General Model Output Discussion

[beng]

not really beng as the eastern upper trough is almost under the ridge, it needs to be east of the centre of gravity of the ridge for it to be a true omega pattern.

One thing that the model keeps showing at times is not too dissimilar to just prior to Christmas.

That is almost an omega block in the northern half with a more mobile W'ly flow south of it.

Thanks John - appreciate your comments as always Looks cold anyway

i've asked this question many times ben and never had a definitive answer. to me, that output is purely representative of the op run. i have looked at it on runs when the op is clearly an outlier and yet it still reflects the op output. nowhere on the page does it mention the word ensemble. if i am right, i think that too much is made of these charts. we pretty well know what they are going to show if we've looked at the operational runs. at T168/T240, we should be looking at ens means, not operational ones.

Hi Nick, If it is just the op,then I agree that it's not that meaningful - it does say it's the mean though at the bottom of the page - and that high pressure anomaly on that chart looks to be centred slightly further East than tonight's operational IMO.

[pyrotech]

I've attached a couple of FAX charts, one of them has a feature that I don't know what it is, the other has the 528 DAM line surprisingly far north.

The feature I don't know is the warm front with the white semcircles rather than black a la normal warm front. Could someone explain that to me.

The other chart. the T120 actually has the 528 DAM line bisecting the country East west. Isn't this likely to bring more marginal conditions to the South ?

Its an upper air warm front, this means that although at height its warm it will not shift the cold air at the surface if and when it hits the UK.

This really has potential for blizzards and serious conditions in my humble opinion as it is a classic set up

[summer blizzard]

isn't monday to wednesday the majority of the working week!? Not the exemption. I really don't think we can make any predictions on dry or wet based on the models as we have seen this last week with predictions by many for a dry cold spell.

The event in question will only last upto 48 hours, however the GFS and ECWMF have differing timeframes.

As for being unable to predict precipitation amounts, this week was forecast to be cyclonic resulting in instibility, however next week is forecast to see higher pressure with precpitation amounts being knifeedge as a result.

As for sunday, i am also sceptical as to precipitation amounts, it is an occlusion running into high pressure with no real low centre formed yet and the 528 dam line to the north, which makes me suspect that things will be marginal as a result and also that there won't be much intense precipitation as a result.

[SizzlingHeat]

cant see sunday being snowy. GFS consistent with NE winds bringing most of the activity further south east and missing britain only leaving a legacy of cloud and drizzle/snizzle

Needs to tilt that wind direction to the ESE then it will be good, cant see it i think the most of the snow has been finished with today in this cold spell. Just cloudy and cold on the weekend

[NorthNorfolkWeather]

Hi NNW

I think you will find that the 528 DAM line loops around the UK in the first instance, leaving us on the right side of it.

yep, I saw that on the 72 hour chart, on that one I was more interested in what is the definition of that "Disconnected" Warm front. Normally, warm fronts ( unlike cold fronts) either have an axis point where the cold front and the warmfront meet, or there is an occlusion, and I understand all of those, but in the 72 hour chart the 'definition' of the warm front is different having 'hollow' rather than solid circles, I would like to know what the implication of that is.

And the 120 chart the one where we have a north south split by the 528 DAM line

[Optimus Prime]

cant see sunday being snowy. GFS consistent with NE winds bringing most of the activity further south east and missing britain only leaving a legacy of cloud and drizzle/snizzle

Needs to tilt that wind direction to the ESE then it will be good, cant see it i think the most of the snow has been finished with today in this cold spell. Just cloudy and cold on the weekend

Umm...where have I heard this before?

[bluearmy]

Hi Nick, If it is just the op,then I agree that it's not that meaningful - it does say it's the mean though at the bottom of the page - and that high pressure anomaly on that chart looks to be centred slightly further East than tonight's operational IMO.

but thats the point Ben - the anomolous mean of the op output between T168 and T240. no mention of ensembles. the other thing is that chart comes out too quickly for it to be ensemble based IMO. the epsgrams aren't available until well after this chart is produced.

anyway, still no definitive answer !!

[NorthNorfolkWeather]

Its an upper air warm front, this means that although at height its warm it will not shift the cold air at the surface if and when it hits the UK.

This really has potential for blizzards and serious conditions in my humble opinion as it is a classic set up

Thanks Pyro,

one of those things, once you rknow it it's easy, until you do, it's a headscratcher.

Edited January 6, 2010 by NorthNorfolkWeather

[SizzlingHeat]

Umm...where have I heard this before?

you have to admit, its not looking the best for sunday at the moment. DP seems a little more marginal with less cold uppers and 528dam seeming to evaporate away to the west. Just feel it will be cloudy and very cold but generally just drizzly on sunday rather than snowy unless the winds veer to the east or se a little more.

[Nath]

The 120 fax chart IMO would bring very severe conditions to a lot of southern and eastern areas. And I dont think the temps are in any way marginal whatsoever. Guaranteed snow from that chart and lots of it.

[Neilsouth]

cant see sunday being snowy. GFS consistent with NE winds bringing most of the activity further south east and missing britain only leaving a legacy of cloud and drizzle/snizzle

Needs to tilt that wind direction to the ESE then it will be good, cant see it i think the most of the snow has been finished with today in this cold spell. Just cloudy and cold on the weekend

Sorry but thats rubbish , this isn't your average cool easterly from a cool/cold europe. Even looking at the gfs precipitation models it goes against what you are posting

[snowspotter]

you have to admit, its not looking the best for sunday at the moment. DP seems a little more marginal with less cold uppers and 528dam seeming to evaporate away to the west. Just feel it will be cloudy and very cold but generally just drizzly on sunday rather than snowy unless the winds veer to the east or se a little more.

Dewpoints look ok to me and you dont need 528 dam or less in a continental flow for snow (at least thats my understanding think you can go to 540 and still get snow)

[pyrotech]

Nothing is set in stone for sunday but here is what i see if it progreses.

Alot of moisture in that warm front with potential to form a low as it crosses over channel into uk

Its a warm front that rides over the cold not moving it.

its crossing a warm English channel. Yes it become occluded over the channel, but could again give moderate to heavy snow over long period.

Meto mention it at 5 days out with advance watch for it.

The models all pick it up but its too far for computers without the important human touch to claim a fix on it.

If your looking for potential then thats it (huge potential for signifigant snow and disruption). atleast it will keep this forum alive over next few days and possibly end servers into meltdown sunday

Edited January 6, 2010 by pyrotech

[SizzlingHeat]

Sorry but thats rubbish , this isn't your average cool easterly from a cool/cold europe. Even looking at the gfs precipitation models it goes against what you are posting

Cant see much precip from this and only very light so drizzle/ snizzle as i suggested. Hope im wrong but just dont think this weekend will deliver

[tinybill]

Umm...where have I heard this before?

i could post my early post i got call a snow rammper!! that showed wide spred snow sat/sun now news 24 weather man was show great concern for this weekend

[Bobby]

you have to admit, its not looking the best for sunday at the moment. DP seems a little more marginal with less cold uppers and 528dam seeming to evaporate away to the west. Just feel it will be cloudy and very cold but generally just drizzly on sunday rather than snowy unless the winds veer to the east or se a little more.

The Met Office are concerned as they already have warnings out for it. I think there's a lot of potential in that set up and expect to see precipitation upgraded as we get closer. NOGAPS show what could happen (and some GFS ensembles). Don't see how it could be marginal also with uppers generally -6 at mildest to -10, unless you're nearer the E/NE coasts.

Edited January 6, 2010 by Barb-

[NorthNorfolkWeather]

I can see why there is concern (from the METO) for Sunday :-

http://www.wzkarten3.de/pics/archive/ra/1996/Rrea00119960126.gif

Not quite the same as what we are looking at for the weekend, because this time the High is a little closer. But the PPN will be associated with the transfer of an upper level cold pool East to West. There will be nothing marginal about it. Minor changes in the charts are obviously possible between now and then, but that archive chart gave widespread heavy snowfall across many parts - even in Northern Ireland.

Thanks Ian

good explanation

[Neilsouth]

Cant see much precip from this and only very light so drizzle/ snizzle as i suggested. Hope im wrong but just dont think this weekend will deliver

gfs cannot accuratly predict precipitation from convective showers , take in point the 4cm we had the other night

[Severe Siberian icy blast]

As we go into the next wk we keep the winds coming all the way bk to the east , so why do the very cold uppers subside? Is it a warm front coming right through the country ?? If so , i still dont understand why the cold aor would vanish .

Comments pl

[weather eater]

Three things to add re precipitation at the weekend

1 The GFS is unreliable for precipitation at that range

2 I can't see the MO issuing a warning if it has no merit

3 We know that from this weeks events that getting precipitation right is frequently a now-cast situation

[pyrotech]

Come on we all know that percipitation amounts and location means nothing on the models this far out.

What we see is a likely hood of an upper warm front approaching the Uk. this with sustained deep cold over the UK.

Any more than that is guess work and most on here know that.

IT HAS POTENTIAL!

Fully agree with weather eaters post.

Edited January 6, 2010 by pyrotech

[Richie V]

i could post my early post i got call a snow rammper!! that showed wide spred snow sat/sun now news 24 weather man was show great concern for this weekend

Indeed, temp never set to rise above -2c here till atleast monday with very severe cold minimas ovet the weekend, the next person to say "marginal" will be whipped naked through the streets of Barnsley with piano wire

Edited January 6, 2010 by Chassisbot

[Nick F]

Less sign of realistic mild invasion from the SW on the 18z tonight - with any Atlantic troughs trying muscle in from the SW keeping further at bay, and a cold easterly looks like continuing in the reliable time frame, at the surface, though uppers do warm up somewhat. GFS can sometimes be a little too progressive in breaking a block down from the SW anyway.

My thoughts for the next few days and also a brief look at the weekend are in my blog just updated:

http://forum.netweather.tv/topic/59644-new-year-cold-spell/page__gopid__1714901entry1714901

[swilliam]

Hi NNW

I think you will find that the 528 DAM line loops around the UK in the first instance, leaving us on the right side of it.

No it does not and we are not - I brought this up when the chart came out last night.

[Joneseye]

Cant see much precip from this and only very light so drizzle/ snizzle as i suggested. Hope im wrong but just dont think this weekend will deliver

The event we have just had over the last 24 hours is proof how these precip charts are useless at this sort of range.

I had been following the front coming south from 5 days out and it was not until 36 hours notice that the GFS picked up on the threat of something more than the light precip that it was showing. The good thing is that we are edging ever closer to finding out.