[Model Output Discussion 29th December - Into mid-Winter.]

On the subject of Euro heights (and apologies mods if this is inappropriate for this thread, it's just a good way to access some of the most experienced members of the forum) can anyone explain to me why they have become so much more persistent and prominent in the winter months of late? 4 slow starts to the season in the Alps due to strong areas of high pressure that refuse to budge...why?

Is it climate change? What is consistently forcing this new pattern to emerge and so consistently.

Any answers or suggestions welcome.

Cheers!

[Model Output Discussion 29th December - Into mid-Winter.]

To my untrained eye, the end of the 0Z ECM isn't as bad as the output has been for much of the winter. Yes, we still have heights over Europe, but with a low in the eastern Med. and some lower heights heading towards the Azores the situation has some more promise to it. Certainly if you advect the situation on by 12 hours then a shot of Pm air would be bringing snow to fairly low levels in NW parts of the UK and Scotland esp. 

 

[Model output discussion - 5th December 2016 - Into Winter we go]

10 hours ago, Steve Murr said:

Hi mate -

There is no way of telling - i dont have access to the ERA data, however the MERRA / NCAR renanalysis is almost the same ( as you would expect )

you can pull a reanalysis chart from 1948 however where do you decide the cut off point it -

I think more importantly for me is looking at the base state 500 plots are for generally average decs, then the anomaly months 

 

 

 

 

 

Thanks Steve, fascinating stuff...wouldn't mind a similar winter to 2009 though, ironically, that would mean a back-loaded rather than front-loaded one this year.

It'll be interesting to see how it all plays out, esp. wrt stratospheric/troposheric (de)coupling this year.

Cheers!

[Model output discussion - 5th December 2016 - Into Winter we go]

7 hours ago, Steve Murr said:

So Why did I ( & the NW team perhaps ) go for a 'front loaded winter' - what does it mean ?

For 'ME' I dont really have any interest in the teleconnections per say, that is simply because they rarely deliver any success in terms of forecasting other that when the major player ENSO completely bulldozes the NH pattern with a super Nino-

What I do follow though is the zonal wind (u) @ 10 HPA across 60N - that gives us a real time framework of where the vortex is in terms of (u) zonal component & if its weak some guage of the meridional component- Its also the end result of all the trop forcing on the strat - 'the sum of all'

The ECMWF compiled a data file of All zonal wind speeds back to 1957 called ERA40 & then redid them at a better resolution called Interim ERA for 1979- 2015-

Whilst the data is not publicly available the key element from this is the climo line that this dataset produced to give us a steer from Nov-March where we should be on the zonal winds. ( I would love a breakdown though of the DJFM seasons though to correlate to our CET & AO/NAO couplet )

There are some key dates & info in climo ( see below ) that we should really get to know as well as records of peaks speeds & lowest speeds- for instance surprise surprise 2015 set many 'day' peak records & yesterday Dec 1981 was the lowest record - again think about that month in the context of blocking.

So key dates.. - all speeds are zonal (u) wind-

December 1st sees a climo ave of 30 M/S westerly ( propergating eastwards )

December 25th sees a climo ave 'peak' of 38 M/S - ironic that its xmas day - so from a winters perspective that period from about 20th -30th the NH is at a time that will have the least amount of blocking.

January 15th- Feb 1st is the biggest reduction of the zonal wind across winter as the PV starts to breakdown

Feb 20th onwards sees the windspeed at less than 50% of the December peak - Which is why traditionally our cold spells do come around & just after valentines day ...

Hi Steve,

Thanks for a highly informative and interesting post, just out of curiosity...has the mean zonal wind speed at 10hPa increased over the time frames of the ERA40 and Interim ERA? As in, are we likely to see higher W'ly wind speeds (on average) during winter than we were say 30 - 40 years ago, when the good old winters of yesteryear still brought frequent frost, snow and HLBing events?

I'm just wondering if climate change has affected the stratospheric wind patterns at all. I know that the surprising wQBO this year was unprecedented, for example, with most (if not all) experts believing the switch to an eQBO was a foregone conclusion. 

Also with the forecast increase in 10hPa zonal wind speeds, would you expect the polar vortex's coherence to increase and its segments to unify?

Cheers!