Model Output Discussion 23/11/2012 18Z onwards

[NickR]

Yes, we need to keep a close eye on developments upstream over N America, as there are signs that the Canadian Vortex may elongate eastwards across the NW Atlantic/S'ern Greenland - which would strengthen the upper flow eastwards across the Atlantic towards NW Europe, with an attack from Atlantic depressions. All past t+168 atm, so wouldn't get too concerned for now until the models keeping showing this scenario.

Chances are though, the block towards Svalbard may have enough strength to suppress the PFJ enough to keep any mild attack from the Atlantic at bay.

Colder air characterised by T850s AOB -5C creeping south on Wednesday & Thursday, though the N'erly flow looks fairly dry to the end of the week, apart from the usual wishbone effect with showers around the coasts, which look to turn increasingly wintry through the week.

That was going to be my question... the cold is coming end of the week... but with the flow on UKMO and ECM (which are different, I know), would there by much of the white stuff (at least initially, on Thurs/Fri/Sat)? And if so would it tend to be limited to certain areas? I'm just trying to get a handle on how to interpret the charts in that respect. Many thanks!

[nick sussex]

Slowly but surely the models inch towards agreeing on the finer detail however still some uncertainty with that troughing over Europe which as you can see later on could have an effect on the later synoptics. However I would have my doubts about that ECM FI output, generally with high pressure near Svalbard the model should be taking more energy se'wards, rather than east.

Part of the reasons for the ECM is a domino effect caused by the track of its Canadian low, remembering here that we need this sliding up the western side of Greenland to develop a stronger ridge to its east, the ECM is still more progressive here than both the UKMO and GFS.

[cyclonic happiness]

The GFS and the ECM do seem to be going over the top somewhat with all the shortwaves.

They can't predict an easterly flow and yet they can predict what half a dozen shortwaves are going to be doing in a week's time??

I don't think so!

FI appears to be getting nearer and nearer, folk would do well to remember that before going into a hissy fit when they see the models this morning.

The models before 144+ look still very good and as other have said, the Meto isn't backing down and that still looks very tasty :-D

[Weather-history]

Hmmmm.... What has happened to the ECM, it looks more the like the GFS with a heightened risk of an Atlantic attack. The depression doesn't actually make it much further east from from that position, but, it's still a bit close for comfort!

GEM looks quite horrific but thankfully all post T200 so really not worth getting overly concerned about.

UKMO looks stunning, I really hope this model will prove correct on this one.

Meteociel GEM and Wetterzentrale GEM look different

[Coast]

would there by much of the white stuff

An excellent, simple way to check the likelihood of snow here:

http://www.netweather.tv/index.cgi?action=wisi;sess=

[Methuselah]

Anyhoo, a cold spell is pretty-much 'nailed-on' now, so let's not get too bogged-down with what may, or may not, happen in the far-reaches of Fantasy Island??

Edited November 25, 2012 by chionomaniac

[NickR]

An excellent, simple way to check the likelihood of snow here:

http://www.netweathe...tion=wisi;sess=

Thanks. Though it's a more prosaic answer I'm after - trying to understand a general sense of how the charts for those days that we are seeing translate into what snow (or not) conditions, whether heavy, showery, etc.

[IDO]

Looking at the GEFS: http://cdn.nwstatic.co.uk/ensimages/ens.20121125/00/t850London.png we are still heading for a 5-7 day cold snap, details to be decided. The ensembles from GFS have been consistent with this for 4-5 days and as the Met and ECMW dont go that far out, they are our most reliable guide. The mean by the end of FI is around 0c, so cool/cold still looking the pattern 15 days plus.

The snap looks like having a northern or eastern (NE) flavour initially but from the micro events could lead to some down south.

The good news is that the Eurasia area is being smothered in cold:

The real cold moves westwards cooling down Eastern Europe. Good for later December?

[Gibby]

Good morning. Here is the latest look at the 00zs from GFS, UKMO,GEM and ECM for today Sunday November 25th 2012.

All models show a similar pattern up to Thursday of this week. The Low pressure from yesterday continues to move away NE taking the rain away with it. The strong winds in its wake move away too through the morning. After a lull in conditions another Low pressure approaches from the West later bringing further rain and strong winds across from the West this evening andd tonight. Through the early and middle days of the week the Low trundles East across the UK with unsettled conditions prevailing for all with further outbreaks of rain or showers in a developing Northerly wind with rather colder conditions for all. The precipitation will mostly be of rain but a little snow over the hills of the North could develop with time.

GFS then shows a complex Low pressure re-establish over the UK once more as a further disturbance runs SE into the general complex pressure pattern over NW Europe. The weather would remain rather cold and unsettled with the snow level falling to more modest hills at times though no major amounts would be expected away from the highest hills. Winds would of become cyclonic variable over the UK over the weekend. Through the early part of FI the weather remains rather cold and unsettled as Low pressure continues to dumb bell around the UK maintaining some wet conditions at times for all and further snow over the hills. Towards the end of the run the complex weather pattern remains with Low pressure pushing a trough North towards the South while the North stays High pressure influenced, so rather cold conditions prevailing here in rather cold weather. The South will see yet more rain, especially in the SW.

The GFS Ensembles show a rather cold spell coming, lasting for a week or so before the trend for a return to nearer to normal temperatures is increasing later in the output with a steady increase in rainfall again later as the less cold conditions move in. There is a lot of spread in the pack later in the run though while the operational is a warm outlier at the end of the run after being on the colder side of the group through the colder phase.

The Jet Stream shows a disruption to the current flow over the South of the UK and English Channel as the ridging I've talked about in recent days takes place over the Atlantic. The flow returns South over Ireland or the UK through next week while turning East across Southern Europe later.

UKMO for Thursday shows Low pressure to the East strengthening late in the week as well as the associated cold North to Northeast flow over the UK. There will be rain or showers at times with an increasing trend for rain to fall as snow over the hills with time.

GEM shows a complex Low pressure structure over and to the SE of Britain late in the week and through the weekend with rain at times and snow over the hills too. It does show though on the last frame of its run, while ataying wet milder air will begin encroachingNorth towards Southern England with time as winds begin to turn SW.

ECM shows a different scenario with time as it's Northerly flow is directed over the UK in association with Low pressure over scandinavia rather than NW Europe. The weather would still be rather cold and showery in the North and east before Low pressure to the NW and a cold front follows a brief ridge across the Uk with rain returning for many before the wether looks like becoming less cold later as the Atlantic bears more influence to the airflow over the UK at the end of the run as winds back Westerly.

In Summary today the cold spell is still on its way. There looks to be between 5-7 days of cold or rather cold weather and with Low pressure still quite close there ould be rain turning to snow at times over the hills of the UK. Further on there are growing signs that the spell might be relatively short as ECM wants to bring the winds back in from the west with time and consequently higher temperatures. No model shows deep cold and snow and the GFS ensembles too support a lessening of the cold as we move towards the end of the run. Until the output settles on what happens behind the Low pressure moving East to Europe in the next few days the pattern will continue to chop and change in the latter stages of each run. UKMO is pick of the bunch for cold this morning for me with no quick exit to milder weather shown from it's day 6 chart. So I think the jury is out at the moment with FI probably beginning as early as t96hrs through things should become clearer by Wednesday of this week. One thing is for sure there is plenty of scope for more copious rainfall from some members for those aras of the UK that least need it.

Don't forget this analysis is available up to 1 hour earlier on my website at http://www.norton-radstockweather.co.uk/page7.htm

[Nick F]

That was going to be my question... the cold is coming end of the week... but with the flow on UKMO and ECM (which are different, I know), would there by much of the white stuff (at least initially, on Thurs/Fri/Sat)? And if so would it tend to be limited to certain areas? I'm just trying to get a handle on how to interpret the charts in that respect. Many thanks!

At the moment, a quick glance at the parameters suggests the white stuff will turn up later this coming week as we see showers turn increasingly wintry from the north. Though settling snow perhaps confined to over the hills of Scotland and NE England looking at the general wind direction, T850s, DPs, temps and 850-1000mb thicknesses. Perhaps more widespread wintriness next weekend though, but showers maybe confined to coasts unless there are troughs in the flow.

[Liam J]

Has the GFS suddenly become the 'one to watch'? Has the 'expert consensus' changed overnight?

Nooo, surely that would go against everything we've learned in here wrt the GFS over the last week, unless theres a much less technical science involved?

Edited November 25, 2012 by Liam J

[NickR]

At the moment, a quick glance at the parameters suggests the white stuff will turn up later this coming week as we see showers turn increasingly wintry from the north. Though settling snow perhaps confined to over the hills of Scotland and NE England looking at the general wind direction, T850s, DPs, temps and 850-1000mb thicknesses. Perhaps more widespread wintriness next weekend though, but showers maybe confined to coasts unless there are troughs in the flow.

Many thanks. That backs up my very basic evaluation of the charts. I think the problem can be that people talk in terms of "it's on" "UKMO says yes", etc., which gives the impression sometimes that it'll be bucketloads of snow and deep cold from the start (ie Friday-ish).

[I remember Atlantic 252]

thickness look good on the GFS, best run so far? slack lows with cold air over us, I need the 522 for snow, next weekend shows that

[Severe Siberian icy blast]

Yes after the overnight gfs and the ukmo it seems as we are really heading in the right direction now, just hope the ECM gets back in line as the 12z last night was good. A bit supprised Gibby doesn't see the snow on any lower ground though , the ukmo looks very wintry to me, as does the gfs. Any thoughts ??

[Frosty.]

The ukmo 00z remains top of the class synoptically for a more prolonged and potent outbreak of wintry weather which looks sustainable well beyond T+144 if it ran further, just as good as the 12z last night, the Gfs 00z is next with a cold wintry outlook with some snow and sharp frosts and temps struggling to rise much above freezing for several consecutive days, the pattern does become more messy but we remain within the cold block, just towards the end of FI does the pattern come under threat but that may induce a battle with northern blocking looking very strong, the Ecm 00z op run is relagated to third spot of the big 3, we still get a cold snap but it doesn't look as strong as the gfs or ukmo, and longevity is cut short but it doesn't look like even the ecm would return us to a mild outlook, a spell of cold zonal would be more likely, similar to what we had in early december last year with cold, strong westerly winds and wintry showers, so ukmo is flying the flag proudly for a potent cold spell of some magnitude, on balance will still appear to be heading towards a prolonged cold spell rather than a short snap but the 12z should clarify the position one way or the other.

[tinybill]

not going to get carried away yet but this looks nice if it comes off with this deep low over the uk

[johnholmes]

I have not had time to do my detailed look using the anomaly charts for 6-15 days or more down the line but will try and do one this evening

[chionomaniac]

not going to get carried away yet but this looks nice if it comes off with this deep low over the uk

If cold rain is your thing Tiny!!

[bluearmy]

Anyone fancy an old fashioned eighties style snow split uk which slowly sinks back south for the period following the initial cold trough?

Mean easterly flow to follow for middle third dec.

[nick sussex]

Not a surprise when you look at the ECM ensemble maps that the coldest solutions for the UK have the more southerly placed troughing, especially on the eastern side of this.

http://www.ecmwf.int...t!2009112700!!/

The northwards extent of this troughing does play a big role in how any Atlantic energy will get directed later, the further south the European trough means that the Arctic high is also further south, as the energy spills east its more likely to disrupt further west, less interaction with the trough over Europe.

Edited November 25, 2012 by nick sussex

[kold weather]

Models have steadily shifted everything southwards, expect that trend to continue as they get to grips with the 'true' strength of the northern blocking (models tend to under-estimate it, especially when its actually a legitimate block, like this one appears to be).

[Weather Boy]

Models have steadily shifted everything southwards, expect that trend to continue as they get to grips with the 'true' strength of the northern blocking (models tend to under-estimate it, especially when its actually a legitimate block, like this one appears to be).

Yes, agreed. I don't wish to ramp (I like to try to be objective) and maybe I am showing my inexperience, but I can't really understand those suggesting that this could only be a relatively short cold snap or that snow might only be confined to high ground. Many runs have shown jaw dropping cold and with low pressure so close to the south east it is hard to see it being a dry flow.

Clearly no intense cold continues indefinitely and there are bound to be less cold days in the overall spell, but the background signals for continued blocking with nothing to shift the initial cold shot are very strong. The only thing to suggest otherwise is FI especially the GFS which we have been firmly told by those with more knowledge than us should be ignored after day 8.

Huge reload potential from the longer range charts generally.

[nick sussex]

Models have steadily shifted everything southwards, expect that trend to continue as they get to grips with the 'true' strength of the northern blocking (models tend to under-estimate it, especially when its actually a legitimate block, like this one appears to be).

Lets hope that southwards adjustment continues especially regarding the ECM. Another thing seems to be less shortwaves appearing, only yesterday we had a couple much further north blocking the Arctic high from ridging down.

I'm pretty sure this is due to the lack of observational data in that region which compounds the already inherent difficulties in modelling these accurately.

Looking at the ECM ensemble mean versus the operational, the mean is far better at 168hrs in terms of being further south.

Edited November 25, 2012 by nick sussex

[Tim Bland]

I think everyone is so desperate to see aflame of snow they (including myself ) at times are missing the bigger picture. It's not even Dec yet! As long as there is blocking in place and the Strat continues to warm there will be plenty of reloads and it will get colder each time. When the blocking subsides we have a chance for widespread snow, then watch as the cold air creeps back..this is as good as it gets in the uk for snow! Reading GPs boats and looking at the overall Synoptics and teleconections it could be an exciting winter !

[kold weather]

The models do have a habit it seems even these days to under-estimate the size of high pressure cells and their relative strength. I think my best examply was back in 2005 with hurricane Katrina. The models forecasted to move W/WNW over Florida and then sharply recurve. Instead it plowed WSW/SW for 2 days before finally lifting out. It turns out the models had under-estimated the expanse of the HP cell by 300% according to the weather balloon information!