This has been a recurring problem for me...it snows (and it has really snowed here) and my car won't start.
The problem is probably my fault...I took the sheet metal leaf catchers (or whatever they're called) off my decklid vents to aid cooling...now the snow really packs in around my battery. And if it packs in, it will create a slow drain situation.
So I took a piece of carpet and cut it to fit over the top of the battery and the connections and have not had the starting problems since.
I thought about putting a plastic bag over the top of the battery, but I didn't want to create a condition where hydrogen gas might collect. The final solution is probably to move the battery up front (which I'll probably eventually do).
Makes me wonder why I live up here. (Oh, I remember...the summers here are great)...