Today is one of those days that makes you want to move to Patagonia. I'm working on a trust review which is about as exciting as a Monday morning History of Magic class with Professor Binns, Nifra_Idril's internet is down so I have no one to help me break up the monotony, and all I want to do is read June's three new chapters of But You Alone but I can't because the dreaded "hoverboss" has returned.
So, to help me survive the next five hours of work (and yes, folks, I do still have at least five hours), I'd like to pose a question to anyone out there who is similarly bored (and please forgive me if there is some part of canon that mentions this. I gave all my HP books away recently, and consequently cannot check this stuff before I open my big mouth): what event, series of events, or general change of heart caused Snape to go to Dumbledore and change sides? Are there any hints in the canon about his motivations for this, beyond just the general repellentness of Voldemort and his groupies?