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

[Tamara]

I think it's just a question of patience.  With the QBO phase and the fact we're in solar max (although the sun's gone quiet again for the moment) - there's a really good chance of a decent warming later on - but probably not for another month.  I think it's quite ominous though that even with the rampant vortex, we're still seeing a below average November CET and the Alaskan ridging, and possible cold shots from the North. As soon as we see some warming later on, I suspect the vortex's going to get crushed (assuming the broad pattern is similar). Cold lovers need to hope for a late Dec warming, rather than late Jan warming though. 

Yes, it keeps being repeated I know, but we have the Alaskan poleward ridging High to thank for making a background fixed +AO pattern more amplified, and thus more conduisive to colder interludes than otherwise would be the case. . On this basis there is growing agreement across the models for the colder incursion for the first week or so of December. That is the positive slant that can be put on this

 

Taking into account the tendency for the models (especially the ECM) to over amplify the jet stream at distance, then it remains to be seen how far south any polar incursion is able to penetrate with the usual shortwave cut-off features to bear in mind which are picked up in the closer time period and form waving boundaries along the Polar front jet which slow down and limit the extent of cold air advection.

 

There have already been good illustrations this morning of why we are very unlikely to see anything sustained beyond a quite brief cold incursion at the December 4/6 -ish time period as the pattern temporarily amplifies. With a -PNA pattern, neutral ENSO conditions in tandem with the -EPO ridge we are destined to persist with only mid latitude ridges on the basis that pressure over the pole is set to remain firmly positive and this will limit the ability (and sustainability) of these ridges to extend northwards as a response to amplifications in the jet stream. The deeper cold will always stay bottled up towards the pole on this basis.

 

We depend upon the background state of the + QBO to weaken over the winter, as predicted, and in this way, with time, relax the westerly ribbon of energy over the polar stratosphere and hopefully, in the way you suggest, create conditions for more significant disturbances of the polar vortex as it becomes less stable and weakens its grip.  In the meantime we continue to depend on the pacific ridge to remain highly amplified and poleward for as long as possible to create the best possible opportunties out of an unfavourable overall pattern. This will become harder to sustain as we go through December and into January as the background AO signal beomes more and more dominant and extensive

 

If the Pacific pattern becomes less favourable i.e an ever deeper -PNA (as some modelling is starting to suggest as we go into December) and the upper vortex intensifies in the absence of any wave breaking (as a result of the Aleution High de-amplifying and becomes less poleward) then this will increase the trough over the US, strengthen further the downstream ridges from Florida, Bermuda to the Azores and correspondingly at the same time revert the bulk of the vortex back to Canada and Greenland. The result will be the pattern will de-amplify and flatten and the PFJ will adjust further northwards as the jet stream aligns SW-NE

 

It would be all eyes then on the latter part of the winter for when greater ammunition might become available to break up the polar vortex and create better blocking opportunties. Its a long long way off obviously and open to speculation, but based on the background factors, I can't see this happening at all until we get at least a few weeks into the New Year and probably late January and February. We best hope that we can keep lining up these transitory polar incursions for the time being

Edited November 27, 2013 by Tamara תָּמָר

[MPG]

Re: missing data on the Gfs 06 op run I'm afraid I'd have to refer you to one of the more experienced and knowledgeable members on this forum in order to give you a comprehensive answer. However, you must admit this is not the first time this has been stated about this particular run. I can honestly say hardly a day goes by that this whole "lack of data issue" isn't brought up by someone or other.

Ok no worries. But I dont think its a lack of data issue. Nice update from Ian F....if you like colder weather.

[Cheshire Freeze]

I don't think that anyone has said that there is no sign of cold, CC. More so, and Gibby is right here, - there are no signs in the current output of long term sustained severe cold for the UK - ie the such that favourably positioned HLB's would produce. Any one who suggests otherwise is kidding themselves. That does not mean that we will not see a spell of below average temperatures - in fact I believe that December will come in slightly below average due to the NW/ SE orientation of the jet stream and those further north are likely to see some tempreratures cold enough for snow at times.

 

There were a couple of good posts from CH and SM earlier that mentioned the stratosphere and wQBO and how that colder oulooks are still possible in spite of the current stratospheric conditions, but sustained HLB's are unlikely in the immediate.

 

Yes, as I said over in the winter thread a few days back, I don't expect December to be a 'bone shaker'....more a mish mash of synoptics ranging from cold spells to slightly above average spells. It wouldn't surprise me in the slightest if we temporarily head back to a less cold scenario post 1st week of December. However, we're seeing a lot of cold pooling to our N within the NWP modelling and even 2-3 days of 'wintry potential' cannot be sniffed at given the prognosis for December by a few members. I'm sure many would be glad to see some snow falling in early December, regardless of its longevity....this time around.

[johnholmes]

Re: missing data on the Gfs 06 op run I'm afraid I'd have to refer you to one of the more experienced and knowledgeable members on this forum in order to give you a comprehensive answer. However, you must admit this is not the first time this has been stated about this particular run. I can honestly say hardly a day goes by that this whole "lack of data issue" isn't brought up by someone or other.

 

Some confuse different data inputs over the basic data for every run with so called missing data. There is a difference.

[Cheshire Freeze]

 

an Fergusson â€@fergieweather13m

Colder spell expected later next week may last somewhat longer than initially suspected but longevity & influence to S UK very uncertain.

 

looks like met are more confident now of a more prolonged cold-spell,for most of the country

 

 

Brilliant!

[Frosty.]

I agree with steve, the mean only provides the broad brush strokes, the finer detail could mean a severe wintry outbreak hitting the north later next week and then sweeping further south...what fantastic news from fergie tweet.

[warrenb]

Well it is easy Steve, the big purple bit is not where it normally is, so the weather isn't going to be what it normally is.

[SMU]

Well it is easy Steve, the big purple bit is not where it normally is, so the weather isn't going to be what it normally is.

 

I like your style...

 

I will take the big yellow bit over Greenland thanks.....

[tight isobar]

I like your style... I will take the big yellow bit over Greenland thanks.....

.yes SM, would be good via Greenland) for more sustainable cold..wouldn't be suprised to see this modeled quite soon either with the current track of evolution.!!!

[garbagebags]

Out in FI but this is a punishingly cold and snowy chart.

[Captain Shortwave]

I have tried to not really look at the UK, and more of the general northern hemisphere pattern whilst looking at the mean. Steve Murrs sentiments on this are perfectly true and the models will tend to smooth out the Atlantic ridge. A couple of things I will say is.

1. The ECM op is probably handling the Canadian region wrong in its latter frames. I don't think a HLB will develop along the northern coastline of Canada and favour more the solution which holds the Alaskan/Newfoundland highs apart with a deep trough developing through North America.

2. I expect the polar vortex to transfer from the Siberian side to the Canadian sector during week 2, by this I mean the Canadian/Greenland sector will perhaps start to dominate over the Siberian sector. Hence the key is how deep a trough we can create over the states which in turn amplifies the ridge in the Atlantic. 

3. Most shockingly I see the 06z GFS op as a very feasible solution which to be honest is a pretty decent result with a decent window for wintry precipitation before the high starts to push into the UK.

A few things related to the pattern remains at and beyond day 10. Firstly of course how potent and how far reaching any cold spell is at the day 10 range and secondly as I mentioned last night, where does the high go? Does it collapse over the UK and slowly sink into Europe, or do we develop a large and strong enough depression over Southern Europe to support a more substantial cold spell. AKA heights to the north east.

Will I ever stop obsessing about Scandi highs, probably not 

 

P.S Whilst unlikely I could say that the GEM solution this morning does have a slight chance of happening, more so than the ECM op in my opinion.

Edited November 27, 2013 by Captain shortwave

[bluearmy]

cant attach the ecm 10 day spread but it does show clustering around the low dropping nw/se into ireland. imo, not a strong enough signal and i'd like to see some more runs before making a call on its trajectory. fwiw, the control follows this route and cuts across the centre of the uk. snow event approx north of manchester - norwich. we shall see.

[mountain shadow]

I like your style...

 

I will take the big yellow bit over Greenland thanks.....

 

I would rather it was Red.

 

:-0

[terrier]

Just checked the gfs ensembles and it seems to me like the op was a cold outliner so I wouldn't discount gibbys assessment just yet

[beng]

 

an Fergusson â€@fergieweather13m

Colder spell expected later next week may last somewhat longer than initially suspected but longevity & influence to S UK very uncertain.

 

looks like met are more confident now of a more prolonged cold-spell,for most of the country

 

 

I assume then that In terms of the influence to the South, the Met Office are no doubt factoring the likelihood of a short-wave developing which won't be picked up yet (or details not certain at least), and which will impact on the depth of cold further south.  Quite likely you'd have to say at this time of year with the relatively warm sea temps etc.

Edited November 27, 2013 by beng

[MR EXTREMES]

But with respect you are using GFS charts to back up data supplied by ECM and those temperature profile map readings are as useless as a chocolate fireguard at that range but hey ho everyone to their own.

Absolutely correct I still refuse to buy into anything but a normal average December and there's a strong possibilities that the month of December will continue with a typical December weather type one blinding ecm chart in fi does not equal 2010 1995 or 1963.And some of the more seasoned model watchers them selfs have really shown very little interest in December developments that says alot in its self vortex is running the model side show.

[Ian Brown]

Yep no sign of cold.....cold, cold where are you cold?!........Oh, wait

 

 

 

Of course this hasn't actually happened yet and any plunge of cold air is subject to the timing of Seaboard depressions and the usual complications associated with getting polar air across the UK.

[Ian Brown]

With regards to Steve's post, I don't agree that it is poor form to go for a return to mild after any initial Northerly, unless we are looking at a Dec 81 scenario, which we are not,  Gibby and whoever else are going with by far the most likely solution, particularly as we see nothing to suggest HLB in the NWP.

[Gael_Force]

Absolutely correct I still refuse to buy into anything but a normal average December and there's a strong possibilities that the month of December will continue with a typical December weather type one blinding ecm chart in fi does not equal 2010 1995 or 1963.And some of the more seasoned model watchers them selfs have really shown very little interest in December developments that says alot in its self vortex is running the model side show.

 

Of course it is, it always does - it is whether it is disrupted, positioned in the western or eastern arctic that makes the difference to our expected weather conditions.

[Frosty.]

The GEFS 06z mean is looking very good for a cold, windy, unsettled blast from later next week into the following week with progressively colder arctic air digging south, so frosts become widespread and sharp and showers turn more and more to hail, sleet and snow with significant accumulations across hills and in the north, showers merging into longer spells of wintry precipitation at times. ..I expect further upgrades as the clock ticks down into the reliable timeframe.

[gottolovethisweather]

Blimey, we are going around in circles, whether the chocolate fireguard will remain partly melted or frozen solid is yet to be determined, but in my eyes and those of the MetO (see above) suggest a new trend is emerging, albeit the severity of which is undetermined at this juncture.

 

To repeat - Anyway, let's move on as this NOT a discussion based around one's individual's analyses over another, it should be about what the various NWP outputs are suggesting, and December is only just around the corner now.

Edited November 27, 2013 by gottolovethisweather

[Nick F]

Those worried about the flatness of the jet shown upstream by the GFS, the modelled shunt of very cold air southeastwards across the UK later next week appears to be linked to displacement E and SE of the upper vortex across Greenland rather than from an increasingly meridional wave pattern working downstream creating trough amplification over us to allow cold air to escape south from more northerly latitudes.

 

Given the very cold deep cold air over Greenland and the northeastern Canada indicated by models, but a strong and fairly flat-ish PFJ which is shunted south by the colder air, a deep 'trigger' low may develop to the W or NW and track SE (as shown by 00z ECM) - with a severe northerly or northwesterly gale ushering in very cold air and snow from the north/northwest - with potential for blizzards for northern Britain a prospect.

 

After the calm and settled weather of recent, what unfolds later next week could come as a shock for some, but of much interest to the weather enthusiast.

 

Whether we see ECM deter idea of a closed upper low circulation develop over N America allowing height rises to extend across the top of Canada towards Greenland to prolong the cold or GFS's intact troughing south across N America from the polar regions with low heights extending across Greenland - remains to be seen.

[Cloud 10]

cant attach the ecm 10 day spread but it does show clustering around the low dropping nw/se into ireland. imo, not a strong enough signal and i'd like to see some more runs before making a call on its trajectory. fwiw, the control follows this route and cuts across the centre of the uk. snow event approx north of manchester - norwich. we shall see.

 

 

Day 10 ECM spread.

 

[Gael_Force]

It's why I don't like analogues much, although I respect the insight (and memory!) of those that post about them.

 

After all,  all of the models are near identical analogues of each other at the start of their respective runs, yet they all look very different at T240 (and the actual weather different to each of them). 

 

It is not about trying to match surface weather for a specific location and point in time  - if we look at upper air analogs in the NH for a similar date, then pick out years where there are corresponding pattern connectors, it can give pointers to the likely broadscale movement down the line.

[mountain shadow]

Senior Forecaster on Netweather mentioning possibilty of Blizzards!!

 

Again, I think we have to be cautious until we get into the Higher resolution on the models. We have been here a hundred times before, where as we get closer to T+0 the pattern flattens and the cold quickly shunts East.