Model Output Discussion - 26Th Dec 21:25-->

[swilliam]

I know the links below are for the 2m temps on the ECM and the 850s for the GFS. However there is alot of disagreement between the ECM/GEFS ensembles.

http://www.knmi.nl/e...E_06260_NWT.png

http://www.wetterzen...De_Bilt_ens.png

I personally think some of these problems are caused by how the GFS has been programmed. Due to our default weather pattern being mild SW,lys once we see the reverse of this the GFS struggles. This zonal machine will always attempt to blast any blocking away and remove any cold pooling ASAP. When you have the AO off the scale this will always cause problems.

Im not surprised NOAA nearly always sticks with the ECM. I tell you what if we didn't have access to the GFS then following the models would be alot easier and less stressful!

You were quite happy with the GFS when it (the parallel now the OP) was relentlessly predicting the pre-Christmas spell though?

The ECM ensembles are excellent and as you say there seems to a major discrepancy with the GFS ensembles. These seem to have changed over the last couple of days. This is the ensemble group for four days ago and you can see after the 4th Jan there is a wide variation of solutions with the mean around -4.

Comparing this to the current ensemble for the same period the mean is now approaching zero. What is also different though is that most of the members are tending to a mild solution but there a few with extremely cold solutions (keeping the mean down). So it seems that the chance of cold are reducing but that if we do get it it could well be more severe. Lets hope the GFS ensembles start moving towards the ECM which is already showing mostly very cold solutions.

Edited December 27, 2009 by swilliam

[Liam J]

in all seriousness, there will be some very heavy snowfall over some parts of the uk and looking at some wind speeds forecast in places, there is potential for blizzards and associated disruption, the devil really is on the detail now the latest gfs run is on its own with no support from where it has the cold air, which is only scotland and the far north of england.

i expect to see the -5 850 over much of wales, with 528 dam somewhere accros the n midlands or slightly furter south.

but we have to get the low pressure in first, and assuming it wont dive into the channel and into france.

i love the snow and cold weather, but im back at work tomorrow and all of last weeks snow has been compacted into thick ice in many places getting about is very difficult ive even ordered some ice grips to slip on my shoes!! for walking, and the prospect of more snow and ice to me is quite worrying, not to mention the people who cant drive in the conditions who pose risks to many other roads users....would have prefered a thaw before the next bash but hey ho.

[TEITS]

You were quite happy with the GFS when it (the parallel now the OP) was relentlessly predicting the pre-Christmas spell though?

Simple answer is because it had support from the other models. However this time the ECM/GFS are very different. When this happens I will always back the ECM.

[Cloud 10]

Latest update from the met office.

UK Outlook for Friday 1 Jan 2010 to Sunday 10 Jan 2010:

On Friday, and over next weekend it is expected to be generally cold with overnight frosts across most areas and occasional wintry showers affecting northern and eastern areas. There is also a risk of some rain or sleet, which may be persistent at times, affecting parts of the south over the weekend. Drier across central and western areas with overnight freezing fog which may persist locally. The following week looks likely to remain cold or even very cold in places, although perhaps closer to normal in the far south at times. Wintry showers look set to continue to affect northern and eastern areas for the rest of the period. There will be a further risk of bands of rain or sleet affecting southern parts at times.

Updated: 1203 on Sun 27 Dec 2009

Edited December 27, 2009 by Cloud 10

[chionomaniac]

Well the operationals have gone on their traditional festive tangent, but study of the ensemble means has continued to provide good overall guidance on the longwave pattern, which continues to see high latitude blocking and 850 hPa temperature anomalies across NW Europe ranging between -1 and -9C over the 15 day period.

The West-based -NAO is depicted by GFS and GEM H5 ensemble mean height anomalies for days 11-15:

http://raleighwx.easternuswx.com/models/cmcensemble/00zCMCENS11-15day500mbHeightAnomalyNH.gif

http://raleighwx.easternuswx.com/models/gfsensemble/00zENS11-15day500mbHeightAnomalyNH.gif

Crucially, that is a flat jet pattern with both model tools extending the trough into the core of Europe which will allow and retain a reservoir of polar air over NW Europe. Prior to this timeframe, both GFS, GEM and ECM ensembles suggest anything between -4 and -9C 850 hPa anomalies to become established across much of northern Europe with southern parts of the UK along the battleground between airmasses.

The teleconnective situation remains unchanged. The AO is severely depressed beyond -4SD. The NAO is also becoming locked negative. Trade winds are increasing ahead of a convective signal returning to the western Indian Ocean which ties in with increased negative mountain and frictional torques sending the Global Wind Oscillation towards phases 7-0 favouring a west-based NAO block. Due to increased angular momentum, fluxes in the coupled ocean-atmosphere system are strongly favouring the northern block to wobble around the North Atlantic, east to west, west to east and so forth for the duration of January reaching a likely peak intensity January 10th - 25th. The sustained outlook I would suggest, is for below or much below average temperatures to prevail.

I am glad that you have posted this GP as you have addressed some concerns that I was going to raise. The first was should we be concerned that the MJO seems to be forecast to take a flight of fancy around unfavourable orbits. However having looked at the strong GWO signal it would appear that the MJO convective signal can indeed be overridden by the GWO.

The next issue was the strong west based -NAO. It appears that the tropospheric negative zonal wind anomalies may get flushed out of the atmosphere within the next few days. As this occurs there will be an increase in westerly winds. With this aligned to the west based strong -NAO is there a chance that the increased strength Atlantic driven systems could drive the battleground further north leaving the southern half of the country in less cold air (not mild) and Northern Scotland in the battleground area. It would only take a small westward shift of the current blocking pattern for this to occur especially if the wobble that you predict occurs a little too far west.

The current predicted shape of the polar vortex is highly indicative of a west based -NAO and any model that suggests blocking to our NE is to be treated with suspicion. The current pattern is on a knife edge and I feel that the further north that you are positioned in the coming weeks the better the chances of snow will be. For those of us in the south it could lead to a very frustrating time watching our fellow NW members further north having repeated snowfalls whilst we can only muster cold rain!

[mcweather]

Just seen the BBC weather for the week ahead and you know what it looked nothing like the GFS would have you believe. Well Well

Snow in Wales and the midlands in the run up to new year then south of the M4 for new years eve and new years day. :lol:

[MR EXTREMES]

UK Outlook for Friday 1 Jan 2010 to Sunday 10 Jan 2010:

On Friday, and over next weekend it is expected to be generally cold with overnight frosts across most areas and occasional wintry showers affecting northern and eastern areas. There is also a risk of some rain or sleet, which may be persistent at times, affecting parts of the south over the weekend. Drier across central and western areas with overnight freezing fog which may persist locally. The following week looks likely to remain cold or even very cold in places, although perhaps closer to normal in the far south at times. Wintry showers look set to continue to affect northern and eastern areas for the rest of the period. There will be a further risk of bands of rain or sleet affecting southern parts at times.

Updated: 1203 on Sun 27 Dec 2009

yep looks like southern england have the worst of the forecast.

so model projections or most of them are right midlands north south of this looking milder around average.

but then again anyone who lives down here and have been reading the threads recently would have or should have realised we do live in the unluckiest place in europe lol.

anyway no more model watching for me ive given up hoping now.

but its looking great for most.

Edited December 27, 2009 by badboy657

[Weather-history]

. The potential good news could come from the comparison chart which Mr_Data posted up for the gfs T+168 projection from 7 days ago, you will all notice that it got that a bit wrong.

I have looked at all the GFS op runs (0z, 06z etc) from last Sunday for this Sunday and not one came up with today's synoptic chart.

Edited December 27, 2009 by Mr_Data

[rmc1987]

Haha no way further south, Northerners shouldn't be so greedy

Forget it, this will be an event for further North. I'd be surprised to see anything more than rain in this part of the country. Not sure about your area as before I've been on the edge of snow but got rain. I'd have to go further to my North for any snow. A crying shame as other parts get a good old time! Can see why winters are generally poor for cold/snow because even when the charts look decent they don't quite deliver here. Still, I had a bit last week so maybe that's my quota for winter ;-)

Edited December 27, 2009 by rmc1987

[BARRY]

Can I ask if there is a way to view these historical runs online, or do you save them all on a daily basis?

subscription to net weather

Edited December 27, 2009 by BARRY

[mcweather]

yep looks like southern england have the worst of the forecast.

so model projections or most of them are right midlands north south of this looking milder around average.

but then again anyone who lives down here and have been reading the threads recently would have or should have realised we do live in the unluckiest place in europe lol.

anyway no more model watching for me ive given up hoping now.

but its looking great for most.

I wouldn't be so sure Bad boy a matter of 50 miles difference on approaching fronts could leave the south with plenty of snow rather and rain or sleet.

[Weather-history]

Can I ask if there is a way to view these historical runs online, or do you save them all on a daily basis?

Here's the archive

Try that again

http://www.meteociel.fr/modeles/gfse_cartes.php?ech=6&code=0&mode=0&archive=1

Edited December 27, 2009 by Mr_Data

[snowlover2009]

subscription to net weather

do you have to pay and do you use the username and password what you are using on the forum?

Here's the archive

http://91.121.94.83/...22706-0-6.png?6

that just shows one chart

[Mark Bayley]

do you have to pay and do you use the username and password what you are using on the forum?

that just shows one chart

https://www.netweath...gi-bin/login.pl for your first part

for the second part you edit the address and change the number, for example http://91.121.94.83/...22706-0-6.png?6

You change the 0-6 part to 0-36 if you want the T36 chart

e.g http://91.121.94.83/...2706-0-36.png?6

Or you could just use this link that Mr Data just posted

http://www.meteociel...ode=0&archive=1

Edited December 27, 2009 by mark bayley

[john w]

Badboy I agree, though last week was actually very good for me, but in terms of actually getting around it was a nightmare.

I think Steve Murr has i correct on the technical board the shortwave over Norway really needs budging!

I need to get my meto book back out!

Edited December 27, 2009 by john w

[Ian Fergusson]

Note the UKMO advisory has been tweaked a short while ago this morning to accomodate the slight shifting of snow bias from latest output for Tues/Wed (e.g., note extension from Glos down into N. Somerset) and further amendments are inevitable. ECMWF ENS postage stamps for 12Z on the 30th want to highlight snow more widely into inland / northern districts of the westcountry (as reflected in the tweaked spatial extent of the advisory) but for now, the clear focus of PPN discrimination (rain v snow) effectively starts M4 northwards and through M5 corridor up into the Midlands, with Wales looking potentially very nasty indeed for blizzards (in the genuine sense, rather than media hyperbole definition); ditto some upland parts of the midlands. Obviously not to be taken for granted at this stage.... even a 50 NM shift north-south is a long, long way on our motorway network! Snowfall risk sinks and extends further southwards by Thursday, however.

Edited December 27, 2009 by Ian Fergusson

[grab my graupel]

Folks, let's not allow this thread to deteriorate. There's been some very good input this morning, and it would be ashame if it were spoiled by a few members who abuse the guidelines

There are plenty of threads available for weather chat etc. so there is no need for this

Thank you

[Cecil Hogmanay Melchett]

Folks, let's not allow this thread to deteriorate. There's been some very good input this morning, and it would be ashame if it were spoiled by a few members who abuse the guidelines

There are plenty of threads available for weather chat etc. so there is no need for this

Thank you

All seems good natured Brian.

Thanks for the updates Ian they are really helpful although the bbc seem to think the snow line will extend to the nw of England!

[cooling climate]

The GFS really does look out on a limb today, with no support that I can see for any of its output

from as early as t60 or so onwards. If the 12z and the 18z continue to show the same synoptics

then the GFS may deserve more attention but at the moment I think it is just plain wrong.

With the output showing fronts and troughs trying to encroach from the sw into the UK, judging by

the difficulty the models are having at t72 -120 looking past t168 is pointless + we do not know yet

just how potent this cold spell is going to be and this will obviously have a effect on the longer term.

I agree with some who have said that this has the makings to be a classic for cold as well as snow,

the potential is most definitely there and I am confident we will see this in the models later on today

and onwards.

Excellent times ahead I feel.

Edited December 27, 2009 by cooling climate

[snowmadchrisuk]

The GFS test can start tonight , GFS has the Midlands min at 0 , -1 . The Met Office have it at -4 . Tomorrow the GFS has a max of 4 deg , The Met Office has our max at 2 degrees.

[Iceni]

I know the links below are for the 2m temps on the ECM and the 850s for the GFS. However there is alot of disagreement between the ECM/GEFS ensembles.

http://www.knmi.nl/e...E_06260_NWT.png

http://www.wetterzen...De_Bilt_ens.png

I personally think some of these problems are caused by how the GFS has been programmed. Due to our default weather pattern being mild SW,lys once we see the reverse of this the GFS struggles. This zonal machine will always attempt to blast any blocking away and remove any cold pooling ASAP. When you have the AO off the scale this will always cause problems.

Im not surprised NOAA nearly always sticks with the ECM. I tell you what if we didn't have access to the GFS then following the models would be alot easier and less stressful!

And another thing I've noticed, GFS 'defaults' to zonal mode at w/es. Stunning string of charts during the week, all buried by a couple of days' default stuff. What's today? Oh it's Sunday — hmmm

[Guest North Sea Snow Convection]

I am glad that you have posted this GP as you have addressed some concerns that I was going to raise. The first was should we be concerned that the MJO seems to be forecast to take a flight of fancy around unfavourable orbits. However having looked at the strong GWO signal it would appear that the MJO convective signal can indeed be overridden by the GWO.

The next issue was the strong west based -NAO. It appears that the tropospheric negative zonal wind anomalies may get flushed out of the atmosphere within the next few days. As this occurs there will be an increase in westerly winds. With this aligned to the west based strong -NAO is there a chance that the increased strength Atlantic driven systems could drive the battleground further north leaving the southern half of the country in less cold air (not mild) and Northern Scotland in the battleground area. It would only take a small westward shift of the current blocking pattern for this to occur especially if the wobble that you predict occurs a little too far west.

The current predicted shape of the polar vortex is highly indicative of a west based -NAO and any model that suggests blocking to our NE is to be treated with suspicion. The current pattern is on a knife edge and I feel that the further north that you are positioned in the coming weeks the better the chances of snow will be. For those of us in the south it could lead to a very frustrating time watching our fellow NW members further north having repeated snowfalls whilst we can only muster cold rain!

You have to bear in mind that the presence of high pressure over Greenland will have the effect (it already is) of drawing the Siberian High further west. This is also being allowed to happen in respect of the flat west based -NAO pattern that GP mentions. I actually think that eyes could too easily go off the ball in respect of the intense cold pooling to the NE - as that is clearly, and almost insidiously, coming more and more into play.

As this happens it is going to get harder for mild air to advance very far north eastwards - and any attempted downstream ridging over europe (as an often consequence of a west based -NAO) is nullified on the basis that the flat southerly jet allows lows to invade europe, which is crucial for keeping cold air advection flooding back southwards and westwards as well as sustaining higher pressure above it to the north east

As much as the cold pooling reservoir looks to me like being underplayed - on the other hand the strength of low pressure to the south west is in danger of being overestimated and over progressed by the models.

We are seeing the first signs of an extensive NH high latitude block extending from Russia to Canada, and this does look like too-ing and fro-ing for some time yet. That is going to be extremely hard to break down.

Edited December 27, 2009 by North Sea Snow Convection

[TEITS]

Just had a bath and whilst lying there the general pattern is becoming clearer especially after reading the Met O forecast/GPs post. The details however remain very uncertain as you will see.

Basically the trend into January is for the AO to remain strongly negative and blocking to be the dominant player. However when GP says W based NAO and this sometimes moving east to west and west to east. What this basically means is the boundary between milder air to the S and colder air to the N will move up and down like a yoyo. If you have a W based NAO then this leaves you open to an attack from the SW and the boundary between the two airmasses moves further N. If the blocking then moves west to east and is centred over Greenland then the boundary moves further S and would include all of the UK. So if you live in Scotland and the far N of England chances are you will remain cold. However further S and you could see a spell of snow turning to rain or a spell of rain turning to snow.

However it isn't as clear cut as this suggests. Only 2 days ago the models didn't have this blocking transferring W with the blocking being centred over Greenland. However the past 48hrs have seen this blocking move further W hence why the risk of attack from the SW. So how do we know the models are correct this time and will this blocking see a W based NAO. The other thing to take into consideration is will the models trend towards bringing a bitterly cold airmass from the NE. If this happens the cold pool of air over the UK could deflect these LP systems.

So in summary the next 2 weeks could see Scotland/N of England remaining cold with further snow at times. Further S the risk of heavy snow but also possibly turning less cold with rain which could be shortlived as the cold air returns.

I shall be curious to see what snowfall amounts members like OON see next month. This also applies to members who live around the Pennines. If I had the money/time I would book myself into a B&B in Buxton next week!

Edited December 27, 2009 by THE EYE IN THE SKY

[West is Best]

The 6z ensembles are all over the place: ridiculous scatter from the word go.

Ignore the run - bin.

Anyone know if GFS related discussions are referring to data problems? The synoptics on runs the past 24 hours are absolutely absurd with lows appearing out of nowhere, high pressures shifting 1000 miles in 2 days, and no relation to other model outputs.

[Evening thunder]

I have been watching the GFS ensembles over the last 2 days and with every run the number of members going for cold has decreased and the number going for mild has increased. I admit I have been looking at my local area and cant really use other locations as i'd be comparing a different location today to what I have been watching. However they were showing nearly every member going for cold in the more extended outlook if I remember correctly, Now look at them.

http://charts.netwea...6/t850Devon.png

Nearly every member going for mild after just a brief cold snap. If that is not a trend then I dont know what is. The mild hump before it has grown as well. Oh well we can hope hope they are not correct and change with the other outputs being nearer the mark, as they easily could be, although im not too sure they will at the moment tbh.

Just seen recent posts about lots of scatter etc, that does seem to be the case. However could it be just the slight differences with the positioning of the low on the ensembles effecting the 850's a lot for that location?

I agree that there is a lot of uncertainty and the GFS does seem a bit on its own compared to the other output, but im not sure we should ignore it completely.

Edited December 27, 2009 by StormMad26