General Model Output Discussion Tuesday December 22Nd:

[BLAST FROM THE PAST]

No-one said it did on the ECM but it did and now does on lots of the ensemble members including the control run this time.

We have to consider that this is also a possible outcome - maybe at this stage probable.

No we don't, there will be no sinking and no model should show sinking....think retrograde thst is the set up.

BFTP

Edited December 24, 2009 by BLAST FROM THE PAST

[kold weather]

Fair points, but who is or has suggested a Bartlett situ is likely to emerge? The main discussion (or arguement started by TEITS) has surrounded the fact that the 12 GFS had much better blocking shown at 168hrs than the 12ECM, but the 18GFS drifted more towards the 12ECM solution. Some saw the highlighting of this fact as a reason to go on the attack and suggest others were simply trying to wind members up, so in light of this I can't see how bringing the B word into the discussion will help at all.

That was just an aside point as to what I thinkyou can rule out in this situation, esp as some ensemble members try and throw up a much more typically zonal flow.

As for the 12z ECM and the 18z GFS they are not in any ways similar...in fact the 12z ECM is FAR closer to the 12z GFS then the 18z in terms of actual evolution and the pattern in the upper atmosphere...

If anything the ECM has moved towards the 06/12z GFS solution rather then the 18z moving to the ECM solution...

For example, at 240hrs the differences are actually total...

The 18z GFS has a PV over Western Greenland...the 12z ECM has a powerful upper high over Western Greenland...theres over a 50dm difference in heights between the two runs up there which is massivly different!

Anyway the 18z is still a fairly cold pattern, nothing too amazing...in fact I'd say if we hadn't just had such an exceptional spell of northern blocking it'd be most likely...but you don't go from -3/4s in the AO to +1/2/3s like the GFS is suggesting in a few days unless there is a huge pattern shift...The 18z does give a slightly more realistic timeframe but even then I think we can safely assume its progressive bias (which it has got as I have discussed recently in the techinical thread, its well known about!) must be playing a part.

The key looking at the models is exactly what happens at 144-168hrs. Both of the models have a more neutral AO pattern develop by then but the GFS instead blows up a Candian vortex, whilst the ECM powers up a huge Scandinavia vortex...this makes such a huge difference...but the 12z ECM is much closer to the 12z GFS then the 18z GFS...as the 12z GFS also developed a stronger Scandi PV.

Edited December 24, 2009 by kold weather

[damianslaw]

Increasing signs in the teleconnections once we pass Boxing Day for a reload of the cold conditions, in reality much of Scotland and N England is not going to see any loss of the cold conditions, just a minor temporary warming through Boxing Day and the 27th, godd news for sport fanatics and post christmas sales shoppers.

I am quite confident that the greenland high is going to reintensify in the run up to the New Year with bitter arctic conditions moving into Scotland early next week and then for all as we head towards New Year - this could set the theme for the rest of the winter, all those banking on a mild and wet winter are very silent at present, it seems all the other factors that many had spoken about potentially overiding El Nino are really coming to fore, late Dec is a pivotal moment for the rest of the winter, it is all very very promising indeed, I don't want to ramp but if the blocking does stay in situ into the New Year, it is going to be a very difficult beast to shift.. wonderful stuff..

[AtlanticFlamethrower]

You do actually make a very good point which I shall try and take on board. When I look at the model output I must admit to focussing on my own location rather than looking at all of the UK. I shall certainly make more of an effort in the future.

Back to the models and its time to have a look at the Iceland SLP ensembles like I did last time. This proved to be a worth while exercise prior to our last cold spell.

At the moment its looking quiet good for the period in question with the mean currently standing at 1022mb.

http://charts.netweather.tv/ensimages/ens.20091223/18/prmslReyjavic.png

Hope you do. You seem to be fairly accurate for your location. But what you say is meaningless for a whole bunch of others, which incites them to post contradicting whatever you said.

How about pick some cities and do some brief forecasts for PPN/Temps for these areas at the bottom of your normal posts?

E.g.

London - PPN low temps okay

Plymouth - PPN none temps no

Bristol - PPN none temps no

Portsmouth - PPN low temps no

Liverpool - PPN some temps no

Leeds - PPN some temps good

Newcastle - PPN some temps good

... if you do this, more proper forecasters might start doing the same.

Edited December 24, 2009 by AtlanticFlamethrower

[TEITS]

Fair points, but who is or has suggested a Bartlett situ is likely to emerge? The main discussion (or arguement started by TEITS) has surrounded the fact that the 12 GFS had much better blocking shown at 168hrs than the 12ECM,

Lets not get into petty arguments because it really isn't worth it.

Simply put you were suggesting the GFS was following a similiar trend to the ECM by sinking the HP. I disagreed with this and highlighted neither model was sinking the HP at +168. Like I said earlier if the HP doesn't retrogress fully to Greenland then this doesn't mean its sinking.

Another way of putting this is if the HP was sinking then we wouldn't of been looking at F.I eye candy on both models.

I prefer to concentrate on what the models are actually showing rather than what may happen. At the moment the models are showing huge potential for all of the UK at various timeframes. Come tomorrow these models may upgrade or downgrade but because I prefer cold weather I prefer to concentrate on the positives rather than worrying about what may go wrong!!

[kold weather]

Worzel, maybe you should learn from what you say....where in that post did I make any reference to the whole run in the post...sure I mentioned 240hrs after as an example of what differences would evolve in the models would bring up because of the pattern at 168hrs but I've not there suggested what part of the run if all the run I'm actually talking about, your just assuming I'm talking about the res tof the run, trust me I was talking about the period you were mentioning and what happens in terms of the evolution.

Ensembles generally suggesting a cold flow still to start Jan off, but have vastly different evolutions, quite a few go with the op run and refuse to raise heights further north again, others follow the ECM...my gut tells me neither are quite right and we will get something much closer to the 0z ECM in the end.

Edited December 24, 2009 by kold weather

[TEITS]

I'd suggest 90% of arguments are unnecessary and would stop as soon as we start to forecast locations in more detail.

Two people are always going to fight over the right forecast label for "Britain" if they live in different regions.

So let's only forecast for our region, and if we forecast for other regions let's make it clear that we are making two forecasts not one forecast.

You have definately given me so good advice and right after xmas this is what im going to do.

Rather than making several posts based on one run I shall make one post containing more detail. I shall start by commenting on the models for E Anglia but then I shall give a brief explanation of what the model output suggests for each region.

Goodnight all.

[johnny1972]

Lets not get into petty arguments because it really isn't worth it.

Simply put you were suggesting the GFS was following a similiar trend to the ECM by sinking the HP. I disagreed with this and highlighted neither model was sinking the HP at +168. Like I said earlier if the HP doesn't retrogress fully to Greenland then this doesn't mean its sinking.

Another way of putting this is if the HP was sinking then we wouldn't of been looking at F.I eye candy on both models.

I prefer to concentrate on what the models are actually showing rather than what may happen. At the moment the models are showing huge potential for all of the UK at various timeframes. Come tomorrow these models may upgrade or downgrade but because I prefer cold weather I prefer to concentrate on the positives rather than worrying about what may go wrong!!

TEITS

Taking not just todays but at least the last 3 days runs I would agree with you that they have shown after slightly milder 2 - 3 days a return to cold/v cold conditions into next week for the new year and possibly beyond. I have looked at the AO and NAO forecasts and they remain very negative ! The jet appears to be still displaced well to the south (Spain), however towards the new year some energy appears to be forecast to go into the northern arm up the west of greenland over the top and down its east coast. I understand the southern arm and its implications however what would be the implications for us if some energy goes into the northern arm as described above??

[Weather-history]

GFS ensemble mean 500hpa chart

http://www.wetterzentrale.de/pics/Rz500m8.gif

A northerly flow there

[AtlanticFlamethrower]

You have definately given me so good advice and right after xmas this is what im going to do.

Rather than making several posts based on one run I shall make one post containing more detail. I shall start by commenting on the models for E Anglia but then I shall give a brief explanation of what the model output suggests for each region.

Goodnight all.

Awesome! Look forward to it.

It's not a coincidence that a couple of the negative posts (the only ones I've noticed) are from Yeovil (Somerset) and Portsmouth (Hampshire).

This region will usually be more marginal than areas north or east in a northerly or easterly... much more effort is needed to persuade these guys. Same for people on coasts.

[kold weather]

One last thing from me...

I suspect what will happen is exactly what happened with this cold spell, the models will be too progressive in trying to get us into the pattern, the ensembles won't really go along with it, the models will probably be rather unagreeable as well in general. The Midlantic ridge forms, possibly a upper high tries to form near Iceland, then we will need a shortwave/PV to swing down towards Scandinavia. As long as that happens thenthe whole lot will be forced up northwards.

Remember the global teleconnections are no different now then they were 2 weeks ago, if anything they are going to be a little bit more favorable with the MJO wave in a decent position and so ther eis no logical reason why we won't get another cold spell, of course the GFS op run is something that could occur but I see no reason why it should just yet...I suspect its picked up the end game and trying to implement it wya too quickly...

[West is Best]

The 0z GFS remains excellent out past T144. I would still like to see a lot more FI support in the ensembles though. Having said this, the operational is one of the mildest members for the key 28-30th December phase, so has the centre of the low further north thus bringing the really cold air off the north-easterly in later. We really want that secondary low (29th) to get squashed on a nice southerly track.

Interesting too to note that the block is largely a mid to north Atlantic high rather than strictly speaking Greenland, which means a toppler is an ever-present danger.

UKMO looks fine out to T144. Awaiting the ECM.

[Eugene]

Yes very mild next tuesday midlands southwards, an amazing temp gradient between the north of england and the midlands, could be tropical for the south midlands while its snowing in the peak district in the north midlands

Very good run overall though for cold weather so cant complain

[Kiwi]

Cracking 0z GFS run once we've got rid of the remnants of our turkey curry! GFS is consistently bringing back cold conditions from Wed 30th. A brisk NE'rly on new years eve is on the cards.

[Snowmad79]

Well the GFS is not as good this morning with regards to the retrogression of the mid atlantic HP where as on the Ukmo it fully retrogresses to Greenland the GFZ wants to place it slap bang over us. However the ensembles do show decent agreement at mid range for 850 temps to plummit towards -10 after a 2 day mild blip on saturday and sunday. Those 2 days could see a decent thaw even for us in the lancashire area with temps maybe going above the 5c mark, Judging by the fact its 2c right now and that a bit of a thaw is already occuring then the temp in the NW could well be fair bit higher than 5c on those 2 days mentioned above..

Waiting on the ECM now.

[West is Best]

The ECM track is much more southerly, which is more in keeping with other GFS members.

Absolutely stonking, pretty sensational, ECM run therefore. There's a fantastic high build north-west and a biting north-easterly set up. This is a fairly fast reload: we're looking as early as Tuesday (T120) for things to begin getting interesting again.

Edited December 24, 2009 by West is Best

[snowmadchrisuk]

On the Ensembles there is 100% agreement for a cold spell between 31st Dec and 3rd January. When I say 100% I mean every single member goes for it.

[Duane S.]

Liking the ECM this morning. Up to +168 and much more believable than the 12z with a strong looking negative NAO taking hold.

Edited December 24, 2009 by s4lancia

[Snowmad79]

Thats is exactly what I wanted to see from ECM up to 168, HP to our NW and that PV looks to be edging into canada. Even more so at 192

Uhmm Tis a good run that ECM isnt it .. PV remaining split with a big chunk of it developing over Scandi. , looks like we have a Greenland High and Polar Scandi-Vortex in our midst

[West is Best]

Liking the ECM this morning. Up to +168 and much more believable than the 12z with a strong looking negative NAO taking hold.

That really is one hell of an ECM run. Fantastic final chart!

I like the fact that the action for this starting is already in swing at T120. As Chris says, even if the GFS scatters later, the next cold snap has excellent support. If the GFS operational track is a little further south, as a lot of ensemble members suggest + ECM, then we're in for another tremendous cold reload.

Those two charts are about as good as it gets in this country!

Edited December 24, 2009 by West is Best

[Iceberg]

We have to remember that we are still talking about FI(the cold air doesn't really take hold until the 31st(which is still 7 days away even though the building blocks are their at 4 or 5 days away).

However the trend is very clear with good consistance for Pressure to build to our west and then north west by 144Z, this is thanks to the ridge which is easily thrown up by the low off the eastern seaboard due to the generally weak atlantic.

The position of the HP at 144 then allows a plume of WAA to become established allowing the a true Greenland high to form by T216.

We have the deep cold air crossing the Arctic and then the PV retrogressing slightly to Northern Canada to allow this.

Once the Greenland high is developed the PV then prevents further movement of the high westwards(which was the really disappointment of this cold spell).

It sounds very very good and highly believable, cold air is then assured, snow as always will be dependent on location and synoptics.

Even with 80% support from the ECM and GFS ensembles for the above(as well as the ops) this could go wrong in several places still.

We are relying on the correct modelling of the low off the eastern seaboard(never easy things to get right).

The PV and high providing the right shape for enough WAA to form a fully fledged GHP.

At the 216 and beyond mark the PV being in the right position, too far east and we get a cold chilly high pressure period, too far west and we get the cold air going too far west (al el the moment) which keeps alot of the uk rather marginal.

Very nice charts this morning if you like Cold though for 2010.

[nick sussex]

OMG! that ecm run is absolutely fantastic, one of the best i've ever seen on the internet, the gfs and ukmo are good also, the ukmo would eventually bring in the cold but the ecm IMO is just outstanding.

Having said this weren't there some dodgy runs leading into Xmas day during the last few winters because of the lack of flight data at this time, i don't think this would effect this mornings runs but perhaps tomorrow might be slightly prone to more error.

Edited December 24, 2009 by nick sussex

[Duane S.]

OMG! that ecm run is absolutely fantastic, one of the best i've ever seen on the internet, the gfs and ukmo are good also, the ukmo would eventually bring in the cold but the ecm IMO is just outstanding.

Having said this weren't there some dodgy runs leading into Xmas day during the last few winters because of the lack of flight data at this time, i don't think this would effect this mornings runs but perhaps tomorrow might be slightly prone to more error.

Yes Nick I'd agree, the whole run is absolutely incredible although I think it's possibly a little bit too progressive in bringing this type of scenario to us. I would have expected (and wanted) to see the +192 at +240. However, it certainly is looking like after a mild(er)few days (in the South at least) we are then heading towards another fantastic cold spell (not that we are really out of this one yet).

[CRACKPOT]

OMG! that ecm run is absolutely fantastic, one of the best i've ever seen on the internet, the gfs and ukmo are good also, the ukmo would eventually bring in the cold but the ecm IMO is just outstanding.

Having said this weren't there some dodgy runs leading into Xmas day during the last few winters because of the lack of flight data at this time, i don't think this would effect this mornings runs but perhaps tomorrow might be slightly prone to more error.

Hi Nick,

I concur, those runs are superb and they bring the cold weather back in quite quickly.

Yes I remember last year some dodgy runs due lower amounts of input data - so the next two or three days, which are now crucial for those of us looking at next weeks cold period will probably throw up a few inaccurate charts.

JK

[londonsnow]

wow to the ecm. puts me in mind to go for a ski weekend in scotland in early jan if there remains consistency in further runs. interesting what nick says about dodgy runs over christmas due to lack of data. i remember that happening last year i think. lots to look forward to after this mildish interlude