  Predicting the severity of the solar eruptive phenomena like flares and
Coronal Mass Ejections (CMEs) remains a great challenge despite concerted
efforts for several decades. The advent of high quality vector magnetograms
obtained from Hinode (SOT/SP) has increased the possibility of meeting this
challenge. In particular, the Spatially Averaged Signed Shear Angle (SASSA)
seems to be an unique parameter to quantify the non-potentiality of the active
regions. We demonstrate the usefulness of SASSA for predicting the flare
severity. For this purpose we present case studies of the evolution of magnetic
non-potentiality using 115 vector magnetograms of four active regions namely
ARs NOAA 10930, 10960, 10961 and 10963 during December 08-15, 2006, June 03-10,
2007, June 28-July 5, 2007 and July 10-17, 2007 respectively. The NOAA ARs
10930 and 10960 were very active and produced X and M class flares
respectively, along with many smaller X-ray flares. On the other hand, the NOAA
ARs 10961 and 10963 were relatively less active and produced only very small
(mostly A and B-class) flares. For this study we have used a large number of
high resolution vector magnetograms obtained from Hinode (SOT/SP). The analysis
shows that the peak X-ray flux of the most intense solar flare emanating from
the active regions depends on the magnitude of the SASSA at the time of the
flare. This finding of the existence of a lower limit of SASSA for a given
class of X-ray flare will be very useful for space weather forecasting. We have
also studied another non-potentiality parameter called mean weighted shear
angle (MWSA) of the vector magnetograms along with SASSA. We find that the MWSA
does not show such distinction as the SASSA for upper limits of GOES X-Ray flux
of solar flares, however both the quantities show similar trends during the
evolution of all active regions studied.
