Model Output Discussion 13/11/12 18Z onwards

[Met4Cast]

Why do members think warmer synoptics in FI are more likely to verify than colder synoptics? I've never understood that! The 18z is fantastic until it gets into the Low Resolution part which is when it falls apart. Models always have trouble with setups from the East, they're pretty much expected to handle this poorly, particularly the GFS

Edited November 13, 2012 by Daniel AKA WMD

[Chris K]

As much as people are excited about looking for winter synoptics (including myself), but what are peoples views on what the models mean for the more closer timeframe?

Just thought it might be useful for any newcomers/learners etc....some of this evenings posts are better suited in the winter thread in my opinion. Not criticising anyone in particular as i do enjoy reading all input by everyone, but at the moment its increasingly turning into a "lets see if it shows what we want" thread rather than "this is what this runs output shows and what it is likely to result in" discussion.

Edited November 13, 2012 by Chris K

[Snowy Easterlies]

Why do members think warmer synoptics in FI are more likely to verify than colder synoptics? I've never understood that! The 18z is fantastic until it gets into the Low Resolution part which is when it falls apart. Models always have trouble with setups from the East, they're pretty much expected to handle this poorly, particularly the GFS

pretty simple answer, this is the UK and those warmer synoptics, for example zonailty or the azores high ridging in are far more common than a raging easterly, so easy to understand the pessimism

not sure if the 18z is better tbh the low looks further east to me, plus people seem to think that the models are always useless with scandi highs when thats not always the case, sometimes the low does power through and that is the end of that

Edited November 13, 2012 by Snowy Easterlies

[bluearmy]

http://www.meteo24.fr/fr/home/meteo-france-et-europe/passion-meteo/ensemble-de-previsions.html?eps=london

The back end of November continues to look pretty chilly for London.

Sunday/Monday look cool behind child front before th next system works ne across the country. Thereafter a more average to mild few days before th mean maxes drop off slowly but surely. I expect this reflects a combination of some runs taking the next cf through whist others begin to drag a continental flow into the se around a building block to our east.

Edited November 13, 2012 by bluearmy

[pyrotech]

The jet is repeadly trying to split. If the blocking is in place and we have a splt jet we will struggle to get real cold air. However these charts on both 12z. And 18z are not showing the blocking correctly. For instance the large area of low pressure 1000mb to our North at the end of the run. Its too shallow for that set up. Until the high over greenland is established the models will struggle to forecast the jet path so everything East of 40w will then be up for grabs. Fi starts at this weekend the models are playing with ideas from there trying to take account of some kind of blocking. Hints of a colder trend is best description, now we need to see if trend tends to go cold or less cold. But expect a rollacoaster ride till after this coming weekend where things should finally start Assembling a pattern one way or other. Remember that 18z gfs often picks up a trend and drops it to later be proven closest to the actual. So is this where it drops a trend to bring the cold flooding back in few days. Alot is right for a brief cold spell but tonights trend from gfs is the wrong way. Like i said thou gfs does this all too often. I. Think Damian is lucky being away for few days as the ride will be more determined by then. I am not disiplined enough to keep away so will try and enjoy the ride.

[Harve]

Why do members think warmer synoptics in FI are more likely to verify than colder synoptics? I've never understood that! The 18z is fantastic until it gets into the Low Resolution part which is when it falls apart. Models always have trouble with setups from the East, they're pretty much expected to handle this poorly, particularly the GFS

It's not that a warmer run is more likely to verify than a colder run (I'm not sure if that's what you're implying), but by its very definition, average is more likely than well below average temperatures, therefore more scepticism should be held over an 'extreme' run than a benign one. The latter part of your post implies we ARE dealing with a set-up from the East - clearly we don't know if that's going to be the case yet.

(of course, there are numerous factors that make cold more likely than mild, and therefore there are times when even a slightly above average run must be looked upon with scrutiny, and vice versa)

Edited November 13, 2012 by Harve

[cfallon]

The jet is repeadly trying to split. If the blocking is in place and we have a splt jet we will struggle to get real cold air. However these charts on both 12z. And 18z are not showing the blocking correctly. For instance the large area of low pressure 1000mb to our North at the end of the run. Its too shallow for that set up. Until the high over greenland is established the models will struggle to forecast the jet path so everything East of 40w will then be up for grabs. Fi starts at this weekend the models are playing with ideas from there trying to take account of some kind of blocking. Hints of a colder trend is best description, now we need to see if trend tends to go cold or less cold. But expect a rollacoaster ride till after this coming weekend where things should finally start Assembling a pattern one way or other. Remember that 18z gfs often picks up a trend and drops it to later be proven closest to the actual. So is this where it drops a trend to bring the cold flooding back in few days. Alot is right for a brief cold spell but tonights trend from gfs is the wrong way. Like i said thou gfs does this all too often. I. Think Damian is lucky being away for few days as the ride will be more determined by then. I am not disiplined enough to keep away so will try and enjoy the ride.

Can you please back this up with charts to illustrate your views. Thanks c

[pyrotech]

No not on my phone will do tomorrow. But its there for you to see. The gfs shows many times in its run a split jet. Both gfs and ecm show pressure rises on 12z over north west europe and greenland. Strength and orientation will make diference thou. Also gfs has a late tropical storm running up usa East coast later next week and ecm shows a tropical low of less intesity same time. I can not post images from my phone but all this can be seen on the netweather charts. As for the gfs having ideas deep in fi then dropping it before bringing it back in reliable timeframe most seasoned followers have noticed it over last two years. Although on balance it can also often go off on a tangent of immoral proportions at times often playing with cold in fi where it stays in fi for weeks. Gfs love it or hate i suppose.

[SnowObsessor90]

Whenever the 18z's in a sober mood it generally doesn't fill me with much confidence about the 00z's to follow and with good reason. Hopefully those fears don't end up being realised come the morning.

Looking at the 18z ensembles only adds to these fears, really not looking forward to the 00zs now.

[Met4Cast]

Looking at the 18z ensembles only adds to these fears, really not looking forward to the 00zs now.

Why? If anything the 18z Ensembles are trending colder at the end of the run than the 12z ensembles were.

12z ENS

18z ENS

That's an improvement in my eyes. As Steve Murr said, the ensembles will likely be a bit late onto the seen with this potential trend, everything looks fine and dandy still from where I'm sitting and the trend continues for the time being.

Edited November 14, 2012 by Daniel AKA WMD

[SnowObsessor90]

Why? If anything the 18z Ensembles are trending colder at the end of the run than the 12z ensembles were.

12z ENS

18z ENS

That's an improvement in my eyes. As Steve Murr said, the ensembles will likely be a bit late onto the seen with this potential trend, everything looks fine and dandy still from where I'm sitting and the trend continues for the time being.

It's just that quite a few of the individual members don't seem all that enthusiastic to me but as you and Steve have said hopefully this is simply a matter of them not quite 'getting it' yet.

[IDO]

The last two runs by GFS have toned down the prospect of a very cold period at the end of the month. The ensembles are now heading back up to cool/below average temps:

http://cdn.nwstatic..../t850London.png

There are slightly more (than previous runs) members being in the average temp camp. During the 0z run the PV was disorganised and split, but this was transient and by the end was regrouping. At the end of FI we have a UK high:

http://cdn.nwstatic....384/npsh500.png

More MLB than HLB here.

Having looked through the GFS individual ensembles yesterday, this was the second most progged outcome, so no surprise the runs may start hinting at this. The GEFS Control run is an outlier for pressure:

http://cdn.nwstatic....prmslLondon.png

In other words, still many possibilities including cold, but a little less confident, from the initial attempt now.

The latest individual members:

http://www.meteociel...&mode=6&ech=384

From average to cool to cold with a couple of mild runs. Cool being the most prevalent. A November 10 outcome not looking likely from this data.

Remains a waiting game, whilst the models sort themselves out. Low confidence in anything over T240 though a cool-cold trend still the likely outcome.

Edited November 14, 2012 by i'm dreaming of...

[Great Plum]

Interesting ensembles this morning... Whilst the op takes the high pressure over the uk route in FI, the ensembles don't know where to go... There is far greater diversity in fi then there has been for a few days...

http://www.netweather.tv/index.cgi?action=charts;type=ens;sess=

[Ian Brown]

I think one thing to point out this morning is that from the synoptic position shown in the reliable and semi-reliable timeframes, it is hard to achieve HLB in the right place for the UK.

Both the GFS and ECM want to take a branch of the jet down towards Iberia, which is a clear signal for HP formation around the mid-latitudes. The GEM remains strongly zonal however.

The ensemble scatter is only reflective of typical uncertainty in the upstream pattern. All things considered I would take a position of a Rex block and hope for retrogression down the line but I wouldn't be confident of losing that Northern arm of the jet.

[bluearmy]

I think one thing to point out this morning is that from the synoptic position shown in the reliable and semi-reliable timeframes, it is hard to achieve HLB in the right place for the UK.

Both the GFS and ECM want to take a branch of the jet down towards Iberia, which is a clear signal for HP formation around the mid-latitudes. The GEM remains strongly zonal however.

The ensemble scatter is only reflective of typical uncertainty in the upstream pattern. All things considered I would take a position of a Rex block and hope for retrogression down the line but I wouldn't be confident of losing that Northern arm of the jet.

Good post Ian. Without wanting to appear patronising, this adds to he thread rather than provoking it. The ens, having shown a little direction yesterday week 2 are struggling big time on the 00z run.

[Gibby]

Good morning folks. Here is the report on the 00zs from the output of GFS, UKMO, GEM and ECM. for today Wednesday November 14th 2012.

All models show a weakening SW flow over Britain an the pressure gradient falls slack later today over Southern Britain. A lot of cloud is lying over the UK but apart from an old front giving some rain over the NW it is mostly dry. Through the day as the light flow backs towards the SE in Southern England drier air filters across from Europe with some mist and fog in the damper air near the surface. By Friday this gives way to a slowly freshening Southerly breeze as a trough advances from the West. Rain will move slowly East across the UK overnight Friday and Saturday. As it clears the weather turns freshen and chillier with a frost likely on Saturday night. As the ridge moves away through Sunday a SW flow develops in association with a deep Low to the NW of Britain and rain returns to Northern and Western areas in particular by Monday.

GFS then shows a deep depression West of Britain with showers or more prolonged rainfall for all areas, heaviest in the West with strong but mild Southerly winds for all. Late in the week the Low sinks South as a ridge builds West from Europe and the North Atlantic to the North of Britain with a trend towards drier conditions spreading down from the North over the weekend. With winds in the East it will feel rather colder but with no real cold too tap into it would be rather chilly rather than desperately cold. Through the rest of FI High pressure becomes dominant over the UK centred near Scotland for some days before receding towards Western Ireland later. The weather would be dry everywhere with a chilly wind in the far South giving way later to quiet conditions with the risk of frost and fog if cloud amounts allow.

The GFS Ensembles show the cooling pattern as before with uppers settling close to the long term mean. There is something of a reduction in the cold chances again this morning with a couple of very mild options in the members towards the end for the North. The weather looks like staying changeable with rain at times in all areas.The operational described above was one of the milder options towards the end.

The Jet Stream shows a flow currently over the North of the UK persisting for a while. In a few days the flow slips South over Britain. Later, towards next week it dips well South to the West of Britain turning North over the UK and over the European High over Europe.

UKMO for midnight on Tuesday shows a mild SW flow over the UK with Low centres near Northern Scoatland and West of Ireland. Spells of rain or showers would occur for all in a fresh to strong but mild SW wind.

GEM too shows Low pressure to the NW or West with a strong Southerly feed and rain at times in generally mild conditions. Rainfall would be copious at times given the proximity of the Lows to the UK.

ECM shows a similar scenario to the GFS operational with Low pressure to the West slipping slowly South to be centred over Biscay and just to the West with an Easterly flow over the UK. Rain over Southern areas would continue at times with drier conditions developing in the North. Temperatures would remain close to normal as the air source remains from Southern Europe.

In Summary it's not good news for coldies this morning as the models have backed away somewhat from both a colder feed from Europe or the North within the time frames of this morning's output. There is blocking in place in abundance but it is in the wrong place at this moment in time to push any meaningful cold towards our shores. Instead we have a changeable pattern with rain at times as Low pressure at first to the West slips South to become a cut off area South of the UK. High pressure could well develop from the North then with our own self developing cold pool a possibility at the surface with attendant problems of frost and fog quite likely late in the period.

[fergieweather]

meto update yesterday was very vague about the cold prospects.in the more reliable time frame what about the possible storm for late sunday latest models look like it will effect only the northern parts of the uk although low confidence in this comming off and thats only 4 days away not over a week away.

Took part in interesting discussion last night with UKMO colleagues re potential snow possibilities for some areas into Saturday. We didn't bother discussing the longer range stuff this time...!!

[Frosty.]

My heart sank when I flipped through the Gfs 00z ens mean because it's persisting with a cool/mild zonal outlook with the flow between sw'ly and nw'ly but a tendancy for the pattern to become flatter later with low pressure to the north and high to the south, the russian high slowly pulls away eastwards over time and the trough to the southwest of iceland slowly moves east so it's an unsettled outlook with wet and windy spells but nothing unusual for mid to late november. The risk of a very cold end to the month seems to be diminishing slowly, much as it pains me to say it, the block is not coming our way according to the mean, it's going away. As for the op runs, they show a more settled further outlook but no cold air to tap into, some fairly mild 850's over europe, lots of yellows and oranges but no blues!

So has our wintry opportunity gone or just been postponed until later in december? I will leave that to the experts.

Edited November 14, 2012 by Frosty039

[Barry12]

I'm sure the models will upgrade again tomorrow, I can see the models upgrading the sooner we get to the reliable time frame and their is less uncertainty.

[quote name=fergieweather'

timestamp='1352882556' post='2403649]

Took part in interesting discussion last night with UKMO colleagues re potential snow possibilities for some areas into Saturday. We didn't bother discussing the longer range stuff this time...!!

[Cloud 10]

Took part in interesting discussion last night with UKMO colleagues re potential snow possibilities for some areas into Saturday. We didn't bother discussing the longer range stuff this time...!!

Looks a bit complicated on saturday looking at the fax chart.

Maybe some back-edge snow from the cold front over scottish hills?

[Weather Boy]

My heart sank when I flipped through the Gfs 00z ens mean because it's persisting with a cool/mild zonal outlook with the flow between sw'ly and nw'ly but a tendancy for the pattern to become flatter later with low pressure to the north and high to the south, the russian high slowly pulls away eastwards over time and the trough to the southwest of iceland slowly moves east so it's an unsettled outlook with wet and windy spells but nothing unusual for mid to late november. The risk of a very cold end to the month seems to be diminishing slowly, much as it pains me to say it, the block is not coming our way according to the mean, it's going away. As for the op runs, they show a more settled further outlook but no cold air to tap into, some fairly mild 850's over europe, lots of yellows and oranges but no blues!

So has our wintry opportunity gone or just been postponed until later in december? I will leave that to the experts.

I think that perhaps this is a bit of an over-reaction to the current runs, bouncing back from an over-reaction to the earlier runs.

At this (long) range, surely what we should be looking for are trends only i.e. whether and to what extent we get blocking. I am not convinced that this kind of range is one where we should be looking at positioning of the block to deliver cold or not.

As we know blocking does not guarantee cold, but if it stays in place for a long time then more than likely cold will come at some point or other. All we should really have been getting from the earlier runs is that it is likely that blocking of some sort will be in place. Whether that is in the right place to deliver cold for the UK is surely too early to be said with any confidence - no matter what recent or the latest model runs say.

[Robbie Garrett]

Just a word of added caution!! Not saying the models are right, but also in November 2010 it played tease.

It dropped the idea on some occasions then came back and counted down the event....

Reason these events are showing is it could synoptically happen.

[AWD]

Looks like tonight & tomorrow morning could see some pretty dense fog in places;

Cloud Base down to 1000m quite widely, locally lower:

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=ukuk&MODELL=gfs&MODELLTYP=1&BASE=-&VAR=lclb&HH=18&PRINT=1&ARCHIV=0&PANEL=0&INFO=0&WMO=

High 2m Humidity across England;

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=ukuk&MODELL=gfs&MODELLTYP=1&BASE=-&VAR=rh2m&HH=21&ZOOM=1&ARCHIV=0&RES=0&PANEL=0&LOOP=0&INFO=1&WMO=&PERIOD=

Visibility down to 50m quite widely across the Midlands;

http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2012/11/14/basis00/ukuk/visi/12111506_2_1400.gif

[snowking]

Just a word of added caution!! Not saying the models are right, but also in November 2010 it played tease.

It dropped the idea on some occasions then came back and counted down the event....

Reason these events are showing is it could synoptically happen.

I must say I realise that the exact synoptics aren't as brilliant as yesterday but they are still loaded with cold potential:

ECH1-240.GIF

Cut off low, HP out of europe ridging NW and HP developing over iceland

UN144-21.GIF

Trough digs further south than ECMWF at 144, and upstream pattern more amplified

There is no denying that the 0z GFS was very poor for cold prospects, but the euros still far from poor and anyone who was looking at exact synoptics during the past couple of days was getting the wrong end of the stick

SK

[offerman]

Hi Ian,

Now wouldn`t that be crazy if that happened again as it did here in Frome, Radstock, Bath, and other surrounding areas!!