Ice dams in Seattle form when warm attics melt snow that refreezes at eaves, forcing water under shingles

https://donovanglhp447.lucialpiazzale.com/why-bad-attic-ventilation-destroys-your-roof-1

Ice dams in Seattle form when warm attics melt snow that refreezes at eaves, forcing water under shingles. Continuous soffit-to-ridge ventilation, air sealing, and eave ice-and-water shield stop hidden winter leaks.