An SSW is said to occur when the mean zonal mean winds reverse at 10 hPa and 60N. No other SSW can be recorded in the following 20 days and the winds need to recover back to positive or it will be a final warming.
We as yet have not had a SSW this winter - in fact we have not had any reversal at any level of the stratosphere. However the warmings that we have experienced in the stratosphere so far and those that are forecast, are now having an effect of the mean zonal winds closer to the troposphere. The mean zonal winds at 100 hPa are forecast to reduce as the vortex reduces. In time I expect this to have an effect tropospherically with more disruption of the tropospheric pv increasing as the month progresses. This will weaken the vortex which will increase the chance of high latitude blocking throughout this month.
I suspect that any blocking to affect us will materialise from the NE, already the GFS strat charts are suggesting splitting to occur in the lower vortex following a displacement further aloft.
No SSW is forecast of yet, but with the likelihood of further wave breaking into the stratosphere following a strong Asian Mountain Torque event the next set of warming could be lower and more pronounced now that the strat has already taken a 'hit'. I still suspect a SSW is in the offing before the end of the month.
Interesting to read this, maybe a few who keep going on about SSW will have a read to
Thanks Chion' and nick. I understand the terminology now
As there seems to be a bit of pessimism regarding cold prospects today I thought i would remind people that two warming events are still on the cards the next one around the 10th Jan then a much bigger event a week later. Hopefully these could lead to something much colder later in Jan.
Edited by user 04 January 2012 17:18:21(UTC)
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Just a quick one, but the warming events continue to have an effect on the stratospheric temperatures and there is forecast to be another major Asian mountain torque event within the next week or so. Take look at the 10hPa temperatures across the Pole now;
http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/html_e/pole10_n.html - Now risen to well above average.
Further warming events are event on the latest ECMWF charts as well;
http://wekuw.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwf10f240.gif - The major warming evident is from the forecasted Asian MT event in the next week or more…
It’s sort of like nibbling away at an apple, eventually you’ll get to the core of the apple and that’s your lot!. The same is happening with the significant polar vortex that has been in place for weeks. These individual warming events are ‘eating away’ at the cold and the significant polar vortex to either weaken it to a state that allows blocking across the northern polar regions or perhaps relocates the PV elsewhere allowing for blocking to develop where it was.
There are now signs in the shorter range models for a change, note the 00Z GFS ENS for example with a downward trend evident beyond mid-month;
Also we are getting some pretty interesting model runs as well now given that the PV is forecast to weaken, take the 00Z EC Det which is attempting to develop a Scandinavia high which would send some bitterly cold air south or south-east potentially…
GEM model, also shows more anticyclonic effects, but this time to the W and NW;
All the signs are there and have been since Christmas that the extremely strong polar vortex is on its way out in some shape or form which could well open the window for a very interesting second half of January….what this space!...
Bit of a warming
The PV is facing death by a thousand cuts.
Bit more of a warming.
Edited by user 05 January 2012 09:18:30(UTC)
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There is now a warming feedback process underway in the stratosphere, with a chain of repeated mountain torgues and wave breaking, that has longer term value in terms of a sustained complete pattern change away from the changeable and strongly cyclonic westerlies of recent months that has lasted to date. We don't yet see a technical SSW, but it is surely only a matter of days before we do.
It won't be like the SSW that occured in late January 2009 amidst an otherwise polar westerly regime. This time round we see the last of the legacy of the autumn westerly QBO downwelling wave which assisted the fast organisation of the polar vortex at the start of the winter now flushing right out of tropospheric influence to be replaced by an increasing easterly phase. Hence ozone has been building slowly and steadily for some time now, albeit from a distincly different base to the start of winter last year, but just as last winter was about to run out of puff, this one is just about to start breathing. The background factors should enable this reversal of pattern with pressure set to start and keep on building over the arctic and a consequent increasingly strengthening period of -AO conditions to be sustained through the rest of the winter and into Spring too. The only question remains is: will the resultant cold air that is expelled from the arctic arrive in this part of the NH or elsewhere? Current early model indications look promising It could be one of those classic end of January, early February scenarios. A bit like 1978 perhaps?
Edited by user 05 January 2012 11:54:42(UTC)
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It will be interesting to see if the Met Office pick up on this warming in there 16 to 30 day outlook tomorrow as Friday is the main day it get's updated.
Not sure if you read Darren's post a few days ago but apparently FI strat outlooks are much more reliable than surface parameters.
I think that post is telescopically challenged....
I have noticed you seem to have a certain vivid scepticism on this subject.... A better analogy might be that rioting in Brixton might be expected to lead to rioting somewhere else with similar underlying issues (or as we are talking abuot the stratosphere here, overlying issues perhaps)
i'm sure that the meto are well aware of forecast events in the strat. they will not change their 32 day forecasts unless the modelling (which takes account of forecast strat developments) reflects this change in the trop. they are currently covering bases for late jan by having a caveat for average - below temps. until the fi modelling strongly points to cold, they will not forecast it.
neil has a point but without analysing closely the fi strat forecasts i wont be able to show how strong it is. anecdotally, i find the upper strat ecm forecasts to be fairly consistent whilst those low down tend to reflect the preceding days 12z 500mb flow. (not surprising really). the past couple of days have seen consistent fi's from ecm 12z so i suspect the overall suite will look consistent. if we got a 12z fi that looks like todays 00z run, the 100hpa chart will be quite different. the upper strat should be better though.
generally very good strat forecasts and by tomorrow, we may have our first forecast of a SSW this winter. all still into the distance though the initial upper warmings have already fed through to the actual upper strat picture.