General Model Output Discussion Tuesday December 22Nd:

[john w]

Very Very surreal pub run for the 18z.

Somebody poisted snow cover charts and I think all models are struggling with this and the thermodynamic effects it is having. Realistically tropical warmth eventually has to be shifted polewards and it may well be worth peopls whiles watching SST's in the gulf etc before getting over excited about amazing runs...though appreciate the state of flux in oceans is less than atmos!

Cant remember all the deep teleconnections theory that GP and others refer but there certainly seems to be potential for cold air to remain close by or over the UK for much of the period. This time last week we have to also remember we all thought it would be over by today. 1. It isnt...there is still 2 inches of snow outside. 2. The relative mild is now not due to x-mas day. There could be snow on x-mas eve for some...though looks like rain for me...then a reload looks plausable by the 29-31st.

In a way, the awful disruption the snow causes makes me not want to see it, how the country would cope if some of those charts came off I do not know....not seen slow ploughs in any contingency plans...only x number of gritters etc etc.

[swilliam]

Point taken - no guarantees, but the GFS conjured this up on the 2nd Dec (a full 15 days away), and if not mistaken it wasn't too far off the mark?

Yes I thought it was more than T240 that the first indications were given. I remember being 'told off' for discussing it as it was obviously implausible.

I think the current predictions for the cold spell are more marginal as it is very easy to see how it can all go wrong. As NS has stated several times we are relying on not having a link up between the two depressions shown below - one over us and the other to the SW.

Looking at the ensembles it is clear that many members do go for this link up leading to the possibility of much milder air over us as indicated by the GEM GME models.

Then we have to worry about the troughing and undercutting Eastwards.

So plenty needs to go in our favour but at the least the possibilities exist. For me I think the marginal situation is highly preferable as it can lead to some serious snowfall instead of the routine falls we have had to date. Also provides much more will it won't it situations and if so where so lots of interest.

Edited December 23, 2009 by swilliam

[kold weather]

Well the 18z is a stunner thats for sure, forgetting the rather poor FI (though even that is still not without its good points of course!) the 18z gives us quite possibly one of the bigger snowfalls we'd have seen in this country for quite a while, its like a more prolonged version of Feb 07...with more favourable time of year and a much colder Europe to draw upon...

The 12z ECM is better then the 0z run BUT once again it starts the process towards a +ve AO and also importantly starts to reuinte the PV probably very close to Greenland...

Not the greatest of signs...but it keeps a strong upper high to the westof the UK which I'd imagine would sink towards the UK if we saw more of the run...and that would likely still give a cold solution and I'd imagine that solution could be one that lasts a while if it were to happen...a trough to our east would keep filtering cold air into Europe, if it sets up further west then the UK would remain in a cold northerly flow...

So, I'm still not seeing any real returns to a milder set-up, the models and the ensembles do seem to suggest a slow return towards +ve AO but with an undercutting jet I'd imagine it wouldn't be the usual breakdown, could well breakdown to something nearly as cold...

Edited December 23, 2009 by kold weather

[swilliam]

A new ice age is definitely about to occur!

I guess we would not all be obsessed about model watching if this was the reality - although we may all be desperately looking for blow torch SWs

[Iceni]

A new ice age is definitely about to occur!

I guess we would not all be obsessed about model watching if this was the reality - although we may all be desperately looking for blow torch SWs

Ummm that chart's The Day After Tomorrow isn't it?

[high ground birmingham]

Well Well Well....are we seeing another twist in the story for a White Christmas.

The 00z GFS has tracked a low that was previously set to track North through the Low Countries and move through into Scandinavia to actually track across the eastern half of England on Christmas Eve night into the early hours of the 25th before moving out into the North Sea

As the low moves north, it will be undercut by relatively colder North winds on the western side of the band which would turn the western edge of the band readily to snow as it then tracks NE and moves into the North Sea.

It is something to watch and dare i say, it would cause a technical White Christmas in London with bookies paying out bucketloads.

Certainly very interesting....

Regards, hgb

[dallas]

HGB, Has to be a fair chance as the min temps seem to decrease as the day progresses too

[Duane S.]

Having not seen the charts for a couple of days I've just had a look. OMG, where did that come from??? I admit to having written off anything good for Xmas day down south, now it looks back on in a potentially spectacular way. This could bring snow to anywhere in the south. On a personal note I am gutted as I will be traveling to France on Xmas Eve.

[Nick B]

Personally not that bothered about whether there is white stuff falling on a particular day myself. Loook at the beautiful block building on the latter part of the 00Z ECM. The trend there is firming up again and showing it consistently. How is it performing atm compared to the GFS? That would set up another few days of cold rather than the GFS toppler scenario of the 00Z. So, which way does your head take you, not your heart?

There you go, Joe!

Edited December 23, 2009 by Nick B

[Frosty.]

No comments on the 0z ECM

in one word...AWESOME

GFS 00z not as wintry as the 18z but still shows next week being wintry with a N'ly which eventually topples just in time for new year but i'm sure this cold spell will run and run. A word on the ukmo 00z, shaping up to similar to the ecm at T+144, the euros offer more of a NE'ly flow with much better alignment with the scandi trough and the high to the northwest..ecm would be a winter wonderland for much of the uk.

Edited December 23, 2009 by Frosty039

[Nick B]

With the ECM the alignment of the low on the East coast of the US is ideal for building the ridge that strengthens into the Greenland High we see at the end of the run. Comparing like for like timings on the other models the building of the block seems hampered - shortwaves possibly? At this stage, of course, we're still talking about 192-240 which is very much FI, but it will be interesting seeing which way it goes over the next 3-4 days. Gotta go...

[West is Best]

H there. Is it me or is the BBC weather just not matching up at times. They say 10c on Christmas day for my area which is a MASSIVE temp jump for 48 hours time.

What's your thoughts ?

I think they're way out. This setup with the PFJ where it is is not conducive to those sorts of maxima. We've just had another very cold night with temps down to -7C as far south as Sussex and Hampshire. It's -6C in Exeter. This embedded cold pool will not, in my opinion, be shifted by such a weak incursion from the south.

Looking ahead, a stunning setup on the ECM for 28th onwards, and not bad at all from the GFS. The overall theme of these runs still remains blocking to north and west, with a very amplified jet whose main arm remains well south of the UK. This continues to be an essentially cold looking pattern with considerable reload potential to me. If it catches people by surprise, we're perhaps not used to it!

[Lincs Observation]

Well Well Well....are we seeing another twist in the story for a White Christmas.

The 00z GFS has tracked a low that was previously set to track North through the Low Countries and move through into Scandinavia to actually track across the eastern half of England on Christmas Eve night into the early hours of the 25th before moving out into the North Sea

As the low moves north, it will be undercut by relatively colder North winds on the western side of the band which would turn the western edge of the band readily to snow as it then tracks NE and moves into the North Sea.

It is something to watch and dare i say, it would cause a technical White Christmas in London with bookies paying out bucketloads.

Certainly very interesting....

Regards, hgb

Morning all

I have just seen the BBC forecast for Christmas day and there is no mention of this at all in fact they say that xmas day will be a quiet and cold day on the whole across the uk, Now this could be because the bbc are using old data or they feel the feature you point out will not be an issue. However been one who lives on the eastern part of the uk id prefer your take on things all day

LO

[bluearmy]

omega blocks over greenland/iceland - they're like bloody buses. you wait 25 years and then two come along one after another!!

it is the pattern over the eastern seaboard thats important here is nick B pointed out. lets hope the dutch ens support the op and that the noaa chitchat supports the ecm ens.

[Polar Continental]

The 0z GFS tones down any mild spell over Christmas and even gives a chance of snow on Christmas night for northern and north western areas, maybe even some central areas too if we are lucky.

Also good model agreement from the GFS and ECM for a reload of cold north easterlies before the New Year. Cold looks like predominating, though nothing severe being shown yet.

[Nick F]

Well Well Well....are we seeing another twist in the story for a White Christmas.

The 00z GFS has tracked a low that was previously set to track North through the Low Countries and move through into Scandinavia to actually track across the eastern half of England on Christmas Eve night into the early hours of the 25th before moving out into the North Sea

As the low moves north, it will be undercut by relatively colder North winds on the western side of the band which would turn the western edge of the band readily to snow as it then tracks NE and moves into the North Sea.

It is something to watch and dare i say, it would cause a technical White Christmas in London with bookies paying out bucketloads.

Certainly very interesting....

Regards, hgb

I'd remain cautious of GFS precip progs for Xmas day - as UKMO keeps the bulk of the rain, sleet and snow over the continent. GFS played catch up for Monday when it showed only Kent/Sussex under frontal wave until 12hrs out when in the end it was much further NW - as UKMO correctly modeled. However, UKMO does suggest an occlusion moving NE across England during the day - which may bring some winteriness across central areas.

Fantastic synoptic outlook from ECM this morning, with Atlantic low drifting east to the SW and S of the UK while height rises build NE towards Greenland across the NW Atlantic, so a NE'erly developing. Key to this happening will the ridge and following amplifying trough coming out of NE Canada, and also the trough over the E Atlantic digging sufficiently SE across western Europe. GFS similar to a point, put it doesn't build the NW Atlantic ridge as far N and hold it over Greenland like ECM.

[TEITS]

Another set of fasinating models and to be honest F.I starts very early.

For starters we have this band of showers moving NE and according to the BBC there is a risk of this turning to snow across N Wales/Midlands/ N England. As I have 3inches of solid ice on the roads/paths due to the compacted snow, whatever falls is going to cause huge problems here.

As for the big day itself and the risk of a technical white xmas still remains and even Carol on the BBC mentioned this. According to the fax chart we shall have a front clearing E in the morning which could bring a wintry mix of sleet, snow. Definately won't be mild with temps in my region predicted to be around 2C.

Back to the longer term and the ECM is excellent although the 0Z GFS isn't as impressive as the 18Z. The ensembles are rather interesting with the mean at -7C for my region for the period in question.

Overall the potential for a return to cold, wintry weather is very much on between Xmas/New Year. The AO/NAO look to remain negative into Jan and this is very much supported by the forecasters in the US. The questions I raised last night still need to be answered but for the time being all we can do is look for the trend rather than the detail.

[Frosty.]

Also good model agreement from the GFS and ECM for a reload of cold north easterlies before the New Year. Cold looks like predominating, though nothing severe being shown yet.

The ecm 00z looks pretty severe to me for much of next week, especially in the north, sub zero temps and snow showers or more persistent snow with drifting IF those charts verified, just depends on your definition of severe really, even the somewhat toned down gfs looks wintry enough, equally wintry to what we are currently experiencing in my opinion.

[TEITS]

The ecm 00z looks pretty severe to me for much of next week, especially in the north, sub zero temps and snow showers or more persistent snow with drifting IF those charts verified, just depends on your definition of severe really, even the somewhat toned down gfs looks wintry enough, equally wintry to what we are currently experiencing in my opinion.

Yes the ECM +168/+192 would bring severe conditions to many. The upper temps around +192 would be around -10C and you would also have a very unstable ENE,ly blowing across the N Sea.

[cooling climate]

On the 0z ECM n/hemisphere charts we see a high pressure cell moving round the eastern side of the

vortex to the north of us this then supports the n/Atlantic ridge to build further north into Greenland.

The vortex itself is pushed over the top of Greenland and down into n/Canada.

On the 0z GFS operational run we do not see this link up and the vortex remains over the north of

Greenland with the consequence that any blocking in the n/Atlantic soon topples.

In future runs it is important that we see the vortex relocate into n/Canada then we will have a much

better chance at sustained blocking to the north and over Greenland.

This evolution is not that different to the beginnings of this wintry spell we are in.

[stewfox]

what were temps like on that night?

-16c in Scotland

It will be interesting what will happwen in the next T36

We have embedded cold in the south and some what more then just a 'mild incurrsion' coming up from the channel

The prediction is rain on coast sleet/snow in land (South of M4 to start) then rain.

The papers are full of 6-9c in the next few days in the south

One here people are looking at the models with a different set of eyes, time will tell who is right

[TEITS]

Another set of fantastic ECM ensembles with the mean actually dropping below 0C and if anything at +240 the ECM OP was warmer than the mean. :lol:

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

I suspect todays Met O 6-15 day forecast will be a little bit more colder, wintry compared to recent forecasts.

[TEITS]

Still showing yesterdays 12z ensembles,you just jumped the gun there!

Mind you,they are still good.!

No they were the 0Z. You need to refresh the page probably.

[Frosty.]

Another set of fantastic ECM ensembles with the mean actually dropping below 0C and if anything at +240 the ECM OP was warmer than the mean.

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

I suspect todays Met O 6-15 day forecast will be a little bit more colder, wintry compared to recent forecasts. :o

I'm really looking forward to their update and hoping they are backing the latest ecm which is actually more wintry looking than the current spell. The weather during the next 48-72 hours will be a forecasting nightmare for parts of england & wales with knife-edge rain turning to wet snow situations.

[Cloud 10]

No they were the 0Z. You need to refresh the page probably.

:o doh! *eats humble pie*