Model Output Discussion - 5th December - 11th December

[A Winter's Tale]

Goodness me, boy what a large downgrade of a low! Let's hope that the northerly doesn't get downgraded.

[guvnor22002]

although its not gone exactly the ecm way i believe ecm was onto something and gfs may gradually come around

[Grimsby Snow Lover]

As I posted in the regional discussions earlier, I had my hunches that this low could sink further South, and although this was only a hunch, it seems to of paid off.

The low is much shallower, and would provide nothing but a seasonal gale.

Unfortunate really, I was hoping for a good old storm.

I am sure there will be plenty more ups and downs regarding Thursday's storm over the next few days BT. At least the damage to property etc should be significantly lower if it was to happen as shown by the 18z run.

[johnholmes]

Its perhaps "important" because the next run(18Z) is another 6 hours of data closer to the event and it might give some indication on what might happen regarding this deep low pressure system. Your idea of comparing today's 12Z run to yesterday's 12Z run is nonsence, seeing as a whole 24 hours of data is filtered in and we see huge differences that it does not tell us an great deal really.

Having said that, the ECM 00Z run will perhaps be more important than this upcoming GFS 18Z run as the GFS might stick to it guns but it does not always mean that this afternoon's ECM output suddenly becomes a total nonsence.

As a professional forecaster the FIRST thing ANY forecaster does is compare how events appear to be shaping up with the last ACTUAL chart not any model output. The next stage is to compare the various models with the 2 charts just mentioned. Of course this gets pretty complex as it involves not just a surface chart but 850, 700, 500, 300, 250 and 200mb charts, along with about 6-12 other indicator charts for what has/is and may happen in the future.

Then the different models will be compared and a 'best fit' arrived at, irrespective of which model appears to provide that out to about T+144. The next stage is to prepare, with the aid of model advice the Fax charts. During which time the forecaster is building up in his mind his and the team view on which forecast path to follow. There is ALWAYS a reluctance, especially at the start of a shift to ditch the previous watch ideas and go on a different path. Almost always it ends up as wrong as the original. The trick, albeit a scientific one with the backing of lots and lots of experience and again the ideas from the team, is to nudge things one way or another. Not the wholesale changes of course we often see on here as the models change tack from run to run. There is a difference, believe me.

The above refers to whether the forecast is for today and tomorrow or the 16-30 day outlook.

Soemtimes its wrong obviously but not very often, the man machine mix used as I've described is the best we have for a long time to come if it ever changes. Lots and lots of output is now almost directly computer generated with only slight human adjustments, for example your flight forecasts from the two main forecast centres of Washington and Exeter but generl public outputs are as I've suggest man-machine.

I hope this may help some of you understand why I do go on about taking a 'less exciteable' attitude shall I say to looking at the models.

[mountain shadow]

Goodness me, boy what a large downgrade of a low! Let's hope that the northerly doesn't get downgraded.

With the system further south this will bring the colder air further south also. Snow showers packing into the north west on Friday morning is a possibilty.

[dixonoid]

18z rolling out, should be interesting. God knows what arguments it might start though!

The Wetterzentral site BTW. What does it say about people who go to that site that they have those seedy advertising?

Cookies are bad for you!!

[nick sussex]

The UKMO goes with its raw output in the fax chart, an awful looking 120hrs chart.

http://www.meteociel.fr/modeles/ukmo2.php?ech=120&carte=2000

[Cloud 10]

Goodness me, boy what a large downgrade of a low! Let's hope that the northerly doesn't get downgraded.

Seems to be better ridging in the atlantic at +120 on the 18z.

[weather_it_will]

Good to see the lows have downgraded on the 18z GFS.

It was getting very silly and boring in here with people talking of mass destruction.

[DaBrigg]

The 18z isnt a downgrade for some, the low still bombs, just later. It drops 20mb in six hours as it moves into the North Sea. It shouldn't be dismissed just yet.

[NickR]

The 18z isnt a downgrade for some, the low still bombs, just later. It drops 20mb in six hours as it moves into the North Sea. It shouldn't be dismissed just yet.

True. WHere would that hit most? I'm thinking here in the NE!

[I remember Atlantic 252]

Saturday dosent look cold to me, northerly seems to have downgraded for the south

[Backtrack]

I am sure there will be plenty more ups and downs regarding Thursday's storm over the next few days BT. At least the damage to property etc should be significantly lower if it was to happen as shown by the 18z run.

Aye plenty of twists and turns yet, it's 5 days away after all.

[Liam J]

Many scenarios will be modelled over the next 4 or 5 days regarding the end of the week, this is still a long way in weather and model outputs.

Very complex situation, all you can say is the conditions are ripe to power up intense depressions this week, even the areas of LP progged for the first half of this week keep changing on the current outputs with many centres spinning round to our west.

[SMU]

http://176.31.229.22...nh-0-180.png?18

could be a crazy pub run.... cold surface high towards Scandi

S

Edited December 11, 2011 by Steve Murr

[A.J]

As a professional forecaster the FIRST thing ANY forecaster does is compare how events appear to be shaping up with the last ACTUAL chart not any model output. The next stage is to compare the various models with the 2 charts just mentioned. Of course this gets pretty complex as it involves not just a surface chart but 850, 700, 500, 300, 250 and 200mb charts, along with about 6-12 other indicator charts for what has/is and may happen in the future.

Then the different models will be compared and a 'best fit' arrived at, irrespective of which model appears to provide that out to about T+144. The next stage is to prepare, with the aid of model advice the Fax charts. During which time the forecaster is building up in his mind his and the team view on which forecast path to follow. There is ALWAYS a reluctance, especially at the start of a shift to ditch the previous watch ideas and go on a different path. Almost always it ends up as wrong as the original. The trick, albeit a scientific one with the backing of lots and lots of experience and again the ideas from the team, is to nudge things one way or another. Not the wholesale changes of course we often see on here as the models change tack from run to run. There is a difference, believe me.

The above refers to whether the forecast is for today and tomorrow or the 16-30 day outlook.

Soemtimes its wrong obviously but not very often, the man machine mix used as I've described is the best we have for a long time to come if it ever changes. Lots and lots of output is now almost directly computer generated with only slight human adjustments, for example your flight forecasts from the two main forecast centres of Washington and Exeter but generl public outputs are as I've suggest man-machine.

I hope this may help some of you understand why I do go on about taking a 'less exciteable' attitude shall I say to looking at the models.

A very, very high quality post John....I think some members either forget (or weren't aware) of your forecasting credentials prior to your Netweather contributions or the fact that for several years you were the Senior Forecaster for this site....New and old members alike could do a lot worse than taking heed of your posts (as well as showing a modicum of respect!)....To the permanent moderating team, although not strictly on-topic, I would appreciate it you would allow this post to stand, and posters replying, please respond via pm so the thread title stays relevant.....many thanks

[Cloud 10]

The nogaps 18z still going for it.

[feb1991blizzard]

The UKMO goes with its raw output in the fax chart, an awful looking 120hrs chart.

http://www.meteociel...=120&carte=2000

Not too bad Nick, Although the High not far enough North for any sustained Northerly we could still get some snow showers for coastal areas after the main storm has passed before the high ridges into the south.

[DaBrigg]

True. WHere would that hit most? I'm thinking here in the NE!

We cant take too much notice of just one run, so speaking strictly hypothetically.... if the 18z came to pass, North Sea coasts would get a nasty back edge NW'ly, while the Channel still gets a tight SWly gradient as the storm passes to the north. It looks like Cornwall would get worse winds with this scenario.

http://www.wetterzentrale.de/pics/Rtavn969.png

http://www.wetterzentrale.de/pics/Rtavn1029.png

http://www.wetterzentrale.de/pics/Rtavn1089.png

[wimblettben]

The nogaps 18z still going for it.

True but with now both the GFS and ECM showing the low much weaker I am more doubtfull of this happening then I would have been before.

I think I better make the most of tomorrows weaker storm now.

[Matty M]

The nogaps 18z still going for it.

I love the way it doesn't go below 950mb! i wonder how low that is!

[nick sussex]

Moving away from the storm you're unlikely to get stuck in a mild flow with the PV elongating up the western side of Greenland.

The Azores high, strong PV combo = mild normally comes about with the PV anchored much further east and not elongated, I'm not convinced the models know what to do with the PV or the Azores high.

The Xmas into New Year period is looking far from settled in terms of pattern, hopes rising given the latest from the stratosphere and the inability of the Azores high to join the party after several attempts.

[Thundery wintry showers]

Good to see the lows have downgraded on the 18z GFS.

It was getting very silly and boring in here with people talking of mass destruction.

I don't think it was silly and boring- there is still potential for serious structural damage from this low, as will probably happen if the 920-950mb low scenarios come off. However, the latest model runs have suggested a greater chance of the low not coming to much.

My opinion on the evolution following the brief northerly around the 18th December hasn't changed- I think a ridge of high pressure moving across the south, giving a few mild days, followed by a return to colder and stormier weather around Christmas, is the most likely scenario, though a more sustained milder/anticyclonic spell as per Ian Brown's predictions can't be ruled out.

[lorenzo]

The UKMO goes with its raw output in the fax chart, an awful looking 120hrs chart.

http://www.meteociel...=120&carte=2000

How far bhack does that long trail south westerly go ??

M Hugo mentioned this earlier today..

[nick sussex]

Not too bad Nick, Although the High not far enough North for any sustained Northerly we could still get some snow showers for coastal areas after the main storm has passed before the high ridges into the south.

I agree it looks okay for cold potential, I use awful alot now to describe these relentless lows!