Hi Mods, just wondering if you will let this topic stand alone as there seems to be a lot of talk on the Model thread about this and although a very interesting subject it would be nice to have two separate threads for those that are interested in one subject or the other or both rather than it all merging together, if not please delete.

If it helps some people throwing all their eggs in one basket on a factor that plays one small part in potentially bring cold weather to these shores, then I'm all for it. It also means that hopefully the MO thread can go back to discussing what the models are showing. 

This is not to say that it is not a fascinating subject and I will be flicking through both threads but I think we need to be a little more level headed regarding it.

It may also be a good thread to talk about the MJO also as I can see that this is having it's fair share of discussion now, so if you would like me to update the title just say

We're far better at using paragraphs though 

One thing I think we can be clear on is that the current warming event in the stratosphere has reached its peak and will gradually dissipate over the next few days. It has undoubtedly been the most significant warming event since January 2013 but arguably falls just short of the definition of even a minor SSW. We will have to wait and see if it does have any significant impact on weather in the coming weeks but I rather doubt it looking at the latest model output.

The greatest warming has been at the 2hPa and 5hPa levels with warming approaching 35C. To be classed as even a minor SSW the warming needs to be more than 25C within a week. The current warming has taken place over about a two and a half week period since mid December so not "sudden" enough to meet the criteria.

Mean temperature data for 5hPa and 2hPa up to yesterday for 65-90N

5hPa http://www.cpc.ncep.noaa.gov/products/stratosphere/temperature/05mb9065.gif

2hPa http://www.cpc.ncep.noaa.gov/products/stratosphere/temperature/02mb9065.gif

The other key aspect of a SSW is the reversal of the zonal winds. Now in fact we have seen a small reversal of the zonal winds at 70-90N. This chart is the forecast for 12z today from yesterday's ECM run which shows a negative zonal flow at all levels from 70 degrees north.

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_f24.gif

However, this reversal of the zonal winds is very short lived indeed and effectively peaked today. The forecasts for 9 Jan and 14 Jan below show we go back to a very positive zonal flow. So I can't see that the reversal of the zonal winds has been anything like long enough or substantial enough to make any noticeable impact on the weather at the surface in the next few weeks.

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_f120.gif

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_f240.gif

One thing I am absolutely certain of, is that some people place for too much emphasis on it as a cold trigger for the UK. 

In the model thread earlier, Kevin Bradshaw mentioned January 1991 and January 2005 which both started off as zonal, sometimes stormy affairs but then became much quieter, and colder later on in the month. Both of those years then saw cold spells in February, 1991 especially so. Did either of those years have any strat warming events early on in the year or at the tail end of the preceding year?

Just because we didn't know about them doesn't mean they weren't influencing our weather

I'll freely admit to being pretty ignorant on SSWs but I did find this:-

http://onlinelibrary.wiley.com/doi/10.1029/2011JD016769/pdf 

Which suggests no SSW prior to Feb 1991, only goes to 2002 so no idea after that.

Some of the other papers I was reading through whilst pretending to work earlier, seemed to suggest that whilst SSW's can/do affect the trop weather patterns the latter can also be true i.e the trop drives the strat.  Must admit most of the stuff I found was fairly technical and went several miles over my head - not the kind of thing it's easy to pick up from reading academic jargon!

There's an animation of the warming in February 1991 on the Martineau site: it was classified as a technical SSW.

http://curriculum.pmartineau.webfactional.com/wp-content/svw_gallery/test/gif/1991_01_28.gif

The MetO issued a statement several days ago saying this. As I mentioned at the time the press reporting and misunderstanding around this topic is now widespread. Those who are using it as a primary forecast signal are struggling more than anyone else this winter. That doesn't of course mean that it's not important.

I have noticed over the past year or two (since the SSW event of January 2013) that any warming, anywhere within the vicinity of the North Pole is regarded as an SSW and there's an assumption that this must plunge us into the freezer.

If only the weather was that simple...

I need another cold snap (preferably with some snow) in January and then we come to the tricky part in February.

So you wanted a SSW thread so much and yet I don't see that many updates on it  ....or is the reality there is no updates on SSW?

Surprisingly quiet in here considering what is being forecast - we now have not one but two warming events with the latter one looking even better, going on the 06z GFS run:

This appears to be the peak of the first one at the moment - this was more intense originally but then downgraded and now slightly upgraded again:

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=168&mode=10&carte=1

Then we have this one in FI which looks even more interesting:

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=360&mode=10&carte=1

No guarantee that will have any effect on the lower atmosphere but warm heights like that are interesting as the possibility is there - is the GFS at the end of the run reacting to this?

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=384&mode=0&carte=1

BTW, Keep up the SSW videos Gavin P, excellent stuff. 

Nothing much happening in the stratosphere at the moment, I assume?

No

The Lyrids occur in the second half of April so there could be an impact on the mesosphere then which may propagate down to the strat.