General Model Output Discussion

[TEITS]

Despite not posting much on here recently I have followed the models and to be honest im very dubious of any output beyond Monday.

The ECM ensembles say it all really.

http://www.knmi.nl/exp/pluim/vijftiendaagse/Data/15DAAGSE_06260_NWT.png

For me personally im not looking for snow to fall on xmas day. At the moment I would say anyone who currently has around 3-5 inches of lying snow are likely to see some of this remain till xmas day. I don't believe the models are suggesting a significant thaw between Tues-Friday. The reason im hoping some of my lying snow remains is I haven't seen this since Dec 1981.

Lets also not forget that we are likely to see min temps drop as low as -10C if not lower over the weekend, with max temps equally struggling. As we know this pool of cold can be rather stubborn to shift.

Edited December 18, 2009 by THE EYE IN THE SKY

[Thundery wintry showers]

GFS 18Z btw would still support a widespread snow cover from the Midlands northwards on Christmas Day- even though the 850s rise a touch, the airmass remains cold at the surface. Only in the south of England would lying snow be likely to thaw substantially in that setup.

[MR EXTREMES]

GFS 18Z btw would still support a widespread snow cover from the Midlands northwards on Christmas Day- even though the 850s rise a touch, the airmass remains cold at the surface. Only in the south of England would lying snow be likely to thaw substantially in that setup.

but is there not a tiny chance that milder air wont make it that far and the whole country stays in the cold zone?.

[Matt12]

but is there not a tiny chance that milder air wont make it that far and the whole country stays in the cold zone?.

I guess there is always a chance - there still seems to be a lot of uncertainty. I am no weather expert, but the ensembles are hinting at a return to milder weather (in the south at least) for around Christmas eve/Christmas day. It, at least, seems the most likely scenario at the moment IMO.

Does anyone else think that the latest charts are a downgrade for the south? It's just that the long-term situation down south seems to have deteriorated a bit since earlier today, with a return to milder weather (but not mild per se) seeming more likely into the new year. Still, things are far from certain, especially considering the inaccurate nature of long-term forecasting.

Matt.

Edited December 19, 2009 by Matt12

[West is Best]

Although the 0z GFS is not brilliant in medium term, and lousy in the long term, notice the huge ensemble scatter which starts at short-range, and the position of the operational:

I'd say it's odds-on for less cold weather, but there is huge uncertainty and model divergence here in a complex setup. Quite how this is all going to pan out seems far from clear, and I still think it's only a matter of time with ensembles like this before we have some eye candy! I'm not sure anything beyond 72hrs, whether cold or mild, currently has any real credibility.

[Iceberg]

I was waiting for the ECM before committing to anything.

Some general agreements now, (saying cold for the whole country until Tuesday/Wednesday) with slow moving snow showers particularly for the west.(good chance that Devon for example will get some of what Kent has received).

Then Thursday a low looks like swinging in, travelling NW from the south coast exiting into the north sea Christmas Day, to the SE of the low it gets less cold and to the NW of the low still plenty cold enough for snow.

The ops and ensemble means tend it keep it further south, but their is a chance it comes north, still lots of uncertainty on it's track, it could just skirt the SE and keep the whole country cold.

As this passes through the cold front introduces the colder air again(for how long no one knows).

I am not saying it's all sorted, but the general synoptics for the week ahead are pretty certainty IMO.

However the detail will determine who gets snow as always.

Anyway very good models and the ECM London Ensembles show that it will likely be a while before we record daytime temps of even 5C. !

[Frosty.]

A cold ECM 00z run throughout, the cold block holding and with an arctic cyclonic flow giving areas of wintry ppn mostly of snow, the gfs is good for the far north but slowly turning less cold from the south just after christmas day, perhaps the gfs has spotted a way out of this freezing spell but it still looks a slow painful process, ukmo 00z keeps it pretty cold out to T+144 so there is still lots of uncertainty about the extended outlook although maybe the end of this cold spell is now slowly coming into focus.

[Optimus Prime]

Go past the 22nd at your peril...

[KTtom]

Yep, a cracking ECM to counteract a wowfull GFS in the longerterm. ECK ends up with a reload with heights re-forming over Greenland and a snowy spell for the UK.

[Frosty.]

Yep, a cracking ECM to counteract a wowfull GFS in the longerterm. ECK ends up with a reload with heights re-forming over Greenland and a snowy spell for the UK.

Yes the ecm 00z is as good as I dared to hope for following that woeful gfs in the mid / late range. the ecm does show the cold relaxing it's grip in the south for a short time before a stunning T+240 which shows a reload. Whichever model is correct here, the breakdown looks slow and scotland should be very cold all next week.

[casparjack]

The ECM looks to keep the cold theme going at least through Christmas day and the latest FAX charts show the attempts by the milder air attacking from the south being repelled, all shaping up quite nicely I would say.

[Methuselah]

Well the breakdown brigade has shut up at last with no breakdown in sight. Staying cold this week with plenty more sleet and snow. Christmas still a long way off, probably gonna be cold and wintry.

The models do seem to indicate a lot of marginality, though...Uppers often the wrong side of -5C???

Is that the Queen pushing a trolley in your sig, OP?

[David-kig]

gfs is poor not mild but very messing week ahead all diffrent mixes of weather

[tinybill]

morning all i can say its what an up date for xmas day the UK going to get snow bound as if we not now appox 10 inches here in snow bound Ipswich with more to come were are my huskies!!!

[Terminal Moraine]

It's looking increasingly likely that the cold weather will hang on until christmas at least, apart from maybe in the far south of Britain. ECM is currently the better run for cold weather with the cold persisting to the very end and even the hint of another cyclonic easterly around 240hrs as milder air attempts to move north.

GFS has milder air reaching all but the far north shortly after christmas but the ensembles reveal that both the control and the operational are among the mildest members after the 25th and there is a good deal of support for the cold weather persisting, even until new year.

[Tom D]

I'm not too worried about the last two GFS runs, the ensembles (which I think are for the 00z run, but either way) show that the operational is one of the mildest runs and so is the control, but most of the others show cold persisting.

Here's the London ensembles

http://charts.netweather.tv/ensimages/ens.20091219/00/t850London.png

http://charts.netweather.tv/ensimages/ens.20091219/00/t2mLondon.png

But the ensembles for Aberdeenshire are very much mild outliers

http://charts.netweather.tv/ensimages/ens.20091219/00/t2mAberdeenshire.png

http://charts.netweather.tv/ensimages/ens.20091219/00/t850Aberdeenshire.png

[johnholmes]

turning to the weather for today

an interesting day watching the frontal zone work south-currently clearing Shetland-the chart below shows where the front is at 06z and the fairly large pressure falls associated with it.

I'll try and post every 3 hours

[johnholmes]

not really looked beyond my own area so far but would imagine coastal areas in the west-along with SW England-most places inland-IF the models show precip of 2mm or more will get snow before it clears with hard frost following.

In the evening night time spell then most inland areas are going to see snow-less so in the north until the lower 850 and 1000-850 thickness values come in during daylight hours.

bit brief but need to go out

for anyone really wanting to know will it snow for 'me'

today is a classic for those with Extra/NMM to use the Guide I've banged on about-it really will tell you as the occlusion comes south-most important does it show precip if not then forget snow anyway-2mm min to give a covering of snow

try it

let me know the results for you

Edited December 19, 2009 by johnholmes

[johnholmes]

use the will it snow guide M and others as well rather than ask countless questions will it do this or that.

I'm not being awkward or rude simply asking that you try to use it for your area

[oldsnowywizard]

perhaps fols are forgetting last feb when we had the short Easterly? the cold air stayed for about 5 days in total, and at least 3 times lows tried to come up from the south to introduce milder air and either failed or brought lots of snow.. cold air is hard to budge..

[TEITS]

Interesting ECM ensembles again.

At one stage the mean on the ECM ensembles did rise above 5C but as you can see the mean stays relatively cold. The 0Z ECM was one of the colder runs towards the end but note how cold the control run goes!

So at the moment the cold weather looks to remain, especially in the N. Beyond this and to be honest it could turn colder between christmas and new year or turn milder. At the moment I favour remaining cold and possibly turning colder and would put the odds towards 60/40 in favour of cold. However thia could easily change the other way.

[johnholmes]

lrf now out see link below

http://forum.netweather.tv/topic/47443-lrf-or-attempting-them/page__st__221__gopid__1653077&

[Timmytour]

I am mindful that in February earlier in the year, great as the first part of it was, there was lots of "evidence" to suggest it was going to persist throughout the month and get even colder.... all of which petered out.

Cold air CAN be hard to shift...but it can shift when you don't want it to!

Edited December 19, 2009 by Timmytour

[Guest North Sea Snow Convection]

I'm sure that the cold air is not going to pushed away very easily at all. Unfortunately however it looks like it is going to be less cold down here with rain in the next 48 hours and onwards from there - but if the ECM was right in its morning output today then a chance that the cold air could return here with time, if those very nice hints of another easterly were to happen. However that is very much in the balance atm.

For northern and quite probably central areas and the midlands too - a very encouraging outlook though, and every chance of quite a bit of snow, especially the further north you go.

[TEITS]

At the moment I would suggest F.I is +72.

I shall use the 06Z +78 as an example.

http://www.wetterzentrale.de/pics/Rtavn781.png

This needs to be watched to see the development and track should this LP develop. Anyone on the N/W side of the LP could see snow and if it tracks NE across the N Sea then you would see a return of the -5C uppers from the N.