Model Output Discussion - 19th - 25th December

[Thundery wintry showers]

If the current outputs verify, the comment about sodden ground will be regionally sensitive- I can't imagine it drying out too much anywhere in Scotland, NW England, Ireland or north Wales for instance. Some parts of western Scotland may well end up exceptionally wet. A good anologue with the setup for 26th-28th December arose in the second week of December 1994 which brought record-breaking rainfall totals to Glasgow (note that that particular one was followed by a sluggish northerly and then a week of colder zonality interspersed with two frosty anticyclonic interludes).

[phil nw.]

A lot of ensemble members seem to go for a northerly around the 28th. In fact it would appear that the operational keeps the mildest air furthest north. So, by no means locked in Bartlett conditions just yet.

Yes C and looking at the thumbnails for the same date we can see the differences in the sypnotic development.

http://www.wetterzen...nspanel1921.gif

a number of members show more amplitude and more ridging of the High.

Although the overall pattern is Atlantic driven any buckling of the flow can give something more interesting and certainly going by the mean line of that Ens. graph the outlook beyond Christmas is not that mild-considering the +NAO setup.

Edited December 20, 2011 by phil n.warks.

[The PIT]

Well apart from mainly mild weather just a brief bit returning pm air at the end of this week this developing Bartlett looks like it will give us a few breezy days but nothing tremendous. This is a pattern that can last for weeks fingers crossed it won't. If Steve's M left the building we know it's bad.

[NorthernRab]

Cloud would be the key to very mild temperatures, especially at night.. the 12z IS a very mild run, and the ensembles don't suggest a cool down, they suggest a horrible mess of confusion and lack of agreement.

First of, I never said the 12z was anything but a very mild run, what I said was that there's nothing solid pointing towards 2 weeks of such weather (there never is for any weather in the UK) - and the ensembles do suggest a cool down, nothing more. Indeed, this mess of confusion and lack of agreement supports my point entirely, any one talking of two weeks of mild weather at this stage is being extremely hasty and arguably foolish.

[ChartViewer]

Yes C and looking at the thumbnails for the same date we can see the differences in the sypnotic development.

http://www.wetterzen...nspanel1921.gif

a number of members show more amplitude and more ridging of the High.

Although the overall pattern is Atlantic driven any buckling of the flow can give something more interesting and certainly going by the mean line of that Ens. graph the outlook beyond Christmas is not that mild-considering the +NAO setup.

Very interesting In depth discussion from GP/CH re GWO in early Jan re possible Northern blocking...what i would be interested in is when that may show on Model runs......If it verifies?......As for now zonality and milder with models showing suedo Bartlett conditions but not a true Bartlett........Models will start to show more Northern blocking if the In Depth discussion about future teleconnections starts to develop.

I know this is often frowned on but maybe now worth looking at the far off reaches of FI and ensembles for signs of colder weather for you coldies

Edited December 20, 2011 by ChartViewer

[lorenzo]

Out of the ensembles you mention Phil, this one is on the flip side of the Bartlett coin..

Nothing zonal looking about those charts and the first time I have seen a 1050 reading over Greenland this year anywhere on the models.. something to watch perhaps..

[Paul White.]

Yes C and looking at the thumbnails for the same date we can see the differences in the sypnotic development.

http://www.wetterzen...nspanel1921.gif

a number of members show more amplitude and more ridging of the High.

Although the overall pattern is Atlantic driven any buckling of the flow can give something more interesting and certainly going by the mean line of that Ens. graph the outlook beyond Christmas is not that mild-considering the +NAO setup.

Just had a look and p13 is my favoured ens. The ENS do seem to be all over the place, IMO nothing nailed as yet.

[phil nw.]

Out of the ensembles you mention Phil, this one is on the flip side of the Bartlett coin..

Nothing zonal looking about those charts and the first time I have seen a 1050 reading over Greenland this year anywhere on the models.. something to watch perhaps..

Just had a look and p13 is my favoured ens. The ENS do seem to be all over the place, IMO nothing nailed as yet.

Yes as Chiono pointed out, at this stage around T180-192 there`s quite a split in the Ens.

It`s also interesting that in the lower resolution part of the run the Op is one of the milldest members.

Maybe it will amount to nothing but with so many members disagreeing it brings some interest and shows post Xmas developments are still uncertain.

Edited December 20, 2011 by phil n.warks.

[nick sussex]

Given some of the bigger changes in the earlier timeframe I wouldn't read too much into the output past 168hrs.

The flat upstream pattern finds a little more amplification and we see that troughing on the ECM, theres quite a northwards shift in the pattern from the earlier 00hrs runs and so this may just be a one run blip.

Later the models sink any ridge quickly as the pattern flattens out again.

There are two important timeframes here, more especially one between 120-144hrs, this is when the ECM phases that shortwave with the main eastern Canadian troughing, later at 192hrs-216hrs is the direction of the jet, this heads east and we see the ridge flatten.

We're actually in a similar situation to a few weeks back, I remember becoming obsessed with phasing upstream!

If the upstream pattern amplifies more than is currently shown, the phasing takes place more favourably digging further south, this forces ridging further north, then the jet bounces ne rather than east and the ridge topples favourably in towards Scandi, an easterly gets pulled west but I think we'll still see this flatten to some extent but you might still get enough surface cold to make things seem more seasonal.

Alternatively the models are close to the mark with just a brief chance of some surface cold mainly reserved for the south and se, or the models have overreacted to some upstream signal and we see the pattern flatten out quickly.

Because the key timeframe is within 168hrs then what changes we can see within that timeframe will determine what option/s we're left with.

Edited December 20, 2011 by nick sussex

[Paul White.]

The 192 hs 12z ECM NH chart does show a split vortex, But I am not sure where we go from here.

http://hw.nwstatic.co.uk/ecmimages/20111220/12/npsh500.192.png

Edited December 20, 2011 by paulwhite22

[phil nw.]

ECM up to T144 pretty much shows the same Euro High/Iceland-Norway low pressure pattern as the GFS and UKMO.

http://www.wetterzentrale.de/pics/Recm1441.gif

http://www.wetterzentrale.de/pics/Rtavn1441.png

http://www.wetterzentrale.de/pics/Rukm1441.gif

Further on ECM still keeps the flow pretty flat and zonal keeping the heights very close to the south

http://www.wetterzentrale.de/pics/Rtavn1921.png

similar to the GFS thus restricting chances of any cold moving down from the North.

[Summer Sun]

The 192 hs 12z ECM NH chart does show a split vortex, But I am not sure where we go from there.

http://www.netweathe...ction=ecm;sess=

We just stay with high pressure and more of the same with temps around the seasonal average

http://www.wetterzen...cs/Recm2161.gif

http://www.wetterzen...cs/Recm2401.gif

Edited December 20, 2011 by Gavin D

[Duane S.]

Just had a look and p13 is my favoured ens. The ENS do seem to be all over the place, IMO nothing nailed as yet.

You'd have to say 3 or 4 showed at least some promise. P13 struck me and had an interesting conclusion, albeit in far away FI land.

ENS are fairly promising, mild-very mild short-term absolutely nailed on now, mild conditions thereafter far from it. I'd agree that you would expect this be in place for 10 days+ but it may only be 7 days before we start to see a change for the better looking at the models hinting at a slight pressure rise above us around the 28th

To anybody trying to learn from this thread don't get discouraged by posters claiming to be able to see into the future on the basis that we have a strong polar vortex and that the models are showing a zonal outlook at present. If GP turns out wrong at least he's offered up some serious science to back up his thoughts, not just switched on his PC 4 times a day and followed the GFS OP frame by frame. Of course this CAN (and indeed, could) become an entrenched pattern but i've seen enough on the flip side to say it certainly won't be hanging around for 6-8 weeks (and I've seen some predicting even longer!).

[phil nw.]

Given some of the bigger changes in the earlier timeframe I wouldn't read too much into the output past 168hrs.

The flat upstream pattern finds a little more amplification and we see that troughing on the ECM, theres quite a northwards shift in the pattern from the earlier 00hrs runs and so this may just be a one run blip.

Later the models sink any ridge quickly as the pattern flattens out again.

There are two important timeframes here, more especially one between 120-144hrs, this is when the ECM phases that shortwave with the main eastern Canadian troughing, later at 192hrs-216hrs is the direction of the jet, this heads east and we see the ridge flatten.

We're actually in a similar situation to a few weeks back, I remember becoming obsessed with phasing upstream!

If the upstream pattern amplifies more than is currently shown, the phasing takes place more favourably digging further south, this forces ridging further north, then the jet bounces ne rather than east and the ridge topples favourably in towards Scandi, an easterly gets pulled west but I think we'll still see this flatten to some extent but you might still get enough surface cold to make things seem more seasonal.

Alternatively the models are close to the mark with just a brief chance of some surface cold mainly reserved for the south and se, or the models have overreacted to some upstream signal and we see the pattern flatten out quickly.

Because the key timeframe is within 168hrs then what changes we can see within that timeframe will determine what option/s we're left with.

A good analysis as usual Nick.

Of course we have yet to view the ECM ens, but it will be interesting to see if they split after T168 like the GEFs.

Certainly there`s enough to keep some interest for post Xmas developments.

[wolvesfan]

Evening all,

ECM,GFS both mods showing a quieter atlantic than we've seen recently,low pressure formation and intensity also seems reduced,could we be seeing a transition period to something more high pressure dominated?.IMHO i wouldn't be surprised to see heights rise further north than we've seen so far this winter,mods are hinting at this currently.

[Liam J]

We just stay with high pressure and more of the same with temps around the seasonal average

http://www.wetterzen...cs/Recm2161.gif

http://www.wetterzen...cs/Recm2401.gif

Most of the charts you post Gavin are well into FI land, also taking each models operational run as gospel can be a fools game.

Not all plain sailing regarding the evolution of the current set up, look at the GEFS ens with quite a split developing around 168hrs.

[nick sussex]

Looking upstream over in the USA they expect the pattern to become more amplified before flattening out again, because of this if you're looking for some colder conditions it's all down to how far north any high can get before the next pulse of jet energy topples this, remember as the pattern amplifies you normally see some slowing of the jet.

This gives a window of opportunity which won't last too long, to at least get some surface cold into the UK we need to see the ridge topple towards Scandi, then as this topples you have a chance of pulling in an east to se flow.

If let's say we get the ridge far enough north then the angle of the jet exiting the eastern USA will determine the topple position of the high.

This comment from NOAA is basically in a nutshell what could be the decisive factor.

...STILL CONSIDERABLE UNCERTAINTY WITH DETAILS OF POTENTIAL ERN

U.S. CHRISTMAS WEEKEND SYSTEM...

[shedhead]

First of, I never said the 12z was anything but a very mild run, what I said was that there's nothing solid pointing towards 2 weeks of such weather (there never is for any weather in the UK) - and the ensembles do suggest a cool down, nothing more. Indeed, this mess of confusion and lack of agreement supports my point entirely, any one talking of two weeks of mild weather at this stage is being extremely hasty and arguably foolish.

With respect, neither did I say I expected 2 week of mild/very mild weather. What I said is any cold pattern is at least 2 weeks away (as you can see below), so I was simply pointing out what the models currently suggest. I don't think you will find many experienced members in here who'd argue that a cold pattern is likely between now and Jan 3rd.

Posted Today, 18:17

As others have said, classic Bartlett conditions likely in the foreseeable now, 13, 14 perhaps even some 15c maxes possible at times between now and New Year, in what is shaping up to be a potentially lengthy mild/very mild spell. Some hope in FI that pressure begins to rise a little father north, but any cold pattern still seems a very long way away, 2 weeks at least I'd imagine based on the current outputs.

Edited December 20, 2011 by shedhead

[Robbie Garrett]

I'm struggling to see where you're getting two weeks of very mild temperatures from? The GFS Ensembles suggest a cool down next week, with wintry showers for some - even the GFS 12hz would see temperatures supressed under any cloud, especially in the NW, whereas in the SE temperatures could fall away quite readily in clear spells as pressure is quite high at times. The lengthening days certainly won't make any difference until well into February anyway.

So am I, the high is providing some cooler temperatures under clear skies, and not till Thursday 22nd December onward's day's don't get longer, not tomorrow. From my experience with Aviation Training, high pressure does not signify good weather and warm temperatures, quite the complete opposite depending on position and flow etc

Also not sure if someone knows the answer to my question, but if the current high as shown in the models drift further east, and the current atlantic ridge rises to the north, is this what we are looking for? I can't really understand the evolution of how such high forms, from what I can see is the jet blasts it's way through it anyway.

[OldMetMan]

Yes, it is a classic Bartlett from the era that we have all lived through and know so well.

Possible though that it may not last, unlike in those winters, as I suspect the models are wrestling with a struggle to change the pattern, which in itself of course may flatten again.

The trend has been maintained in the 12Z GFS, and the 12Z ECM, with cold air coming south and HP to the NW, so despite the time distance, it's a distinct possibility I think, and one that I can recall happening in the past (for instance the end of December 1970).

Yes, it's all a matter of whether the mobility will take over again and simply displace the HP and cut off any possible polar air incursion, taking us back more or less where we started. If the Omega block did stick (I like that expression!), then how it would affect the uk would obviously depend on where the axis of the upper ridge lies; it would need to be around 20-30W to allow the cold air to get anywhere near us.

My own view on how upper long waves increase in amplitude is that it might only need a deep LP say to engage a particular upper trough, and thus increase its amplitude, for the process to ripple downstream, with corresponding high amplitude ridge, then trough and so on. This is what the models seem to be trying to deal with so it could go either way really.

[BLAST FROM THE PAST]

Isn't a Bartlett a stagnant HP system over Europe and not a moving/transient feature? I wouldn't say we're headed in Bartlett territory. Having said that the general pattern shown by models looks reasonable to me with mixed temps but some failry mild days maybe had towards New Year.

BFTP

Edited December 20, 2011 by BLAST FROM THE PAST

[shedhead]

Isn't a Bartlett a stagnant HP system over Europe and not a moving/transient feature? I wouldn't say we're headed in Bartlett territory. Having said that the general pattern shown by models looks reasonable to me with mixed temps but some failry mild days maybe had towards New Year.

BFTP

Fairly mild Blast?? 850Hpa temps of between 5-7c for most tomorrow, so 11-12c looks like being widely available and 13, perhaps 14c locally. I'd call that very mild, with a repeat performance possible on Thursday too, albeit perhaps not quite so warm overall.

Edited December 20, 2011 by shedhead

[Frosty.]

the models are wrestling

I would pay to watch the models wrestle, are you selling tickets for this event ian?

The models show a colder day on friday and a frost overnight but then slowly becoming milder on xmas eve and day. The meto update today points to an unsettled westerly pattern with the air cold enough at times in the north to produce wintry showers but shortlived cold snaps seperating phases of average and milder temps, pretty much what we have seen through most of december so far.

Edited December 20, 2011 by Polar_ Low

[Frosty.]

Isn't a Bartlett a stagnant HP system over Europe and not a moving/transient feature? I wouldn't say we're headed in Bartlett territory. Having said that the general pattern shown by models looks reasonable to me with mixed temps but some failry mild days maybe had towards New Year. BFTP

Neither would I, it's just IB trying to wind everyone up and he seems to enjoy it. There is no sign of the B and we will probably remain in a broadly similar pattern to the last 3 weeks but minus the cold weather we have seen in the last few days.

[nick sussex]

The ECM ensemble maps at 168hrs show some support for that ridge to the west:

http://www.ecmwf.int...t!2009112700!!/

The control and operational run closely matched.

The extended ECM De Bilt ensembles show the major clustering past day 10 turning less cold, the control run looks to keep high pressure in charge over in Holland, this cold surface flow given the pattern would have a chance of extending into more especially southern and eastern areas of the UK.

http://www.weerplaza...?type=eps_pluim

Because the initial placement of the ridge is effected by events in the eastern USA in terms of amplification I'd be a bit wary of reading too much into the post 168hrs output until we see whether the models have got this correct.

Edited December 20, 2011 by nick sussex