This latest easterly QBO period is on track to become the "strongest" episode on record. Below I have plotted the QBO along with an integrated QBO index which very simply sums the monthly QBO across each full easterly period.
So far this current -QBO period has an integrated magnitude of -280.62 ... which falls just short of the 2001 -QBO period with a magnitude of -280.79.
The mean is -191.6 and standard deviation is 48.6.
Data so far for January 2013 suggests the monthly QBO should come in negative once again. It's possible the recent SSW has helped stunt the descent of the westerlies, and is prolonging the easterly QBO.
This will put the -QBO period at 18 months long ... behind only 2001 which was 19 months.