Ron informs me that his neighbor went up on the roof and cleared the gutters of ice and debris (the leak was strictly at the ceiling / wall junction), and we agreed that in future extreme winters the gutters have to be kept clear. It does not appear that the roof was inherently leaky, rather that an intolerable amount of water built up. (Just as the roofs that are collapsing from the weight of snow are not inherently prone to collapse.)