Model Output Discussion 13/11/13 >

[fergieweather]

Why worry about the ukmo, its flip flopping with the rest of them, at least the ecm 0z op is more wintry and synoptically superior to the 12z last night..it's crucial what mogreps is showing..over to you ian :- )

MOGREPS-15 heads into unbiased/cyclonic S/SW territory just a tad earlier than EC but ultimate conclusion from UKMO is (timing differences aside), a gradual return to average temps early Dec into trend period.However, analysis of 00z suites not due until circa 1030hrs. Edited November 17, 2013 by fergieweather

[phil nw.]

Yes the 'northerly' now looks completely different to what looked on the cards a few days ago - and with norherlies you normally have a greater leeway than with easterlies, where your timeframes for accuracy are T72, maximum T96.

 

I disagree Phil and the trend is there in the NWP for the erosion to come from the North from day 12 onwards, but of course that is a long way off.

That's speculation though Ian.

There is no trend to zonal on that ECM output out to day 10.or for that matter on the NAEFs

http://176.31.229.228/modeles/gens/naefs/run/naefsnh-0-0-240.png?12

 

A split flow seems the current setup with the block around the uk or just n of us.

Allow me to speculate then- there's as much chance of a more southerly jet taking over with continued support for a block.

Edited November 17, 2013 by phil nw.

[forecaster]

And that's the language I'm inviting people to be careful about. People come on here for guidance and if they see terms like 'warm sector' they may get thoroughly confused. It's a very non-empirical term so if you want to be scientific post the actual T850 upper air temp variations. However, just so we're crystal clear: there is no warm sector. It is just less bitterly cold. 

 

I disagree with this. I think you're wrong, and this is why. We could add "warm sector" to the model dictionary if it's not there yet. 

 

"Warm sector" is a recognised term that has been in use for.....I'm not sure.....possibly since the early 20th century. It's a key term in the conceptual description of cyclones.

 

A warm sector noted on a chart tells you more than the 850hPa temperatures. Why? Because to draw fronts they will have been considering both moisture and temperature. Hence it's not "more scientific" to talk about T 850hPa rather than the warm sector, in fact it's more limited.

 

It's relative, not absolute, the same way that all frontal notation is. So just because the warm sector isn't "warm" that doesn't mean you have to call it a "milder sector". If you want to go down that direction, start calling summertime cold fronts "cool fronts" or "not quite so very hot fronts". 

[shaky]

MOGREPS-15 heads into unbiased/cyclonic S/SW territory just a tad earlier than EC but ultimate conclusion from UKMO is (timing differences aside), a gradual return to average temps early Dec into trend period.However, analysis of 00z suites not due until circa 1030hrs.

I swear just yesteday or day before ian you were saying it was supporting a e/northeasterly winds in the 15 day timeframe.has it changed that much in the space of 48 hours.

[Summer Sun]

Latest from Gibby, freezing fog could become a problem from the weekend once high pressure builds

 

The General Situation. The UK lies in a benign and slack pattern currently with a weak front across Central areas which will reactivate later as a wave runs NE along it. To the North the weather will be clearer and colder with wintry showers flooding into the North and West tonight. Light rain across Central areas will become heavier from the SW through the day and extending back further North while Southern areas stay cloudy and misty but mostly dry. A cold front crosses SE late tonight and tomorrow with a cold and blustery NW flow developing for all up to midweek with showers, increasingly wintry over the North and West but not many reaching the SE. On Wednesday a Low sinks SSE down the North Sea with a spell of rain and hill sleet and snow for a time before a swing of winds to the NE on Thursday maintains cold weather and returns us into a day of sunshine and scattered wintry showers mostly in the East and SE. By the weekend High pressure will lie over the UK having moved down from the NW with dry and fine weather for all areas but with extensive mist, freezing fog and frost problems developing overnight and slow to clear, if at all through the daytimes.

 

GFS then wobbles the High pressure area around at times taking it slowly to the West of the UK while maintaining a ridge across the UK for some considerable time before it sinks South to allow a strong Atlantic Westerly flow to bring milder and cloudy conditions with rain at times particularly in the North and West to close the run.

 

UKMO closes it's run with High pressure positioned across the UK with light winds and cold conditions prevailing with widespread night frosts and fog patches but bright and crisp days, the fog chiefly across Northern areas as something of a NE flow will continue to blow across SE Britain preventing the formation of this.

 

GEM holds a cold Northerly flow across the UK late next week and weekend with wintry showers continuing to affect many Northern and Eastern areas while the West and SW see little of these with bright and cold conditions and frost at night. Then early next week the pattern collapses as Low pressure winds up in the North Atlantic and pushes milder and unsettled weather across all areas with rain at times towards the middle of next week.

 

NAVGEM today shows a chilly Northerly flow reluctant to leave the East of the UK next weekend with further wintry showers especially near North Sea coasts. Many Southern and western areas would be mostly dry and rather cold with frost at night. This East/West split is then held out to the end of the run.

 

ECM this morning shows High pressure over Iceland a week from now moving SE with a ridge ahead of it over the UK. The weather would be cold with frost and fog by night becoming more extensive towards the end of the run as the core of the High pressure sits directly over the UK. A light NE flow remains over the far SE keeping the worst of any fog patches away from down here. It will be cold everywhere.

 

The GFS Ensembles today show that High pressure will generally rule the roost across the UK for the foreseeable future. The eneral trend os to shift it to the NE, unlike the operational solution before then weakening as Atlantic low pressure moves in far out in the outer reaches of the run. Rainfall amounts look like being relatively small for the time of year with most likely towards the North at first and again towards the end of the run.

 

The Jet Stream shows the flow to the North turning South over the UK through this week before splitting North and South of the UK as a UK based anticyclone looks likely to develop through the latter end of the week, weekend and possibly into the week to follow.

 

In Summary the weather looks like turning colder for all. Deep cold is not expected though and there will be a lot of dry weather to be found over the UK once a rather unsettled phase of weather through the middle of this coming week disperses. Through this period rain and showers will turn wintry over higher ground but once more this morning no great amounts look likely from any output. Of more importance will be the marked increase in the incidence of frost which will affect all areas from quite early in the coming week. Then once the expected High pressure moves down from the NW freezing fog looks like becoming an additional hazard with the chance of it's failure to clear from notorious fog hollows by day in which instance it will stay very cold. So all in all the last 10 days or so of November offer very seasonal late Autumn weather with a lot of dry weather with overnight frosts and fog, slow to clear at times and the chance of some showers, wintry on hills as a precursor to this through the coming working week.

 

http://www.norton-radstockweather.co.uk/Model-Analysis(2859336).htm

Edited November 17, 2013 by Summer Sun

[Gibby]

It might sound to many like blowing my own trumpet but you will never find I use terminology like 'warm sectors' in my analysis as I always reflect that the vast majority know nothing of such terms and just at the end of the day want to know what the hard facts of the weather are likely to be over their heads. If I used those terms on my website my inbox would be full of requests to explain what I meant. However, I do concede that many on here are very knowledgeable folk and it seems fine if terms are used when in discussion with other likely knowledgeable folk. Sorry for being off topic.

 

P.S. Thanks to Summer sun for posting my analysis across each night and morning. it saves me a lot of time.

Edited November 17, 2013 by Gibby

[shedhead]

I definitely agree with this, but also, now that the charts are not so good at t144, it's important that we don't start assuming that means that they will verify either! I general, we can be quite confident about what will happen in the next 72 hours, sometimes have a good idea of the general idea for a couple of days after that but anything beyond and it is very uncertain! A slight change one way on the 168 chart for ECM (posted above by radiohead) could produce a very cold chart, but equally that could not happen either!

I agree Joe...but there is a huge difference between looking at 168hr means and spouting endless one liners about how the -5c 850Hpa line has moved 23 miles farther south on the T+168hr. It's going to be a very long and probably very disappointing winter for anyone who thinks most cold/very cold senarios in the T+144hrs and beyond range will verify as shown. Far better imo to view these type of charts at that range as nothing more than a guideline to the overall synoptics, not as a way of viewing which parts of London will see snow and which parts will see rain. 

Edited November 17, 2013 by shedhead

[Frosty.]

Less cold sector sounds better, some mixing out of the cold 850's, kind of watering them down before the next cold surge once the low pushes further east opening up a backwash of cold arctic air, just like the Ecm 00z op run is showing.

[Ian Brown]

MOGREPS-15 heads into unbiased/cyclonic S/SW territory just a tad earlier than EC but ultimate conclusion from UKMO is (timing differences aside), a gradual return to average temps early Dec into trend period.However, analysis of 00z suites not due until circa 1030hrs.

Thanks Ian that fits in with a set-up of the High gradually declining E/SE.

[beng]

I think what we are seeing is a trend for lower heights at Northern latitudes in FI as the models reflect the Strat cooling. Time for changes of course but our mid-latitude High looks like coming under pressure from the jet.

That's true if you use the GFS, however ECM says something very different. In fact its stratospheric forecast is just beginning to hint at something quite tasty. I think it's too early to conclude that the jet will run over the top and sink everything - if that's what you're suggesting.

[MPG]

The ECM ensemble mean is solidly behind a below average spell of weather , it splits the PV and keeps low heights to the south.The GFS ensemble mean is totally different to its operational output, this stretches the PV to the north and brings in a Scandi high before too much energy spills over the top towards day 10.Overall its a very confused picture because of these differences, in terms of upstream NOAA didn't think much of this mornings GFS run and view it as an outlier solution but that update was done before they viewed the ECM. So we won't know what they think of that till this evening.

Cant ask for a better setup then nick! Ideal for the chance of cold effecting the UK (its still autumn too guys)

[fergieweather]

I swear just yesteday or day before ian you were saying it was supporting a e/northeasterly winds in the 15 day timeframe.has it changed that much in the space of 48 hours.

It still is. But I'm referring to what happens beyond that E-SE phase. Anyway, update later.

[ARNOTT ad]

What is the point in potential updates and reading from the background signals because things can and have looked decent but at the end of the day it looks pretty simple from continuing model output and stratospheric input that the over riding signal is for milder zonality because the PV continues to be far too strong doing us no favoiurs! Remind me of this post if I'm wrong.

[Airedalejoe]

Bitterly cold! have you just come back from Dubai? I have to disagree re the term warm sector, this is widely used by meteorologists. In terms of this shortwave now that the models generally agree on the track it would need a huge correction westwards to give an all snow event and this would still be largely confined to higher ground anyway. Yes it will turn colder and maybe much colder if blocking takes hold further north or east but in terms of the next week I really don't think its anything that unusual for November.

I'm somewhere in the middle! Just watched the latest forecast on BBC and the high on Tuesday is forecast to be 3C, not bitterly cold but not usual for 19th November!I've suffered many winters here where probably everyday exceeded 3C, so the outlook for the week is definitely at least cold.We've already had plenty of frosts here and the coming weeks cycle commute looks another chilly one!!

[Tamara]

Indeed, when you now look back over the hype of the last 3 or 4 days some of the things said regarding the early to middle part of next week frankly now look way off the mark.  The main trouble again stemmed from many folks refusal to accept that models really do struggle to nail the detail in the 144-168hr range when the weather is not coming from the west, along with the fact they rarely pick up any shortwave spoilers until within T+120hrs.  Taking the often very clean looking charts at 144hrs and beyond and expecting them to verify as shown when weather is coming from the north or east always has been foolhardy...and frankly still is. WiB mentioned the potential confusion for new members when terms like 'warm sector' are use when the weather is cold, but imo they are likely to become far more confused by all the calls for cold/very cold charts to verify when often a week or more away. 

Rather deja vu here from the other evening I think. I would repeat once more that the expectation has always been for an atlantic high with a question mark over the degree of amplification associated with it. No hype whatsoever attached to that, and any persistence in trying to perpetuate that is totally unhelpful and misleading - its simply the solid reality. Every model and genuine forecaster has agreed with this. Of course from a preference point of view, then many who read this thread have been hoping for the best degree of amplification possible, not just in terms of a suitable track for the mid week feature to provide some wintry interest, but also in terms of how this might further prolong and intensify the colder pattern with further heights building in terms of at least a mid latitude to high latitude block. Maybe it is trying to play on this that is the root motive for the hype suggestion?

 

What we are looking at is a below average spell of weather for what is still afterall the mid to latter part of November and there remains the probability that a blocked spell of weather will sustain below average  temperatures and at least some wintry potential for several days at least. That is the most we can gauge atm.  However, looking at the models in terms of an overview this morning, then there is plenty to be satisfied about, relatively, from a cold weather fan point of view.

 

Split flow energy - which always causes model minefields and further associated adjustments are very much part of the  equation and I think that Phils post f.e is carefully balanced in this respect in terms of no likelihood for any early return to definitive atlantic weather. Anyone pretending to be wiser about any one model being right on these energy equations is deluding themselves as well as attemting to delude everyone else. Its more about trying to read between the lines and making assessments based on the best available data at any given time - not trying to appear wiser after the event when further data is available.

 

As just posted, we see possible signals in the further outlook (MOGREPS to 15 days) that the blocking signal may fade, but then in terms of the bigger picture we can look at further amplification potential courtesy of possible repeated lower stratosphere wave breaking into the arctic and any unsettled flatter regime leading to a further atlantic ridging scenario into December. This is of course a long way off, and very uncertain and indeterminate in timing, but an entirely feasible theme of how the macro pattern might re-cycle.

 

Putting aside the permuations of possible outcomes in the mid to longer term - it all makes for a very positive and interesting start to the winter season for model watching.

Edited November 17, 2013 by Tamara תָּמָר

[MR EXTREMES]

well I been saying what fergieweather been saying for days its clearly the signal I think we coldies like to hold on to the hope of Greenland highs and scandi highs.

 

reality is that the whole trend we were looking at days ago is going to collapse and every model has suggested this with eye candy then revert back to what is much more realistic.

 

without a split or weakened vortex and a weaker jet stream is never going to go far and by the first week of December I think its possible we could well be back into zonal weather type although I don't see anything above average which forecasters have been very keen to predict for winter through out.

 

well enjoy the colder air whilst it lasts and Greenland heights should be discounted this winter as vortex will stick around its home in greenland.

[BLAST FROM THE PAST]

I swear just yesteday or day before ian you were saying it was supporting a e/northeasterly winds in the 15 day timeframe.has it changed that much in the space of 48 hours.

Its smelling the coffee I reckon regrettably, I think GFS is more on the money than ECM here.  This will be a cold snap rather than a spell before business resumes to a westerly dominated flow.  The block ECM has, will it hold that long?.  One thing I'm pretty certain Madden has December well wrong.  I think RJS is more on the money there.

 

 

BFTP

[snowangel32]

So in the space of 48 hours evrething has flipped, so is the met office thought now that we could have a average December if fergie is saying they expect a shift to sw, w dominated scenario not good news for potential flooding lakes and rivers are still so high. Can't belive the dramatic changes the last few days oh well at least there's still the rest of winter to go.

[itsnowjoke]

Less cold sector sounds better, some mixing out of the cold 850's, kind of watering them down before the next cold surge once the low pushes further east openi ng up a backwash of cold arctic air, just like the Ecm 00z op run is showing.

Is this the kind of setup like 2010? Edit just read above post so everything has changed now Edited November 17, 2013 by itsnowjoke

[bluearmy]

Indeed, when you now look back over the hype of the last 3 or 4 days some of the things said regarding the early to middle part of next week frankly now look way off the mark.  The main trouble again stemmed from many folks refusal to accept that models really do struggle to nail the detail in the 144-168hr range when the weather is not coming from the west, along with the fact they rarely pick up any shortwave spoilers until within T+120hrs. 

often true and probably so this week but this 'spoiler' is only a couple hundred miles away from giving a decent snowfall to large parts of the UK. In the grand scheme of things that means you could so easily by awry with your post. I accept that the main cause of the aggro is the behaviour of the depressions in the west Atlantic. However, that was spotted quie a few days ago by many on here.Mogreps 15 for the end of the month is interesting. The 12z ECM ens were showing big spread for London temps and the more precipitous runs were beginning to show their hand.

[MR EXTREMES]

the gfs has reinforcement from the azores in the latter frames can this help not sure because to the north sees some very angry looking low pressure although very far out.

 

and blast from the past I agree I think RJS could well be on the money.

 

the high in the alantic 1040mb not bad but where does it go where can it go to be honest might be best if it just sticks out there for awhile until a gap shows then fill perhaps aiding a better block allowing them deep lows to slide down the northsea into se Europe helping pull in a colder flow just an idea.

 

as you can see the colder upper air is being sucked round towards central france.

Edited November 17, 2013 by model rollercoaster

[chionomaniac]

Long term (extending well into December) HLB's are probably not on the cards. However, even without the use of the GFS GLAAM pages which are not currently updating,  we know that the lower strat is vulnerable to tropospheric wave action from possible MT's. There will come a point though when the strong upper vortex strat conditions will overwhelm the lower strat and any trop wave activity will be dampened considerably. In the meantime, though, I would not write off the longevity of any cold snap until we see firm evidence that the pressure on the lower vortex from the trop has eased off.

[nick sussex]

So in the space of 48 hours evrething has flipped, so is the met office thought now that we could have a average December if fergie is saying they expect a shift to sw, w dominated scenario not good news for potential flooding lakes and rivers are still so high. Can't belive the dramatic changes the last few days oh well at least there's still the rest of winter to go.

Remember that can work both ways. So what might be a zonal signal in two weeks might well be revised, theres a lot of uncertainty even at T144hrs.

[Snowy L]

Its smelling the coffee I reckon regrettably, I think GFS is more on the money than ECM here.  This will be a cold snap rather than a spell before business resumes to a westerly dominated flow.  The block ECM has, will it hold that long?.  One thing I'm pretty certain Madden has December well wrong.  I think RJS is more on the money there.

 

 

BFTP

 

 

GFS couldn't be further from what everything else is pointing at. A North Siberian high FI, really? This when the bulk of the vortex is likely to be in that position. And then they show the area to our North filled with low pressure systems....exactly where the split in the vortex is expected to happen. ECM 0z is far more clued up imo and anything is possible until mid-december.

[Frosty.]

The Gfs 06z follows the 00z with the initial arctic surge south followed by a pocket of less cold air and then another midweek southward surge of arctic air, so a mix of persistent rain, sleet and wet snow, the snow mainly for more elevated land but not ruling out wintryness at sea level at times, unlike anything we have seen so far this autumn, this is at least a wintry cocktail of weather with some snow around, perhaps disruptive snow across the interior of scotland, again especially on higher ground. Then the 6z turns anticyclonic but cold air from the arctic blasts is not washed away, it would be a cold settled spell with light winds and widespread sharp frosts and freezing fog.