Welcome Blue -
I'm really glad you're here - you need lots of support right now, just like we all do. I don't think anyone knows why or how we can change so drastically when we drink. Personally, I think we lash out at others because of our own pain and unhappiness. Alcohol lowers our inhibitions to the point where we react without thinking (rather like two-year-olds do).
I think it's a wonderful idea to talk to your dad, maybe in your own time. Anyway, welcome to the forum!