Model Output Discussion: 12Z (22/11/12) And On...

[Karl83]

The BOM is where it's at tonight, perfect evolution as the Arctic high sets up home close to northern Norway sending the shortwaves packing towards Biscay. Shame it's just the BOM!

http://www.meteociel...&mode=1&carte=1

http://www.meteociel...ode=0&archive=0

How accurrate is the BOM Liam? Only ever look at GFS ECM and UKMO so should I be taking note of this models output?

[Duane S.]

The models never ever get a proper handle on Greenland heights. Is seems to me they are underplaying height rises in that area compared to what we are expecting from the anomaly projections.

Lets not look for a breakdown until the cold actually arrived.

Yep, I've seen this before from the models. Signal is robust for strong blocking, plenty of fantastic FI charts reflecting this as we get to around T- 5 / 6 days it has a wobble and goes flat before its back on with full on ridging into the more reliable timeframe.

I say the BOM has it nailed

[Ian Brown]

The ECM is different again but the important thing is that it does not do what the GFS does in the medium timeframes, so I wouldn't worry about the T216 and T240 charts which is possibly an unlikely outcome if the T144-192 charts are correct.

[blizzard81]

The BOM is where it's at tonight, perfect evolution as the Arctic high sets up home close to northern Norway sending the shortwaves packing towards Biscay. Shame it's just the BOM!

http://www.meteociel...&mode=1&carte=1

http://www.meteociel...ode=0&archive=0

It may just be the BOM but no one can deny it's consistency these last few days. The question is - consistently correct or

consistently wrong?? I don't think we have long to wait for the answer now. I am as confused as the models right now but there is

something in the back of my mind that tells me the BOM performed well in the run up to the Nov/Dec 2010 cold spell or was it the 2009/2010 winter

or indeed both? It would be great to get an update from GP right now so he can give us his thoughts on which models he thinks are in tune with his

thoughts for the next ten days.

[Liam J]

How accurrate is the BOM Liam? Only ever look at GFS ECM and UKMO so should I be taking note of this models output?

I can't really answer that tbh, the BOM is an Australian weather model so I'd doubt it's accuracy for our part of the world is going to be setting any standards. I wouldn't discount it altogether though - It has been the most consistent model over the last number of days......

Edited November 23, 2012 by Liam J

[weather_it_will]

However there remains big variations in the charts for next weekend/ The roller-coaster is get to go on for a few more days yet.

I would not be surprised if we are are still uncertain with the models at T+24 showing different variations as we get close to next weekend.

Any snow event as to who will get it, often cannot be predicted until literally a few hours before it arrives.

People should just enjoy the rollercoaster of upgrades and downgrades, but not worry about exact details until within 48 hours or less.

[Mark Neal.]

Interesting charts being thrown out at the moment. The key thing though is that we keep seeing no sign of a strengthening vortex in mid-range and good signs of northern blocking. ECM- Looked good to me. UKMO- Superb. Well lets put it this way the weather charts showing up are better than last year, but you can't please everyone!

[chris55]

The BOM is where it's at tonight, perfect evolution as the Arctic high sets up home close to northern Norway sending the shortwaves packing towards Biscay. Shame it's just the BOM!

http://www.meteociel...&mode=1&carte=1

http://www.meteociel...ode=0&archive=0

Yep, look how the Azores high ridges northwards and allows the trough to duck underneath, this is going to be an important evolution IMO.

UKMO would follow a similar path

ECM fails due to the Low off southern Greenland

All to play for though!!!!

[Ian Brown]

I can't really answer that tbh, the BOM is an Australian weather model so I'd doubt it's accuracy for our part of the world is going to be setting any standards. I wouldn't discount it altogether though - It has been the most consistent model over the last number of days......

The BOM has performed abysmally over the last couple of winters after initially receiving much hype.

The ECM ensembles will be interesting, as will the 18Z as of course the key evolutions are in the medium range now.

[weather eater]

One or two of you appear to be missing the obvious here, today between 96hrs and 168hrs, we have had three different GFS evolutions, two different ECM evolutions, two different UKMO evolutions, and several other models with other evolutions, what that should be telling you, is that the models haven’t yet got a handle on that crucial period.

Edited November 23, 2012 by weather eater

[Dunstable Snow]

Agree that some of the output tonight is not what we would ideally want but this is all part of the experience of watching/interpreting and commenting on the models. This was never going to be a straightforward process and now that we are within timescales where shortwaves are modelled into the synoptic output the roller coaster of emotions are heightened.

My preference for charts becoming reality would definately be the BOM output but somehow I just cant see that happening. It looks far too clean and straightforward. Would be a great way to start the winter though !

I actually think the comment on here has by and large been balanced, mature and humorous, certainly more so than I have seen in the past. This makes the thread a much more pleasant read and helps to keep expectations at realistic levels.

Cheers.

[Frosty.]

The latest GEFS 12z mean is very encouraging for much colder prospects way into FI with an increasingly cold Ely to NEly airflow from a very cold source in NE Europe, very cold and unsettled with low pressure in control so we would see most of the precipitation eventually turn more to snow with temps struggling to get much above freezing and some very frosty nights, high wind chill and when winds drop light, a lot of freezing fog, it all adds up to a very wintry cocktail of weather from towards the end of next week and then at least the following week to ten days. So when you add the very wintry ecm 12z op run and the ukmo 12z to the above, it all sounds very promising indeed but if you are looking for mild, you are out of luck until beyond T+300 hours.

[nick sussex]

Its interesting how the models group together in terms of how they split the low to the west and the pattern in the eastern USA and Europe.

GFS , NOGAPS and JMA

UKMO , BOM and GEM

ECM does disrupt that low but stands alone when you look at its northwards push of that troughing and where it sends the Arctic high in FI.

It has been consistent with this view over the last few runs so is it leading the pack or just consistently wrong?

Edited November 23, 2012 by nick sussex

[VillagePlank]

GEFS 850hPa 12z Analysis,

[Karl83]

I can't really answer that tbh, the BOM is an Australian weather model so I'd doubt it's accuracy for our part of the world is going to be setting any standards. I wouldn't discount it altogether though - It has been the most consistent model over the last number of days......

Cheers Liam.

[Methuselah]

GEFS 850hPa 12z Analysis,

Thanks for that, Karl; t's a perfect expression of current state of the GFS's inherent uncertainty. What happens if you extend your analysis to include the other models?

[VillagePlank]

Thanks for that, Karl; t's a perfect expression of current state of the GFS's inherent uncertainty. What happens if you extend your analysis to include the other models?

The name's Mark

Yes, this a reasonably reliable analysis that helps us figure out how little or how much certainty we have when we head into FI. Unfortunately, I need a source for the numbers, so I cannot do an analysis of the other models or even, say, a cross model median (which would be very handy, since the ensemble runs are almost never normally distributed, and we shouldn't really be using the 'mean')

Edited November 23, 2012 by Boar Wrinklestorm

[cooling climate]

ECM operational will I think be on the mider side of its ensembly

members tonight and rather loses the plot after t144.

The GFS baring the short wave fiaso would be a lot more like the

UKMO.

A very cold spell is on the way I think but some of the operational

model runs just don't know it yet.

[Methuselah]

The name's Mark

Yes, this a reasonably reliable analysis that helps us figure out how little or how much certainty we have when we head into FI. Unfortunately, I need a source for the numbers, so I cannot do an analysis of the other models or even, say, a cross model median (which would be very handy, since the ensemble runs are almost never normally distributed, and we shouldn't really be using the 'mean')

Sorry about that, Mark - the old noddle's getting fried!

It's a shame, that; we need a handle on these things!

[AWD]

Looks like more wet & windy weather for the south this weekend.

The GFS;

http://cdn.nwstatic.co.uk/gfsimages/gfs.20121123/12/36/airpressure.png

has a potent depression heading up from Biscay, but the rain would be the main problem I think, with the winds nothing too severe;

http://cdn.nwstatic.co.uk/gfsimages/gfs.20121123/12/36/ukprec.png

The ECM has it even deeper, with some intense winds around southern & western coasts, transferring east later;

http://cdn.nwstatic.co.uk/ecmimages/20121123/12/ecmslp.024.png

http://cdn.nwstatic.co.uk/ecmimages/20121123/12/ecmslp.048.png

Notice another developing depression after this one too, this doesn't develop into much on this run but one too watch for now.

Edited November 23, 2012 by AWD

[VillagePlank]

Sorry about that, Mark - the old noddle's getting fried!

It's a shame, that; we need a handle on these things!

It does help, even with the old GEFS, to look at the probabilities: the area between the dotted line is the area where 68% of the runs have pegged their temperature, so in that respect it's 'odds-on' Doesn't mean it's right (or wrong) but does help to ground oneself when the uber-fantastic charts are doing the rounds. So, for instance, there's a less than 32% chance of getting to the nominal -8C 850hPa rule of thumb for (certain) snow given precipitation.

All these charts are for London, Heathrow, btw.

Edited November 23, 2012 by Boar Wrinklestorm

[offerman]

Big lesson, dont get to carried away with cold runs which i do as mild seems to be trying to get back in, cold not so likely as on some arlier runs but still possible.live in hope.

[Karl83]

Looks like more wet & windy weather for the south this weekend.

The GFS;

http://cdn.nwstatic....airpressure.png

has a potent depression heading up from Biscay, but the rain would be the main problem I think, with the winds nothing too severe;

http://cdn.nwstatic....2/36/ukprec.png

The ECM has it even deeper, with some intense winds around southern & western coasts, transferring east later;

http://cdn.nwstatic..../ecmslp.024.png

http://cdn.nwstatic..../ecmslp.048.png

Notice another developing depression after this one too, this doesn't develop into much on this run but one too watch for now.

Links not working dude.

[David Morse]

Interesting to see that the ECMWF is now reflecting the GFS run from earlier today showing HP off the Irish west coast and no low to the south of the UK at 240hrs; giving cold but dry instead of the 00Z much wetter set up? So the GFS not so uncertain?

[Gibby]

Good evening. Here is the report on the 12zs from GFS, UKMO and ECM for tonight Friday November 23rd 2012.

All models show a continuation of unsettled weather into the beginning of next week when the models diversify somewhat in their respective outcomes. In the mean time Low pressure is moving up from the SW in the next 24 hours with rain and strong winds developing once more across Southern and Central regions tomorrow. By Sunday this moves away NE as another brief respite develops through the latter half of the day. By Monday yet another depression runs into the SW of England with further heavy rain and perhaps strong winds developing once more through the day.

GFS then shows this Low pressure drift slowly East into Europe over the following days setting up a rather cold North to Northeast flow with further rain at times and snow on higher Northern hills. Later in the week further Low pressure reinforces the general complex Low pressure over NW Europe with rain and strong winds in temperatures on the cold side of normal with some snow still on Northern hills. Through the early days of FI the South continues to bear the brunt of further rain as Low pressure remains close by. With time the Lows do give way as pressure rises with a period of drier weather with frost and fog occurring before milder weather moves in, all in association with deep Low pressure near Iceland bringing occasional rain and much milder conditions to end the run.

The GFS Ensembles show a rather cold spell developing early next week with low pressure keeping the unsettled theme going with rain at times falling as snow at times on Northern hills. The operational was a mild outlier at the end although there is a trend starting to emerge of a gradual drift towards normal 850's deep into the run.

The Jet Stream shows a ridging through the North Atlantic replacing the Eastward moving flow over Southern Britain currently. In a week or so the flow continues to be ridged at high latitude in the North Atlantic with the returning arm moving South to the West of the UK then East over Southern areas of Europe.

UKMO tonight shows Low pressure centred over SE Europe on Thursday of next week with a cold and increasingly cold NE flow developing through the latter half of next week with rain at times, falling increasingly as sleet or snow over the hills with time.

ECM shows Low pressure at more Northern latitudes in its latter stages keeping the very coldest weather away from the UK. nevertheless a cold North flow will deliver some wintry showers at times with any clearer skies overnight permitting frost to form. By the end of the run High pressure from the Atlantic begins to topple over the Uk with a cold and frosty spell developing with time but at least very much drier by then.

In Summary a colder spell is on the way. This does not necessarily mean drier though as Low pressure remains a feature of the weather especially in the South and Southeast of Britain. With High pressure developing to the North and Northeast of the UK some much colder air is waiting in the wings to come down over the UK, though GFS and ECM do their best to hold the worst of it at bay with GFS maintaining very wet conditions over the South for a while. The lesson to be drawn from tonight's output is not to take charts too literally. They are subject to change at short notice and most certainly will. The bigger picture though is right for UK cold and there will be further up and downgrades over the coming days before a clearer picture of what the measure of cold over the UK will surface.