Hail forms when frozen water drops are lifted in turbulent wind regimes during thunderstorms. The frozen drops of water increase in size and eventually fall to earth as hail having been driven by a combination of gravity and wind forces. Hail stones vary in size from pea size (1/4 inch diameter, little roof damage), through marble size (3/4 inch in diameter, threshold damage to roof materials) to golf ball size (11/2 inch in diameter, typically severe damage to roofing materials). Hail size distributions tend to be localized with some roofs damaged, while others are not. Wind direction plays an important role, as well as roof pitch. A direct impact of hail on a shingle is more damaging than that of a glancing blow.
Assessing hail damage is often accomplished by a roof inspection, which usually occurs several days to several months after the hail event. Determination of whether hail actually fell at a site can be made through statements and weather reports. Inspection of thin, aluminum fixtures helps verify hail impact.