Model Output Discussion October 2012

[chionomaniac]

Time for a new thread to cover the month of October.

Will the second month of Autumn be blocked, or mild and wild.

Please keep on topic, respect others and no text speak!

[syed2878]

This is the discussion from NOAA. I don't know how this would effect us here in the u.k i'm sure some1 who know's mor than me could explain to us i my self still learning regarding the moddels it's y i don't post here much.

PRELIMINARY EXTENDED FORECAST DISCUSSION.

1000 AM EDT SUN SEP 30 2012

VALID 12Z THU OCT 04 2012 - 12Z SUN OCT 07 2012

　

MEDIUM RANGE FORECAST AND MUCH OF THE NORTH AMERICAN CONTINENT

WILL FEATURE 2 FULL LATITUDE LONGWAVE TROUGHS...SEPARATED BY A

MAJOR LONGWAVE RIDGE OVER THE WESTERN THIRD OF THE CONUS AND

CANADIAN ROCKIES.

A WELL-DEFINED UPPER-LEVEL TROUGH AXIS INVOF 90W (EASTERN

CANADA/USA) AND NORTHWEST FLOW ALOFT WILL ROTATE A SERIES OF

MID-LEVEL SHORTWAVES AND CANADIAN FRONTS FROM CENTRAL CANADA INTO

THE LOWER 48. THESE RATHER DRY AND SHALLOW AIRMASSES SHOULD

PROVIDE SOME LARGE DIURNAL TEMPERATURE SWINGS ALONG AND EAST OF

THE ROCKIES...WITH EACH NEW AIRMASS MODIFYING AS THEY SPREAD

ACROSS THE EASTERN THIRD OF THE NATION.

MODEL GUIDANCE ALSO IN GOOD AGREEMENT WITH LONGWAVE RIDGE AXIS

MIGRATING EASTWARD FROM 140W TO 130W ALONG THE WEST COAST OF NORTH

AMERICA BETWEEN DAYS 5-7 AND WITH THE GENERAL SCENARIO FOR ENERGY

TO UNDERCUT THE RIDGE ALONG THE WEST COAST INVOF 35-40N. THE

OPERATIONAL 00Z ECMWF AND GFS DO DIFFER ON THE TIMING OF ENERGY

ALONG THE CALIFORNIA COAST...BUT ARE WELL-WITHIN THE ENSEMBLE

MEANS TO WARRANT A BLENDED APPROACH ACROSS THE SOUTHWEST US LATE

IN THE PERIOD.

VOJTESAK

[Gibby]

No time for a full report this morning so a quick Summary from me today

All models are set on giving us an unsettled week this week as Low pressure to the North of the UK maintains control of the weather with showers or longer spells of rain in a cool and blustery West wind.

The Euros then bring High pressure in and across the UK over the weekend, taking it away SE into Europe early next week with its attendant fine and dry weather with overnight mist and fog patches. GFS prefers to keep a weak frontal trough across Southern Britain over the weekend with rain at times with any better weather more likely in the North. Then through next week the Euros appear to set up a rather warm South to Southeast flow with a lot of cloud and some outbreaks of rain, heavy in places as troughs from a mid Atlantic Low become entwined North to South over the UK. GFS on the other hand builds pressure out in the Atlantic ramping up Low pressure north of Britain to deliver bands of rain and showers in quite cool conditions down over the UK in potentially stormy conditions at times for the far North.

In Summary these differences could remain for several more days as the axis point is at the weekend in the way the models handle the exit of this weekends depression along with how any High pressure ridge at the weekend behaves.

Edited October 1, 2012 by Gibby

[Polar Maritime]

Very stormy and cold Polar Maritime flow from GFS FI this morning, with snow over the Far North of England and Scotland. With -8 uppers just touching the far North of Scotland and -4 uppers down to the Midlands.

Edited October 1, 2012 by Polar Maritime

[johnholmes]

for those new to this game the above post could be called 'cherry picking'. Its true enough but its 14 days out and GFS is not very good at being correct that far out. It might be correct on this occasion no one knows.

What would have been more helpful PM would have been a little bit of explanation from you about how far ahead this was and that some 48 hours or so previously it had a 'warm' looking ridge?

Newcomers do beware of cold/warm looking charts without any explanations, but it is good at showing you what the posters preference is!

The posts by the likes of Gibby, see above, are the ones to look for a balanced view, frosty as well, there are others who try and give a balanced view.

Edited October 1, 2012 by johnholmes

[Polar Maritime]

for those new to this game the above post could be called 'cherry picking'. Its true enough but its 14 days out and GFS is not very good at being correct that far out. It might be correct on this occasion no one knows.

What would have been more helpful PM would have been a little bit of explanation from you about how far ahead this was and that some 48 hours or so previously it had a 'warm' looking ridge?

Newcomers do beware of cold/warm looking charts without any explanations, but it is good at showing you what the posters preference is!

The posts by the likes of Gibby, see above, are the ones to look for a balanced view, frosty as well, there are others who try and give a balanced view.

I made it very clear John that the charts i have posted are in FI... After Gibbys fantastic post as usual giving us all a balanced view as does Frosty and others. I threw these in to show the first sign's of colder weather in the charts this year. It was just an observation.

Edited October 1, 2012 by Polar Maritime

[Methuselah]

The problem is, though, that repeated postings of cherry-picked cold and/or snowy charts gives the impression that that's a likely outcome; when, in fact, the very opposite is more often the case...

[Polar Maritime]

The problem is, though, that repeated postings of cherry-picked cold and/or snowy charts gives the impression that that's a likely outcome; when, in fact, the very opposite is more often the case...

But this is not the case?

[BLAST FROM THE PAST]

Why not add what one sees is going to or could happen or identifying a feature that a model is picking up on or not? If everyone did running commentaries this thread would be dead in the water. Gibby, Frosty give a thorough run down of what models show, pointless everyone else doing that.

BFTP

[Radiating Dendrite]

To be fair, there is nothing wrong with a bit of cherry picking so long as it is pointed out by the poster.

We are here to discuss the model output, there is nothing specifying time frames. If we cannot discuss then we may as well just have Gibby post a summary here everyday and that's it.

[summer blizzard]

It may look warm on that chart but heights building over the Arctic would deliver cooler weather down the line.

[chionomaniac]

Right, enough discussion on cherry picking and more on the output please.

I will start in suggesting that the GFS and ECM are very similar to this Friday but it is after this that things change dramatically. And the changed is shown quite clearly between the GFS and ECM by T+240.

The GFS is cranking up the motor on the polar vortex as seen below:

whereas the ECM continues the slumber with some long wavelength Rossby waves thrown into the mix almost splitting the vortex in two:

So which model is right?

And can we tell? Well the GFS pressure ensembles from the latest available GFS run (00Z) for Rejkavic suggest a great deal of uncertainty regarding it's own output - not that we can take certainty anyway at this range from the GFS!

The ECM mean while is less bullish about the blocking pattern, but it is still there in the mean ensemble chart:

Looking further afield the MJO is set to stall and lose amplitude in phase 6,- this adds credence to an ECM solution. However, with a large positive Asian MT adding westerly momentum to the atmosphere, overriding the the MJO signal, this could leave us somewhere in between the GFS and ECM with less pronounced Rossby waves and mid latitude HP cells sitting over us.

[shedhead]

Good post by Chio and not a cherry in sight... Definately some fairly marked disagreement in the overall pattern from the big two, but as is often the case in this type of senario they will eventually come together with some sort of half way house solution...again as alluded too by Chio.

Edited October 1, 2012 by shedhead

[johnholmes]

Regarding the coming weekend I would recommend the site link below for seeing how the main models may change over several days for the same future time and date. It is something not yet available in such ready and easy format on Net Wx but is hopefully something Paul can set up when he has time.

http://www.weatheron...10010000&HH=102

There are as you can see various ideas from the different models on different runs on how the weekend may turn out, unsettled, coolish with high pressure giving a flow from north of west or milder with a flow from south of west. Or more settled again with various places for the surface ridge to be bewteen WNW and WSW close by the UK.

How long it may take the models to come up with the correct version is hard to say.

For what its worth the anomaly charts issued a week or so ago were not that clear. The overall concensus seemed to be that the 500mb flow would be westerly with some ridging close by the west of the UK, which would give a surface flow probably from north of west. But a rather smaller prob of the height anomaly being WSW of the UK thus favouring a somewhat milder flow from south of west at the surface.

It will be interesting to see which is closer to what actually transpires.

And just to show how variable GFS can be at fairly distant FI a chart for 14 October where the 00z showed deep cold air from a deep low in the North Sea, the 06z version is below.

Edited October 1, 2012 by johnholmes

[IDO]

This week there is a trough over the UK that dilly dallies giving coolish showery weather. This Saturday the jetstream is pushed north by a flat HP, preceded by a small LP feature that straddles the south giving a not too promising day or so down here. HP from Sunday (for 5-6 days) looking more promising now and the S/SE may get some SE'lys or southerly's if the HP sits nicely. But although GFS getting more consistent with the HP scenario, compared to the 06z run they are not so good on the finer details yet.

According to GFS 12z Op run it looks like after this weekend the PV weakens allowing some cold air to seep to southern latitudes . As per the usual this is centred on the mid/east coast of the US. So on this run lots of colder weather there. The UK gets HP ridging giving most of the UK some settled av/above av. temps.. Later stages of FI on the op run has a low mixed in with HP before another Atlantic high builds in from the west promising a further spell of deja vu, settled weather, coinciding to the PV becoming rather subdued (17th)...

[chionomaniac]

The 12Z GFS actually pushes a shortwave over the country on Saturday which would pretty wet and unpleasant for England and Wales.

This is not picked up by the UKMO 12Z, which keeps an intermediate high - however I wouldn't rule it out looking at Friday's UKMO T+96 chart. Tonight's ECM and the fax charts should help because I think that the weekend dictates what happens thereafter.

Edited October 1, 2012 by chionomaniac

[Gavin Hannah]

GFS is determined to bring Atlantic HP into the game throughout it's latest run, only to see it continuously bowled out the way by the subsequent incoming Low.

[I remember Atlantic 252]

I hope GFS is wrong for friday, showing a horrible shortwave washout day, ECMWF and UKMO do not develop it, hope they are right

[chionomaniac]

Well, no shortwave on the ECM tonight though the intermediate weekend high is just that - before the next trough moves in.

[ANYWEATHER]

Well, no shortwave on the ECM tonight though the intermediate weekend high is just that - before the next trough moves in.

Yes True, but Gfs has been fairy consistent with its output recently, !!

[chionomaniac]

Yes True, but Gfs has been fairy consistent with its output recently, !!

Is that in as away with the fairies?

[ANYWEATHER]

Is that in as away with the fairies?

Ok,Got the spelling Wrong!!!

[Gibby]

Good evening. Here's my take on how the 12zs look tonight.

All models show an unsettled week to come with showers or rain at times in a brisk and sometimes strong Westerly flow. A complication in this is the chance of a small disturbance spawned from the remains of tropical storm 'Nadine' steaming East over Southern Britain through Thursday night with heavy rain in tow, exiting to Europe on Friday. GFS does show this on a much later trajectory, passing over through Saturday.

GFS then shows high pressure developing over Britain on Sunday with cool and bright conditions developing for all with some mist, fog and frost problems overnight. The model then shows High pressure in control for the next week with an axis lying from the East Atlantic and the UK with continuing fine if rather cloudy conditions at times. Later in FI High pressure moves gently away East and weakens with Low pressure moving SE from Greenland towards the SW approaches setting up a rather cold and unsettled few days for the South while the North sees the best chance of drier conditions persisting, thanks to High pressure over Scandinavia.

The GFS Ensembles show 850's never straying that far from the early october average. some copious rain amounts are show for the South later this week while thereafter a much drier regime is shown. Further North rainfall is more noticeable in the second half of the period.

The Jet Stream is shown to continue streaming East over the UK for the next 5-6 days. In the outer reaches of the predictions tonight the arm affecting the UK weakens and is replaced by a Northern arm which ridges North to a position North of the UK by the end of the high resolution part of the run.

UKMO for noon on Sunday shows High pressure close to the East of Britain with an anticyclonic feed of winds over the UK from the East in the South and South in the North. The weather would be dry and bright for many with some bright or sunny intervals after Saturday nights mist, fog and frost patches have cleared away.

ECM shows a similar scenario to UKMO at 144hrs before it pulls the Atlantic Low pressure gently in towards our shores and bringing a change from the dry and bright weather of the weekend to more unsettled conditions with rain at times for all by the end of the run.

In Summary and at first sight there is not much in common between GFS and ECM again tonight, though the trend for a SE moving pressure pattern is a common theme shared by them at the end of their runs. The specifics are not really worthy of dwelling over as they will ultimately change when the evolution become clearer and shared. In the mean time we must expect further changes in the coming days as FI appears to be at t120 at the moment.

[IDO]

It appears that GFS & ECMW are closely progged till T120. Then the difference is that ECMW has the HP very transitory, as it is pushed away by the Atlantic low. Both models have this Low but the difference is upstream. ECMW has a HP grow off the US Eastern seaboard and as this develops and edges east it pushes the LP through the UK. Both models have the US within the trough but GFS has the HP develop above the LP so keeping settled conditions for a lot longer, before being squeezed out by the LP (at T276). From a layman's point of view it is easier to go with the ECMW scenario, as it looks more reasonable. The GFS ENS are a halfway house having HP hold on till mid next week before LP takes reign, but it looks closer to ECMW Op run. So now not so sure of a HP respite next week.

Edited October 1, 2012 by i'm dreaming of...

[summer blizzard]

Interesting high latitude profile...