Winter Model Discussion 12Z 09/01/13> The hunt for cold ?

[EGHH]

My (poor) understanding was that the control run is based on the actual data collated at 00z, 06z, 12z, and 18z and pugged into the compuer forecasting model. These data are then pertubated a little and these also run (albeit at a lower resolution i.e. quicker). The forecasters then use their experience to judge which of the pertubations is most likely to be true and this becomes the operational run.

Please correct me if I'm really off the wall with my understanding.

I doubt it to be honest. The control run is simply the same set of initialization data as the operational run but run at the same (generally lower) resolution as the rest of the ensemble. Essentially you'll see cases where the operational and the control agree (so the higher resolution of the operational isn't crucial in finding the evolution) and cases where the control goes off on it's own - indicating a situation that's sensitive to resolution, thus error (or smaller scale features). The remainder of the ensemble runs are created from initialization data that is tweaked in a special, statistically significant way. The results of these run show how sensitive the evolution is to errors in the initialization data.

It is done thus because it's impossible to sample the whole atmosphere at the same time. So, the observation data that is received is assimilated into yet another model, which produces an approximation of the whole atmosphere at the initialization point. You see, this is an approximation of an approximation of... so the ensembles show how sensitive the situation is to these errors in the start point and, in a sense, how sensitive the current base state of the atmosphere is to change. That's before you even get into the computational approximations (parameterisations) to the thermodynamic equations that the models need to solve.

I think most forecasters will use graphs derived from the ensemble prediction systems to show the variablity in possible outcomes and use this data as a guide as to how certain one can be about a certain forecast parameter - such as temperature, precipitation etc. I think looking at them synoptically (other than characterising them by GWL type, for instance) is little more than of passing interest.

A more thorough look at how to use ensemble products can be found here:

http://www.ecmwf.int/products/forecasts/guide/user_guide.pdf

[No Balls Like Snow Balls]

What is shannon entropy-

Its the new sexy word of the week, highly in fashion, only to disappear in a weeks time for something else.

[Met4Cast]

What is shannon entropy-

It's the term the MO use when predictability drops

[Methuselah]

What is shannon entropy-

The degree of turbulence in the River Shannon? I'm glad someone-else is as in-the-dark as I am!

[EGHH]

What is shannon entropy-

See here, Steve:

http://forum.netweather.tv/topic/75477-winter-model-discussion-cold-hunting-080113-00z-onwards/page__view__findpost__p__2469633

[adalton]

What is shannon entropy-

http://en.wikipedia.org/wiki/Entropy_(information_theory)

Make of that what you will !

[Yarmy]

What is shannon entropy

Uncertainty, in a nutshell. Comes from Information Theory. I actually studied it in a Maths course many moons ago, but I only first heard it used in relation to forecasting by Ian F on here.

[JP1972]

In information theory, entropy is a measure of the uncertainty in a random variable.^[1] In this context, the term usually refers to the Shannon entropy, which quantifies the expected value of the information contained in a message.^[2] Entropy is typically measured in bits, nats, or bans.^[3]

[snowbob]

What is shannon entropy-

technical term for who knows

[Shunter]

What is shannon entropy-

A female meteorologist from Abbey Wood... Steve .....lol

Seriously.....it relates to the measurement of uncertainty

http://en.wikipedia.org/wiki/Entropy_(information_theory)

[BurntFishTrousers]

I thought everyone knew what Shannon Entropy was

[mountain shadow]

Ian Ferguson introduced the phrase a couple of days ago and basically means the models dont have a clue and any solution is possible.

[Coast]

and back to the models........

[Methuselah]

Or a polite alternative to 'WTF!'? Ian Brown, take note?

[johnholmes]

This SSW malarkey: Well it would seem that there is definitley some strong correalation between this and hemispheric blocking. Now is this an accepted fact by meteorological organisations and if so is it factored into the modelling process once taking place, or is it still the case that the models are reacting to atmospheric changes that are as a result of SSW? So basically are the models proactively instructed by the SSW data or are they merely responding and always trying to catch up to the data?

Sorry to be OT ................not.

your last bit is correct, they are responding to what the actual data at the start of the run shows way up into the Stratosphere nothing else, no data fed in to suggest one thing or any other.

Ian Ferguson introduced the phrase a couple of days ago and basically means the models dont have a clue and any solution is possible.

quite wrong as I suspect you know-its a meteorological phrase with a precise if hard to understand for a layman meaning.

Try their web site or e mail them if you really would like the correct answer.

[nick sussex]

Or a polite alternative to 'WTF!'? Ian Brown, take note?

Yes that will go down in net weather folk lore! Where were you when those immortal words were mentioned!

Lets hope the GFS drops its current trend otherwise you might need to add an extra server to the swear filter!

[johnholmes]

the the Shannon entropy

this link will keep you occupied for a while

http://www.bing.com/...Box&FORM=IE8SRC

What is entropy used to be a favourite on Met O promotion boards-I suspected it was because even the senior staff wanted someone to give them a simple accurate explanation!

Edited January 9, 2013 by johnholmes

[memories of 63]

I doubt it to be honest. The control run is simply the same set of initialization data as the operational run but run at the same (generally lower) resolution as the rest of the ensemble. Essentially you'll see cases where the operational and the control agree (so the higher resolution of the operational isn't crucial in finding the evolution) and cases where the control goes off on it's own - indicating a situation that's sensitive to resolution, thus error (or smaller scale features). The remainder of the ensemble runs are created from initialization data that is tweaked in a special, statistically significant way. The results of these run show how sensitive the evolution is to errors in the initialization data.

It is done thus because it's impossible to sample the whole atmosphere at the same time. So, the observation data that is received is assimilated into yet another model, which produces an approximation of the whole atmosphere at the initialization point. You see, this is an approximation of an approximation of... so the ensembles show how sensitive the situation is to these errors in the start point and, in a sense, how sensitive the current base state of the atmosphere is to change. That's before you even get into the computational approximations (parameterisations) to the thermodynamic equations that the models need to solve.

I think most forecasters will use graphs derived from the ensemble prediction systems to show the variablity in possible outcomes and use this data as a guide as to how certain one can be about a certain forecast parameter - such as temperature, precipitation etc. I think looking at them synoptically (other than characterising them by GWL type, for instance) is little more than of passing interest.

A more thorough look at how to use ensemble products can be found here:

http://www.ecmwf.int.../user_guide.pdf

Wow. Thanks for the clarification (!) So... the butterfly flappinf its wings in the Amazon is even more important than I thought

[SMU]

So its 2013's catchphrase.....

Like ...

The 06z is Shannon Entropy or

Will it snow in Shannon Entropy...

Only 60 mins to go so i will be back then....

[JP1972]

So is a SSW Event the only event which can lead to such model confusion or (God forbid) are there others?

[legritter]

Afternoon all, over the worse of me flu and realy feeling good about the modells and data .this post is aimed at new folk etc .GFS showing as much as 30MB difference on some of its charts later next week .but as iv stated before you can read between the lines .if you take this mornings run we now have GFS bringing in an active atlantic depression ,in one way there is a reason for that somewhere in the modelling ,and there is i think as much possibility that this could indead arrive but most likely on a different track or equally as modelled or even shoot off s/east into europe .A good run from a cold perspective tonight from ECM would go down a treat ,but remember if it isnt theres always tomorrow .now going by current modelling and data as of mid day today the period sat to next wed could deliver the goods for some .we have in my opinion nearly, if not all the ingredients for a perfect cake but some will get a slice and some will miss out .it will be very interesting to watch unfold and i would suggest any new members to pop into the learning area and read up on SNOW and whats needed synoptically etc .also get off computer and take a look at cloud formations and wind directions .dont forget FAX Charts from Met office updated a couple of times per day and with the human touch which i can assure you is done with love and dedication as iv watched professional meteorologists prepare these many times whilst i was quite often a guest when i was in the ROY Met society .just one hour till GFS will it tie the NOOSE Ready for the drop .enjoy as its always been [weather] a roller coaster ,cheers

[SnowBallz]

This SSW malarkey: Well it would seem that there is definitley some strong correalation between this and hemispheric blocking. Now is this an accepted fact by meteorological organisations and if so is it factored into the modelling process once taking place, or is it still the case that the models are reacting to atmospheric changes that are as a result of SSW? So basically are the models proactively instructed by the SSW data or are they merely responding and always trying to catch up to the data?

Sorry to be OT ................not.

SSW isn't my expertise (chio, especially for that) but my understanding is that there is evidence of an immediate modelled relationship between stratosphere and troposphere, as the effects can be modelled owing the fact that the upper atmospheric temperature readings will be included into the calculations. There will be a part of the algorithm which determines the equation that deals with a warm/cold stratosphere, and how this propagates down through to the troposphere in time.

What I gather from Ian Fergie, is that the extreme variance (Shannon entropy) comes about more from a lack of confidence in NWP being able to correctly model the longer range cause:effect, of the SSW; namely a more blocked pattern, owing to an obliterated PV. In essence, I think the NWP prefers to revert to default, whereas the SSW hypothesis theorises something completely opposite. I would imagine that, as time progresses and the SSW effect is both more pronounced and comes within higher-res range, that such variance would tend to moderate.

So, in summary, I think we see some immediate effects of the SSW within NWP - but I would imagine that the propagation rate/decay is what drives a great deal of the entropy within the short-term. Not wanting to speak out-of-turn, but I'd imagine the folks at Exeter retain the view that the more substantial effects of the SSW, ie: the more blocked, sustained pattern, is yet to be picked up in NWP. I've no idea when that may come about, but I'm sure Ian Fergie will let us all know when there is greater confidence from his colleagues in the mid-long term outlook.

Complete novice when it comes to SSW, so please don't take the above as gospel: chio is the oracle on that, me thinks.

[garbagebags]

Very simple (if slightly OT) question.

Are the models more reliable in summer or is it the same?

[nick sussex]

As I'm bored waiting for the next installment of model drama I've decided to subject you all to yet more upstream charts!

Heres the DGEX which is the extended mesoscale model for the USA at 96hrs from the 06hrs run:

Its not an easy chart to read but theres much less energy heading ne in the wake of the shortwave moving ene:

Heres the GFS 06hrs run:

You can see thats already developing a distinct shortwave to the sw.

Heres the link for the DGEX site:

http://www.emc.ncep.noaa.gov/mmb/mmbpll/dgexops.conus/

Edited January 9, 2013 by nick sussex

[Mark Neal.]

Just like to add my views on model output at the moment. We can't have great confidence in what happens beyond the end of the weekend, I was started to think we were going to get even more model agreement then the 6z GFS came online and turned the other way. Its worth mentioning that despite that, there are still more ensembles supporting cold thereafter than say a few days ago so an improvement of such. Would be fantastic to see 12z GFS/UKMO/ECM sing from the same hymn sheet, but most importantly from my viewpoint will be to see more ensembles support aswell. Anyway enough of me nattering on, enjoy the 12z evening entertainment!