Hail Forecast Services are designed to provide forecasts specifically with a focus on hail and associated hail damage risk.
Hailstorms are defined as thunderstorms that produce hailstones. The general global definition of a severe hailstorm is one that produces hail that causes damage and seems to be consistently linked to hailstones greater than 2cm in diameter.
The development hailstorms is nothing particularly unusual but it does have much to do with the level of the freezing level. When atmospheric profiles consists of warm moist air at the surface and colder air aloft, if this moist air rises due to instability and heating or is forced upwards, conditions are in place for hailstones to be produced and reach the ground. Generally, the stronger the updraft, the more likely the larger hailstones will be able to be contained in the updraft, grow even larger and eventually overcome the updraft force due to its weight and fall to the ground. Other factors are rotating updraft that are able to sustain generally the largest hailstones. These rotating storms are called supercells and produce most of the giant hailstone events.