Looking at the last two outputs from NOAA and ECMWF-GFS and comparing to the outputs over the previous 4-5 days and it is hard to see any marked change in upper air pattern.

All 3, to some degree, have kept, as they show below, the coldish north of west flow into the UK. ECMWF-GFS are colder at 500mb over/close by the UK than NOAA is. They suggest sub 540DM and have shown heights closer to 528DM earlier this week. NOAA has kept around 546DM or just below. For surface temperatures to get above normal for March requires values closer to 552DM. All 3 versions keep an upper trough east of the UK which MIGHT indicate unsettled rather than settled. The general patterns suggest the surface high pressure is never going to be all that far from western areas, its exact location will not be fixed as it moves around from NW to about WSW at times of the UK. So I cannot see a mild weather pattern in the next 2 weeks developing. A milder day or so but overall a below normal temperature pattern tending more towards colder than milder.

See links below

noaa

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

ecmwf-gfs

http://www.meteo.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

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Posted
  • Location: Lincoln, Lincolnshire
  • Weather Preferences: Sunshine, convective precipitation, snow, thunderstorms, "episodic" months.
  • Location: Lincoln, Lincolnshire

Looking over the potential for snowfall this weekend, it looks like the main frontal system moving southwards on late Saturday and into Sunday will produce mostly rain and sleet at low levels, with snow on high ground. Into Sunday, the easterly flow to the north of it will be associated with a dry stable layer starting at around the 750-800hPa level but vigorous convection below it, so we can expect fairly shallow convection and a fair amount of cloud, with a mix of scattered snow showers and some sunny intervals. Most of the showers are likely to be concentrated near North Sea coasts but a few well-scattered showers may also break out inland on Sunday afternoon thanks to solar heating.

As we head into Monday, a low pressure system to the south of the English Channel may throw up another frontal zone and this may well produce significant snowfalls on its northern flank as it engages the cold air, but at the moment its positioning is still prone to revision. Further north, the dry stable layer associated with the easterly is forecast to strengthen and penetrate to lower altitudes and thus the weather is likely to turn increasingly dry and cloudy. I think many places to the east of high ground will have up to a few centimetres of snow on Monday morning, but larger 5-10cm falls will only be localised.

The skew-t forecasts for Hull show this up quite well, with a dry stable sector above the 750hPa level at 2100 on Sunday, but by Monday night it extends below the 850hPa level and the implication is dry cloudy conditions:

http://nwstatic.co.uk/gfsimages/tempskew/skew0.762959337866963.png

http://nwstatic.co.uk/gfsimages/tempskew/skew0.0596456528446687.png

On Tuesday and Wednesday as the winds swing around to the north the weather is set to turn somewhat brighter with a scattering of wintry showers and temperatures of 5-8C by day, before it turns colder and more unsettled again at the end of the week.

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Posted
  • Location: Kilmersdon Radstock Somerset
  • Weather Preferences: None Really but a snow lover deep down
  • Location: Kilmersdon Radstock Somerset

Good morning. Here is the latest report of the 00z output from GFS, UKMO and ECM for today Sunday March 10th 2013.

All models show the cold spell having reached all but the far SW of England this morning with cloudy skies and still some snow over parts of East Anglia and the Midlands slipping South and dying out. Further rain from a Low pressure area down to the SW moves East over Southern Britain later today and tonight giving snow in the extreme South while all other areas see an increase to near gale NE winds, penetrating cold conditions and snow showers towards Eastern areas pushing further west at times. This setup lasts through tomorrow too with slight accumulations of snow in places in the extreme South and over Eastern areas. By midweek winds are shown to back Northerly and decrease with brighter skies and more scattered snow showers but sharp frosts at nights. All models also agree on a milder spell of weather developing later in the week as Low pressure to the NW deepens and sends cloud, rain and hill snow slowly East across the UK late in the week.

GFS then shows a wet and unsettled interlude with rain and strong winds giving way to colder winds again from the NW with wintry showers for a time. Through FI today a more conventional SW flow steadily develops with milder air with rain at times, the heaviest of which will be in the NW of the UK.

The GFS Ensembles show good support for the milder solution later in the week but are less supportive of the much milder winds that the operational shows for the South in Week 2 preferring to keep rather chilly and unsettled conditions going.

The Jet Stream continues the Southern latitude theme of late though a new arm does develop over the North Atlantic and over the UK late next week.

UKMO for the end of the week shows Low pressure sinking slowly South towards the Hebrides with SW winds over the UK bringing less cold conditions with rain and showers as we move into next weekend.

GEM shows a vigorous SSW flow by the weekend with wet and windy weather spreading to all areas in near average temperatures by then. Later in the weekend and start of the new week the weather stays very unsettled with a complex and deep structure of Low pressure near or over the UK delivering spells of heavy rain and showers at times in near to average temperatures.

ECM shows deep Low pressure governing the UK's weather throughout the latter stages of it's run as it revolves around our island giving very unsettled and rather cold weather with rain or sleet and heavy wintry showers all in the mix as we move through the weekend and start of next week.

In Summary the cold spell will weaken later in the week as the developing Low pressure close to the NW later this week deepens and extends it's influence over all areas. Rain or shower are likely for all with temperatures becoming dependent on the position of the Low complex. Whatever happens it still looks as those looking for sustained dry, milder and settled weather will be waiting some while yet from this morning's output.

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Posted
  • Location: Llanwnnen, Lampeter, Ceredigion, 126m asl (exotic holidays in Rugby/ Coventry)
  • Location: Llanwnnen, Lampeter, Ceredigion, 126m asl (exotic holidays in Rugby/ Coventry)
Posted
  • Location: Kilmersdon Radstock Somerset
  • Weather Preferences: None Really but a snow lover deep down
  • Location: Kilmersdon Radstock Somerset

Good morning folks. Here is this mornings report on the 00zs from GFS, UKMO, GEM and ECM for today Monday March 11th 2013.

All models show Low pressure over Northern France with a biting and bitterly cold NE flow over the whole of the UK. Through the coming days the Low to the South is shown to move away East as High pressure slips South to the West of the UK. Winds back through North towards the West by the middle of the week as well as decrease considerably. Snow showers will plague Eastern areas throughout this spell with some more prolonged snowfall possible in the SE today. Through the middle of the week showers will turn from snow more to sleet and rain in Southern and Western areas from Wednesday before Low pressure develops to the NW at the end of the week brings more general rainfall and less cold conditions at least to the South and West but still the risk of further snowfall over some Northern and Eastern areas, especially over the hills.

GFS then shows a complex Low structure over the UK next weekend with rain at times and showers at others, sometimes heavy, with hail, thunder, sleet and snow all possible in temperatures still below average though less cold than at present. Longer term pressure remains locked into Low pressure mode over and around the UK with further heavy rain and showers with sleet and snow at times in the North and East, especially but not exclusively over the hills.

The GFS Ensembles show the cold weather of the first three or four days of this week giving way to somewhat less cold but unsettled conditions which last then throughout the rest of the run. With uppers still on the cold side of average for most areas some wintry precipitation mixed in with the rainier spells are likely at times.

The Jet Stream shows an unabated flow across Southern latitudes still before a new wing sets up further North moving SE over the British Isles.

UKMO shows Low pressure over Ireland at the weekend with cyclonic winds over the UK with spells of rain and showers for all, heavy at times and falling as now on Northern hills.

GEM shows spiralling Low pressure over and around the UK next weekend and beyond with frequent heavy showers and longer spells of rain with hail and thunder possible as well as sleet and snow over the hills in rather cold and windy conditions.

ECM too shows a similar pattern over the weekend as the others before contracting Low pressure out into the Atlantic at the end of the run bringing less cold air into Southern and Western areas with troughs delivering rain at times here. In the North and East rather colder conditions continue with rain too but also the risk of snow at times, especially over higher elevations. It will be windy at times nationwide.

In Summary Spring remains on hold with the current very cold conditions moderating to something more tolerable but still rather cold by the end of the week. Snow and sleet showers will continue through the week gradually turning more to rain late in the week with a very unsettled spell to come next weekend with a lot of rain for some and still some snow in the North and East at times, especially but not exclusively over the hills. Thereafter, Northern blocking remains dominant keeping the UK in the breeding ground for further deep Low pressure and further rainfall in temperatures somewhat on the cold side of normal, especially towards the North and East where the risk of snowfall at times remains.

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Posted
  • Location: Lincoln, Lincolnshire
  • Weather Preferences: Sunshine, convective precipitation, snow, thunderstorms, "episodic" months.
  • Location: Lincoln, Lincolnshire

It still looks the same to me as yesterday, though perhaps not as intensely cold from the ECMWF.

GFS is going for a slow-moving trough with some slow-moving fronts around on Friday/Saturday but then three days of sunny intervals and scattered wintry showers follow on Sunday/Monday/Tuesday, with thunder possible locally in the south. Then we get a transition to warm southerlies. UKMO/ECMWF give more chance of snow with a front probably moving south on Sunday/Monday followed by brighter conditions for the north with snow showers, before low pressure attacks from the SW with potential frontal snow and a potential change to milder conditions thereafter.

The difference between GFS and UKMO/ECMWF is clear to see at 144 hours away:

http://www.wetterzentrale.de/pics/Recm1441.gif

http://www.wetterzentrale.de/pics/Rukm1441.gif

http://www.wetterzentrale.de/pics/Rtavn1441.png

I think we are likely to get a warmer last week of March with the main trough setting up to the west of the British Isles, even if UKMO/ECMWF verify, while the GFS is probably being too progressive in bringing in a warmer regime. We could potentially end up with an overcast and wet south-easterly with fairly cool days and high night-time minima, of the type that we had prior to the current cold spell. If the trough sets up far enough to the north/west then high daytime temperatures and bright sunshine are certainly possible though.

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Posted
  • Location: Lincoln, Lincolnshire
  • Weather Preferences: Sunshine, convective precipitation, snow, thunderstorms, "episodic" months.
  • Location: Lincoln, Lincolnshire

Looking at the nearer-term, slow-moving fronts are likely to be an issue for the next couple of days, with one over SE England and one over northern Scotland tomorrow, bringing cool cloudy wet weather, and a mix of sunshine and showers over northern and western England and much of Wales, and some of the heavier showers may be wintry. These zones of weather are well picked out by the fronts on the latest FAX chart:

http://www.wetterzentrale.de/pics/brack0.gif

Sunday looks like being a day of sunshine and sharp, locally thundery, showers (again the heavier showers may be wintry) except in the northern half of Scotland where a front will make it dull and wet for most, with some snow over high ground.

The GFS appears to have fallen into line with UKMO/ECMWF in sending that weakening front over northern Scotland southwards during Monday and Tuesday, and the front is likely to feature mostly rain and sleet but with some northern-flank snow possible. This will introduce a colder east to north-easterly flow with a mix of sunshine and snow showers for eastern Scotland and possibly north-east England. It won't be as potent as the cold blast on Monday earlier this week, but maxima of 2-4C are suggested quite widely. There is still some uncertainty about how far south the front will get, and anywhere underneath the front is likely to be grey and cold with bits of rain and sleet. UKMO/ECMWF still appear to have the cold air getting further south than GFS which could push the sunshine-and-snow-showers regime down into Lincolnshire and East Anglia.

There are indeed hints that it is going to warm up into the last third of March, but I'm seeing a recurring theme of persistent low pressure to the SW and pressure remaining quite high to the north and north-east. This would most likely translate to cloudy, breezy and wet weather with slow-moving frontal systems and an emphasis on high night-time minima, rather like during the few days prior to the current cold spell. If the Atlantic trough shifts north of about 55N then we could be in with a shot at some brighter, showery returning polar maritime type weather, which can often feel warm in the sunshine in between the showers, but there is instead a consistent theme of the trough being stuck at around 50N so cloudy and wet looks the most likely outcome to me.

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Posted
  • Location: Llanwnnen, Lampeter, Ceredigion, 126m asl (exotic holidays in Rugby/ Coventry)
  • Location: Llanwnnen, Lampeter, Ceredigion, 126m asl (exotic holidays in Rugby/ Coventry)

Weather guide for West Wales and the Midlands.

Headline: Cold/ cool: Showers or longer spells of rain, sleet or snow; night frost and some fog

http://forum.netweather.tv/blog/309/entry-4582-weather-guide-monday-18th-to-sunday-24th-march-2013-midlands-west-wales/

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Posted
  • Location: Lincoln, Lincolnshire
  • Weather Preferences: Sunshine, convective precipitation, snow, thunderstorms, "episodic" months.
  • Location: Lincoln, Lincolnshire

A rather complex synoptic situation at the moment with various fronts circulating around the low pressure. Into tomorrow and Tuesday the synoptic picture looks like simplifying with a frontal system stuck over northern England, which looks set to give a wintry mix of precipitation at low levels and snow on high ground. Into Tuesday as colder air pushes down from the north-east the precipitation is likely to turn increasingly to snow for all.

http://www.wetterzentrale.de/pics/brack0a.gif

This is the FAX chart for 00Z Tuesday showing that persistent frontal system.

Sunshine and showers can be expected both to the north and south of the frontal system. To the south the showers will mostly fall as rain, hail and sleet, while to the north it will be a case of snow and graupel showers firing in off the North Sea.

There is strong cross-model agreement that into Wednesday we will get sunshine and snow showers over eastern Scotland and north-east England, with a few well-scattered flurries perhaps over Lincolnshire and East Anglia, with cloudy weather and some light sleet or snow for the south of England, and dry sunny weather elsewhere. Again I think the FAX chart is probably the best illustration:

http://www.wetterzentrale.de/pics/brack2.gif

After that, the setup continues to look reminiscent of the 21st March 2001 and there are serious question marks over how long the cold air will hang on for.

The GFS, although it brings milder air quickly into the southern half of England, looks quite a snowy run for southern Scotland and northern England as the fronts are projected to become slow-moving on Friday/Saturday with temperatures close to freezing over those areas. During next Sunday and Monday (a long way off of course!) the GFS shows the fronts buckling back southwards again with brighter weather and snow showers following into the northern half of Britain with maxima close to freezing.

The GFS is essentially the halfway house solution tonight because the ECMWF run would push the milder air up as far as northern Scotland by Saturday whereas the UKMO, with its "slider" to the south, would most likely see the frontal boundary kept further south, therefore with increased chance of snowfalls in the southern half of Britain with brighter conditions further north and snow showers for the north-east.

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

In the difficult pattern for the models to try and give detail I believe most of you will benefit from not trying to put ANY detail on any run at anything beyond about T+48-72 at the moment. For this time in March it is a fairly rare looking set up so little wonder the models are struggling going from a cold option to a mild one or vice verca.

Even the anomaly charts are not at all straight forward. A fairly westerly flow over the past couple of days (I've been away for the previous 5 days so not seen anything in that period) and the 00z output from ECMWF-GFS was still not out prior to leaving this morning.

It looks a pattern of fairly cold unsettled westerlies at 500mb with the possibility of both northward extension of milder Atlantic air and colder air from somewhere north of 55N to the west of the UK.

Certainly not much sign away from the far SW of any real mild air and about a 60% risk of a fairly notable snowfall from about the Peak north to the Southern Uplands before this weekend, with a smaller risk for hills south of this. Just how far north this band gets is for the models at probably T+24 to give better guidance. How low the snow gets is another largely unknown factor.

Good model watching and however much some castigate UK Met I suspect watching their changing Fax charts will be as good a guide as any along with their text forecasts on the web. Some will disagree I know but I would suggest to new folk this may well be the best guide (as it of course should be) to this very interesting complex and difficult forecast spell this week, let alone further ahead?

just to add this to the above looking at the NOAA charts over the last 3 days

Noaa 8-14

And pretty similar to last issues but contour height s uk is now down to 540dm

So its predicted over the last 3 days to fall from 552dm to 540dm, quite a significant drop with little change in pattern, height anomalies in the same period.

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

Edited by johnholmes
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Posted
  • Location: Lincoln, Lincolnshire
  • Weather Preferences: Sunshine, convective precipitation, snow, thunderstorms, "episodic" months.
  • Location: Lincoln, Lincolnshire

Just thought I would post this in here, from the main model output thread:

A slow-moving front is currently keeping things pretty grey over parts of southern Scotland and northern England, with snow on the northern flank of the system and with brighter showery weather for the north and south of the country. Into tomorrow the front will still be there but it is set to weaken, so the brighter showery weather should establish more widely:

http://www.wetterzen...ics/brack0a.gif

The GFS is going for a mix of sunny intervals and scattered wintry showers away from that frontal system, though cloud may well remain quite stubborn along the frontal belt.

I think Thursday/Friday may well be an all rain event in parts of southern and south-western Britain, and the heavy rainfall may lead to renewed flooding problems:

http://cdn.nwstatic..../60/h500slp.png

http://cdn.nwstatic....0/ukmaxtemp.png

but once the belt gets to the Midlands it is likely to start turning to snow at low levels. There is currently fairly strong agreement on a significant frontal snow event over northern England, perhaps into southern Scotland, on Friday/Saturday before the front gradually fizzles out.

http://cdn.nwstatic..../84/h500slp.png

http://cdn.nwstatic....4/ukmaxtemp.png

UKMO, ECMWF and GFS are now all agreed on the return of a cold easterly flow after Saturday. Despite the cold 850hPa temperatures I have a feeling that if this verifies it will be a mainly dry, cloudy and cold type of easterly- the GFS precipitation outputs aren't suggesting much showery activity over the North Sea except in eastern Scotland, and with a straight airflow off the continent there is a high probability of a dry stable capping layer developing at around 700-850hPa. An east to north-easterly regime may be more likely to bring snow showers to eastern areas but it currently isn't what the models are showing.

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

Staying away from the hugely interesting discussion about where the snow will fall and lie over the next 72 hours and looking further ahead.

Say 10 days and more.

Up to the last 2-3 days the 500mb anomaly charts have, from some time before the onset of the current cold spell, been showing the blocked pattern. There have been brief hiccups but overall their performance to me has been very good. Over the last 2-3 days there have been some slight changes which suggested a possible change in upper air pattern from the current mostly blocked type. This seems to be showing more and more although I still have not got the 3 days of consistency I prefer before hanging my hat on their output. Nevertheless all 3 by this morning have got a similar pattern showing.

The NOAA chart from last evening is below

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

As you can see most of the +ve areas, still showing on the 6-10 day outlook have gone and the –ve area and flow into the UK from south of west are much more in evidence. Also the heights suggested for the Channel area are now tending up rather than down as they had previously been showing.

This morning and the output from ECMWF-GFS also has little sign of any +ve heights although both show a suggestion of a slight ridging in the UK area. The major idea is the –ve area in the Atlantic and the flow at 500mb from south of west into the country-see below

http://www.meteo.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

Like I said it is early days but I do believe that a major pattern change is about 70% on the cards around or by the end of the month with a milder south of west upper flow taking over for the UK. Detail on actual timing, and the extent of any warming up is not possible but an idea of an overall warming up from the current fairly unusual length of cold spell at the moment looks odds on.

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Posted
  • Location: hertfordshire
  • Location: hertfordshire

I also posted this in the model thread but I was wondering if John H. of Ian F. could answer

my query.

Since 6am this morning the 24th the 2m temperature has slowly dropped across the s/e to around

-1c at midday here in herts( truely amazing) from around -0.5c. Now I know colder uppers are working

there way down from the north but at midday upper 850 temps in Herts are only around -6c

and without any heavy snow falling (only light and intermittent grains) surely these uppers

on their own are not enough to support such low 2m temps.

We have cloud cover and around 3 inches of laying snow which helps and of course low

dew points off the continent but I am still amazed at just how cold it is.

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

sorry CC been away since Friday so not really clued up on the surface or lower atmosphere wind profiles.

The cold pool of air over/around the UK will be the cause in spite of the strong at times gale force surface flow-sorry not able to help more.

Looking further ahead with my trusty 500mb charts, not time to show tonight, but they are not markedly different from what showed last Thursday evening and Friday morning.

What does this mean?

Well in short for those looking for spring warmth, not a lot it would seem.

I'll do a fuller update tomorrow.

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Posted
  • Location: hertfordshire
  • Location: hertfordshire

sorry CC been away since Friday so not really clued up on the surface or lower atmosphere wind profiles.

The cold pool of air over/around the UK will be the cause in spite of the strong at times gale force surface flow-sorry not able to help more.

Looking further ahead with my trusty 500mb charts, not time to show tonight, but they are not markedly different from what showed last Thursday evening and Friday morning.

What does this mean?

Well in short for those looking for spring warmth, not a lot it would seem.

I'll do a fuller update tomorrow.

Thanks for the reply. Can you tell me where you can get access to skew-t diagrams and would

there be access to previous days. Chionomaniac proposed that a very cold surface layer may

have moved across from the continent which could be a good call I think.

The temps yesterday started to rise from about 3pm and maxed out around midnightish before

dropping again.

Funnily enough this evening was again warmer than during the afternoon, Weird or what.

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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.

Thanks for the reply. Can you tell me where you can get access to skew-t diagrams and would

there be access to previous days. Chionomaniac proposed that a very cold surface layer may

have moved across from the continent which could be a good call I think.

The temps yesterday started to rise from about 3pm and maxed out around midnightish before

dropping again.

Funnily enough this evening was again warmer than during the afternoon, Weird or what.

We may see intense continental nightime cooling of surface air that is displaced by the strong east flow and arrives during our day time - thus cooling during the day here without sunshine to moderate. Certainly for yesterday the surface continental temperatures for the preceding 24 hours ( especially at night) were exceptionally low.

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