The answer to 'why is my skylight ice dams' is that ice dams are a common issue with skylights, caused by heat escaping through the skylight and melting snow on the roof. This can lead to water backing up under the shingles and leaking into the home.
Some common causes of skylight ice dams include poor insulation around the skylight, inadequate ventilation in the attic, and excessive heat buildup in the home. Symptoms may include icicles forming around the skylight, water stains on the ceiling, and pooling water near the skylight.