Yep - inspectorD is right on. You need to keep the roof the same tepature as the surrounding air to avoid this. I see no venting. You have heated air from your house melting the snow on the roof. The melted snow then runs down to the eave and freezes again causing your issue. Ideally only the sun and air temp should melt the snow on your roof, not your furnace.
Unfortunately that's a tough area to insulate and ventilate properly.