American Meteorological Society Certification (AMS) Practice

The formation of hail in thunderstorms is primarily associated with updrafts and downdrafts within the storm. In a strong thunderstorm, powerful updrafts can carry water droplets upwards into extremely cold regions of the atmosphere. When these droplets reach altitudes where temperatures are below freezing, they can freeze and begin to grow as additional droplets collide with the ice nuclei and freeze upon contact—this is known as accretion.

As the process continues, the updrafts may allow the growing hailstones to be lifted repeatedly through these cold areas, accumulating more layers of ice until they become too heavy for the updrafts to support them. Eventually, when they fall, they can cause significant damage, which is a distinguishing characteristic of severe thunderstorms.

Stable air movement, convection currents in clear skies, and high humidity levels in surrounding air do not contribute to the same process of hail formation that is specifically associated with the dynamics of a thunderstorm's updrafts and downdrafts. Stable air movement typically leads to less turbulent conditions, while convection currents in clear skies do not involve the intense lifting and cooling needed for hail formation. High humidity levels, while important for storm development, do not directly cause the freezing and growth of hailstones like the turbulent air