Model Output Discussion - 21st - 28th November

[Radiating Dendrite]

I do find it amusing that when there's a cold chart in FI people are like "oh that's just eye candy it won't happen" and when a bartlett or gloomy pattern appears it's like "oh just my luck we're now going to get a bartlett high".

From now on I'm going to completly stop looking at cold and mild FI charts as they are useless.

I never suggested that FI was going to be correct.

Was simply explaining what the 6z run showed.

[A Winter's Tale]

I never suggested that FI was going to be correct.

Was simply explaining what the 6z run showed.

I wasn't directed at you as you didn't say things like it's bound to happen but some other people on thread might think that anything that's good in FI will never happen and anything that's bad is guaranteed.

[Alex]

NAO is forecast to head negative, this could help blocking to our north but for cold we depend on where the trough sits - ideally we need it to sit to the east of the UK.

To me December will be make or break for the mid winter period because we need the building blocks to be showing, otherwise we could end up with a more 06/07 type winter.

[A Winter's Tale]

NAO is forecast to head negative, this could help blocking to our north but for cold we depend on where the trough sits - ideally we need it to sit to the east of the UK.

To me December will be make or break for the mid winter period because we need the building blocks to be showing, otherwise we could end up with a more 06/07 type winter.

I wouldn't be surprised if December ends up being one if not the ONE for this winter as certainly do see the potential for colder weather in the 2nd half which could lead on into a cold January.

[Radiating Dendrite]

NAO is forecast to head negative, this could help blocking to our north but for cold we depend on where the trough sits - ideally we need it to sit to the east of the UK.

To me December will be make or break for the mid winter period because we need the building blocks to be showing, otherwise we could end up with a more 06/07 type winter.

The NAO is just used to show whether pressure will be low or high in the North Atlantic.

It is not a "driver" like the QBO is for example.

[nick sussex]

Regarding the UKMO further outlook, you can look at it two ways, on one hand it seems better than the output we're currently seeing but also I sense they're still factoring in the Euro high continuing to ridge north at times.

They obviously expect a bit more upstream amplification than is currently showing on any of the operational runs, low level snow in the north is unlikely with a flat jet.

I'm yet to be convinced of this, until I see a PM flow progged within 144hrs then I wouldn't read too much into that further outlook.

In terms of the upstream pattern there is a little uncertainty regarding a trough moving through the USA going by this mornings first NOAA update.:

THE

GUIDANCE CONTINUES TO SHOW A HIGH DEGREE OF SPREAD WITH THE

HANDLING OF THE MAJOR TROUGH AMPLIFYING OVER THE CENTRAL AND

EASTERN UNITED STATES...WITH SEVERAL MODELS CUTTING OFF A LOW OVER

THE SOUTHEAST...AND OTHERS...INCLUDING THE ENSEMBLE MEANS AND

UKMET...KEEPING THE WHOLE LONGWAVE INTACT ENOUGH TO PROGRESS TO

THE TROUGH AXIS TO THE EAST COAST BY MID PERIOD.

This does impact on the high near Newfoundland which impacts on that troughing to the north of the UK.

Edited November 23, 2011 by nick sussex

[johnholmes]

This does impact on the high near Newfoundland which impacts on that troughing to the north of the UK.

And I'm quite sure that the principal forecaster at Exeter is well aware of all those factors before he started to write his 6-15 and 16-30 day outlooks.

For those new to the model thread UK Met have access to and use, as they see fit, ALL model ouputs from every model centre in the world, including the ECMWF you will see mentioned at times run out to T+32 days (once per week), along with their own variety of models, from global down to a few Km's.

[georgiedre]

so then jh does this mean that we should listen to them as supposed to the models? also i believe the 16 - 30 day meto further outlook gets updated on friday ( i believe) do u think that this will be updated to coldera pattern? im lost at the moment lol . thanks

[lorenzo]

The nae forecast system is the one being used to firm up the later cold incursions.

Good to see the flat line across US disrupted giving some potential beyond this Atlantic battering for a change in the jet.

Mean charts highlighting the ne Usa ridge and Atlantic trough.

Ecm just refusing to let go of the hp to our east.

[Frosty.]

The Gem 00z shows a Northerly outbreak next week, albeit brief but it also suggests the best charts for further cold snaps and I have also noticed the meto 6-15 day update has slowly trended more wintry with each passing day. It was hard to see anything wintry on the Gfs and Ecm operational runs but they look at all the ensembles and their own high rez ensemble model to get a clearer picture so maybe the risk of snow in the north next week is worth keeping an eye on although the south will probably not have any snow for the next few weeks. The only part of the uk likely to see any wintry weather at times within the reliable timeframe is the far north of scotland where the stormiest and coldest weather will be from friday onwards.

[johnholmes]

so then jh does this mean that we should listen to them as supposed to the models? also i believe the 16 - 30 day meto further outlook gets updated on friday ( i believe) do u think that this will be updated to coldera pattern? im lost at the moment lol . thanks

I think anyone with a meteorological training would say that the mix of human and machine is the best, better than a human alone, indeed a human due to the huge compexities of physics and maths, is unable to work out a forecast beyond 24 possibly 48-72 hours in a settled or very unsettled situation. The machine on its own has to be interpreted before any forecast can be issued, hence why you see sometimes on this thread so many apparently contradictory versions of what the models are showing. One thing one has to be, as far as humanly possible, when doing this task is impartial, no leaning to mild, cold, wet, windy, foggy, sun, snow situations etc but straight down the line with an estimation of what the weather will be having assessed all the various parameters from the various mdels. Complex for sure but with a lot of training and experience its not that difficult. So yes the human-machine mix, which is what the Met O forecasts are SHOULD be the best. Yep, they will get it wrong at times, weighting the wrong paramater is the usual error but overall better than the models in my view.

yes about the ECMWF, the latest I am able to get from the Office is that it runs 1x weekly. Thus, apart from any amendments which subsequent events force on the principal forecaster, and trying to make the start of the 15 day fit with the daily updated 6-15 day, then its once a week. That is not all they look at but I am unable to get anything else other than,' we use other in house outputs' from them!

hope that helps the specific question from georgiedre and anyone else who may be interested.

Edited November 23, 2011 by johnholmes

[georgiedre]

cheers jh.

i for one hope that the weather gets a push in the right direction towards xmas day..... heres to hoping...

[shedhead]

Edited November 23, 2011 by shedhead

[Isolated Frost]

Just a small guide that hopefully everyone will find interesting, if not useful for this winter

It's quite quick, and not very detailed, and focuses only on the 850mb, and hp influences... just a quick note that these averages for the most part are vague and depend on exact conditions.

For much of winter, 850mb temperatures average between -2c in northern scotland, to around 1c in southern england. Generally, if you see values around the freezing mark from December to February on the 850mb charts, this would indicate rather average weather, possibly slightly above average weather if you are under lp or are very close by, and perhaps slightly below average under high pressure.

Temperatures between 1-4c 850mb are what we usually are accustomed to, apart from in colder spells. This usually means that the weather will be slightly above average (above average under low pressure and average with high pressure). All depends usually on cloud cover (high cloud cover would usually mean suppressed maxima, but mild minima, and low cloud cover/clear skies usually give slightly above average maxima, but cooler minima, however this does not always happen).

At the higher end, 4-8c 850mb temperature indicates very mild weather, often by day and by night. This in a normal example with a sw wind and hp nearby would give a max of say 13-15c under clear skies, around 9-11c under cloudier/wetter skies, and minima of around 4-6c under clear skies, 7-9c under cloudier/wetter skies. In the mildest scenario, 850's above 8c can occur, this gives temperatures more likely in September, perhaps getting past 16-18c!

Now, to go back a bit, under -1c to -4c uppers (850mb temperatures), we would expect slightly cooler weather (especially so by day under a easterly/southeasterly flow and especially so by night under a northwesterly/westerly scenario, usually). Under a maritime flow, you can expect snow/sleet at about 1250m under -1c 850's, and about 600m under -4c 850's. Under a continental flow, you can expect snow/sleet at about 750m under -1c 850's, and about 300m under -4c flows, but this is a general rule, and there can be many exceptions. Of course under a continental flow, precipitation is harder to get, unless you have a very unstable north east/east flow with much colder uppers travelling over the north sea.

-4c to -8c upper temperatures usually give snow throughout the nation, especially under a continental flow. -8c uppers would deliver maritime-source snowfall to sea level, whilst -6c continental source air generally would. For much of England, Scotland, Wales and Northern Ireland, land is between 50-300m above sea level and so -6c/-7c maritime source air and -5c/-6c continental source air would deliver snow (but you need cold uppers to give moisture from the north sea, generally -7c or less). This temperature of upper air usually gives very cold air.

Below -8c and snow is certain. Usually very cold air from the north or north east would give this, but if easterlies align themselves perfectly, we can get very cold air from them (up to -18c/-19c reaching east anglia/se england is possible and has happened under potent easterly flows!).

For those living near the north sea, or generally are affected snow-wise by north east or east winds, not only does the 850's need to be under -5c, but the difference between the 850's and the sea temperatures must be 13c or more to deliver snow (i.e. -6c 850s, 6c sst's = no precipitation, -6c 850's, 8c sst = some precipitation, snow). This is why some areas got so much snow of the north sea last year, a combination of cold air (-7c to -11c 850's often) and very warm seas as they haven't cooled down yet (the average november sst's on the east coast are between 7c and 11c), gave intense snowfalls due to large moisture.

I know this is rather cold-orientated, but it's more of a winter guide, and so is dedicated to more wintry weather.

[Grimsby Snow Lover]

Just a small guide that hopefully everyone will find interesting, if not useful for this winter

It's quite quick, and not very detailed, and focuses only on the 850mb, and hp influences... just a quick note that these averages for the most part are vague and depend on exact conditions.

For much of winter, 850mb temperatures average between -2c in northern scotland, to around 1c in southern england. Generally, if you see values around the freezing mark from December to February on the 850mb charts, this would indicate rather average weather, possibly slightly above average weather if you are under lp or are very close by, and perhaps slightly below average under high pressure.

Temperatures between 1-4c 850mb are what we usually are accustomed to, apart from in colder spells. This usually means that the weather will be slightly above average (above average under low pressure and average with high pressure). All depends usually on cloud cover (high cloud cover would usually mean suppressed maxima, but mild minima, and low cloud cover/clear skies usually give slightly above average maxima, but cooler minima, however this does not always happen).

At the higher end, 4-8c 850mb temperature indicates very mild weather, often by day and by night. This in a normal example with a sw wind and hp nearby would give a max of say 13-15c under clear skies, around 9-11c under cloudier/wetter skies, and minima of around 4-6c under clear skies, 7-9c under cloudier/wetter skies. In the mildest scenario, 850's above 8c can occur, this gives temperatures more likely in September, perhaps getting past 16-18c!

Now, to go back a bit, under -1c to -4c uppers (850mb temperatures), we would expect slightly cooler weather (especially so by day under a easterly/southeasterly flow and especially so by night under a northwesterly/westerly scenario, usually). Under a maritime flow, you can expect snow/sleet at about 1250m under -1c 850's, and about 600m under -4c 850's. Under a continental flow, you can expect snow/sleet at about 750m under -1c 850's, and about 300m under -4c flows, but this is a general rule, and there can be many exceptions. Of course under a continental flow, precipitation is harder to get, unless you have a very unstable north east/east flow with much colder uppers travelling over the north sea.

-4c to -8c upper temperatures usually give snow throughout the nation, especially under a continental flow. -8c uppers would deliver maritime-source snowfall to sea level, whilst -6c continental source air generally would. For much of England, Scotland, Wales and Northern Ireland, land is between 50-300m above sea level and so -6c/-7c maritime source air and -5c/-6c continental source air would deliver snow (but you need cold uppers to give moisture from the north sea, generally -7c or less). This temperature of upper air usually gives very cold air.

Below -8c and snow is certain. Usually very cold air from the north or north east would give this, but if easterlies align themselves perfectly, we can get very cold air from them (up to -18c/-19c reaching east anglia/se england is possible and has happened under potent easterly flows!).

For those living near the north sea, or generally are affected snow-wise by north east or east winds, not only does the 850's need to be under -5c, but the difference between the 850's and the sea temperatures must be 13c or more to deliver snow (i.e. -6c 850s, 6c sst's = no precipitation, -6c 850's, 8c sst = some precipitation, snow). This is why some areas got so much snow of the north sea last year, a combination of cold air (-7c to -11c 850's often) and very warm seas as they haven't cooled down yet (the average november sst's on the east coast are between 7c and 11c), gave intense snowfalls due to large moisture.

I know this is rather cold-orientated, but it's more of a winter guide, and so is dedicated to more wintry weather.

A very useful and helpful explanation there, thanks for putting the effort into writing it. That certainly explains why last December we received over a foot of snow from the NE as the 850's were very cold indeed.

Edited November 23, 2011 by Grimsby Snow Lover

[nick sussex]

For those that read the NOAA update its that uncertainty regarding the troughing in the USA and Canada that could have an impact in Europe.

Here this trough amplifies and turns more into an inland runner moving NE, this has a downward push on that trough near the UK as we see those deep low heights begin to lift away from Greenland.

The only way to push that trough far enough east and south is to get that more amplified pattern and some temporary pressure rises to the nw.

The UKMO has a similar pattern at 144hrs although heights to the north are a bit lower, the Euro high is still desperate to stay on the scene though, I'd say the output so far this evening is a little better in terms of a chance of some PM air but we need more east and south movement in the pattern.

We must see pressure fall in central Europe and that ridge thrown ahead of the troughing is still a problem.

The upstream trough and its effect around the Greenland area will now be pivotal, you have to have this amplifying as much as possible and heading NE towards western Greenland.

This could force just enough WAA into Greenland to kick the pattern se, anyway lets see what the ECM does later.

Edited November 23, 2011 by nick sussex

[shedhead]

For those that read the NOAA update its that uncertainty regarding the troughing in the USA and Canada that could have an impact in Europe.

Here this trough amplifies and turns more into an inland runner moving NE, this has a downward push on that trough near the UK as we see those deep low heights begin to lift away from Greenland.

The only way to push that trough far enough east and south is to get that more amplified pattern and some temporary pressure rises to the nw.

12 run so far is a lot more amplified in the medium range, but can we believe it, will ECM or UKMO back it and will it ultimately lead to anything better further down the line?

[Weathizard]

Although a completely different evolution we end up with the same thing shown in previous runs, a monster high

[Grimsby Snow Lover]

If only charts from the far reaches of FI could be believed. Is it me or is the high in the Atlantic regressing into Greenland at the end of the 12z run? This was would surely deliever some cold and snow to our shores. Before I get shot down I am only 'hoping' I fully know this will of gone by the pub run. I just couldn't resist. On the plus side though next week is still looking fairly unsettled with a more seasonal feeling about it.

Edited November 23, 2011 by Grimsby Snow Lover

[The PIT]

Well Saturdays storm delayed by 12 hours into Sunday Morning. Also further south. If it stays the same some very strong damaging gusts possible across northern england down to northern wales. Plenty of time for change though as Yesterdays and Todays 12 oz show.

The cold stuff as ever remains well out into deep FI and still not very potent.

[Liam J]

GFS 12z has delayed landfall some 12 hrs and moved the storm and area of severe gales further south to affect more areas Saturday evening onwards, although not as deep as previous runs it's still very potent and could cause big problems with damaging and potentially storm force winds with gusts in excess of 70-80mph.

Areas at highest risk include - Western Scotland, Northern Ireland, Northern England and North Wales.

Things may change on future runs.

Edited November 23, 2011 by Liam J

[weathe20]

and whats this showing?

[MattH]

If only charts from the far reaches of FI could be believed. Is it me or is the high in the Atlantic regressing into Greenland at the end of the 12z run? This was would surely deliever some cold and snow to our shores. Before I get shot down I am only 'hoping' I fully know this will of gone by the pub run. I just couldn't resist. On the plus side though next week is still looking fairly unsettled with a more seasonal feeling about it.

Hey all...

Interesting one this, well sort of, as the latest EC 32 day update (as of Tue) was signalling that towards the middle of December pressure is forecast to rise with a +ve pressure anom evident to the W of the UK. Clearly in what specific state is anyones guess, but an interesting comparison. It should be noted as well that there have been several individual EC ENS members which have signalled a temporary ridge to the W and N'ly over the UK. Generally outlier members overall, but still they have been evident.

Clearly a very unsettled and increasingly colder, near seasonal, outlook is forecast over the next 7 to 10 days at least. There is little sign for a change from this pattern, so all 'coldies' can hope for is this kind of setup for a day or two before the next low breaks down the ridge etc.

A far cry from this time last year, but the reasons why have and continue to be discussed in great quality and quantity within the 'statospheric warming' thread and also the more significant model analysis thread (sorry can't remember its actual name!).

Cheers, Matt.

[Isolated Frost]

and whats this showing?

Southerly polar/frontal jet, southerly subtropical ridge, immense northern blocking, cold easterly winds with hell of a lot of precipitation for s parts due to a biscay low. yum!

[Grimsby Snow Lover]

and whats this showing?

Im guessing a more southerly tracking low possibly leading to an Easterly if I'm reading the chart correctly.