The answer to 'why is my skylight hail damage' is that hail can crack or shatter skylights due to the impact force. Hailstones, even small ones, can strike the glass or plastic skylight material with enough force to cause visible damage. Common symptoms include cracks, holes, or spider-web patterns in the skylight.
The best solution is to have a professional roofing contractor inspect the skylight and determine if it needs to be repaired or replaced. Attempting to DIY a skylight repair can be dangerous and may not fix the underlying issue. A professional will be able to properly assess the damage and recommend the safest and most effective solution.