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Guest North Sea Snow Convection

Actually breaking down that ratio further of CW/-AO and NAO the return is nearer 80% for when a CW occurs in Dec.

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

there really are some good thought provoking posts in here.

A 'model' no pun for the 'model thread' perhaps?

well we can but hope!

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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
It is actually interesting to try to come at the significance of stratospheric warming events in terms of increased chances of winter cold weather from another angle. And that is wrt the Canadian Warmings, which are early season events (Nov, Dec) and are linked to the intensification of the stratopsheric Aleutian High and the tropospheric Aleutian Low pressure system. The nature of these events are minor compared to MMW events and generally only leads to a very temporary reversal of polar westerlies at best, but are still enough to disrupt the polar vortex from its normal frequent winter routine for a while, and at an early stage of seasonal development, and thereby provide the opportunity for cold weather in the early winter and perhaps the better start to winter - may mean increased chances for a better stratospheric environment for the rest of the winter and all that entails for the weather patterns.

To try and illustrate this and correlate the importance of these CW's it is worth looking at some facts. There have been 22 CW between 1951/52 and 1981/82. But only 3 since 81/82! Now, we often speak of the warming trend of winters over this period since the 80's, so food for thought there perhaps?

Why should these figures be as they are though with the drop off in occurence of CW's?

How about shifts in the PDO? We know the PDO shift to positive was 1976 so a good lag time correlation to the figures supplied above in terms of the domination of El nino events (in turn in context of what I describe in a moment about the pacific).

We also know of the recent PDO shift back to negative, so what of the future here? The implications of a negative phase ie a cooler pacific and fewer El Nino's meaning less tropical activity over the longer term. This might have favourable implications for the Aleutian Low and a better pacific set-up which in turn might increase the frequency of CW's again. This in turn might alter the AO/NAO patterns with a better feedback set-up created in the late autumn/early winter. More -AO/NAO means more cold. So it is a virtuous cycle. In this suggested supposed scenario it might mean we would be getting back to a warmer winter stratospheric cycle and this in turn might mean that we are not relying on late season events to kill off a strong dominant PV and not having high latitiude blocking arriving only in late Feb/Mar and well into the Spring when it is too late for any real cold weather.

To back the possible significance of what I am suggesting - note that over all the above occurences seen of the CW , 75% of them saw a -AO/NAO over that period.

So if we can correlate this sort of link and trend with the CW, what could we do with the MMW? And thereby reinforce the importnace of having the stratosphere on our side for winter. The other aspect is that of the solar minimum and its disposition to the sort of intensity of SSW that we are currently seeing. Maybe some regime changes that might mean better times ahead.

That might put a little meat on the bones for discussion regarding Cheeky Monkey's question and SF's comments just now.

Thank you Tamara for that post. I haven't had enough time as I would like recently to look in detail at these events to look for any correlations. But that is truly illuminating. Hopefully we can see a pattern shift that can set up a new post modern type of winter. Who knows?

c

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Posted
  • Location: Cambridge (term time) and Bonn, Germany 170m (holidays)
  • Location: Cambridge (term time) and Bonn, Germany 170m (holidays)

Excellent post Tamara. The question for me, too, will be -

Will the PDO remain negative as in the 60s, or will it follow the ways of the past 2 coolings, i.e. short-lived events?

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Posted
  • Location: hertfordshire
  • Location: hertfordshire

post-7011-1234726113_thumb.png

Another view showing the zonal winds at the bottom of the chart (light green) appearing again after the positive westerlies (orange splodge for want of a better word) interrupted the propagation.

PS I picked this up from a post by Brogdale over on two.

Also if you look back through previous years it correlates very well i think with cold spells during those years and also some of the much milder winters such as 89-90 etc.

In conclusion i would say cold weather to definitely make a return.

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Guest North Sea Snow Convection

thanks guys - I think that sort of correlation gives some food for thought :D

At face value we see the 10hPa temps forecast to slide below average. We will all keep monitoring of course the zonal wind response in accordance with that. Maybe this will eventually provide the shake-up needed for those bottled up negative zonal anomalies we have been commenting on for so long now?. The 30hPa levels are slower to fall.

It is getting pretty late now for deliverance of coldest synoptics, nonetheless you can't help thinking that the trend back to a cold stratosphere, if verified, could ironically, provide the spark we need? March can still give some good times, even if not the best we would have liked.

temps.gif

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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
thanks guys - I think that sort of correlation gives some food for thought :D

At face value we see the 10hPa temps forecast to slide below average. We will all keep monitoring of course the zonal wind response in accordance with that. Maybe this will eventually provide the shake-up needed for those bottled up negative zonal anomalies we have been commenting on for so long now?. The 30hPa levels are slower to fall.

It is getting pretty late now for deliverance of coldest synoptics, nonetheless you can't help thinking that the trend back to a cold stratosphere, if verified, could ironically, provide the spark we need? March can still give some good times, even if not the best we would have liked.

temps.gif

The zonal winds are just pottering about slowly forecast to go above average within the next week.

post-4523-1234785231_thumb.png

The forecast propagation that was seen yesterday is no longer forecast today which is a shame because it was this type of propagation that I reckon would be needed to kick start the spring. Time for it to change again though closer to the time.

http://strat-www.met.fu-berlin.de/cgi-bin/...t=all&var=u

Looking at the 100 hPa level we have signs that the lower pressure keeping part of the polar vortex over western Greenland is heading west over Canada. I would think that this will allow the Azores high to ridge north and allow a northerly air stream to develop. Even though no true Greenland high is likely to develop this northerly airflow may still be quite potent and could possibly be a recurring theme if the main Siberian vortex stays where it is. Again something to keep an eye on.

Today:

post-4523-1234785702.gif

T+120:

post-4523-1234785729.gif

Certainly no sign of the strong northern blocking that one would expect if good propagation had occurred. I am very dubious at how much propagation of the residual negative zonal wind anomalies will and can occur. If it does require a kick start from above I doubt whether the upper / mid stratospheric vortex will be capable of reforming to enough strength for this to occur. However I will continue to monitor.

c

Edited by chionomaniac
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Guest North Sea Snow Convection

Perhaps just best to assume and restrict any expectations, at least for now, to just the amplified route for any northerly incursion(s) that any PV movement allows to return a colder feel. It at least looks as though the main theme of the winter is going to continue, after this milder interlude, with lower heights over europe than usual and the polar jet wanting to come south. Even if the northerly blocking does remain ellusive for us, and the MMW for whatever reason, despite its strength, doesn't pull the surface trigger.

Over and out for now - have a good day all :huh:

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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.

The zonal mean wind cross section forecast does seem to jump around a bit. However I am starting to pick up the first signs of a trend in that there does appear that propagation of the easterly winds that have been hanging around in the middle strat for the best part of the month are showing signs of working there way down and joining us. Now, if they do propagate down they still have to be in the right place to affect us with some high level blocking to create a more northerly or even easterly flow. Presently they look like they may just affect up to 70N.

T+120:

post-4523-1234859517_thumb.png

T+192

post-4523-1234859549_thumb.png

T+240

post-4523-1234859616_thumb.png

The Easterly winds that indicate the start of the MMW at 60N and 10 hPa are also forecast to revert back to westerly around the 21/21 February.

http://strat-www.met.fu-berlin.de/cgi-bin/...mp;forecast=all

That is an amazing 30 days easterly winds at this level which has never been recorded during winter before. Perhaps it is no coincidence that as the easterly reverses at this level that propagation finally occurs?

c

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Posted
  • Location: Ireland
  • Location: Ireland
The Easterly winds that indicate the start of the MMW at 60N and 10 hPa are also forecast to revert back to westerly around the 21/21 February.

http://strat-www.met.fu-berlin.de/cgi-bin/...mp;forecast=all

That is an amazing 30 days easterly winds at this level which has never been recorded during winter before. Perhaps it is no coincidence that as the easterly reverses at this level that propagation finally occurs?

c

Thank you for the update CN.

Even as a newcomer to this topic, the reversal of the winds back to westerly around the 21/22 February as indicated would seem like a very logical tigger so to speak, for the main thrust of propogation to the surface & is perhaps the very beginning of the period when we will start to experience the effects on the ground?

SA. :)

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Guest North Sea Snow Convection
Thank you for the update CN.

Even as a newcomer to this topic, the reversal of the winds back to westerly around the 21/22 February as indicated would seem like a very logical tigger so to speak, for the main thrust of propogation to the surface & is perhaps the very beginning of the period when we will start to experience the effects on the ground?

SA. :)

Hi SA

I think assuming that final propagation does occur, I think we may well be in the wrong place to benefit from it.

But it would go to show that remarkable events, and it has been extraordinary, don't always provide remarkable effects on a widespread global level - and our own location is very small under that perspective :)

Edited by North Sea Snow Convection
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Posted
  • Location: Brighton (currently)
  • Location: Brighton (currently)
Hi SA

I think assuming that final propagation does occur, I think we may well be in the wrong place to benefit from it.

But it would go to show that remarkable events, and it has been extraordinary, don't always provide remarkable effects on a widespread global level - and our own location is very small under that perspective :)

Are you expecting blocking to mainly take place in the Pacific, like Brickfielder suggested in his post yesterday?

Karyo

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Posted
  • Location: Ireland
  • Location: Ireland
Hi SA

I think assuming that final propagation does occur, I think we may well be in the wrong place to benefit from it.

But it would go to show that remarkable events, and it has been extraordinary, don't always provide remarkable effects on a widespread global level - and our own location is very small under that perspective :)

Hi Tamra,

Indeed, that is often the case and it's so very diffcult to get patterns in place that effect our own needle in the global heystack, but as you say, the event has been extraordinary.

Don't give up hope fully yet, you never know, we might just reap some of the effects.

SA. :)

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Guest North Sea Snow Convection
Are you expecting blocking to mainly take place in the Pacific, like Brickfielder suggested in his post yesterday?

Karyo

Hi Karyo

I think that might be right yes :)

The downstream effects of that on our side of the globle will keep us changeable with too much energy in the system

Edited by North Sea Snow Convection
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Posted
  • Location: Brighton (currently)
  • Location: Brighton (currently)
Hi Karyo

I think that might be right yes :)

The downstream effects of that on our side of the globle will keep us changeable with too much energy in the system

Thanks Tamara,

even if that happens i am glad that the propogation is now starting to reach it's final stage. I am keen to see blocking develop as a result of the stratospheric warming, even if it is on the other side of the world!

Besides, there are still possibilities for something tasty here. Another ((weaker) block in the northeast Atlantic could force the jet southwards or in a nw-se axis as the models currently show.

Karyo

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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.

It appears that the short term zonal wind forecast is up there with the best of the GFS as far as mammoth changes are concerned. Yesterday it looked that finally some significant propagation of the zonal easterly winds down to the troposphere was about to occur. Big, big change in the forecast today with that propagation forecast completely reversed.

Yesterday

post-4523-1234948509_thumb.pngpost-4523-1234948517_thumb.png

Today

post-4523-1234948552_thumb.pngpost-4523-1234948559_thumb.png

A large pinch of salt needed here.

c

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

hi Ch

yes this branch of meteorology is no different from any other, it has its spectacular successes but it will also get it wrong at times. There is no one perfect forecasting tool. All we can do is keep researching and trying to find the best combination of drivers/teleconnections into the nearer time scale synoptic outputs. Slowly, probably very slowly this will improve as we understand more. Its still a otally fascinating branch of it though.

3 out of 4 right this autumn/winter is not bad going in my view.

Edited by johnholmes
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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
hi Ch

yes this branch of meteorology is no different from any other, it has its spectacular successes but it will also get it wrong at times. There is no one perfect forecasting tool. All we can do is keep researching and trying to find the best combination of drivers/teleconnections into the nearer time scale synoptic outputs. Slowly, probably very slowly this will improve as we understand more. Its still a otally fascinating branch of it though.

3 out of 4 right this autumn/winter is not bad going in my view.

Yes John.

I think the stratosphere forecasts on the whole have ben pretty accurate for most of the winter. The errors and difficulties have been in forecasting the MMW, especially the positioning of the split vortices and any subsequent propagation. From what could have been a very promising situation it is very frustrating but that's life. No toys thrown out of my pram. There is always spring and next winter.

c

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Posted
  • Location: Ireland
  • Location: Ireland

Regardless of whether we see effects down the road from the MMW event, this thread is a truly excellent educational piece and most definately one for the archives.

Throughout the winter, CN, NSCC, GP, JH and others, you have kept us updated on a daily basis regarding events surrounding our stratosphere and this thread is a credit to all of your efforts.

Meteorology is an area of science comprising of a multitude of influences - the condition and state of the statosphere being one of these major influences.

Coupled with teleconnections, the accuracy of the guidance arising from these sources has been very very good during this winter season.

The main propogation & effects have not occured to date, but hey, there's a learning experience from it & we can investigate the reasons as to why this didn't occur. However, this is no way detracts from the hours and hours of work that have gone into this thread.

Who knows, we may yet see an impact upon our own weather patterns from these events.

Best Regards,

SA. :)

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Guest North Sea Snow Convection
Who knows, we may yet see an impact upon our own weather patterns from these events.

Best Regards,

SA. :)

Hi M :)

Thanks for your kind comments towards those who have followed this.

We see the zonal wind returns to westerly predicted at 10hPa and 30hPa

fluxes.gif

The slow nature of this return to 'normal service' against the extraordinarily long period of polar easterly days does rather make me think it maybe not surprising that the models are struggling with propagation forecasts. Could some kind of 'torque' effect occur in the layers of the stratosphere, wherby bottled up easterlies meet emerging westerlies at the top of the stratosphere? A bit like covergence zones of very different airmasses we see in some synoptic set-ups with our surface weather - where the effects can be sudden, unpredictable (and sometimes higher impact) ?

Maybe for all the forecasting, it could be that effects, whatever they maybe, arrive by 'looking out of the window' and not intently studying the stratosphere forecasts? lol! We have nowcasts on the model threads with volatile surface patterns - maybe it will a case of that happening here?

In terms of the forecasting it is significant IMO how brilliantly ECM predicted this event, and how the forecast magnitude verified so well. Now however maybe it is the time where forecast models struggle in terms of how this event is 'cycled' thought the system? We might well not get a freeze out of this but feelings of 'unfinished business' still strike a chord with me. At least somewhere in the NH anyway.

Edit: according to latest forecasts it won't be until 26th Feb that both 10hPa and 30hPa zonal winds have returned to westerly. So that will be a period from 23 Jan to 26 Feb that zonal winds at these levels will have been easterly. So maybe will have to wait till then until anything more definitive is picked up?

Edited by North Sea Snow Convection
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Posted
  • Location: Worcestershire
  • Weather Preferences: Forecaster Centaurea Weather
  • Location: Worcestershire
Yes John.

I think the stratosphere forecasts on the whole have ben pretty accurate for most of the winter. The errors and difficulties have been in forecasting the MMW, especially the positioning of the split vortices and any subsequent propagation. From what could have been a very promising situation it is very frustrating but that's life. No toys thrown out of my pram. There is always spring and next winter.

c

I wouldn't be too hasty to write this one off. Those reversals in zonal winds extend right up to 50 hPa. Does this mean the event is at an end ? Emphatic no - these types of up and downs are very consistent with a downwelling wave (the propagating nodes).

It's interesting to note the view that we almost have an inversion trap over the polar field with colder air of lower pressure being held at the moment by warmer column 200 - 300 hPa. This may be related to the overall hemispheric flow pattern with large +ve zonal wind anomalies showing across 30-40N preventing any meridionally orientated Rossby Wave Dispersal (perhaps also why the amplification which the models were suggesting has been toned down).

At some poimt, might we see the balance tipped ? Concentrated convection over the eastern Pacific (MJO active in phases 7 and 8 might be the trigger to look for in this respect. Currently very inactive:

http://www.bom.gov.au/bmrc/clfor/cfstaff/m...Last40days.html

A very slow warming of the middle and lower troposphere does seem to be happening but it's painfully slow.

Edited by Glacier Point
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Posted
  • Location: Dorset
  • Location: Dorset

Just a point but if the ECM did such a good job forecasting the warming when we were still in a below average situation and I believe it did, then surely ECM must know what triggered it, or at least have a very good idea ?.

Edited by Iceberg
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Guest North Sea Snow Convection

There was a spell in Dec 2007 I think I remember when the reverse of the current situation might have applied and there was a warm(er) tropospheric layer down at the surface whilst the upper stratosphere was cold following the strong cooling event at the beginning of that month. This situation lasted a while until the warm layer was dispersed and the positive pressure anomaly over Scandinavia that was the manifestation of the warm tropospheric layer (and had suggested a cold easterly incursion to last beyond the first day or so of Jan 08 was blown away by the return of the atlantic)

No coincidence that the Greenland polar vortex strengthened at that time and went on to dominate the rest of the winter. Another example where the connection between upper and lower atmosphere demonstrated its work.

Edited by North Sea Snow Convection
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Posted
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet

Interesting comments from you all, i would think that if zonal winds wont go westerly until the the 26th, then we will probably see a renewed cold shot sometime soon (perhaps a repetative northerly pattern), i dont think that the breakdown will fully occur until Mid-March, and the peak probably not until sometime in April in terms of westerly zonal winds, so March on the cold side, April on the warm.

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Posted
  • Location: Scone, Perthshire
  • Location: Scone, Perthshire

Am i right in thinking that we have a warm layer, of easterly winds, effectively bottled up in the lower stratosphere and waiting to be pushed into the the trophosphere by a cooling of the stratosphere higher up? if so as long as this propogates down eventually we could still be looking at a cold march. It's not possible that these easterly winds can have vanished so surely they must reach the surface eventually, right? Or was this MMW the final warming and no significant stratosphere cooling is going to occur and force them down?

Matt

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