Model output discussion - 5th December 2016 - Into Winter we go

[snowwman]

6 minutes ago, Steve Murr said:

When you say negative CETs do you mean sub ave or sub zero?

Sub zero.

[blizzard81]

16 minutes ago, Steve Murr said:

Good link

The Merra reanalysis will be very similar to the ERA interim reanalysis

it does surprise me around the negative CETS- did you consider the 2 week propergation window?

next level of analysis is whats the best case scenario with no SSW...

PS

just adding to that - The SSW correlations are more concentrated towards the -AO not UK CET

so a SSW enhances the probability of a cold outbreak in the UK-

I did some personal research on 62/63 & 100% the SSW caused that opening outbreak of cold

anyone want any proof? Look at the 10hpa warming on 12-13 Dec 1962- same as 2009

S

Would be interesting to look at Jan 87, late Dec/Jan 78/79, Dec 81. Were these famous cold spells preceded by ssw's?

[SMU]

13 minutes ago, snowwman said:

As I recall, the SWW in 1962 happened way after the cold set in on in late December. I'll try to recover some of the data and get back to you.

Ive already checked on NCAR its 12th & 13th over siberia...

bang on 2 weeks later was the propergation-

Im on the road at the mo- will add a post in winter thread later

 Will tag you

s

[SMU]

12 minutes ago, blizzard81 said:

Would be interesting to look at Jan 87, late Dec/Jan 78/79, Dec 81. Were these famous cold spells preceded by ssw's?

http://www.meteo.mcgill.ca/~pmartineau/updated_graphs/svw_anim/all_gif/1981_12_05

[blizzard81]

1 minute ago, Steve Murr said:

http://www.meteo.mcgill.ca/~pmartineau/updated_graphs/svw_anim/all_gif/1981_12_05

Well, that answers 1981, cheers Steve.

[snowwman]

6 minutes ago, Steve Murr said:

Ive already checked on NCAR its 12th & 13th over siberia...

bang on 2 weeks later was the propergation-

Im on the road at the mo- will add a post in winter thread later

 Will tag you

s

28th January:

 

http://www.google.co.uk/url?q=http://www.columbia.edu/~lmp/paps/martius%2Bpolvani%2Bdavies-GRL-2009.pdf&sa=U&ved=0ahUKEwiS9uf5q-zQAhUnDcAKHU-lC2oQFggQMAA&usg=AFQjCNHwBsKhcXo9vyQQs7Z8d0W3ruKn4A

 

, so couldn't have caused it. Not a criticism of your reaearch, Steve- in fact I'm a fan of your posts. Just thought I'dd add a little of my own research so we wouldn't be as worried about 10hPa forecasts from various models!

Edited December 11, 2016 by snowwman

[SMU]

I will look later - however I didnt check whether a secondary warming perpetuated the winter

ERA data suggests no warming events - however obviously thats relating to the technical definition

Edit checked your link - agrees with ERA- which is surprising as when you look at the warming on 12:12:62 it was epic !

 

here it is

Edited December 11, 2016 by Steve Murr

[snowwman]

3 minutes ago, Steve Murr said:

I will look later - however I didnt check whether a secondary warming perpetuated the winter

ERA data suggests no warming events - however obviously thats relating to the technical definition

It's surprizing how much variation there is between sources. As you suggest, it depends on how you define them. I do wonder, given all this, whether the weather models have properly integrated what we think we know about SSW data into their output.

[Starsail]

5 minutes ago, snowwman said:

Sub zero.

 

19 minutes ago, snowwman said:

I'd like to re run my analysis, but I concluded the last time that a split strat is positively harmful for our chances of cold.

With the focus that many people put on the stratospheric temperature, split pv's and ssw's it would seem almost incredible that your findings, if true, have been overlooked. I think people can agree that LRF's and global drivers are rightly under scrutiny just now. Lorenzo made a very honest, heart felt post a few days back where his exasperation was almost palpable. The conclusion may be that the forecast regarding blocking is actually not far off the mark but in terms of conditions on the ground on our small island, it would be hard to make a case for a front loaded winter (yet).

I have followed with real interest developments from early November.The front loaded winter, due to start early December initially, then mid December, now last third of December looks like it may not happen at all. Is it possible that in all the complexities, there could be something very simple, that is overlooked. I suspect the answer is no, but your post Snowman gives food for thought.

 I used a very crude measure to evaluate the progress of such a forecast. From early December, I looked at the T850 GEFS ensemble mean for 15th December on the 00z, for my area and it oscillated +/- 2 C around the 0 C line but at no point was there any suggestion of something in the offing.regarding cold. The shorter range models simply did not buy it.

 

 

 

[Nouska]

35 minutes ago, blizzard81 said:

Would be interesting to look at Jan 87, late Dec/Jan 78/79, Dec 81. Were these famous cold spells preceded by ssw's?

http://ds.data.jma.go.jp/gmd/tcc/tcc/products/clisys/figures/db_hist_pen_tcc.html

You'll get historic strat charts for 30mb at the above link. Also offers 100mb, 500mb and sea level which allows you to follow the downward propagation. It's set for five day sections but you can change to ten days or more.

Edit - as Steve says below it is the angle and shape which is important - my link has the geopotential heights shown rather than the degree of warming.

 

Edited December 11, 2016 by Nouska

[SMU]

Ive got a few hours spare tonight I will go over the data- however just to point out its not the warming at fault its the resultant shape of the subsequent vortex post propergation that is crucial....

[snowwman]

10 minutes ago, Starsail said:

 

With the focus that many people put on the stratospheric temperature, split pv's and ssw's it would seem almost incredible that your findings, if true, have been overlooked. I think people can agree that LRF's and global drivers are rightly under scrutiny just now. Lorenzo made a very honest, heart felt post a few days back where his exasperation was almost palpable. The conclusion may be that the forecast regarding blocking is actually not far off the mark but in terms of conditions on the ground on our small island, it would be hard to make a case for a front loaded winter (yet).

I have followed with real interest developments from early November.The front loaded winter, due to start early December initially, then mid December, now last third of December looks like it may not happen at all. Is it possible that in all the complexities, there could be something very simple, that is overlooked. I suspect the answer is no, but your post Snowman gives food for thought.

 I used a very crude measure to evaluate the progress of such a forecast. From early December, I looked at the T850 GEFS ensemble mean for 15th December on the 00z, for my area and it oscillated +/- 2 C around the 0 C line but at no point was there any suggestion of something in the offing.regarding cold. The shorter range models simply did not buy it.

 

 

 

The important thing is don't take my word for it- I'm not a pro and have very limited access to data, and that data might contradict other data, but I concluded in honesty what I did from what I had. I would hope that any of what we know about the strat would be of a better quality than my own research, and that human error is minimized, in the implications for the model output.

 

And about the shape of the vortex, exactly, Steve- that's what it's about.

Edited December 11, 2016 by snowwman

[Banbury]

3 hours ago, Ed Stone said:

Come on guys? What's new? I torture myself over yet another mundane-looking GFS run only to discover that an epidemic of optimism has suddenly pervaded the thread...Perhaps I missed something whilst watching all those goals, on MoTD, last night?

Come on peeps - what gives?

It gives us some decent cold dry days which is the next best thing to snow in Winter

Hope you didn't miss the utd goal

[Tamara]

4 hours ago, Catacol said:

Morning all. Key chart for me is the GWO forecast at the moment. Can't easily post the full package here, but if you go to the university of Albany page you can see the modelling recorded for each of the last 5 days and get a sense of prediction v reality. Today's chart here

 

Note the actual transition is working back towards phase 5 without going negative at all. But the forecasts continue to want to move into a Nina like low AAM state.Very clear to me that the models continue to struggle to read the global momentum budget accurately. Not sure why this would be the case - Tamara will know more - but the implication is that the models are seeing a more flat pattern than will actually occur. MJO moving towards phase 6-7-8 will only help to promote more amplification, low amplitude or not.

So as stated before I'm not going to change my view until the drivers change, and for now they are still in place. The ridge forecast to sit with its core over Southern Norway to me is likely to be at a higher latitude than this, and accounting for steeper wavelengths I'd shift it a bit further west.

In terms of timing I don't think much has changed either. This process starts mid month and will evolve from there. The dice haven't quite rolled for us yet, but if this general prognosis can stay on track then at some stage, before too long, wintry potential may follow.

This, an opportunity to provide balance to the stated positives given yesterday. No more, no less than that

The problem is that whilst there has been a case, as you rightly say, for models overreacting to the atmospheric signals, and I have stated this myself a few times recently - there continues to be no consensus signal, (yet), of your very good analysis gaining the confidence it needs, within the window of opportunity that has been available.

To try and explain this better, there was a time when the Pacific pattern was viewed as a friend stratospherically (a cross polar stratospheric ridge) to go on and imprint itself our side of the pole courtesy of height rises to our NW. This had widespread support across a wide spectrum of agencies and professional organisations - and whilst they did not promise snow and polar bears with instead some weighting to anti-cyclonic conditions rather than "cold instability" the METO also supported this overall type of evolution alongside the good support of ECM and GloSea5 extended ensembles

It felt somewhat contradictory at the time to post this (I referred to myself personally as conceivably to be seen as a bore and killjoy by posting it), but there was already a downside risk, however relatively low at the time:

Extracted 24 November:

---------

Delays and shortfalls - then the hallowed Pacific Ridge will not sustain as a poleward feature (as part of a cross-polar ridge pattern for sympathetic downstream higher latitude height rises) and will entail a typical Pacific winter Nina like pattern at mid latitudes with early winter reliance on some cold zonality and brief arctic topplers before, potentially, the Atlantic jet increasingly flattens out as maximum stratospheric weakness is not utilised and seasonal wavelengths change further to couple the Annular mode 'unfavourably'.

Its to be emphasised here that this is a low risk scenario at present.

However, if traction increases to consolidate an eastwards signal in the tropics as consensus modelling, there are continued signs to show that the Pacific favours a ENSO neutral with a +AAM tinge then stratospheric weakness will be utilised with the Pacific ridge very much a friend in terms of being part of a cross polar stratospheric induced ridge - that is the beginning of a period for snow and ice.

The latter constitutes a deliberate ramp, but you get the picture. The former represents something less exciting - but whatever the models, the professional consensus etc may suggest - it cannot (yet) be dismissed.

--------

We have not yet fully arrived at all the less appealing scenarios I suggested in that post  - however the "destructive" tropical phase I talked about yesterday (and which constituted the less appealing option warned of in the italicised post) has come to being. Why otherwise is NWP as poor as it currently is.

The requirement for a return to the autumn "constructive" tropical forcing that saw the amplification feedbacks grow through the period is growing larger and larger every day that it cannot be forecasted in sufficient confidence to return .

The positive highlights of a return to those feedbacks (the good news) were outlined yesterday (enlarged in terms of Siberian and sea ice feedbacks etc), and they remain valid. However, having unfortunately arrived at the first stage of what was considered "low risk" set against consensus modelling and opinion in the last third of November - then I think that current and upcoming extended modelling this week will give important insight into the "make or break" aspect of this.

NB: Make or break in context of the extended period - not the whole winter!  I also say this as one who is generally usually reluctant to get caught up in model ensemble set swings and analysis

The latest from GloSea5, taken at face value is not wholly encouraging it has to be said - however one might want to interpret a mobile and zonal pattern. Should it arrive of course - and yes confidence is still low in this, as stated by Ian F, at time of typing

That said, set against all the possibilities which still exist (better or worse) winter is not over in any sense of the phrase, but the G5 data does suggest one corner of provisional sign-posting to me at least that vortex intensification is at risk of being given an increasingly better chance of overcoming and turning around the "constructive"  interactions that have seem a weak and unstable polar vortex to end autumn and begin winter. Without the tropospheric amplifying feedbacks, the disconnect that was discussed yesterday between the top of the stratosphere and the downward echelons, ( and which can still prevail) is nevertheless, diminished - in those circumstances

@CatacolYour analysis of AAM and GWO is really good, based on return of "constructive" (amplifying) tropical forcing turning around the current falling angular momentum phase, but what was low risk in late November is now undeniably higher risk - especially as there continues frustrating lack of model consensus that the tropics will play ball in the way many wish. This, at a time, when the polar vortex is tightening and being very ready to take advantage of an atmospheric circulation that has stopped bearing its gifts at the very time that it is most needed to sustain the pre-season promise.

Based on intra-seasonal timelines, and the last active amplitude tropical cycle that occurred in November, I think that we will see the next active amplitude eastward progressing one in January. Set against ENSO expectations which have fortunately followed some of the early scepticism I had of La Nina, and as underpinned by the resolutely neutral signal from the SOI, then there continues to be decent supporting logic that low angular momentum has a floor limit - hence the GEFS plots exaggerated in the way you suggest.

But something within the tropics and extra tropics could certainly do with supporting angular momentum, and hence boosting amplification and preventing the vortex taking over more completely, in the meantime.

To weight this accordingly, it would be unfortunate irony, that as the ocean signal starts to extend its hand to the disconnected +AAM atmosphere, the latter decides to head in the direction the ocean has been commanding through the summer and autumn!!. That type of scenario would end us up with a season much like winter 2014/15 - with an increasingly neutral ENSO but a diffident atmospheric Nina signal and Phase 1,2,3 GWO orbits and an amplified Pacific dictating the downstream wavelengths

Have a look at the archives and see what type of synoptic patterns predominated in 14/15 - with only two brief cold incursions/topplers. One in the Christmas/New Year week, and the other c/o of a displaced vortex away from Greenland the end of January and early February

This, as per usual, is most certainly not a forecast - but it is a further attempt to help manage expectations. By that I mean the less appealing possible solutions - as well as the much better ones (which remain valid as discussed yesterday)

Long way to go yet, but it does no harm (or shouldn't do any harm) to keep setting out both the pros and cons.

 

[Catacol]

38 minutes ago, Tamara said:

 

To weight this accordingly, it would be unfortunate irony, that as the ocean signal starts to extend its hand to the disconnected +AAM atmosphere, the latter decides to head in the direction the ocean has been commanding through the summer and autumn!!. That type of scenario would end us up with a season much like winter 2014/15 - with an increasingly neutral ENSO but a diffident atmospheric Nina signal and Phase 1,2,3 GWO orbits and an amplified Pacific dictating the downstream wavelengths

 

Thanks Tamara - your balanced opinion is very valid (if not entirely welcome!!!) The dice have not been kind so far - Indian Ocean interference with the Pacific signal leading to lower than predicted latitude of blocking, then made all the worse by the ironic reality that the weak vortex has turned that poorly positioned block into a super block that is hard to shift. I tell you now - if the dice roll poorly again and the atmosphere switches to a Nina pattern just at the most crucial point of winter (and just when the oceanic Nina signal is fading out) then something valuable in my house is going to get broken. We would be truly unlucky in that case, with - as you point out - a strengthening trop vortex enhancing the poor Pacific signal. I would be forced to abandon any hope of proper cold over the next 4-6 weeks in that case.

So let's bang a drum for the Pacific, trust that AAM will rise again in the short/medium term and have confidence that we can get some high lat blocking in place. However it's starting to feel a bit like a game of tennis - 3 break points at 0--40 lending confidence to the ultimate outcome of the set, but the next 2 returns have hit the net via unforced errors and suddenly the tension has risen. We could do with a double fault right now!!

Edited December 11, 2016 by Catacol

[Scandinavian High.]

Cfs is going for the beast from the east Christmas week .

[Ali1977]

Lack of comments say it all, boring Dec with little chance of anything white from the Sky unfortunately!! Early Jan not sounding great neither so will have to settle for a 1947 rather than 63 type winter

[Summer Sun]

Quite a change between the 06z and 12z with the high still hopeless for snow though

 

Edited December 11, 2016 by Summer Sun

[stewfox]

6 minutes ago, Ali1977 said:

Lack of comments say it all, boring Dec with little chance of anything white from the Sky unfortunately!! Early Jan not sounding great neither so will have to settle for a 1947 rather than 63 type winter

GFS 12Z updating. 86% complete, 14% left all to play for.  Actually as SS as said some changes.

Edited December 11, 2016 by stewfox

[igloo]

im not sure whats worse the UKMO the GFS or the GEM all are shocking for cold one thing to point out is the front loaded winter looks to be in tatters so can we be sure of a mild second half im not 

[Banbury]

13 minutes ago, stewfox said:

GFS 12Z updating. 86% complete, 14% left all to play for. 

Not really sure what you are looking for? Snow hasn't been on the cards all winter and still isn't.

But if its seasonal chilly weather you want , here it is..................which is ok

Edited December 11, 2016 by Paul

[knocker]

Personally I think this far from boring but everyone to their own Anyway the wrap around and the question...where to from here?

 

Edited December 11, 2016 by knocker

[Summer Sun]

Well the one positive so far is the 850's lowering for the Xmas period

We might get lucky and see a frost on the 25th....

[Dennis]

winter is make some progress

[Ali1977]

The sooner we get rid of the high the better , it looks like FI the PV weakens which happened in the 06z. The Alps need snow, if we can get some fronts heading W to E down that far then we may have some chance of getting some WAA far enough North to create a proper block and not a rubbishy Euro one. 

Better looking NH for sure, Alps getting some snow too.

Edited December 11, 2016 by Ali1977