Model Output Discussion 18th Nov.2013-12z onwards.

[ARNOTT ad]

Can some people please show a little more optimism. It's not a competition of let's see where we can find and force in mild weather

[Severe Siberian icy blast]

Other than a few days next week NAO shows little sign of going negative for any lengthy period

although the graph is misleading as we all know its only indicative of what the models are showing. Its not a background signal . Or a driver. Its simply as reliable as the models themselvs. Which at the minute are far from it . Edited November 28, 2013 by Severe Siberian icy blast

[Mucka]

Lot's of discussion about whether we should side with the Operationals or ensemble suits when there is such divergence but I don't see how anyone can declare the Op to be right and ensembles wrong or vice versa - such divergence simply highlights the uncertainty and that is all that should be taken from it IMO. After all the very purpose of having ensembles is to weigh up confidence in any one outcome, they are just another forecasting tool and we should never dismiss data if we are looking without bias to formulate a forecast.

What does help confidence in the operational output though is cross model support and consistency run to run, after all if the ECM this morning was poor who would still dismiss GFS ensembles? And if GFS was poor but its ensembles and ECM Op good then wouldn't it be the Op that was dismissed and the ensembles lorded - this is confirmation bias and we all have it to a lesser or greater degree. Sometimes it helps (when we get lucky) and sometimes it hinders (when we get unlucky).

I am very pleased with my overall record on picking up long range signals (14 days+) but to be fair it is more difficult putting the detail to that as it comes closer so far as it affects are our small Island and what we will actually experience ion the ground.

It is extremely difficult to call our weather so far out (8 days+), especially in a situation as complex and fluid as this although we can have more confidence in one solution than another.

I think on probability we will at least get a good Arctic blast of 2 or 3 days but I can't have high confidence in any one outcome at the moment.

Edited November 28, 2013 by Mucka

[Summer Sun]

GFS out to t114 and I can't see much change to the 06z run

 

[Cecil Hogmanay Melchett]

Bit off a differnce in the low exiting the Eastern seaboard at 114h.Other than that,very similar.

[bluearmy]

no judgement but the jet into the west coast states is flatter and stronger ......................

[Snowman.]

Low exciting the seaboard is further south and hasn't split yet.

 

 

Also more energy in USA with the low further east.

 

Expecting a different run from this.

Edited November 28, 2013 by SN0WM4N

[Cecil Hogmanay Melchett]

no judgement but the jet into the west coast states is flatter and stronger ......................

Yup,spotted that Nickl.

[Mucka]

no judgement but the jet into the west coast states is flatter and stronger ......................

 

Well that may be no bad thing since it may mean less energy spilling out toward Greenland downstream.

I think the bigger player is how the shortwave/low behaves and interacts with our trough.

 

Quite different to the 00z at the mid range which shows how volatile and open to change things still are.

Edited November 28, 2013 by Mucka

[Methuselah]

Can some people please show a little more optimism. It's not a competition of let's see where we can find and force in mild weather

I have plenty of optimism, ARNOTT. it comes form the almost certain knowledge that I, you, the GFS, the METO - not even James Madden  - do not know what things will be like in, say, a month from now...

Edited November 28, 2013 by A Boy Named Sue

[Cecil Hogmanay Melchett]

Hmm not sure im going to like where this run is going,the jet seems much stronger which may inhibit the ridge in the western tlantic.

[Matty M]

the 1040hPa high has been replaced with a 1000hPa low near Newfoundland at 162hrs.......

[Captain Shortwave]

the 1040hPa high has been replaced with a 1000hPa low near Newfoundland at 162hrs.......

Yeah that high is now about 1000 miles further south and having fun in Florida 

UKMO at day 6

Nice to see the uncertainty exponentially increase as the start date of the "cold" spell approaches 

Frankly the GFS looks a mess over North America, I mean it's showing pretty much a slack pressure pattern over the northern states and Southern Canada.

Edited November 28, 2013 by Captain shortwave

[radiohead]

Significant NH changes on the 12Z GFS by T168. It's worth remembering that the 06Z and 0Z GFS operational runs were significantly colder than the majority of the ENS so it wouldn't be surprising to see a less severe cold plunge in FI on this run.

[Snowman.]

I would love to think that this run could be better if we still get some amplification as the low in the Atlantic is removed. 

[johnholmes]

the 1040hPa high has been replaced with a 1000hPa low near Newfoundland at 162hrs.......

 

which shows the I was going to say futility but will change it to the variablity of GFS from run to run at these time scales. Have you any idea how the 12z today at 144h approximately compares to the 12z 168h for yesterday?

 

Looking on Wx Online 3 out of the last 4 issues for the same time show low pressure close by Newfoundland, only the Tuesday 12z showed high pressure rather than low pressure. So in terms of continuity low pressure seems favoured for the same time, that is Thursday 12z 5 December. Mind you that is not to say it will be thus. But it does show how run to run variability is quite often not shown if you compare the same time GFS issue for some time, the same time/date, in the future?

Edited November 28, 2013 by johnholmes

[ARNOTT ad]

And led up the garden path yet again why do the models constantly produce such poor Synoptics over us (if you like cold weather). Always seems so easy in other parts of the world!

[OldMetMan]

Hi folks,

As we approach the official start of winter, I thought I would weigh in with some thoughts on where we are and what the current model trends are showing.

Looking at the current hemispheric 500mb flow, what strikes me is the number and amplitude of vortices and of course, the strong upper ridge over us. Very meridional I think for this time of year, and gives me the impression that large-scale blocking may be the trend in the next few weeks.

I am intrigued by the northerly the GFS has been depicting for several runs, for around the end of the first week of December and, given the current upper ridge position, looks to be an entirely plausible development, as upper highs positioned as of now, have a strong tendency to retrogress with LP and an amplifying upper vortex forming and heading down into Europe. As to the axis of the coldest air and its persistence, much depends on whether the upstream pattern supports it by increasingly amplified long waves, which is what I was suggesting may happen above.

In my view, the current corresponding jet positioning, structure and strength is quite distorted and again suggests to me the possibility of widespread hemispheric blocking:

It all looks rather fragmented, the strongest areas being in the W Pacific and NW Atlantic, but with weakish flow over the E Pacific and much of N America, also a quite pronounced sub-tropical jet crossing N Africa.

Assuming the GFS is picking up on a definite cold trend here, (and the ECM as well) which of course is by no means certain this far off, I think we need as ever to closely watch upstream developments, particularly in the E pacific and over the E US/Canada, to see if the upper flow is amplifying noticeably, and thus whether any cold Arctic blast will persist near or over us, as the wave pattern becomes more static.

Mid-latitude HP across the Atlantic this time of year has a number of possible outcomes, one of which is the persistence of what we have now, with minor shortwaves heading SE around the E fringe, or the HP could just slip SE to bring us a mild SW flow. However, given the strong NW Atlantic jet, some strong cyclonic development looks likely in the short- to mid-term, with LP heading E and then SE, making the Arctic blast a strong possibility as the HP moves W.

One other thing that has caught my attention is the depth of cold air over Greenland and the Canadian Arctic. Quite intense for this early in the season.

Some interesting possibilities for early winter blocking I think.

[Mucka]

Yeah that high is now about 1000 miles further south and having fun in Florida 

UKMO at day 6

Nice to see the uncertainty exponentially increase as the start date of the "cold" spell approaches 

Frankly the GFS looks a mess over North America, I mean it's showing pretty much a slack pressure pattern over the northern states and Southern Canada.

 

 

GFS looks like another outlier, only this time on the mild side. No doubt the ensembles will go the other way. â€‹ 

 

Seriously though, GFS is so wildly different to  the 00z that we can't have any confidence in either run, probably best to stick with the Euros for now.

UKMO is quite consistent witht his mornings run and look okay to me at 144h though a chart another 12h or 24h would be much more revealing. 

Still it is much more akin to the GFS 00z than the GFS 12z so I wouldn't say bin this GFS run but I would say treat with extreme scepticism for now.

[Joe Levy]

And led up the garden path yet again why do the models constantly produce such poor Synoptics over us (if you like cold weather). Always seems so easy in other parts of the world!

I don't understand the pessimism. Firstly, this run hasn't finished. Secondly, it is only one run. Sure, it's not as clean or as clear cut as some of the previous runs, but that is to be expected. Patience is a virtue that might come in handy at the moment!

[MR EXTREMES]

yep gfs has the ian brown famous channel of doom.

well was expecting the whole lot to be futher south the pressure being forced north is just to much and the low heights are just coming out of the states moving northeast but high pressure is not far enough north and high is futher east over us pushing a near miss situation this happens all the time when things are not blocked to our nw strong vortex does not help.

 

I think as it gets closer to a realistic timeframe it shows why really its not worth banking anything any later than t144 and that's pushing it.

its not a 09/10 type of set up we are seeing its totally different in many aspects.

Edited November 28, 2013 by emotional rollercoaster

[Cecil Hogmanay Melchett]

And led up the garden path yet again why do the models constantly produce such poor Synoptics over us (if you like cold weather). Always seems so easy in other parts of the world!

You obviously wern't here in 2009 2010 when we saw amazing synoptics..

[karlos1983]

we've gone from this

to this

 

In the space of 6 hours. Fantastic!

 

Not a pretty Fl, PV right where we don't want it. Hopefully we see this as an outlier.

 

Edited November 28, 2013 by karlos1983

[Tim Bland]

To be honest I alsways rate the 12Z over the 06z as it is more often correct.  Not good news im afraid. Lets hope there's no backtrack from the ECM later or this could be the first major dissapointment of the winter... Just glad it not actualy even winter yet!

[radiohead]

we've gone from this

to this

 

In the space of 6 hours. Fantastic!

 

They don't call it Fantasy Island for nothing!

 

Anyway, let's see what the ECM does later.