In Depth Model Discussion, Analysis and Summaries

[shedhead]

Beijing has actually updated and is going for largely blocked weather, though I'm not sure the blocks are in quite the right position for cold?

http://cmdp.ncc.cma....203GLZ500L1.GIF

How accurate have these forecasts been out of Beijing? Hard to have a great deal of confidence when they can't even get todays date correct...22nd??

[Glacier Point]

Or are they simply based on 'what happened before' i.e. taking years with similar to present MJO conditions and plotting the average of what subsequently happened?

you got it. What is interesting is how well these have verified since October. One would have thought, the further away from the event the more diffuse the impacts, but apparently still remarkably good hemispheric fit nearly 60 days after the event, and with a strong polar vortex which has only had subtle differences in terms of the polward positioning of ridges and troughs.

Edited December 20, 2011 by Glacier Point

[syed2878]

This article on whatsupwiththat said the november amo went neggertive since 1996.

[Gavin P]

How accurate have these forecasts been out of Beijing? Hard to have a great deal of confidence when they can't even get todays date correct...22nd??

For some reason they are always dated 22nd of the month.

As for reliability, I've not been looking at this model long enough to say, but I do prefer this model and the JAMSTEC model to CFS and ECM, personally.

[Downburst]

Beijing has actually updated and is going for largely blocked weather, though I'm not sure the blocks are in quite the right position for cold?

http://cmdp.ncc.cma....203GLZ500L1.GIF

Position is good there for British Isles to experience cold from a blocked north atlantic if it comes off. So pressure modeleratly higher then normal to your north on average, lower to your south on average. Blocked.

[03jtrickey]

you got it. What is interesting is how well these have verified since October. One would have thought, the further away from the event the more diffuse the impacts, but apparently still remarkably good hemispheric fit nearly 60 days after the event, and with a strong polar vortex which has only had subtle differences in terms of the polward positioning of ridges and troughs.

Thanks GP, this is really helpful.

[Nick B]

Beijing has actually updated and is going for largely blocked weather, though I'm not sure the blocks are in quite the right position for cold?

http://cmdp.ncc.cma....203GLZ500L1.GIF

The key word in the model here is 'Mean', I think. Even if accurate, this chart covers quite a long period and during that time there will be fluctuations in exact positioning of blocks, and would allow for some pretty good cold spells for our part of the world... if it were to verify. I would say it would allow for undercutting lows and battleground snow scenarios, especially if a nice big slab of cold air were sitting waiting for any low pressure areas to approach. I would happily take that chart as a summation of January to March.

[Alex]

you got it. What is interesting is how well these have verified since October. One would have thought, the further away from the event the more diffuse the impacts, but apparently still remarkably good hemispheric fit nearly 60 days after the event, and with a strong polar vortex which has only had subtle differences in terms of the polward positioning of ridges and troughs.

Hi GP, good to see lots of posting on here from you. My question is simple say we have a falling angular momentum, a decreasing ao but the nao stays positive. Firstly is this possible? One would assume that the nao would likely stay positive if the arctic stays cold with no sudden SSW. Secondly what would the impacts be for us?

Lastly say we have everything going for an Atlantic blocked pattern but a delay occurs until feb for this, will the increased solar strength have any impact as we have been used to December/January blocking in recent years and I assume there is a chance we could end up with a blocked pattern dissimilar to recent years and end up the wrong side or say end up with a Feb 2005 scenairo?

Sorry for the few questions, just getting my head around some of the bits. Cheers.

[Snowmad79]

I hope GP's update which ties in with a colder second half winter comes to fruition, I mean it's been a while since we had a good blocked setup in the typically colder second half of winter. It's keeps my optimism levels up to know better winter weather could still be around the corner.

[BLAST FROM THE PAST]

Thanks Stew, very interesting re the conflicting signals and your summary. 1st week of weakening +AO then week 2 transition to more blocked pattern.

I think and agree a timing of second week of Jan for anything different to occur to what we've had through Dec and likely to see in next two weeks seems about right. Although a weakening +AO and a shifting in the jetstream pattern may be classed IMO as a transition period as it 'could' lead to the change.

As an aside period 9-13 Jan is potential pivotal period for this winter IMO. Stromy period and maybe a 'trigger' LP to switch the pattern, either a channel LP or LP that moves almost on a NNW / SSE axis undercutting building pressure to our ENE and pressure rising quickly behind in the Atlantic/Greenland as the jet becomes meridional and main energy shifts south. Composites are not IMO a bad reflection of where we may head.

BFTP

Edited December 20, 2011 by BLAST FROM THE PAST

[Earth Wind and Snow]

I hope GP's update which ties in with a colder second half winter comes to fruition, I mean it's been a while since we had a good blocked setup in the typically colder second half of winter. It's keeps my optimism levels up to know better winter weather could still be around the corner.

Yes agree with that - last winters snow prospects ended here on 26th December and despite some promising charts at times after that - nothing materialised from Jan to March except some frosts - hopefully this year we will have some snowy weather to look forward to in the second half of winter

Finally I think we should respect GP's analysis as he obviously has more knowledge than most of us have put together - of course he cannot always be correct - if he was he would be a billionaire - however its analysis from people like GP, JH, BFTP etc.that helps people like me get a better understanding of a subject I love but unfortunately don't fully understand - keep up the good work guys...............whether your thoughts for second half of winter come to fruition or not I will enjoy learning from your analysis and thoughts.........

[Glacier Point]

A futher line of analysis here for January guidance.

Taking GFS 00z as being the less impressive stratosphere temperature forecast for day 10 at 10hPa:

shows the dipole like profile with warm air over Alaska and eastern Asia and cold air and Europe.

Composites for a similar profile during the last 10 days of December:

Rolled forward, they suggest 30 hPa values with the warmest air centred over the Canadian sector for January:

The tropospheric response is not overly impressive for the UK but this masks a distinct split in the month. Composites for these years taken on the 15th, 20th and 31st of January show a developing pattern, most notably a negative NAO look and note that upper low off Newfoundland:

January overall H500:

Splits:

Rolled forward again, February is a full blown block centred towards Scandinavia. Atlantic once again featuring low pressure.

A note also for angular momentum. The latest relative and total angular momentum plots depict a decrease in mean zonal westerly winds across the mid latitudes. This has been present since mid November and marks the end of the raging westerlies that have bulldozed any hint of blocking. This doesn't mean blocking will take root everywhere and anywhere. We have just returned to normal flow conditions which should allow for more amplification and perhaps the underlying patterns to emerge.

All of which underlines the case for a steady pattern change mid January although we are already getting hints in the modelling that there is getting underway - those changes being most obvious to us in terms of troughing in the western Atlantic and trough diving into Europe, -NAO and blocking starting to develop North Atlantic to Scandinavia in time.

Edited December 21, 2011 by Glacier Point

[UV-RAY]

As ever GP a most enjoyable read even if most of it went over my head One quick question, would you expect any blocking pattern to be NE based or from the East?

[Glacier Point]

Those composites for the stratospheric profile appear to suggest a northerly route to start with a trough over Europe, then shifting round to more of an easterly during February. This more or less ties in with the other lines of analysis, and of course the winter forecast.

[phil nw.]

Thanks GP.

So if things follow those comps.the first change would likely be the Euro high being pulled north West and a Scandi trough digging into Europe as the flow becomes more meridonal.

Hints in recent output of some Atlantic ridging and Scandi troughing but the current pattern looking to flatten the first attempts.

[Isolated Frost]

Interesting stuff as we currently enter a very mild zonal phase, without doubt there will be a shift which I believe will see progressively colder conditions for Eastern and then Southern Europe, but I don’t believe we will see the complete erosion or displacement of the now well established PV.

It seems you're talking more with a mod*rn winter based view rather than the forecasted expectations, we see strat warming (by no means a ssw) across the siberian/alaskan part of the arctic over the next few days and it does seem that the arctic high will ridge more closer towards the geographical pole itself. That pv over greenland, possibly moving into scandi seems to be flimsy and fragile in my opinion, and with the subtropical ridge carrying colder air now on it's northern periphery, I do feel as if heights may well build towards Greenland as we progress through January.

It's not a progressive pattern when compared to your mod*rn winter theory periods, the atlantic gradient should simmer down and then heights will gradually build to the nw, the ssw looks a fair favourite in mid-jan and so I do believe that with some tampering with positioning of the pv and movement of that pfj, we could be in for a noticeably colder final half of winter.

And I must say, for your signature, it's like it's 2007 all over again... the stratosphere is going to play an important part in the shaping of the final two months of winter, and we shall definitely see who turns out to be correct in it all.

And thanks GP for them composites, rather likely in the scheme of things i'd say. End of the 'zonal dirge', as IB puts in so thoughtfully, will be soon I think. Game on.

[Isolated Frost]

I think at 9 or 10 you probably had a far greater understanding and maturity than certain older members here, IF!

Thanks chiono

Latest gfs run (I know it's not too wise to look into it without seeking the trends) shows that the arctic high ridges off nr n greenland, but that trough feature is nearer svalbard, scandi and so the main arctic energy flows into scandi, and e europe looking and what should progress afterwards.

The atlantic isn't active though- as opposed to some 'zonal express' expectations going round here.

The subtropical ridge seems devoid of much action, with a colder high, developing in canada/north us moving across easily through the relatively blocked atlantic- infact the only pfj action we can really see is that waa into w greenland, due to a 1040mb high just a few frames back.

I think a blocked atlantic for much of early january is the most likely option imo, with most atlantic systems shuttling n'wards, giving more unsettled conditions to northern parts, but a pretty settled outlook for southern parts, with the main arctic energy going into scandi/e europe...

Dry and mild for most, before some amplification and an overall slight pattern change, and it's all go imo. A long way to go, but the 'zonal express' is not on my mind.

[lorenzo]

I noticed a dip in Mountain Torque figures today.. seems quite sudden compared to the chart from a couple of days back..

Where would this be reflected in the models? Does this mean a lessening of the strength of the Atlantic Jet or indicate a shift south?

[sebastiaan1973]

Not looking good according to EC

[coldwinter]

An even bigger dip in mountin torque figures today, what effects could this have, surely a good sign?

[lorenzo]

Jet profile looking intense over Asia.

[Glacier Point]

Following on from last postings...the idea of height rises over Canada and the central North Atlantic having looked bonkers a few days ago, now looks like a real player.

You'll be now familiar with this idea of the MJO in October as a possible predictor to the winter ? Well, add December's mean pressure anomaly to that impressive portfolio.

Predicted from MJO composites..

Observed through 25/12/11:

On any measure, that is a high correlation score and, following equally impressive performance in October and November, we now have to give this method a lot of respect for January. The predicted pattern for Janaury based on those MJO composites..

This suggests the development of a substantive mean trough solution for the North-east Pacific, ridging into Canada (which is where our warming of the stratosphere will definately help), a mid Atlantic ridge and transfer of the mean trough currently over Iceland further south and east towards NW Europe (with a consequent rise in heights to the NE). The last bit I've bolded because I think it is the bit of most relevance to us in terms of how we benchmark model outputs in the coming 2-3 week period.

As a slight negative, angular momentum remains close to average, strongly positive frictional torques levering in westerlies across the sub-tropics and preventing a wholesale fall in relative angular momentum which would take the GWO into a more favourable phase 1-2 type orbit to set up blocking in the North Atlantic. That said, I would be favouring low pressure to take control with a much more NW-SE axis to the jet setting up with the potential for a number of northerly attacks for the UK.

[Cecil Hogmanay Melchett]

Thats a stunning composite for January.

doesn't look likely for the first week though IMO.

[lukemc]

Thats a stunning composite for January.

doesn't look likely for the first week though IMO.

Wow looks good to me - at least if you like cold and snow - good things come to those who wait I am sure your time will come!

Luke

[Tom Montalbano]

Hi Stewart,

Really interesting reading on those composites, as you say they look a pretty good match. As Nick S stated, on the MO thread, ECM seem to be picking up a signal for the beginnings of a more amplified flow upstream, in around a weeks time. You can see this happening on the NH charts for t144/168 , below:

http://www.meteociel...H1-144.GIF?26-0

http://www.meteociel...H1-168.GIF?26-0

Do you feel that ECM are calling this right, timescale wise?

It would certainly start to match the Western part of that January pressure anomaly analogue, i.e Eastern Pacific, Canada/U.S. Then hopefully that amplification eventually spreading to our side of the Atlantic with the axis of the jet tilting NW/SE and a trough digging down through us, into Europe.

Regards,

Tom.

Edited December 26, 2011 by TomSE20