HAIL refers to frozen rain droplets which usually range between 5 – 50 mm in diameter.
The frozen rain droplets usually have a concentric layer of ice and being white and opaque in character. Hail is a form of precipitation that falls on the earth’s surface in form of small ice pellets or hailstones.It is associated with extreme instability in the atmosphere resulting from uplift of air by convective currents
Hail forms due to the condensation of moisture in the lower atmosphere followed by strong rising air currents. The water droplets are therefore pushed up to the freezing point to form ice pellets which are thick and dense enough to overcome the uprising air currents. Consequently, ice falls on the earth’s surface in the form of hailstones.
It usually occurs in unstable cumulonimbus clouds where vertical uplift or rise of air is strong enough to carry condensed droplets above to great heights of the freezing level where they are turned into ice crystals at a very high altitude
The initial droplets freeze above the freezing point hence condensation nuclei is ice.
After being carried upwards to greater heights by the uprising air currents, an additional layer of ice is formed on the original ice nucleus by collision and coalescence with supercooled water vapour/droplets around.
The pellets fall and rise many times until when the weight of the enlarged ice crystals is sufficiently great to overcome any uprising current. Finally, the crystals fall as hailstone due to gravity