1536 replies to this topic

[SteveB]

Don, on 22 December 2009 - 22:07 , said:

Thanks Stuart. Liking the sound of your thoughts for January! The only thing that's concerning me slightly at the moment is the recent increase in solar activity, although I can't say I really know much about it.

It is annoying, but will have little effect on our weather. And even with the activity, it still at low levels.

[Optimus Prime]

Isn't there something like a 5 year lag in Solar output from sun to earth?

[SteveB]

Optimus Prime, on 23 December 2009 - 11:20 , said:

Isn't there something like a 5 year lag in Solar output from sun to earth?

There is a general consensus that there is a lag, but nobody really knows what the time span is. Many have guessed & 5 years sounds fair enough.

Edited by SteveB, 23 December 2009 - 11:25 .

[badboy657]

SteveB, on 23 December 2009 - 11:24 , said:

There is a general consensus that there is a lag, but nobody really knows what the time span is. Many have guessed & 5 years sounds fair enough.

i think maybe 3 years i think the effects are being felt right now but not here in southern england lol.

but on a serious note america and most of europe without jumping the gun to much 2008/2009 and maybe 2010 looking alot different to years proceeding thease,

so although a little activity on the sun and with it set to go quiet again in the next day or two who knows,

but where in a minimum the last time this happen ws in the mini ice age maybe we will not suffer as much but another couple of year and where know for sure.

im certain it causes effects with the jet and this is one big factor in a cooling climate.

but to be honest im waiting to see how this winter turns out

and merry christmas.

Edited by badboy657, 24 December 2009 - 00:32 .

[BLAST FROM THE PAST]

There is a lag with the solar irradiance but effects from the suns magnetic fields and disturbances are felt almost real time. The slight waking up of the sun will only send out disturbances bringing stormy periods. Reminders of what IMO has set up this winter and last winter. Solar and lunar driven pattern... The jetstream heading south [has been for 3 years now], the approx 36 year Perturbation cycle and since Feb 2007 been in La Nina domination phase. This cycle snugly fits with the NAO and when in La Nina domination state a -ve NAO cycle dominates. -ve PDO IMO directly affects the El Nino effect as we see this winter. There is lots more to it but that is the very basic gist

BFTP

[SteveB]

BLAST FROM THE PAST, on 24 December 2009 - 10:53 , said:

There is a lag with the solar irradiance but effects from the suns magnetic fields and disturbances are felt almost real time. The slight waking up of the sun will only send out disturbances bringing stormy periods. Reminders of what IMO has set up this winter and last winter. Solar and lunar driven pattern... The jetstream heading south [has been for 3 years now], the approx 36 year Perturbation cycle and since Feb 2007 been in La Nina domination phase. This cycle snugly fits with the NAO and when in La Nina domination state a -ve NAO cycle dominates. -ve PDO IMO directly affects the El Nino effect as we see this winter. There is lots more to it but that is the very basic gist

BFTP

Hi Blast,

Where do you think we will go from here as far as cycle24 into cycle25 is concerned. Do you think this is cycle24 peak?.

[Glacier Point]

http://raleighwx.eas...htAnomalyNH.gif

http://raleighwx.eas...htAnomalyNH.gif

Long range ensemble mean height anomaly tools day 11-15 have, if anything, become more aggressive towards height rises further north building into Greenland. If there is a weakness here, the models are not showing it.

[Jim_AFCB]

To answer Steve B's question - Cycle 24 is just getting underway. Solar minimum looks to have been Dec 08, Cycle 24 max is likely to be about 2013 or so.

[BLAST FROM THE PAST]

SteveB, on 24 December 2009 - 15:44 , said:

Hi Blast,

Where do you think we will go from here as far as cycle24 into cycle25 is concerned. Do you think this is cycle24 peak?.

Merry Christmas all...Steve 25 anticipated to be MAUNDER minimum values. Cycle 24 will be building but weak and fairly long.

BFTP

[pyrotech]

BLAST FROM THE PAST, on 24 December 2009 - 23:28 , said:

Merry Christmas all...Steve 25 anticipated to be MAUNDER minimum values. Cycle 24 will be building but weak and fairly long.

BFTP

I agree it will probably be weak, for more on the effects of solar min for uK see http://forum.netweat...37&qpid=1630978

Merry xmas all and freesing cold new year !

Edited by pyrotech, 25 December 2009 - 00:20 .

[Steve Murr]

I thought id tag this one onto the model output this eve-

Since the advent of the internet & the 'archives' on the forum every year since around 2000- even back in the snowatch days on the BBC forum ( some will remember this) we have all referred to Winters of old, the 63's, 47's, 79's ,85's etc etc- We place these with fond memories close to our hearts & are we are all very quick to post up images of what used to be-

Since the advent of this -
http://www.wetterzen...cka20091216.gif

some 10 days ago where the first pressure rise over greenland developed -this winter has had a whiff of a classic about it-
Weary seasoned posters would have been sceptical about the pattern redeveloping in such a short space of time- especially with such familiarity as the last evolution, however as we edged to Christmas day & now almost beyond we see a potential 'classic' pattern developing- which in my opinion has a BETTER chance of sustaining cold & the UK seeing widespread snow- ( we havent done half bad this time round though)more of that in a moment & the reasons why-

Firstly the evoltion thats being progged for the early part of next week is marginal at best, dont get me wrong we have a chance of something widespread, but as it stands the angle of attack, surface cold ahead of the front & upper air conditions do NOT favour a widespread snow event-

If we take the ECM 120 which seems the middle ground-
http://www.meteociel...H1-120.GIF?25-0
We see that the system moving along the channel bears the resemblence & hallmarks of that classic snow event in the making- but we are missing the vital ingredient- HP to our NE...
We have seen a lot of Southerly tracking lows already- both this year & last year- the shallow shortwaves that skip along the coast- however the South & south east have seen rain events from ALL these- even central areas havent favoured much better-

Take this chart for instance from the 8th of Feb this year-
http://www.wetterzen...00120090208.gif
The UK in a cold run of Northerlies & very cold surface air prevailing over the UK- that shortwave undercut some of the UK but the cold got lifted out to quickly for most- it was a quick snow to rain event for nearly all- snow lasting less than 20 mins!!

This has been the plight of the UK for some time-
now look at a couple of classics-

http://www.wetterzen...00119820108.gif JAN 1982- the Irish & welsh should have fond memories here-

http://www.wetterzen...00119960206.gif Widespread snow over the central belt of the UK-

http://www.wetterzen...00119781230.gif THis lead to one of the most significant blizzards over the UK for many many years-
So what have we learnt-
Undercutting troughs- even if they are elongated require HP DIRECTLY to the NE to force the dry air undercut at the surface- with the only exception being if a shortwave is traversing EAST under a East based iceland block ( again more about that later)

Back to the ECM 120-
http://www.meteociel...H1-120.GIF?25-0

The trough over Norway is cutting the supply of cold off from the Scandi region- where the coldest airmass originates from-
Sure we have a cold feed from the East but just not cold enough-

taking the 18z at face value its a total rain event for the UK, taking the ECM at face value its a rain event for most in the South - with snow over the North & west & elevation a great assist here-
Is there still hope for the mid part of next week- well yes- but we will need to be VERY VERY lucky with a quick flip back from the models to a track along the brest peninsula through & out East- even then thats not the end of the story - we will need minimal north sea track as well from an upper air perspective-

Excluding what I think is dodgy outputs this eve I think there is a zone from yorkshire through to wales that does see snow ( mainly away from the East coast), although PERHAPS not as significant as initially touted ( I hope im wrong with that)

This wasnt the reason of this post though really- its the background signal though & for the people that want to decipher things into more detail the finite differences between a Greenland block & Iceland block- Also how the amplification of the jet determines a Northerly over an Easterly- even though the blocking seems to be in the same place- ( & why a circular iceland block favours a Channel low as opposed to a Greenland block which favours a polar low)

The background NH signal is a negative AO which if by now you dont know I will breifly summarise-
High pressure at the pole & low heights forced into the mid lattitudes- by definition this then means that theres LOTS more air coming south out of the pole: in this situation as you will usually have 3 or 4 standing waves along with the higher polar pressure zone- - The eastern sides of the standing waves have huge amounts of COLD air advection moving South & the western sides have lots of warm air advection moving North-
Note:- this is why in negative AO months the UK can be warm as we can still be on the wrong side of any potential blocking-

What we are seeing now at day 5-10 is a rapid change in the modality of the NAO ( after a brief rise ) -
http://www.esrl.noaa.../images/nao.png it will appear here in the next few days-

The modality change is showing that Greenland has a rapid rise in Pressure & areas towards the azores will drop pressure- the significance is that the AO is dropping to 3/4 Standard deviations below zero & the NAO is heading that way-
this is the PERFECT menu of cold for NW europe-

Teleconnections however do not give us 'local detail'-- local being the United Kingdom- this boils down to what type of blocking actually exists- as there are Many types-
East based NAO, West Based NAO, mid atlantic block, iceland block-....

What we saw develop last week was Clearly a Greenland block- Very central to Greenland---- this & west based Greenland Highs favour the NW UK & Scotland & NI- as they generally end up with NW winds over the UK-

Fax for the 20th- 2009
http://www.wetterzen...cka20091220.gif

Reanalysis for 9th dec 1981-
http://www.wetterzen...00119811209.gif

Note the central Greenland blocking - almost west based NAO-
note the flow over the UK is generally NW- with the trough also west over scandi-

Going back to last week the reason the pattern loaded to a Northerly & even N.westerly was because of the initial jet profile & the fact that it was VERY amplified North / South-
We got a flow that went directly north up western greenland then returned sharp south southwards over iceland- hence the Northerly flow & how the vortex got shunted to the NE part of the UK-
Also importantly here - note how close the shortwaves got to the southern part of the UK in the southern arm of the jet--- they didnt....
because the Northerly flow kept them a long way South-
http://www.wetterzen...cka20091221.gif

look towards Portugal......

We now though see a different pattern setting up which as I mentioned earlier seems to be the same- but with a couple of key differences-

*) NAO block (high pressure) looks to be positivly tilted & circular as opposed to the squashed sharp North /South oval shape it had last week-
*) at a SLIGHTLY more favourable locale V last week ( we are talking more EAST based)
*) Pressure core looks to be centred towards the SE coast of Greenland
*) THe jet flow off the states is less amplified over the top & doesnt look to cut a sharp gradient back directly south through iceland like it did before-

What does this all mean-

Look at these 3 charts-

ECM 168- http://www.meteociel...H1-168.GIF?25-0


GFS 168-http://91.121.94.83/modeles/gfs/run/gfsnh-0-168.png?18

GFS ENSEMBLE MEAN at 144-
http://www.wetterzen...ics/Rz500m6.gif

They all agree on a curved East ISH based NAO block that is in closer proximity to Iceland than we have seen in many a year...

What does this all mean-

It means the background signal for cold for the UK is developing at around 96-144, once completed it will force the pattern to where we want it & because of THIS angled flow of set up- ( note the waeker amplified flow off the states)
http://91.121.94.83/...snh-0-96.png?18 IE more positivly tilted -
the net result will be a more Easterly component in the air as its curving westwards on the southern side of the high as opposed to southwards before-

this will eventually deliver for everyone, with a HIGH chance of a snow event coming up from the South west into Southern UK- this is why both models- ECM & GFS are modelling this-

GFS 192-
http://91.121.94.83/...nh-0-216.png?18 notice the block centring more over Iceland- ICELAND BLOCK= Perfect for the UK-

ECM-
http://www.meteociel...H1-240.GIF?25-0 Almost an Iceland block- but the key is the curved flow over the atlantic- the shortwave will roll & Spin eastwards because its pathway is being vented & circulated from inflow on the NE quadrant > NE >SW & inflow from the SW quadrant >SW> NE-

In Summary then-

I think we are on the eve of a very special period in UK weather- MAYBE a classic in the making, I think the classic charts come though in the latter half of next week towards the weekend with an attack from the NE & the south west-
If we get a wdespread snow event from the inital low pressure tracking along the channel then treat it as a bonus for the UK.............
fingers crossed this could be the one-

If we get the iceland block I would rate a higher chance of seeing a temporary link up with a Siberian /arctic type high pressure that has been lurking all winter-
S

[danm]

Steve Murr, on 26 December 2009 - 00:45 , said:

I thought id tag this one onto the model output this eve-

Since the advent of the internet & the 'archives' on the forum every year since around 2000- even back in the snowatch days on the BBC forum ( some will remember this) we have all referred to Winters of old, the 63's, 47's, 79's ,85's etc etc- We place these with fond memories close to our hearts & are we are all very quick to post up images of what used to be-

Since the advent of this -
http://www.wetterzen...cka20091216.gif

some 10 days ago where the first pressure rise over greenland developed -this winter has had a whiff of a classic about it-
Weary seasoned posters would have been sceptical about the pattern redeveloping in such a short space of time- especially with such familiarity as the last evolution, however as we edged to Christmas day & now almost beyond we see a potential 'classic' pattern developing- which in my opinion has a BETTER chance of sustaining cold & the UK seeing widespread snow- ( we havent done half bad this time round though)more of that in a moment & the reasons why-

Firstly the evoltion thats being progged for the early part of next week is marginal at best, dont get me wrong we have a chance of something widespread, but as it stands the angle of attack, surface cold ahead of the front & upper air conditions do NOT favour a widespread snow event-

If we take the ECM 120 which seems the middle ground-
http://www.meteociel...H1-120.GIF?25-0
We see that the system moving along the channel bears the resemblence & hallmarks of that classic snow event in the making- but we are missing the vital ingredient- HP to our NE...
We have seen a lot of Southerly tracking lows already- both this year & last year- the shallow shortwaves that skip along the coast- however the South & south east have seen rain events from ALL these- even central areas havent favoured much better-

Take this chart for instance from the 8th of Feb this year-
http://www.wetterzen...00120090208.gif
The UK in a cold run of Northerlies & very cold surface air prevailing over the UK- that shortwave undercut some of the UK but the cold got lifted out to quickly for most- it was a quick snow to rain event for nearly all- snow lasting less than 20 mins!!

This has been the plight of the UK for some time-
now look at a couple of classics-

http://www.wetterzen...00119820108.gif JAN 1982- the Irish & welsh should have fond memories here-

http://www.wetterzen...00119960206.gif Widespread snow over the central belt of the UK-

http://www.wetterzen...00119781230.gif THis lead to one of the most significant blizzards over the UK for many many years-
So what have we learnt-
Undercutting troughs- even if they are elongated require HP DIRECTLY to the NE to force the dry air undercut at the surface- with the only exception being if a shortwave is traversing EAST under a East based iceland block ( again more about that later)

Back to the ECM 120-
http://www.meteociel...H1-120.GIF?25-0

The trough over Norway is cutting the supply of cold off from the Scandi region- where the coldest airmass originates from-
Sure we have a cold feed from the East but just not cold enough-

taking the 18z at face value its a total rain event for the UK, taking the ECM at face value its a rain event for most in the South - with snow over the North & west & elevation a great assist here-
Is there still hope for the mid part of next week- well yes- but we will need to be VERY VERY lucky with a quick flip back from the models to a track along the brest peninsula through & out East- even then thats not the end of the story - we will need minimal north sea track as well from an upper air perspective-

Excluding what I think is dodgy outputs this eve I think there is a zone from yorkshire through to wales that does see snow ( mainly away from the East coast), although PERHAPS not as significant as initially touted ( I hope im wrong with that)

This wasnt the reason of this post though really- its the background signal though & for the people that want to decipher things into more detail the finite differences between a Greenland block & Iceland block- Also how the amplification of the jet determines a Northerly over an Easterly- even though the blocking seems to be in the same place- ( & why a circular iceland block favours a Channel low as opposed to a Greenland block which favours a polar low)

The background NH signal is a negative AO which if by now you dont know I will breifly summarise-
High pressure at the pole & low heights forced into the mid lattitudes- by definition this then means that theres LOTS more air coming south out of the pole: in this situation as you will usually have 3 or 4 standing waves along with the higher polar pressure zone- - The eastern sides of the standing waves have huge amounts of COLD air advection moving South & the western sides have lots of warm air advection moving North-
Note:- this is why in negative AO months the UK can be warm as we can still be on the wrong side of any potential blocking-

What we are seeing now at day 5-10 is a rapid change in the modality of the NAO ( after a brief rise ) -
http://www.esrl.noaa.../images/nao.png it will appear here in the next few days-

The modality change is showing that Greenland has a rapid rise in Pressure & areas towards the azores will drop pressure- the significance is that the AO is dropping to 3/4 Standard deviations below zero & the NAO is heading that way-
this is the PERFECT menu of cold for NW europe-

Teleconnections however do not give us 'local detail'-- local being the United Kingdom- this boils down to what type of blocking actually exists- as there are Many types-
East based NAO, West Based NAO, mid atlantic block, iceland block-....

What we saw develop last week was Clearly a Greenland block- Very central to Greenland---- this & west based Greenland Highs favour the NW UK & Scotland & NI- as they generally end up with NW winds over the UK-

Fax for the 20th- 2009
http://www.wetterzen...cka20091220.gif

Reanalysis for 9th dec 1981-
http://www.wetterzen...00119811209.gif

Note the central Greenland blocking - almost west based NAO-
note the flow over the UK is generally NW- with the trough also west over scandi-

Going back to last week the reason the pattern loaded to a Northerly & even N.westerly was because of the initial jet profile & the fact that it was VERY amplified North / South-
We got a flow that went directly north up western greenland then returned sharp south southwards over iceland- hence the Northerly flow & how the vortex got shunted to the NE part of the UK-
Also importantly here - note how close the shortwaves got to the southern part of the UK in the southern arm of the jet--- they didnt....
because the Northerly flow kept them a long way South-
http://www.wetterzen...cka20091221.gif

look towards Portugal......

We now though see a different pattern setting up which as I mentioned earlier seems to be the same- but with a couple of key differences-

*) NAO block (high pressure) looks to be positivly tilted & circular as opposed to the squashed sharp North /South oval shape it had last week-
*) at a SLIGHTLY more favourable locale V last week ( we are talking more EAST based)
*) Pressure core looks to be centred towards the SE coast of Greenland
*) THe jet flow off the states is less amplified over the top & doesnt look to cut a sharp gradient back directly south through iceland like it did before-

What does this all mean-

Look at these 3 charts-

ECM 168- http://www.meteociel...H1-168.GIF?25-0


GFS 168-http://91.121.94.83/modeles/gfs/run/gfsnh-0-168.png?18

GFS ENSEMBLE MEAN at 144-
http://www.wetterzen...ics/Rz500m6.gif

They all agree on a curved East ISH based NAO block that is in closer proximity to Iceland than we have seen in many a year...

What does this all mean-

It means the background signal for cold for the UK is developing at around 96-144, once completed it will force the pattern to where we want it & because of THIS angled flow of set up- ( note the waeker amplified flow off the states)
http://91.121.94.83/...snh-0-96.png?18 IE more positivly tilted -
the net result will be a more Easterly component in the air as its curving westwards on the southern side of the high as opposed to southwards before-

this will eventually deliver for everyone, with a HIGH chance of a snow event coming up from the South west into Southern UK- this is why both models- ECM & GFS are modelling this-

GFS 192-
http://91.121.94.83/...nh-0-216.png?18 notice the block centring more over Iceland- ICELAND BLOCK= Perfect for the UK-

ECM-
http://www.meteociel...H1-240.GIF?25-0 Almost an Iceland block- but the key is the curved flow over the atlantic- the shortwave will roll & Spin eastwards because its pathway is being vented & circulated from inflow on the NE quadrant > NE >SW & inflow from the SW quadrant >SW> NE-

In Summary then-

I think we are on the eve of a very special period in UK weather- MAYBE a classic in the making, I think the classic charts come though in the latter half of next week towards the weekend with an attack from the NE & the south west-
If we get a wdespread snow event from the inital low pressure tracking along the channel then treat it as a bonus for the UK.............
fingers crossed this could be the one-

If we get the iceland block I would rate a higher chance of seeing a temporary link up with a Siberian /arctic type high pressure that has been lurking all winter-
S

Brilliantly informative post, especially for someone like me who is just learning what exactly to look out for beyond the blatantly obvious. Let's hope it all pans out in the way you are describing. We are long overdue a classic winter. Me being one month shy of 24, the only real severe cold spell i can remember is Feb '91. Feb '09 was the closest we've got since then down here in the SE, but not close enough.

Thanks Steve!

[Optimus Prime]

To compare this years current arctic blocking with previous years you can clearly make out there are some exceptional height rises over the arctic;


Compare this to the unsettled westerly winter of 1998/1999


December 2000 is the only date I can come up with since 1998 that had decent blocking action in the arctic;


The main reason why winter 2000/2001 wasn't as cold as what it could have been was because of a deep feature which had developed and ran up from the west


And heights lowered over the Arctic region.

Unfortunately the GFS N.Hemisphere charts aren't working at the moment so I can't see what's likely to happen over that region over the next 10 days but looking at what we got currently it's hard to see why this winter won't be cold.

[Steve Murr]

Evening ALL-

going on from yesterdays output/post- of note in the evolution now is the fact that the NAO is more a west based greenland block as opposed to last nights iceland block-



Its difficult to know where to begin tonight, so many posts, so much model evaluation-

I suppose seeing as nearly all the models have a grip on the 'type' of track the low is going to take then there isnt much point of disucssing it- other than to say that I still think the trough will elongate along the channel perhaps giving a better profile of colder air to the central & possibly southern portions of the UK-
Its also pointless to post up maps for snow as the track/ elongation of the trough has a direct impact on the PPN distribution- however the marker laid out of Central wales has been pretty rigid from the start & again I cite that this area could be the hardest hit- especially at some minor elevation-

The subsequent evolution then becomes almost tantalising for everyone because if the 'proper'cold is unleashed from the East then that will certainly keep everyone happy-

We do have a problem though - as this surge from the East that I highighted the potential for last night has a rather annoying posive tilted shortwave sitting in the flow over southern Norway-
here it is firmly in the way on the GFS at 150-

http://91.121.94.83/...nh-0-150.png?18

now, no amount of willing from the residents of NW are going to force it South east- it needs to get pushed that way-
Also VERY VERY important here is the fact that when the Siberian/ artic high starts ridging west we do NOT have an infinite timeline to delivery the Easterlies-
We have a window of about 24/36 Hours tops- After this the block that origially started moving wsw piles up on the Eastern flank of the shortwave - the westerly vector then just loses its momentum & things start to head south ( yep you guessed it- towards central Southern Europe)

WHo remembers this- the huge failed easterly-
http://www.wetterzen...00120070220.gif

See the positive shortwave over Norway it will not just turn over & face the right way- the southern arm of the jet is moving NE from iberia-

Now look at this example-
http://www.wetterzen...00119870110.gif
The jet flow is moving SE through the UK over france - which on turn rotates the shortwave the way we want it- with the northern flank moving back to face ne> Sw NOT AS WE SAW IN 2007 SE>NW.

Its going to be VERY hard to get an Epic easterly from this ( after the initial set up)
the shortwave moving into the SW approaches at around 162 is coming in at EXACTLY the angle we dont want it- because its NE quadrant is acting against the force of the siberian high moving SW-

Ian browns favourite this one- although another epic fail-
http://www.wetterzen...00120010203.gif
looks great but the southerly jet moving NE kills the flow stone dead ( even though shetland did well out of it)
http://www.wetterzen...00120010204.gif

TO Deliver an easterly we need a flow around t160- that goes either miles & miles further south so a shortwave undercuts the trough over Scandi & supports the cold moving west or the Iberian ridge is much further west & actually that shortwave heads up still NE but it goes towards iceland- as the jet will loop up then back SE like we want it-

In all reality whilst it looks great the killer may well be the southern arm moving North over the atlantic which would again be typical of the UK's luck- with the motto if anything can go wrong it will- even with a cut off greenland high thats now modelled as being slightly more west based & not an iceland block.....

in Summary- plenty available to keep up on our toes especially between 42-96, thereafter a slight lull- but good consensus in modelling of a NE flow, then the probability of the jet sweeping it away to leave us at best with SE winds-

Best chance of sustained cold from the East is if the upper trough gets undercut as it will force it west ( GFS ens PTB 13)

cheers
Steve

[BLAST FROM THE PAST]

Great analysis Steve..as usual.
Now I think the models have it wrong with the sustained SW over Norway....I expect movement of this to allow bitterly cold NE'lies.....AFTER NEW YEAR! Expect a different picture come Tues and for Big Steve's favoured outlook. The real cold in my method isn't due until 3rd onwards.

BFTP

[Sno' problem]

Stunning posts there, really appreciated!

[Glacier Point]

One of the eye-taking developments at the moment is some extreme cold pooling over Scandinavia within the 7-10 day timeframe.

Both GFS and GEM ensemble mean height anomalies programme an exceptionally strong positive height anomaly over Greenland and wedge of cold air drawn out of northern Siberia into the longwave trough t168:



This contains some exceptionally cold air, of the order -20C to -28C 850 hPa values. Ensemble means show this as 850s between -12 and -9C anomaly.



The synoptic pattern thereafter will decide whether or how far west that cold air gets.

As per postings of late, the surge in angular momentum during the middle part of December will leave mountain and frictional torques as the likely determinants for the movement of the Global Wind Oscillation through phases 0-5-6-7. Phases 7 and 0 trend the blocking ridge further west. Phases 5 and 6 trend the blocking ridge further east. Within a 10 - 15 day timeframe, the GWO is likely to shift from orbit in phase 0/7 towards phases 5 and 6 as angular momentum increases once more. Model guidance and assessment of teh GWO suggests a phase 0-7 solution for the first third of January, possibly migrating towards phases 5-6 middle part of the month.

The further east the block, the greater the probability of undercutting lows triggering westward advection of the cold upper pool. Therefore, reasonable expectation that we will see at least some westward motion of that deep cold air, potentially resulting in a very severe spell of wintry weather middle to later third January, in addition to the potential within the more immediate timeframes. However, this is unlikely to be a rapid advection as heights over Scandinavia will be hindered by the polar vortex trending for mean trough solution. The key though is the likely duration of this pattern as it has every chance of being sustained over the large part of January.

[johnholmes]

thanks Stewart-I must agree with most of your conclusions although I'm still not certain that we won't get a rather more Atlantic flow for a time, but mainly rPm air other than the far south where temporary Tm inputs would be likely. The majority of teleconnections to me seem to suggest that, even if we did not have this quite intense cold pool you draw attention to, then the overall pattern would suggest blocked in some area north of the UK for longish periods.

[Glacier Point]

The ocean-atmosphere coupling continues to advertise a prolonged below average spell of winter weather, coinciding with our coldest period of the winter.

Latest TAO Triton mean zonal wind flow data plot is very interesting and might suggest that we may see a rapid MJO wave-related progression of the ocean-atmosphere coupling which preserves a convective signal east of the Dateline. Notice on the plot below that the westerly wind burst centred east of 180 degrees is continuing (solid -NAO signal) whilst easterly winds (tropical supression) are developing across much of the tropical Indian Ocean.



This ties in with the rapid migration of the MJO, now centred in phase 3 with traceable convection associated with this tropical wave in the eastern Indian Ocean. Notice on this plot the convective activity centred east of the Dateline:

http://cawcr.gov.au/...m/OLR/m.3d.html

http://cawcr.gov.au/...Last40days.html

What this tends to suggest is that any Nina-ish type flow is going to be very restricted and that the atmospheric system is being more responsive to forcing from El Nino.

Total and relative angular momentum has fallen in line with a return of convective signal to the Indian Ocean with much of this removal of westerly winds resulting from negative mountain and frictional torques:

http://www.esrl.noaa...m.sig.90day.gif

http://www.esrl.noaa...0day.gif<br />
http://www.esrl.noaa...0day.gif<br />
http://www.esrl.noaa...ltauf.90day.gif

Mean zonal westerly wind anomalies persist across much of 20N-35N in the Pacific however indicative of El Nino conditions. Taking the state of torques and persistent wind flows, it is likely that any falling off of angular momentum has likely bottomed out with the next move upwards.

Frictional torques are likely to remain close to or below average c/o the west wind anomaly in the tropics and inverted pressure patterns which drive the negative torque. As frictional torques largely govern the magnitude and sign of mountain torques, it is unlikely that mountain torques will spike very positive over the next 10 days or so.

This should ensure that the Global Wind Oscillation orbits in low amplitude phase 0-7-6-5, potentially becoming snagged around phase 5-6 towards mid month. At present, the GWO is in phase 0 which teleconnects to the projected pressure anomaly pattern across days 6-10.

http://raleighwx.eas...htAnomalyNH.gif

Composite reanalysis for phases 5-6 indicate that the GWO will trend the mean blocking ridge to work its way back east towards days 11-15, towards Iceland with lows being forced underneath the block. The GFS ensemble mean height anomaly for this period (500hPa) tends to support this notion:

http://raleighwx.eas...htAnomalyNH.gif

Temperatures across this period are likely to remain depressed, particularly so during days 6-10 and not returning to above average during this time. Obviously, at this time of year, beow average conditions are likely to present potential for snowfall, especially given a pronounced trough just to the south west of the UK allowing surface depressions to attempt to work up into the cold reservoir of air lodged over NW Europe. In so far as our locale is concerned, I think mean troughs around NW Europe and depressed jetstream are the more probable, with a trough dropping into Scandinavia from the polar region.

Phase 6 composite for the GWO likely to represent the best fit for days 11-15 (allowing for greater negative height anomalies across much of northern Europe):

Edited by Glacier Point, 28 December 2009 - 20:42 .