Funny, that happened to my garage last month. The ice built up from the melting off of the Subi (wife's, X gets to enjoy the cold) under the edge of the door creating a gap.

I only had a half a foot high drift, tapering to nothing in two feet, by the width of the door.

Suprised the shit out of the wife. Took about a day and a half to build that up, with 40 - 60 mph winds.

Where the hell is that global warming, it's been freaking cold up here. Woke up yesterday to a blamy 5 below and 20 mph winds.