Model Output Discussion 1st Nov.2013

[That ECM]

Loving the output at this time. Firstly, it looks like becoming a lot drier on the whole. Secondly, there looks like a lot less wind. Thirdly, there are a number of possibilities to cold. Much to be resolved for sure but wind and rain as a general theme is not one of them.

[Frosty.]

The Ecm 00z T+240  screams reload potential due to the angle of the jet with lows dive bombing southeastwards drawing arctic air south, arctic air and low pressure from this point onwards = SNOW  

[tinybill]

morning  something  for the cold  lovers to wake up to

[Mark Neal.]

The 00z run is a thing of beauty on the GFS. A greenland high and low pressure over the country with a cold flow from the continent. Similar scnes have been propping up in the ensembles.  Still a good 7-10 days away, so plenty of chopping and changing to go. But looks like a cooler/colder spell is becoming more and more likely with support gaining.  Got a feeling some of the op runs in the next few days will be interesting to say the least, the 00z just a start? 

[I remember Atlantic 252]

Deep FI of course but the chart on 00Z GFS for Wed 20th Nov, looks virtually same as Wed 20th Nov '96

[bluearmy]

the ecm ens have finally settled on a mid atlantic ridge in 10 days time. its a shallow mean feature but the spreads reveal its a banker. currently forecast to be centred just south west of greenland.  also low heights over southern europe. what the spreads on uppers reveals is a massive range of solutions over the northern states and fairly large to our northwest. whilst an amplified pattern over the atlantic seems a given around the 20th, there is no way of knowing if we see a west based -NAO with average flow across us, a mid lat high over the uk or indeed a trough just to our southeast with a cold noreaster.  whilst some will question the 'putting back' of the possible cold wrt to previous days ops, it should be noted that the 20th has always been the favoured date on the ecm ens.

[lorenzo]

Another precarious winter countdown begins.. hard frost up here this morning, feeling like Winter already,look forward to when everyone else can join the fun.

 

ECM @ Day 10

 

ECM vs GFS, GFS much sharper.

 

GFS

 

GEM - really ramps that low and provides that west based solution.

 

GEFS for same time frame

 

Maybe am getting chart fatigue, I always thought the 12z runs were more bullish for cold solutions, seems the 00z is the new 12z !

 

 

 

 

[Chess01]

Whats the chance of the longevity of this cold spell Could we get blocking over the north or is this just a cold snap

[Severe Siberian icy blast]

the ecm ens have finally settled on a mid atlantic ridge in 10 days time. its a shallow mean feature but the spreads reveal its a banker. currently forecast to be centred just south west of greenland.  also low heights over southern europe. what the spreads on uppers reveals is a massive range of solutions over the northern states and fairly large to our northwest. whilst an amplified pattern over the atlantic seems a given around the 20th, there is no way of knowing if we see a west based -NAO with average flow across us, a mid lat high over the uk or indeed a trough just to our southeast with a cold noreaster.  whilst some will question the 'putting back' of the possible cold wrt to previous days ops, it should be noted that the 20th has always been the favoured date on the ecm ens.

Yes it's always been the 20th in my books, when the models first get signal of a pattern change they are always too progressive , with what appears at first to be a pattern in deep fi getting no closer. But once they pick the trend things move forward . There seems to be a signal of low pressure dropping down the North Sea . With the wrap around northeasterly winds could bring a lot interest . And what looks to me a very clear signal of low pressure in Southern Europe , which is always a good sign if it's cold your after.What a very different set up we have on our hands to what many forecast for November. It's been a cold start in the main for many , and now signs of a cold second half of the month which may well bring it in the below average temp catagory . Shows we it's not all about the strat . But mainly !!

[The Northern Ramper]

Whats the chance of the longevity of this cold spell Could we get blocking over the north or is this just a cold snap

We haven't nailed the start of it yet.

[Cloud 10]

Interesting comparing the operational runs of the GEM,GFS and ECM at day 10,in that they all model the polar vortex differently but the result at least for the UK is similar,with some sort of cold shot.

 

 

GEM.. GFS.. ECM..

 

 

The main thing is that all 3 have a high pressure anomaly in the Mid-Atlantic,which as BA mentioned

above has good support from the ECM ensemble mean.

 

 

 

edit..

 

The 00Z NAEFS would likely give quite a cold spell.

 

Meteociel - Cartes Ensemble NAEFS ( North American Ensemble Forecasting System)

Edited November 10, 2013 by Cloud 10

[Radiating Dendrite]

People need to calm down a little, this is still ten days away and is a fairly bog standard northerly from what I can see.

The charts can change dramatically within the 72 hour time frame! I think some are getting carried away as this is the first cold shot to have appeared on the models, but a little perspective is required.

We are already having will it snow in my back garden questions!

Edited November 10, 2013 by Radiating Dendrite

[snowking]

I think at this stage so that Nick doesn't have to hand out the prozac too early it may be best, at least for a short while, to temper expectations just a little.

 

First of all lets take a look at the positives. It should be of no surprise at this juncture to see the sort of ensemble mean setup depicted by the two major suites as below at day 10:

 

 

An amplified pattern over the Atlantic, most likely leaving the UK under some sort of mean North to North-Westerly flow - risk of West based negative NAO aside as discussed  by BA.

 

The trouble is at 10 days away as we have seen winter after winter there is always the potential for some smaller scale spoilers to throw a spanner in the works. The most obvious thing to say at the time of writing is that anybody expecting more than a toppler scenario based upon current output will most likely be sorely disappointed.

 

The primary reasons at the moment for not building expectation too highly are twofold.

 

First of all if we take a look at the projected NAO/AO outlooks (bear in mind the ECMWF NAO projection is still 12z yesterday):

 

 

 

Whilst we see an overall tendency towards lower values of both indexes, what is most crucial to note is that the higher resolution outputs are currently the most amplified solutions - hence seeing some of the operational runs that are currently being thrown at us. What this means is that the majority of the ensemble suite are throwing out slightly less amplified patterns overall - something closer to the classic mid atlantic ridge toppled as opposed to something closer to a Greenland-based high. Now of course it could be argued that on many occasions in the past its been a case of the higher resolution operationals/controls leading the signal ahead of the ensemble mean suites. Such an occurrence could be on the horizon here too, but at present that is mere speculation and something that we will simply have to monitor over the coming days.

 

But I think that overall the chances of the first wintry blast of weather in around 10 days time for the UK are now looking pretty good based on current NWP. The second reason though that I would just warn against, at this juncture, anybody getting too excited over the prospect of a cold spell that would give widespread lowland snowfall is both the time of year and the current SST profile around and to the North of the UK:

 

 

Bearing in mind the most likely N/NW flow, and the amount of warmer water such a flow will encounter to the North of the UK at present - I would suggest the likelihood of some modification of 850's the closer we get to the timeframe, which is pretty standard fare for a Northerly at this time of year in the UK.

 

The other thing to be wary of is any sort of expectation, based purely on face value current output, of this to become a more extensive cold spell. We are all too aware of the discussions that have been taking place about the chicken vs the egg (stratosphere vs troposphere) and so I won't go too deeply in to that. But needless to say whether you're looking at the stratosphere or the troposphere, in order to achieve something more extensive in terms of cold spells you need some sort of major disturbance to the polar vortex, and unfortunately thats just something that isn't shown at present.

 

Even if we manage to see some sort of uptick in mountain torquing in the Northern Hemisphere in around 10 days time, with much of the activity at present in the Southern Hemisphere:

 

We still need a favourable flow of energy towards the location of the Polar Vortex, and at the moment E-P Flux is not moving polewards at all:

 

 

And neither is it forecast to:

 

 

And the final kick in the teeth for the hopes of anything longer lasting is that even though the GEFS suite maintains the negative NAO signal out to day 16, it is unfortunately a West-based signal, as was suggested by BA:

 

 

So right now I would say we are looking pretty good for the first wintry blast of the season, and that's something I'm sure we'll all be looking forward too as the summer hibernators start to come out of their caves, and I am sure this place will become rather more lively over the coming 10 days or so, with plenty of triumphs and tantrums to look forward to. But to avoid the latter a little it would be wise at present to place expectations towards something more of the late 90's early 00's toppler variety.

 

A re-loading pattern? Maybe so. Even in a pattern with a raging polar vortex mid-atlantic ridges can still deliver successions of cooler NWly flows to the UK, particularly when we are seeing the upstream amplification as strong as it is. But for now that remains speculative.

 

SK

Edited November 10, 2013 by snowking

[Summer Sun]

ECM has now delayed the cold pushing it back to t240 this morning

 

[bluearmy]

Naefs 00z is indeed sypntically scrumptious from a cold pov. However, despite mean output looking good, thicknesses and uppers aren't really there yet. We must not forget that it's still November and to see proper snowfall (ie. sustained) will require an injection of colder uppers. there are still plenty of hurdles to overcome but given where we were a week ago, it's clear that much can change within a relatively short space of time. Amplification is coming. Where we sit within the pattern and how cold we could get if we end up in a favourable place remain the questions.

Great post SK but I would point at the euro low anomaly as being the interesting feature. That should drag the jet south such that we stay north of the PFj. Of course, the SST's and time of year are even more relevant in that set up.

Edited November 10, 2013 by bluearmy

[BLAST FROM THE PAST]

 

 

 I am not a greedy man I can promise you.  The above chart [chart of the week so far for me] would 'feed' me for a few weeks until the run up to Christmas.  Honestly..........if Auguste Renoir painted charts, this would be one of them

 

 

BFTP

Edited November 10, 2013 by BLAST FROM THE PAST

[Frosty.]

ECM has now delayed the cold pushing it back to t240 this morning

 

I don't mind a slight delay as long as it comes

[Tamara]

I think at this stage so that Nick doesn't have to hand out the prozac too early it may be best, at least for a short while, to temper expectations just a little.

 

First of all lets take a look at the positives. It should be of no surprise at this juncture to see the sort of ensemble mean setup depicted by the two major suites as below at day 10:

 

An amplified pattern over the Atlantic, most likely leaving the UK under some sort of mean North to North-Westerly flow - risk of West based negative NAO aside as discussed  by BA.

 

The trouble is at 10 days away as we have seen winter after winter there is always the potential for some smaller scale spoilers to throw a spanner in the works. The most obvious thing to say at the time of writing is that anybody expecting more than a toppler scenario based upon current output will most likely be sorely disappointed.

 

The primary reasons at the moment for not building expectation too highly are twofold.

 

First of all if we take a look at the projected NAO/AO outlooks (bear in mind the ECMWF NAO projection is still 12z yesterday):

 

gefs_nao_00.pngeps_nao_12.png

 

gefs_ao_00.png

 

Whilst we see an overall tendency towards lower values of both indexes, what is most crucial to note is that the higher resolution outputs are currently the most amplified solutions - hence seeing some of the operational runs that are currently being thrown at us. What this means is that the majority of the ensemble suite are throwing out slightly less amplified patterns overall - something closer to the classic mid atlantic ridge toppled as opposed to something closer to a Greenland-based high. Now of course it could be argued that on many occasions in the past its been a case of the higher resolution operationals/controls leading the signal ahead of the ensemble mean suites. Such an occurrence could be on the horizon here too, but at present that is mere speculation and something that we will simply have to monitor over the coming days.

 

But I think that overall the chances of the first wintry blast of weather in around 10 days time for the UK are now looking pretty good based on current NWP. The second reason though that I would just warn against, at this juncture, anybody getting too excited over the prospect of a cold spell that would give widespread lowland snowfall is both the time of year and the current SST profile around and to the North of the UK:

 

Bearing in mind the most likely N/NW flow, and the amount of warmer water such a flow will encounter to the North of the UK at present - I would suggest the likelihood of some modification of 850's the closer we get to the timeframe, which is pretty standard fare for a Northerly at this time of year in the UK.

 

The other thing to be wary of is any sort of expectation, based purely on face value current output, of this to become a more extensive cold spell. We are all too aware of the discussions that have been taking place about the chicken vs the egg (stratosphere vs troposphere) and so I won't go too deeply in to that. But needless to say whether you're looking at the stratosphere or the troposphere, in order to achieve something more extensive in terms of cold spells you need some sort of major disturbance to the polar vortex, and unfortunately thats just something that isn't shown at present.

 

Even if we manage to see some sort of uptick in mountain torquing in the Northern Hemisphere in around 10 days time, with much of the activity at present in the Southern Hemisphere:

 

We still need a favourable flow of energy towards the location of the Polar Vortex, and at the moment E-P Flux is not moving polewards at all:

 

And neither is it forecast to:

 

And the final kick in the teeth for the hopes of anything longer lasting is that even though the GEFS suite maintains the negative NAO signal out to day 16, it is unfortunately a West-based signal, as was suggested by BA:

 

gefs_z500anom_nh_65.png

 

So right now I would say we are looking pretty good for the first wintry blast of the season, and that's something I'm sure we'll all be looking forward too as the summer hibernators start to come out of their caves, and I am sure this place will become rather more lively over the coming 10 days or so, with plenty of triumphs and tantrums to look forward to. But to avoid the latter a little it would be wise at present to place expectations towards something more of the late 90's early 00's toppler variety.

 

A re-loading pattern? Maybe so. Even in a pattern with a raging polar vortex mid-atlantic ridges can still deliver successions of cooler NWly flows to the UK, particularly when we are seeing the upstream amplification as strong as it is. But for now that remains speculative.

 

SK

Excellent post SK  This does indeed sum up recent throughts in the stratosphere thread. Yes there is more to what makes up our weather patterns than the conditions in the stratosphere - but we do need a profile here that is conduisive for a more sustained blocking pattern and at present this isn't in place. So, as stated, a ridging (and flattening thereafter) atlantic set-up is most likely.

 

However, there is every chance for the pattern to be a cyclical one and a further improved one if sequential mountain torques occur in tandem with the very amplified Pacific High pressure pattern

Edited November 10, 2013 by Tamara תָּמָר

[BLAST FROM THE PAST]

Some good posts re tempering expectations, lets not jump the gun.  However, something I've noticed...we've had a fairly overall mild run over last few weeks with some lively action the last couple......but out of innocuous set ups the temp ain't half plummeted at times around here.  After the rain past through on Friday I was at my lad's school guy fawkes fete cooking a bbq, it got really cold really quickly.  Maybe my aging bones......but its not the first time over last couple of weeks its been much chillier than expected.  We only had a 'Scotland' Northerly last night and it was really cold this morning.......imaging what it would be like from the arctic

 

re topplers, they are fine this time of year and if a run gets going it sometimes leads to each toppler being a tad more amplified and potent than the previous one, which each one being like a softener body shot to the AZH / Euro trying to get a stranglehold. 

 

 

 

BFTP

Edited November 10, 2013 by BLAST FROM THE PAST

[Summer Sun]

Latest from Gibby

 

The General Situation. The first week is fairly agreed upon taking us up to and including next weekend. High pressure is building down to the SW with a light NW flow over the UK today with sunny periods and a rather cold crisp day for many. Through tonight a warm and cold front move NE and SE respectively over the UK each giving a spell of rain with the warm front raining temperatures to mild levels briefly while the cold front brings colder, fresher weather back to all areas by Tuesday. Over the rest of Tuesday and Wednesday another ridge brings dry and rather cold conditions with the likelihood of a frost on Tuesday and maybe Wednesday night before a rinse and repeat pattern of milder, windier and wetter weather moves SE across the UK on Thursday. The end of the week and much of the weekend will see a lot of dry and bright weather before yet another trough feeds in from the NW later next weekend.

 

GFS then shows week 2 starting with Low pressure steadily taking over from the NW before deepening rapidly as it move SSE over the UK. High pressure builds North over the Atlantic and then NE across Northern Sea areas allowing a cold NE flow on the lee side of a deep Low to the SE. Then as this fills and a ridge collapses South over the UK an unstable north to Northwest flow sets up late in the run. All areas would see rain and strong winds over this period with some snow on hills in the North extending to all areas later as winds swing NE. The North would tun drier if cold and frosty before the Northerly flow at the end return wintry showers South across Northern and Eastern areas later.

 

UKMO shows next Saturday with a large High close to South-Western Britain with a strong Westerly flow across the North of the UK and a weaker one in the South. All of Britain would lie under a lot of cloud with some rain in the North but a lot of dry weather over the South if rather cloudy and mild.

 

GEM shows High pressure too down to the SW next weekend before it builds across the UK following a weak front with a little rain, in turn followed by cold, quiet weather with fog and frost night and well into the day for many. A further change then takes hold in the shape of a GFS type solution as deepening Low pressure slips SE towards the UK towards the middle of next week with rain and gales followed by wintry showers in a cold and strong West or NW wind.

 

NAVGEM today shows a trough sliding SE over Southern Britain next Sunday with some rain but pressure here remains high and this is likely to be snubbed out in preference to dry and quiet weather with the risk of persistent fog. In the North fresher Westerly winds will keep thing rather cloudy with occasional rain possible and average temperatures.

 

ECM today shows a more active trough crossing SE over Southern Britain next Sunday with some rain before a drier Monday under a ridge is the precursor to a spell of very windy West then NW winds for all. A spell of squally rain will move quickly SE over Britain followed by a cold and showery NW flow for all. Wintry showers would be widespread over the North and West in particular with snow down to modest levels at times in the North.

 

The GFS Ensembles show a fairly average bunch today with the mean for this run largely hugging the long term mean values. This is made up by some members showing rather cold weather and some mild which can hide the undulating pattern to the weather over the period. After a dry period through the middle of the week over the South occasional rain returns for all but no large amounts are hinted at.

 

The Jet Stream shows the flow powering further North over the Eastern Atlantic through this week as pressure builds to the SW of the UK. It then crosses East to the north of Scotland before slipping down over Europe. Despite accuracies falling away thereafter the flow seems to maintain a more north of the UK element while some other elements show a tilt of the flow WNW to ESE over the UK later in Week 2.

 

In Summary the weather remains typically Autumnal through the remainder of the month with something for almost everyone shown this morning. The first and most important point is that rainfall amounts in the saturated parts of the South will be less prominent over this period with longer dry spells thanks to a build of pressure close to the SW. This in turn will keep relatively mild conditions given the time of year though polar maritime incursions will make for rather colder interludes with the odd wintry shower and frost at night chiefly in the North. Thirdly, there is a trend shared between models of a shift in the Jet flow to a more WNW to ESE trajectory over the UK at the same time as High pressure to the SW loses it's grip somewhat in the second week and if this unfolds a situation such as GFS, GEM and ECM show for week 2 could develop bringing strong winds and rain and more importantly an injection of much stronger cold air across the UK with a wintry mix to precipitation then possible almost anywhere, all this due to a sharp pressure fall over Europe. As always though this continues to be shown at times just beyond arms length and as a result must be taken very cautiously.

 

http://www.norton-ra...is(2859336).htm

[shedhead]

Another excellent post from SK as well as others, who like me continue to urge caution. Asking about the potential longevity of any cold spell that isn't progged to develop until 9 or 10 days hence is rather pointless imho, but that said there does appear to be genuine hope of some 'colder' weather for the final third of the month. Once the models get a better grip of the background signals I'm sure (as is often the case) a downgrading of the cold will start to emerge, both in terms of depth and longevity, but a toppler set up does look very possible at this stage and as Blast said yesterday even this has to be preferrable to a 3000 mile draw from Bermuda.

[Summer Sun]

NAO still showing hints of going negative during the second half of this month though with a fair amount of scatter

 

[Barry12]

GFS 6Z AT 240

 

 

336

 

 

384

 

Edited November 10, 2013 by Barry95

[Summer Sun]

GEM has other ideas going for a deep low instead of any northerlies

 

 

If it went on a bit longer we may well see a northerly developing, possibly gale force winds with it, but in the short term anything from the north remains at t240 or beyond depending on which model you view

Edited November 10, 2013 by Summer Sun

[shedhead]

You've been around long enough SS to know we only believe GEM when showing summer heatwaves and winter blizzards..... 

Edited November 10, 2013 by shedhead