Model Output Discussion:

[nick sussex]

It seems that most seem to think the ECM 12z will verify and already talking imby snow depths, a bit premature as the models could still do to us what they did on sunday morning if anyone can remember that nightmare. I would say there is reasonable agreement now that the atlantic milder weather will only succeed during the next 2 to 3 days before slowly being forced back south westwards but the level of confidence regarding depth of cold and duration is still low.

Very true Frosty, we've been here before so should be even more cautious than normal given the last week. Having looked over the output again I've decided I don't like the GFS or UKMO as they pass my nerve shredding threshhold, too much needs to go right, far too many shortwaves need to play ball with those. The ECM has a simpler route to cold with the Atlantic trough more favourably tilted, my advice to people is to hope the ECM calls this right upto 144hrs. As I've always said get the cold first then worry about the snow.

[Polar Continental]

For non E Anglia/SE members it should be pointed out that the ECM is only showing the potential for snow for a small portion of the country !

The lower resolution on the ECM (24hours) can be deceiving; the chart at T168 could look very different as it evolves in and out over a period a few hours, the 8c to 10c 850s would bring great instability as they push in from a relatively warm north sea. Many eastern areas of the country would be at risk of heavy snow, with moderate falls pushing well inland.

Have noticed someone saying its crazy talking of snow depths at this stage, remember this is the model discussion thread and it is here to discuss what the varying synoptic could deliver and evolve into.

Edited February 3, 2010 by Polar Continental

[Richard Lake]

Very true Frosty, we've been here before so should be even more cautious than normal given the last week. Having looked over the output again I've decided I don't like the GFS or UKMO as they pass my nerve shredding threshhold, too much needs to go right, far too many shortwaves need to play ball with those. The ECM has a simpler route to cold with the Atlantic trough more favourably tilted, my advice to people is to hope the ECM calls this right upto 144hrs. As I've always said get the cold first then worry about the snow.

Nick, if we see such agreement tomorrow then I think this forum will explode. If we see the flip.. I dare not think about it.

The great thing is despite everything plenty of the UK already has the cold, I've seen 3cms last friday, tonight I have another unexpected snowfall, must be about 3cms right now and still falling heavily. All this at a coastal location!

Current conditions tell a tale.

[Ian Fergusson]

Crazy to start talking about snow depths and distribution when last night people were talking about flooding and Feb maximum temperature records possibly being broken. Don't even know the basic synoptic set up yet.

Anywhere could get a lot of snow from the runs tonight.

Indeed. And what's all this slightly combative nonsense appearing in certain posts about supposed "competitors", etc, in the mid/long range forecasts??? It did make me chuckle.

I mean come on...... it's science discussed on this thread, I hope, not soccer.

Good, evolving science is about embracing shifting ideas and well-proven outcomes - irrespective of the supposed 'competition'. And if the folks at the likes of NOAA and UKMO can embrace this basic notion and attend symposia together in Exeter (and they do) quite happily without having to wear respective GFS/GM scarves and shout abuse at each other, then that says it all, surely.

Robust, non-preconceptual science (of ANY discipline) isn't about what you wish for, nor what you wish against.

'Wishing' is the unique human emotion that distinguishes well-judged scientific analysis from religion and voodoo.

So let's await the scientific consensus and leave wishful thinking / ill-judged notions of 'competition' on the sidelines..... please?

[cold snap]

Another day of model madness.

Models are excelent tonight

ECM 9/10

GFS 8/10

UKMO 8/10

To all moderators expect toys out of pram if the 18Z is a backtrack,

I for one may punch the computer.breathtaking stuff.

Edited February 3, 2010 by cold snap

[Jason T]

fingers crossed for rest of tonights and tomorrows runs. truly stunning.

[Glacier Point]

Second this Nick. And whereas GP may not be right every time he is right more often than any of his competitors. Especially with the medium range forecasts - the 10 day plus. And with logical and well explained reasoning and reacting quickly to teleconnective pattern changes I think that NW and us are very lucky to have him.

Thanks guys, some fair criticism and also praise welcomed.

There is a clear instance of a teleconnective change influencing our thinking over the last 48 hrs.

There has been a large increase in westerly winds across the tropics over the last 7-10 days associated with a fairly routine westerly wind burst associated with an El Nino base state.

During the last wind burst in early December, the extratropics embraced this westerly surge which was a clear signal for high latitude ridges. That was a relative no-brainer once we established the wind burst was underway.

This time round, the uncertainty surounding the downwelling waves associated with the warming of the stratosphere and seasonal differences in wavelengths have put a question mark about any movement of the anomalously strong west winds out of the tropics. Until 48 hours ago when it became apparent that momentum transport across 30N was underway. The only question then was how much.

Tonight's data run suggests that relative angular momentum has reached its greatest anomaly this winter, albeit much of this coming in the southern hemisphere. Interestingly the upper atmosphere is contributing to a significant negative zonal wind anomaly across the high latitudes within the upper atmosphere indicative of the stratospheric warming. Both take us back to the same point in the atmosphere as we were mid December.

Increases in torques will futher add momentum to the extratropics ensuring high latitude blocking structures. The main position for these looks to be Canad and western Greenland, but also a transient ridge over Iceland helping to draw the cold air to our NE back over the northern half of the UK, potentially further south with low pressure encroaching to the south west. This is the guidance for the Global Wind Oscillation undergoing a phase 5-6 type orbit.

Composites for these two phases (just 16 calander dates) are putting up the same 500 hPa height anomaly patterns as featuring in the medium term model guidance:

Therefore, high confidence in the general pattern of NWP.

I'm still thinking this will be a brief cold interlude, mainly because when angular momentum falls, the high will tend to sink towards the UK. A la ECM operational 12z. This is the most probable evolution but the timing will ultimately depend on the duration of time that the GWO spends in phases 5 and 6.

[kold weather]

The set-up is quite simple in some respects, in that if we get an easterly of any decent strength, we are pretty much certain to drag in much colder air, there is some VERY cold to the east and IF we get the easterly, then its likely going to have temps between say -12 and -16C.

I have to admit I'm gutted to have broken my laptop a few days ago, so if any big blast comes along then I'm going to miss a big chunk of it...haha I never do have much luck with these!

So in conclusion, any straight easterly will probably contain some VERY cold weather, and remember the North Sea is cold and the Baltic is frozen for the most part now as well so in theory a blast as strong as Feb 91 is quite within reach.

GP, I totally agree with regards to this probably being a shorter cold shot then in Dec/Jan, I suspect a 5-7 day deep cold spell with maybe a little more cold at the end depending on how useful the high over the top of us is.

Edited February 3, 2010 by kold weather

[Ian Fergusson]

Thanks guys, some fair criticism and also praise welcomed.

There is a clear instance of a teleconnective change influencing our thinking over the last 48 hrs.

There has been a large increase in westerly winds across the tropics over the last 7-10 days associated with a fairly routine westerly wind burst associated with an El Nino base state.

During the last wind burst in early December, the extratropics embraced this westerly surge which was a clear signal for high latitude ridges. That was a relative no-brainer once we established the wind burst was underway.

This time round, the uncertainty surounding the downwelling waves associated with the warming of the stratosphere and seasonal differences in wavelengths have put a question mark about any movement of the anomalously strong west winds out of the tropics. Until 48 hours ago when it became apparent that momentum transport across 30N was underway. The only question then was how much.

Tonight's data run suggests that relative angular momentum has reached its greatest anomaly this winter, albeit much of this coming in the southern hemisphere. Interestingly the upper atmosphere is contributing to a significant negative zonal wind anomaly across the high latitudes within the upper atmosphere indicative of the stratospheric warming. Both take us back to the same point in the atmosphere as we were mid December.

Increases in torques will futher add momentum to the extratropics ensuring high latitude blocking structures. The main position for these looks to be Canad and western Greenland, but also a transient ridge over Iceland helping to draw the cold air to our NE back over the northern half of the UK, potentially further south with low pressure encroaching to the south west. This is the guidance for the Global Wind Oscillation undergoing a phase 5-6 type orbit.

Composites for these two phases (just 16 calander dates) are putting up the same 500 hPa height anomaly patterns as featuring in the medium term model guidance:

Therefore, high confidence in the general pattern of NWP.

I'm still thinking this will be a brief cold interlude, mainly because when angular momentum falls, the high will tend to sink towards the UK. A la ECM operational 12z. This is the most probable evolution but the timing will ultimately depend on the duration of time that the GWO spends in phases 5 and 6.

Fascinating stuff & analysis - thanks for the detailed post.

[chionomaniac]

Indeed. And what's all this slightly combative nonsense appearing in certain posts about supposed "competitors", etc, in the mid/long range forecasts??? It did make me chuckle.

I mean come on...... it's science discussed on this thread, I hope, not soccer.

Good, evolving science is about embracing shifting ideas and well-proven outcomes - irrespective of the supposed 'competition'. And if the folks at the likes of NOAA and UKMO can embrace this basic notion and attend symposia together in Exeter (and they do) quite happily without having to wear respective GFS/GM scarves and shout abuse at each other, then that says it all, surely.

Robust, non-preconceptual science (of ANY discipline) isn't about what you wish for, nor what you wish against.

'Wishing' is the unique human emotion that distinguishes well-judged scientific analysis from religion and voodoo.

So let's await the scientific consensus and leave wishful thinking / ill-judged notions of 'competition' on the sidelines..... please?

Perhaps competitor was the wrong word, Ian!

Hopefully I didn't touch a nerve there!

[Alex95]

Another thing I've noticed today is the tendency for the continental feed to be brought forward from Sunday/Monday to Saturday, so the easterly can get going quicker. This is surely a good sign, and there can't be too many flips at +72 or less! By +72 on both the ECM and GFS the pattern is locked imo, but especially the ECM. As for snow this isn't a Southeastern event, if anything places like East Anglia, North East England and Central Southern England would get the largest snow events from the ECM 12z, with most other places away from the far NW getting reasonably good dumpings. This is hypothetical of course as it is outside of the reliable timeframe, but it is extremely premature to write off a snowy cold spell and label it a dry one, even in the NW there is always a possibility of snow events cropping up. This isn't new advice, its been said by many before, but some seem to forget how good an unstable NE/E flow can be.

[Ben_Cambs]

Wouldnt the Dutch De Bilt ensembles be out now? Because I dont have the link, as I keep forgetting to save the link. Very likely to be a cold set of ensembles....

[Altostratus]

Right, the models now do have the evolution nailed.

What do we have? Pressure build from the NW, ridging down and the Atlantic negaitvely tilted as the jet goes SOUTH. It was all about looking NW and was always all about the jet digging south. The coldest period 9-13 Feb. Snow for SE and E areas come Sun/Mon. We will see LPs move W to E along N France or the channel.

This is solar driven and a pattern I have been advocating since January. I have been and remain confident that there will be no more backtracking as the models have picked up on the solar driven signal. By mid Feb the block will sink and a LP will move in on NW to SE axis.

Never in doubt......not.

ECM is quite beautiful......................and correct.

BFTP

Blast, please don’t take this personally, but your over-confidence is bordering on arrogance at times; particularly when the weather in question has not happened. I'm not just referring to this post by the way. We are all entitled to make predictions/forecasts and that in part makes the forum an interesting place, but your implied confidence at that range is rather misleading. Your forecasts might well prove to be correct. If that’s the case, perhaps we should all take note of your methods. As always, the proof will be in objective assessment after the events.

I agree that this evening’s outputs are excellent. With better cross-model agreement we have taken a massive step in the right direction - the odds seem to have swung in favour of a cold spell for now. Taking an averaged look across the big three, I wouldn’t be surprised to see the cold spell upgraded with subsequent runs, with the possibility for even tighter gradients. Let’s not carried away though – let’s concentrate on getting that cold air flow established. Having said that, it looks like quite a fast moving pattern, with the cold air and instability arriving almost simultaneously – as usual, the timing and coincidence of these events hold the key to any snow potential.

Edited February 3, 2010 by Altostratus

[Ian Fergusson]

Perhaps competitor was the wrong word, Ian!

Hopefully I didn't touch a nerve there!

You didn't - just trying to defuse anything descending into a bun-fight! I appreciated what you meant in the wider sense! And back to the (utterly compelling) models......! Best, Ian

[londonsnow]

Thanks guys, some fair criticism and also praise welcomed.

There is a clear instance of a teleconnective change influencing our thinking over the last 48 hrs.

<snip>

Fascinating read GP. Many thanks

Edited February 3, 2010 by shuggee

[Cloud 10]

The usual quality update there from Glacier Point.

I have flipped this chart he posted to a uk perspective and it is quite striking how similar it is to the 12z ecm at 168hrs.

Edited February 3, 2010 by Cloud 10

[kold weather]

The key period really is coming up soon, IF we keep to the south of the jet stream between 120-144hrs then the easterly flow will kick in and with building heights over Iceland/Greenland there can only be one evolution and thats into a much colder pattern, however if we don't get to that point or the LP in the Atlantic is not tilted right then obviously things become much trickier, we could evolve into a colder pattern still but that requires yet another bite of the cherry. With SST's as they are at the moment I'd be very interested in just how cold temps could go but we shall see.

Ensembles are pretty good overall its also got to be said, the op run sort of went for a half hearted version of both evolutions up for offer, before finally settling on the colder evolution, but by that time the severe cold has somewhat drained away.

[Ben_Cambs]

ECM Dutch De Bilt ensembles: http://www.knmi.nl/w...nsemble_en.html

or: http://www.knmi.nl/exp/pluim/

Edited February 3, 2010 by Snowman0697

[sebastiaan1973]

I'm still thinking this will be a brief cold interlude, mainly because when angular momentum falls, the high will tend to sink towards the UK. A la ECM operational 12z. This is the most probable evolution but the timing will ultimately depend on the duration of time that the GWO spends in phases 5 and 6.

Thanks GP! I wonder what makes the GWO spends time in phase 5 & 6? Is there any chance the GWO will spend some time in phase 5 & 6?

[Frosty.]

Very true Frosty, we've been here before so should be even more cautious than normal given the last week. Having looked over the output again I've decided I don't like the GFS or UKMO as they pass my nerve shredding threshhold, too much needs to go right, far too many shortwaves need to play ball with those. The ECM has a simpler route to cold with the Atlantic trough more favourably tilted, my advice to people is to hope the ECM calls this right upto 144hrs. As I've always said get the cold first then worry about the snow.

I think we are reaching the tipping point with the models now with the balance of power shifting towards cold and having just read the latest detailed analysis from GP, the likelihood of a cold spell has increased further, interestingly, the models next week on the ecm especially, have a Jan 1987 look about them which had a 4-5 day bitter spell with ENE'ly winds and heavy snow showers with maxima of minus 4c.

[kold weather]

Karl, well the thing is if we have a cold upper flows to our east any decent drag back westwards on an easterly airflow then as I said earlier odds are quite decent of getting a very potent cold airflow. Whether or not it'd go that cold I'm not sure but we shall see. The key is also as much about how quick we can drag in the cold air as whether we get the flow in. to get a severe shot (which whilst somewhat unlikely still, its plausable) we really need the flow being quite strong and occuring as soon as probably 120-144hrs. any longer and that cold pool wiil become to moderate somewhat, and whilst still obviously decently cold we probably have a 48-72hrs time window to get the real severe stuff to our part of the world before it starts to moderate upwards in terms of temps.

[January Snowstorm]

Worth pointing out the dewpoints over Scandi next week are as low as -30, which is North pole stuff.

A Northeasterly should be very potent!!

[damianslaw]

As I stated yesterday, the models are increasingly now taking notice of the upstream signals which have been there to see for a few days now i.e. as we head towards the middle of Feb northern blocking will be the main player in our weather, the idea of low pressure steamrolling over the country into Scandanavia was never going to happen given the teleconnections. Rightfully they are showing most of the energy in the jet transferring on a southerly course withlower heights moving into central southern europe.

The low in the mid atlantic will stall later this week and track south easterly, at the same time heights will be ridging in form the east bringing a light easterly, then we have a classic undercutting scenario, and crucially heights building over Greenland at the same time. The evolution says a cold north easterly feed next week, with heights moving to the NW and then probably dropping over the country. For Scotland and N England the mild air forecast this week doesn't really look like getting a look in now.

To sum up - short term unsettled for all, mild in the south, average temps at best in the north, by the weekend, a light easterly feed with average temps for all, early next week increasingly colder, chance of snow for many with north easterly feed setting in.

[qseghj6]

The lower resolution on the ECM (24hours) can be deceiving; the chart at T168 could look very different as it evolves in and out over a period a few hours, the –8c to –10c 850's would bring great instability as they push in from a relatively warm north sea. Many eastern areas of the country would be at risk of heavy snow, with moderate falls pushing well inland.

Have noticed someone saying it's crazy talking of snow depths at this stage, remember this is the model discussion thread and it is here to discuss what the varying synoptic could deliver and evolve into.

Do you think from a true blown easterly it would be possible to predict potential snow depths or streamer likelyhoods purely from sea surface temperature ?

Do the models take this into account ?

Its looking relatively mild out there !

[Optimus Prime]

Compared to the average the seas very cold;

http://weather.unisys.com/surface/sst_anom.gif