A word on the modern winter-
Data: Straight from Meto in terms of NAO.
Data: Straight from NOAA in terms of AO
Is there a 'new modern winter'.
Yes clearly there is- The incidence of positive NAO winters are becoming more frequent, overlapped by the peak at how strong that positivity is-
So more positive more often is the strapline.
However in isolation when there is an AO month / period whilst slightly declining the depth of Negativity is also increasing ( who remembers in 2009 NOAA had to revise their AO scale to include -6 )
This data goes some way to underpinning the fact that winters are getting more extreme - but normally more mildly extreme although on occasion still cold extreme ( Mar 13 / Dec 10 )
So if we wanted to define a modern winter it wouldnt be so much to rule out all cold synoptics but to say that cold episodes have been greatly reduced but when they do arrive ( true cold episodes ) they may well be more longer lasting & extreme - this all against the ever increasing underlying warmth.
Of course in the next 5-10 years you may have a poat modern winter where the decoupling of the troposphere V the strat in November due to a non existent thermal Gradient may see Novembers & Decembers become much colder due to blocking before the Strat zonal wind sinks down...
This year maybe year 1 !!!