TORRO Hailstorm Intensity Scale

A scale devised by the Tornado and Storm Research Organization (TORRO), an association of professional and amateur meteorologists headquartered in England, to rate the intensity of hailstorms. It depends on two factors, the diameter of the hailstones and the damage done. The diameter is rated by a size code, which starts at 1 for hailstones 5 to 10 millimeters in diameter and ends at 10 for those over 125 millimeters. The intensity scale itself runs from H1 to H10, each step characterized by a description of damage and a range of size codes. For example, an H7 hailstorm seriously damages car bodies and light aircraft, shatters slate and shingle roofs and pits brick and stone walls, and the hailstones range in size from size code 6 (“hen's egg”) to 9 (“melon”). Full details are given on the organization's website,

The organization cautions that the damage descriptions are based on British experience and “may need to be modified for other countries.”


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