Hail damages the roof by breaking down the shingle over time. Rarely is the hail damage large enough to cause immediate leaking, however over time the roof will continue to deteriorate until the point that water can penetrate inside the home. Hail damage doesn’t usually look like large holes or cracks in the shingle but instead is commonly just slight damage to the surface of the shingle with very few missing granules or remnants of impact. However, over time the damage expands and becomes worse. Hail damage isn’t always noticeable immediately following a hailstorm. If you suspect your roof may have been damaged in a hail storm it is important to have a qualified roofing professional inspect your roof as soon as possible.
Source - Rowin Construction