In Depth Model Discussion, Analysis and Summaries

[BLAST FROM THE PAST]

From having watched GP's winter forecast, I cannot recall one instance of when any cold spell was either 'nailed-on' or, even, assigned some daft %age probability...IMO, most, if not all, such prognostications have been made in the MOD thread by NW's 'panel of experts'...

But then I guess it's always easier to say GP's wrong (after a mere 13 days!) than to say: sorry peeps, I completely misread the signals, and chose instead to treat the model-runs as Gospel?

I got it wrong!

In bold indeed....way too early to write anything off, Ok it looks like its heading the wrong way for now but as I alluded in a post elsewhere, if the models changed so quickly from a stormer of an outlook last week, could they at some stage spring another surprise down the line? I wouldn't be surprised if they they did or went even more zonal as I have to say the models have bemused me a bit recently, well not hard I suppose as they even hade the Met boys in Exeter scratching their heads.

BFTP

[SMU]

http://forum.netweather.tv/topic/75272-winter-model-discussion-the-hunt-for-cold-12th-dec/page__st__220#entry2445674

Post 229 by CC sums my post up with images-

S

[TEITS]

the weather has proved time over that you cannot forecast ANY surface conditions for the UK for more than a week ahead-

S

I do have to agree with the above. Despite all the advances in computing power and forecasting techniques I haven't really seen an improvement in forecasting when it comes to the detailed surface conditions for the UK. When I think back to watching those weekly forecasts on a Sunday lunchtime in the 1980s then I don't feel as though we have advanced.

The improvement since the 1980s is with regards to the general weather patterns over a longer time period but as we have seen this doesn't always improve the accuracy of the forecasts on the actual surface for the UK.

I would actually go as far to say that in some respects our forecasts have taken a backwards step especially the BBC forecasts. I find the nowcasting by the Met O/BBC has been dreadful at times during recent winters. Far too much reliance on computer models instead of using the obvious sat/radar.

[SMU]

I bet Auntie beeb has a lot to do with that with timeslots....^^

S

[chionomaniac]

Frustrating times, The clock is ticking for December- Is GP's early forecacst a bust- well does it matter?- not really - the weather has proved time over that you cannot forecast ANY surface conditions for the UK for more than a week ahead-

We could all celebrate getting the H5 pattern right ( if that was the case) however if the actual surface conditions are at the opposite end of the scale- what are we actually celebrating?

S

I agree to certain extent Steve.

However, to say that there is no point working so hard to predict the upper air pressure anomalies because they have no correlation to the lower weather received is misleading and a little short sighted. We may have missed out this week - but in the grand scale of things it was a near miss. To use one near miss to base the whole concept of using upper air anomalies is complete nonsense. Blocking pattern H5 anomalies are always going to be more unpredictable to be able to nail down surface details than say a zonal pattern because of their very nature and yes slight weaknesses in these patterns can lead to shortwaves developing. If GP had predicted a H5 anomaly zonal pattern that would have had far more success at the surface because the pattern would have been far more predictable if it were correct.

To suggest that it is waste of time trying to predict these H5 anomalies is very disappointing from you. I think that surface temperature anomalies correlate pretty well to the H5 blocking patterns (as has this one) and I am sure that had the recent temperature anomaly been accompanied by some snow your post would have a totally different flavour to it.

c

[johnholmes]

John - You missed the point-

How far do you go with calling the Ensemble Means accurate-

As an example- for around 5-7 days on the GFS ( & Quoted from Matt Hugo the ECm 32 DET) had an extended Scandi high from Western Russia all the way to southern greenland-

In the means this was touted at day 12 right down to day 6.

Then suddenly it changed & the Positive height anomaly over scandi went neutral & we lost the blocking- so whilst across the whole hemisphere it may be pretty good- even across Northern Europe its pretty good, the bottom line is the Ensemble mean smoothed out the shortwave pattern- like it always does post day 5.

As a result that long consistent period of NH ens means being NEARLY right amounted to nothing oncethe s/wave pattern came into view.

So is it inaccurate? no, probably not, was it useful- in the context of the UK, no- as ALL the forecasts for a long cold period from the east were wrong.

Also not one model got the strength of the atlantic right- with a negative anomaly.

S

S

best we agree to disagree Steve. The 500mb charts I use daily, that is ECMWF-GFS 00z output and the 6-10 and 8-14 NOAA output each evening, weekends included, are as my statistics show I would think(?) that the 500mb pattern is pretty well defined for the 6-15 day time period. I always use the caution that all 3 must be pretty similar to both themselves and each other over, preferrably a 3 day time slot. That is why, to some extent, I was late using them to show that the cold spell, regardless of synoptic charts of 2x or 4x daily would not last beyond this coming weekend.

I predict only for the Uk and the anomaly checks are there for you and everyone else to see, accept or reject but with a 'success' rate of about 70% at 10 days sometimes 15 it is as good as we are likely tio get as amateurs with the data available on the web to us.

No you are wrong to say they are no use or were no use over the change from block to mobility now occurring-well that is my view.

Equally, just seeing the post from ch about temperature values, the 500mb charts are quite useful also, not just in predicting does it look like being unsettled or settled, indeed even with a knowledge of upper air charts, how unsettled and fairly good guidance on where on the Atlantic/European area this will occur, but they are quite good at giving a reasonable idea of surface temperatures. Cold, very cold, mild, very mild, average(to long term averages) etc.

Edited December 13, 2012 by johnholmes

[Interitus]

http://forum.netweat...20#entry2445674

Post 229 by CC sums my post up with images-

S

This is the ensemble chart posted by CC compared to GFS +6h (analysis more or less)

Of course there are small differences but can anyone honestly say that was a bad forecast, at 7 days out?

Then we had a couple of days of operational runs showing the easterly; CCs chart had it in the distance at day 9 and could've chosen a better chart as the next run on the 6th at 0z it had the easterly starting in earnest as close as 144h, There was a fair amount of ensemble support though the mean was never as extreme. This was enough to suggest at the possibility of this cold spell, which as has been pointed out has occurred, being more severe. But it's not enough to dust down your sledge though, and by the next day 7th and subsequently we get

which is pretty much correct with what we have today 6 days later. So we had the suggestion over a couple of days of a possibly colder spell of weather at a about a week hence, but this didn't last long and based on the climatology would probably would've had a high skill score hence not as reliable. If anyone is seriously saying the models were poor it displays a lack of understanding and interpretation.

[bluearmy]

I'm posting this in here as it might be a significant moment in the winter nwp thus far. maybe this is nothing new, but the behaviour of the modelling of the vortex/polar field through GEFS fi on the individual members is something to watch. i certainly havent noticed this array of activity on the gefs runs until today. perhaps an initial reaction to the warming upcoming whilst there is still strong wave 1 activity ongoing ? if this is what we have to look forward to beyond xmas on future model runs, there is going to be a wide variation of solutions.

[Gibby]

Good evening folks. here is the report on the 12z output from GFS, UKMO and ECM for this evening Thursday december 13th 2012.

All models show the breakdown already taking shape out to the west of the UK with pressure already quite low and falling further over the next 24 hours as an active system of fronts cross NE over the UK with deep Low pressure closing in on the West of the UK. A strengthening wind from the South will blow the remains of the frostiness still being experienced by many away overnight with cloud and rain following in from the SW to reach SW England and much of Wales by morning. After several hours of rain amounting to between 10-20mm for many brighter skies will follow in behind with temperatures rising abrubtly as winds decrease and veer SW later tomorrow. Any remaining rain and hill snow in the North will clear tomorrow night leaving a showery SW flow with some heavy and prolonged showers likely at times in the South and West. The output moves into next week showing the Low responsible for the coming rain filling up as it drists East across the UK on Monday with further rain at times for all then. By Tuesday a brief interlude of drier weather is shown by all models as a weak ridge crosses East through the day.

GFS then shows a slightly backed West position of the next Low pressure midweek meaning that the fronts become complex and with a strong wind shear across them meaning heavy and squally rain followed by a return to sunshine and showers soon after midweek. By Friday this Low has become absorbed by a new Low in the SW approaches and this one threatens an awful lot of rain and resultant flooding risk to the SW in strong to gale SE winds. All through this period temperatures will hold close to normal for much of the time though with the High pressure block orientated somewhat different tonight there is the potential for a colder feed from Europe to migrate across NE areas of the UK with time. In FI tonight a brief incursion of Continental air makes it to all areas for a time before the Atlantic moves up a gear again and pushes Low pressure back into the British Isles with a wet and windy Christmas the likely result from this run. The end of the run sees the potentially stormy and wet weather continue with rain and squally showers everywhere.

The GFS Ensembles show a fairly flat, average pattern close to the seasonal average for the foreseeable future. The colder blip from the operational is not well supported with most members preferring to maintain the average and wet Atlantic based pattern throughout. There are a handful of colder options on offer late in FI to balance the story for those looking for cold but there is no definitive trend indicated.

The Jet Stream shows a strong arm rattling across the Atlantic towards Western Europe making landfall at around 50 deg N and maintaining that position over the English Channel give or take a hundred miles or so until the end of the reliable time frame.

UKMO for midday on Wednesday shows Low pressure to the West of Ireland with a cold front having crossed East in the previous 12 hours or so. In its wake will be windy and relatively mild conditions with heavy showers, more especially but not exclusively in the South and West.

ECM tonight shows a complete about turn tonight which will please the cold camp considerably. With the pattern backed West at 144 hours as per GFS an undercut takes place in the trough associated with a mid Atlantic deep depression which having brought yet another spell of heavy rain across Southern Britain stalls over the Midlands and sheered away East. A new depression on a more Southerly track out to the SW is similar to GFS's evolution and on this run is a trigger to flood cold air from Europe back over the UK next Friday turning rain to sleet and snow quite widely, especially over the hills in the South. The East wind would become strong and biting temporarily with wintry showers near Eastern coasts. At the end of the run pressure has recovered with a frosty day on day 10 putting us back into a similar position to where we have been in the last few days with the Atlantic knocking on the door of the UK under a collapsing High.

In Summary tonight there is a little more hope for 'coldies' again as a backing West of the pattern has opened the door ajar to a chance for cold weather from Europe to put it's toe into UK air space in a week or so. As far as GFS is concerned it is not well supported from it's ensembles and we'll have to wait a couple of hours to see where the ECM operational lies within it's pack. In the mean time the weather looks extremely volatile and simply 'dire' at times with spells of unwelcome rain in a strong wind and temperatures close to normal. IMO the output tonight goes to prove how a couple of hundred miles in the position of Low pressures can have far reaching implications down the line and just goes to show that the weather in the UK is never straightforward and quick to make fools of us all. The biggest problem of all though is getting it to be shown in the closer time range and to get it to verify at all.

[Gibby]

Good morning folks. Here is this morning's review of the 00z output of the big four GFS, UKMO, GEM and ECM for today Friday December 14th 2012.

All models show an unsettled spell bedding in over the UK today as Low pressure moves in towards Western Britain from off the Atlantic with an active front carrying strong winds and heavy rain NE across the UK with a spell of hill snow for Northern Britain for a time. Following on behind winds will decrease and turn more WSW with showers chasing the rain away from the South and west by the end of the day. For the rest of the weekend and the early days of next week the UK stays under the influence of the steadily filling depression as it drifts its way across the UK and loses it's identity by Tuesday. This means a weekend of sunshine and showers with some heavy and prolonged showers for the South and West but far fewer in the North and East with some longer drier spells. By the start of next week all areas will see some more occasional rain before a drier and brighter interlude spreads slowly in from the West on Tuesday in slightly less mild weather by then.

GFS then takes us through the middle and end of next week with a new area of Low pressure out to the West of the UK with a strengthening SW flow bringing another spell of wet and windy weather spreading NE again over the UK. This also fills as it drifts across the UK by next weekend though maintaining the unsettled and occasionally wet conditions for all. In FI today the pattern remains locked with Christmas Day and Boxing Day looking particularly wet and unsettled days with normal temperatures as the UK lies under complex Low pressure. With little change to end the run with only brief somewhat colder and brighter interludes it looks like a green Christmas still from GFS today.

The GFS Ensembles show a period of normality with regard to uppers and surface temperatures as Low pressure from the Atlantic remains the driving force to the UK weather right out to beyond Christmas. As usual there is plenty of spread between the members late in the run though there is no real trend towards anything reliable cold even though uppers fall back a little later especially for northern locations.

The Jet Stream shows a streak racing across the Atlantic towards Northern France persisting for the foreseeable future, becoming more of a sine wave pattern later next week at a similar latitude, still to the South of the UK.

UKMO for midnight on Thursday sees Low pressure out to the west of the UK with a strong and unstable SW flow over the UK with rain or showers at times in a continuation of generally mild conditions. The heaviest of the rain will continue to be towards the South and West.

GEM today shows Low pressure too out to the West of the UK drifting slowly East and filling through the following days maintaining the unsettled feel before yet another Low drifts towards the UK with rain bearing fronts crossing NE by day 10.

ECM finally also shows Low pressure out to the West drifting East into the UK and extending SE towards Italy later. High pressure is maintained over Russia with a cold Easterly flow over Northern Europe which towards the end of the run pushes the Easterly flow across some Northern and Eastern areas of the UK dragging colder and drier conditions to most areas by day 9 with Low pressure piling up to the West endorsing a cold and windy day with rain and sleet towards Southern and western Britain to end the run.

In Summary this morning the weather looks like staying windy and unsettled with spells of rain and showers across the UK for most of the next two weeks. There are a few indications of a resurgence of the High pressure block to the NE, notably once more from the ECM Operational (though not as good as last night) exerting a limited influence to parts of the UK towards Christmas but there is very limited support for this theory at present with the more likely scenario remaining that the Atlantic will continue to bring further rain and green conditions over Christmas with temperatures close to normal.

[johnholmes]

Just a very quick comment re anomaly charts for this morning-I do NOT say this will happen but there is a glimmer on the ECMWF version and even a little on the GFS of POSSIBLE changes. I'll keep an eye on it and update in here if necessary.

[Severe Siberian icy blast]

Just a very quick comment re anomaly charts for this morning-I do NOT say this will happen but there is a glimmer on the ECMWF version and even a little on the GFS of POSSIBLE changes. I'll keep an eye on it and update in here if necessary.

Well every time you've said this even if you mention it before you get your 3 in a row consistency it's always led to big changes, so I take that as a very good sign.

Ones are so quick to write off this December , I even read one or two writing off the snow chances until mid January , how bizarre !

Thanks for your insight John .

[johnholmes]

Well every time you've said this even if you mention it before you get your 3 in a row consistency it's always led to big changes, so I take that as a very good sign.

Ones are so quick to write off this December , I even read one or two writing off the snow chances until mid January , how bizarre !

Thanks for your insight John .

don't get too excited yet, by tomorrow it may not be there, check the NOAA issue this evening to see if it hints at anything similar-if not then best ignore it for now!

[Severe Siberian icy blast]

don't get too excited yet, by tomorrow it may not be there, check the NOAA issue this evening to see if it hints at anything similar-if not then best ignore it for now!

Ok thanks for the heads up John , did you say ignore it for now? Im sorry I have no idea what that word means when linked to the weather !!

[MR EXTREMES]

Just a very quick comment re anomaly charts for this morning-I do NOT say this will happen but there is a glimmer on the ECMWF version and even a little on the GFS of POSSIBLE changes. I'll keep an eye on it and update in here if necessary.

ive just been through all the model outputs and im not convinced the zonal train is going to continue for the duration of the runs.

thats a pretty impressive block into ne europe and even shows signs of gaining strength.

the jet at the moment seems to be our friend if cold is what your looking for.

remember how quick the fi cold spell this week came into the realiable whos to say this active alantic could lose energy fast more so if the vortex gets to its rest place quicker.

im not ramping but i think a change is coming sooner than later maybe not for atleast a week but shortly after.

[Rocheydub]

A lot of talk about this model and that actually modelling the Atlantic better than easterlies etc etc.

FWIW, this is my take on it. If the models predict a HP over Scandi, Greenland etc, it relies on a decent angle on any approaching Low cell to interact correctly to bring cold/snowy weather to our shores. Being 3/500 miles out on this makes all the difference and can cause massive downgrades/upgrades regarding our small islands.

However, if they are 3/500 miles wrong on Low pressure systems approaching our shores, it generally makes little or no difference, as we will normally get hit with winds and rain anyway. So it's probably just a perception that it handles low pressures from the west better than say a northerly or easterly!

Because of where we live, in between a warm ocean (thanks to the NAD), and a continental landmass, getting cold to our shores is much more difficult than a lot of people think. So I think, the models don't actually handle differing weather patterns any differently, or any better, just that getting the correct synoptics to get cold to us is just that much more difficult, and sure, that isn't the models fault... That's mother natures job!

So to summarise. Anyone got any way of re-directing the NAD to our south? Maybe the med or somewhere like that?

[J10]

http://forum.netweat...-december-2012/

The latest Alps forecast has now been released, and the synoptic extract from it has been shown below.

Daily Synoptic Summaries

Starting with today's actual synoptic charts -

Temp guide at 850HPa sub -10c very cold, -5c cold, 0-5c cool, 0 to +5c mild, above +5c very mild

Sat 15 December - There is a large area of High Pressure (1056mb) centred over Russia, with south to South Easterly winds over Eastern Europe, and Northern Scandinavia, very cold here. There is low pressure covering much of the Atlantic, lowest pressure around 970mb to the west of the UK. This is feeding in mild SW winds over the UK and much of Northern and Central Europe, including Southern Scandinavia and the Alps. Further South there is High Pressure over Southern Europe as the Azores High ridges eastwards, bringing mild or very mild weather here.

Sun 16 December - The general pattern very similar, however the air mixing out over Northern and Eastern Europe, turning less cold over much of Scandinavia, and less mild over other parts of North Eastern Europe, this fringing the Alps, so not quite so mild here. The low pressure over Atlantic, weakening, but still rather unsettled and mild over the UK. Further South there is still High Pressure over Southern Europe, bringing mild or very mild weather here.

Mon 17 December - Synoptically again similar, but the low pressure now over the UK (99mb) and continuing to weaken. Cool over the UK, much of Northern mainland Europe, cold over Scandinavia and over Russia with the High Pressure still strong (1048mb). Still mild over Southern Europe. The Alps in between the cool weather to the North and mild weather to the south, with 850HPA around 0c.

Tue 18 December - High Pressure continues to dominate over Russia, Eastern Europe and into Scandinavia, so cold or very cold here. Cool over much of Europe with weak low pressure over the low countries. Still mild over Southern Europe, low pressure further east, the Azores high keeping things more settled over Iberia, Pressure also starting to rise over Western parts of the UK, cool in the east, mild in the west.

Wed 19 December - High Pressure (1052mb) continues to dominate over Russia, Eastern Europe and into Scandinavia, so cold or very cold here. A deep area develops over the Atlantic bringing unsettled conditions and very mild air into Southern parts of the UK. Also turning milder over western parts of mainland Europe, but still cool over Eastern Europe, this divide splitting the Alps in Half.

Towards Weekend - The High Pressure Over Russia remains a constant, so very cold here and into Scandinavia, cool also over Eastern Europe. The Azores High staring to ridge back into Southern parts of the UK, and cooler again after the mild weather of midweek. As has been often the case this week, the Alps very much in between weather systems.

Edited December 14, 2012 by Jackone

[phil nw.]

Gibby`s 12z summary copied from the main Model thread.

Good evening. Here is the report on the 12zs from GFS, UKMO and EM for tonight Friday December 14th 2012. There will be no report from me tomorrow morning but I should be OK for the 12zs later in the day albeit rather late.

All models show low pressure covering much of the Atlantic Ocean and the British Isles with a front moving steadily North over Northern Britain tonight. A showery West to South-West airflow covers Southern and Western areas with this weather type extending to many other areas overnight. The weekend and start of next week shows the Low pressure filling slowly as the complex system moves over the UK before losing its identity by Tuesday.

GFS then shows a weak ridge of High pressure crosses East on Tuesday ahead of the next Low pressure zone setting up in the Atlantic. Rain moves NE over Wednesday followed by breezy NW winds and showery conditions for a time. With pressure rising to the South winds back SW by the weekend carrying very mild air NE over all areas with rain and drizzle in the North and West. Through FI tonight the trend is for the mild weather to persist in the run up to Christmas with Christmas itself shown to be very windy and wet at times with temperatures dropping back to normal or somewhat below in the period between Christmas and New Year for a time in the North.

The GFS Ensembles show very uninspiring conditions for those looking for cold and snow tonight. After a mild snap for a time next week temperatures fall back to near the normal for all areas. The colder blip from the operational after Christmas is without support with very few colder options at all through the run. There is plenty of precipitation shown for all areas through the run and virtually all will no doubt be rainfall.

The Jet Stream shows the flow blowing strongly Eastwards over the Atlantic to France over the coming 4-5 days. Later in oscillates North over the UK late next week.

UKMO for midday on Thursday shows Low pressure West of Ireland with a broad trough East over Northern Britain. Southern areas once more come under the influence of a breezy SW flow with heavy showers in generally mild conditions.

ECM shows a similar pattern to UKMO at 144hrs though with a separate Low pressure centre over the UK as opposed to the trough UKMO shows. The end result would not be too dissimilar though on the ground with outbreaks of rain and showers all over the UK in cyclonic winds. Later in the run little change is shown with Low pressure re-establishing close to the UK with further heavy rain and showers for all.

In Summary tonight it looks like a very unsettled spell of weather for all of the UK for the coming two weeks. There will be spells of rain or showers for all, always heaviest in the South and West while things remain relatively mild. GFS shows a very mild slot for a time prior to Christmas while conversely ECM shows somewhat cooler conditions, but not cold especially in the North at the same time point with rain for all. There is little desire for any model to want to bring us back under cold conditions either from the East or North through this outlook period.

[SMU]

I agree to certain extent Steve.

However, to say that there is no point working so hard to predict the upper air pressure anomalies because they have no correlation to the lower weather received is misleading and a little short sighted. We may have missed out this week - but in the grand scale of things it was a near miss. To use one near miss to base the whole concept of using upper air anomalies is complete nonsense. Blocking pattern H5 anomalies are always going to be more unpredictable to be able to nail down surface details than say a zonal pattern because of their very nature and yes slight weaknesses in these patterns can lead to shortwaves developing. If GP had predicted a H5 anomaly zonal pattern that would have had far more success at the surface because the pattern would have been far more predictable if it were correct.

To suggest that it is waste of time trying to predict these H5 anomalies is very disappointing from you. I think that surface temperature anomalies correlate pretty well to the H5 blocking patterns (as has this one) and I am sure that had the recent temperature anomaly been accompanied by some snow your post would have a totally different flavour to it.

c

to be honest C I even be bothered to comment anymore-

The Strat thread & the winter forecasts are all good to a certain point & that is- very broad brush sweeping ideas about the anomalies-

Thus far the H5 anomalies for 01-12th dec 2012- are nothing like the NW forecast, no blocking over southern greenland- which is where the core of the forecast was aimed at- the height profiles for that region are very much neutral or slightly pos due to the Siberian ridge- also that slight + anomaly will reduce over the coming days- Like I said it doesnt really matter & things can change into Jan, however all that time spent....

Why do you think the METO gave up- with ALL those minds focussed with all the info we have plus more-

All ive heard since 15th Nov is Warming this warming that- Charts from the ECM + 10 day -@ 10 HPA showing warmings-

One day they might come off- or when they do they might connect with the troposphere-

Theres no harm in having all these threads running- but sadly in real life on the plot of land we live its all to broad brush & chaotic to forecast X=Y. where X is some form of wavebreaking where Y is the UK.-

Good luck in the strat thread- I hope some more info becomes available to support the thought process & link - however with such a small sample size & with ever changing annual & seasonal tropospheric forcings I feel you will always be chasing your tail.

S

[johnholmes]

Ok thanks for the heads up John , did you say ignore it for now? Im sorry I have no idea what that word means when linked to the weather !!

a quick look at the ECMWF-GFS and the NOAA issue last evening=forget it as they all 3 again show a similar idea of a mainly westerly flow.

I'll do an update on my supposed Friday issue some time today as time allows.

[Paul]

Why do you think the METO gave up- with ALL those minds focussed with all the info we have plus more-

Obviously you're entitled to your opinion Steve, not sure I agree with some of it but each to their own

All I would say though is that the Met Office didn't give up on producing lrf's and the like, they gave up putting them out there publicly. They have in fact invested a fair amount in lrf and extended mid-range forecasting with a good chunk of that being based on research into the stratosphere and its affects.

http://iopscience.iop.org/1748-9326/7/3/034031/

http://www.bbc.co.uk/news/science-environment-19584302

[johnholmes]

posting my late Friday meander through the last week and outlook with the 500mb anomaly charts and a tongue in cheek look with one other item!

6-The weekly look at the anomaly charts and anything else relevant.pdf

[phil nw.]

After today`s outputs it`s hard to see anything other than a Westerly Atlantic type of pattern establishing for the next week at least.

T72hrs fax

There are some minor differences in the outputs around days 4-5 with the angle of the Atlantic trough but with the pattern eventually showing the jet tilting more sw-ne and pushing those Iberian heights ahead it scuppers any lingering chances of anything from the east.

GFS mean jet at T96hrs.

The ens 500hPa means and NAEF`s all indicate a mean Atlantic trough near the UK and still some heights further south and a rather flat flow.

The temp.graph showing fairly average 850`s for London in week 2(Christmas week)so it would be reasonable to call for a continuation of next weeks outlook, perhaps somewhat cooler especially if we can get any ridging into the pattern on the Atlantic side.

Edited December 15, 2012 by phil n.warks.

[Gibby]

Good evening. Here is the report on the 12zs from GFS, UKMO and ECM.

All models show a consistency with there output over the period until the end of the next working week. Low pressure is in firm control at the moment out to the NW with a showery SW flow over the South and West while things remain rather drier in the North and East with some sunny intervals everywhere. Temperatures will continue stay near to normal over the coming week for most. The showery theme continues until Tuesday when the Low fills and moves away East with a ridge of High pressure bringing a colder and drier interlude before further Low pressure moves into the UK from the West by Wednesday carrying freshening winds and rain slowly North and East over the UK to be followed by further unsettled conditions with rain or showers at times to end the week.

GFS then moves into next weekend with a warm front moving NE in a strong SW wind carrying a band of rain followed by dry but cloudy conditions in the SE half of the UK with temperatures well above normal. Through FI tonight the operational shows the pressure pattern as High pressure to the South and Low to the North with rain at times in near normal temperatures and strong winds. Christmas is shown to be governed by a broad and strong WSW flow over the UK with rain at times in temperatures well up to normal. Later in the run the pattern collapses as Low pressure over the UK slides South bringing the usual phantom Easterly on the final day of the run though things wouldn't become particularly cold.

The GFS Ensembles show a mixed pattern but nothing very cold is shown tonight. Uppers do fall back later in the run in the North indicating that these areas are likely to fall on the colder side of Low pressure at times with frequent bouts of rain shown often nationwide.

The Jet Stream shows the current direct West to East flow just to the South of the UK begins to oscillate as we move into the latter part of next week as higher pressure sets up for a time to the South.

UKMO for noon on Friday shows a complex Low pressure belt stretching from the Western Atlantic all the ay East through Britain and the North Sea. The weather would continue to be fairly unsettled with rain at times in near normal temperatures in the South and perhaps a bit on the cold side further North.

ECM shows Low pressure over the Atlantic too with this moving East into the UK in time for Christmas making Christmas Day rather colder than the previous days as well as unsettled with cyclonic winds dragging lower temperatures down and maybe some snow on the northern hills.

In Summary tonight the pattern looks like remaining rather unsettled with rain at times. It will generally be too mild for snow away from Northern hills at times due to repeated Low pressure carried on a strong jet East over the Atlantic and across the UK with little chance of much disrupting this pattern to anything seriously cold anytimee soon. Christmas looks like being green rather and white though it may not be partucularly warm.

There will be no report from me again tomorrow morning. I am really busy with work at the moment and this includes Sunday in this weekend so as today I'l be here for the 12zs at the usual times tomorrow.

[Glacier Point]

to be honest C I even be bothered to comment anymore-

The Strat thread & the winter forecasts are all good to a certain point & that is- very broad brush sweeping ideas about the anomalies-

Thus far the H5 anomalies for 01-12th dec 2012- are nothing like the NW forecast, no blocking over southern greenland- which is where the core of the forecast was aimed at- the height profiles for that region are very much neutral or slightly pos due to the Siberian ridge- also that slight + anomaly will reduce over the coming days- Like I said it doesnt really matter & things can change into Jan, however all that time spent....

Why do you think the METO gave up- with ALL those minds focussed with all the info we have plus more-

Theres no harm in having all these threads running- but sadly in real life on the plot of land we live its all to broad brush & chaotic to forecast X=Y. where X is some form of wavebreaking where Y is the UK.-

S

Steve

I disagree fundamentally with your assessment of the winter forecast to date that it is somehow way off of the mark on current anomalies and the somewhat inward and parochial approach to medium, long and seasonal range forecasting that is being put forward here.

Here is the forecast MSLP anomaly for December and alongside it the observed H5 anomaly pattern and the H5 and MSLP composite analogue packages used so you can see where I was coming from.

Forecast> Observed>

Analog H5> (note the Scandinavian / Siberian anomaly depicted)

Analog MSLP>

Broadly, these look a very good fit across all of the key anomalies, with the one around southern Greenland being the least impressive, but the European context with troughing depicted very well.

This is demonstrated in the surface temperature anomalies. Again, forecast and observed anomalies to date with the composite analogue for reference alongside.

Forecast> Onserved>

Analogue>

That demonsrates a very good verification to date, especially in terms of the temperature distribution suggesting the core of the cold in Europe.

Obviously, the data over the next 7-10 days is going to be not consistent with this forecast, although speculating ahead too far looks problematic given model variability. For interest, I've attached ECM day 1-5 and GFS days 6-10 and 11-15 H5 ensemble mean height anomalies to give an illustration of where we might end up.

I would suggest on this basis, a retained +ve height anomaly across the northern latitudes and troughing over Europe, which essentially will verify the pressure forecast, much of which was put together in October.

Both the Forecast and the Preview made great play on a negative phase of the AO and NAO. So far, and projected, we have seen both indices in a negative state, the AO definately more so than I would have anticipated.

How useful are any of these indices for a relatively small surface area such as the UK ? Well, to answer this, it's worth understanding where we are coming from.

There is a wealth of model data coming at us, both medium, long and seasonal range. In applying some degree of thought process, using an understanding of the dynamical processes in the atmosphere, we are attempting to spot a good run from a bad one. In the words of Ed Berry, this will give an edge on those using NWP alone on average.

I must stress this on average as clearly there will be instances that I and others have been and will be wrong. This doesn't undermine the approach at all, far from it. It will be very easy to pick examples of where it didn't go right (last week's failed easterly for example). However, I suspect due to the complexity of the subject matter, rarely do we see examples of the numerous successes being cited. For example, the idea that increasing angular momentum picked up in late October would lead to a major vortex disruption (and strongly negative AO phase) in late November and December deserves special mention, as does the identification of precursor patterns and timings for the vortex disruption and upcoming warming event well in advance of any NWP. These continue to strengthen the belief that we are actually winning here. Both the mechanism and outcome were well forecast at a hemispheric scale.

So how do we reconcile the small surface area of the UK and use of such predictive macro scale techniques ?

The use of the AO and NAO strike me as a particulalry good example here. The AO and NAO can be negative and the UK might end up warmer than normal but on a European scale, they might be particularly good representations. Certainly from some of our commercial clients, especially those involved with the energy sectors, the European context is vital given the interconnectivity of the gas markets. Within long range forecasts, the use of AO / NAO forecasts is now becoming pretty much mainstream.

Overall though, and taking say 10 rolls of the dice, a -NAO / -AO pattern will deliver cold for the UK. Probably eight or nine times out of ten. This is the key point underpinning all of the analysis and forecasts, a probablistic basis is premised on the various dynamical processes delivering by a loading of the dice in one particular favour.

On a related note, last week's failed easterly was attributed wrongly IMO to a microscale feature cutting off the supply of cold air and preventing blocking from forming. The key aspect that was incorrectly modelled was the anomalous ridge that developed in the sub-tropics and removed any notion of a trough between the Azores and Iberia. In fact, the reverse happend.

This ridge developed in response to about as macro scale feature as you can get.

Anomalous westerly winds developed in two discrete Rossby wave trains emerging from the tropical Pacific and Atlantic. These are clearly visible in the OLR anomaly plot from 13/12/12.

These had the net impact of pumping the sub-tropical ridge and making it impossible for any westward extension of the ridge to our east.

Interestingly, I suspect that the sharp increase in solar activity four weeks ago was the route cause of this. High levels of solar activity are thought to increase the height of the tropopause thereby strengthening the Hadley and Walker circulations. The increasing strength and northward projection of the sub-tropical ridge are certainly consistent with this, as is the angular momentum anomaly for the tropics which suddenly dropped from postive to negative in this timeframe.

This will be worth monitoring because solar activity has since plummeted and now stands at very low levels. Will the lagged impact of a reduction in solar activity work it's way through the system in the next 3-4 weeks ? This will be very interesting in the coming weeks because of the advertised warming of the stratosphere (see Strat thread) and also the emergence of an increase in +ve frictional torques:

There was a dual peak in frictional torques in November which preceeded the sudden increase in tendency of relative angular momentum at the end of November. If the frictional torques begin to deliver increasing angular momentum, then we will effectively be building the foundations of the next cold pattern, at a distance of 3-4 weeks.

Edited December 15, 2012 by Glacier Point