General Model Output Discussion

[If Wishes made Weather]

Would I be correct in suggesting that if other ECM ensemble members are indicating colder temperatures in Amsterdam, they are therefore suggesting air sourced further to the East, or is it an indication of higher pressure, or both?

On the PPN question, although it does appear that we are looking at some PPN (snow I guess) here tomorrow night into Sunday morning, it looks like around 2 cm. What is to indicate that if the ECM largely verified as shown this evening with, say, 36 hours Easterly, that this would bring more than 5 cm per day?

[kold weather]

For a 2nd time tonight I'm stunned....

The ECM is in the milder side of the ensembles and thats quite exceptional, how many times can you say that a run like the 12z ECM was a MILDER run on the ensembles, quite frankly this is looking like a severe cold spell...and I don't think I've ever used that wording to describe a cold spell before...

[nick sussex]

ECM was a slight mild outlier? My goodness that is unbelievable!

However, since we are only looking at De Bilt, could it be that the coldest uppers have been advected too far west (i.e. over us), whereas the other ECM members would like the colder temps over the Netherlands?

Basically in these types of patterns the De Bilt ensembles are very useful, the ensembles tell us a few things an onshore flow is unlikely as we would normally see quite a few rise above zero as the sea modification negates some of the cold for that region, generally they strongly suggest a very cold easterly or ene flow. Also at present we're not expecting a west east battleground for example those scenarios with the high too far east with the uk at the cusp of the cold air, we could then say perhaps the cold air doesn't make it across the Channel, in a nutshell given the set up if its freezing cold over there its very likely to be the same for the UK especially more southern and se areas.

To be honest having seen those ensembles theres lots i'd like to add but won't for superstitious reasons as i dont want to jinx things!

Edited January 1, 2010 by nick sussex

[Mikel Nimbus]

Basically in these types of patterns the De Bilt ensembles are very useful, the ensembles tell us a few things an onshore flow is unlikely as we would normally see quite a few rise above zero as the sea modification negates some of the cold for that region, generally they strongly suggest a very cold easterly or ene flow. Also at present were not expecting a west east battleground for example those scenarios with the high too far east with the uk at the cusp of the cold air, we could then say perhaps the cold air doesn't make it across the Channel, in a nutshell given the set up if its freezing cold over there its very likely to be the same for the UK especially more southern and se areas.

Thanks Nick. It's fascinating the clues you can pick up from the ensembles.

[kold weather]

Basically in these types of patterns the De Bilt ensembles are very useful, the ensembles tell us a few things an onshore flow is unlikely as we would normally see quite a few rise above zero as the sea modification negates some of the cold for that region, generally they strongly suggest a very cold easterly or ene flow. Also at present were not expecting a west east battleground for example those scenarios with the high too far east with the uk at the cusp of the cold air, we could then say perhaps the cold air doesn't make it across the Channel, in a nutshell given the set up if its freezing cold over there its very likely to be the same for the UK especially more southern and se areas.

Yep because we are tapping into the exact same pool. In simple terms its going to be very cold regardless as long as the upper low behaves somewhat close to what the models expect...this is because the cold pool from the Arctic comes down just as the Greenland high decays, that serves to keep the cold air in place as it has nowhere to go as the forcing over the top of the Greenland high from the jet is gone...therefore it doesn't even matter if we get a high over the top of us or a beast from the east because the upper cold is over the top of us, its going to be severely cold...thats why there is such big agreement on freezing conditions, because even under rather different evolutions of the surface pattern, we keep the cold. Its for once a win-win evolution!

[West is Best]

I'm a little concerned that the ramping up of events in FI, deliberately also by those who seem to want then knock it down, is in danger of deflecting attention away from the more immediate prospects. Model outputs continue to demonstrate a lot of very cold weather across the UK over the next 5 days or so, with some places experiencing some snow.

As this is on the back of a cold December (3C or thereabouts in the CET) this is all rather more than we've been used to in recent years.

There's really no need to get drawn into saying things we do not need to about Armageddons etc. Such attention-seeking is a distraction from the really cold opening week of January 2010 which all the models so uniformly demonstrate this evening.

Enjoy!

Edited January 1, 2010 by West is Best

[sebastiaan1973]

Excellent ENS! Really amazing.

The ENS. average keeps the whole period below zero.

http://www.weerplaza...im.asp?r=midden

at http://www.winterplaza.nl/default.asp?r=noord you can check the ice for the north of the Netherlands.

The needed ice thickness for the Elfstedentocht is 15 cm! But being Dutch I know a lot of the route is not filled with ice yet.

Edited January 1, 2010 by sebastiaan1973

[Stu_London]

Agree largely with the sentiments of SnowBallz and others with their feet firmly planted on the ground, even if we are about to enter what may prove to be a notable cold spell which I expect to be on a par with the one just before Christmas (will be very suprised if I end up with more than 3 separate snow events and 20cm lying snow at any given time)

I think some members (who should have been around long enough to know better) have got a bit carried away with ramping which is a bit of a shame as whilst the output continues to show charts that can be intpreteted as the day after tomorrow, it creates a positive feedback effect on the forum as newer inexperienced members constantly look to the rampers for guidance thus encouraging even more ramping.

I don't have any specific data to back this up but in my experience of 6-7 years of watching the GFS, UKMO and ECM, I would say that in winter it fails to deliver on cold weather expectations in excess of 85% of occasions. Around 10% of the time it would deliver cold as per expectations but almost always from a very short time period. On some rare occasions, some very short term situations have cropped up that exceed cold weather expectations.

I hope everyone looking for cold and snow gets lucky, but the percentage call is that it aint gonna any where near as severe as some would on here would have you believe.

[Paul]

Come on folks - play the game here, we see many gripes and moans when these model threads go off topic, so help the team and the rest of the community by sticking to the topic of the models.

There are will it snow, regional, general chat, bbc forecast and model moods/chat threads availble on the forums, so please use them and don't clutter this thread with posts that aren't relevant to the discussion.

[grab my graupel]

Evening folks

Just mention that we are having to remove/delete far too many posts again.

As there are plenty of threads for other topics, can we please keep this to discussing the models?

Thanks

Brian

[Shunter]

Dont wish to spoil the party so to speak but there is some milder air now spreading into the Northern Isles which at Skye for instance has increased temps by 7c in the past three to four hours. Would this be the upper air warm sector of the LP that will travel down the country tomorrow? If so is there any chance that this mild sector will reduce as the trough moves south?

Seems incredible that temperatures can be so high considering the source of this air.

The link below shows clearly a number of Northern sites reporting temps between +2C/+4C at 9pm

http://www.weatheronline.co.uk/cgi-bin/aktframe?TYP=temperatur&KEY=UK&LANG=en&ART=tabelle&JJ=xxxx&SORT=2&INT=24

[johnholmes]

Agree largely with the sentiments of SnowBallz and others with their feet firmly planted on the ground, even if we are about to enter what may prove to be a notable cold spell which I expect to be on a par with the one just before Christmas (will be very suprised if I end up with more than 3 separate snow events and 20cm lying snow at any given time)

I think some members (who should have been around long enough to know better) have got a bit carried away with ramping which is a bit of a shame as whilst the output continues to show charts that can be intpreteted as the day after tomorrow, it creates a positive feedback effect on the forum as newer inexperienced members constantly look to the rampers for guidance thus encouraging even more ramping.

I don't have any specific data to back this up but in my experience of 6-7 years of watching the GFS, UKMO and ECM, I would say that in winter it fails to deliver on cold weather expectations in excess of 85% of occasions. Around 10% of the time it would deliver cold as per expectations but almost always from a very short time period. On some rare occasions, some very short term situations have cropped up that exceed cold weather expectations.

I hope everyone looking for cold and snow gets lucky, but the percentage call is that it aint gonna any where near as severe as some would on here would have you believe.

Re your first para.

so how many places in the UK, away from hills, have had 20cm from a single snowfall, in the past 20 years? I ask as that may show what your expectations are of winter. I live in one of the most snowless parts of the UK, yet so far since 1 December I have had 7 days of falling snow and 9 of snow covering the ground along with a mean temperature over the past 22 days of 1.8C.

Cautious as I am and with over 40 years of professional weather watching, I think (not yet had time to fully check) that what is going to be, in my view, a further 7 more probably 10-15 days of similar temperatures with some snow in there, makes a wintry spell of 30+ days, will/would make this cold spell fairly unique, for this area, in probably the last 30 years.

So yes balanced posting is my hope by us all, be it the rampers or perhaps yourself and snowballz.

[TEITS]

Hi Dave I do agree with what you say in regards the short term, however much of the buzz earlier was in regards the ECM and its later output, now without doubt that was a brilliant run, an easterly of old. But lets be honest this is not the first time this winter that a model run has shown an extended easterly blast, and as yet these have not come off, short blasts, .

I could be wrong but so far this winter very few model runs have indicated an E,ly. Ever since the cold spell occured in Dec the general trend has been with a Greenland block bringing N/NE/NW/W,lys. This to my knowledge is the first time a true E,ly has been progged.

Now I do understand what your saying. However in my opinion it isn't so much whether an E,ly will develop but more the duration thats uncertain. The 12Z ECM certainly suggests a prolonged E,ly but to be honest even if the E,ly flow only lasts 48hrs this would still bring heavy snowfall into E areas.

At the moment im just sticking with the +96/+120 and im very eager to see tonights updated fax charts.

I think some members (who should have been around long enough to know better) have got a bit carried away with ramping which is a bit of a shame as whilst the output continues to show charts that can be intpreteted as the day after tomorrow, it creates a positive feedback effect on the forum as newer inexperienced members constantly look to the rampers for guidance thus encouraging even more ramping.

Lets be fair though this is the model discussion thread and much of the excitement is because we're discussing the ECM output.

What I find amusing is you said something similiar at the beginning of Dec and look what happened!

Aslong as members realise charts in FI are subject to change then I can't see the problem. However much of the excitement is due to the charts around +96/+120.

[AtlanticFlamethrower]

I've been following the ENS spagetti for the last week or so and right now it's pretty clean out to T96, which suggests the short term evolution of the current weather pattern is fairly narrow.

You could not say this a few days ago at the time when the GFS was determined to forecast the low pressure system on a too Northerly trajectory. Then parts of this ENS chart was rather tangled at T48/72 and a complete mess before T96.

Now all the different runs are fairly consistent which gives greater support to the Easterly idea. Too early to know whether it is a dry or snowy Easterly, but the possibility of a snowy Easterly cannot be ruled out.

This is T96

This is T144

[Stu_London]

Re your first para.

so how many places in the UK, away from hills, have had 20cm from a single snowfall, in the past 20 years? I ask as that may show what your expectations are of winter.

I would respectfully draw your attention to the fact that I used the word 'notable' to describe what might be upcoming and what happened before Christmas and couldn't agree more that these events are not common. Since moving to London in 1992, I could probably count on one hand such events.

I'm just trying to keep an open realistic mind on events - it doesn't make it any less interesting as a observer.

Lets be fair though this is the model discussion thread and much of the excitement is because we're discussing the ECM output.

What I find amusing is you said something similiar at the beginning of Dec and look what happened!

Aslong as members realise charts in FI are subject to change then I can't see the problem. However much of the excitement is due to the charts around +96/+120.

Fair enough, I can see why the output (particularly the ECM) is exciting.

Re: my comments in early December, I don't think they were that far off given some of the scenarios being played out on the forum. Yes, the cold spell did deliver (by chance, my location was probably one of the most favoured away from the Highlands) plenty of people got nothing which would have been disappointing to them given what they were told in the days leading up to it.

[PB22]

To be quite frank, these are the best forecast models on show in internet history, and if people cannot be allowed to discuss them without getting excited then it really is a sorry state of affairs. Those of us who are "veterans" at this game are more than aware of all the cavets that come with looking at model output beyond T+120, but given that we are already in a cold set-up with a whole range of other factors seemingly in our favour, then this is really a whole new ball game. If people cannot be allowed get enthusiastic about the current output without being shot down, then we may as well all just give up the game now.

Anyway, on topic, the 18Z GFS is now rolling out and Sunday is cold, cold, cold:

http://www.wzkarten.de/pics/Rtavn421.html

http://www.wzkarten.de/pics/Rtavn422.html

http://www.wzkarten.de/pics/Rtavn4217.html

[weather eater]

I could be wrong but so far this winter very few model runs have indicated an E,ly. Ever since the cold spell occured in Dec the general trend has been with a Greenland block bringing N/NE/NW/W,lys. This to my knowledge is the first time a true E,ly has been progged.

Now I do understand what your saying. However in my opinion it isn't so much whether an E,ly will develop but more the duration thats uncertain. The 12Z ECM certainly suggests a prolonged E,ly but to be honest even if the E,ly flow only lasts 48hrs this would still bring heavy snowfall into E areas.

At the moment im just sticking with the +96/+120 and im very eager to see tonights updated fax charts.

I can't give you specific dates without trawling through past model threads, but the models have progged extended easterlies mid range onwards 2 or 3 times since mid December only to be gone the next run, downgraded if you like to a short blast before swinging round to NElys or a northerly. In regards this evenings ECM, it would be fair to argue that several recent runs on the ECM, GFS and GEM have hinted at, or tried to bring in an easterly, so this evening ECM could well be considered a continued trend in that direction, indeed you yourself indicated that this might happen a few days back. Excellent situation short term as you say, but the ECMs extended easterly I would take with a pinch of salt for the time being, along with winter Armageddon posts.

[johnholmes]

back to the next 12-24 hours and a question asked some little time ago about less cold air in the far north.

You are correct in drawing the attention of posters to this.

As the low tracks south, with its troughs, possible fronts, then note where the air is being drawn from, its from the west where higher temperatures and dewpoints are a feature. Indeed this area of less cold air is still around the the area of Torshavn. This somewhat less cold air has always been there, the source of the coldest air is east of north, more towards the Norwegian coast than perhaps the north where we often look for the lowest dewpoint air.

As the low tracks south, then for coastal areas, particularly in the west, then rain or sleet is the more likely type of precip, until any cold undercutting that may occur later, but for central areas, with the wind being re modified again over a cold land mass then sleet and snow seem more likely. The deep cold air starts to come south, off the Norwegian coast, during tomorrow, into the Shetlands by about dawn then spreading south across the country.

It MAY be the reason why UK Met have not yet issued any more widespread snow warnings for areas other than those already out?

[kold weather]

I can't give you specific dates without trawling through past model threads, but the models have progged extended easterlies mid range onwards 2 or 3 times since mid December only to be gone the next run, downgraded if you like to a short blast before swinging round to NElys or a northerly. In regards this evenings ECM, it would be fair to argue that several recent runs on the ECM, GFS and GEM have hinted at, or tried to bring in an easterly, so this evening ECM could well be considered a continued trend in that direction, indeed you yourself indicated that this might happen a few days back. Excellent situation short term as you say, but the ECMs extended easterly I would take with a pinch of salt for the time being, along with winter Armageddon posts.

The BIG difference this ti is it actually doesn't matter *at all* what happens with regards to the synoptics because of the way this evolves, it will bring at least 2-3 days with uppers below -10C and I'd guess ice days galore simply because we get a cutoff upper cold pool that hangs over the UK...thats why ther eis such big agreement at least upto 192hrs with regards to the strength of the cold and is also why the ECM are amazingly cold...

With the December set-up small differences made a huge difference to the actual weather and whether we got the cold pool shot at the UK...in this set-up the whole lot comes down from the north, its not some fairly narrow region of cold but rather a wide region of sub -10C air.

The ECM of course is somewhat the snowy extreme IMO...but by no means is it even close to the coldest of the shots, as can be shown very nicely by the ECM ensembles, most of those ensembles I'd guess have the cold pool being advected a little further north then the ECM op run...

Now just watch the 18z backdown somewhat lol!

[Frosty.]

I think the models have the general pattern nailed now for next week, it is going to become colder and colder from the north and then north east with hp to the nw and lp to the east and south east. The high does look like building in across northern britain after midweek with a long draw easterly across the south. I really like the gfs 12z in FI with the high pushing northeast into scandinavia and an E'ly for all areas with low pressure approaching from the southwest..classic stuff if it happens with snow flurries in the east and maybe some snow events from the sw. Those ecm ensembles are incredible, to think there are colder solutions than the op run as kold mentioned is quite staggering, this has all the makings of an epic cold spell to rival any of those from the past, to think that Jan 2010 might be mentioned in the future in the same breath as Jan 1979, Feb 1985-1986, Jan 1987 etc..

[Thundery wintry showers]

Indeed, the GFS has toned up the warmer air in recent runs (a consequence of the shortwave being placed further west with each run- shortwaves tend to have warm cores) and it seems the other models have done the same. As a result this event is pushing warm side of marginal for many western areas, and temporarily in the south. I also suggest that near east coasts of Scotland and NE England, the precipitation may start off sleety before turning to snow during the afternoon. For the south a rain to snow event is likely.

As for the longer term outlook, as often happens many people have started arguing from two opposing positions when the reality lies somewhere in between. We cannot trust outputs past T+144 because model accuracy drops markedly past that timeframe, regardless of what model we're using. For that reason, the prolonged easterlies in FI cannot be taken as gospel any more than ECMWF's south-westerlies last night.

But it's looking strongly odds-on that we are set to have a high pressure area centred over or to the north of Britain in a week's time, so there are two main possibilities: either the easterly downgrades and we get the high stuck on top of Britain, or something similar to the ECM's extended output actually verifies. So while I think it's premature to ramp up the easterly prospects in FI, it's also premature to write them off, when there is a fair amount of support for them.

[NorthNorfolkWeather]

I've been looking at the models and I'd like some guidance on Omega blocks. In the 2 attached pictures, we have an omega block at 30 hours over Greenland, and another out in FI at 228, this time centered north of the Shetlands off the Norwegian Coast.

Apart from about 2 charts in the sequence to 228, the is, to my untrained eye only 2 charts where there is not an omega block north of us. My limited understanding is that there is Warm Air Advection (WAA) to produce a block of this type.

A couple of questions

Is this type of block normally a long lasting affair? Especially considering that we had one in December as well

What is the transport mechanism? And does the WAA over Greenland and later the Shetlands mean that those areas are anomolously (sp) warmer? I'm assuming that is the answer is yes for the Greenland block, it will still be mighty cold compared to what we get

Edited January 1, 2010 by NorthNorfolkWeather

[PB22]

Tonight's T+96 and T+120 FAX charts:

http://www.meteociel.fr/ukmo/fax/fax96s.gif

http://www.meteociel.fr/ukmo/fax/fax120s.gif

Looks more akin to the UKMO output at this stage.

[Thundery wintry showers]

The upcoming setup also reminds me a bit of mid-February 1969:

http://www.wetterzentrale.de/archive/ra/1969/Rrea00119690214.gif

http://www.wetterzentrale.de/archive/ra/1969/Rrea00119690215.gif

http://www.wetterzentrale.de/archive/ra/1969/Rrea00119690216.gif

...although I expect a high to settle over or to the north of us, which isn't what happened in Feb 1969:

http://www.wetterzentrale.de/archive/ra/1969/Rrea00119690217.gif

http://www.wetterzentrale.de/archive/ra/1969/Rrea00119690218.gif

http://www.wetterzentrale.de/archive/ra/1969/Rrea00119690219.gif

[kold weather]

Not quite as good from the 18z with regards to the easterly as the upper high is a little further to the SE so the high pressure builds over the UK instead...however as I said before it still is very cold because of the broad evolution...and of course its a much snowier run overall then the 12z, esp for the Midlands region...

So broad evolution not quite as good as the 12z, but still stunning and very cold indeed!