From the pictures I've seen on here with ice and snow. Maybe there is a buildup of ice around the window gasket, which expands behind the gasket and then melts with heat running down behind the dash and pooling on the floor.
It ain't easy being cheesy:
Sometimes I make decisions like famous people.
George Armstrong Custer "lets go over that hill, I think those are friendly indians!"
Titanic's Captain Smith "What icebergs? Full speed ahead!"