Model Output Discussion - Tuesday 20:25 -->

[SLEETY]

Huge northern blocking being advertised today by all models.

http://www.meteo.psu...0z/hgtcomp.html

The GFS ensemble mean shows at 410m height anomaly over Greenland t144 through t216 and a day 11-15 anomaly of 258m with a souhward displaced jet and classic -AO pattern. That is cold and the wedge of cold air to our east will have to back west under such a regime - which is why the UKMO is not a problem as the milder Atlantic air would get deflected southwards over time.

I think you can appreciate just how much the idea of high pressure to the south or west of the UK as programmed by the last two 00z ECM operationals was bogus, based up a non-weather model based assessment.

The composites for GWO phase 4 plus enhanced northern blocking continue to represent the likely pattern for the forseable future.

This means that unlike so many of the recent cold events, getting precipitation will not be a problem.

Meantime, I'm seeing some real goodies being brought into the January shop, to be unwrapped mid January on.

Excellent post.

If we cant get a decent wintery blast from whats about to come,than i truly give up with the UK ever seeing a bitter and long lasting cold spell again.

[nick sussex]

The freebie ecm ensembles today are for Luxembourg, good agreement for the operational run, however for days 9 and 10 its a milder solution than many of the other members.

http://www.ecmwf.int/products/d/sampler/epsgrams/europe/page.html

In terms of the ukmo i'm not saying this can't develop into something better but this just adds one more variable because even if the cold has to back west how many times has it done so to our north!equally the angle of attack of the low is not good, yes it's just one run but we don't want to see this, one complication leads to another and another.

[Typhoon John]

Very good outputs this morning; I very much like the ECM. If the block to the North manages to develop I think it should last through til Christmas. Perhaps worth a bet on a White Christmas for London? I'm sure the odds will dramatically shorten over the next week.

I just hope the detail is right and we get a dumping here in the North East. But looking at how the period will develop I think the chances of missing out will be slim.

[Iceberg]

The UKMO 144Z is a really interesting chart IMO and to really appreciate it you need to look at the N.Hemisphere chart.

I admit I was wrong about it being dire. Thanks GP for making me look at it again, the lack of any Azores High, means a souterhly Jet it very likely, given the WAA, position of the high and the position of the other Highs in the Arctic, the high probably would build, giving us a bit more of a NE E weather direction.

I think it would take a little while to get there and might or not might lead to cold, particularly to the south, but a return to the Atlantic conveyor it is not.

[cooling climate]

As I said in a earlier post UKMO post t144 would lead to a very cold east northeasterly,

not that I think its correct but as GP pointed out in his post this morning with that much

of a block to the north any lows coming in from the sw are going to undercut.

The - AO rules this upcoming pattern and with the AMM (atmospheric angular momentum)

dropping it looks like it could very well be a long and wintry spell of weather.

Because of the synoptic pattern and its possible implications are something we have been dreaming

about for years and years is almost certainly about to take place it is making it very hard for

some people to take in.(also past failures)

The evidence in the models etc is totally overwhelming now that we are heading for a wintry

spell of weather to rival perhaps 1981 in cold and snow and dare I say even surpass it.

A very cold and wintry spell of weather is a lock as far as I am concerned.

[TEITS]

In terms of the ukmo i'm not saying this can't develop into something better but this just adds one more variable because even if the cold has to back west how many times has it done so to our north!equally the angle of attack of the low is not good, yes it's just one run but we don't want to see this, one complication leads to another and another.

Certainly hear what your saying Nick and we definately don't want to see a trend towards our block trending even further N along with the LP systems.

However im really mistrusting of the models when it comes to blocking. For example look what happens when we have a Scandi HP, the models are always too progressive in breaking this down. Maybe the reality will be our Greenland block ridging even further S than the models suggest and we pull in a bitter ENE,ly from Scandi.

[reef]

If you find your posts gone then they've most likely been moved to the cold spell general discussion thread. Please try to keep this thread on topic and try to avoid one-liners.

Thanks

[nick sussex]

The UKMO 144Z is a really interesting chart IMO and to really appreciate it you need to look at the N.Hemisphere chart.

I admit I was wrong about it being dire. Thanks GP for making me look at it again, the lack of any Azores High, means a souterhly Jet it very likely, given the WAA, position of the high and the position of the other Highs in the Arctic, the high probably would build, giving us a bit more of a NE E weather direction.

I think it would take a little while to get there and might or not might lead to cold, particularly to the south, but a return to the Atlantic conveyor it is not.

So at least i've found another member who originally thought it was dire! Your last sentence sums it up for me, may or may not lead to cold.

I always view things from a what can go wrong next scenario as this seems to work well in recent winters, the best route to cold IMO is always the quickest and simplest, less time for that unexpected variable to pop up

Anyway i don't want to cremate the issue, who am i to spoil the upbeat mood in here!

Regarding EITS post yes i agree they're always poorly modelled and especially with trying to break down blocking too soon. Anyway i'm going to have another double espresso and put on my happy face and am going to stop being grumpy this morning!

Edited December 9, 2009 by nick sussex

[TEITS]

Following on from my previous post I have found a good example of what im on about.

Look at these charts for Dec 25th 1978. Note the track of the LP systems and the blocking to the N.

http://www.wetterzentrale.de/archive/ra/1978/Rrea00119781225.gif

However following on from this on the 27th the LP systems are begining to track further S, even though we have a S,ly!

http://www.wetterzentrale.de/archive/ra/1978/Rrea00119781227.gif

On the 31st we finally see the UK on the cold side of the jet and blizzards hit the UK.

http://www.wetterzentrale.de/archive/ra/1978/Rrea00119781231.gif

Now in saying all of this I do agree with Nick because the quicker the better because if we're looking for the cold airmass to arrive at +192 then more can go wrong. However in saying this if you want a blizzard then you need LP systems to be tracking near to the UK and then its just a case of luck i.e being on the N side of the LP. Although what often happens is the LP is pulling in much colder E,lys so rain turns to snow.

For me personally I would prefer my snow to come via convection and these LP systems can go to Spain/France.

[Lewis]

Following on from my previous post I have found a good example of what im on about.

Look at these charts for Dec 25th 1978. Note the track of the LP systems and the blocking to the N.

http://www.wetterzentrale.de/archive/ra/1978/Rrea00119781225.gif

However following on from this on the 27th the LP systems are begining to track further S, even though we have a S,ly!

http://www.wetterzentrale.de/archive/ra/1978/Rrea00119781227.gif

On the 31st we finally see the UK on the cold side of the jet and blizzards hit the UK.

http://www.wetterzentrale.de/archive/ra/1978/Rrea00119781231.gif

Now in saying all of this I do agree with Nick because the quicker the better because if we're looking for the cold airmass to arrive at +192 then more can go wrong. However in saying this if you want a blizzard then you need LP systems to be tracking near to the UK and then its just a case of luck i.e being on the N side of the LP. Although what often happens is the LP is pulling in much colder E,lys so rain turns to snow.

For me personally I would prefer my snow to come via convection and these LP systems can go to Spain/France.

Ensembles not great?

Shorter time they are more supportive but after day 6 it messy as out!

[Southender]

Following on from my previous post I have found a good example of what im on about.

Look at these charts for Dec 25th 1978. Note the track of the LP systems and the blocking to the N.

http://www.wetterzentrale.de/archive/ra/1978/Rrea00119781225.gif

However following on from this on the 27th the LP systems are begining to track further S, even though we have a S,ly!

http://www.wetterzentrale.de/archive/ra/1978/Rrea00119781227.gif

On the 31st we finally see the UK on the cold side of the jet and blizzards hit the UK.

http://www.wetterzentrale.de/archive/ra/1978/Rrea00119781231.gif

Now in saying all of this I do agree with Nick because the quicker the better because if we're looking for the cold airmass to arrive at +192 then more can go wrong. However in saying this if you want a blizzard then you need LP systems to be tracking near to the UK and then its just a case of luck i.e being on the N side of the LP. Although what often happens is the LP is pulling in much colder E,lys so rain turns to snow.

For me personally I would prefer my snow to come via convection and these LP systems can go to Spain/France.

Agreed. I don't know about you but here in SE Essex we always end up on the wrong side of any lows zipping in. Giving us rain or wet snow/sleet at best. Give me a Thames Streamer anyday. Although Feb's one was very poor for here, which was most strange.

[Paul Sherman]

Agreed. I don't know about you but here in SE Essex we always end up on the wrong side of any lows zipping in. Giving us rain or wet snow/sleet at best. Give me a Thames Streamer anyday. Although Feb's one was very poor for here, which was most strange.

See Thread Below about Feb'09

[snowmadchrisuk]

Ensembles not great?

Shorter time they are more supportive but after day 6 it messy as out!

I think the problem is , there not sure how far North the high will be , Obviously if the High is over Scotland then 850's in the North are going to be higher than in the South. If you look on the ensembles the further South you go the better they become. For my Area the mean is -5 with a lot of members going for colder. Anyway let's see what 6z makes of things.

[Altostratus]

I missed all of yesterday’s runs and was expecting to see another disappointment this morning. I was pleasantly surprised. The UKMO is a big doubt though and on reflection, the ECM isn’t great either. It will certainly be cold, but I’m looking for something spectacular, a bit like the GFS 00Z. Anyway, eyes down – let’s see what the 06Z brings.

[Yeti]

Well if one thing is true it's certainly that any cold is well-deserved - people here are amazed by just how unseasonably warm it has been recently! As we can see though the -5s should arrive here Friday night and ought to be nudging into the SE a day or so later:

http://www.wetterzentrale.de/pics/Rtavn662.png

http://www.wetterzentrale.de/pics/Rtavn902.png

Ice days already on the continent and I imagine it will feel pretty raw under that high in Britain, especially where any fog lingers, and with some pleasant winter sunshine around too especially away from the S.

See Thread Below about Feb'09

OH the memories!

Edited December 9, 2009 by Yeti

[Guest North Sea Snow Convection]

I'm another one who wouldn't want to see the block trending north along with low pressure systems. We could easily end up in a position where the south of the UK is under yet another dreadful rainfest whilst the colder air and snow is on the poleward side of the lows further north. I too would prefer a straightforward convective north easterly and the lows much further away to the west.

The UKMO *should* lead to a proper undercut and an easterly but I would agree that it is an unwanted complication and more mild rain to have to deal with first. It looks overly progressive to me - although obviously it can't be ignored.

However, as I said clearly before, no point looking seriously at detail yet whilst the overall pattern is getting into place.

There is overall agreement for high latitude blocking of the sort we have not seen at this time in December for quite a long time. Lets hope it sets up in such a way for our benefit

Edited December 9, 2009 by North Sea Snow Convection

[Cloud 10]

Good run so far from the 06z gfs,high a bit further north,cold a bit further south,this could go the way of the peach !

[Pennine Ten Foot Drifts]

Ensembles not great?

Shorter time they are more supportive but after day 6 it messy as out!

Well yes, but the mean, the control and the op all stay below -5 for a six day stretch from 15th to 21st, which isn't too bad !

[johnholmes]

Taking a rather wider view of the overall models then this link shows that ALL models are having their best run for accuracy at 6 days in over a month.

http://www.emc.ncep..../html/acz6.html

It certainly does not make 6 days down the line in this area a certainty but does give a good deal of confidence for forecasters using the models that the cold spell WILL occur.

Don't expect the detail to be there until T+72 and where/when will it snow-how much etc etc until T+24. At T+12 watch the radar and sat pictures-visual and infra red-take note of what if I may describe them as reliable posters.

and once more the jh request-try the will it snow in the Guides.

I shall be using next week to gather actual events to use in the video being prepared, still with a slight hope we can get it on the site before Christmas.

Edited December 9, 2009 by johnholmes

[bluearmy]

The massive height rise over greenland is certain. what happens to the jet to our south and the interaction of that with the mass of cold air plunging sw is causing the models a lot of problems. this is a rare pattern(especially early in the season with higher sst's north sea and lower in the med than might be expected). the bones are there but to expect to see flesh more than 4 days out is pretty futile IMHO. great runs to look at but the chance of verification? not high as far as detail is concerned. what i will say, remembering the heady days of the seventies/early eighties, is dont under estimate the power of a mass of very cold air. the models certainly will.

[Tim Bland]

First flakes appear in the SE on Sat night in this run then the coild backs off again until late on Tues when the wind Veers more Easterly picking up moisture from the north sea. Expect more widespread snow by Weds on this run

[chionomaniac]

We never seem to get the cold air on this run, a tad worrying?

A terrible run with everything delayed

Cold dry and frost in sheltered spots is all I see

Not at all. Read bluearmy's post. The Scandi shortwave act's as a block preventing the cold from reaching us sooner. But it will be poorly modeled at that range. It would only require a slight change in the modeling for full on cold to actually reach a lot sooner. As ba says the bones are brilliant!

[snowmadchrisuk]

Slower , but the same result , Trend over the last few runs has been to move that really cold pool of air to the North East towards the Uk , and that is why it is slower as it is taking a SW route to the Uk instead of moving directly Westwards towards us. This is all very good because air as cold as what is heading towards us will take some shifting , and the Atlantic would have to make several snowy attempts before it even stands a chance of winning the battle.

Edited December 9, 2009 by snowmadchrisuk

[TEITS]

Seems my post was deleted for posting on the 06Z in the model discussion thread.

Anyway as I said in my deleted post the cold is delayed but the longer term potential was better. However even at +144 we are going to see many more changes but the general pattern remains intact which is good news.

What a snowfest in F.I.

[Guest North Sea Snow Convection]

That little low moving down the north sea takes its time but it is like a finger stuck in a dyke and it unleashes some big cold and a ferocious north easterly gale behind it!! Of course it is not going to go exactly like the 06z suggests, but next week looks very interesting indeed to say the least!