Courtesy of the University of Minnesota extension service, here is a diagram of an ice dam. This is what happens when you mix up the lethal cocktail of lots of snow on your house, extended periods of below freezing temperatures, and uneven heat loss through your (in our case uninsulated) roof.
Water started running down the inside of the picture window in the living room tonight. It's stopped for the moment as I'm sure everything has frozen up for the night. Now we know what the big discolored area on the floor under that window is. I'm sure it's been doing it for years. Arrgh.
The forecast tomorrow is in the 40s, which I don't think is going to be warm enough to melt the dam (but will certainly melt all the snow above it), but what do I know. It's the biggest piece of ice I've ever seen, cross your fingers.