Nouska

There is a very cold pool of upper air modelled to traverse central UK on Saturday - cold enough to support polar low development but I don't know if all other parameters would be favourable. If current modelling looks to verify, please make sure you factor in the possibility of power outages when planning the festivities and feasting for next weekend.

For anybody not sure what a negative EPO ridge is, an illustration. https://www.theweathernetwork.com/news/articles/epo-what-you-need-to-know/43796/0 Similar to the PNA pattern but more focus on the EPAC rather than CONUS. Add a strong wave2 from Eurasia and the vortex is squeezed down over us - in theory. In practice - a good example December 2010.

Why don't you pm @SylvainTV - he visits regularly and would clarify for you. I know the percentages are reflective of the ensemble probability section but not how they are derived so interested in the answer too. http://www.meteociel.fr/modeles/gefs_cartes.php?ech=6&code=0&mode=26&carte=&proba=1

you have lots of company in the confused corner - including the Met Office boffins! The only blame to be apportioned should be on not looking across a wider spectrum of model output - a lot did not concur with the idea of a blocked pattern conducive to the cold and snow so many desire. This is maybe the fault of some not understanding the climatology the anomalies are set against or just assuming northern blocking to the north west was an automatic cold signal. We'll no doubt, in time, have a forensic assessment of where things went wrong for this month but failure is part of the advancement process and maybe lead to better forecasts somewhere in the future. Nick and Tamara are both right in their critique - too many butterflies fluttering all over the globe but Tamara does do a great job as our resident lepidopterist.

That's interesting because the JMA has done a fairly quick change between the output on the eighth of the month to that of the twelth. Albeit, one is weekly and the other is monthly the indication was more of the same for first two weeks of January. Latest seasonal for January 'might' depict what you are seeing in your models? At least, it is the first indication of low height anomaly to the south - an artefact of the digging trough leaving residual cut-off troughiness in the westerns Med? http://ds.data.jma.go.jp/gmd/tcc/tcc/products/model/map/4mE/map1/zpcmap.php

Frequent and strong wave attacks though and a very distorted shape for a lot of the time. Mouseover format for January and February 1986. ERA interim data on Meteociel. http://www.meteociel.fr/modeles/archives/archives.php?mode=2&month=1&day=1&year=1986&map=4&hour=0&type=era&region=nh

Precisely! They run it regularly but we see a snapshot in time which is frozen for a month. As CS says, we need to update our understanding with the weekly products to get the evolving picture.

That would certainly be a dire situation down here if projection becomes reality. How did it perform for last JFM ..... GloSea forecast. Reanalysis

Good summary. One of the other useful functions of the site that gives the UKMO 168 chart is the ability to 'quick look' at tropical cyclone genesis forecasts in the other basins. http://ruc.noaa.gov/hfip/tcgen/ In this case, option NIO (northern Indian Ocean) and use the loop function to compare all the listed models day 1-7. It looks to me that the MJO forecast from some models is following the projected path of Vardah - being it is the strongest signal at present but if something else develops further east who knows. Perhaps ECM is correct in not being misled by a short lifespan cyclone?

Why would one even consider seasonal modelling programs as being a tool for forecasting conditions for snow? The most powerful mesoscale models struggle at lead times of twenty four hours. You only need to spend time in the model thread to witness how the same chart can be interpreted in so many different ways. It all depends on seeing confirmation (or not) of personal preference bias.

I think you are confusing impartial realism for ramping - after all, by your own admission, it is the default setting in a maritime climate. As for the bit in bold about extensive blocking not materialising so far ..... That image seems to agree with the supercomputers - don't you think - it is the December anomaly to date. Maybe the problem is not with the computers but the brains that interpret the information.

Here's the link. http://acdb-ext.gsfc.nasa.gov/Data_services/Current/seasonal_strat/seasonal_strat.html

Just looking through Levi Cowan's site at his analogues based on the November pattern - some nice winters in there for cold lovers and does validate some of the MO comment about seeing shades of '62. A lost opportunity or a sign of what may still be?

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.

There are some charts of the GloSea5 strat modelling for the winter of 15/16 in the PDF for presentation to MedCOF5. Pages ten and eleven. http://medcof.aemet.es/images/doc_events/medcof5/docMedcof5/presentaciones/MedCOF5_Brookshaw.pdf I don't think they did a presentation for this winter at the most recent conference.

If you look at the last ECM46 ensemble mean chart (Christmas week) for 500-1000 thickness - you can see why models are having such difficulties in solution. Such a narrow corridor between quite extreme thickness values and just tiny oscillations in the pattern give very different outcomes as surface conditions. It could be some time before this is resolved.

LOL, that reminds me of living in Canada - the strange sight of the hubby outside, dressed in parka and salopettes, tending the BBQ while wife and kids indoors, all cosy, awaiting the delicious feast being prepared for them. Nope, I'll be in Surrey - no BBQs there - look at the theta E and any ideas of that should be quickly dismissed.

This is the FIM forecast so will be a bit different in the modelling of the strat to the one a couple of posts up. Note the difference in the wind speed between 10mb and 25mb. Shame there are no more layers to look at but it could be useful to monitor whether the very high speed winds are propagating down. 10mb 25mb http://fim.noaa.gov/FIM/Welcome.cgi?dsKey=fim_jet&domain=201&run_time=08+Dec+2016+-+12Z

I remember musing in the ENSO thread as to whether such a dramatic end to the winter vortex would leave a 'memory imprint' to see in the new winter season. This was also predicated on the QBO anomaly. I've no expertise in this field - just like to ponder some of my pattern knowledge, in another field, on to atmospheric behaviour. Probably mad, but there you go!

Much will depend on the positioning and whether it is tropospheric wave led or SSW downward propagation. Time delay plays a big part in looking at patterns at the surface. Late November 2010 split. tropospheric led Mid January SSW 2013 split Mid December 2009 tropospheric led. An edit to say that the '09 and '10 wave patterns are, according to recent research, very typical of solar minimum/early ascent stage of solar cycle. Tendency for strong ridging through Greenland - Kamchatka route, connecting Atlantic to Pacific ridge and thus cross polar flow.

I hope they have plenty of 'juice' in the DECIDER function - it is going to be getting a very thorough work out in the coming days - maybe even weeks. http://www.ecmwf.int/sites/default/files/elibrary/2015/13419-decider-visualising-range-possible-weather-scenarios-medium-range-and-monthly-forecast-periods.pdf The new monthly update due out tonight will have the same starting data as this last ECM run - does not bode well for a clearer path to beyond the Christmas period. The late run modelling from ECM does reflect how it saw the week three period, as per last EC46. Deep, cold troughing exiting NE Canada but that was on a steep SE trajectory which allowed heights to build to our north. All a matter of how the big vortex cogs are expected to position from the starting data. I suspect the models are having real difficulty in not having a coherent tropospheric PV and not being able to create a stable one.

The one long range model I have been impressed by - NCAR CESM - had been consistently showing a very cool picture for February - blinked last month - now back again . I know it is ice anomaly coupled but no idea as to whether it has stratosphere forecasting abilities. This sees the October/November pattern re-establishing with the cold managing to penetrate as far as the UK. This is the model that Dr Ventrice has been singing the praises of, from a USA point of view. A rare success in model terms for October too, Eurasia wise. http://www.cesm.ucar.edu/about/

They both said +336 - my apologies. That would make more sense and better too as more ppn signal in the Med.

A very different picture on the ppn and 850 temp charts to previous runs. Unfortunately the axis seems to go way south and only brush the coasts - nothing penetrating far enough in for what people are looking for. It is remarkable how two sites can present the precipitation anomaly for the 336 to 504 timeframe so differently.

I think the parallel run is probably more representative of those members. Parallel run only available in the archive back to third day of December but good continuity in this blocked scenario for pre Christmas week. Last four runs with most recent first. GIF for the latest run. GIF 06Z