General Model Output Discussion

[Tom D]

Can't help but think the 18z GFS has completely overblown the Atlantic low by 20mb or so. Doesn't fit in place with the ECM or any other models how deep that low is by T+165 and how close to us it is.

[swilliam]

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.

I think they are the mean of the ops for the several days in question. Not the mean of the ensembles and the days in question. If it was it would not show any features as it would be so smeared out (like the average of the ensembles shown on wetterzentral but also averaged over several days). So yes you are right they are not very helpful these charts as they show the average of several days charts but everyone seems to like them.I think the average of the ensembles are more useful but no one seems to use them.

Edited January 6, 2010 by swilliam

[Richie V]

For those that think it will be marginal see Nick f's blog

"Into the weekend, upper cold pool moves in as a bitterly cold easterly kicks in, 850 temps of -10 to -12C across England and Wales on Saturday, and with it snow showers or longer spells of snow at times penetrating well inland across central areas from the N Sea both Saturday and Sunday, heaviest falls always across the east though. Even Ireland doesn't look like escaping, with the cold uppers and easterlies bringing snowfall onshore off the Irish Sea by Sunday."

[cyclonic happiness]

I feel a bit of a backtrack from the 18z the high that was progged to sink in FI is now holding it's own much further north, yes it's pulling up southerlies but it is FI and the highs movement north is a very good sign, and also the fact it's not budging eastwards.

I see no atlantic breakthrough proper, maybe just a 'less cold' blip.

[NorthNorfolkWeather]

Interesting 'Pub Run'. Nothing really from the South West up to the T184, although we are in a SSE by then. Uppers are varying a bit, almost unusual to see 850's of -4 rather than -10. Still not warm by any means.

After that we go into a standard GFS progresive low, so we'll discount that until it's in the range of the fine grained model

[kold weather]

It'd become very marginal for the coasts by Sunday afternoon I'm pretty sure about that, temps and dew points both getting upto 1-2C suggests to me unless we get heavy precip it'll all be getting very sleety for those on the east facing coasts, inland it probably wouldn't be nearly as much an issue...but trust me those onshore winds can be huge problems, I found that out today where it took heavy snow to finally get it settling....that was all thanks to an onshore flow just raising those daytime temps too much despite constant light snow throughout pretty much all the day.

However its something that needs watching IMO, it doesn't look that intense BUT it looks very prolonged, therefore got to be thinking there could be some decent falls and amounts away from the coasts IMO.

Once again the GFS creates another huge dartboard low at 144hrs, yet another 955mbs low progged...I seem to recall the low for Sat in the Atlantic was progged at 955mbs, now only at 965mbs briefly...this 10mbs difference can make a big difference to what happens and the likelyhood of a cutoff low.

Edited January 6, 2010 by kold weather

[Optimus Prime]

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 precip charts are pretty useless. The DP may well be marginal right on the coast but inland it ain't gonna be a problem. History has shown us it can snow at -3c 850 HPA with low level cold moving in from the East/SE I don't think you quite understand the semantics of all this.

[thegreat316]

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.

think you are wrong there, gfs did a good job over 72 hours out locating the heavy ppcn

over 3 days out and almost a bullseye

[Tom D]

think you are wrong there, gfs did a good job over 72 hours out locating the heavy ppcn

over 3 days out and almost a bullseye

Thing is, didn't it then disappear for about 5 runs then reappear shortly before the event happened?

[NorthNorfolkWeather]

It'd become very marginal for the coasts by Sunday afternoon I'm pretty sure about that, temps and dew points both getting upto 1-2C suggests to me unless we get heavy precip it'll all be getting very sleety for those on the east facing coasts, inland it probably wouldn't be nearly as much an issue...but trust me those onshore winds can be huge problems, I found that out today where it took heavy snow to finally get it settling.

Hi Kold, depends so much on wind speed. The jan 87 dump in North Norfolk was so good because we has 30mph+ winds that gave us a 3 hour blizzard to get the snow on the ground, after that is was a simple top up. However I still feel disappointed when I saw rain come at us from the South East after a great week in the snow. 22years, and my son has NEVER seen snow like that since, but he can't remember it as he was 16 months old :unsure:

[Bobby]

Latest NOGAPS

Only NOGAPS but ties in with Met Office warnings... several inches widely there.

[NorthNorfolkWeather]

Latest NOGAPS

Only NOGAPS but ties in with Met Office warnings... several inches widely there.

Almost as important, look at the rain heading into Portugal and the Iberian Peninsula

[Nick F]

It'd become very marginal for the coasts by Sunday afternoon I'm pretty sure about that, temps and dew points both getting upto 1-2C suggests to me unless we get heavy precip it'll all be getting very sleety for those on the east facing coasts, inland it probably wouldn't be nearly as much an issue...but trust me those onshore winds can be huge problems, I found that out today where it took heavy snow to finally get it settling....that was all thanks to an onshore flow just raising those daytime temps too much despite constant light snow throughout pretty much all the day.

Yes, possible the North Sea coasts from Humber down to Kent could see sleet or rain, but 850mb temps and 850-1000mb thicknesses remain pretty low during Sunday, so snow shouldn't be a problem inland, especially with the snow cover.

[thegreat316]

Thing is, didn't it then disappear for about 5 runs then reappear shortly before the event happened?

yes weekend it slightly and moved it further west on latter runs but moved it back only the run before it happend

[bluearmy]

the ecm precip charts for monday show an increasing amount of frontal precip in the southwest. it would appear from the latest T120 FAX that the cold pool moving across on sunday will come to rest in the sw approaches where it will sit and throw instability northeastwards. could be some interesting surprises early next week for the southwest and wales methinks. remember feb this year - similar evolution, except we have a much denser cold pool of air in place and a stronger block to hold the shortwave in place once it forms.

[casparjack]

Come on folks - there is a thread with the mysterious title of January CET to discuss exactly that.

In my defence, it was a comment at the end of my reply, then I answered a direct question. It is also relevant to the discussion as the CET thread is largely dead, whereas we are now at a critical point and surely the model thread has a direct correlation with the ultimate CET figure, which many people find interesting?

Well I do anyway...

[Bobby]

the ecm precip charts for monday show an increasing amount of frontal precip in the southwest. it would appear from the latest T120 FAX that the cold pool moving across on sunday will come to rest in the sw approaches where it will sit and throw instability northeastwards. could be some interesting surprises early next week for the southwest and wales methinks. remember feb this year - similar evolution, except we have a much denser cold pool of air in place and a stronger block to hold the shortwave in place once it forms.

Where do you see the ECM precip charts, I know it was on an Icelandic site but I forget.

[bluearmy]

Where do you see the ECM precip charts, I know it was on an Icelandic site but I forget.

http://en.vedur.is/weather/forecasts/atlantic/#teg=temp&type=prec

[Eugene]

The last two GFS OP's in FI look like outliers to me, looking at the 12Z ensemble mean on wetterzentrale pressure remains high until towards the end and even then it looks slack, i think future GFS runs in FI will show HP over europe keeping us cold.

[Nick F]

T+96 and T+120 fax updates show frontal system developing across south on Sunday, still there on Monday too, with low developing in SW approaches, as I think bluearmy mentioned:

http://cache.netweather.tv/fax/PPVM89.png

http://cache.netweather.tv/fax/PPVO89.png

Could bring more prolonged snow across south inland if came off, though perhaps sleet/rain near south coast given less cold upper air the front separates from the near continent. Though quite a way off still to likely verify like that.

[J10]

the ecm precip charts for monday show an increasing amount of frontal precip in the southwest. it would appear from the latest T120 FAX that the cold pool moving across on sunday will come to rest in the sw approaches where it will sit and throw instability northeastwards. could be some interesting surprises early next week for the southwest and wales methinks. remember feb this year - similar evolution, except we have a much denser cold pool of air in place and a stronger block to hold the shortwave in place once it forms.

A repeat of that could be very nice indeed. I also think that the cold will last longer than the GFS is forecasting, as usual it is being over progressive IMO.

[summer blizzard]

Have been looking at the modeling and the low forecast for sunday is currently just west of the Azores, not a formed low yet but you can see it as a feature on the cold front of the bigger low, it will be interesting to watch this feature and see the diffference between the GFS and ECWMF.

[weather eater]

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

Yes we are,

Edited January 6, 2010 by weather eater

[summer blizzard]

As suspected, the feature on sunday has been downgraded, though it looks like the Met Office are backing the ECWMF soulution over the GFS for the early part of next week, with a developing low in the fray, this could bring some prolonged and heavy snow, though with the 528 dam line well north, again i do think that things could be marginal.

[Bobby]

As suspected, the feature on sunday has been downgraded, though it looks like the Met Office are backing the ECWMF soulution over the GFS for the early part of next week, with a developing low in the fray, this could bring some prolonged and heavy snow, though with the 528 dam line well north, again i do think that things could be marginal.

The DAM line is near and with this sort of feed and bitterly cold uppers of -6c to -10c I don't see any marginality away from wind facing coasts. Just flicking through the GFS ensembles and I think there's a general upgrade in intensity and duration of the precipitaion from earlier runs if I recall right.