Hail Forecast and Information

onion-skin-structure-hailstone-6ht-august-2014Hail forecasting although part of the overall spectrum of weather and storm forecast can be an art where skill in forecasting and experience of previous events can improve accuracy. Hail forecasting involves a specific set of parameters – namely moisture and relatively warm air at the lower levels and cool to cold drier air aloft. Ideally, a thin warm layer should reside just above this warm moist layer at the surface we call the ‘cap’. This cap acts as a lid for convection allowing the energy and convection to build becoming maximised during the afternoon and finally breaking through to form thunderstorms. Generally once this happens, in the right environment, hailstorms will form.

In some circumstances, the cap strength can be critical and once or if it breaks, explosive thunderstorm development occurs. In the right conditions such as these and with cold air aloft, very large to giant hailstones can be spawned by the evolving thunderstorms.

Another important parameter that can assist in longevity of the storm life cycle is wind shear – that is increasing wind speed with height and and backing or veering profiles down towards the surface (from the northeast in the southern hemisphere and southeast in the northern hemisphere.

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