General Model Output Discussion Tuesday December 22Nd:

[Geordiesnow]

In many respects, the ecm at 144 hours looks similar to the UKMO but i think the UKMO have got better height rises in Greenland therefore, i would bet on a ne'ly if the UKMO went a bit further ahead.

ecm also looks similar to the UKMO's 6-15 day forecast so another cold and snowy spell is far from in the bag.

Be interesting what the GFS 18Z shows us.

[weather eater]

I've not posted much of late, been rather busy, but I have been following the models and have seen almost every ECM, GFS and UKMO run. For me, the GFS as it has been for quite a while now, far more consistent than the ECM, which seems to throw up wildly different evolutions every run. In terms of dream synoptics I would echo a couple of recent posts in regards model projections and what we eventually get. Lets be honest, while we have seen some excellent cold and snow over the last few days it has not matched one or two of the projected evolutions from the models, so its always best to temper expectations with a healthy dose of realism. Before anybody jumps I'm not complaining, we have had the best spell of snow that I've seen for a good few years and while not in a truly memorable category its still been pretty good. Its snowing here as I type that's three days in the last four, can't remember the last time that that happened where I've been living. A lot has been mentioned about the models getting to grips with events, FI stands at 72 hours etc, I don't feel that's been the case, we have seen a very complex synoptic pattern in our neck of the woods over recent days, difficult to nail, but the trend has been much the same. IMO the colds going nowhere fast its just unclear when and how it’s going to hit us after a brief warm up, I do feel its coming and maybe those that have missed out this time will get a taste.

[shuggee]

Interesting to see the verification stats for T+120 over the last week. GFS/ECM seem very much neck and neck and as was suggested by many members on here both struggled with the evolution after the initial UK cold at the weekend. UKMO up there too:

[dallas]

Interesting to see the verification stats for T+120 over the last week. GFS/ECM seem very much neck and neck and as was suggested by many members on here both struggled with the evolution after the initial UK cold at the weekend. UKMO up there too:

Shuggee, hope it's not a dumb question but which line shows what actually occured?

Cheers

Dallas

[shuggee]

The actual pressure spread of the day of verification gives a score of 1 (see the 'y' axis up the side). Each line then shows a model's individual score (see the key for which colour represents which model). The nearer to 1 - the more accurate the 6 day forecast :lol:

[03jtrickey]

Shuggee, hope it's not a dumb question but which line shows what actually occured?

Cheers

Dallas

None of the lines show what actually occurred. If there was a line to show this, it would be a straight line along the top of the graph (y=1). The closer a point is to 1, the closer the respective model was to what actually happened.

Edited December 23, 2009 by 03jtrickey

[dallas]

Cheers Shuggee and tricky.........got it................good tool that!

[swilliam]

Still lots of scatter on the ensembles in the South and Midlands for the period 29 - 31 Dec so no guarantee of cold next week yet.

Looking at the members this seems to be mainly because the trough extension from the LP to the SW is aligned poorly or further North allowing much milder air Northwards.

eg pb 1

They do all then converge on the 1st at a T850 of -8 here - indicative of the Northerly

Thereafter there is enormous scatter again and this is due to whether the blocking high becomes established over Greenland or not. A lot of members have this hightoppling e.g. pb 11

leading to + zero uppers

This then goes on to be a huge Euro high

But to illustrate that if this happens we should not panic - even this evolves into something interesting with -5 uppers.

Indicative of the large amounts of cold air around us at present.

So for medium term cold we need to keep a watch on the position and direction of the troughing from the LP in the SW and the building of the ridge to Greenland. Hopefully the higher resolution of the OP and Control (which is also stonking) mean that they will be the favoured solution and the ensembles will trend towards them.

Edited December 23, 2009 by swilliam

[conor123]

A lot of ensembles are very mild for next week because we don't know how far North the big storm is going to get yet, fingers crossed it will get far enough to give us Midlanders a blizzard! then move south again to give an arctic blast, 12z GFS lower resolution was great.

[Uncle_Barty]

Anything that breaks the run of cold rain, more cold rain and yet more cold rain over the past few days will do for me.

1050 Greeny high showing up as the 18z rolls out

http://www.wzkarten.de/pics/Rtavn361.png

[ScottSnow]

Again people saying that chart will bring snow on Jan 1st and so on need to be reminded that snow is a very marginal and can be very hard to forecast even a few hours beforehand as the past few days have proved. Looking at charts for anyhting +120hrs should just be looked at for the overall trend from the past few days.

Others and I said there would be a cold spell three weeks ago based on GFS trends and have been proved correct. The overall pattern at the moment is again for another spell of colder weather coming around the New Year. To go into specifications would be silly but as the past week has shown once you actually get the cold weather in place then snow is possible almost anywhere but it is very hard to forecast accurately. Some of the best snowfalls are the ones that evolve very quickly(Cairngorm mountain received almost 2ft of snow last night that wasn't forecast and the snowfall in the south east on monday night I believe wasn't forecast accurately).

Also we have had nearly a week of lying snow here and at least a couple of ice days this has been an excellent cold spell for me and I hope the models are correct and we are in for more of the same. I'm going skiing up in the pennines near Alston tomorrow !!!

Interestingly after last winter and this cold spell, what are the implications on the 'even larger teapot' theory ?

[leroys35]

ecm ensebles exteded mild outlier for the op and control check them out

[phil nw.]

Sorry to divert attention from the 18z but look at this fax just out for T120hrs.

Full of promise for something very wintry somewhere across the UK i think.

[Uncle_Barty]

with the 546 line close to the south coast.. just very wet, especially down south.

[DAVID SNOW]

Sorry to divert attention from the 18z but look at this fax just out for T120hrs.

Full of promise for something very wintry somewhere across the UK i think.

Yep

Scotland

[phil nw.]

with the 546 line close to the south coast.. just very wet, especially down south.

Indeed for your location yes,as it stands,but further north....

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=114&mode=1

with the cold air modelled to push south.

I think you have to agree it`s not a bad chart,if you like cold.

[cyclonic happiness]

IF that set up at T+120hrs was to materialise it would take a long time to get the cold air south across all parts of the country, in fact it might never happen. with some very mild air and a lot of rain affecting the far south as we move towards year end.

But that low is moving rapidly eastwards, so would introduce a really cold flow first from the northeast, then from the north, it's the potential in that chart that is the most exciting

[TEITS]

IF that set up at T+120hrs was to materialise it would take a long time to get the cold air south across all parts of the country, in fact it might never happen. with some very mild air and a lot of rain affecting the far south as we move towards year end.

Wrong.

The natural progression from the +120 Fax chart is this. Very slowly you would gradually pull in colder NE,lys. Look at the 18Z GFS +120 chart and then compare to the UKMO and you will see they are very similiar. Now note on the 18Z GFS +156 it takes only 36hrs before the -5C isotherm is in the S coast.

Lets stick with what the models are actually showing.

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

Cold air coming down from the north, low pressure skirting beneath the south coast!

[leroys35]

any one seen the ecm ensembles mild outliers for op and control

[TEITS]

Cold air coming down from the north, low pressure skirting beneath the south coast!

I've been meaning to say this for ages but I love your sig. If anyone doubts a model run in the future that is suggesting a very cold spell then they must read your sig. Fair enough its wise to be cautious but your sig shows that at times these very cold model runs go can in our favour.

Classic E,ly about to develop on the 18Z!

http://www.wetterzentrale.de/pics/Rtavn2401.png

Edited December 23, 2009 by THE EYE IN THE SKY

[high ground birmingham]

Unfortunately the 18GFS has drifted rather more towards the 12 ECM at T+168hrs, with heights falling across Greenland and the HP sinking slowly south. That having been said it's still a very encouraging run towards the end of the high resolution output, with hopefully time for upgrades as the period unfolds.

Huh?????????

Are you viewing the same charts as me?? or are you simply trying to wind people up?

How can the high sink south when there is a low pressure system over Southern France/Northern Spain??

[cyclonic happiness]

There's nothing wrong with the ECM or the latest GFS, they are both scenarios that most of us would have killed for in the darker days of "the noughties"

[bluearmy]

well it wont go any further north HGB so i get the feeling that if it doesnt stay still, it has to 'sink' to an extent. all in low res and worzel is rihgt in saying that it is similar to the ecm in the fact that the high is held in situ by lower heights to the north. its worse in the fact that the high isnt 'cut off' although the run evolves into mid lat high in our vicinity

[nick sussex]

Another good run from the gfs 18hrs and we're slowly closing in on being able to call a major snow event for locations lucky enough to remain on the northern flank of the low but also close enough to the main precip. The fax chart for 120hrs is very exciting with colder air likely to undercut any rain soon changing this over to snow, then it's really down to how long the low takes to clear away in terms of how much snow could fall.

There are differences however across the model guidance and between runs, one run strong Greenland high, the next high near Iceland with lower heights to the far north so this for the moment is a major variable. At the moment i've delayed shovel watch due to my concerns over any possible phasing between both lows which would mean a delay to the cold. It's crucial both lows dont interact too early,the key here is the sw low throws a shortwave east towards France at just the right time, for this reason i would delay any ramping for a few more days.

I'd also like to say i totally agree with cyclonic happiness's post, let's not be too greedy here the ecm and gfs are both very good and in many previous winters would have been welcomed with open arms.

Edited December 23, 2009 by nick sussex