Hi ba, from what I understand (still learning) the vortex cold air will flow south where there is least resistance forced from warming in the strat above.
This makes trying to make a forecast based on a warming almost impossible.I think the met office have made big steps on trying to do this demonstrated in 2013 when they forecasted a change in December 2012.
It does worry me that there is no mention of a pattern change in there medium range forcast but who now's what's being said behind closed doors.
Anyway it's all a mile better than last year so lets hope there isn't any more horrors for people this christmas.