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

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ECM ensemble mean generally shows a flow from the N/NW from +144 to +240.

EDM1-240.GIF?26-12

As I said yesterday im personally not expecting much from the initial N,ly. What is uncertain is what happens next? I would not discount the chance of a much colder NE/E,ly developing but this is more likely to develop into the 2nd week of Jan.

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11 minutes ago, Steve Murr said:

Morning All-

nice reply @Catacol will add a reply later-

A model standoff today between the ECM & GFS/UKMO -

The favoured scenario is the toppling type high pressure- with no cross polar flow-

ECM mean also doesnt particularly support the op either although 168 is better in terms of high pressure locale..!

Im surprised Ian mentioned the PNA as a link into the pattern - we used to talk about that years ago, maybe its just the slight negative pattern thats appearing with the SE ridge- however from the ECM perspective thats not the driver- its the huge -EPO ridge

The link here being that often the teleconnective link of a deep -EPO is a amplified atlantic ( even a Greenland high ) hence why the Meto update from Ian is elluding to varying degrees of atlantic amplification ...

some notable near -300 EPO dates

23/12/1962 = -301.14

29/01/1963 = -482.90

08/01/1977 = -288.04

06/12/2009 = -411.03

20/11/2010 = -289.72

The current GFS forecast drops to about -260 signalling the strong positive height anomaly in the Eastern pacific -

IMG_1175.PNG

ECM is probably the strongest with the forecast & at day 10 has a full on HUGE -EPO/-NAO link a la 1963 - 

we have seen the ECM go off on these tangents before - but not really since its upgrade - 

Its of course the mecca of scenarios however all things considered a low end <20% of varifying....

S

ukmo-

Rukm1441.gif

GFS-

Rtavn1441.gif

Ukmo looks more amplified to me stevie ..

Edited by Polar Maritime
To detach quote.

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Gfsp doesn't quite get the first northerly but still brings a cold ne as the high flattens. Thereafter the ridge drifts se across us before the following amplification splits the NH pattern in combo with N Pacific ridging. This is a fairly consistent parallel pattern. Currently looks like the second bite at the cherry more likely than the first although as ever, gettting the pattern in earlier is less fraught with shortwave drama 

starting to look like all roads lead to cold but still too early to tell your folks! 

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Good morning folks. Models are beginning to liven up after an early december slumber. I was looking at the ensemble means for early part of Jan. With a Nly blast just after new year and then what looks a collapse into much colder air 5days later.  The position of the high in the atlantic looks  crucial but I suspect it will ridge northwards. t850control-168.pngt850control-264.png

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Not UK related, but it is quite fascinating how almost all GEFS are showing deep cold for Turkey. Hope nobody has a holiday booked for it. 

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55 minutes ago, knocker said:

The ext EPS this morning is indicating a trough over Scandinavia, mild ridging in the Atlantic thus an upper flow from the WNW with temps a little below average. Pretty mundane fayre.

Is it too late to say bah humbug:D

Models look better today than yesterday if it's cold wintry weather you fancy for the new year period as most of us do!:cold-emoji:

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3 minutes ago, fergieweather said:

The 00z EC ENS to d15 and clusters look anything but mundane to me. Markedly below average TMax against climatology (taking Reading as an example).

Excellent post, best of the morning in EVERY sense!! :rofl:

Edited by northwestsnow

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2 minutes ago, fergieweather said:

The 00z EC ENS to d15 and clusters look anything but mundane to me. Markedly below average TMax against climatology (taking Reading as an example).

Markedly below average in January, that is pretty cold and definitely cold enough for snow. Still gutted I'm going to miss the 02-06th Jan but I have a feeling it's the 2nd week that could start bringing in the very cold air!! Beast anyone!!

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1 minute ago, fergieweather said:

The 00z EC ENS to d15 and clusters look anything but mundane to me. Markedly below average TMax against climatology (taking Reading as an example).

Cheers, thought so because like I said there was significant cold showing on yesterdays.

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I presume knockers 'mundane comment was based on the mean upper flow showing on the eps. Taking anomolies into account would reveal a less mundane likelihood  and of course, if the less settled cold solution is the one that verifies, all those 'more mundane' runs won't be there to deliver the 'mundane' mean chart in the first place! 

the eps in the 8/10 day period more retrogressive than yesterday and, dare I say it, not dismissive of the op solution potential. 

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9 hours ago, Catacol said:

Steve - Agreed that the AO profile has not been what we wanted, but not convinced this is down to propagation from the stratosphere. If you look at the arctic profile it doesnt appear at all that the increasing strength in the SPV has caused any great response. (Apologies for these links - I dont know how to convert a pdf graphic into something that will work any better.)

https://acd-ext.gsfc.nasa.gov/Data_services/Current/seasonal_strat/zmplots/U___lat_p_70N-90N_zm.pdf

There is a growing response down to about 70hpa - but above that really little in the last few weeks to show a connect.

Add to this the vertical profile for closer to our own latitude - and again the response is hardly dramatic. There is a degree of correlation here now as zonal speeds in the troposphere have picked up now - but go back over the time series you quote and I dont see it.

https://acd-ext.gsfc.nasa.gov/Data_services/Current/seasonal_strat/zmplots/U___lat_p_50N-70N_zm.pdf

The question I guess is - how have we ended up with a +AO when semi pros and experts from Cohen to GP to even the extended models such as GLOSEA didnt see it? I dont have an answer here... and GP's post implies that perhaps he is currently unsure too.... but I dont think it is as simple as a troposphereic vortex whipped up by the SPV. Is there something in the loss of sea ice we dont understand yet? Or has the QBO profile - which everyone admits is different to any predicted profile we have seen before - had a greater than expected impact?

Therefore I dont think you can draw a straight line comparison between AO and SPV.

The teleconnections have all gone muted and hard to predict. GWO and MJO are both pretty neutral at present. SPV is strong - but actually TPV (as argued above) is not dominant. As IanF has posted recently - even the Met are scratching their heads a bit at the list of neutral signals and the lack of any clear forcing for the second third of winter. Given all this I suppose the chances for an unexpected turn of events through January are greater than normal. Could we see an unexpected HLB form as a result of a small tip in the teleconnective package? Perhaps. Its frustrating at the moment trying to glean where the forcings are heading in the medium term... but perhaps we ought to try and be a bit optimistic and enthusiastic at the same time, given that the envelope of uncertainty feels so great.

 

Hi Mate

a nice reply-

I think the reality & argument for me is that  there was some delay in propergation to the lower levels however the 'actual' observed trop pattern ( especially AO ) was near identical to the strat- so whilst the lower levels didnt signal immediate response in terms of overall zonal wind speeds, the pattern & shape it took most certainly didnt portray a disconnect - especially post the 15th when we ramped up to +4.5 AO.

So I dont really see how anyone can argue a trop 'pattern' disconnect as the facts from the AO timings indicate the total opposite-

Also just adding into Nick F's post- im not in the catagory that because the PV has been strong that will carry through - ive posted every few days to update on the strat zonal means highlighting Jan 2-4 as the peak before a sharp decline towards the climo average - its very clear here now - The mean chart shows the strat from 1HPA down to 10HPA loses its strength from the 5th

IMG_1176.PNGIMG_1177.PNG

& around the 6-7th we are back down to average ---

Note the 30HPA response as well

IMG_1178.PNG

 

Based on that then Im not sure what the fuss is about 'now' in terms of the 5-10 day forecast where GP & Nick forecasting a disconnect when we are already on the way back down from the strat top down & we have a small amplitude wave working its way across the pacific inducing a moderate -EPO ridge, thats no disconnect - its a standard wave propergation.

From the 4th we are back in the game for MLB ( again I tried to define last night ) -552 contour up to 70N -

The only disconnect would be ( & fair play if so ) would be the full on ECM solution cross day 9-10 which shows a full on vortex split - this looks very unlikely given the 'overall' state of the strat but of course never say never - I did post about 10 days ago the state of The trop at The time of the very first day of the 10HPA deceleration when we had SSWs ( dont know if you read it ) & the -EPO/-NAO was a strong feature- I personally think based on that & no evidence that a SSW is on the way that the ECM is to over amplified & will revert post day 8 to a slightly flatter scenario with no cross polar flow- NB thats not discounting the Northerly alltogether & subsequent cold, just saying the second phase of retrogression looks iffy!!

phase 1 Atlantic ridge to topple into phase 2 Scandi would be more probable than phase 1 atlantic ridge into holding situ before phase 2 full on vortex split..

S

 

Edited by Steve Murr

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31 minutes ago, carinthian said:

Rejoice at that chart from ECM for snow lovers. Nice Mid -Atlantic block and Arctic sourced air mass pushing into deepest Western Europe.  The chart from UKMO out to 168t in almost the reliable time span shows the cold front leaving the South coast of England followed by a much colder flow across the British Isles, wintry showers for some in the East of North flow.

 C

ECMOPEU00_240_1.png

ukm2.2017010200.168.lant.troplant.prp.fcst.gentracker.png

Hi again, just looking at that pressure pattern flow along the cold front exiting the south coast of England/ Northern France on Day 7. Could just be a delay with the clearance , possible by 12 to 24 h . Could change the timing in the outlook forecast period with possible weather type near to the front boundary but will clear through eventually. However, even at this shorter range open to change but will be in the forecasters mind, I would think.. Its all looking better, thankfully. Nearer to home in the Eastern Alps , 10c forecast in the village today at 1650m absl ! What bit of snow we have is going to disappear rapidly today.

 C

ukm2.2017010200.168.lant.troplant.prp.fcst.gentracker.png

Edited by carinthian

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Its as if the minute we start saying the northern hemisphere drivers mjo ao wind speeds all point to poor cold prospects,the weather does its own thing and says let's give the uk some cold. And when they we're showing potential in November early December we get a period of nothing followed by a couple of storms. 

Just goes to show how hard it must be for the experts to produce medium range forecasts. 

Looking forward to the prospects moving forward cold in by New Year's Day then reload potentials and a cross polar flow from the ecm right at the end but I do feel thats going off on one a bit but I'd take it. Get the cold in first as they say ......

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Gfs 06z moves closer to the ecm regarding amplification in the atlantic!that 168 hours chart from the ukmo looks really good for cold and what looks like snow showers following on from the north sea across north east england!!

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6z upgrades the cold!:cold::D

Better run with very cold air and snow showers filtering into N Scotland by the 2nd!

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8 minutes ago, northwestsnow said:

6z upgrades the cold!:cold::D

Better run with very cold air and snow showers filtering into N Scotland by the 2nd!

But still flattens out as per gfs continuity - slightly different set up in the nw Atlantic at day 8 so interesting to see if we go northerly by T300.

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7 minutes ago, northwestsnow said:

6z upgrades the cold!:cold::D

Better run with very cold air and snow showers filtering into N Scotland by the 2nd!

Yup, but as several others have said - its really what happens into the 2nd week of January that will more likely be of relevance. A little too much mobility hindering suitable jet amplification that can be sustained for more than 48 hours. More likely the ECM remains an outlier in the T120-144 timeframe and will correct itself in the next run.

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