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Model Output Discussions 06z 04/11/16

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11 minutes ago, bluearmy said:

Crewe, it's going to be a cold start to winter - 'exactly what did you expect to see from the window of a Torquay hotel room! Hordes of wildebeest etc etc' 

IMG_0477.PNG

 

If you chose to interpret a three week ahead broad background as meaning widespread snowfall then more fool you. As steve posted, we were in the raffle but Eastern Europe has won first prize and we have to make do with the coldest end to November since 2010 and  the coldest first third dec for quite a few years too. 

I interpret low heights running to our S as low heights running to our S. It's a pretty big miss by the model if you ask me. Of course I'm going to equate Low heights to the S and HP to the N as potentially snowy....given the time of year etc. It was a realistic expectation. 

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9 minutes ago, Nick F said:

Think we'll start to see plenty more teasers now from GFS FI over the coming days ... which will have Sidney running for Knocker's Woodshed.  Just a question of waiting for the ridges and troughs to position favourably to bring the deep cold in.

If I'm reading the ec46 means correctly then this amplification of the HP N/NW should be signaled within a couple of days towards the end of the EXT EPS.

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Just now, knocker said:

If I'm reading the ec46 means correctly then this amplification of the HP N/NW should be signaled within a couple of days towards the end of the EXT EPS.

Good to read Knocker...let's hope we do indeed see some signs of this in the EPS. We can have a little more confidence in the scenario then!

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8 minutes ago, Man With Beard said:

I'm with you Crewe. I'm in total agreement about the background signals but making deterministic predictions beyond D14 for a small island is a very dangerous game. Now I'm sure our loved and respected posters do not mean to be so deterministic (and loved seeing Tamara post a 1962 chart!), but I fear a level of expectation in here that I've never seen before. Don't do it folks. The weather respects no-one!

I will never know as much as Tamara but 1962 has no relevance to the here and now . I love the cold and snow and I'm a huge fan of Winter but ever Winter writes its own story without stealing a yesteryears script

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P17 if you want to send yourself to bed all hot and flustered.

gensnh-17-1-384.png

http://www.meteociel.fr/modeles/gefs_cartes.php?ech=192&code=17&mode=0&carte=1 

As for the overall ensembles bit of mix though blocking favoured and a 'breakdown' of the block faster much like the 18z OP, sending lows into the high from the trough disruption out to the west to breakup its claim on the UK. Overall i'm not sure how much I can trust it.

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I got mixed feelings about tonights ECM, i thought short term of the run did not look as good as previous runs with the ridging collapsing quicker than previous runs however it manages to keep high pressure in control for the UK and does not sink it. I think when you consider some previous ECM FI runs showed the mild SW'lies coming in at 216/240 hours and no it does'nt then that is something encouraging I think.

I find it a bit unbelieveable some are already moaning about the potential spell of high pressure and hope its get blasted away by the jet and have a return to Atlantic conditions but for me, if this happens it will be the biggest waste of time ever as any cold pools that develop to our NE will get pushed away and we start from square one and be feeding on scraps.

It will be interesting how the Pacific ridge into the Arctic will affect the output also, espcially if it does attack the PV over the pole(which is quite strong atm).

I think there is a case people want too see positive results from this potential now and you can understand that but even if the models did show some form of an easterly at 168 hours then all it will do is raise expectations levels and then expect it will remain the same until 0 hours which will hardly ever be the case

One thing that does concern me is the potential for the high to collapse as per the 18Z GFS, some ECM runs initially have shown this and quite a few GFS runs have shown this to be the case also so its certainly a possibility.

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Stick to the Models and then ... you are all Noosed by the neck ' We are and will be in for a Massive Block for a wee while (5th december) Then Atlanic train rushes in with Rain swept Snow ' Wind from the East is all i can see ' pushing Westwards with Blizzards in the South ... and Some Snow to the North at some time ' all in all WINTER IS HERE TO STAY .

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4 hours ago, Summer Sun said:

Judah Cohen has updated his blog well worth a read

http://www.aer.com/science-research/climate-weather/arctic-oscillation

Cracker!

EDI/T - actually not quite as good as I thought, we're in with a 50/50 shout. still decent though.

Edited by feb1991blizzard

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GFS comes up with a shortwave spoiler that prevents better ridging Northward in the short term.

gfsnh-0-84.png

But conversely it develops as it rolls down the Eastern flanks which helps reamplify in the mid term - swings and roundabouts? 

gfsnh-0-138.png

We are almost always better off with energy travelling SE than NE though and getting better northward push of positive heights so rather it did one.

UKMO much better with no spoiler SW even withe energy seemingly running NE as looks like next low would result in WAA  reinforcing the block.

UN96-21.GIF?29-05UN120-21.GIF?29-05

Also hints of heights dropping central/Eastern Europe. Would liked to have seen the 168/192 :(

Overall it is as you were, perhaps slightly disappointing if we are still hoping for upgrades and good undercut. (moreso GFS)


GFS ensembles.

Shortwave spoiler very much in evidence within the ensemble suit which results in a much flatter pattern through the short/med term within many members but on one or two it helps sharpen the Scandi trough as mentioned previously and better orient the block.

If FI was 140 it is probably now T120 or even T96 until shortwave dramas are resolved. (at least with GFS)

Staying chilly through the first week of December regardless.

graphe6_1000_264_91___.gif

Edited by Mucka

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Just a word of warning that this could all be the models over doing the signal, background or not. I am still not seeing a consistent signal for forcing either in the Pacific or Atlantic. On this morning runs the mid-latitude block (UK HP) sinks and we get a zonal milder flow with an abundance of rain. 

gfsnh-0-240.pnggemnh-0-240.png

GEM going that way, with the PV getting a bit more energy. This being a continuation of the 18z mean that was distinctly insipid.. The current output in FI remains poor for cold on the GEFS, not a great purview for upcoming cold and if anything the trend has been away from the current cold spell to a milder more unsettled outlook. Obviously stuff happening but I would be less than optimistic based on the last few runs and the wait for a consistent cold pattern remains illusive.

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7 minutes ago, IDO said:

Just a word of warning that this could all be the models over doing the signal, background or not. I am still not seeing a consistent signal for forcing either in the Pacific or Atlantic. On this morning runs the mid-latitude block (UK HP) sinks and we get a zonal milder flow with an abundance of rain. 

gfsnh-0-240.pnggemnh-0-240.png

GEM going that way, with the PV getting a bit more energy. This being a continuation of the 18z mean that was distinctly insipid.. The current output in FI remains poor for cold on the GEFS, not a great purview for upcoming cold and if anything the trend has been away from the current cold spell to a milder more unsettled outlook. Obviously stuff happening but I would be less than optimistic based on the last few runs and the wait for a consistent cold pattern remains illusive.

It does seem the past 3 GFS runs take colder air away from the UK. How is ECM looking?

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Wow big difference between current temperature in de Bilt (-7C) and last GFS prediction (-0.5 to -1C) and this is the case across the whole of the Netherlands 

Screenshot 2016-11-29 06.59.38.png

Edited by ArHu3

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The next couple of days.

This can essentially divided into two. N. Ireland and Scotland and England and Wales. There is a sharp frost in places in the Latter this morning, down to -^c and could be lower, and tomorrow could well be a little lower, Sunny during the day and no wind so mot unpleasant. For Scotland and N.Ireland ore cloud, little frost and even some light drizzle tracking south over Scotland. The same tomorrow and becoming quite breezy from the NW as the HP tilts and systems sneak around to the north.

1hourprecip_d02_18.png1hourprecip_d02_27.png2mmintemp_d02_44.png

And on to the GFS

I'm sure we are all familiar by now with upstream forcing and the Atlantic trough that deconstructs with a cut off upper low that tracks SE towards the western Mediterranean. This morning this low itself also deconstructs spawning another little blighter from it's northern flank and a shallow surface low just to the SW of Cornwall with associated fronts by Monday.

gfs_z500a_natl_22.pnggfs_6hr_precip_eur3_27.png

From here the high pressure slips south and becomes orientated more SW/NE which allows the trough to encroach whilst at the same time producing some very impressive WAA over the UK. I think this is better illustrated using the GEFS anomalies this morning.

gefs_z500a_5d_nh_51.pnggefs_t2ma_5d_eur_51.png

A quick summation

High pressure remains influential until the beginning of next week but with much more cloud and thus the quite low temps will be avoided albeit it will remain dry. We then have the little skirmish in the south west on Monday  The high pressure then drifts SE and warm zephyrs from the south west become established with frontal systems encroaching from the west by midweek. I'm not believing a word of this without confirmation from other sources.

Edited by knocker

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ECM 144 pick of the mornings output so far for the mid term

ECH1-144.GIF?29-12

 

Edited by Mucka

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UPDATE TO MY RECENT POST WITH LATEST DR JUDAH COHEN REPORT

Please refer to my full report posted on Sunday, November 27th on page 202 of this thread.

Dr Judah Cohen’s Latest Arctic Oscillation Report:

Judah Cohen published his latest AO report late last night (on November 28th). Given the excitement on here yesterday, I feel that this makes vital reading. Here is the link:

http://www.aer.com/science-research/climate-weather/arctic-oscillation

I copy his summary below:

“…..Summary

The Arctic Oscillation (AO) is currently slightly negative and is predicted to remain close to neutral through mid December.  I continue to expect large model volatility in the near term due to challenges predicting downward propagation of circulation anomalies related to the ongoing weak polar vortex (PV) event.  Though once the PV weakening event peaks next week, model confidence could improve.

The current negative AO is reflective of mostly positive pressure/geopotential height anomalies in the Arctic especially on the North Atlantic side. With positive heights over Greenland and Iceland and negative heights in the eastern North Atlantic, the North Atlantic Oscillation (NAO) is currently also negative and the NAO is predicted to remain negative over the next two weeks.  This is a reversal of recent winters where the NAO has remained positive even when the AO has been negative.

However I do not believe that variability associated with the AO currently best explains anticipated weather across the Northern Hemisphere (NH).  Instead I believe that the circulation associated with the polar vortex (PV) best explains the large-scale weather patterns across the NH continents.

The main PV center is predicted to reside over northwest Siberia for the first half of December with a second much more minor center over the Western United States sliding west into the eastern North Pacific with a Canadian high pressure center separating the two.

The stratospheric PV is predicted to begin winter near record weak, polar opposite to last winter when it was near record strong to start winter.  In contrast to last winter when maritime flow crossed the continents unimpeded, this winter PV circulation shows little to none maritime flow across the continents.

Siberia, which has been cold since the rapid advance of snow cover across the region in October, is predicted to remain cold. That cold air will begin to bleed into Western Asia and Eastern Europe but whether it makes it to Western Europe remains a question.

North America where record low snow cover and warm temperatures highlighted November is predicted to experience a dramatic reversal.  Strong ridging/positive geopotential height anomalies centered over the Aleutian’s, will allow cold air to pool in Alaska and Western Canada for the first half of December.  More expansive cold air should also favor a more rapid expansion of snow cover across the continent.   

Eurasian snow cover was observed to be well above normal across Eurasia for the month of October. Also Arctic sea ice extent remains well below normal especially in the Barents- Kara seas.  High Eurasian snow cover and low Arctic sea ice in the Barents-Kara seas favor first, a strengthening Siberian high and a weakened polar vortex (PV) in winter and a cold pattern across the NH continents.  I believe though that due to the strong anomalies in snow and ice this cycling has been accelerated this fall……”

Here is part of his more detailed look at the “Impacts”:

“….Impacts

With the official start of meteorological winter this week, I would like to spend more time discussing in today’s blog my thoughts for the upcoming winter; what gives me confidence in the forecast and what contributes to uncertainty in the forecast.  My focus in the fall is Siberia, beginning with the snow cover advance across the region in October.  The snow cover advance was impressive, especially south of 60°N.  Following the rapid expanse of snow cover temperatures reversed from above normal to below normal during the month of October in Siberia, which further intensified and became more expansive in November.  The rapid advance of snow cover also contributed to an early an impressive northwestward expansion of the Siberian high.  I consider the development of all three: Siberian snow cover, Siberian temperature anomalies and the Siberian high-pressure as nearly textbook for precursors for a negative winter AO and at least one significant weak PV event during the winter.

Beginning in November my focus starts shifting from Siberia to the Arctic.  I with my colleagues and other research groups have shown that low Arctic sea ice is also related to a northwestward expansion of the Siberian high, a weak PV mid to late winter and cold temperatures across the continents.  Also this research has shown that the region in the Arctic where this relationship is strongest is in the Barents-Kara seas.  Currently the largest negative departures in sea ice extent are in the Barents-Kara seas and based on the predicted weather pattern that is unlikely to change into the foreseeable future.  Therefore Arctic sea ice extent anomalies are also nearly ideal as precursors for a negative winter AO and at least one significant weak PV event during the winter.

Other research groups have shown that the region most sensitive to Barents Kara sea ice anomalies is Asia more so than North America and Europe.  Also my research has shown that the relationship between fall Siberian snow cover and winter temperatures is strongest in Siberia.  Therefore based on these two research results, my confidence is highest for a cold winter in Siberia and surrounding regions.  However it is my belief that increased vertical energy transfer between the troposphere to the stratosphere related to extensive Eurasian snow cover and reduced sea ice allows a climate anomaly that is at first local to Siberia to become hemispheric in scope.  Increased absorption of energy in the polar stratosphere leads to a weakened PV.  The modulation of the PV from a strong to weak state can then distribute the cold air initially confined to the Arctic to other regions of the NH including Europe, Southern Canada and the US depending on the evolution of the circulation related to the weakened PV state.

It is my opinion that the rapid advance of Siberian snow cover and strong development of the Siberian high contributed to record strong upward Wave Activity Flux (WAFz)/poleward heat flux.  This in turn is predicted to result in a near record warm polar stratosphere and weak PV this week.  Typically following a significant sudden stratospheric warming (SSW)/weak PV event the AO averages negative and temperatures below normal for large regions of the NH continents for up to four to six weeks.  Given that the current SSW/weak PV is predicted to peak this week therefore my expectations are for the AO to average negative and cold temperatures to become more widespread for much of December and possibly into early January.  The rapid advance of Siberian snow cover, the reduced sea ice in the Barents-Kara seas, the strong response by the Siberian high and WAFz and the weak PV for most of the fall give me confidence in the overall forecast. 

Now for what I consider the most important uncertainties related to the winter forecast.  First I do believe there can be too much of a good thing.  Typically the significant weakening of the PV related to the rapid advance of snow cover occurs in mid-winter with a peak frequency in January.  This maximizes the impact of the atmospheric response to snow cover variability on winter means.  However with the rapid advance in Eurasian snow cover and strong and accelerated atmospheric response, the PV weakening began even before winter started and will peak the first week of December.  Therefore the full impact of the extensive October snow cover will likely be complete with most of the winter still ahead.  Therefore the success of the forecast will likely depend on at least one further weakening of the PV later this winter.  Our research (Furtadoetal_GRL16.pdf) has shown that snow cover favors an earlier and sea ice a later winter weakening of the PV. Therefore I do believe that the low sea ice in the Barents-Kara seas favors a subsequent SSW/weak PV later this winter.  An analog for this scenario would be the winter of 2009/10. 

Another uncertainty is that for the sake of simplicity, we study the mean response to SSW/weak PVs but variability among individual events is large.  Of greatest importance is the tropospheric response, which can range from a response that dominates the tropospheric circulation to one that is negligible.  So how much the troposphere responds to the current PV weakening is still unknown.   Related to this question is what I observed last winter, multiple troposphere-stratosphere coupling events can occur in relatively short succession and interfere with each other.  I believe that the near term tropospheric circulation favors decreased WAFz/poleward heat flux but at some point it is likely to become more active and that could both cause a rapid rise in temperatures at the surface and strengthen the PV as occurred last December with a long lasting warm bias on winter temperatures.

Another uncertainty is the quasi-biennial oscillation (QBO).  Last winter it was in the westerly phase that may have contributed to deflecting vertical WAFz to the equator rather than the pole resulting in a strengthening of the PV rather than a weakening during the early winter.  Normally an easterly QBO would occur this winter but the westerly phase for the first time observed repeated itself that could once again deflect WAFz away from the pole and towards the equator.  But given that the PV has been record weak so far it is hard to argue that this has been the case.  Finally there are two more uncertainties unique to North America.  During November, record warm temperatures and record low snow cover extent was observed.  How much of these anomalies will persist into December is still unknown.  Based on the latest weather model predictions those anomalies should be erased fairly quickly, however, the built up warmth will persist longer if model forecasts are wrong.  Also the recent cold streak in Siberia has likely significantly contributed to strong cooling of sea surface temperatures in the North Pacific erasing the southern half of the warm “blob” in the eastern North Pacific.  The warm blob is thought to have contributed to ridging along western North America that inhibited the penetration of mild maritime air across the North American continent in 2013/14 and 2014/15.  Colder SSTs could contribute to a stronger North Pacific jet and the deeper incursion of maritime air across North America.

Briefly in the near term model predictions of strong ridging/positive geopotential height anomalies near the Aleutians and near Great Britain and Iceland is highly anomalous.  If this forecast verifies it will block the incursion of mild maritime air across North America and Eurasia respectively.  This should allow the intensification and expansion of cold air in both continents especially across Alaska and Western Canada and Siberia, at least initially…..”  

Judah continues with his usual look at the near term, the next few weeks and further ahead. This part contains many maps, charts and diagrams and is far too long for me to reproduce here.

Brief Comment:

Whilst much of what Judah says suggests that we remain on course for at least a cold or very cold first half to Winter 2016/17, considerable caution and continuing patience should still be adopted. There “may” be a delay until significant cold reaches Western Europe and the UK but the renewed deep cold developing over Siberia and displacements of much of the Arctic cold from high latitudes towards many middle latitudes as December progresses should surely put Western Europe and the UK in the firing line. The models, indicators and forecasts seem likely to remain in a very uncertain state in the short term. The next 2 to 3 weeks might be decisive in determining the path to Winter cold (or otherwise) and things should become much clearer. I strongly believe that coldies will not be disappointed.

Next Update:

I’ll try and manage my next full report in 2 week’s’ time. If there are any dramatic changes in direction before then, I may post another interim update.

 

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There should be quite an interesting contrast between ECM and GFS 2m temp ensembles in FI this morning,

Sometimes it as though there is only one model output to chew over but fair to say the chances of tapping into any colder uppers from the evolution of block look slim.

Whether it be continued blocking and surface cold or the high declining SE and milder SW flow setting in., I see no reason to promote one outcome over the other  probability wise based on this mornings output.

ECM/GFS 192 comparison.

ECH1-192.GIF?29-12gfsnh-0-192.png

Edited by Mucka

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The ECM relentless in its HP blocking around the Uk. This is becoming a notable period of Local blocking since the 23rd November. Can't believe it really- if only it was summer:D

Edited by Matthew Wilson

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