Model Output Discussion: 12Z (20/11/12) And On...

[BLAST FROM THE PAST]

Yep, E and NE flow by t168, much quicker than the 12z. is it right though? ....Steve M ta for that.

BFTP

[nick sussex]

From a purely IMBY perspective I'm liking this GFS run as it brings lots of snow to the Pyrenees and we don't end up with the unfavourable looking troughing of the ECM.

Interestingly the mystery of the UKMO upstream pattern continues, its the latest at phasing those two lows and really looks like the odd one out across the output.

The fax chart sticks to the raw output but I just can't see all the rest of the output being wrong and it being right especially given its recent poor performance in terms of verification.

Edited November 20, 2012 by nick sussex

[MKN]

Out to 168 its a fantastic output. If that was to verify ud have to be pleased from a cold view point. Good to see the cold starting to come into semi reliable time frame.

Edited November 20, 2012 by SnowTornado

[Met4Cast]

As many on here have said, the 850hPa temperatures are often modelled wrong until closer to the time frame, the 18z upgrades the 850hPa temperatures slightly, not significantly but it should be enough to cheer a few of the "850hPa temperatures not cold enough" posters.

[Matty M]

Can that low over west russia act as a trigger, certainly more chance of a colder initital push on this run. (Of course usual over analysing caveats apply)

[Weathizard]

The high looks to be more powerful and moving towards Norway at 216h, looks a better run in the reliable timeframe, I'm not even going to look at FI though, looks to be a stormer coming here is all I will predict.

Edit; Couldn't help myself, pub run lives up to its name

Edited November 20, 2012 by Weathizard

[Eskimo]

I have to say, I've been following the models for nearly 6 years now and I have really learnt a hell of a lot. The last few years have been absolutely superb in terms of looking at cold and snow, and long may it continue!

[Geordiesnow]

As many on here have said, the 850hPa temperatures are often modelled wrong until closer to the time frame, the 18z upgrades the 850hPa temperatures slightly, not significantly but it should be enough to cheer a few of the "850hPa temperatures not cold enough" posters.

It probably won't as those hpa temperatures are not cold enough for snow really, wintry showers is a possibility though and it should be bright showery type airflow, kind of similar to what western areas will face this Friday into Saturday.

To be honest, if any blocking does occur, because of the nature of the weather patterns before any blocking occur, its going to be a struggle to attract much cold air as there is no real bits of PV droppping into our side of the Arctic when the blocking does arrive but if we give it time and orientations of the high and low pressures become favourable then the cold uppers should arrive, if it become unfavourable, then they won't.

Current trends do suggest we may lack any sustained cold air unfortunately but it is very early days, the ridge is not forecast to occur for over 100 hours away, alot of variables will change before we have a real firm idea how cold it may get but the trend is for the outlook to turn cooler after a mild few days or so.

[MKN]

850s are around -4 or below for most the UK from 150 right out to the end of the run almost. We can get snow with 850s of just -1 so why people are worried bout the lack of cold I have no idea.

[Met4Cast]

It probably won't as those hpa temperatures are not cold enough for snow really, wintry showers is a possibility though and it should be bright showery type airflow, kind of similar to what western areas will face this Friday into Saturday.

To be honest, if any blocking does occur, because of the nature of the weather patterns before any blocking occur, its going to be a struggle to attract much cold air as there is no real bits of PV droppping into our side of the Arctic when the blocking does arrive but if we give it time and orientations of the high and low pressures become favourable then the cold uppers should arrive, if it become unfavourable, then they won't.

Current trends do suggest we may lack any sustained cold air unfortunately but it is very early days, the ridge is not forecast to occur for over 100 hours away, alot of variables will change before we have a real firm idea how cold it may get but the trend is for the outlook to turn cooler after a mild few days or so.

The point I was making is that the GFS often tends to model the 850hPa temperatures wrong and we see small upgrades as it gets closer to the time frame, whilst this current upgrade might not be sufficient for anything wintry away from the tops of the hills, it is indeed an upgrade on previous runs. Several minor upgrades can lead to something more substantial, not saying that it will but the GFS does do that a fair amount.

Wasn't we expecting minor upgrades as it got closer anyway? Something that Steve Murr has alluded to several times. Too early to be looking at the specifics anyway, was just commenting on the upgrade and definitely wasn't suggesting we'd see snowfall from it.

18z FI not too bad either and keeps the signal for Northern Blocking, looking at that purely for fun though given the recent wild swings.

Edited November 20, 2012 by Daniel AKA WMD

[swfc]

Well the area of low pressure which moves sse then becomes the most mobile low pressure system in history?it defies logic in its movement and on that basis id put the reliable time frame at 140hrs even given the ecm

[Weathizard]

850s are around -4 or below for most the UK from 150 right out to the end of the run almost. We can get snow with 850s of just -1 so why people are worried bout the lack of cold I have no idea.

Yes I agree, 18z is a goodun though to my eyes, wont take it too seriously until we have some consistency from the GFS, although its important we all don't take this FI as gospel just because it shows what we want, because I think we'll be very disappointed.

Edited November 20, 2012 by Weathizard

[BLAST FROM THE PAST]

Interesting 18z, it moves towards the ECM in FI. Wonder if the block will get sheered away as it goes too far north. Although after doing that it shunts eastward again, FI for a reason! Cold period though no doubt closing in fast and I'd take 18z over 12z IMBY reasons.

BFTP

Edited November 20, 2012 by BLAST FROM THE PAST

[Geordiesnow]

Despite some good looking synoptic charts on the 18Z, we fail to attract the -10hpa into the UK at all which for late November is pretty poor really so it does prove that if the blocking sustains, it does not mean we will attract the much colder upper air temperatures, especially if the orientations of the high and low pressures become unfavourable.

I think the lack of cold air is probably a bit of an issue in fairness, I think there was talk that one 06Z run showed some great synoptic charts yet despite that, we still fail to attract the real cold uppers. Lets hope the lack of an Arctic PV this Autumn won't come back to bite us in the backside.

Still, whilst the current charts don't excite me in terms of snow potential, in terms of the potential for a more blocked set up, then they are interesting indeed.

[SMU]

THe 18 z is quite messy & probably wide of the mark but MEH!- who cares..

Remember 850 temps from the east after being embedded for 10/15 days will certainly not have to be sub -5C- to produce snow...

Lets get past day 5 then make assumptions around snow... you never know we may get some wintry weather this weekend!

S

[Liam J]

850s are around -4 or below for most the UK from 150 right out to the end of the run almost. We can get snow with 850s of just -1 so why people are worried bout the lack of cold I have no idea.

Yes, in a way this true but only during certain set ups, eg - frontal snow events with heavy & persistent precipitation. To be guaranteed snow to most levels at this time of year then you need uppers at or below -6/-7c perhaps even lower if you want to see snow down to sea level, especially on windward facing coasts during sunshine and snow showers types. Then you need to be looking at air thickness and dew points..... Just a brief explanation.

[Eskimo]

Despite some good looking synoptic charts on the 18Z, we fail to attract the -10hpa into the UK at all which for late November is pretty poor really so it does prove that if the blocking sustains, it does not mean we will attract the much colder upper air temperatures, especially if the orientations of the high and low pressures become unfavourable.

I think the lack of cold air is probably a bit of an issue in fairness, I think there was talk that one 06Z run showed some great synoptic charts yet despite that, we still fail to attract the real cold uppers. Lets hope the lack of an Arctic PV this Autumn won't come back to bite us in the backside.

Still, whilst the current charts don't excite me in terms of snow potential, in terms of the potential for a more blocked set up, then they are interesting indeed.

With all due respect Geordie, have you not read dozens of posts saying, "Once the blocking is in place, the cold uppers will follow"?

[nick sussex]

850s are around -4 or below for most the UK from 150 right out to the end of the run almost. We can get snow with 850s of just -1 so why people are worried bout the lack of cold I have no idea.

For snow showers the general rule is around -8 uppers off a northerly, for an easterly you need minimum -6.

For frontal snow you can get that with 850's just below freezing but that only really comes about when you have had much colder conditions for a length of time, Atlantic fronts moving in from the sw can produce that frontal snow with a flow ahead of the precip from east/se imparting lowish dew points.

It's easier to get frontal snow on the continent simply by the fact that in many of those situations you're not dealing with any sea modification.

To get really good North Sea convection the bigger temperature differential the better hence if you see sub -10 uppers across with a strong flow and live on the east coast then thats generally the time to get the sledge out!

Just think of the North Sea as one of the Great Lakes in North America, with the right synoptics it can turn into a snowmaking machine.

Edited November 20, 2012 by nick sussex

[Met4Cast]

Despite some good looking synoptic charts on the 18Z, we fail to attract the -10hpa into the UK at all which for late November is pretty poor really so it does prove that if the blocking sustains, it does not mean we will attract the much colder upper air temperatures, especially if the orientations of the high and low pressures become unfavourable.

I think the lack of cold air is probably a bit of an issue in fairness, I think there was talk that one 06Z run showed some great synoptic charts yet despite that, we still fail to attract the real cold uppers. Lets hope the lack of an Arctic PV this Autumn won't come back to bite us in the backside.

Still, whilst the current charts don't excite me in terms of snow potential, in terms of the potential for a more blocked set up, then they are interesting indeed.

It's like smashing your head into a brick wall in this thread sometimes!

[Snowmadsam]

Right, lets take this objectively. If this did happen, then it's best to get COLD before any precipitation. That's focus on getting cold first.

With regards to the 850's snow CAN fall at above -5. An example is November 2005. (I feel like I am in one of my many exams saying that!)

C before S guys.

[SMU]

here we go - one of the biggest snow events for the UK

http://modeles.meteociel.fr/modeles/reana/1996/archivesnh-1996-2-6-0-0.png

quote john kettley that eve- SOME HEAVY SNOW NOW FALLING IN THE CHANNEL ISL-

Uppers

http://modeles.meteociel.fr/modeles/reana/1996/archivesnh-1996-2-6-0-2.png

-2 C from the continent..........

S

[AWD]

here we go - one of the biggest snow events for the UK

http://modeles.meteociel.fr/modeles/reana/1996/archivesnh-1996-2-6-0-0.png

quote john kettley that eve- SOME HEAVY SNOW NOW FALLING IN THE CHANNEL ISL-

Uppers

http://modeles.meteociel.fr/modeles/reana/1996/archivesnh-1996-2-6-0-2.png

-2 C from the continent..........

S

Interesting, also note thicknesses higher than the standard 528DAM.

[J10]

For snow showers the general rule is around -8 uppers off a northerly, for an easterly you need minimum -6.

For frontal snow you can get that with 850's just below freezing but that only really comes about when you have had much colder conditions for a length of time, Atlantic fronts moving in from the sw can produce that frontal snow with a flow ahead of the precip from east/se imparting lowish dew points.

It's easier to get frontal snow on the continent simply by the fact that in many of those situations you're not dealing with any sea modification.

To get really good North Sea convection the bigger temperature differential the better hence if you see sub -10 uppers across with with a strong flow and live on the east coast then thats generally the time to get the sledge out!

Just think of the North Sea as one of the Great Lakes in North America, with the right synoptics it can turn into a snowmaking machine.

From a northerly you can snow from -6 to -8c. but obviously the colder the better.

Some great synoptic charts I wouldn't get too hung up about the depth of cold at this stage.

[chris55]

THe 18 z is quite messy & probably wide of the mark but MEH!- who cares..

Remember 850 temps from the east after being embedded for 10/15 days will certainly not have to be sub -5C- to produce snow...

Lets get past day 5 then make assumptions around snow... you never know we may get some wintry weather this weekend!

S

This is a good point Steve, and I was just thinking the same thing. I just checked the Dewpoints, and although they are not especially low they are falling. A sustained easterly/continental airmass settling over us may change the parameters we are used to for forecasting snow. Our normal Atlantic airflow mix will be irrelevant because all our air is coming from the east.

Edited November 20, 2012 by chris55

[khodds]

Can I make a suggestion? Can people not comment on a run unless they are absolutely certain of what a chart is showing? As I've said before, its very confusing for beginners. I really should stop reading this thread as its only serving to wind me up. Sifting thru the rubbish until I find a poster I can actually put my trust in - thankfully I have worked that one out. Keep up the good work - you know who you are!