Model Output Discussion

[azores92]

yes, gripping stuff at the moment i have to say. both models show heights developing over the pole, and to our south. all we need is the low to our north to fill in/move away, and we have a lot of potential. the ensembles show how things could go either way, and they show how much cold is waiting in the wings to our north and east. its likely we will start off reasonably mild, but this could aid us into developing a cold spell imo. however, its still a little far away to be pinpointing details onto it, and things could change, but its just a thought.

Edited December 4, 2009 by azores92

[Pennine Ten Foot Drifts]

Well, on a light-hearted note, TEITS, that's stating the bleeding obvious ...unfortunately nobody on this planet has yet managed to perform that particular trick!

So we look as well - or some of us do - at what the tendency in recent years has been, which is to continue to offer the theoretical possibility (which there certainly still is), but never really to deliver it in practice...that is to say, in profound and/or prolonged cold terms, of a sort which used to come along from time to time. It was always the exception, the probability was never high; but as you would expect in an even statistical playing field, now and again it came off. And inevitably that begs the question of why it has been so long - much longer than ever before in the CET record, as I set out here: .

In another post, TEITS, you talked of "our previous bad luck", and suggested that assuming that it will continue "isn't really scientific". I would gently suggest that ignoring the current run of 'bad luck' is also not very scientific, since its unprecedented length suggests that there has been, in fact, more than just 'bad luck' going on here.

I must admit osmposm I missed that post, and I think it neatly encapsulates what many people secretly believe but are reluctant to accept. This morning's models again show 'potential', but I bet if we dug up the relevant threads for the past five years for the period late Nov.-mid. Dec there would be many posts talking about how 'things look different/promising/better this year compared to the last few'............., and we all know what actually transpired. And I have to say that what I am seeing now in the models, and what I have been seeing for the last few weeks, is nothing different in the reliable timeframe to recent previous winters. True the 'big one' we're all waiting for might be just around the corner, but as osmposm's figures show, the chances of it actually coming to fruition really are considerably less now than they were twenty+ years ago - the statistics prove it.

[Methuselah]

If anything's ever really 'nailed on' surely it's almost the case with the disorganized PV??? And, IMO, it's the state of the PV (and the resulting distribution of cold air 'oop north') that's the greatest cause for optimism:

For years, we've had occassional 'good' synoptics, but without any substantial sources of cold air? This time though, if things stay as they are, when the right synoptics arise, there will be some proper cold...Has there ever been a winter (with PVs in their present state) during which there has been no cold weather at all???

That said, I agree with Steve Prudence...FI is FI because it's so very highly unlikely to materialize; and 'plausibiliy' doesn't really mean much, either, IMO. And, in answer to Dave - it could well be the case that none of the runs or ensemble members is right? :o

I must admit osmposm I missed that post, and I think it neatly encapsulates what many people secretly believe but are reluctant to accept. This morning's models again show 'potential', but I bet if we dug up the relevant threads for the past five years for the period late Nov.-mid. Dec there would be many posts talking about how 'things look different/promising/better this year compared to the last few'............., and we all know what actually transpired. And I have to say that what I am seeing now in the models, and what I have been seeing for the last few weeks, is nothing different in the reliable timeframe to recent previous winters. True the 'big one' we're all waiting for might be just around the corner, but as osmposm's figures show, the chances of it actually coming to fruition really are considerably less now than they were twenty+ years ago - the statistics prove it.

True enough... :o

[Nick F]

You'd be hard pushed to get anything cold out of the 00z ECM and GFS ops, though I suppose you can seek solace in some of the ensemble runs. Think there maybe some imagination running wild in some of the posts - going to great lengths to bring cold that is clearly not in the offing!

I was slightly optimistic of a cold spell earlier this week, but the models have backed away from a ridge building to the NE and a S'erly tracking jet and instead we have a Euro/Bartlett developing into the medium range - as ECM and GFS support a mid-Atlantic trough with WAA over SW Europe.

We have a strong jet racing across the N Atlantic and N Pacific, which looks like lasting 10 days at least, so could be towards end of month until we see some cold potential.

I must admit osmposm I missed that post, and I think it neatly encapsulates what many people secretly believe but are reluctant to accept. This morning's models again show 'potential', but I bet if we dug up the relevant threads for the past five years for the period late Nov.-mid. Dec there would be many posts talking about how 'things look different/promising/better this year compared to the last few'............., and we all know what actually transpired. And I have to say that what I am seeing now in the models, and what I have been seeing for the last few weeks, is nothing different in the reliable timeframe to recent previous winters. True the 'big one' we're all waiting for might be just around the corner, but as osmposm's figures show, the chances of it actually coming to fruition really are considerably less now than they were twenty+ years ago - the statistics prove it.

100% agree with that post. We are pained to accept the inevitable and what has tended to happen in recent years as models back away from their FI cold uptopia set-ups!

[Glacier Point]

H5 GFS ensemble mean anomaly for days 11-15 picks out a distinctive 3-wave pattern with a 200m height anomaly over the Arctic and 3 separate upper lows - Pacific, Atlantic and Siberian. The operational ECM 8-10 day also shows this pattern.

3-wave patterns tend to be quite stable features and they generally retrogress (seems odd but the core of the lows gets pulled back west as energy running along the equatorward side of the trough gets absorbed into the middle atmosphere). The other steering factor is the large upper ridge centred over the Pole setting an anticyclonic flow around the higher latitudes. The GFS means from t168 onwards substantiate the retrogressing uppers - some way out but logical if we get the split vortex and Nino-driven lows maintain station.

As stated yesterday, the longer this persists, the chances of cold air backing west increase. Still not realistic within a 7 - 10 day timeframe but very, very significant hemispheric developments.

[cooling climate]

You'd be hard pushed to get anything cold out of the 00z ECM and GFS ops, though I suppose you can seek solace in some of the ensemble runs. Think there maybe some imagination running wild in some of the posts - going to great lengths to bring cold that is clearly not in the offing!

I think the extended ensembles of the 0z ECM run will show a very cold pattern developing.

plenty of positives to take from this mornings runs for a much colder pattern to develop from

around mid month onwards.

[Frosty.]

You'd be hard pushed to get anything cold out of the 00z ECM and GFS ops,

Thanks for saving me the bother of looking then. I missed the 18z run but understand it was a good one for coldies, how often does the following run bring things down crashing and burning.

[Iceberg]

Sorry to disagree with you Nick but there are positives for cold out of the 00Z ops.

I've concentrated on the ECM below simply because it shows things clearly.

As Pete said the split PV is highly likely now, this doesn't automatically lead to cold as I've said previously but it can.

During El Nino years we are never going to really get rid of the strong southern arm of the Jet and the chances of an Omega block are very slim. (I don't think we will see one of those this winter). However the southerly dive that GFS has been toying with in it's extended, extended version i.e 300+ does open the door for some very cold weather.

ECM is now showing exactly that on the chart below, the jet isn't going anywhere except southern spain and northern Africa on that chart.

I am in no way saying that it will happen, but there are signs that it might maybe 50%, this doesn't mean a 50% chance of cold though as we could end up with a slack low, HP and southerlies, but we could equally end up with blocking to the north dragging in something very cold come the latter part of the 15-18th of December.

So wet and windy to the 10th, pretty much nailed.

More settled weather upto the 15th, very likely, starting in the south and pushing NW across the the UK.

Divergency beyond this with either a return to wet and windy, continuing settled and rather boring or getting much colder.

[Typhoon John]

We seem to be entering a key point in the development of the Winter pattern. How exactly the vortex splits and where the vorticies end up will determin how things develop afterwards. At the moment it's far from clear cut but there are some encouraging signs that we won't end up with a deep vortex stuck over Greenland. It's also good to see the cold to our East building.

We're still on track with the potential for something special to develop by the end of the month but not before then. The models seem to be picking up on some of the signals and trying to shift the pattern too quickly but we're not quite there yet in terms of vortex split and GWO progression - there's a long way to and still time for things to go wrong.

But it's encouraging all the same - but then there always seems to be something to be encouraged by at this time of year!

[Climate Man]

Yes, great post. I believe you are spot on. The split in the PV and northern height rises are showing regularly and there is a fair chance of the building blocks falling into place.

[cooling climate]

In case this has not been posted before I think this is a excellent link that goes some

way to explaining the the relationships between the GWO, AAM and MJO.

It helped me to get a better understanding on these complex teleconnects.

http://www.esrl.noaa.gov/psd/map/clim/gwo_maproom_new.htm

Plus this one from Ed Berry.

http://www.deepconvection.com/11HPC/11HPC_Berry.ppt

[chionomaniac]

H5 GFS ensemble mean anomaly for days 11-15 picks out a distinctive 3-wave pattern with a 200m height anomaly over the Arctic and 3 separate upper lows - Pacific, Atlantic and Siberian. The operational ECM 8-10 day also shows this pattern.

GP, I find this post really interesting - on an analysis point of view.

Two of the three troughs we can put down to the split in the polar vortex. That leaves us with the Atlantic trough - the troublesome one. Why does that remain? Well imo it is due to the GWO pattern that you have been illustrating for weeks now. And if ever that we need an example as to why all teleconnections are important here it is. Well done for picking it out. Here I am praying for some positive frictional and mountain torques to add some positive GLAAM into the atmosphere and reduce that trough.

Patience and timing is what we need!

[Weather-history]

Definite pressure rise trend in the GFS ensembles for Manchester.

http://91.121.93.17/pics/MT2_Manchester_ens.png

[Radiating Dendrite]

I take it that if the high was to retrogress north (over us possibly) then we would be looking for a rise in pressure in the ensembles and then a slight drop as the high pressure core shifted further NW/NE?

It seems that trends are certainly starting to grow, the trough backing west, height rises in the artic and the Euro High drifting north. I am eagerly anticipating the 06z

[TEITS]

Think there maybe some imagination running wild in some of the posts - going to great lengths to bring cold that is clearly not in the offing!

Strongly disagree.

A cold spell might not be obvious in the model output but you can clearly see how one could develop. You have to take into account that the models in F.I will not precisely model exactly where the pressure systems will be.

Check the GEM at +168.

http://www.wetterzentrale.de/pics/Rgem1681.gif

Surely even you can see how a bitter cold spell could develop from that chart. The models have consistently hinted at a split PV with increasing heights to our N.

Im 80% convinced that around mid month HP will be influencing our weather. However whether this is HP centred over the UK or we see a bitter blast from the NE/E is still uncertain, yet possible!

[snowmadchrisuk]

Strongly disagree.

A cold spell might not be obvious in the model output but you can clearly see how one could develop. You have to take into account that the models in F.I will not precisely model exactly where the pressure systems will be.

Check the GEM at +168.

http://www.wetterzentrale.de/pics/Rgem1681.gif

Surely even you can see how a bitter cold spell could develop from that chart. The models have consistently hinted at a split PV with increasing heights to our N.

Im 80% convinced that around mid month HP will be influencing our weather. However whether this is HP centred over the UK or we see a bitter blast from the NE/E is still uncertain, yet possible!

I Agree totally in that you can clearly see how a cold spell could develop , but I'd like to see higher pressure to our North and low pressure to our South East to avoid the dreaded BA****

[bluearmy]

signs on the fi output of another east pacific ridge. maybe we have to go around the block again (2 to 3 weeks) and hope that the orientation of the atlantic jet and trough are better by then for us. the current trend is for the trough to back westwards in a week or so but it still wants to send energy northeastwards. double whammy for us - no chance of any cold via greenland height rise getting past this energy to bring a northerly and no way of heights rising over scandi to deliver an easterly. sorry, but i agree with nick F on this one. maybe a cold spell due to an inversion pre xmas but the chance of 'real cold' before the big day looks further away to me.

[Iceberg]

Well the 06Z is out (at least to 144Z) and the reliable timeframe shows the Jet diving south after leaving N.America from here a settled spell is pretty much guaranteed and at long last an end to the constant LP conveyor.

[snowmadchrisuk]

6z FI Is not a good run unless you like Euro high's I know this doesn't start until FI but there again nor does our pressure rise. Also 6z FI removes the blocking up North and places deep low pressure over Greenland. I expect this will be a mild outlier because it leaves the uk stuck it a mild rut, While to our East they have -25 850's .

Edited December 4, 2009 by snowmadchrisuk

[Guest North Sea Snow Convection]

Well the 06Z is out (at least to 144Z) and the reliable timeframe shows the Jet diving south after leaving N.America from here a settled spell is pretty much guaranteed and at long last an end to the constant LP conveyor.

That much is true I agree. And I am happy and relieved about seeing some light emerging now at the end of the November and into December 'dark tunnel'

Whilst quite a few things have to still fall in place to go a stage further in getting the cold spell that so many of us want, I don't go along at all with some of the outright dismissals that are being made atm.

The real analysis shows the possibilities - we are looking at a vortex split and -AO here - which is a lot different, for eg, to a temporary amplification in an Azores ridge to Greenland in a +AO/NAO situation and a 36 hour northerly (which is the absolute limit of expectation in that sort of scenario).

With a real arctic ridge, it is quite feasible for a mid latitude high to get absorbed by such a ridge. Whether it actually happens or not is of course debateable - but the chances of it happening cannot be simply totally dismissed.

Edited December 4, 2009 by North Sea Snow Convection

[Frosty.]

The 06z is a huge disappointment, we have another week of very unsettled weather and next week looks much milder than this week with temps between 11-13c most days, then we have high pressure building northeast through the uk with fine weather and temperatures returning to where they should be at around 7-8c 45f. There is no sign, no hint of anything wintry on the 6z run, even the 00z showed potential at the end but the 6z is a poor run from a wintry perspective although at least it shows an end in sight to the flooding problems, that is the only good news from this run.

[cooling climate]

I may well be wrong but I fully expect the 06z operational run of the GFS to be a mild

outlier towards the end of the run.

I just could not see the high sinking to the south like that, there would almost certainly

I think be cyclonegenisis underneath the high.

It is however deep FI at that range and must be taken with the proverbial amount of

salt, however the trend again is excellent for cold prospects.

[Stu_London]

The 06z is the most plausible operational run I have seen in the last 3 days.

It is a good demonstration of how many cold solutions in FI have gone the way of the pear.

[Shunter]

NOAA have completely discounted the 00z GFS run this morning in favour of the ECM solution ( 3/12 & 4/0 runs ).

http://www.hpc.ncep.noaa.gov/preepd/preepd.html

[reef]

Strongly disagree.

A cold spell might not be obvious in the model output but you can clearly see how one could develop. You have to take into account that the models in F.I will not precisely model exactly where the pressure systems will be.

Check the GEM at +168.

http://www.wetterzentrale.de/pics/Rgem1681.gif

Surely even you can see how a bitter cold spell could develop from that chart. The models have consistently hinted at a split PV with increasing heights to our N.

Im 80% convinced that around mid month HP will be influencing our weather. However whether this is HP centred over the UK or we see a bitter blast from the NE/E is still uncertain, yet possible!

Theres a bit of irony here. You reply to Nick who suggests theres a lot of imagination is involved in some posts and then bring out a chart from the FI-end of the GEM (a not particularly reliable model anyway) suggesting how it 'could' proceed to a cold spell. Problem is that model goes out to T+240 and it leads to... mild southerlies:

http://www.wzkarten.de/pics/Rgem1921.gif

And T+240 is no better either:

http://www.wzkarten.de/pics/Rgem2401.gif

As it stands its safe to say theres nothing in the next 7 days that will bring anything even remotely wintry. The annual chase for the carrot on a stick has begun it seems. FI will always be dominated by chaos theory, even in the mildest winters there will always be T+300 easterlies. Its sometimes good to be positive, but you might as well say every chart could lead to a cold spell if you go this route.