FI Charts ( T120+ onwards) Winter 2020 **READ MOD NOTE IN FIRST POST**

John Hutton wrote: »

As a layman, can I ask a sincere question. There are lots of (exciting/scary depending on your perspective) charts posted, immediately followed by a consensus opinion that the charts do not mean much at all and probably won't materialise. If this is the case, what is the point of these charts if they never/rarely materialise?

I'm not having a go at anyone here, obviously they have a point in the context of this thread and for discussion etc, but I mean why are they made in the first place?

Others can give a more scientifically detailed explanation, but essentially, for several reasons, each day forward from your starting point adds a little more inaccuracy to the charts, and this accelerates exponentially once you reach day five and beyond. So in other words, the charts for later today are probably extremely accurate, for tomorrow are probably very accurate, for Wednesday are probably still quite accurate but slipping a lot, for Thursday are only fairly accurate and for Friday are a bit of a long shot. From Friday and beyond, you're into "anybody's guess" territory.

However, because these models are run several times per day (four times for the GFS, twice for the ECM and UKMO), you can start to build a better picture of what might be coming down the line by taking several runs in a row of all the models and trying to spot trends.

The reason most of us are cautioning that FI models should be considered highly hypothetical right now specifically, is because of the ongoing stratospheric event. Detailed stratospheric modelling is a relatively new science for these models and we have seen time and time again that when there is a large amount of uncertainty regarding developments high up in the atmosphere, the charts which are directly relevant to our weather tend to reflect that and swing wildly from one potential conclusion to another every time the models are run. This tends to continue until events transpiring in the stratosphere are "locked in" and the models can be more certain as to their effects closer to the surface.

To summarise, essentially, all of these charts are theoretical possibilities of what might happen a week or two from now. And each specific event is directly connected to other events around the world. When you look at a chart which is fifteen days away, it's a valid possibility of what the weather might do - but if you change one little variable on say day ten - for example, if a high pressure system which is expected to move away from its current location instead stays where it is - then the chart for day fifteen, which assumed that this feature would stay where it was, will be completely written off as a solution. But we can't know that until we get to day ten and see if the HP system does indeed move.

So essentially, these models are interesting for talking about the theoretical possibilities as to what might happen with our weather, but they must be considered only as potential outcomes among dozens of other possibilities. Until we have major improvements in (a) computing power, and (b) the amount of data we're able to collect about the current state of the weather at any given moment, model accuracy will continue to decline with each day you move away from your starting point in time. Thus, at the moment, charts with a timestamp of more than 120 hours (some would say 144 these days but the consensus is still that 120 is the gold standard) should be regarded as possibilities, but possibilities among many, many others.

Lads, what links do youse use to view the chats ?
There are so many charts on each of the models that I have no idea which is which... thanks

carltonleon wrote: »

Lads, what links do youse use to view the chats ?
There are so many charts on each of the models that I have no idea which is which... thanks

One of the easier ways to be view the basic parts of the main models is an Italian App you can download on app stores called "Meteo Models". One thing is for each model run you must clear the previous run by clicking a giant button on the home page. V easy to use after that.

carltonleon wrote: »

Lads, what links do youse use to view the chats ?
There are so many charts on each of the models that I have no idea which is which... thanks

From Netweather

https://www.netweather.tv/charts-and-data

hatrickpatrick wrote: »

On these points, a quick question: For as long as I can remember, veteran forecasters here and elsewhere have generally regarded the 6z and 18z GFS runs with suspicion, due as far as I know to their initialisation dataset being incomplete when compared with the 0z and 12z runs, and furthermore that while the 0z and 12z are lo-res from 192h onwards, the 6z and 18z runs are lo-res the entire way through.

Is this still the case, and does it also apply to the new parallel runs as well? It's for this reason that I've generally tended to disregard the 6z output in particular if it massively contradicts the overnight 0z run, but given how many times the GFS has been upgraded over the past decade, this view of run-to-run reliability could well be entirely out of date.

Aren't the 6Z and 18Z better at short-range verification compared to the other two runs? I'd imagine they'd keep them in their different configurations for that reason.

Also it's good to have disagreement in models!

Kermit.de.frog wrote: »

Good UKMO. Building blocks in place by day 5. Once we get that "trigger" low pressure to the northwest ready to move southeast it puts us in a good position for cold by day 7/8.

That will do Frog that will do.

Rougies wrote: »

Have I gone mad or is the 12z GFS late today?

yes it's delayed on the NOAA server, irritating!

Rougies wrote: »

Have I gone mad or is the 12z GFS late today?

Yep.. it's late - connection issue apparently.

The GFS is out on another platform according to our own MT over on netweather. Not as good a earlier runs today and cold spell short lived but battleground opportunities. Lads it’s never straightforward but plenty twists and turns yet.

There will be another meltdown on Nethweather if it isn't.

It could be an outlier, but what M.T.Cranium omits to mention is on a few runs now the GFS had wanted to make the cold spell brief. The good news is the models are building towards a colder turn, but if you are looking for a week or more of ice days you maybe disappointed. Personally i could live with a short cold spell, if it was very snowy- with the possibility of one major frontal snow event. That could happen if the boundary between competing airmasses were to be over Ireland.

nacho libre wrote: »

Personally i could live with a short cold spell, if it was very snowy- with the possibility of one major frontal snow event. That could happen if the boundary between competing airmasses were to be over Ireland.

Yep I'd be happy with a brief cold onslaught too. A good dumping be very welcome.

bazlers wrote: »

10 days away people many rides left on this roller coaster. I wont be happy until i see the words epic and historic and not just on netweather ; )

Oh I've held my season ticket for many years on here. The thrill is seeing thing slowly come together and then enjoy the loop da loops 😆

Mount Vesuvius wrote: »

Oh I've held my season ticket for many years on here. The thrill is seeing thing slowly come together and then enjoy the loop da loops 😆

Its like Christmas MV the build up can be better than the day itself. Lets hope we get mamy many many days looking forward to this one. Might just go our way.