Winter Model Discussion 18Z 12/2/13 onwards.

[Gary_R_Walker]

A few things to note this morning .

The ECM again has the PV dropping toward to us from the pole , it looks vicious , and with it associated very very cold air .

The other thing, the gfs ens , are now hinting at mojor cold outbreak , the op was an outlier for Gloucestershire Throughout , and there is some ens now dropping through the roof . This happens in the past leading to something big.

I'm becoming more confident by the day.

Just two days ago.

[Jason M]

As has been commented on the GEFS are actually pretty good. It may well be that ECM is an outlier at 850 level (indeed I'd wager it probably is).

One advantage we do have over last feb though is that pressure is much lower over the UK. Last feb, it was the sheer scale of the heights rather than uppers that were an issue. IF we can tap some decent cold air, we will be in with a shout this time.

Jason

[weather eater]

It happens because very very cold weather is not common in the uk..so any model showing it should be viewed with caution.....even this winter the models have hinted at a 47 or 63 spell at least twice.......only for us to end up with average cold spells......but this is to be expected...I dont understand the charts but I think I understand what the models are and are not....they offer a range of possibilities ..they are not a forecast...thats were the meto come up in...and every time the models have hinted (or more than hinted) at a severe spell this winter they have advised caution, I have seen many posts on here have given them stick for not backing the models...but every time they have been correct...(I dont see much praise).....

Yet every time people build up there hopes...ignore the words of caution here, worse still ignore the meto FORECAST......and trhen blame the models for watering down a severe cold spell that nobody actually ever forecast.....

I rather agree, unfortunately plenty do think of the models as a forecast and that then tends to lead the debate, even people who claim otherwise read the models as a forecast when it suits them. This thread of course is for discussing the models, so really you cannot blame people for doing just that, despite some difficulty’s it works well, catering for several levels of ability is not easy.

The fact that the models are not a forecast is why some of us exercise caution about taking model runs at face value, models can and do change for the better or worse depending on what the viewer wants to see. Some on here are very good at reading and interpreting the models, others and I include myself in that, try to use logic and experience to add something to the thread, that’s why I was cautious about the runs the ECM was producing a few days ago, logic and experience suggest models evolutions change over time and that the ECM has a tendency to over develop height rises over Greenland, a reader of models should be able to tell you what may happen instead, unfortunately sometimes it seems that some have their thinking clouded by what they want to see. What I love the most about this thread, is that most of the time it demonstrates that the actual weather that comes our way will make fools of us all, including those that seem the wisest, when I see certain members suggesting that others are being lead by ignorance I just know that egg on the face is just around the corner and can strike anyone.

[Frosty.]

Meto's caution yday re any v cold/snowy outbreak looks backed up by this morning's model runs (bar gfs)....at this stage.

Although GP's post earlier seems to maybe question?

It's the first time we have had cross model agreement on the Easterly and at this range there will always be some variability in potency and longevity but the great news is this current relatively mild weather is not going to last beyond the weekend, very pleased with the trend now.

[No Balls Like Snow Balls]

From experience the majority of us know that major freezes will always be shown outside the reliable and then gradually be watered down as we come closer to the actual event, this has happened over many years. We also know that we quite often see small upgrades within the T72 period which quite often prolongs our cold and even deepens it.

[nick sussex]

Of course it had to happen! it was only a matter of time that the GFS would pick up the baton then deliver a very good run at the same time that the Euros decide they're going off the idea.

The ECM is similar to yesterday evenings with only a small window now for any convection and this is probably more reserved for ne areas as the flow turns se and the colder uppers are directed further north, the UKMO looks like directing any cold pool more due west but looks quite dry away from the far se, the GFS blows the Euros out of the water with a strong easterly good cold pool and lots of convection. Unfortunately you wouldn't back it now that the Euros have decided to move away from that idea.

I think its looking like more any snow will have to come from fronts moving into the sw and south and thats if the surface flow is cold enough ahead of the fronts, overall turning colder but chances for a convective easterly have fallen today regardless of the zero to hero GFS.

The problem with the ECM is that one run could be a rogue, two in a row start to look like a trend, if it doesn't backtrack this evening then it looks like once again a convective easterly for the UK has bitten the dust.Certainly I'd love to see the GFS verify but you can't really trust a model that took so long to pick up the right pattern and then goes to the other extreme.

Last chance this evening to see whether the Euros bring that more potent easterly in.

[Duane S.]

Certainly looks like an increasing stronger signal for more of a West based -NAO. So at the moment (subject to much change of course) we are on for a cold spell of a few days next week then maybe it's watch out in the SW approaches as the Atlantic tries to edge back in through that route. And with that comes the big snow potential (obviosuly with the breakdown potential to boot). That's how I'm reading it at the moment anyway.

[No Balls Like Snow Balls]

For those stressing about warmer uppers than we may like see below from Twitter

850mb temps maybe misleading next week. Airmass could be particularly cold below 850mb (5000ft) given dry, continental airmass.

Personally I think we can look forward to some very cold days and nights.

[weather eater]

For those stressing about warmer uppers than we may like see below from Twitter

850mb temps maybe misleading next week. Airmass could be particularly cold below 850mb (5000ft) given dry, continental airmass.

Personally I think we can look forward to some very cold days and nights.

Yes cool by day, cold at night is how I would read it, my comments on cold air masses were more about how the ECM evolution has changed and were not suggesting that it will be mild, much will depend on cloud cover, one of the features this winter has been that other than for a brief period we have not seen really cold night time minima’s, certainly in my neck of the woods clear nights and sunshine have been rare, even for this part of the country (I miss East Anglia).

[nick sussex]

Looking at the ECM postage stamps for T168hrs a variety of orientations and placements of the high:

http://www.ecmwf.int/samples/d/inspect/catalog/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!168!pop!od!enfo!enplot!2009112700!!/

[No Balls Like Snow Balls]

Yes cool by day, cold at night is how I would read it, my comments on cold air masses were more about how the ECM evolution has changed and were not suggesting that it will be mild, much will depend on cloud cover, one of the features this winter has been that other than for a brief period we have not seen really cold night time minima’s, certainly in my neck of the woods clear nights and sunshine have been rare, even for this part of the country (I miss East Anglia).

Yes one thing that has disappointed me this winter is the lack of ice days in my neck of the woods and even more so the very cold nights, normally where I live I could look forward to severe frosts on a lot of occasions but this winter i could count them on 1 hand. Hopefully this high pressure spell can put that right.

[Jason M]

Yes cool by day, cold at night is how I would read it, my comments on cold air masses were more about how the ECM evolution has changed and were not suggesting that it will be mild, much will depend on cloud cover, one of the features this winter has been that other than for a brief period we have not seen really cold night time minima’s, certainly in my neck of the woods clear nights and sunshine have been rare, even for this part of the country (I miss East Anglia).

If ECM veirified I actually think it would be bitterly cold at ground level. Very low dew points combined with a decent E/SE breeze. Probably looking at temps of plus 1 or plus 2C a best under slate grey skies for much of England. Another characteristic would be the small differebce between Min and Max temps. At 2M level this run probably sits the middle of the pack, its just warm at 850 level.

[KTtom]

Gem is without doubt the run of the morning if you want a frigid easterly:

[Summer Sun]

The ECM ensemble is in agreement to t168 this morning its looking like an easterly swinging round to a south easterly by the end of the week

Beyond this there is less agreement as you would expect at that range

[Purga]

Looks like another slip towards downgrade from ECM this morning. More of a cold dry picture and with the loss of retrogression towards GH shown a couple of runs back but hopefully we can get some frosty nights and sunshine by day and maybe a few flurries in the East / SE. A change from endless grey skies and marginal sleety stuff!

[snowblizzard]

Yes cool by day, cold at night is how I would read it, my comments on cold air masses were more about how the ECM evolution has changed and were not suggesting that it will be mild, much will depend on cloud cover, one of the features this winter has been that other than for a brief period we have not seen really cold night time minima’s, certainly in my neck of the woods clear nights and sunshine have been rare, even for this part of the country (I miss East Anglia).

The problem as I see it, is the lack of really cold air on the continent especially North West Europe!

http://www.wetterzen...cs/Reurmett.gif

It's been the problem for most of this winter if you've been looking for a really frigid/snowy spell like Jan 1987 when the temperature in Moscow was below -30c we had -15c uppers across most of the UK and right out into the Atlantic!

I think at that point we had 1048mb high centred over Iceland.

Edited February 15, 2013 by snowblizzard

[shaky]

Looking at the ECM postage stamps for T168hrs a variety of orientations and placements of the high:

http://www.ecmwf.int/samples/d/inspect/catalog/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!168!pop!od!enfo!enplot!2009112700!!/

Most of them look quite good and very cold!!

[MR EXTREMES]

wow the gfs wants to play looking good from the gfs no greenland heights though which is dissapointing be nice to have sausage block from scandi to iceland.

gfs doing its second run of the morning lets see where this is heading ukmo still solid to be expected and certainly enjoy the ukmo although it dont seem like the colder easterly flow has moved forward this morning still around t144 for the ukmo.

[MR EXTREMES]

Most of them look quite good and very cold!!

indeed most though seem to be a more se flow instead of a direct east would like to see a ne flow but i think this is unlikely looking at the position of heights.

[randomwalk]

Rule No 1 of chart watching in the internet age. Don't take any operational after 144 seriously no matter how good or bad it looks.

It might be a possble trend but thats about it.

Rule no 2 The 500 mb hieght anomily charts that JH bangs on about will give you a far better idea of how things might go in the longer term

than any operational output.

So no point talking about downgrades past 144 on a cold spell that hasn't even arrived yet and if you are going to comment then take a look the 500mb charts and you might be pleasantly surprised.

http://www.cpc.ncep....y/814day.03.gif

Sounds like a very good steer to me This logic seems to imply then that forecasting 500mb charts is easier/more reliable and hence less volatile than the surface pressure equivalents. Anomalies are presumably forecast heights compared to long term averages. Yourself and JH for example are clear advocates of this approach. Some of us, well me at least , would like to know why, i.e. what is it that makes it so much better. I would be grateful to hear your thoughts.

[johnholmes]

At long last the GFS version of 500mb anomaly charts has finally got to showing an almost identical pattern to how ECMWF has gradually altered its pattern in a perfectly acceptable slow change over the past 3-5 days. They both now, as ECMWF, has all along, just about mirror that shown by NOAA over the past few days, so a reasonable confidence can be given to the pattern shown below, complex though it is, of having a decent chance of being close to what we will see somewhere in the 7-15 day time frame.

Make of it what you will for the surface and temperatures let alone anything that may fall from the skies!

http://www.meteo.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

and the NOAA output from last evening

http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php

[TEITS]

The problem as I see it, is the lack of really cold air on the continent especially North West Europe!

http://www.wetterzen...cs/Reurmett.gif

It's been the problem for most of this winter if you've been looking for a really frigid/snowy spell like Jan 1987 when the temperature in Moscow was below -30c we had -15c uppers across most of the UK and right out into the Atlantic!

I think at that point we had 1048mb high centred over Iceland.

During 1987 we actually had uppers of around -18C.

I never look for a repeat of Jan 87 anymore because it really was a unique event. Very rare to have an incredibly cold airmass that bitter to advect SW and then have the perfect synoptics to bring this to the UK.

This is why at this stage im not that concerned with the UKMO/ECM. For the UK it really is a fine margin if we can get the perfect placement and orientation to advect the cold pool perfectly for the UK. I expect changes with regards to convective potential on every single model run over the next few days.

Better 06Z with the SW further W.

http://www.wetterzentrale.de/pics/Rtavn781.png

[swilliam]

Looking at the ECM postage stamps for T168hrs a variety of orientations and placements of the high:

http://www.ecmwf.int...t!2009112700!!/

Yes a large number of options for the position and orietation of the high. What is noticable though is that at this stage most of them do not have the high very far N (mid Norway seems to be about the limit). Also the majority are aligned NW-SE meaning E-SE flow at best (on average remember). This means the most likely chance for significant snow is from fronts approaching from the SW. Having not had this for several winters it seems to be a recurring event this season.

Edited February 15, 2013 by swilliam

[TEITS]

. Also the majority are aligned NW-SE meaning E-SE at best (on average remember). This means the most likely chance for significant snow is from fronts approaching from the SW. Having not had this for several winters it seems to be a recurring event this season.

A SE,ly flow will generally bring shower activity to Scotland and NE England but rarely for E Anglia/SE. However the long fetch across the N Sea could potentially make it marginal. Ideally we want a ENE,ly that will suit nearly everyone.

[shaky]

indeed most though seem to be a more se flow instead of a direct east would like to see a ne flow but i think this is unlikely looking at the position of heights.

but dont you think that we could get a few more organised precipitations in that south east flow from the near continent!!for e.g.trailing fronts maybe from germany all the way into the uk!!

During 1987 we actually had uppers of around -18C.

I never look for a repeat of Jan 87 anymore because it really was a unique event. Very rare to have an incredibly cold airmass that bitter to advect SW and then have the perfect synoptics to bring this to the UK.

This is why at this stage im not that concerned with the UKMO/ECM. For the UK it really is a fine margin if we can get the perfect placement and orientation to advect the cold pool perfectly for the UK. I expect changes with regards to convective potential on every single model run over the next few days.

Better 06Z with the SW further W.

http://www.wetterzentrale.de/pics/Rtavn781.png

Blimey what a change from yesterday and that actually looks better than the ecmwf for around about the same time frame!!