ECM ensemble for London from the 12z:

http://www.weathercast.co.uk/services/ensemble-forecast.html

Some consistency to the extent that the main cluster continues to predict colder conditions from around Day 9-10.  What has changed is that the trend beyond Day 9-10 has moved towards a clearer trend for a tight cluster of members showing cold conditions, i.e maxima around 3C.

I haven't been checking the output that closely over the last few days but the 18z ENS for GFS are pretty good at a glance. A fairly clear cold cluster in evidence in FI at least, which is encouraging given the rather boring run (not sure if this is a strengthening or weakening trend though?).

Well this is just too classic isn't it? ECM producing a stunner and GFS blasting the Atlantic through at a time when we really need that not to happen.

Roll the clock back several years and I'd be backing ECM based on GFS' fairly dependable overcooking of the jet stream, but these days model bias has become a more regional affair; for example GFS has a problem with making U.S. troughs too energetic and also seems to be overly keen on bombing out shortwave lows as they near the UK.

ECM may well have an over-amplification tendency that becomes pronounced from around day 7, which is something to bear in mind tonight of course.

Here's the thing though - we have a lot of signals at play which shout for a lot of amplification. The AAM is a good measure of the atmospheric response to these signals, and the outlook in the short term has it climbing about as high as it gets following an off-the-scale torque event, which is bound to encourage warm airmasses to travel poleward - meaning great support for warm air advection in directions supportive of mid-Atlantic ridges extending to Greenland, for example.

GEFS then suggest a considerable drop-off BUT I have witnessed a large to at times very large negative bias with this model in recent times - going too low by as much as 2 units on the y-axis for example. This suggests that the GFS model is seeing too much of a signal to re-introduce westerly momentum beyond 8 or 9 days range, which is precisely when it all starts to fall apart on the 12z and 18z op runs.

My recent discoveries about the GFS model and AAM lend a lot of support to suspicions I developed over the past few winters that read as follows;

When the background signals point toward sustained amplification, ECM's bias in that direction helps it to land closer to the mark than GFS, which is undone by its bias in the opposite direction. I say closer to the mark because ECM does still tend to overdo things a bit on some occasions.

By contrast, if the signals indicate a loss of amplification is due, that's when ECM tends to end up wide of the mark for a short time while GFS fares well. Notice that I've not seem ECM take that long to get back on track; a flat zonal setup in winter is inherently easier for the models to figure out due to it's closeness to climatology.

Applying all of that to the here and now and there's plenty of reason to be positive as it would seem that GFS ought to trend toward a more amplified scenario over the coming 5 days, as it's ensembles adjust the longer-term AAM outlook upward.

I wish I could place total faith in this but it would be downright unusual if there weren't exceptions to the rule!

Great post James as usual.

However, and sorry for the stuck record, but until cross-model agreement exists at 120hrs, and the vastly experienced forecasters in Exeter radically change the tone of the extended text, the entertaining solutions delivering uk wide snow and ice currently being churned out will stay exactly that - entertaining.

I do not have an advanced knowledge of meteorology - it's not my area of expertise - but what I do have is years of experience of model watching and more bitten hands than I care to remember so I for one take all the virtual output with a huge amount of scepticism until the above conditions prevail.

That said the discussion must continue as is because that is the precise purpose of this excellent thread. With that in mind, some of the solutions on the 18Z GEFS are truly astonishing 😎🤓

The ECM has a very cold cluster of ensembles, this is actually the modal option so one is in that difficult situation where the single most likely situation is very cold and wintry but it is still in the minority. 

GFS parallel.

Incidentally, I really hope that when the GFS parallel becomes 'the GFS' in April we don't have to wait an additional 5 hours for it. That would really take the fun out of model watching

Anyway the GFSP ends on a fairly promising note at day 10, with a height rise (albeit a less impressive one) over the arctic and a southern jet. 

Nobody else up yet? :)

GFS 00z op run is unspectacular today but the ensembles are certainly trending colder. Still lots of scatter but some chilly options there!

http://www.wetterzentrale.de/pics/MT8_London_ens.png

ECM is not quite as stellar as the last run but still serves up a whopping North Pole high and rips the vortex apart.

http://www.wetterzentrale.de/pics/Recmnh2401.gif

BTW thanks to Stormchaser for the informative post about AAM and model bias.

There are colder options on the GEFS0z this morning but the postage stamps are very messy and I wouldn't call a cold spell (snap or incursions are different) on this evidence. I'd be very surprised if Exeter makes major changes to their 30 day outlook today, unless of course MOGREPS / ECM are a lot more supportive.  

GEFS PS 300 hour

At least that "kill all humans" type dartboard low plotted for around the 11th Jan on the 18z GFS is gone on the 00z. Although, probably be back on the 12z.

Without starting a "but this model is better than that model" argument, the reason why I seem to "focus" on the GFS for medium range forecasting and picking out trends is that it does seem to have a better understanding of the Atlantic in general, while ECM and GEM are good at "sniffing out" unusual pattern changes from an early stage - even though they seldom come to fruition come nearer the time anyway.

Morning all.

More vile, repulsive unremittent tripe, some interest in the ENS if its colder weather your after- but there are a broad range of options available from milder to cold weather so ...... more runs needed.

A good Mean yet again from the ECM whether it's a 3 day toppler or something more significant is still unknown. But the coldest spell of winter so far is likely to start about the 12th/13th .

http://www.wetterzentrale.de/pics/Reem2161.html

It certainly looks ever more likely that a short (how short is more uncertain) cold spell is on the cards. My only small concern is that it was originally shown as around the 5th before new year and then it moved to the 9th and now it's the 12th.

I'm rubbish with historical data, but i do recall a year (prehaps 2008/2009??) when a cold spell was shown at around 8-10 days out for nearly the entire winter and it never actually materialised.

I'm sure that won't happen again

The models always seem to show cold spells occurring earlier than they actually do (if they ever do of course!)

I'm not sure why. I suppose they pick up the signals but then overreact move everything into position faster than the real atmosphere manages somehow!

The failed New Year cold spell never really had any ensemble support. This spell seems to have but whether it's a toppler or 3 week snowmageddon or somewhere in between is any ones guess.

Yes that's a good point, although I do recall one year when it just seemed the cold always remained in that timeframe and never arrived. FWIW I do feel the ens are on to a bit of pattern change and I'm expecting this particular cooler spell to last a little longer than most expect.

Fascinating viewing at the moment whatever your fancy.

HERE IS MY LATEST ANALYSIS USING DATA SUPPLIED BY THE NWP OUTPUT COVERING 5 OF THE WORLDS MOST POWERFUL WEATHER COMPUTERS ISSUED AT 09:00 ON MONDAY JAN 4TH 2016

THE CURRENT GENERAL SITUATION A deep depression is moving slowly East and SE while filling slowly across Southern Britain with a showery flow across the South. North and East Britain will be affected by slow moving occluded troughs in a strong SE to East flow.

http://www.wetterzentrale.de/pics/Rtavn001.gif

CURRENT SNOW FORECAST AND FREEZING LEVEL OVER THE UK The freezing level across the British Isles ranges from between 2000ft just to the NE of Scotland to above 5000ft over SW England. Snowfall can be expected across the hills of Scotland today and tomorrow especially the mountains of NE Scotland

http://www.snow-forecast.com/maps/dynamic/uk

http://www.natice.noaa.gov/pub/ims/ims_gif/DATA/cursnow.gif

MODELS-2 WEEK HEADLINE Continuing unsettled and very windy at times with further heavy rain or showers at times. Perhaps drier and colder for many later next week

THE GFS JET STREAM FORECAST The main theme of the Jet Stream today shows the Jet Stream incessantly crossing quickly East across the Atlantic and Southern England and France. Low pressure remains close by over the UK with the flow moving slightly further North in the second week but maintaining a strong and undulating profile across the Atlantic and the British Isles still even at Day 14.

http://www.netweather.tv/index.cgi?action=jetstream

GFS OPERATIONAL The theme of the GFS operational run today shows 14 days of unsettled and often windy conditions with gales and severe gales at times. In the first week rainfall will be very variable under slow moving Low pressure with colder air across the North giving rise to some snowfall over the hills. Then in the second week a severe storm is shown with severe gales for the South early next week which is the forerunner of a more undulating pattern between wet and windy spells and brighter colder weather with more scattered showers is shown but with only short drier spells in largely average temperatures still present late in the run.

GFS CONTROL RUN The theme of the Control Run is very similar to the Operational run this morning with the wet and very windy spell continuing over the next 10 days or so with a build of pressure across the UK late in the two week period bringing a change to fine and dry conditions for many with temperatures close to average with some night frosts and perhaps occasional rain again in the NW later as a SW flow there is renewed.

http://www.wetterzentrale.de/pics/Rtavn1441.gif

http://www.wetterzentrale.de/pics/Rtavn3841.gif

http://www.meteociel.fr/modeles/gefs_cartes.php?code=0&ech=144&mode=0&carte=0

http://www.meteociel.fr/modeles/gefs_cartes.php?code=0&ech=384&mode=0&carte=0

UKMO The UKMO today shows a continuation of very wet and windy weather at times through the rest of this week and the weekend as Low pressure remains deep and centred across both the UK and the Atlantic Ocean with cyclonic winds across the UK throughout bringing rain and strong winds at times with some snow on northern hills and temperatures near to average.

http://www.wetterzentrale.de/pics/Rukm1441.gif

THE FAX CHARTS The Fax Charts show a continuation of the unsettled spell with strong winds and rain at times on troughs repeatedly driven across the UK in a SW flow decelerating and becoming slow moving early in the week across the NE of the UK with broadly windy and showery SW winds elsewhere.

http://www.weathercharts.org/ukmomslp.htm#t120

GEM GEM this morning also shows an unsettled and often windy 10 days of weather to come across the UK with temperatures near average for most of the time. Winds will exceed gale or severe gale at times especially near coasts of the South and West. Later in the period winds are shown to turn to a colder NW or North flow and with continued unsettled weather across the UK rain will turn to snow at times and frost at night will become more widespread as pressure becomes High to the West and Low to the East.

http://www.wetterzentrale.de/pics/Rgem2401.gif

NAVGEM NAVGEM like UKMO shows continued Low pressure dominance just to the West and over the UK for the entire week long run with maintained unsettled weather with wind and rain at times mixed with brighter and showery spells in temperatures generally close to average.

http://www.wetterzentrale.de/pics/Rnvg1681.gif

ECM ECM today shows little respite in the wet and windy theme again this morning gradually drying out later next week as the whole Low pressure belt shifts east from the Atlantic over the UK to Northern Europe later with a pressure rise to the west allowing winds to turn more Northerly for a time early next week bringing wintry showers South to many areas and frosts at night at least for a time. unfortunately the mouth watering chart for coldies for day 10 has not been replicated this morning.

http://www.wetterzentrale.de/pics/Recm2401.gif

ECM 10 DAY MEAN The 10 day mean chart looks similar to last nights with low pressure likely to lie to the NE in 10 days with Low pressure in the Western Atlantic too. In between and angled just to the West of the UK is a void where higher pressure is likely sufficient to at least offer an opportunity of drier and somewhat colder weather for a time at least across the UK.

http://www.wetterzentrale.de/pics/Reem2401.gif

NOTABLE TRENDS & CHANGES FROM PREVIOUS RUNS The theme of the output longer term today shows no significant let up in the basically wet and windy conditions though a growing trend for High pressure to build temporarily at least to the West of the UK is hinted at still from 10 days.

31 DAY HISTORICAL VERIFICATION STATS FOR GFS, UKMO & ECM The verification Statistics of GFS, UKMO and ECM show at 24 hours ECM ahead at 99.6 pts with UKMO at 96.5 pts and GFS at 99.4 pts. At 3 days ECM is leading with 97.6 pts to UKMO's 96.8 pts while GFS lags behind at 96.3 pts. At 5 days ECM leads with 89.5 pts to UKMO at 87.6 pts then GFS at 86.5 pts. Then at 8 Days ECM still leads at 64.5 pts over GFS's 60.7 pts. Finally at Day 10 ECM leads GFS at 46.2 pts to 45.7 pts.

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day1_PMSL_MSL_G2NHX.png

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day3_PMSL_MSL_G2NHX.png

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day5_PMSL_MSL_G2NHX.png

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day8_PMSL_MSL_G2NHX.png

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day10_PMSL_MSL_G2NHX.png

MY THOUGHTS All eyes will be drawn towards the ECM model this morning which did throw out a mouthwatering change in the weather next week resulting from High pressure development to the West and NW. Unfortunately but perhaps not surprisingly this has been watered down this morning but the general message is still present. S how does this fit in with the rest of the output this morning. Well in the interim period the general message for the next week or so remains very unsettled with Low pressure well South of normal positions across the UK or just to the West. While rainfall amounts will be very variable due to a lot of days of showery weather some longer spells of rain are still likely for all as troughs cross NE in the flow still getting hung up across NE Britain where some of the wettest weather will be experienced. Some of the showers will be heavy and squally too with hail and thunder possible across the South and West at times. Temperatures over the next week look like maintaining largely average values, cold enough at times for some snow across the hills of the North and NE. Then we come to next week when there remains plenty of evidence for limited change with rain and wind at times continuing in an Atlantic flow to other output which shows a drier interlude developing as the earlier mentioned rise of pressure to the West takes place. This would switch winds to a more northerly direction across the UK at least for a time with colder air moving South with some wintry showers at times near exposed coasts and hills and some frosts at night. My thoughts this morning remain as last night and I still think that despite a dampening down of the colder message within the models this morning I feel that colder weather will arrive from the North next week. It more importantly will mean drier weather for many with far less wind and rain and with lower temperatures overall frosts at night could develop, something quite rare this Winter so far. As for snowfall we need more runs and clarification nearer the time the exact synoptics later next week but if the Northerly flow does develop for a time then the usual areas exposed to the North could see some snow in the form of showers

Next Update on Tuesday January 5th 2016 at 09:00 approx

Well to be fair what is being modelled is not a delay in the cold snap/spell, it is a totally different cold snap/spell. 

This is the current picture of the "failed easterly" http://www.wetterzentrale.de/pics/Rtavn001.gif

After this there is then a continuing transition to the potential for some form of cold by around the 13th - that has not been moved. Whether it happens or not is another matter entirely! At this range it is worth watching but not worth getting overly excited about (and consequently disappointed if it doesn't happen).

Agreed.

As Martin mentioned yesterday in his always excellent model summary, if there is to be an eventual change away from the recent pattern, it will have to start from somewhere. It is encouraging IMO to see the models at least contemplate the idea of a pattern change of some kind; that is a lot more than could be said for any of the regular model output we saw over the past two months. Whether any change comes to fruition or not is another matter, but let's cross that bridge when we get to it.

Cheeky little snow event for Friday on this mornings GFS run

Evaporative cooling will play a major part on the northern side due to slack winds - (based on Q's KT earlier last week)