honestly!I was there at Christmas and it was ok, my friends were there for New Year and it was better you could ski all the way down to the bottom of the mountain, I would imagine now its pretty much like it was at Christmas, maybe a little better.
There were a few ski runs open and the snow cannons were on every day, it was much better than pamps was at New Year, I would say you will be ok in Bansko they are geared up with the snow cannons providing the weather is cold enough to use them.
There is no way that it's -9'C in Bansko at the moment. At night it drops to below 0'C but not as much as that. During the day recently it has been as much as 12'C according to some websites!