General Model Output Discussion

[andy_leics22]

The last BBC forecast I saw was 11am this morning and the forecaster (forget his name) actually said the ppn would reach Southern Midlands, then move south again soon after. Yeah, beats me too

That is the forecast I saw too, truly baffled me because the GFS totally goes against that in every way imaginable. It even goes another 100-200 miles further North after it hits the Midlands. That is the complete opposite of what the BBC say will happen, couldn't be more different.

[nick sussex]

Still baffled by the lack of significance given to the snow potential tomorrow night onwards for here - where is the major snow potential in this chart - Central Scotland or the M4 corridor? Central Scotland.png

I think especially towards the west Midlands and east Wales where there could be a very big snow event, though still some margin for error but lots of precip, a steep temp gradient is a recipe for major disruption. I can understand you think perhaps theres a bias in here but i think its the case that theres just alot more members from further south. Equally the media concentrate on further south as i think they believe it's just more common up there. However looking at the temps and the amount of snowfall generally in Scotland its been a great cold spell for you up there and quite noteworthy given recent winters.

[SteveB]

That is the forecast I saw too, truly baffled me because the GFS totally goes against that in every way imaginable. It even goes another 100-200 miles further North after it hits the Midlands. That is the complete opposite of what the BBC say will happen, couldn't be more different.

But hasn't the GFS 12z brought the snow line back around 100miles south. & the ECM & UKMO + the GEM have never shown it that far north anyway.

GFS was on it's own, & now it's backing down.

[izi]

That is the forecast I saw too, truly baffled me because the GFS totally goes against that in every way imaginable. It even goes another 100-200 miles further North after it hits the Midlands. That is the complete opposite of what the BBC say will happen, couldn't be more different.

yeh - still baffled here too... gfs much further north still. I dont see how it has fallen 'inline' in terms of where the prcipitation is predicted to fall by it.

[lorenzo]

Can someone please explain the Three Letter Acronyms used on the model threads and also what the different charts represent.

I am not completely daft but basic terminology explanation would help us 'lay' readers dip into this thread.

Presumably one is for air temps at a certain height = potential for snow. And another is for precipitation.

If any one is patient enough to do this would be appreciated as i cant understand why folk are arguing between different charts validity or strengths or weaknesses.

[bennytes]

Can someone please explain the Three Letter Acronyms used on the model threads and also what the different charts represent.

I am not completely daft but basic terminology explanation would help us 'lay' readers dip into this thread.

Presumably one is for air temps at a certain height = potential for snow. And another is for precipitation.

If any one is patient enough to do this would be appreciated as i cant understand why folk are arguing between different charts validity or strengths or weaknesses.

start here lorenzo

http://forum.netweather.tv/forum/24-learning-area/

[anvilhead]

is that some sort of polar low off the n coast of scotland on that chart ?

[Guest North Sea Snow Convection]

Can you give us a link or quote it?

If you look in any number of the winter threads it has been posted by Yamkin at various times during this afternoon

Some consolidated agreement now taking place between the models, as suggested by both GFS and UKMO - with a further step taken towards the evolution of a cold easterly late this week

[Frosty.]

Excellent upgrades today in terms of increasing cold and duration from the gfs, ecm and ukmo BUT the meto update today was poor for the south with rain and sleet and constant threat of mild incursions although with these type of charts and if the ecm remains very wintry, i'm sure the update will be somewhat different tomorrow.

[Geordiesnow]

GFS has trended the mild air to be further southwards however thus far, it still has the low the most furthest North closely followed by the UKMO but at least the trend is further southwards on this run.

Decent UKMO run, not as good as the GFS regarding the easterly flow, much more slacker and shortwaves perhaps coming into play but as we know, those small details can change and them shortwaves can develop into longer outbreaks of PPN for some lucky people.

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

Looking cold at T+408!

[Thundery wintry showers]

I'll do an update on the blog about the next 48 hours with a look into the start of the New Year early this evening.

Just as a comment about those not accepting what the northern hemisphere markings show.

You are of course entitled to your opinion but do take my word for it-ECMWF on 80% if not more of occasions is superior to GFS and the other models.

It not only does better in this area, as it should, talk to the people on the forum who Storm chase in the US, and ask them which model they have most faith in and also the US forecast centres say in the summer, let alone now if you read the NOAA daily 6-14 day outputs.

Of course it will be wrong at times, but its less wrong and far less often than GFS is.

Don't misunderstand me, GFS at times can be stunningly accurate from a long way out but overall ECMWF is the better of the two.

...

I remember that during my 12Z model checks, running from T+96 to T+144, I found that the ECMWF was comparably prone to getting it wrong as the GFS, but whereas GFS sometimes threw up wildly inaccurate scenarios, the ECM would rarely do so, usually at least finding something that bore resemblance to the correct evolution. UKMO was usually let down by its T+144 outputs, and while the latest model performance charts don't seem to illustrate this for the Northern Hemisphere as a whole, I've seen a lot of over-progressive T+144 UKMO charts in the last few weeks.

Both UKMO and GFS 12Z have shown strong signs of a backtrack towards this morning's ECMWF run. It must have been a bit embarrassing for the people at GFS to have their model prog the low pressure significantly too far north even at just T+36 or so.

[Lowestoft]

Looking cold at T+408!

Sadly I know nothing about all this model watching stuff, but it does seem very scientific and clever. When you state T+408 does this mean 408 hours from now? If it does could one of the weather scientists explain to me how this chart above can be taken seriously? Thanks.

Edited December 28, 2009 by Lowestoft

[03jtrickey]

Sadly I know nothing about all this model watching stuff, but it does seem very scientific and clever. When you state T+408 does this mean 408 hours from now? If it does could one of the weather scientists explain to me how this chart above can be taken seriously? Thanks.

We can't really take that chart seriously since as you say it's way too far out. I think it was posted lightheartedly :lol: That model can be useful for looking at seasonal trends but it changes frequently. Last time I looked (yesterday) it was very mild at that timerange!

Edited December 28, 2009 by 03jtrickey

[kent]

Sadly I know nothing about all this model watching stuff, but it does seem very scientific and clever. When you state T+408 does this mean 408 hours from now? If it does could one of the weather scientists explain to me how this chart above can be taken seriously? Thanks.

It cant, bin it its utter fantasy at that range. Even plus 72 cant be taken as fact.

[izi]

Sadly I know nothing about all this model watching stuff, but it does seem very scientific and clever. When you state T+408 does this mean 408 hours from now? If it does could one of the weather scientists explain to me how this chart above can be taken seriously? Thanks.

it cant :lol: anything T+100~ should be taken as trend watching, not gospel

edit: i type to slowly obviously :-P

Edited December 28, 2009 by izi

[Grimsby Snow Lover]

Sadly I know nothing about all this model watching stuff, but it does seem very scientific and clever. When you state T+408 does this mean 408 hours from now? If it does could one of the weather scientists explain to me how this chart above can be taken seriously? Thanks.

Im not a weather scientist but I can assure you that it will most definetly change, as this is over a week away. Still nice to look though. The thing to look out for is to see if it is repeated over the next few runs.

[Michael Fishermans Friend]

you don't take it seriously it is a 'very rough' guideline - I've never seen a model which goes out that far either :lol: - it is 408 hours, probably turn out to be the opposite, but looking good in up to early next week (fingers crossed).

[Tom D]

Sadly I know nothing about all this model watching stuff, but it does seem very scientific and clever. When you state T+408 does this mean 408 hours from now? If it does could one of the weather scientists explain to me how this chart above can be taken seriously? Thanks.

Well that's a particularly long range chart, to be looked at to assess trends for medium-long term forecasting.

Most members usually say after +200 is the work of 'fantasy island', in that it usually changes dramatically with each run or completely over-progresses the situation (creating 1060 high pressures and 950 lows for example).

[Lowestoft]

Thanks to you all for explaining that.

[phil nw.]

http://www.meteociel...h=36&carte=2000 fax 36 hrs

Further north also

Interesting 12z GFS and Fax v.close together now regarding the placement of the frontal boudaries for T36hrs.

http://www.meteociel.fr/ukmo/fax/fax36s.gif

http://www.meteociel.fr/ukmo/fax/fax36s.gif

The fronts stalling across central england and wales.

If that verifies the snow would turn to rain,at least for a while in S.Wales and places just north of the M4,currently shown as the sweet spot for heavy snow.

This is going to continue change subtly over the next 12hrs or so i think.

[Guest North Sea Snow Convection]

Looking at the UKMO this evening at that suggestion of 515 dam air, how does that compare to the airstream of Jan 1987. Obviously it doesn't translate to as cold as that unique occasion - but what sort of level did we see then? Any technical expert know more on this subject?

Edited December 28, 2009 by North Sea Snow Convection

[Thundery wintry showers]

During the exceptional easterly outbreak of 11-14 January 1987, thicknesses nudged below 500 dam in parts of south-east England. There's no way we'll be able to sustain a pronounced enough easterly flow for long enough to bring thicknesses that low over to the British Isles- but usually, anything below about 522 dam gives a very high probability of falling and lying snow.

[TEITS]

Hi does that mean its further north from the last faxes!! thanks

If anything the front on the +48hr fax chart is further S from my region. Although for SW its slightly further N.

http://www.meteociel.fr/ukmo/fax/fax48s.gif

I cannot really see much difference except the alignment of the front.

[jaydee]

Interesting 12z GFS and Fax v.close together now regarding the placement of the frontal boudaries for T36hrs.

http://www.meteociel.fr/ukmo/fax/fax36s.gif

http://www.meteociel.fr/ukmo/fax/fax36s.gif

The fronts stalling across central england and wales.

If that verifies the snow would turn to rain,at least for a while in S.Wales and places just north of the M4,currently shown as the sweet spot for heavy snow.

This is going to continue change subtly over the next 12hrs or so i think.

i can,t see cardiff getting any thing as we are close to the sea ,but can anybody tell me i am wrong ,i would love to see snow as it was when i was 13 years old in the storm of 1963 it was something to behold .