Model Output Discussion October 2012

[johnholmes]

Funny, was just looking at that Nick.

It now seems verly likely that the existing and programmed anomalies will leave us with a solid anomalous ridge over large parts of the Arctic, centred over Svalbard.

There were periodic phases where this type of anomaly persisted in October, notably none in the 1990s and few in the 1980s.

Roll these forward into November, little change. I'll leave others to take these into the winter thread but note the development of a set wave pattern across the NH with well defined ridges and troughs.

A very simplistic comment is look in the CET figures for the subsequent winters shown at the bottom of the last chart Stewart (GP) shows!?

[JP1972]

Apologies for my stupidity/lack of knowledge, but could the more knowledgeable please provide a laymans explanation of what everyone is so excited about and what this means for the British Isles.

Many thanks and apologies again.

Edit: Sorry Mods that my post is off topic too.

Edited October 11, 2012 by JP1972

[Gibby]

Apologies for my stupidity/lack of knowledge, but could the more knowledgeable please provide a laymans explanation of what everyone is so excited about and what this means for the British Isles.

Many thanks and apologies again.

Edit: Sorry Mods that my post is off topic too.

I think what your reading is the embryonic signs of things that happen in the model output threads of weather forums in winter. The most knowledgeable people are very good at examining and extrapolating charts from 19 bla bla and so on and what it might evolve into but fail to realise that Weather has a mind of it's own, is not a respecter of past events and will do what is relevant to the time. I have been around some 50 years or more studying weather and I have been caught out many a time thinking that winter armageddon is coming, only to be disappointed 24 hours later by rain lashing on the window panes. My best advice is to take things one day at a time because forecasting winter weather is as chancy as winning the lottery and for what it's worth the current northern blocking is only serving to give us a very wet Autumn spell and will bear no impact on what the Winter 2012/13 holds in store for us.

Edited October 11, 2012 by Gibby

[peterf]

wise words Gibby.

[davehsug]

Thanks Gibby, nice to see some balance. A few getting carried away by something that could look completely different in a weeks time.

[camiscool]

Euro high back at end of run

[Catacol]

A very simplistic comment is look in the CET figures for the subsequent winters shown at the bottom of the last chart Stewart (GP) shows!?

5 of the 12 Decembers that followed that november chart GP posted are in the top 20 coldest decembers in the UK since 1878. Specifically: 2010, 1961, 1968, 1976 and 1981.

Edited October 11, 2012 by Catacol_Highlander

[JP1972]

Again off topic ...

But thanks very much for your reply Gibby.

I read your model summaries (as I'm sure many others do) every day so quite pleased with your no-nonsense and middle of the ground reply.

So are people assuming that things are happening in the background which may or may not affect the UK?

I think it would be nice to debate this in this thread so that the less knowledgable can learn.

Edited October 11, 2012 by JP1972

[snow drift]

I think what your reading is the embryonic signs of things that happen in the model output threads of weather forums in winter. The most knowledgeable people are very good at examining and extrapolating charts from 19 bla bla and so on and what it might evolve into but fail to realise that Weather has a mind of it's own, is not a respecter of past events and will do what is relevant to the time. I have been around some 50 years or more studying weather and I have been caught out many a time thinking that winter armageddon is coming, only to be disappointed 24 hours later by rain lashing on the window panes. My best advice is to take things one day at a time because forecasting winter weather is as chancy as winning the lottery and for what it's worth the current northern blocking is only serving to give us a very wet Autumn spell and will bear no impact on what the Winter 2012/13 holds in store for us.

The problem does not lie with the posters who look at the output and (with reason and explanation) give their opinion to what may lay ahead. In fact it is fascinating and much can be learnt from reading such posts even if it does not pan out the way someone may have suggested. I love looking at the models and trying to work out what the weather may have in store a couple of weeks or so down the line. Similarly, I enjoy reading posts that talk about what may happen further down the line.

The problem is when some read these posts, take them as a done deal, run round telling friends and family that this is going to happen two weeks on Wednesday only for it to change and be left to look foolish. Then blame the posters for getting wrong.

If you look at the output you can see blocking and the chance that this will mean colder weather. Even the METO are suggesting this may be the case. Now if after reading this you feel it’s a done deal and you run round telling everyone and it changes, then please look inwards not outwards for the fool.

There are some that can be over enthusiastic in terms of the output and what this may mean. Cut through this but do not be surprised if people are, it is bound to happen when you think that we as a group study the models and discuss them in detail yet most people would think we are mad.

I enjoy your summaries but enjoy looking further down the line and enjoy reading posts on what may happen further down the line. GP's (and others) take on what may happen, although confusing to my little brain, is what I like more than anything else. So much can be learnt from reading such posts. So let’s not knock those who give this a go.

Edited October 12, 2012 by snow drift

[trickydicky]

I think what your reading is the embryonic signs of things that happen in the model output threads of weather forums in winter. The most knowledgeable people are very good at examining and extrapolating charts from 19 bla bla and so on and what it might evolve into but fail to realise that Weather has a mind of it's own, is not a respecter of past events and will do what is relevant to the time. I have been around some 50 years or more studying weather and I have been caught out many a time thinking that winter armageddon is coming, only to be disappointed 24 hours later by rain lashing on the window panes. My best advice is to take things one day at a time because forecasting winter weather is as chancy as winning the lottery and for what it's worth the current northern blocking is only serving to give us a very wet Autumn spell and will bear no impact on what the Winter 2012/13 holds in store for us.

The people who you refer to are the reason why I read this thread. If I want to know what the weather will do in the next 2 or 3 maybe 4 days, which tends to be the period you cover, then I can watch TV forecasts. However, they dont talk about background signals and what MIGHT happen in 1, 2 or 3 weeks time, so I come on here to find out, because I find it interesting. Everyone, whether a complete newcomer or an ex Met Office forecaster of half a century's experience, knows that nothing over that period of time is set in stone. What you are effectively saying is that forecasting the weather is hard, so why bother trying.

[Supacell]

The people who you refer to are the reason why I read this thread. If I want to know what the weather will do in the next 2 or 3 maybe 4 days, which tends to be the period you cover, then I can watch TV forecasts. However, they dont talk about background signals and what MIGHT happen in 1, 2 or 3 weeks time, so I come on here to find out, because I find it interesting. Everyone, whether a complete newcomer or an ex Met Office forecaster of half a century's experience, knows that nothing over that period of time is set in stone. What you are effectively saying is that forecasting the weather is hard, so why bother trying.

The forecasts I read from Gibby on this thread always go further out than 2-4 days but it then become an idea of what MAY happen based on the current models and not what WILL happen. I too find reading what will happen over the next 2-3 months entertaining but I would not then make plans around the fact that current CFS charts are showing snow in December etc. I think that Gibby's forecasts are some of the most balanced and easy to understand for the masses on this or any site. There can be problems with some people cherry picking signals that they want to see out of the many charts that are available, and if other people take this as gospel then it does lead to disappointment. I have done this many times in the summer at the first signs of thunderstorms - but have learnt, over time and disappointment, that ahead of 2-5 days (dependent on the situation) is just an idea not a definite.

Anyway, I'm off back to lurk in the convective thread until next April

Edited October 12, 2012 by Supacell

[Frosty.]

Just happy I am not!

Wait and see, take care not to do any knee jerk reactions, play it much as they are doing until they have more corroborating evidence for one way or the other.

Very wise words as it now looks like sunday will be a fairly benign day with just a little rain up north but it does look rather cloudy with limited brightness. it just highlights how the models struggle with systems approaching from the south.

[chionomaniac]

The beauty of the model thread is that we can have the wonderful down to earth analysis from Gibby that explains what is likely to occur in a no nonsense way, alongside the more speculative reasoned analysis of what could occur from the likes of GP. The thread is here for all to benefit from both sides of the coin and should not be based on either one or the other. And so let us not continue debating this but on what the models are showing. Thanks.

An example of how autumnal northern blocking can simply fade away in this morning's GFS........

[BLAST FROM THE PAST]

The beauty of the model thread is that we can have the wonderful down to earth analysis from Gibby that explains what is likely to occur in a no nonsense way, alongside the more speculative reasoned analysis of what could occur from the likes of GP. The thread is here for all to benefit from both sides of the coin and should not be based on either one or the other. And so let us not continue debating this but on what the models are showing. Thanks.

An example of how autumnal northern blocking can simply fade away in this morning's GFS........

And that is the crux of the model thread? What the models are showing and how likely they are to maintain and be right? And they are showing unusual northern blocking and a jetstream way south of normal.

Models are trending away from neartime cold and it appears to me that we may see any colder thrust more backend of the month. A more stormy and wet period looks likely first with a very southerly tracking jetstream. Certainly not the usual autmn fayre.

BFTP

[Gibby]

Good morning. Here is the morning look at the 00zs from the big three models this morning.

All models show a very complex set up with a Westerly flow developing over the UK with a showery trough moving East into SW Britain through the day. In the far North yesterday's Low moves slowly away NE though the next 24 hours. This pattern remains for the weekend with Low pressure covering the air space over Britain delivering further showers with a disturbance running East over the English Channel on Sunday increasing a risk of more continuous rain in the far South for a time. On Monday a weak ridge of High pressure may bring a dry and brighter day before all models show a deep Low pressure approaching the West on Tuesday with a band of wind and rain sweeping NE over all parts.

GFS then shows complex Low pressure centres swirling around close to Western Britain for a week or so with strong Southerly winds and rainfall for all, heaviest in the West. Late in the run High pressure does build over the UK with dry and bright weather replacing the rain though fog and frost problems overnight would be introduced.

The GFS Ensembles maintain the changeable and sometimes wet pattern with 850's averaging close to the long term mean through the period of the run. There is no clear trend of anything other than average conditions being maintained in an Atlantic based flow of winds throughout.

The Jet Stream is shown to maintain a position close to or South of Southern Britain for the next week or so.

UKMO for midnight on Thursday shows a complex and deep Low pressure centre over NW Ireland and Scotland with a SW flow over Britain as a whole. Troughs embedded in the flow would ensure spells of rain and heavy showers in temperatures close to normal.

ECM too shows a chain of Low pressure from a position west of the UK to the South of Greenland. These amalgamate to form one deep complex Low pressure near NW Britain for the rest of it's run, filling slowly later. There would continue to be spells of rain and showers in strong winds for all with winds and temperatures easing back a bit later.

In Summary there is no change in the overall pattern from last night this morning. Low pressure remains in total domination with plenty of rain and showers likely in the next few weeks. GFS does offer a dry up at the end of it's run but it's too isolated in nature to be taken as a new trend. As always it won't be raining all the time and with low pressure programmed to be just West of Britain for much of the period temperatures should hold there own near to normal with the heaviest rainfall likely in the Western half of the UK.

[Glacier Point]

Mischievous Ed..

The GEFS ensemble mean at t360 (yes that far out) comes up with a stonking positive anomaly over the Arctic. At that range, this is a very strong signal, mirrored by the ECM which suggests a sharp negative zonal wind anomaly over high latitude (big -AO signal).

[Frosty.]

This highlights the uncertainty there was yesterday, it was beginning to look very disturbed on sunday across southern britain with a vigorous depression bringing heavy rain and gales to the south but a few hours later and now sunday is looking much drier with some brightness but fairly cloudy.

Edited October 12, 2012 by Frosty039

[chionomaniac]

What? Do you think that the GFS 00Z run could possibly be defaulting to a preset pattern, Stewart?

Now come on!

[BLAST FROM THE PAST]

Mischievous Ed..

The GEFS ensemble mean at t360 (yes that far out) comes up with a stonking positive anomaly over the Arctic. At that range, this is a very strong signal, mirrored by the ECM which suggests a sharp negative zonal wind anomaly over high latitude (big -AO signal).

One to watch Stew, Dec 2010 anomaly was picked up very early too due to the strength of it

BFTP

[BLAST FROM THE PAST]

This highlights the uncertainty there was yesterday, it was beginning to look very disturbed on sunday across southern britain with a vigorous depression bringing heavy rain and gales to the south but a few hours later and now sunday is looking much drier with some brightness but fairly cloudy.

Its the BBC,lets see the tea time forecast, it will likely be different again...but interesting to see the big change.

BFTP

[johnholmes]

Its not the BBC but the Met O Fred, and simply highlights my post last evening about not doing knee jerk reactions. To me the Met O have not done any knee jerk reaction, simply refined the outlook. They always stressed the uncertainty, showed where ONE model had the rain and said keep watching.

Again I have no idea why weather systems from S-SSW give so much trouble. I would be very surprised if a small team are not working away trying to discover what is the problem from that direction.

By this time tomorrow the actual system can be tracked by surface and upper air observations as well as satellite so back to 'seat of the trouser' type forecasting for me. However I don't think Met staff have that luxury and have to accept the model outputs.

adding to the above after looking just quickly at the GFS output at 500 and 300mb along with the 3 latest Fax charts from UK Met.

These shows a path consistent with the upper air on GFS for the next 48 hours, that is running ENE from its 00z position, initially not deepening possibly even filling slightly before starting to deepen a little but not much.

The upper air pattern is looking consistent with no major deepening.

The next system - surface and upper air is perhaps the one that shows signs of deepening?

Edited October 12, 2012 by johnholmes

[BLAST FROM THE PAST]

Indeed John, they are going with each model run and this current crop of 'presenters' don't cut the mustard IMO. There is not enough interpretation in there.

BFTP

[SMU]

Mischievous Ed..

The GEFS ensemble mean at t360 (yes that far out) comes up with a stonking positive anomaly over the Arctic. At that range, this is a very strong signal, mirrored by the ECM which suggests a sharp negative zonal wind anomaly over high latitude (big -AO signal).

The GFS image above shows a PERFECT standing 4 wave pattern supported but a very large positive height anomaly over the pole-

In order to understand how rare this type of pattern is & what it means you can associate it with a single blocking high, a 2 wave pattern & then 4 wave Pattern -

It also directly correlates to the timespan & longivity of a particular type of pattern persisting for a long period of time-

So a SINGLE waved pattern is where you you have just ONE mid to high Lattitude High pressure blocking the flow-

Around the Hemisphere this could be in the states as a +PNA high, or a -PNA High ( west or east High pressure) An Aleution High or even a Russian high-

On the single highs the rest of the hemisphere can operate normal mobile conditions,the real influence of that single high comes on the western & Eastern flanks-

Single High pressure situations for the UK are often a Mid atlantic high, a Greenland High or a Scandi high, longivity of these is generally 3-5 days as to sustain it the whole hemispshere needs to loaded to blocking, you find with one high they usually subside & move back towards the equator or for greenland usually fade away -overcome by the jet.

A two wave pattern is a lot stronger patter & can lock off half the hemishere leaving the polar vortex cut off over the other half of the arctic-

Typically for us the most common cold ones for us are the Big + PNA high & Greenland high OR the greenland high & the Scandi High-

heres a good example of a solid 2 wave pattern

http://modeles.meteociel.fr/modeles/reana/1963/archivesnh-1963-1-31-0-0.png

Note the 2 huge high pressures with the vortex split & squashed underneath-

The longivity of these- because the jet has been split & slowed or the jet has been large scale displaced is sometimes 10 days PLUS-

Now for a 4 wave pattern youve got to scour the archives- the starting point is finding extreme negative AO's because you cant break low values on just one standing high or even 2-

( just a note with big -AO's the blocking still needs to be in the right place for us)

Anyway MOST- AO months-

Feb 2010- -4.266

Jan 1977- -3.767

Dec 2009- -3.413

However we want to find the most -AO days to find the best 4 wave pattern-

ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.ao.index.b500101.current.ascii

I have gone through the daily index fairly quick & found whagt I think are the 3 lowest days although I may ghave missed a couple-

lowest AO

Jan 15 1977 -7.433

http://modeles.meteociel.fr/modeles/reana/1977/archivesnh-1977-1-15-0-0.png

Jan 19 1985 -6.3

http://modeles.meteociel.fr/modeles/reana/1985/archivesnh-1985-1-19-0-0.png

Mar 5 1970 -6.3

http://modeles.meteociel.fr/modeles/reana/1970/archivesnh-1970-3-5-0-0.png

On all the charts the pole has huge +VE anomalies & several standing waves-

The 4 wave pattern is the holy grail of MID LATTITIUDE cold- as on this type of pattern can be locked up to a month- poss longer-

For reference our historic months that we always trawl out every winter, dec 81, Jan 63 & so on have -AO's on average of -4 - with a few -5's thrown in-

So if your looking at the ensemble data longitivty of cold generally starts around -3 values-

if we look at todays GFS ensemble mean we are seeing -4 values reached which is rare as hens teeth on October-

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao_index_ensm.shtml

2002 sticks out as a very low reading ,month with a -5 in there

http://modeles.meteociel.fr/modeles/reana/2002/archivesnh-2002-10-18-0-0.png

& Oct 1981 sticks as as consistently low....

Anyway- gone off on a tangent a little-

have a gd day

S

[johnholmes]

Indeed John, they are going with each model run and this current crop of 'presenters' don't cut the mustard IMO. There is not enough interpretation in there.

BFTP

don't blame them too much, they are fully trained forecasters in the main and have to 'toe the party line' much more than in my day, the days of the likes of Bill and Ian. Even then the red line would ring at times after an Ian broadcast with the head of that department complaining about his presentation.

[chionomaniac]

I found a 4 wave pattern Steve - it just hasn't happened yet!